JP4159963B2 - Resist laminate and pattern forming method - Google Patents

Description

  The present invention relates to a resist laminate and a pattern forming method that are suitably used for a method of forming a resist pattern through a step of exposing using a low acceleration electron beam.

  In general, in semiconductor manufacturing, by selectively exposing a resist laminate in which a resist film is formed on a substrate such as a silicon wafer, a resist pattern is formed on the resist film, and dry etching is performed using the resist pattern as a mask. A pattern is formed on a substrate.

  As one of resist pattern forming methods, a three-layer resist method is known (for example, see Patent Document 1). In this method, first, a base material containing a film-forming resin is applied onto a substrate, and this is heated to form an organic film, on which a silica-based resist film (intermediate layer) is formed. Then, a resist film (upper layer) is further provided thereon. Next, a resist pattern is formed on the upper layer by an ordinary lithography technique, the pattern is transferred to the intermediate layer using the resist pattern as a mask, and then the organic film is etched using the patterned intermediate film as a mask to form a pattern on the substrate. Form. By this method, a resist pattern having a high resolution and a high aspect ratio can be formed.

In recent years, resist patterns have been miniaturized rapidly due to advances in lithography technology. Recently, a resolution capable of forming a contact hole pattern of 90 nm or less, and further 70 nm or less has been demanded.
However, the resolution of the fine contact hole pattern as described above is said to be the limit even in lithography using an ArF excimer laser capable of producing a fine pattern most suitable for mass production.
On the other hand, lithography using electron beam drawing has been proposed for a long time as a microfabrication technology for realizing high resolution, but because of the drawing, the throughput per wafer is poor, and it is widely used as a mass production technology. I have not done it.
However, in recent years, with a view to mass production technology using an electron beam, attempts to improve such a drawing defect have been actively made, and broadly classified as EPL (Electron Projection Lithography: Electron Projection Lithography). A method of exposing by low-acceleration electron beam irradiation called lithography using an accelerated electron beam stepper and LEEPL (Low Energy Beam Projection Lithography) is proposed.
As a positive resist composition proposed as a resist material suitable for a method using an electron beam exposure process, generally, as a base resin, a part of hydroxyl groups of a polyhydroxystyrene resin are acid dissociable, dissolution inhibiting groups. A chemically amplified positive resist composition containing an acid generator and an acid generator is used. Examples of acid dissociable, dissolution inhibiting groups of the base resin include so-called acetal groups such as chain ether groups typified by 1-ethoxyethyl groups or cyclic ether groups typified by tetrahydropyranyl groups, and tert-butyl groups. Tertiary alkyl groups, tertiary alkoxycarbonyl groups represented by tert-butoxycarbonyl groups, and the like are mainly used (see, for example, Patent Documents 2 and 3).

What is most important in the above-described lithography using electron beams is the electron beam transparency of the resist film. The electron beam permeability of the resist film is more influenced by physical factors such as the thickness of the resist film than the physical properties of the resist material. Further, the lower the acceleration voltage during electron beam irradiation, the lower the transparency. Therefore, when using a low acceleration electron beam having a relatively low acceleration voltage such as LEEPL, for example, an acceleration voltage of about 2 kV, it is necessary to use a thin film resist process in order to ensure the transparency of the resist film to the electron beam. It is thought that there is.
However, until now, sufficient studies have not been made on a resist laminate suitable for lithography using a low acceleration electron beam and a pattern forming method.
JP 2001-51422 A JP-A-8-262721 JP 2002-341538 A

  An object of the present invention is to provide a resist laminate and a pattern forming method that are suitably used for lithography using a low acceleration electron beam.

The first aspect of the present invention for solving the above-mentioned problems, on the base plate, and dry etchable lower organic film, the intermediate layer, and an upper resist film a resist laminate obtained by laminating in this order,
A resin component (A ′) in which the upper resist film has an alkali-soluble structural unit (a1) and a structural unit (a2) having an acid dissociable, dissolution inhibiting group, and the alkali solubility is increased by the action of an acid; And an acid generator component (B) that generates an acid upon exposure, and a positive resist composition for low-acceleration electron beams having an acceleration voltage of 2 to 5 kV, and the structural unit (a1) in the resin component (A ′) ) Or (a2) is a resist laminate having a polycyclic group.
A second invention of the present invention that solves the above-mentioned problems is a low-acceleration electron beam having an acceleration voltage of 2 to 5 kV with respect to a laminate forming step for forming a resist laminate and an upper resist film of the resist laminate. A step of forming a resist pattern on the upper resist film by performing alkali exposure, a step of transferring a pattern to the intermediate layer by performing oxide etching using the resist pattern as a mask pattern, and the resist pattern And a step of performing dry etching of the lower organic film using the pattern of the intermediate layer as a mask pattern and sequentially forming a lower layer pattern on the lower organic film.

  Note that in this specification, “exposure” includes electron beam drawing and irradiation through a mask.

  ADVANTAGE OF THE INVENTION According to this invention, the resist laminated body suitably used for the method of forming a resist pattern through the process exposed using a low acceleration electron beam, and the pattern formation method are realizable.

Hereinafter, the present invention will be described in detail.
≪Resist laminated body≫
The resist laminate of the present invention is a substrate in which a dry-etchable lower organic film, an intermediate layer, and an upper resist film are laminated on a substrate, and a low acceleration electron beam is applied to the upper resist film. It is used for the resist pattern formation method which performs exposure, It is characterized by the above-mentioned. The low acceleration electron beam is an electron beam typically used in the LEEPL process.

{Upper resist film}
As a material for the upper resist layer, a resist composition proposed as a resist material suitable for a method using an exposure process by electron beam irradiation can be used.
As such a resist composition, as a resin component, a resist composition using one or more alkali-soluble resins or resins that can be alkali-soluble, which are usually used as base resins for chemically amplified resists Is mentioned. In the former case, a so-called negative type resist composition is used, and in the latter case, a so-called positive type resist composition. In the present invention, a positive resist composition is used.

  In the negative resist composition, a crosslinking agent is blended together with the acid generator component. When an acid is generated from the acid generator component by exposure during the formation of the resist pattern, the acid acts to cause cross-linking between the resin component and the cross-linking agent, resulting in alkali insolubility. As the crosslinking agent, for example, an amino crosslinking agent such as melamine, urea or glycoluril having a methylol group or alkoxymethyl group is usually used.

The positive resist composition for a low acceleration electron beam preferably used in the present invention has a resin component (A) (hereinafter referred to as component (A) having an acid dissociable, dissolution inhibiting group and increasing alkali solubility by the action of an acid. And an acid generator component (B) that generates an acid upon exposure (hereinafter also referred to as component (B)).
In the component (A), when an acid generated from the component (B) acts upon exposure, the acid dissociable, dissolution inhibiting group is dissociated, thereby changing the entire component (A) from alkali-insoluble to alkali-soluble.
Therefore, if exposure is performed through a mask pattern in the formation of a resist pattern, or if post-exposure heating (PEB) is performed in addition to exposure, the exposed area turns into alkali-soluble while the unexposed area remains insoluble in alkali. A positive resist pattern can be formed by alkali development.

In the present invention, as the positive resist composition for low acceleration electron beam used for the upper resist film, the following positive resist compositions for low acceleration electron beam (I) and (II) are particularly high resolution. The resist film is preferably used because it has excellent dry etching resistance, reduced film thickness, and a resist film suitable for a method of forming a resist pattern through an exposure process using a low acceleration electron beam.
That is, what is most important in lithography using an electron beam is the electron beam transparency of the resist layer. The electron beam transparency of the resist layer is more influenced by physical factors such as the film thickness of the resist layer than the physical properties of the resist material, and the lower the acceleration voltage during electron beam irradiation, the lower the transparency. Therefore, when using a low acceleration electron beam having a relatively low acceleration voltage, for example, an acceleration voltage of about 2 kV, a thin film resist process is used to ensure the transparency of the resist layer to the electron beam. However, conventionally used resist materials do not have sufficient dry etching resistance for use in thin film resist processes, and there is a problem in that film loss occurs during dry etching.
On the other hand, according to the study by the present inventors, there is a correlation between the dry etching resistance and film reduction of the resist film and the solubility in an alkali developer, and the residual film ratio after alkali development is 80. % Of the above-described positive resist composition (I) for low acceleration electron beam has been improved, and a method for forming a resist pattern through a step of exposure using a low acceleration electron beam has been improved. A resist film suitable for the above can be obtained. In addition, exposure using a low-acceleration electron beam, in which the above problems are improved, is also achieved by a positive resist composition for low-acceleration electron beam (II) using a resin having a specific structural unit as a base resin. A resist film suitable for the method of forming a resist pattern through the steps is obtained.

  In the present specification, the “constituent unit” means a monomer unit constituting the polymer.

"Positive resist composition for low acceleration electron beam (I)"
The positive resist composition (I) has a residual film ratio after the alkali development of the upper resist film of 80% or more. When the residual film ratio is 80% or more, the dry etching resistance of the resist film obtained using the low-acceleration electron beam positive resist composition (I) is improved, and the film loss during dry etching is reduced. The Therefore, it can be suitably used for a method of forming a resist pattern through a step of exposing using a low acceleration electron beam.
Here, the “residual film ratio” means the film thickness of the resist film formed by applying the low-acceleration electron beam positive resist composition (I) on the substrate and pre-baking, and the resist film at 23 ° C. Compared to the film thickness after development with an aqueous 2.38 mass% tetramethylammonium hydroxide solution for 60 seconds, (film thickness of resist film after development) / (film thickness of resist film before development) × 100 ( %). It is preferable that the film thickness before the alkali development of the resist film used in the measurement of the remaining film ratio is within a range used in a normal thin film process, for example, 50 to 100 nm. The reason why the positive resist composition for low acceleration electron beam (I), which has high resistance to an alkali developer, is also excellent in dry etching resistance is not clear, but is presumed to be due to a bulky skeleton in the resin skeleton. .
The remaining film ratio is more preferably 90% or more, still more preferably 95% or more, and the closer to 100%, the more preferable.

The remaining film ratio can be adjusted by a known method such as adjusting the type and blending amount of the component (A) and the component (B) and the kind and blending amount of any component blended with them.
For example, the type of the acid dissociable dissolution inhibiting group (A) is a bulky group such as an adamantyl group, the protection rate by the acid dissociable dissolution inhibiting group is increased, the mass average molecular weight is increased, and a dissolution inhibitor is blended. Even if it is a site that is not an acid dissociable, dissolution-inhibiting group, by introducing a bulky group such as an adamantyl group into the resin side chain, the alkali solubility in the unexposed area is increased and the remaining film ratio is increased. be able to.

  In the low acceleration electron beam positive resist composition (I), as the component (A), any resin generally used in the positive resist composition can be used as long as the residual film ratio is 80% or less. Polymers used as the component (A ′) in the positive resist composition (II) described later, such as the polymer (A′1) and copolymer (A′2) described later are preferable. Used for. Further, the type and blending amount of the component (B) and other components optionally added are the same as those of the positive resist composition (II) for low acceleration electron beam described below.

"Positive resist composition for low acceleration electron beam (II)"
[(A) component]
The low-acceleration electron beam positive resist composition (II) has a component (A ′) having an alkali-soluble structural unit (a1) and a structural unit (a2) having an acid dissociable, dissolution inhibiting group, A resin component (A ′) whose alkali solubility is increased by the action of an acid, wherein at least one of the structural units (a1) or (a2) has a polycyclic group (hereinafter referred to as polymer (A ′)) It may be said that). By using the polymer (A ′) having at least one of the structural unit (a1) or (a2) having the polycyclic group, the positive resist composition (II) for low acceleration electron beam is used. The resist film obtained has improved dry etching resistance, reduced film loss during dry etching, and a high-resolution resist pattern. Therefore, it can be suitably used for a method of forming a resist pattern through a step of exposing using a low acceleration electron beam.
The reason why the dry etching resistance is improved by using the polymer (A ′) and the film loss during the dry etching is reduced is that the dry etching resistance is improved by the polycyclic group and the resist film is formed by the polycyclic group. It is conceivable that the hydrophobicity of the surface is increased, the resist film surface is hardly soluble, and film loss is reduced.
Here, the “alkali-soluble constituent unit” means a constituent having a polar group such as a hydroxyl group or a carboxy group in the constituent unit, and a monomer that derives the constituent unit is soluble in an alkali such as an alkali developer. Means a unit.

  As the structural unit (a1), structural units derived from hydroxystyrene or α-methylhydroxystyrene, that is, the following general formula (I)

［式中、Ｒは水素原子またはメチル基を表す。］
で表される構成単位（ａ１１）、後述する（ａ１２）のようなアルコール性水酸基を有する脂肪族多環式基含有（メタ）アクリル酸から誘導される構成単位、（メタ）アクリル酸から誘導される構成単位等が挙げられる。なかでも、上記構成単位（ａ１１）と（ａ１２）は、ドライエッチング耐性が高い、容易に入手可能で低価格である等の理由から、好ましく用いられる。
なお、「（メタ）アクリル酸」とは、メタクリル酸とアクリル酸の一方あるいは両方を意味する。

[Wherein, R represents a hydrogen atom or a methyl group. ]
A structural unit derived from (meth) acrylic acid, a structural unit derived from an aliphatic polycyclic group-containing (meth) acrylic acid having an alcoholic hydroxyl group such as (a12) described later. And the like. Among these, the structural units (a11) and (a12) are preferably used because they have high dry etching resistance, are easily available, and are inexpensive.
“(Meth) acrylic acid” means one or both of methacrylic acid and acrylic acid.

  In formula (I), R is a hydrogen atom or a methyl group, and is preferably a hydrogen atom. When R is a hydrogen atom, the protection rate of the hydroxyl group can be improved, and the contrast can be improved. Further, the dissolution rate after development can be increased. The position of the hydroxyl group may be any of the o-position, the m-position, and the p-position, but the p-position is preferred because it is readily available and inexpensive.

As the structural unit (a2), for example, the structural unit (a11), the structural unit (a12), and the structural unit derived from (meth) acrylic acid listed in the structural unit (a1), the phenolic hydroxyl group, alcoholic Examples include those in which a hydrogen atom of a hydroxyl group or a carboxyl group is substituted with an acid dissociable, dissolution inhibiting group that is publicly known or is being filed by the applicant.
As the conventionally known acid dissociable dissolution inhibiting groups, those proposed as acid dissociable dissolution inhibiting groups in chemically amplified KrF positive resist compositions and ArF positive resist compositions may be appropriately used. For example, a chain or cyclic tertiary alkyl group such as a tert-butyl group, a tert-amyl group, a 1-methylcyclopentyl group, a 1-ethylcyclopentyl group, a 1-methylcyclohexyl group, a 1-ethylcyclohexyl group, Cyclic ether groups such as a tetrahydropyranyl group and a tetrahydrofuranyl group can be used, such as a 1-lower alkoxyalkyl group substituted at the 1-position with a chain, branched or cyclic alkoxy group having 1 to 8 carbon atoms. The acid dissociable, dissolution inhibiting group that has been filed by the applicant is represented by the general formula (II) of the polymer (A′1) described later.

  The polycyclic group in the polymer (A ′) having at least one of the structural units (a1) or (a2) having a polycyclic group may be an aliphatic polycyclic group or an aromatic polycyclic group. An aliphatic polycyclic group having 10 to 16 carbon atoms or an aromatic polycyclic hydrocarbon group having 10 to 16 carbon atoms is preferable. Among these, an aliphatic polycyclic group is preferable because the line edge roughness of the resist pattern and the rectangular shape of the cross-sectional shape are improved.

Examples of the aliphatic polycyclic group having 10 to 16 carbon atoms include groups in which one or two hydrogen atoms have been removed from bicycloalkane, tricycloalkane, tetracycloalkane, or the like. Specific examples include groups in which one or two hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane, or tetracyclododecane. Such a polycyclic group can be used, for example, by appropriately selecting from a large number of proposals in conventional ArF resists. Among these, an adamantyl group, a norbornyl group, and a tetracyclododecanyl group are industrially preferable, and an adamantyl group is particularly preferable.
By having an aliphatic polycyclic group, high resolution is obtained, and the resist pattern has a rectangular cross-sectional shape.

Examples of the aromatic polycyclic group having 10 to 16 carbon atoms include groups obtained by removing one or two hydrogen atoms from naphthalene, anthracene, phenanthrene, pyrene, and the like. Specific examples include 1-naphthyl group, 2-naphthyl group, 1-anthracenyl group, 2-anthracenyl group, 1-phenanthryl group, 2-phenanthryl group, 3-phenanthryl group, 1-pyrenyl group, and the like. A naphthyl group is particularly preferred industrially.
By having an aromatic polycyclic group, sensitivity is improved, throughput is high, and productivity can be improved.

  The fact that at least one of the structural units (a1) or (a2) has a polycyclic group is sufficient if the polycyclic group described above is organically bonded. The polycyclic group may further have an alkali-soluble functional group such as a hydroxyl group or a carboxyl group, or a lower alkyl group such as a methyl group, an ethyl group or a propyl group, or an acid dissociable solution. It may be contained in a part of the inhibitory group. Specific examples include structural units (a12) and (a21) described later.

The proportion of the structural unit (a1) in the polymer (A ′) is preferably 50 to 95 mol% of all structural units constituting the polymer (A ′), and preferably 60 to 85 mol%. More preferred. Thereby, moderate alkali solubility is obtained.
The proportion of the structural unit (a2) in the polymer (A ′) is preferably 5 to 45 mol% of all the structural units constituting the polymer (A ′), and preferably 15 to 40 mol%. More preferred. Thereby, it is possible to sufficiently ensure alkali insolubility in the unexposed portion of the resist film when forming the resist pattern.

  The polymer (A ′) has a mass average molecular weight (polystyrene conversion by gel permeation chromatography (GPC), the same applies hereinafter), 2000 to 30000, preferably 4000 to 20000 before being protected with an acid dissociable, dissolution inhibiting group. After protection, it is 3500-33000, preferably 5500-23000. By setting the mass average molecular weight to 30000 or less, sufficient solubility in a resist solvent can be secured, and by setting the mass average molecular weight to 2000 or more, the dry etching resistance of the resulting resist pattern is improved and film loss is improved. Moreover, there exists a tendency for a residual film rate to become high, so that a mass mean molecular weight is large.

In the present invention, the positive resist composition (II) for a low acceleration electron beam containing the polymer (A ′) is further subjected to the conditions of the positive resist composition (I) for the low acceleration electron beam, that is, the remaining amount. It is preferable that the film rate is 80% or more.
The remaining film ratio can be improved, for example, by increasing the ratio of the polycyclic group in the polymer (A ′) or increasing the mass average molecular weight of the polymer (A ′).

  The component (A ′) preferred in the present invention has the structural unit (a1), and a part of the hydrogen atoms of the hydroxyl group of the structural unit (a1) is protected by an acid dissociable, dissolution inhibiting group, and Examples thereof include a polymer in which the structural unit (a1) has a polycyclic group, or the acid dissociable, dissolution inhibiting group has a polycyclic group, or has both of them. Examples of the polymer include the following polymer (A′1) and copolymer (A′2). By using the following polymer (A′1) or copolymer (A′2) as the component (A ′), the dry etching resistance necessary for this thin film resist process can be secured, and at the time of dry etching The reduction in film thickness is reduced, a resist pattern with high resolution is obtained, and the occurrence of pattern defects (development defects) in the resist pattern after development can be suppressed. This is considered to be because the resin component content in the resist film is reduced by reducing the thickness.

<Polymer (A'1)>
The polymer (A′1) has the structural unit (a11), and a part of the hydrogen atoms of the hydroxyl group of the structural unit (a11) is represented by the following general formula (II).

［式中、Ｒ^１は炭素数１〜５のアルキル基を表し、Ｒ^２は炭素数１〜５のアルキル基または水素原子を表し、Ｘは脂肪族多環式基または芳香族多環式炭化水素基を表す。］
で表される酸解離性溶解抑制基により保護されている構成単位（ａ２１）を有する重合体である。

[Wherein R ¹ represents an alkyl group having 1 to 5 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms or a hydrogen atom, and X represents an aliphatic polycyclic group or an aromatic polycyclic carbonization. Represents a hydrogen group. ]
The polymer which has the structural unit (a21) protected by the acid dissociable dissolution inhibiting group represented by these.

In Formula (II), R ¹ is a linear or branched alkyl group having 1 to 5 carbon atoms, and is a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, or a tert-butyl group. , A pentyl group, an isopentyl group, a neopentyl group, and the like. Industrially, a methyl group or an ethyl group is preferable.

R ² is an alkyl group having 1 to 5 carbon atoms or a hydrogen atom. Examples of the alkyl group having 1 to 5 carbon atoms can be the same substituents as in the case of the above-described R ^1. Of these, R ² is preferably a hydrogen atom industrially.

X is an aliphatic polycyclic group or an aromatic polycyclic group, whereby a high residual film ratio can be achieved. In addition, improvement in etching resistance and reduction in film loss are achieved.
Examples of X include the same as those mentioned for the polycyclic group. Among these, an aliphatic polycyclic group is preferable because the line edge roughness of the resist pattern and the rectangular shape of the cross-sectional shape are improved.

  Specific examples of preferred acid dissociable, dissolution inhibiting groups for the structural unit (a21) are shown below.

[Structural unit (a3)]
In addition to the structural units (a11) and (a21), the polymer (A′1) is further represented by the following general formula (III):

［式中、Ｒは水素原子またはメチル基を表す。］
で表される構成単位（ａ３）を有する共重合体であってもよい。

[Wherein, R represents a hydrogen atom or a methyl group. ]
The copolymer which has the structural unit (a3) represented by these may be sufficient.

In the formula (III), R ³ is a linear or branched alkyl group having 1 to 5 carbon atoms, and is a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, or a tert-butyl group. , A pentyl group, an isopentyl group, a neopentyl group, and the like. Industrially, a methyl group or an ethyl group is preferable.
n is 0 or an integer of 1 to 3. Of these, n is preferably 0 or 1, and is particularly preferably 0 industrially.
In addition, when n is 1 to ³ , the substitution position of R ³ may be any of the o-position, m-position and p-position, and when n is 2 or 3, any substitution The positions can be combined.

  In the present invention, the structural unit (a3) is not essential, but when it is contained, the alkali solubility can be controlled by the content, and the residual film ratio can be controlled. This also has the advantage that the line edge roughness can be reduced and a good isolated line can be obtained. When the structural unit (a3) is used, the content is preferably 0.5 to 25 mol%, more preferably 3 to 20 mol% of the total of the structural units constituting the polymer (A′1). When the structural unit (a3) is more than the above range, the alkali solubility tends to be low, the line edge roughness is increased, and a good isolated line tends not to be obtained.

In the positive resist composition (II), as the polymer (A′1), one type may be used alone, or two or more types may be mixed and used.
When two or more kinds of mixtures are used as the polymer (A′1), the polymer having the structural unit (a11) and having the structural unit (a21), or the structural unit (a11) ), Any two or more selected from copolymers having the structural unit (a21) and the structural unit (a3) can be combined. That is, those having different mass average molecular weights of those polymers and those having different proportions of the respective structural units can be arbitrarily mixed and used. Preferably, the polymer having the structural unit (a11) and the structural unit (a21) and the polymer having the structural unit (a11), the structural unit (a21), and the structural unit (a3). A mixture with a polymer is used. By using such a mixture as the polymer (A′1), the formed resist pattern has a good rectangular shape and an excellent isolated line can be obtained.

The mass average molecular weight of the polymer (A′1) before being protected with the acid dissociable, dissolution inhibiting group (in terms of polystyrene, the same shall apply hereinafter) is preferably 2000 to 30000, and more preferably 5000 to 20000. By setting the mass average molecular weight to 30000 or less, the solubility in a resist solvent can be improved, and by setting the mass average molecular weight to 2000 or more, the dry etching resistance of the resulting resist pattern is improved and film loss is improved. Also, a good resist pattern shape can be obtained.
Further, the larger the mass average molecular weight, the higher the remaining film ratio.
Further, the degree of dispersion of the polymer (A′1) before being protected by the acid dissociable, dissolution inhibiting group (the value obtained by dividing the mass average molecular weight by the number average molecular weight; the same applies hereinafter) is small. Monodispersion is preferable because of excellent resolution. Specifically, 2.0 or less is preferable, and 1.5 or less is more preferable.

In the present invention, the structural unit (a11) is 50 to 95 mol%, preferably 60 to 85 mol%, based on the total of all structural units constituting the polymer (A′1). The proportion of (a21) is 5 to 45 mol%, preferably 15 to 40 mol%.
When the polymer does not have the structural unit (a3), the content ratio of the structural unit (a21) is preferably 5 to 35 mol%, more preferably 20 to 20%, based on all the structural units. 30 mol%.
When the polymer has the structural unit (a3), the content ratio of the structural unit (a21) is preferably 5 to 35 mol%, more preferably 10 to 20 mol, based on all the structural units. %.
By setting the content ratio to be equal to or higher than the lower limit value of the above range, good contrast can be obtained, and by making the content ratio equal to or lower than the upper limit value of the above range, an effect of preventing development defects can be obtained.

The polymer (A′1), for example, after polymerizing a monomer corresponding to the structural unit (a11) in which the hydrogen atom of the hydroxyl group is not protected, a part of the hydrogen atom of the hydroxyl group of the structural unit (a11), It can be produced by a method of protecting with an acid dissociable, dissolution inhibiting group by a known method.
Alternatively, a monomer corresponding to the structural unit (a21) in which a hydrogen atom of a hydroxyl group is protected with an acid dissociable, dissolution inhibiting group is prepared in advance, polymerized by a conventional method, and then hydrolyzed to inhibit acid dissociable dissolution. It can also be produced by a method in which a part of the acid dissociable, dissolution inhibiting group of a hydroxyl group protected with a group is replaced with a hydrogen atom.

<Copolymer (A'2)>
The copolymer (A′2) is essentially composed of the structural unit (a11) and the structural unit (a12) derived from an aliphatic polycyclic group-containing (meth) acrylic acid ester having an alcoholic hydroxyl group. It is a copolymer which has as a unit and a part of hydrogen atoms of the hydroxyl group of the structural unit (a11) and the alcoholic hydroxyl group of the structural unit (a12) are protected with an acid dissociable, dissolution inhibiting group.
In addition to the first structural unit (a11) and the second structural unit (a12), the copolymer (A′2) has the same structure as described in the polymer (A′1). You may have a unit (a3).

[Structural unit (a12)]
The structural unit (a12) is a structural unit derived from an aliphatic polycyclic group-containing (meth) acrylic acid ester having an alcoholic hydroxyl group.
Since the structural unit (a12) has a lower solubility in an alkaline developer than the structural unit (a11), the copolymer (A′2) is obtained by converting some of the hydrogen atoms of the hydroxyl groups of the conventional polyhydroxystyrene to acid. The solubility in an alkali developer in a state where the acid dissociable dissolution inhibiting group is eliminated is lower than that of the resin protected with the dissociable dissolution inhibiting group. For this reason, sufficient insolubility with respect to an alkaline developer can be obtained even with a protection rate lower than that of a conventional polyhydroxystyrene resin, thereby achieving a high residual film rate. In addition, improvement in etching resistance and reduction in film loss are achieved. Furthermore, high resolution can be achieved while suppressing development defects caused by the acid dissociable, dissolution inhibiting group.
That is, in the copolymer (A′2), instead of the structural unit (a11), a structural unit capable of introducing an alcoholic hydroxyl group that is less alkaline soluble than the phenolic hydroxyl group into a part of the base resin side chain ( By using a12), the solubility in an alkaline developer is lowered. Further, since it contains an aliphatic polycyclic group having an alcoholic hydroxyl group, it is excellent in high resolution and dry etching resistance.
The structural unit (a12) in the copolymer (A′2) may be a structural unit derived from an aliphatic polycyclic group-containing (meth) acrylic acid ester having an alcoholic hydroxyl group as long as it has such an action. There is no particular limitation.

  Examples of the polycyclic group constituting the aliphatic polycyclic group having an alcoholic hydroxyl group include groups in which one hydrogen atom has been removed from bicycloalkane, tricycloalkane, tetracycloalkane, and the like. Specific examples include groups in which one hydrogen atom has been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane, and tetracyclododecane. Such a polycyclic group can be appropriately selected and used from among many proposed ArF resists and the like. Of these, an adamantyl group, a norbornyl group, and a tetracyclododecanyl group are industrially preferable.

As the structural unit (a12), in particular, a structural unit derived from an adamantyl group-containing (meth) acrylic acid ester having at least one alcoholic hydroxyl group represented by the following general formula (IV) is preferably used. it can.
Among the structural units (a12) represented by the following general formula (IV), the structural units represented by the following general formula (IVa) are most preferable.

（式中、Ｒは水素原子又はメチル基、ｘは１〜３の整数である。）

(In the formula, R is a hydrogen atom or a methyl group, and x is an integer of 1 to 3.)

  Among the structural units (a12), the structural unit derived from an acrylate ester is more than the structural unit derived from a methacrylic acid ester with respect to an alkali developer in a state in which the acid dissociable dissolution inhibiting group is eliminated. Since the solubility is high, the protection ratio by the acid dissociable, dissolution inhibiting group can be increased to improve the contrast. Therefore, it is more preferable to use a structural unit derived from an acrylate ester having an alcoholic hydroxyl group as the structural unit (a12) in order to improve resolution while suppressing development defects. It is preferable that 80 mol% or more of the structural unit (a12) is a structural unit derived from an acrylate ester having an alcoholic hydroxyl group, and 100 mol% is more preferable.

[Acid dissociable, dissolution inhibiting group of copolymer (A′2)]
In the copolymer (A′2), hydrogen atoms of some of the hydroxyl groups of the structural unit (a11) and the alcoholic hydroxyl groups of the structural unit (a12) are protected with acid dissociable, dissolution inhibiting groups. There is a need.
Examples of the acid dissociable, dissolution inhibiting group include the same groups as those described above for the structural unit (a2). Among these, in particular, 1-lower alkoxyalkyl group substituted at the 1-position with a chain, branched or cyclic alkoxy group having 1 to 8 carbon atoms, that is, 1 represented by the following general formula (V) -A lower alkoxyalkyl group is preferred. Specific examples thereof include linear or branched alkoxyalkyl groups such as 1-ethoxyethyl group and 1-isopropoxyethyl group, and cyclic alkoxyalkyl groups such as 1-cyclohexyloxyethyl group. Of these, a 1-ethoxyethyl group is preferred because of its excellent resolution performance.

（式中、Ｒ^４は炭素数１〜４のアルキル基を表し、Ｒ^５は炭素数１〜８の鎖状又は分岐状のアルキル基、または炭素数５〜７のシクロアルキル基を表す。）

(In the formula, R ⁴ represents an alkyl group having 1 to ⁴ carbon atoms, and R ⁵ represents a linear or branched alkyl group having 1 to 8 carbon atoms or a cycloalkyl group having 5 to 7 carbon atoms.)

In the present invention, the hydroxyl group protection ratio in the copolymer (A′2) (the ratio at which the hydrogen atom of the hydroxyl group is replaced by an acid dissociable, dissolution inhibiting group) is the hydroxyl group of the structural unit (a11) and the structural unit (a12). It is preferable that it is the range of 10 mol% or more and 35 mol% or less of the sum total with these alcoholic hydroxyl groups, and it is more preferable that it is 20 mol% or more and 30 mol% or less.
By making the protection ratio of the hydroxyl group below the upper limit of the above range, pattern defects (development defects) of the resist pattern after development can be effectively prevented. On the other hand, when the protection ratio of the hydroxyl group is not less than the lower limit of the above range, the etching resistance is improved and the film loss is reduced. In addition, degradation of resolution performance can be suppressed. Moreover, the higher the hydroxyl group protection ratio, the higher the remaining film ratio.

  In the copolymer (A′2), the hydroxyl group protected by the acid dissociable, dissolution inhibiting group may be the hydroxyl group of the structural unit (a11) or the alcoholic hydroxyl group of the structural unit (a12). Although not particularly limited, only the hydroxyl group of the structural unit (a11) (phenolic hydroxyl group of hydroxystyrene), or both the hydroxyl group of the structural unit (a11) and the alcoholic hydroxyl group of the structural unit (a12) are acid dissociable, dissolution-inhibited. It is preferably protected by a group. Further, although depending on the acid dissociable, dissolution inhibiting group, it is more preferable that both the hydroxyl group of the structural unit (a11) and the alcoholic hydroxyl group of the structural unit (a12) are protected with an acid dissociable, dissolution inhibiting group.

In the copolymer (A′2), the molar ratio of the structural unit (a11) and the structural unit (a12) of the copolymer before protection with the acid dissociable, dissolution inhibiting group is 95: 5 to 75:25. It is preferable that it exists in the range of this, and a more preferable range is 82: 18-78: 22.
When the structural unit (a12) is more than the above range, the solubility in the developing solution is insufficient.

  In the copolymer (A′2), the total of the structural unit (a11) and the structural unit (a12) of the copolymer before protection with the acid dissociable, dissolution inhibiting group is the copolymer (A′2). It is preferable that it is 90 mol% or more of the total of all the structural units constituting 2). When it is less than 90 mol%, the resolution tends to deteriorate. The total of the structural unit (a11) and the structural unit (a12) is more preferably 95 mol% or more, and may be 100 mol%.

In the present invention, the structural unit (a3) is not essential, but if it is contained, advantages such as an improved depth of focus and further improved dry etching resistance can be obtained.
In the case of having the structural unit (a3), the proportion of the structural unit (a3) in the copolymer (A′2) is 0.5 to 10 of the total of all the structural units constituting the copolymer (A′2). It is preferable that it is mol%, More preferably, it is 2-5 mol%. When the structural unit (a3) is more than the above range, the solubility in the developer tends to deteriorate.

In the copolymer (A′2), the mass average molecular weight of the copolymer before some of the hydrogen atoms of the hydroxyl group are protected by the acid dissociable, dissolution inhibiting group is preferably 2000 or more and 8500 or less, more Preferably they are 4500 or more and 8500 or less. When the mass average molecular weight is 8500 or less, the dry etching resistance of the resulting resist pattern is improved, and film loss is improved. Moreover, generation | occurrence | production of a microbridge can be prevented. Moreover, heat resistance is favorable in this mass mean molecular weight being 2000 or more. Further, the weight average molecular weight of the copolymer after being protected with the acid dissociable dissolution inhibiting group is preferably 8600 or more and 20000 or less, more preferably 9000 or more, from the protection ratio of the acid dissociable dissolution inhibiting group. It is preferable that it is 15000 or less.
The microbridge here is a kind of development defect, for example, a defect in a line-and-space pattern in which a portion close to the surface of an adjacent resist pattern is connected by a resist and is in a bridged state. Microbridges are more likely to occur as the mass average molecular weight is higher and the post-exposure heating (PEB) temperature is higher.

  Further, the dispersity (Mw / Mn ratio) of the copolymer (A′2) before part of the hydrogen atoms of the hydroxyl group is protected by the acid dissociable, dissolution inhibiting group is monodisperse with a small dispersity. And excellent in resolution. Specifically, it is 2.0 or less, preferably 1.7 or less.

The copolymer (A′2) is, for example, a copolymer of a monomer corresponding to the structural unit (a11) whose hydroxyl group is not protected and a monomer corresponding to the structural unit (a12) whose hydroxyl group is not protected. Then, a part of the hydrogen atom of the hydroxyl group of the structural unit (a11) and / or the structural unit (a12) can be produced by a method of protecting with an acid dissociable, dissolution inhibiting group by a known method.
Alternatively, a monomer corresponding to the structural unit in which the hydroxyl group of the structural unit (a11) is previously protected with an acid dissociable, dissolution inhibiting group is prepared, and this monomer and the monomer corresponding to the structural unit (a12) are copolymerized by a conventional method. Then, by hydrolysis, a part of the hydroxyl group protected by the acid dissociable, dissolution inhibiting group is changed to a hydroxyl group, and if necessary, the hydroxyl group of the structural unit (a12) is inhibited by a known method. It can also be produced by a method of protecting with a group.

  In the low-acceleration electron beam positive resist composition (II), the component (A ′) may be either the polymer (A′1) or the copolymer (A′2). It may be a mixture of

  In the positive resist composition (II), the content of the component (A) or the component (A ′) may be adjusted according to the resist film thickness to be formed. And 5 to 25 mass%, more preferably 7 to 20 mass%.

[Component (B)]
As the component (B), any conventionally known acid generator for chemically amplified photoresists can be appropriately selected and used.
Among the acid generators, onium salts and oxime sulfonate compounds having a fluorinated alkyl sulfonate ion as an anion are preferable.

Examples of onium salts include diphenyliodonium trifluoromethanesulfonate, (4-methoxyphenyl) phenyliodonium trifluoromethanesulfonate, bis (p-tert-butylphenyl) iodonium trifluoromethanesulfonate, triphenylsulfonium trifluoromethanesulfonate, (4-methoxy Phenyl) diphenylsulfonium trifluoromethanesulfonate, (4-methylphenyl) diphenylsulfonium nonafluorobutanesulfonate, (p-tert-butylphenyl) diphenylsulfonium trifluoromethanesulfonate, diphenyliodonium nonafluorobutanesulfonate, bis (p-tert-butylphenyl) ) Iodonium nonafluorobutane sulfonate, To Phenylsulfonium nonafluorobutanesulfonate, (4-trifluoromethylphenyl) diphenylsulfonium trifluoromethanesulfonate, (4-trifluoromethylphenyl) diphenylsulfonium nonafluorobutanesulfonate, tri (p-tert-butylphenyl) sulfonium trifluoromethanesulfonate, etc. Of onium salts.

  Examples of oxime sulfonate compounds include α- (methylsulfonyloxyimino) -phenylacetonitrile, α- (methylsulfonyloxyimino) -p-methoxyphenylacetonitrile, α- (trifluoromethylsulfonyloxyimino) -phenylacetonitrile, α -(Trifluoromethylsulfonyloxyimino) -p-methoxyphenylacetonitrile, α- (ethylsulfonyloxyimino) -p-methoxyphenylacetonitrile, α- (propylsulfonyloxyimino) -p-methylphenylacetonitrile, α- (methyl Sulfonyloxyimino) -p-bromophenylacetonitrile and the like. Of these, α- (methylsulfonyloxyimino) -p-methoxyphenylacetonitrile is preferred.

As the component (B), one type of acid generator may be used alone, or two or more types may be used in combination.
(B) The usage-amount of a component is 0.5-30 mass parts with respect to 100 mass parts of (A) component or (A ') component, Preferably it is 1-10 mass parts. If the amount is less than 0.5 parts by mass, pattern formation is not sufficiently performed. If the amount exceeds 30 parts by mass, a uniform solution is difficult to obtain, which may cause a decrease in storage stability.

[Component (C)]
The positive resist composition (II) can be produced by dissolving the material in an organic solvent (C) (hereinafter referred to as component (C)).
As the component (C), any component can be used as long as it can dissolve each component to be used to form a uniform solution. Conventionally, any one of known solvents for chemically amplified resists can be used. Two or more types can be appropriately selected and used.
For example, ketones such as γ-butyrolactone, acetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone, 2-heptanone, ethylene glycol, ethylene glycol monoacetate, diethylene glycol, diethylene glycol monoacetate, propylene glycol, propylene glycol monoacetate, dipropylene glycol Or polyhydric alcohols such as monomethyl ether, monoethyl ether, monopropyl ether, monobutyl ether or monophenyl ether of dipropylene glycol monoacetate and derivatives thereof, cyclic ethers such as dioxane, methyl lactate, lactic acid Ethyl, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate , It can be mentioned esters such as ethyl ethoxypropionate. These organic solvents may be used independently and may be used as 2 or more types of mixed solvents.
The amount used is not particularly limited, but is a concentration that can be applied to a substrate or the like.

[(D) component]
In the positive resist composition (II), a nitrogen-containing organic compound can be further added as an optional component (D) in order to improve the resist pattern shape, the stability over time, and the like.
A wide variety of nitrogen-containing organic compounds have already been proposed, and any known one may be used. However, amines, particularly secondary aliphatic amines and tertiary aliphatic amines are preferred. Here, the aliphatic amine means an amine of alkyl or alkyl alcohol.

Specific examples of the component (D) include trimethylamine, diethylamine, triethylamine, di-n-propylamine, tri-n-propylamine, tripentylamine, tri-n-heptylamine, tri-n-octylamine, di- alkylamines such as n-heptylamine, di-n-octylamine, tri-n-dodecylamine, diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, di-n-octanolamine, tri-n-octanolamine And alkyl alcohol amines. Of these, secondary or tertiary aliphatic amines having an alkyl group having 7 to 15 carbon atoms are preferred. By having an alkyl group having 7 to 15 carbon atoms, the aliphatic amine can be evenly distributed because it is difficult to diffuse in the formed resist pattern. In the present invention, an alkylamine such as tri-n-octylamine is particularly preferable.
These may be used alone or in combination of two or more.
These are normally used in the range of 0.01 to 5.0 parts by mass with respect to 100 parts by mass of component (A).

[(E) component]
In addition, for the purpose of preventing the sensitivity deterioration due to the blending with the component (D) and improving the resist pattern shape, the stability of holding, etc., as an optional component (E), an organic carboxylic acid or an oxo acid of phosphorus or Derivatives thereof can be included. In addition, (D) component and (E) component can also be used together, and any 1 type can also be used.
As the organic carboxylic acid, for example, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, salicylic acid and the like are suitable.
Phosphorus oxoacids or derivatives thereof include phosphoric acid, phosphoric acid di-n-butyl ester, phosphoric acid diphenyl ester and other phosphoric acid or derivatives thereof such as phosphonic acid, phosphonic acid dimethyl ester, phosphonic acid- Like phosphonic acids such as di-n-butyl ester, phenylphosphonic acid, phosphonic acid diphenyl ester, phosphonic acid dibenzyl ester and derivatives thereof, phosphinic acids such as phosphinic acid, phenylphosphinic acid and their esters Among these, phosphonic acid is particularly preferable.
(E) A component is used in the ratio of 0.01-5.0 mass parts per 100 mass parts of (A) component.

[Other optional ingredients]
The positive resist composition (I), (II) for low acceleration electron beam used in the present invention further has an optional miscible additive, for example, an additional resin or coating for improving the performance of the resist film. A surfactant, a dissolution inhibitor, a plasticizer, a stabilizer, a colorant, an antihalation agent and the like for improving the properties can be appropriately added and contained.

  The upper resist film can be formed, for example, by applying the above-described resist composition solution on the intermediate layer according to a conventional method.

{Middle layer}
There are no particular restrictions on the material of the intermediate layer and the forming method, but a material having a silicon content in the polymer of 5 to 30%, preferably about 5 to 15%, and a forming method using the same can be used. Since the matching with the positive resist composition for low acceleration electron beam according to the first or second invention of the present invention is good, the following hard mask forming composition is preferably used.

"Composition for hard mask formation"
The composition for forming a hard mask contains an alkali-soluble resin (A _HM ) and a photoacid generator (B _HM ). As the alkali-soluble resin (A _HM ), the following structural units (s1), (s2) and A ladder-type silicone copolymer comprising (s3) is used (it can also be referred to as an antireflection film-forming composition because it has an antireflection function).
Structural unit (s1): a (hydroxyphenylalkyl) silsesquioxane unit, that is, a structural unit represented by the following general formula (S-1) or (S-1 ′).
Structural unit (s2): An (alkoxyphenylalkyl) silsesquioxane unit, that is, a structural unit represented by the following general formula (S-2) or (S-2 ′).
Structural unit (s3): An alkyl or phenylsilsesquioxane unit, that is, a structural unit represented by the following general formula (S-3) or (S-3 ′).

（式中のｎは１〜３の整数である）

(Where n is an integer of 1 to 3)

（式中のＲ^６は炭素数１〜４の直鎖状又は枝分れ状低級アルキル基、ｎは１〜３の整数である）

(Wherein R ⁶ is a linear or branched lower alkyl group having 1 to 4 carbon atoms, and n is an integer of 1 to 3)

（式中のＲ^７は炭素数１〜２０の直鎖状又は炭素数２〜２０の枝分かれ状又は炭素数５〜２０の脂環状又は単環又は多環式アルキル基又はフェニル基である）

(Wherein R ⁷ is a straight chain having 1 to 20 carbon atoms, a branched chain having 2 to 20 carbon atoms, or an alicyclic, monocyclic or polycyclic alkyl group or phenyl group having 5 to 20 carbon atoms)

As R ⁶ in the general formulas (S-2) and (S-2 ′), a methyl group is most preferable.
As the R ⁷ in the general formula (S-3), a lower alkyl group of 1 to 5 carbon atoms, a cycloalkyl group or a phenyl group having a carbon number of 5 to 6, to adjust k value (extinction coefficient) It is preferable because it is easy.
In the general formulas (S-1), (S-1 ′), (S-2) and (S-2 ′), the —OH group and the —OR group are any of the o-position, m-position and p-position. However, the p-position is preferred industrially.
The structural units (s1), (s2) and (s3) are usually represented by the above general formulas (S-1), (S-2) and (S-3), or (S-1). '), (S-2') and (S-3 ').
This ladder type silicone copolymer preferably has a mass average molecular weight (polystyrene conversion) in the range of 1500 to 20000.

  The content ratio of these structural units is 10 to 90 mol%, preferably 15 to 85 mol%, structural unit (s2) 0 to 50 mol%, preferably 10 to 40 mol%, and structural units (s1). s3) It is selected within the range of 1 to 90 mol%, preferably 15 to 85 mol%.

  The structural unit (s2) in this is for adjusting the solubility with respect to alkali to suppress film loss and to prevent roundness generated in the cross section of the resist pattern. Since this is the same as the (alkoxyphenylalkyl) silsesquioxane unit, which is the starting material of the (hydroxyphenylalkyl) silsesquioxane unit, it can be easily introduced by suppressing the dissociation degree of the alkoxy group. This is advantageous.

The photoacid generator (B _HM ) is a compound that generates an acid upon irradiation with light, and has been conventionally used as a component of a general chemical amplification type positive resist composition. In the composition for forming a hard mask, it can be appropriately selected from those used so far.

Preferred acid generators (B _HM ) include, for example, diphenyliodonium trifluoromethanesulfonate or nonafluorobutanesulfonate, bis (4-tert-butylphenyl) iodonium trifluoromethanesulfonate or nonafluorobutanesulfonate, triphenylsulfonium trifluoromethanesulfonate Or onium salts such as nonafluorobutanesulfonate, trifluoromethanesulfonate of tri (4-methylphenyl) sulfonium or nonafluorobutanesulfonate, bis (p-toluenesulfonyl) diazomethane, bis (1,1-dimethylethylsulfonyl) diazomethane, Bis (isopropylsulfonyl) diazomethane, bis (cyclohexylsulfonyl) diazomethane, bis (2,4- It can be mentioned diazomethane-based compounds such as methyl phenylsulfonyl) diazomethane. Particularly preferred among these are onium salts having a decomposition point of 250 ° C. or lower, such as triphenylsulfonium trifluoromethanesulfonate, triphenylsulfonium nonafluorobutanesulfonate, and 7,7-dimethyl- of bis (p-tert-butylphenyl) iodonium. Bicyclo- [2,2,1] -heptan-2-one-1-sulfonate and the like.

These photoacid generators (B _HM ) may be used alone or in combination of two or more. The content is selected in the range of usually 0.5 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the alkali-soluble resin (A _HM ). If the photoacid generator is less than 0.5 parts by mass, it is difficult to form a film, and if it exceeds 20 parts by mass, the solution is not uniform and storage stability is lowered.

In addition to the above essential components (alkali-soluble resin (A _HM ) and photoacid generator (B _HM ), the hard mask forming composition may contain a crosslinking agent (C _HM ) as necessary. The crosslinking agent suitably used in the present hard mask forming composition can form an appropriate film as a hard mask material by crosslinking the (A _HM ) component when the hard mask forming composition is heated or baked. Any compound having two or more reactive groups, for example, divinylbenzene, divinylsulfonic acid, triacryl formal, glyoxal or polyhydric alcohol (meth) acrylate, melamine, At least two amino groups of urea, benzoguanamine, or glycoluril are substituted with a methylol group or a lower alkoxymethyl group Preference is. In which also, in particular the following formula

で表される架橋剤が最も好ましい。
これらの架橋剤は、（Ａ_ＨＭ）１００質量部あたり１〜１０質量部の範囲で用いることができる。

The crosslinking agent represented by is most preferable.
These crosslinking agents can be used in the range of 1 to 10 parts by mass per 100 parts by mass of (A _HM ).

Next, in the hard mask forming composition suitably used in the present invention, in addition to the above-mentioned (A _HM ) component, (B _HM ) component and (C _HM ) component, if necessary, further (D _HM ) component As a linear polymer.
As this linear polymer, polyolefin, polystyrene, polyvinyl acetate, polyamide, or the like can be used, but an acrylic polymer, particularly an acrylic polymer in which an adamantyl group is bonded to a side chain is particularly preferable.

Examples of such linear polymers include (d ₁ ) general formula

（式中、Ｒ^１は水素原子又はメチル基、Ｒ^２は低級アルキル基である）
で表わされる単位１０〜６０モル％、好ましくは２０〜４０モル％、（ｄ_２）一般式

(Wherein R ¹ is a hydrogen atom or a methyl group, and R ² is a lower alkyl group)
In units 10 to 60 mol% homology, preferably 20 to 40 mol%, _{(d 2)} the general formula

（式中のＲ^３は水素原子又はメチル基である）
で表わされる単位３０〜８０モル％、好ましくは２０〜５０モル％、及び（ｄ_３）一般式

(Wherein R ³ is a hydrogen atom or a methyl group)
30 to 80 mol%, preferably 20 to 50 mol%, and (d ₃ )

（式中、Ｒ^４は水素原子又はメチル基である）
で表わされる単位１０〜５０モル％、好ましくは２０〜４０モル％からなる線状共重合体を挙げることができる。
上記一般式（ｄ_１）中のＲ^２としては、炭素数１〜５の低級アルキル基、特にメチル基やエチル基が工業的な面から好ましい。

(Wherein R ⁴ is a hydrogen atom or a methyl group)
A linear copolymer comprising 10 to 50 mol%, preferably 20 to 40 mol% of a unit represented by
As R ² in the general formula (d ₁ ), a lower alkyl group having 1 to 5 carbon atoms, particularly a methyl group or an ethyl group is preferable from an industrial viewpoint.

The linear polymer of the (D _HM ) component preferably has a mass average molecular weight in the range of 5000 to 20000.
This ( _DHM ) component is mix | blended in the ratio of 10-100 mass parts per 100 mass parts of ( _AHM ) component.

Next, the hard mask forming composition suitably used in the present invention includes the (A _HM ) component, the (B _HM ) component, the (C _HM ) component, and the (D _HM ) component optionally mixed. In addition, conventional ionic or nonionic surfactants can be included to further impart dispersibility and coating uniformity.

  These surfactants are added at a ratio of 0.05 to 1.0 part by mass per 100 parts by mass of the total solid content.

  The composition for forming a hard mask used in the present invention can be easily applied to a substrate such as a silicon wafer having an organic film as a base material by a conventional spin coating method to form a desired hard mask. it can. In the conventional resist process, considering that it is necessary to form an oxide film on a base material by vapor deposition and to apply a resist film thereon, the process is greatly simplified.

  The composition for forming a hard mask is dissolved in an appropriate solvent when used and used as a solution. As the solvent used in this case, the same solvent as the component (C) described above can be used.

  If desired, the hard mask forming composition may further include compatible additives such as sensitizers, additional resins, plasticizers, stabilizers or developed images to make them more visible. A commonly used colorant or the like can be added.

  An intermediate | middle layer can be formed by apply | coating the solution of the composition for hard mask formation mentioned above on the lower layer organic film mentioned later according to a conventional method, for example.

{Lower layer organic film}
The lower organic film is an organic film that can be etched by a conventional dry etching method. This organic film is desirably insoluble in an alkaline developer used for development after exposure. By using such a lower organic film, first, selective exposure of the upper resist film is performed by lithography using a low acceleration electron beam, alkali development is performed to form a resist pattern, and then the resist pattern is used as a mask. For example, after the pattern is transferred to the intermediate layer using oxide etching with a halogen-based gas, the lower organic film is dry-etched using the intermediate layer pattern as a mask, so that the upper resist film and the intermediate layer are formed on the lower organic film. The resist pattern is transferred. As a result, a pattern with a high aspect ratio can be formed without causing pattern collapse.

  The organic film material for forming the lower organic film does not necessarily require sensitivity to an electron beam or light like the upper resist film. In the manufacture of semiconductor elements and liquid crystal display elements, resists and resins that are generally used may be used.

Moreover, since it is necessary to transfer the upper resist pattern and the intermediate layer pattern to the lower organic film, the lower organic film is preferably a material that can be etched by oxygen plasma.
As such a material, it is easy to perform etching with oxygen plasma, and at the same time, it has a strong resistance to fluorocarbon gas used for etching a silicon substrate or the like in a later process. The main component is at least one selected from the group consisting of polyimides.
Among these, a novolak resin and an acrylic resin having an alicyclic moiety or an aromatic ring in the side chain are preferably used because they are inexpensive and widely used and have excellent dry etching resistance in the subsequent steps.

As the novolak resin, those generally used for positive resist compositions can be used, and i-line and g-line positive resists containing a novolac resin as a main component can also be used.
The novolac resin is a resin obtained by, for example, addition condensation of an aromatic compound having a phenolic hydroxyl group (hereinafter simply referred to as “phenols”) and an aldehyde under an acid catalyst.

  Examples of phenols include phenol, o-cresol, m-cresol, p-cresol, o-ethylphenol, m-ethylphenol, p-ethylphenol, o-butylphenol, m-butylphenol, p-butylphenol, 2, 3 -Xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, 2,3,5-trimethylphenol, 3,4,5-trimethylphenol , P-phenylphenol, resorcinol, hydroquinone, hydroquinone monomethyl ether, pyrogallol, phloroglicinol, hydroxydiphenyl, bisphenol A, gallic acid, gallic acid ester, α-naphthol, β-naphthol and the like.

Examples of aldehydes include formaldehyde, furfural, benzaldehyde, nitrobenzaldehyde, and acetaldehyde.
The catalyst for the addition condensation reaction is not particularly limited. For example, hydrochloric acid, nitric acid, sulfuric acid, formic acid, oxalic acid, acetic acid and the like are used as the acid catalyst.
The novolak resin has a mass average molecular weight of 3000 to 10000, preferably 6000 to 9000, and more preferably 7000 to 8000. If the mass average molecular weight is less than 3000, it may sublime when baked at a high temperature. If the mass average molecular weight exceeds 10,000, dry etching tends to be difficult, which is not preferable.

  As the novolak resin that can be used in the present invention, a commercially available one can be used, and in particular, the mass average molecular weight (Mw) is 5000 to 50000, preferably 8000 to 30000, and the molecular weight is 500 or less, preferably A novolak resin having a content of low nuclei of 200 or less in the gel permeation chromatography method is 1% by mass or less, preferably 0.8% by mass or less. The content of the low nucleus is preferably as small as possible, and is desirably 0% by mass.

The “low molecular weight having a molecular weight of 500 or less” is detected as a low molecular fraction having a molecular weight of 500 or less when analyzed by GPC using polystyrene as a standard. “Low-nuclear bodies having a molecular weight of 500 or less” include monomers that have not been polymerized and those having a low degree of polymerization, such as those obtained by condensing 2-5 molecules of phenols with aldehydes, depending on the molecular weight. .
The content (mass%) of the low-nuclear body having a molecular weight of 500 or less is graphed with the analysis result by the GPC method taking the fraction number on the horizontal axis and the concentration on the vertical axis. It is measured by determining the percentage (%) of the area under the curve of the low molecular fraction.

By setting Mw of the novolak resin to 50000 or less, excellent embedding characteristics with respect to a substrate having fine irregularities are excellent, and by setting Mw to 5000 or more, etching resistance to a fluorocarbon gas or the like is excellent, which is preferable. .
In addition, when the content of the low-nuclear body having a molecular weight of 500 or less is 1% by mass or less, the embedding property with respect to the substrate having fine unevenness is improved. Although the reason why the embedding property is improved by reducing the content of the low nuclei is not clear, it is presumed that the degree of dispersion becomes small.

  As the acrylic resin, those generally used for positive resist compositions can be used. For example, a structural unit derived from a polymerizable compound having an ether bond and a polymerizable compound having a carboxyl group can be used. Mention may be made of acrylic resins containing derived structural units.

  Examples of the polymerizable compound having an ether bond include 2-methoxyethyl (meth) acrylate, methoxytriethylene glycol (meth) acrylate, 3-methoxybutyl (meth) acrylate, ethyl carbitol (meth) acrylate, phenoxy polyethylene glycol (meta And (meth) acrylic acid derivatives having an ether bond and an ester bond such as acrylate, methoxypolypropylene glycol (meth) acrylate, and tetrahydrofurfuryl (meth) acrylate. These compounds can be used alone or in combination of two or more.

  Examples of the polymerizable compound having a carboxyl group include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; 2-methacryloyloxyethyl succinic acid, and 2-methacryloyloxyethyl. Examples include maleic acid, 2-methacryloyloxyethyl phthalic acid, 2-methacryloyloxyethyl hexahydrophthalic acid and other compounds having a carboxyl group and an ester bond, and acrylic acid and methacrylic acid are preferred. These compounds can be used alone or in combination of two or more.

  The soluble polyimide is a polyimide that can be made liquid by the organic solvent as described above.

  The lower organic film can be formed, for example, by applying a solution of a base material as described above onto a substrate according to a conventional method.

<Board>
The substrate is not particularly limited, and a conventionally known substrate can be used. For example, a substrate for an electronic component or a substrate on which a predetermined wiring pattern is formed can be exemplified.
More specifically, examples of the substrate include a silicon wafer, a metal substrate such as copper, chromium, iron, and aluminum, and a glass substrate.
As a material for the wiring pattern, for example, copper, aluminum, nickel, gold or the like can be used.

{Film thickness of each layer}
In the resist laminate of the present invention, the upper resist film, the intermediate layer, and the lower organic film have a total thickness from the balance of throughput in consideration of the target aspect ratio and the time required for dry etching of the lower organic film, Preferably it is 1 micrometer or less, More preferably, it is 0.7 micrometer or less, Most preferably, it is 0.5 micrometer or less. The total lower limit value is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.15 μm or more.
The thickness of the upper resist film is preferably 50 to 150 nm, more preferably 50 to 100 nm. By setting the thickness of the upper resist film within this range, there is sufficient permeability to a low acceleration electron beam. In addition, there are effects that a resist pattern can be formed with high resolution and sufficient resistance to dry etching is obtained.
The thickness of the intermediate layer is preferably 10 to 100 nm, more preferably 20 to 80 nm. By setting the thickness of the intermediate layer within this range, there are effects that a resist pattern can be formed with high resolution and sufficient resistance to dry etching can be obtained.
The thickness of the lower organic film is preferably 50 to 500 nm, more preferably 100 to 400 nm. By setting the thickness of the lower organic film within this range, it is possible to form a resist pattern with a high aspect ratio and to obtain sufficient etching resistance during substrate etching.

  In addition, the resist laminated body of this invention includes the laminated body in which the resist pattern is formed in the upper layer resist film, the intermediate | middle layer, and the lower layer organic film, and the laminated body in which the resist pattern is not formed.

≪Pattern formation method≫
In the pattern forming method of the present invention, the laminate forming step of forming the resist laminate of the present invention, and the upper resist film of the resist laminate are exposed with a low acceleration electron beam, alkali-developed, and Forming a resist pattern on the upper resist film, performing a pattern transfer to the intermediate layer by performing oxide etching using the resist pattern as a mask pattern, and using the resist pattern and the intermediate layer pattern as a mask pattern The pattern forming method is characterized by sequentially performing dry etching of the lower organic film and sequentially forming a lower layer pattern on the lower organic film.

The pattern formation method of this invention can be performed as follows, for example.
<Laminated body formation process>
First, a resist composition or a resin solution for forming a lower organic film is applied on a substrate such as a silicon wafer with a spinner or the like, preferably at 200 to 300 ° C. for 30 to 300 seconds, preferably 60 to 180. Bake treatment is performed under heating conditions for seconds to form a lower organic film.

  Then, on the lower organic film, the above-described composition for forming a hard mask is applied with a spinner or the like, and prebaked for 40 to 180 seconds, preferably 60 to 90 seconds under a temperature condition of 70 to 130 ° C., Further, the intermediate layer is formed by baking at 200 to 250 ° C. for 60 to 120 seconds.

  Next, a solution of the resist composition such as the low-acceleration electron beam positive resist composition (I) or (II) is applied onto the intermediate layer formed as described above with a spinner or the like. Pre-baking is performed for 40 to 120 seconds, preferably 60 to 90 seconds under a temperature condition of ° C. to form an upper resist film, and a resist laminated body in which a three-layer resist is laminated on a substrate is obtained.

<Pattern formation process>
Next, the upper resist film of the resist laminate may be drawn by directly irradiating a low acceleration electron beam without passing through a mask pattern. Preferably, a low acceleration electron beam exposure apparatus such as “LEEEPL” is used. ”(Product name, manufactured by Ripple Co., Ltd., acceleration voltage 2 kV), and selectively exposed through a desired mask pattern. By performing exposure through the mask pattern, there are advantages such as improving the throughput and forming a resist pattern with a small interval (pitch size) between patterns.
“LEEPL” is a pattern in which a sample and a mask are brought close to each other (for example, about 50 μm), irradiated with a parallel low-acceleration electron beam, and a pattern is transferred. A normal-size mask is used as the mask. Therefore, there is an advantage that the manufacturing cost is lower than that of a mask used in the reduction projection exposure method of photolithography. Further, since it is not affected by the proximity effect, a highly accurate pattern can be formed.
The acceleration voltage of the low acceleration electron beam is preferably 2 to 5 kV, and most preferably 2 kV, for example.

  Subsequently, PEB (post-exposure heating) is applied for 40 to 120 seconds, preferably 60 to 90 seconds, under a temperature condition of 80 to 150 ° C. Subsequently, this is developed using an alkali developer, for example, an aqueous solution of 0.1 to 10% by mass of tetramethylammonium hydroxide. In this manner, a resist pattern (upper layer resist pattern) faithful to the mask pattern can be formed on the upper layer resist film.

  Next, using this resist pattern as a mask pattern, a pattern (intermediate layer pattern) is transferred and formed on the intermediate layer. For the formation of the intermediate layer pattern, the upper layer resist pattern is used as a mask, and the intermediate layer etchant (a gas capable of etching the intermediate layer), for example, when the intermediate layer is a silicon-based film, is oxide-etched with a halogen-based gas. In addition, these etchants and etching conditions can be performed by a well-known method.

Next, by using the resist pattern and the intermediate layer pattern as a mask pattern and dry etching the lower organic layer, a pattern (lower layer pattern) faithful to the mask pattern can be obtained.
Known dry etching methods include chemical etching such as downflow etching and chemical dry etching; physical etching such as sputter etching and ion beam etching; and chemical and physical etching such as RIE (reactive ion etching). This method can be used.
The most common dry etching is parallel plate RIE. In this method, first, a resist laminate is put in a chamber of an RIE apparatus, and a necessary etching gas is introduced. When a high frequency voltage is applied to the holder of the resist laminate placed in parallel with the upper electrode in the chamber, the gas is turned into plasma. In the plasma, there are charged particles such as positive and negative ions and electrons, and neutral active species. When these etching species are adsorbed on the lower resist layer, a chemical reaction occurs, the reaction product is detached from the surface and exhausted to the outside, and etching proceeds.
Examples of the etching gas include oxygen and sulfur dioxide. Etching with oxygen plasma is preferably used because it has a high resolution and is widely used.

By etching the substrate using the lower layer pattern thus obtained as a mask, a fine pattern can be formed on the substrate. The pattern obtained as described above can be used for manufacturing a semiconductor or the like as follows, for example.
As an etching method at this time, an etching method using a halogen-based gas can be preferably used.

As described above, the resist laminate of the present invention is suitably used in a method for forming a pattern through a step of exposing using a low acceleration electron beam.
In particular, when the above-described positive resist composition (I) or (II) is used as a material for the upper layer resist film, compared to a chemically amplified positive resist composition using a conventional polyhydroxystyrene resin, Since a resist layer having excellent etching resistance and reduced film thickness can be formed, the resist layer can be thinned, and thus can be effectively used in a pattern forming method having an exposure process using a low acceleration electron beam. .

Hereinafter, the present invention will be described in detail with reference to examples.
Reference Example A method for preparing a composition for forming a hard mask is shown below.
As the (A _HM ) component, a copolymer (mass average molecular weight 7000) composed of 72 mol% of p-hydroxybenzylsilsesquioxane units and 28 mol% of phenyl silsesquioxane units was used. This (A _HM ) component 100 3 parts by weight of 7,7-dimethyl-bicyclo- [2,2,1] -heptan-2-one-1-sulfonate of bis (p-tert-butylphenyl) iodonium as (B _HM ) component And 5 parts by mass of tetrabutoxymethylglycoluril as a cross-linking agent and 35 parts by mass of an acrylate type polymer represented by the following chemical formula [Chemical Formula 16] as a linear polymer were added to propylene glycol monoether monoacetate and propylene Mixture with glycol monopropyl ether (mass ratio 6.2 / 93.8) 300 It was dissolved in the amount unit, to prepare a hard mask-forming composition.

[Example 1]
First, component (A′2) was prepared. That is, a copolymer obtained by reacting p-hydroxystyrene with adamantanol methacrylate for deriving a structural unit in which R is a methyl group in the general formula (IVa) by a known polymerization method in the presence of an acid catalyst. A polymer (molar ratio 80:20, mass average molecular weight (Mw) 8000, dispersity (Mw / Mn) 1.2) and ethyl vinyl ether are reacted in a known manner under an acid catalyst to obtain the above copolymer. Resin (X) in which the hydrogen atom of the hydroxyl group of the coalescence was protected with 1-ethoxyethyl group was obtained.
As a result of analyzing this resin (X) by ¹ H-NMR, the number of 1-ethoxyethoxy groups relative to the total number of hydroxyl groups of p-hydroxystyrene and adamantanol was 25%. From this, it was recognized that the protection ratio of a hydroxyl group was 25 mol%. Moreover, Mw of resin (X) was 10,000 and Mw / Mn was 1.2.

  Using this resin (X) as component (A′2), 100 parts by mass of component (A′2), 8 parts by mass of triphenylsulfonium trifluoromethanesulfonate as component (B), and trioctyl as component (D) 0.8 parts by mass of amine and 0.32 parts by mass of salicylic acid as component (E) are dissolved in propylene glycol monomethyl ether acetate (hereinafter referred to as “PM”) to obtain a solid content concentration of 3.5% by mass. A positive resist composition for low acceleration electron beam was obtained.

The obtained positive resist composition for low acceleration electron beam was applied on a silicon wafer using a spinner and soft-baked at 100 ° C. for 90 seconds to form a positive resist layer having a thickness of 70 nm. .
Next, this resist layer was subjected to post-exposure heating (PEB) treatment at 110 ° C. for 90 seconds, and further paddle-developed with an aqueous 2.38 mass% tetramethylammonium hydroxide (TMAH) solution at 23 ° C. for 60 seconds. Water rinsing was performed using pure water for 30 seconds. After carrying out shaking drying, after heating and drying at 100 degreeC for 60 second, the film thickness of the positive resist layer was measured, it was 67 nm. From this result, it can be seen that the remaining film ratio was 95%.

  Further, the obtained positive resist composition for low-acceleration electron beam was uniformly applied at a film thickness of 70 nm on an 8-inch silicon substrate subjected to hexamethyldisilazane treatment, and baked at 100 ° C. for 90 seconds. To form a film. The substrate was subjected to mask transfer with a low acceleration electron beam exposure device LEEPL (manufactured by Ripple Co., Ltd., acceleration voltage 2 kV), baked at 110 ° C. for 90 seconds, developed with 2.38% TMAH aqueous solution for 60 seconds, pure water After rinsing and shaking off for 30 seconds, baking was performed at 100 ° C. for 60 seconds. By this treatment, a resolution of 80 nm was obtained for the line and space (L / S) pattern and 80 nm for the contact hole (C / H) pattern. Defects were measured using a surface defect observation apparatus KLA2132 (product name) manufactured by KLA Tencor, and the number of defects in the wafer was evaluated to be zero.

  Next, using the L / S pattern with a line width of 80 nm formed above as a mask, an etching rate test for performing dry etching on the substrate was performed. That is, when an etching rate was measured using a mixed gas of oxygen and tetrafluoromethane as an etching gas, the etching rate was 1.2 times slower than that measured in the same conditions in Comparative Example 1 described later, which was excellent. It was found to have etching resistance.

[Example 2]
In Example 1, except that the adamantanol methacrylate used for the synthesis of the component (A′2) was replaced with an adamantanol acrylate in which R is a hydrogen atom in the general formula (IVa). In the same manner as in Example 1, the hydroxyl group of the copolymer (molar ratio 80:20, mass average molecular weight (Mw) 7700, dispersity (Mw / Mn) 1.2) was protected with a 1-ethoxyethyl group (Y )
As a result of analyzing this resin (Y) by ¹ H-NMR, the number of 1-ethoxyethoxy groups relative to the total number of hydroxyl groups of p-hydroxystyrene and adamantanol was 30%. From this, it was recognized that the protection ratio of a hydroxyl group is 30 mol%. Moreover, Mw of resin (Y) was 9700 and Mw / Mn was 1.2.
Next, a positive resist composition for low acceleration electron beam was prepared in the same manner as in Example 1 except that the resin (Y) was used instead of the resin (X), and the remaining film ratio was measured. As a result, the remaining film rate was 95%.

  A resist pattern was formed in the same manner as in Example 1 using the obtained positive resist composition for low acceleration electron beam. As a result, a resolution of 80 nm was obtained for the line and space (L / S) pattern and 80 nm for the contact hole (C / H) pattern. Defects were measured using a surface defect observation apparatus KLA2132 (product name) manufactured by KLA Tencor, and the number of defects in the wafer was evaluated to be zero.

  Further, when the etching rate was measured in the same manner as in Example 1, it was found that the etching rate was 1.2 times slower than that measured in the same conditions in Comparative Example 1 described later, and had excellent etching resistance. .

[Example 3]
First, the component (A′1) was prepared. That is, poly (p-hydroxystyrene) (mass average molecular weight (Mw) is 8000, dispersity (Mw / Mn) is 1.2) and adamantoxyvinyl ether are reacted in a known manner under an acid catalyst, A resin (Z) in which a part of the hydrogen atoms of the hydroxyl group of (p-hydroxystyrene) was protected with an acid dissociable, dissolution inhibiting group represented by the above formula (II-a) was obtained.
As a result of analyzing this resin (Z) by ¹ H-NMR, the number of acid dissociable, dissolution inhibiting groups represented by the above formula (II-a) relative to the number of hydroxyl groups of p-hydroxystyrene was 30%. From this, it was recognized that the protection ratio of a hydroxyl group is 30 mol%. Moreover, Mw of resin (Z) was 12000 and Mw / Mn was 1.2.
Next, a positive resist composition for low acceleration electron beams was prepared in the same manner as in Example 1 except that this resin (A′1) was used as the component (A), and the remaining film ratio was measured. As a result, the remaining film rate was 95%.

  A resist pattern was formed in the same manner as in Example 1 using the obtained positive resist composition for low acceleration electron beam. As a result, a resolution of 80 nm was obtained for the L / S pattern and 80 nm for the C / H pattern. Defects were measured using a surface defect observation apparatus KLA2132 (product name) manufactured by KLA Tencor, and the number of defects in the wafer was evaluated to be zero.

  Further, when the etching rate was measured in the same manner as in Example 1, it was found that the etching rate was 1.4 times slower than that measured under the same conditions in Comparative Example 1 described later, and the etching resistance was excellent. .

[Example 4]
In Example 3, the poly (p-hydroxystyrene) used for the synthesis of the component (A) is a copolymer of p-hydroxystyrene and styrene (molar ratio 85:15, mass average molecular weight (Mw) is 8000, Except that the dispersity (Mw / Mn) was changed to 1.2), in the same manner as in Example 3, a part of the hydrogen atoms of the hydroxyl group of the p-hydroxystyrene constituent unit contained in the copolymer was represented by the above formula ( A resin (W) protected with an acid dissociable, dissolution inhibiting group represented by II-a) was obtained.
As a result of analyzing this resin (W) by ¹ H-NMR, the number of acid dissociable, dissolution inhibiting groups represented by the above formula (II-a) with respect to the number of hydroxyl groups of p-hydroxystyrene was 25%. From this, it was recognized that the protection ratio of a hydroxyl group was 25 mol%. Moreover, Mw of the resin (W) was 10,000, and Mw / Mn was 1.2.
Next, a positive resist composition for low acceleration electron beam was prepared in the same manner as in Example 1 except that this resin (A1) was used as the component (A), and the remaining film ratio was measured. As a result, the remaining film rate was 95%.

  A resist pattern was formed in the same manner as in Example 1 using the obtained positive resist composition for low acceleration electron beam. As a result, a resolution of 80 nm was obtained for the L / S pattern and 80 nm for the C / H pattern. Defects were measured using a surface defect observation apparatus KLA2132 (product name) manufactured by KLA Tencor, and the number of defects in the wafer was evaluated to be zero.

  Further, when the etching rate was measured in the same manner as in Example 1, it was found that the etching rate was 1.4 times slower than that measured under the same conditions in Comparative Example 1 described later, and the etching resistance was excellent. .

[Comparative Example 1]
In Example 1, instead of the resin (X) as the component (A), a part of the hydroxyl groups of poly (p-hydroxystyrene) (mass average molecular weight 8000, dispersity 1.2) are 1-ethoxyethyl groups. A known positive resist composition used conventionally was prepared in the same manner as in Example 1 except that the protected resin component (hydroxyl protection ratio was 35 mol%) was used, and the remaining film ratio was measured. As a result, the remaining film rate was 75%.

  A resist pattern was formed in the same manner as in Example 1 using the obtained positive resist composition. As a result, although 90 nm resolution was obtained for the L / S pattern and 90 nm resolution was obtained for the C / H pattern, the pattern top was rounded, the remaining film ratio of the unexposed area was large, and the pattern was poor. there were.

  The film thickness reduction of the resist using the positive resist compositions of Examples 1 to 4 was smaller than the film thickness reduction of the resist using the positive resist composition obtained in Comparative Example 1. This shows that the etching resistance of the resists using the positive resist compositions of Examples 1 to 4 was good.

[Examples 5 to 8, Comparative Example 2]
Using the positive resist compositions obtained in Examples 1 to 4 and Comparative Example 1, a resist laminate was produced by the following procedure, and a resist pattern was formed using the resist laminate.
First, on an 8-inch silicon wafer, a solution of a commercially available base material (product name TBLC-100, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied using a spinner and soft-baked at 230 ° C. for 90 seconds. A lower organic film having a thickness of 300 nm was formed.
Next, the above hard mask forming composition is applied onto the lower layer using a spinner, subjected to a soft baking process at 90 ° C. for 90 seconds, and subsequently a baking process at 250 ° C. for 90 seconds, thereby forming a hard film having a thickness of 55 nm. A mask layer (intermediate layer) was formed.
Next, the positive resist composition obtained in Examples 1 to 4 or Comparative Example 1 was applied to the intermediate layer using a spinner, and subjected to a soft baking treatment at 100 ° C. for 90 seconds, whereby a film thickness of 70 nm was obtained. A positive resist layer (upper resist film) was formed, and a resist laminate in which a three-layer resist layer was laminated on the substrate was obtained.

  Next, using a low-acceleration electron beam exposure apparatus (“LEEEP” (manufactured by Leaple Co., Ltd., acceleration voltage 2 kV), a low acceleration electron beam with an acceleration voltage of 2 kV is irradiated through a predetermined mask pattern, and then at 110 ° C. The film was subjected to a post-exposure heating (PEB) treatment for 90 seconds, followed by paddle development with an aqueous 2.38 mass% tetramethylammonium hydroxide solution at 23 ° C. for 60 seconds, and then rinsed with pure water for 30 seconds. After drying, it was dried by heating at 100 ° C. for 60 seconds to form a C / H pattern having a pore diameter of 70 nm in the upper layer.

Then, using the obtained resist pattern as a mask pattern, an oxide film (oxide) etching apparatus (“TCE-7811X” manufactured by Tokyo Ohka Kogyo Co., Ltd.) is used for the intermediate layer, and the pressure is 300 mTorr, CF ₄ / CHF ₃ / The resist pattern was transferred to the intermediate layer by performing oxide film etching under the conditions of He = 75/45/200 (sccm), output 1200 W, processing temperature Upper: 25 ° C., Lower: 20 ° C. Next, using this resist pattern and the intermediate layer pattern as a mask, a parallel plate type plasma etching apparatus (manufactured by Tokyo Ohka Kogyo Co., Ltd., “GP2”) is used for the lower layer, a pressure of 0.4 Pa, and a mixed gas of oxygen and nitrogen Reactive ion etching was performed under the conditions of a flow rate of 20 cc / min, an RF output of 1000 W, and a processing temperature of 25 ° C. to form a resist pattern.

The cross-sectional shapes of the C / H patterns of Examples 5 and 6 were excellent with high rectangularity, and C / H patterns with a line width of 70 nm were formed with good resolution. The cross-sectional shapes of the C / H patterns of Examples 7 and 8 were slightly inversely tapered, but there was no practical problem. The reason for this shape is considered to be that the resist surface hardly dissolves due to the bulky and highly hydrophobic acid dissociable, dissolution inhibiting group.
On the other hand, the film thickness of the resist pattern of Comparative Example 2 was severe, and the cross-sectional shape of the C / H pattern was a top landing shape in which the peripheral edge of the hole was rounded. Further, a C / H pattern having a line width of 70 nm could not be formed.

Claims (21)

A resist laminate in which a lower organic film capable of dry etching, an intermediate layer, and an upper resist film are sequentially laminated on a substrate,
A resin component (A ′) in which the upper resist film has an alkali-soluble structural unit (a1) and a structural unit (a2) having an acid dissociable, dissolution inhibiting group, and the alkali solubility is increased by the action of an acid; And an acid generator component (B) that generates an acid upon exposure, and a positive resist composition for low-acceleration electron beams having an acceleration voltage of 2 to 5 kV, and the structural unit (a1) in the resin component (A ′) Or at least one of (a2) has a polycyclic group. In the positive resist composition for low acceleration electron beam, the structural unit (a1) of the resin component (A ′) is represented by the following general formula (I):

[Wherein, R represents a hydrogen atom or a methyl group. ]
Resist laminate according to claim 1, further comprising a structural unit (a11) THAT represented. In the low-acceleration electron beam positive resist composition, the resin component (A ′) has the structural unit (a11), and a part of the hydrogen atoms of the hydroxyl group of the structural unit (a11) is: Formula (II)

[Wherein R ¹ represents an alkyl group having 1 to 5 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms or a hydrogen atom, and X represents an aliphatic polycyclic group or an aromatic polycyclic carbonization. Represents a hydrogen group. ]
The resist laminate according to claim 2, which is a polymer (A′1) having a structural unit (a21) protected by an acid dissociable, dissolution inhibiting group represented by: The polymer (A′1) is further represented by the following general formula (III)

[Wherein, R Represents a hydrogen atom or a methyl group, R ³ represents a linear or branched alkyl group having 1 to 5 carbon atoms, n represents an integer of 0 or 1-3. ]
The resist laminated body of Claim 3 which has a structural unit (a3) represented by these. The resist laminate according to claim 4 , wherein both R in the general formula (I) and R in the general formula (III) are hydrogen atoms. The resist laminate according to any one of claims 3 to 5 , wherein the polymer (A'1) before being protected by the acid dissociable, dissolution inhibiting group has a mass average molecular weight of 2,000 to 30,000. Item 7. The resist laminate according to any one of Items 3 to 6 , wherein the proportion of the structural unit (a21) in the polymer (A′1) is 5 to 35 mol%. The resin component (A ′) has the structural unit (a11), and a structural unit (a12) derived from an aliphatic polycyclic group-containing (meth) acrylic acid having an alcoholic hydroxyl group, and The copolymer (A'2) according to claim 2, wherein a part of the hydroxyl group of the structural unit (a11) and the alcoholic hydroxyl group of the structural unit (a12) are protected by an acid dissociable, dissolution inhibiting group. Resist laminate. The resist laminate according to claim 8, wherein the copolymer (A'2) before being protected by the acid dissociable, dissolution inhibiting group has a mass average molecular weight of 2000 or more and 8500 or less. 10 to 35 mol% of the total of the hydroxyl group of the structural unit (a11) and the alcoholic hydroxyl group of the structural unit (a12) constituting the copolymer (A′2) is protected by the acid dissociable, dissolution inhibiting group. The resist laminate according to claim 8 or 9, wherein In the copolymer (A′2) before being protected by the acid dissociable, dissolution inhibiting group, the molar ratio of the structural unit (a11) to the structural unit (a12) is 95: 5 to 75:25. resist laminate according to any one of claims 8-10. The resist laminate according to any one of claims 8 to 11 , wherein the structural unit (a12) is a structural unit derived from an adamantyl group-containing (meth) acrylic acid ester having an alcoholic hydroxyl group. The resist laminate according to any one of claims 8 to 12 , wherein the structural unit (a12) comprises only a structural unit derived from an aliphatic polycyclic group-containing acrylate ester having an alcoholic hydroxyl group. The acid dissociable, dissolution inhibiting group, the 1-position number 1 to 8 chain carbons, branched, or claims 8 to any one of the 13 is an annular substituted 1-lower alkoxyalkyl group with an alkoxy group The resist laminate according to Item. The copolymer (A′2) is further represented by the following general formula (III)

[Wherein, R represents a hydrogen atom or a methyl group, R ³ represents a linear or branched alkyl group having 1 to 5 carbon atoms, and n represents an integer of 0 or 1 to 3]
Resist laminate according to any one of claims 8 to 14 having in a structural unit represented by (a3). According to any one of the polymer (A'1) or copolymer (A'2) claims 2-15 dispersion degree is 2.0 or less before being protected with the acid dissociable, dissolution inhibiting group Resist laminate. The positive resist composition for low-acceleration electron beams further contains a nitrogen-containing organic compound (D), and the (D) component is a secondary or tertiary aliphatic having an alkyl group having 7 to 15 carbon atoms. comprising an amine, a resist laminate according to any one of claims 1-16. A stack forming step of forming a resist laminate according to any one of claims 1 to 17 with respect to upper resist film of the resist laminate, exposure by low-acceleration electron beam at an acceleration voltage 2~5kV Performing an alkali development to form a resist pattern on the upper resist film, performing an oxide etching using the resist pattern as a mask pattern, transferring the pattern to the intermediate layer, and the resist pattern and the intermediate A pattern forming method comprising: sequentially performing dry etching of the lower organic film using a layer pattern as a mask pattern, and forming a lower layer pattern on the lower organic film. The pattern formation method according to claim 18 , wherein the exposure with the low acceleration electron beam is performed through a mask pattern. The pattern formation method according to claim 19 , wherein the oxide etching is performed with a halogen-based gas. The dry etching, a pattern forming method according to claim 19 or 20 wherein the etching using oxygen plasma.