WO2001096065A1

WO2001096065A1 - Method for polishing work

Info

Publication number: WO2001096065A1
Application number: PCT/JP2001/004838
Authority: WO
Inventors: Hisashi Masumura; Shunichi Ikeda; Koji Kitagawa
Original assignee: Shin-Etsu Handotai Co., Ltd.
Priority date: 2000-06-13
Filing date: 2001-06-08
Publication date: 2001-12-20
Also published as: TW490358B

Abstract

A method for polishing the surface of a disc-like work by sliding the surface of the work on an abrasive cloth while holding the back of the work with a work holding plate, characterized in that a back face coating film (6) having a thickness at the peripheral part smaller than that of the central part of the work (W) or so formed that the peripheral part of the back face of the work is exposed is formed on the back face of the work, and the surface of the work is polished while holding the back face of the work with a work holding plate (1) through the back face coating film. By the method, the edge rounding is suppressed when such a disc-like work required to have a very precise flatness, such as a semiconductor wafer is polished.

Description

Description Workpiece polishing method Technical field

The present invention relates to a method for polishing a work, and more particularly, to a polishing technique for a circular work requiring a high flatness such as a semiconductor wafer. Background art

Conventionally, when polishing the surface of a circular workpiece such as a semiconductor wafer or the like with a polishing cloth, for example, as shown in FIG. 3, a holding plate 16 attached to a holder 11 which is rotating itself is used. The work W is held by vacuum suction, etc., and the abrasive 15 is supplied onto the polishing cloth 13 attached to the rotatable surface plate 12 from the abrasive supply device 14. Then, the surface (working surface) of the work W is slid against the rotating polishing cloth 13 while applying a load to the polishing cloth 13, whereby the surface is polished.

As a method for holding the work W, a packing pad is provided on the holding surface of a holding plate made of metal or the like to fix the work, or a method for holding the work W For example, there is a method of attaching a mark to a holding plate such as a glass or a glass via an adhesive pad or the like.

For example, a semiconductor wafer is made into a mirror wafer by polishing as described above, but when a circuit is formed on the surface of the mirror wafer to produce a semiconductor wafer, one wafer is manufactured. Therefore, it is desirable to obtain as many devices as possible, and for that purpose, the wafer must be as flat as possible over the entire surface, especially near the outer edge. . More specifically, under the current standard, it is only necessary that high flattening be performed in a region excluding a certain region (for example, an outer periphery of 3 mm) from the outer peripheral end of the wafer. High flatness in the area up to 2 mm and even 1 mm ゥ Ehas are being requested.

However, when the wafer is polished using the holding plate as described above, there is a problem that the periphery of the wafer is excessively polished and so-called peripheral dripping occurs.

FIG. 4 schematically shows a cross section around the wafer after polishing. At the time of polishing, the peripheral portion of the wafer 21 is excessively polished as compared with the central portion, and a peripheral sag 24 is formed in a peripheral portion near the chamfered portion 23 on the polished surface 22 side.

This peripheral sag 24 often occurs in a region within about 5 mm from the outer peripheral edge force of the evaporator irrespective of the diameter of the antenna.

Peripheral sag is more abrasive at the periphery than at the center of the ewa, due to various factors, such as the periphery being exposed to newer abrasives than the center of the eha. One of the causes is local pressure generated around the wafer during polishing. Most of the polishing cloth used for polishing semiconductors and wafers is made of a viscoelastic material such as artificial leather or nonwoven fabric. When polishing a wafer with a load, the polishing cloth sinks. As a result, local pressure is generated in the periphery of the wafer, and the periphery is overpolished, flatness is impaired, and peripheral dripping occurs.

A method has also been proposed in which the polishing cloth is hardened to suppress sinking and thereby suppress overpolishing of the peripheral portion. However, the use of a hard polishing cloth causes mechanical damage to the work surface (surface to be polished). May cause.

In addition, there are various specifications for the flatness of the mirror surface and the wafer, and the flatness is evaluated by the worst value of the measured values, although it is evaluated on the entire surface of the wafer or on the local classification. In such a case, there is also a problem that if the peripheral area is sagged in the measurement area, the entire wafer is regarded as defective. Disclosure of the invention

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in consideration of the following problems. An object of the present invention is to provide a polishing method for suppressing peripheral sagging when polishing a circular work requiring extremely precise flatness.

In order to achieve the above object, according to the present invention, there is provided a method of polishing by holding a back surface of a circular work with a work holding plate and sliding a surface of the work on a polishing cloth. Forming a back coat film on the back surface of the work that is thinner at the periphery than at the center of the work or exposed at the periphery at the periphery, and through the back coat film. A work polishing method characterized in that the work back surface is polished while the back surface of the work is held by a holding plate.

In this way, a back coat film is formed so that the back of the work is exposed at a thinner portion or at the periphery than at the center of the work, and the work is formed through the back coat film. By holding the back of the work with the holding plate, the polishing pressure (pressing force) of the work against the polishing cloth is relatively smaller at the periphery than at the center of the work, or almost uniform in the plane. become. As a result, sinking of the polishing cloth in the peripheral portion is reduced, so that excessive polishing of the peripheral portion of the work can be prevented.

In this case, it is preferable that the back coat film of the work is thinned in a region within 5 mm from the outer peripheral end portion of the work or that the back surface of the work is exposed. .

When polishing the wafer, as described above, the peripheral sag easily occurs in a region within 5 mm from the outer peripheral edge of the wafer. As a result, if the thickness of the back coat film is changed in that region, the peripheral region can be polished. Sagging can be effectively prevented.

The back coat film is formed by forming a uniform coat film on the entire back surface of the work, and then thinning or removing the peripheral portion of the coat film. More specifically, a uniform coating film is formed on the entire back surface of the work by spin coating, and the peripheral portion of the coating film is reduced in thickness. Or, remove the surrounding area while rotating the work This can be achieved by supplying a solvent that dissolves the coating film to the part.

By forming the back coat film in this way, a desired back coat film can be easily formed, and the back surface of the work is held through the back coat film. Grinding by holding the board makes it possible to reliably prevent the peripheral sagging.

As described above, when polishing a circular work that requires extremely high flatness, such as a semiconductor wafer, the thickness of the work is thinner at the periphery than at the center of the work. Is used to form a back coat film with the back of the work exposed at the periphery, and to polish the work surface by holding the back of the work with a holding plate via the back coat film. As a result, overpolishing of the peripheral portion of the work can be suppressed.

In particular, by applying the present invention to polishing that requires extremely high flatness, such as a semiconductor wafer, peripheral sagging is prevented, and a polishing agent or the like is used. Since contamination on the backside of the wafer can be prevented, very high flatness can be achieved over the entire surface up to the outer peripheral edge of the wafer, and excellent surface characteristics can be achieved. Mirror surface can be used as an e-mail. Such a mirror surface wafer can form a circuit over the entire surface, and can improve the productivity and yield of semiconductor devices. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram showing a state in which a wafer on which a back coat film according to the present invention is formed is held.

FIG. 2 is a schematic explanatory view showing a part of a step of forming a back coat film according to the present invention.

FIG. 3 is a schematic side view showing one example of a wafer single-side polishing apparatus. FIG. 4 is a view showing a portion around the wafer after polishing by a conventional method. FIG.

FIG. 5 is a graph showing the amount of displacement of the thickness of the peripheral portion of ENO measured after polishing in the example and the comparative example.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings, but the present invention is not limited thereto.

The polishing method according to the present invention can be applied to the polishing of a circular work of a thin plate requiring a high flatness, but a preferable example will be described for polishing a semiconductor wafer.

First, the manufacturing process of semiconductor wafers before polishing is described. The raw materials such as silicon are melted by the Chiral key method (CZ method) and the floating zone melting method (FZ method). The semiconductor ingot grown from the liquid is sliced into a wafer. Next, after performing rough surface chamfering and lapping of the obtained wafer, etching is performed to remove processing strain and the like on the wafer surface. In some cases, surface grinding is performed instead of wrapping.

The wafer subjected to such a process is subjected to surface polishing in order to make the surface flatter and more mirror-finished. In the present invention, first, the back surface of the wafer before polishing is placed on the center of the wafer. A thinner coat is formed on the periphery or a back coat film with the back of the wafer exposed at the periphery is formed, and the back of the wafer is held by a holding plate via the back coat film to hold the back of the wafer. Perform polishing.

As described above, there are various methods for holding the wafer when polishing the wafer, but the present invention can be applied to any of the embodiments.

For example, when using a holding plate that sucks and holds through a through-hole, the conventional method involves direct contact of the entire back of the wafer with the holding surface of the holding plate. The wafer is held and polished, but in the present invention, before the wafer is held by such a holding plate, the center of the wafer is placed on the rear surface of the wafer. A back coat film made of resin or the like with the back of the wafer exposed at the periphery is thinner at the periphery or at the periphery.

As the material of the back coat film, it has an appropriate hardness, has a resistance to the abrasive component, aluminum alloy, and has good adhesiveness to the wafer, and is further polished. The material is not particularly limited as long as it can be easily removed thereafter, and a photo resist or other synthetic resin is used. In particular, polyvinyl butyral (PVB) resin can be suitably used.

The method of forming the back coat film is not particularly limited, either. After forming a uniform coat film on the entire back surface of the wafer, the peripheral portion of the coat film is thinned or removed. By doing so, a back coat film having a desired shape can be easily formed.

For example, a solution obtained by dissolving PVB resin in isopropyl alcohol (IPA) is applied to the back (holding surface) of the wafer by spin coating.後 After uniformly applying PVB resin to the entire back of the wafer, 溶剤 while rotating the wafer, supply a solvent (eg, IPA) that dissolves the coat film to the surrounding area, It can be thinned or removed.

FIG. 2 is a schematic explanatory view showing an example of a method of removing a peripheral portion of a coat film formed on the entire back surface of the wafer. The wafer W having the coating film 6 formed on the entire back surface by spin coating or the like is rotated so that the center of the wafer W is positioned on the rotating shaft 3 of the rotating table 2. Place on top. Next, while rotating the wafer W, a solvent 5 such as IPA is supplied to the periphery of the wafer through the solvent supply nozzle 4 to dissolve the periphery of the coat film 6. To be thinned or removed. In addition, the coating of the entire back surface by the spin coating and the thinning processing of the peripheral portion can be performed continuously. After thinning or removing the peripheral part of the coat film in this way, it is dried by heat treatment (evaporation of IPA), and has an appropriate hardness. It is possible to form a back coat film having good adhesiveness to the film and also having resistance to an abrasive component such as aluminum alloy.

The formation of the PVB resin film can be easily performed by spin coating, for example, when the concentration of the PVB resin in the IPA is about 0.2 to 5.0% by weight. Abrasives can be applied by removing the surrounding area by IPA and then performing a heat treatment at a temperature of 50 ° C to 200 ° C for 30 seconds to 720 seconds. It is possible to form a PVB resin film having an excellent resistance to the component Al and a moderate hardness.

The method for forming the back coat film according to the present invention is not limited to the above example. For example, a resin is applied to the entire back surface of the wafer by spin coating or the like, and then dried. You may wipe off the resin from the surrounding area before cleaning.

Alternatively, from the beginning, a resin may be applied only to the central portion so that the rear surface of the wafer is exposed in the peripheral portion of the wafer, and the back coat film may be formed.

Other methods include immersing the periphery of the wafer in a solvent, rotating the wafer, and removing the back coat film only at the periphery, or filling the center of the back coat film with a film. There is a method such as removing the film after protecting it with a film and removing only the periphery.

The back coat film should be thinned within 10 mm, especially within 5 mm from the outer edge of the wafer, or formed by exposing the back of the wafer. Is preferred. As described above, in single-side polishing, the polishing pressure increases from about 5 mm in the peripheral portion regardless of the wafer diameter, and the peripheral sag tends to occur. Therefore, the back coat film is thinned within 1 O mm from the outer peripheral edge of the wafer, particularly within a region of 5 mni, or formed by exposing the back surface of the wafer. The rear of the wafer through the back coat film By holding the wafer with the holding plate and polishing the surface of the wafer, it is possible to polish the surface of the wafer by providing a gap between the holding plate and the peripheral portion of the wafer. Can be more effectively prevented.

The back coat film may be completely removed, particularly in the area of 5 mm or less around the wafer, or may be thinned to have a substantially uniform thickness in the periphery. Alternatively, the thickness may be gradually or gradually reduced from the 5 mm force at the periphery of the wafer to the edge of the wafer.

Also, in order to more effectively prevent or reduce the occurrence of peripheral sagging, the thickness of the back coat film around the wafer, especially at the outermost periphery and at the center of the wafer The difference between the thickness and the thickness is at least when the back coat film is formed or polished after forming the back coat film with a uniform thickness in the wafer surface. It is preferable that the value be larger than the value of the peripheral sag. In particular, it is preferable that the difference in thickness be at least twice the value of the peripheral sag. However, even if the difference in thickness is too large, it is necessary to form the back coat film thickly, and when polishing, the periphery of the wafer is not sagged, but not sagged. It is preferable that the practical upper limit of the difference in thickness is about 5 times the value of the peripheral sag, since it may result in a rounded shape.

In the present invention, as described above, after forming a back coat film that is thinner at the periphery than at the center of the wafer or that exposes the back of the wafer at the periphery, the rear coat film is formed through the back coat film.保持 Hold the back of the wafer with a holding plate and grind it. FIG. 1 shows a state where the wafer is held on a holding plate by the method according to the present invention.ゥ The wafer W has the rear coating film 6 thinned. ゥ The periphery of the wafer is suction-held on the holding plate 1 with a gap provided between the holding surface 1 and the holding surface 7 of the holding plate 1.

The wafer W held in this manner is polished by applying a load to the polishing cloth in the same manner as in the prior art, so that the wafer W The polishing pressure is relatively smaller in the peripheral portion than in the central portion of the wafer or substantially uniform in the plane, and the local pressure received from the polishing cloth is reduced. As a result, the sinking of the polishing cloth in the vicinity of the wafer is also reduced, so that the surrounding portion is not excessively polished, and it is possible to prevent the occurrence of sagging around the wafer.

The back coat film according to the present invention not only prevents the generation of peripheral sag as described above, but also serves as a protective film for preventing the back surface of the wafer from being stained by an abrasive or the like. Also works.直接 If the back of the wafer is held directly by the holding plate, abrasives and polishing gas generated during polishing may get into between the holding plate and the wafer, and the back of the wafer may be contaminated. However, by holding the wafer through the back coat film as in the present invention, it is possible to prevent the back surface from being contaminated by abrasives or the like. In particular, when a thin back coat film is formed at the periphery rather than at the center of the work, the above-mentioned coat film exists over the entire back surface of the wafer. It can completely prevent contamination by chemicals.

After polishing, the coating film is removed from the entire back surface of the wafer, but the wafer is immersed in a solvent used for thinning or removing the back coating film on the peripheral portion, and the back film is removed. G The entire film may be removed. For example, in the case of a PVB resin film, IPA can be used. Also, except for treatment with IPA or before treatment with IPA, the membrane is washed with ozone-added water to decompose the coat film, and then a mixed solution of ammonia and aqueous hydrogen peroxide (so-called SC - 1 solution) and N a OHZH ₂ 0 be One by the and this treatment with Al force Li solution of ₂ such as Ru is in this and mosquitoes easily removed.

In the above description, the case where the holding plate that holds by suction through the through-hole is used is described. However, the present invention is not applied only to such a holding method, for example, a packing pad. The same applies to the case where a holding plate provided with a slot is used, and a circular workpiece can be polished.

In addition, adhesives, wax, etc. are applied to plates such as ceramics and glass. When polishing the wafer by pasting the wafer through the adhesive, apply these adhesive mixes thinner at the periphery of the wafer than at the center of the wafer or expose the back of the wafer at the periphery. In this case, it may be applied to the back of the wafer and adhered to the plate.

In other words, the back coating film according to the present invention is an adhesive that is attached to the back of the wafer in order to attach the “ano” to such a ceramics glass plate or the like. It also contains agents and waxes.

The application method is not particularly limited. In this case, too, the adhesive agent is uniformly applied to the entire back surface of the wafer by spin coating or the like. The solvent can be supplied to the peripheral portion while rotating the peripheral portion, and the peripheral portion can be thinned or removed. As a solvent for the wax, IPA or caustic soda water can be used, and the wax in the peripheral portion can be easily thinned or removed. In this case as well, it is preferable that the thickness is reduced within a range of 1 Om m, particularly within 5 mm from the outer peripheral edge of the wafer, or that the back surface of the wafer is exposed.

The wafer polished by forming the back coat film according to the present invention is a mirror-finished wafer having excellent flatness over the entire surface of the wafer, in which generation of peripheral sag is suppressed.ゥ The rate of non-defective products of eha can be significantly improved. Also, by using such an antenna, a circuit can be formed over the entire surface, and the productivity and yield of semiconductor devices can be significantly improved. You.

Furthermore, in the present invention, since a back coat film having a desired shape is formed on the back surface of the work to suppress overpolishing, a general work holding plate conventionally used is used. This has the advantage that it can be used as is.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example) A spin coater is provided on the entire back surface (holding surface) of a silicon wafer (diameter: 200 mm, thickness: 735 / i in) obtained by slicing the ingot. A PVB resin (IPA solvent) was applied by coating, and then an IPA solution was supplied to the peripheral area within 5 mm from the surrounding area as shown in Fig. 2 to form a thin film. Thereafter, heat treatment was performed to form a back coat film having a thickness of 1.2 μππ at the central portion and a thickness of 0.2 μππ at the peripheral portion.

The wafer is sucked and held on the holding plate as shown in FIG. 1 through the back coat film thus formed, and the wafer is polished under the following polishing conditions. Was.

Polishing equipment: Vacuum adsorption type Makiha polishing equipment

Abrasive cloth: SUBA600 (Made by Dale)

Abrasive: Colloidal silica abrasive (particle size: several tens of nm, silica concentration: 2.5 wt%, pH = 10.5)

Polishing load: 300 gf / cm ²

Relative speed: 50 m / min

Polishing time: 15 minutes

Polishing allowance: 10 μm

After polishing, the wafer was treated with ozone-added water, and then the wafer was immersed in an IPA solution to remove the back coat film.

(Comparative example)

After applying a uniform thickness of PVB resin (IPA solvent) by spin coating to the entire back surface (holding surface) of the silicon wafer of the same size as the wafer used in the examples. Then, heat treatment was performed to form a back coat film having a thickness of 1.Ο μππ on the entire back surface of the wafer.

The wafer was adsorbed and held through the back coat film thus formed, and the primary polishing of the wafer was performed under the same polishing conditions as in the example.

After polishing, treat with ozone-added water. Was immersed to remove the back coat film. The wafer thickness distribution (excluded area: 2 mm around the 周辺) around the ゥ wafer polished in the above examples and comparative examples was measured using a capacitance type thickness measuring instrument. Figure 5 shows the results.

As can be seen from this graph, in the wafer polished in the comparative example, the outer peripheral edge force of the wafer, the position force of 18 mm, and the position force of 5 to 6 mm from the position force of 18 mm It can be seen that there is almost no displacement of the thickness in the range of, but that it drops sharply from a position about 5 mm around the periphery, and that peripheral sag has occurred. On the other hand, the wafer polished in the example had a thickness displacement of 0-1 in a range from 5 mm to 2 mm from the outer edge of the wafer. It is on the order of μm, and very high flatness is achieved over the entire surface of the wafer.

Even if a plurality of wafers are attached to the glass plate with an adhesive so that the backside of the wafer is exposed in the peripheral area, polishing is performed with a notch. As in the case of the above embodiment, very high flatness was achieved over the entire wafer. Note that the present invention is not limited to the above embodiment. The above-described embodiment is merely an example, and any of those having substantially the same configuration as the technical idea described in the claims of the present invention and having the same operation and effect will be described. Anything is included in the technical scope of the present invention.

In the above embodiment, the case where the semiconductor wafer is polished has been described as an example. However, the object to be polished to which the present invention can be applied is not limited to the semiconductor wafer, and a high flatness of the entire surface is required. It can be applied to the polishing of circular workpieces. The size of the work is not particularly limited.

Claims

The scope of the claims

1. In the method of holding the back of a circular work with a work holding plate and polishing the surface of the work by sliding the surface of the work into a polishing cloth, the back of the work is more peripheral than the center of the work. Polishing the work surface by forming a back coat film that is thin in the part or the work back surface is exposed in the peripheral part, and holds the back of the workpiece with the holding plate via the back coat film A method of polishing a work, characterized by performing polishing.

2. The back coat film of the work is thinned in an area within 5 mm or less from the outer peripheral end of the work, or is formed by exposing the back surface of the work. The method for polishing a work according to claim 1, wherein the polishing is performed.

3. The back coat film is formed by forming a uniform coat film on the entire back surface of the work, and then thinning or removing the peripheral portion of the coat film. 3. The method for polishing a workpiece according to claim 1 or claim 2, wherein

4. A uniform coating film is formed by spin coating on the entire back surface of the work, and the work is rotated by rotating the work to reduce or remove the peripheral portion of the coat film. 4. The method for polishing a work according to claim 3, wherein a solvent for dissolving the coat film is supplied to the peripheral portion while performing the polishing.