JP3645381B2 - Manufacturing method of semiconductor device, information terminal, head mounted display, car navigation, mobile phone, video camera, projection display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention disclosed in this specification relates to a thin film semiconductor having crystallinity. Further, the present invention relates to a method for manufacturing the thin film semiconductor. The present invention also relates to a semiconductor device using the thin film semiconductor. Further, the present invention relates to a method for manufacturing the semiconductor device.
[0002]
[Prior art]
A technique is known in which a silicon film having crystallinity is formed on a glass substrate or a quartz substrate, and a thin film transistor (hereinafter referred to as TFT) is manufactured using the silicon film.
[0003]
This thin film transistor is called a high temperature polysilicon TFT or a low temperature polysilicon TFT.
[0004]
The high-temperature polysilicon TFT is a technique that uses a relatively high-temperature heat treatment such as 800 ° C. or 900 ° C. or more as a means for producing a crystalline silicon film. This technology can be said to be a derivative technology of the IC manufacturing process using a single crystal silicon wafer.
[0005]
Naturally, as a substrate on which the high-temperature polysilicon TFT is manufactured, a quartz substrate that can withstand the heating temperature is used.
[0006]
On the other hand, the low-temperature polysilicon TFT uses an inexpensive glass substrate (which is naturally inferior in heat resistance to a quartz substrate) as a substrate.
[0007]
For the production of the crystalline silicon film constituting the low-temperature polysilicon TFT, a laser annealing technique is used in which the glass substrate is heated to 600 ° C. or less and the glass substrate is hardly damaged by heat.
[0008]
The high-temperature polysilicon TFT has a feature that TFTs with uniform characteristics can be integrated on a substrate.
[0009]
On the other hand, the low-temperature polysilicon TFT is characterized in that it can use a glass substrate that is inexpensive and easy to increase in area.
[0010]
In the current technology, there is no significant difference in characteristics between the high-temperature polysilicon TFT and the low-temperature polysilicon TFT.
[0011]
That is, in terms of mobility, those having about 50 to 100 (cm ² / Vs) and S values of about 200 to 400 (mV / dec) (V _D = 1V) are obtained in both cases.
[0012]
This characteristic is greatly inferior to that of a MOS transistor using a single crystal silicon wafer. Generally, the S value of a MOS transistor using a single crystal silicon wafer is about 60 to 70 (mV / dec).
[0013]
At present, high-temperature polysilicon TFTs are superior in terms of uniformity of TFT characteristics and high reproducibility when a large number of TFTs are manufactured on the substrate with a number of hundreds × several hundreds. . Further, the high-temperature polysilicon TFT is advantageous in that various process conditions and manufacturing apparatuses in the conventional IC process can be used.
[0014]
[Problems to be solved by the invention]
Currently, TFTs are used to integrate an active matrix circuit and a peripheral drive circuit of an active matrix type liquid crystal display device on the same substrate. In other words, the active matrix circuit and the peripheral drive circuit are formed with TFTs on the same substrate.
[0015]
In such a configuration, the source driver circuit of the peripheral drive circuit is required to operate at more than a dozen MHz. However, the current circuit composed of high-temperature polysilicon TFTs and low-temperature polysilicon TFTs has a margin of operating speed of only several MHz.
[0016]
Therefore, at present, the liquid crystal display is configured by dividing the operation (referred to as division driving). However, this method has a problem that a striped pattern appears on the screen due to a subtle shift in division timing.
[0017]
As future technology, in addition to the peripheral drive circuit (consisting of a shift register circuit and a buffer circuit), an oscillation circuit, a D / A converter, an A / D converter, and a digital circuit for performing various image processing are further provided on the same substrate. It is considered to be integrated on top.
[0018]
However, the oscillation circuit, the D / A converter, the A / D converter, and the digital circuit that performs various types of image processing are required to operate at a higher frequency than the peripheral drive circuit.
[0019]
Therefore, it is difficult to construct these circuits with high-temperature polysilicon TFTs and low-temperature polysilicon TFTs obtained by the current technology.
[0020]
Note that an integrated circuit constituted by a MOS transistor using a single crystal silicon wafer has been put into practical use that can operate at 100 MHz or higher.
[0021]
An object of the invention disclosed in this specification is to obtain a thin film transistor that can constitute a circuit that requires the above-described high-speed operation (generally, an operation speed of several tens of MHz or more).
[0022]
It is another object of the present invention to provide a thin film transistor capable of obtaining characteristics comparable to a MOS transistor manufactured using a single crystal silicon wafer. It is another object to provide a manufacturing means thereof. It is another object of the present invention to provide a semiconductor device having a function required by a thin film transistor having such high characteristics.
[0023]
[Means for Solving the Problems]
One of the inventions disclosed in this specification is:
A semiconductor device using a thin film transistor having a crystalline silicon film formed on a substrate having an insulating surface as an active layer,
The crystalline silicon film has a crystal structure having continuity in a predetermined direction, and has a crystal grain boundary extending in the predetermined direction,
In the thin film transistor, the direction connecting the source region and the drain region and the predetermined direction have a predetermined angle,
A thermal oxide film having a thickness larger than that of the crystalline silicon film is formed on the crystalline silicon film.
[0024]
Examples of the crystalline silicon film having the above crystal state are shown in FIGS. FIG. 7 shows a further enlargement of a part of FIG. 6 and 7 are photographs obtained by observing the surface of a crystalline silicon film having a thickness of 250 mm with a transmission electron microscope (TEM).
[0025]
The crystalline silicon film as shown in FIGS. 6 and 7 can be obtained by employing the manufacturing process as shown in the first embodiment.
[0026]
6 and 7 show a state in which a continuous crystal structure extends from the lower left to the upper right of the drawing. Also shown is a state in which a large number of crystal grain boundaries are formed substantially parallel to the direction in which the continuity of the crystal structure extends.
[0027]
That is, in the direction perpendicular to or substantially perpendicular to the direction in which the continuity of the crystal structure exists (the direction from the lower right to the upper right in FIG. 6 or FIG. 7), there are a large number of clear crystal grain boundaries. The crystal structure is discontinuous in that direction. That is, the continuity of the crystal structure is impaired in this direction.
[0028]
In the direction in which the continuity of this crystal structure extends, the continuity of the lattice structure is almost maintained, and the scattering and trapping during the movement of carriers is very small compared to other directions. Yes.
[0029]
That is, it can be considered that the direction in which the crystal structures are continuous is a substantially single crystal state that is not or hardly affected by scattering from the crystal grain boundary.
[0030]
In order to obtain the above configuration, it is important to make the thickness of the thermal oxide film constituting the gate insulating film larger than the thickness of the crystalline silicon film constituting the active layer.
[0031]
The formation process of the thermal oxide film constituting the gate insulating film is an important requirement for obtaining the above crystal structure and obtaining a TFT having high characteristics as described later. This is because during the formation of the thermal oxide film, interstitial silicon atoms existing in the crystalline silicon film and silicon atoms having an unstable bonding state are used for the formation of the thermal oxide film. This is because the effects of improvement and reduction of defects in the crystalline silicon film can be obtained.
[0032]
In particular, according to the formation of the thermal oxide film, the above-described unique crystal structure can be obtained in a remarkable state. (If a thermal oxide film is not formed, the continuity of crystals with many line defects will be impaired.)
[0033]
Further, the configuration of the invention defines the relationship between the direction in which the crystal structure is continuous and the direction connecting the source region and the drain region of the thin film transistor. If high-speed operation is aimed, it is preferable that the direction in which the crystal structure is continuous and the direction connecting the source region and the drain region match or approximately match. Thus, a structure in which carriers can move most easily in the operation of the MOS thin film transistor can be obtained.
[0034]
In addition, the characteristics of the obtained thin film transistor can be controlled by setting the angle formed by the two directions to a predetermined value. For example, when a large number of thin film transistor groups are formed on the same substrate, the characteristics of the transistor groups can be made different by forming a plurality of groups having different angles formed by the two angles.
[0035]
Further, in the case of a thin film transistor in which an active layer having an N-shaped, U-shaped, or M-shaped shape is bent, the following may be performed. That is, in the case of a thin film transistor in which the line connecting the source region and the drain region is not a straight line but is bent, the following may be performed.
[0036]
In this case, the direction of continuity of the above-described crystal structure may be set in accordance with the movement direction of carriers in the channel region (the movement direction of carriers as a whole).
[0037]
In this case as well, the highest speed operation can be expected when the angle formed by the carrier movement direction and the crystal structure continuity direction is 0 °. Of course, this angle can be set as required.
[0038]
Other aspects of the invention are:
A semiconductor device using a thin film transistor having a crystalline silicon film formed on a substrate having an insulating surface as an active layer,
The crystalline silicon film has anisotropy in the extending direction of the crystal grain boundary,
In the thin film transistor, the direction connecting the source region and the drain region and the extending direction have a predetermined angle,
A thermal oxide film having a thickness larger than that of the crystalline silicon film is formed on the crystalline silicon film.
[0039]
Other aspects of the invention are:
A semiconductor device using a thin film transistor having a crystalline silicon film formed on a substrate having an insulating surface as an active layer,
The crystalline silicon film has anisotropy in the extending direction of the crystal grain boundary,
In the thin film transistor, a direction in which carriers move in the channel region and the extending direction have a predetermined angle,
A thermal oxide film having a thickness larger than that of the crystalline silicon film is formed on the crystalline silicon film.
[0040]
The crystalline silicon film in the invention disclosed in this specification is obtained by the following steps.
[0041]
(1) A metal element that promotes crystallization of silicon typified by nickel is introduced into the amorphous silicon film, and further subjected to heat treatment for crystallization.
[0042]
(2) A thermal oxide film is formed by heat treatment in an atmosphere containing a halogen element.
[0043]
(3) The thermal oxide film of (2) is removed.
[0044]
(4) A thermal oxide film functioning as a gate insulating film is formed again.
[0045]
As the metal element, nickel is extremely preferable in terms of reproducibility and effects. In general, as the metal element, one or a plurality of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au can be used.
[0046]
When nickel element is used, the concentration of nickel finally remaining in the silicon film is approximately 1 × 10 ¹⁴ atoms / cm ^{3 to} 5 × 10 ¹⁸ atoms / cm ³ .
[0047]
The upper limit of the concentration can be reduced to about 5 × 10 ¹⁷ atoms / cm ³ by narrowing down the conditions for forming the thermal oxide film for performing gettering and the conditions for introducing the metal element. This concentration can be measured using SIMS (secondary ion analysis method).
[0048]
Generally, the lower limit of the nickel concentration is about 1 × 10 ¹⁶ atoms / cm ³ . This is because it is usually difficult to eliminate the influence of the nickel element adhering to the substrate and the device in view of the balance with the cost, and the above-mentioned nickel element remains.
[0049]
Of course, it is possible to further reduce the concentration of nickel element remaining in the crystalline silicon film by reviewing the overall manufacturing process, thoroughly cleaning steps, and thoroughly cleaning the apparatus. .
[0050]
Therefore, when a general manufacturing process is followed, the concentration of the remaining nickel element is 1 × 10 ¹⁶ atoms / cm ^{3 to} 5 × 10 ¹⁷ atoms / cm ³ .
[0051]
In addition, in the thermal oxide film manufacturing process, a gradient or distribution is generated in the nickel element concentration distribution in the thickness direction of the obtained crystalline silicon film due to the movement of the metal element into the thermal oxide film.
[0052]
Generally, a tendency that the concentration of the metal element increases toward the interface where the thermal oxide film is formed is observed. Further, depending on the conditions, a tendency that the concentration of the metal element increases toward the substrate or the base film, that is, toward the interface on the back surface side is also observed. (This difference greatly depends on the quality of the amorphous silicon film used as the starting film)
[0053]
Further, when a halogen element is included in the atmosphere when forming the thermal oxide film, the halogen element also exhibits a concentration distribution similar to that of the metal element. That is, the concentration distribution becomes higher toward the front surface and / or back surface of the crystalline silicon film. (The difference in concentration distribution depends on the quality of the starting film)
[0054]
The crystalline silicon film in the invention disclosed in this specification preferably has a final film thickness of 100 to 750 mm, more preferably 150 to 450 mm. With such a film thickness, a unique crystal structure in which crystallinity continues in one direction as shown in FIGS. 6 and 7 can be obtained in a more remarkable form with good reproducibility.
[0055]
The final thickness of the crystalline silicon film needs to be determined in consideration of reducing the thickness by forming the thermal oxide film.
[0056]
Other aspects of the invention are:
Forming an amorphous silicon film over a substrate having an insulating surface;
Selectively introducing into the amorphous silicon film a metal element that promotes crystallization of silicon;
A step of performing crystal growth in a direction parallel to the substrate from the region where the metal element is selectively introduced to the other region by performing heat treatment;
Forming a first thermal oxide film by heat treatment in an oxidizing atmosphere containing a halogen element;
Removing the first thermal oxide film;
Forming a second thermal oxide film in an oxidizing atmosphere containing a halogen element;
Have
The finally obtained silicon film has a thickness smaller than that of the second thermal oxide film.
[0057]
By adopting the above configuration, the effect of forming a thermal oxide film in an oxidizing atmosphere containing a halogen element can be greatly obtained.
[0058]
In addition, the configuration of other inventions is as follows:
Forming an amorphous silicon film over a substrate having an insulating surface;
Selectively introducing into the amorphous silicon film a metal element that promotes crystallization of silicon;
A step of performing crystal growth in a direction parallel to the substrate from the region where the metal element is selectively introduced to the other region by performing heat treatment;
Forming a first thermal oxide film by heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element;
Removing the first thermal oxide film;
Forming a second thermal oxide film by heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element;
Have
The finally obtained silicon film has a thickness smaller than that of the second thermal oxide film.
[0059]
If the effect of forming the second thermal oxide film in an oxidizing atmosphere containing a halogen element is to be enhanced, the heat treatment temperature is preferably set to 800 ° C. to 1100 ° C. as in the above configuration. . If this temperature is low, the effect is greatly reduced, so care must be taken.
[0060]
Other aspects of the invention are:
Forming an amorphous silicon film over a substrate having an insulating surface;
Selectively introducing into the amorphous silicon film a metal element that promotes crystallization of silicon;
A step of performing crystal growth in a direction parallel to the substrate from the region where the metal element is selectively introduced to the other region by performing heat treatment;
Forming a first thermal oxide film by heat treatment in an oxidizing atmosphere containing a halogen element;
Removing the first thermal oxide film;
Forming a second thermal oxide film in an oxidizing atmosphere containing a halogen element;
Have
The thickness of the finally obtained silicon film is smaller than the total thickness of the first thermal oxide film and the second thermal oxide film.
[0061]
As described above, the effect of forming the thermal oxide film can be significantly obtained by making the total of the two thermal oxide films larger than the film thickness of the finally obtained crystalline silicon film. it can.
[0062]
Specifically, a crystalline silicon film having a unique crystal structure as shown in FIGS. 6 and 7 can be obtained, and by forming an active layer using the crystalline silicon film, the S value is reduced. A TFT having particularly excellent characteristics such as mobility of 200 (cm ² / Vs) or more at 100 mV / dec or less can be obtained.
[0063]
Other aspects of the invention are:
Forming an amorphous silicon film over a substrate having an insulating surface;
Selectively introducing into the amorphous silicon film a metal element that promotes crystallization of silicon;
A step of performing crystal growth in a direction parallel to the substrate from the region where the metal element is selectively introduced to the other region by performing heat treatment;
Forming a first thermal oxide film by heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element;
Removing the first thermal oxide film;
Forming a second thermal oxide film by heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element;
Have
The film thickness of the finally obtained silicon film is smaller than the total film thickness of the first thermal oxide film and the second thermal oxide film.
[0064]
In order to obtain the maximum effect of forming the thermal oxide film, it is very important to set the heating temperature as high as 800 ° C. to 1100 ° C. as in the above configuration.
[0065]
By adopting the steps as described above, the crystalline silicon film disclosed in this specification can be obtained, and further, a MOS thin film transistor utilizing the peculiarity of the crystal structure can be obtained.
[0066]
As a method for introducing a metal element, a method of applying a solution containing the metal element, a method by a CVD method, a method by a sputtering method or a vapor deposition method, a method by a plasma treatment using the electrode containing the metal, a gas adsorption method The method by can be mentioned.
[0067]
As a method for introducing a halogen element, a means for containing HCl, HF, HBr, Cl ₂ , F ₂ , Br ₂ , CF ₄ or the like in an oxidizing atmosphere (for example, an oxygen atmosphere) can be used.
[0068]
It is also effective to utilize the action of wet oxidation by introducing hydrogen gas and moisture (water vapor) together in the atmosphere during the formation of the thermal oxide film. This is effective in forming a highly smooth thermal oxide film in a shorter time.
[0069]
The temperature for forming the thermal oxide film is extremely important. If a TFT having a S value of 100 (mV / dec) or less can be obtained with a single element as described below, and an S value of 100 (mV / dec) or less is obtained, the heating temperature during the formation of the thermal oxide film Is preferably 800 ° C. or higher, more preferably 900 ° C. or higher.
[0070]
The upper limit of the heating temperature is suitably about 1100 ° C., which is the upper limit of the heat resistant temperature of the quartz substrate.
[0071]
DETAILED DESCRIPTION OF THE INVENTION
In the technique of obtaining a crystalline silicon film by crystallizing an amorphous silicon film by heating, by performing a heat treatment in a state where nickel element is held in contact with a part of the surface of the amorphous silicon film, Crystal growth is performed in a direction parallel to the substrate from the partial region to another region.
[0072]
Then, a first thermal oxide film is formed on the surface of the silicon film subjected to the crystal growth. This thermal oxide film is formed by performing a heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element.
[0073]
Then, the thermal oxide film is removed. The crystalline silicon film thus obtained has a structure in which crystal grain boundaries extend in a specific direction as shown in FIGS. 6 and 7 and the crystal structure is continuous in that direction.
[0074]
The action of forming the thermal oxide film will be described as follows. That is, according to the formation of the thermal oxide film, interstitial silicon atoms existing in the silicon film and silicon atoms having an unstable bonding state are used for forming the thermal oxide film. As a result, the crystal structure of the obtained crystalline silicon film becomes clearer, and the defects present in the film are greatly reduced.
[0075]
The first thermal oxide film also serves to remove (getter) metal elements that contribute to crystallization from the silicon film. In other words, the metal element that has moved from the silicon film to the thermal oxide film during the formation of the thermal oxide film is removed to the outside by removing the thermal oxide film.
[0076]
In the invention disclosed in this specification, the second thermal oxide film is formed after removing the first thermal oxide film.
[0077]
This second thermal oxide film is
(1) Directly formed on the surface of the exposed crystalline silicon film.
(2) A silicon oxide film formed by CVD (generally a silicide insulating film can be used) is formed and then formed.
These are roughly divided into two timings.
[0078]
Secondly, the thermal oxide film is preferably formed in an oxygen atmosphere containing a halogen element.
[0079]
The action of the second thermal oxide film is basically the same as that of the first thermal oxide film. However, the effect on the crystal structure is more important than the effect of gettering the metal element.
[0080]
【Example】
[Example 1]
This embodiment relates to a method of performing crystal growth in a direction parallel to a substrate, called lateral growth, by selectively introducing a metal element that promotes crystallization of silicon into an amorphous silicon film. .
[0081]
FIG. 1 shows a manufacturing process of this embodiment. First, a silicon oxide film having a thickness of 3000 mm is formed on the quartz substrate 201 as the base film 202. Note that the base film 202 is not particularly necessary if the surface of the quartz substrate has good smoothness and sufficient cleaning.
[0082]
In addition, the use of a quartz substrate as a substrate is a preferable choice at present, but the substrate is not limited to quartz as long as the substrate can withstand the heat treatment temperature.
[0083]
Next, an amorphous silicon film 203 serving as a starting film for the crystalline silicon film is formed to a thickness of 500 mm by low pressure thermal CVD.
[0084]
Next, a silicon oxide film (not shown) is formed to a thickness of 1500 mm and patterned to form a mask indicated by 204. This mask has an opening formed in a region indicated by 205. In the region where the opening 205 is formed, the amorphous silicon film 203 is exposed.
[0085]
The opening 205 has an elongated rectangle having a longitudinal direction in the depth direction and the front direction of the drawing. The width of the opening 203 is suitably 20 μm or more. Further, the length in the longitudinal direction may be formed with a required length.
[0086]
Then, a nickel acetate solution containing 10 ppm of nickel element in terms of weight is applied. Then, spin drying is performed using a spinner (not shown) to remove excess solution. The amount of nickel element introduced can be controlled by the concentration of nickel element contained in the solution.
[0087]
In this way, a state in which the nickel element is present in a state as indicated by a dotted line 206 in FIG. In this state, a state is obtained in which the nickel element is selectively held in contact with a part of the amorphous silicon film at the bottom of the opening 205.
[0088]
Next, heat treatment is performed at 600 ° C. for 8 hours in a nitrogen atmosphere containing 3% of hydrogen and containing as little oxygen as possible (also in a nitrogen atmosphere). Then, crystal growth proceeds in a direction parallel to the substrate 201 as indicated by 207 in FIG. FIG. 9 shows a schematic view of this crystal growth state as viewed from above.
[0089]
This crystal growth proceeds from the region of the opening 205 into which nickel element is introduced toward the periphery. This crystal growth in a direction parallel to the substrate is referred to as lateral growth or lateral growth.
[0090]
The surface of the laterally grown crystalline silicon film obtained by this crystal growth has a very smooth surface compared to conventional low-temperature polysilicon and high-temperature polysilicon. This is considered due to the fact that the extending directions of the crystal grain boundaries are roughly aligned.
[0091]
A general silicon film called polycrystalline silicon or polysilicon has a surface roughness of ± 100 mm or more. However, when lateral growth as shown in this example is performed, it has been observed that the unevenness of the surface is ± 30 mm or less. This unevenness deteriorates the interface characteristics with the gate insulating film, and is preferably as small as possible.
[0092]
In the heat treatment conditions for the above crystallization, this lateral growth can be performed over 100 μm or more. Thus, a silicon film 208 having a laterally grown region is obtained.
[0093]
The heat treatment for crystal growth can be performed at 450 ° C. to 1100 ° C. (the upper limit is regulated by the heat resistance of the substrate). If a certain amount of lateral growth distance is ensured, the temperature of the heat treatment is preferably set to 600 ° C. or higher. However, the crystal growth distance and crystallinity improvement by raising the temperature beyond that is not so great. (Therefore, heat treatment at about 600 ° C. to 650 ° C. is sufficient when considering economic efficiency and process simplification)
[0094]
Then, the mask 204 made of a silicon oxide film for selectively introducing nickel element is removed.
[0095]
In this state, nickel element is unevenly distributed in the film. In particular, the nickel element is present at a relatively high concentration in the region where the opening 205 is formed and the tip portion of the crystal growth indicated by 207.
[0096]
Therefore, it is important to avoid these regions in forming the active layer. That is, it is important that there is no region in which the nickel element is unevenly distributed in the active layer.
[0097]
Laser irradiation may be further performed after crystallization. That is, crystallization may be further promoted by laser light irradiation. This laser light irradiation has the effect of dispersing the mass of nickel elements present in the film and facilitating removal of the nickel elements later. Note that even if laser light irradiation is performed at this stage, the lateral growth does not proceed further.
[0098]
As the laser light, an excimer laser having a wavelength in the ultraviolet region can be used. For example, a KrF excimer laser (wavelength 248 nm) or a XeCl excimer laser (wavelength 308 nm) can be used.
[0099]
Next, heat treatment is performed at 950 ° C. in an oxygen atmosphere containing 3% by volume of HCl, and a thermal oxide film 209 is formed to a thickness of 200 mm. As the thermal oxide film is formed, the film thickness of the silicon film 208 decreases by about 100 mm. That is, the film thickness of the silicon film is about 400 mm. (Figure 1 (C))
[0100]
In general, a thermal oxide film formed on the surface of a silicon film has substantially the same thickness rising on the surface and the distance of oxidation proceeding inside. Therefore, for example, when a 100 熱 thermal oxide film is formed on the surface of a 100 珪 素 silicon film, the thickness of the silicon film is reduced by 50 、, and a 50 Å thick silicon film and a 100 Å thick thermal oxide film formed on the surface are formed. Become.
[0101]
In the above process, silicon elements having an unstable bonding state in the film are used for forming the thermal oxide film in accordance with the formation of the thermal oxide film. And the defect in a film | membrane reduces and higher crystallinity can be obtained.
[0102]
At the same time, nickel elements are gettered from the film by the formation of a thermal oxide film and the action of chlorine.
[0103]
Naturally, nickel element is taken into the thermal oxide film at a relatively high concentration. And the nickel element in the silicon film 208 is relatively reduced. In this way, the state shown in FIG.
[0104]
When the thermal oxide film 209 is formed, the thermal oxide film 209 is removed. In this way, a crystalline silicon film 208 with a reduced nickel element concentration is obtained.
[0105]
The crystalline silicon film thus obtained has a structure in which the crystal structure extends in one direction (this direction coincides with the crystal growth direction) as shown in FIG. 6 or FIG. That is, it has a structure in which a plurality of elongated cylindrical crystals are arranged in parallel through a plurality of crystal grain boundaries extending in one direction.
[0106]
Next, by patterning, a pattern 210 composed of a lateral growth region is formed. This island-like region 210 will later become the active layer of the TFT.
[0107]
Here, the pattern is positioned so that the direction connecting the source region and the drain region and the crystal growth direction match or approximately match. By doing so, the direction in which the carriers move and the direction in which the crystal lattice continuously extends can be matched, and as a result, a TFT with high characteristics can be obtained.
[0108]
Then, after the pattern 210 is formed, a thermal oxide film 211 is formed to a thickness of 300 mm. This thermal oxide film is obtained by performing a heat treatment at 950 ° C. in an oxygen atmosphere containing 3% HCl.
[0109]
By forming the thermal oxide film 211, the film thickness of the pattern (pattern to be an active layer) 210 is 250 mm.
[0110]
In this step, the same effect as that in the case where the thermal oxide film 209 is formed can be obtained. The thermal oxide film 209 becomes a part of the gate insulating film of the TFT.
[0111]
In this embodiment, the film thickness (250Å) of the active layer 210 made of a crystalline silicon film finally obtained is thinner than the film thickness (300Å) of the second thermal oxide film 211. By doing so, an effect can be obtained in order to obtain a unique crystal structure as shown in FIGS. 6 and 7 according to the formation of the thermal oxide film.
[0112]
Thereafter, a silicon oxide film 304 constituting a gate insulating film together with the thermal oxide film is formed to a thickness of 1000 mm by plasma CVD. (Fig. 2 (A))
[0113]
Next, an aluminum film for forming a gate electrode is formed to a thickness of 4000 mm by sputtering. This aluminum film contains 0.2% by weight of scandium.
[0114]
The reason why scandium is contained in the aluminum film is to suppress generation of hillocks and whiskers in the subsequent process. Hillocks and whiskers are needle-like or stab-like protrusions resulting from abnormal growth of aluminum during heating.
[0115]
When the aluminum film is formed, a dense anodic oxide film (not shown) is formed. The anodic oxide film is formed using an ethylene glycol solution containing 3% tartaric acid as an electrolytic solution, an aluminum film as an anode, and platinum as a cathode. In this step, an anodic oxide film having a dense film quality is formed on the aluminum film to a thickness of 100 mm.
[0116]
This anodic oxide film (not shown) has a role of improving adhesion with a resist mask to be formed later.
[0117]
The film thickness of this anodic oxide film can be controlled by the applied voltage during anodic oxidation.
[0118]
Next, a resist mask 306 is formed. Then, using this resist mask, the aluminum film is patterned into a pattern indicated by 305. In this way, the state shown in FIG.
[0119]
Here, anodic oxidation is performed again. Here, a 3% oxalic acid aqueous solution is used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film 308 is formed by anodizing with the aluminum pattern 305 as the anode.
[0120]
In this step, the anodic oxide film 308 is selectively formed on the side surface of the aluminum pattern because the resist mask 306 having high adhesion exists on the upper portion.
[0121]
This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness is 6000 mm. The growth distance can be controlled by the anodic oxidation time.
[0122]
Then, the resist mask 306 is removed. Next, a dense anodic oxide film is formed again. That is, the anodic oxidation using the above-described ethylene glycol solution containing 3% tartaric acid as an electrolytic solution is performed again.
[0123]
In this step, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 309 because the electrolytic solution enters the porous anodic oxide film 308.
[0124]
The dense anodic oxide film 309 has a thickness of 1000 mm. This film thickness is controlled by the applied voltage.
[0125]
Here, the exposed silicon oxide film 304 is etched. At the same time, the thermal oxide film 300 is etched. This etching uses dry etching. Then, the porous anodic oxide film 308 is removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG.
[0126]
After obtaining the state shown in FIG. 2D, impurity ions are implanted. Here, in order to manufacture an N-channel thin film transistor, P (phosphorus) ions are implanted by a plasma doping method.
[0127]
In this step, regions 311 and 315 that are heavily doped and regions 312 and 314 that are lightly doped are formed. This is because the remaining silicon oxide film 310 functions as a semi-transmissive mask, and some of the implanted ions are shielded there.
[0128]
Then, the region into which the impurity ions are implanted is activated by irradiation with laser light (or strong light using a lamp). Thus, the source region 311, the channel formation region 313, the drain region 315, and the low concentration impurity regions 312 and 314 are formed in a self-aligned manner.
[0129]
Here, a region 314 is referred to as an LDD (lightly doped drain) region. (Fig. 2 (D))
[0130]
Note that when the thickness of the dense anodic oxide film 309 is increased to 2000 mm or more, an offset gate region can be formed outside the channel formation region 313 with the film thickness.
[0131]
The off-gate region is also formed in this embodiment, but since the size thereof is small, the contribution due to its existence is small, and the drawing becomes complicated, so it is not shown in the drawing.
[0132]
In order to form an anodic oxide film having a dense film quality as thick as 2000 mm or more, an applied voltage of 200 V or more is required, so care must be taken regarding reproducibility and safety.
[0133]
Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 316. As the interlayer insulating film, a layer made of a resin material may be used on the silicon oxide film or the silicon nitride film.
[0134]
Then, contact holes are formed, and a source electrode 317 and a drain electrode 318 are formed. Thus, the thin film transistor shown in FIG. 3E is completed.
[0135]
The TFT shown in this embodiment can have a very high characteristic that has not been obtained in the past.
[0136]
For example, a high-performance NTFT (N-channel TFT) having a mobility of 200 to 300 (cm ² / Vs) and an S value of 75 to 90 (mV / dec) (V _D = 1V) can be obtained. . A high-performance PTFT (P-channel TFT) having 120 to 180 (cm ² / Vs) and an S value of 75 to 100 (mV / dec) (V _D = 1V) can be obtained.
[0137]
In particular, the S value is a surprisingly good value of 1/2 or less compared to the values of the conventional high-temperature polysilicon TFT and low-temperature polysilicon TFT.
[0138]
[Example 2]
The present embodiment relates to an example in which the gate insulating film forming method is devised in the configuration shown in the first embodiment.
[0139]
FIG. 3 shows a manufacturing process of this example. First, a crystalline silicon film 208 having a lateral growth region is obtained according to the steps shown in FIGS. In this case, the amorphous silicon film as the starting film is 500 mm.
[0140]
After obtaining the crystalline silicon film, a thermal oxide film 209 is formed to a thickness of 200 mm by performing a heat treatment at 950 ° C. in an oxygen atmosphere containing 3% HCl. (Fig. 3 (A))
[0141]
Next, the thermal oxide film 209 is removed. Then, by patterning, a pattern 210 that will later become an active layer of the thin film transistor is formed. (Fig. 3 (B))
[0142]
Next, a gate insulating film 304 is formed to a thickness of 1000 mm by plasma CVD. (Figure 3 (C))
[0143]
Next, heat treatment is performed at 950 ° C. in an oxygen atmosphere containing 3% HCl to form a thermal oxide film 211 with a thickness of 300 mm. (Fig. 3 (D))
[0144]
At this time, the thermal oxide film grows inside the CVD oxide film 304 and is formed in a state as shown in FIG.
[0145]
When the manufacturing process shown in this embodiment is adopted, the gate insulating film is constituted by a laminated film of the thermal oxide film 211 and the CVD oxide film 304.
[0146]
When the manufacturing process shown in this embodiment is employed, the interface state density at the interface between the gate insulating film and the active layer can be lowered.
[0147]
Example 3
This embodiment shows a manufacturing process of an active matrix circuit portion of an active matrix liquid crystal display device.
[0148]
FIG. 4 shows an outline of the manufacturing process of this example. First, according to the steps shown in FIGS. 1 and 2, the state shown in FIG. 2D is obtained. (State shown in FIG. 4A)
[0149]
Next, as a first interlayer insulating film, a silicon nitride film 401 is formed to a thickness of 2000 mm by plasma CVD. Further, a polyimide resin film 402 is formed by spin coating. In this way, the state shown in FIG. As the resin material, polyamide or polyimide amide can be used in addition to polyimide.
[0150]
Next, contact holes reaching the source region 311 and the drain region 315 are formed, so that the source electrode 403 and the drain electrode 403 are formed. These electrodes are formed by a laminated film of a titanium film, an aluminum film, and a titanium film. Note that the source electrode 403 is formed to extend from the source line. (Fig. 4 (C))
[0151]
A part of the drain electrode 403 is used as an electrode for forming an auxiliary capacitance.
[0152]
After the source and drain electrodes are formed, a polyimide resin film 404 is formed as a second interlayer insulating film. In this way, the state shown in FIG.
[0153]
Next, an opening is formed in the resin interlayer insulating film 404, and a black matrix (BM) 405 made of a laminated film of a titanium film and an aluminum film is formed. The black matrix 405 functions as an electrode for forming an auxiliary capacitor in addition to the function as an original light shielding film.
[0154]
After the black matrix 405 is formed, a polyimide resin film 406 is formed as a third interlayer insulating film. Then, a contact hole to the drain electrode 403 is formed, and a pixel electrode 407 made of ITO is formed.
[0155]
Thus, a structure in which the polyimide resin film 406 is sandwiched between the pattern of the black matrix 405 functioning as an auxiliary capacitor and the pattern of the pixel electrode 407 is obtained.
[0156]
Example 4
The present embodiment is an example in which, in the configuration shown in the first embodiment, a method of forming a contact for a gate electrode or a gate wiring extending from the gate electrode is devised.
[0157]
In the configuration shown in Example 1 (see FIG. 2) or Example 3 (or Example 3), the side surface and the upper surface of the gate electrode are covered with an anodized film having a dense film quality.
[0158]
Such a structure has a great effect in terms of suppressing hillocks and wiring shorts when forming an electrode made of aluminum.
[0159]
However, there is a problem that it is relatively difficult to form a contact due to its strong film quality.
[0160]
The present embodiment relates to a configuration that solves this problem. FIG. 5 shows a manufacturing process of this example. The detailed production conditions and the like of the same reference numerals as in the other examples are the same as those in the other examples.
[0161]
First, as shown in FIG. 5A, an active layer pattern 210 made of a crystalline silicon film is obtained. Then, a state in which the thermal oxide film 211 and the CVD oxide film 304 are stacked is obtained.
[0162]
Here, a process of forming a CVD oxide film first and then forming a thermal oxide film is employed.
[0163]
When the state shown in FIG. 5A is obtained, an aluminum film is formed, and a silicon nitride film is further formed to a thickness of 500 mm. Then, patterning is performed using the resist mask 306 to obtain a state in which the aluminum pattern indicated by 305 and the silicon nitride film 501 formed thereon are formed. (Fig. 5 (B))
[0164]
When the state shown in FIG. 5B is obtained, a porous anodic oxide film 308 is formed with the resist mask 306 disposed, and an anodic oxide film 309 having a dense film quality is formed.
[0165]
These anodic oxide films are selectively formed only on the side surfaces of the aluminum pattern 307 to be gate electrodes. This is because the silicon nitride film 501 exists on the upper surface of the aluminum pattern.
[0166]
When the formation of the anodic oxide film is completed, the resist mask 306 is removed. Further, the exposed silicon oxide film 304 is removed, and a part of the thermal oxide film 211 is also removed.
[0167]
In this way, the state shown in FIG. After obtaining the state shown in FIG. 5C, the resist mask 306 is removed, and the porous anodic oxide film 308 is further removed.
[0168]
Further, the silicon nitride film 501 is removed. In this way, the state shown in FIG. In this state, doping of an impurity imparting a conductivity type is performed by a plasma doping method.
[0169]
As a result, the source region 311, the low concentration impurity regions 312 and 314, the channel region 313, and the drain region 315 are formed in a self-aligned manner.
[0170]
After the impurity doping is completed, laser light irradiation is performed to anneal the damage caused during the doping and activate the doped impurities.
[0171]
In this way, the state shown in FIG. Next, an interlayer insulating film 502 is formed. Then, contact holes are formed to form a source electrode 317, a gate extraction electrode 503, and a drain electrode 318, and the state shown in FIG.
[0172]
In this step, the contact hole to the gate electrode 307 can be formed relatively easily because no anodized film is present on the upper surface of the gate electrode.
[0173]
Although the drawing shows that the source / drain electrode and the gate electrode are formed on the same cross section, the gate extraction electrode is actually formed in a portion extending from the gate electrode 307. .
[0174]
Example 5
The present embodiment is an example in which a glass substrate is used as the substrate in the configuration shown in the first embodiment.
[0175]
In this embodiment, a Corning 1737 glass substrate having a strain point of 667 ° C. is used as the substrate. Then, heat treatment for crystallization is performed at 600 ° C. for 4 hours.
[0176]
The heat treatment for forming the thermal oxide film is performed at 640 ° C. in an oxygen atmosphere containing 3% by volume of HCl. In this case, the thickness of the formed thermal oxide film is about 30 mm after a processing time of 2 hours. In this case, the effect is small as compared with the case where heat treatment at 950 ° C. as shown in Example 1 is applied.
[0177]
Example 6
The present embodiment is an example in which HCl is not contained in the atmosphere in forming the thermal oxide film in the configuration shown in the first embodiment. In this case, the gettering effect of nickel is small as compared with the case where HCl is contained in the atmosphere.
[0178]
Example 7
The present embodiment is an example in the case where the laser light is irradiated after the thermal oxide film is formed in the configuration shown in the first embodiment. In this way, crystallization can be further promoted.
Example 8
This embodiment shows an example of a semiconductor device using a TFT. FIG. 8 shows examples of various semiconductor devices.
[0179]
FIG. 8A shows what is called a portable information terminal, which calls and displays information necessary for an active matrix liquid crystal display device 2005 provided in the main body 2001 from an internal storage device, Information accessed via the line can be displayed.
[0180]
As a form of the display device, an active matrix EL display device may be used. Various information processing circuits and memory circuits are integrated as integrated circuits 2006 using TFTs on the same substrate as the active matrix circuit constituting the display device.
[0181]
Further, the main body 2001 is provided with a camera unit 2002, and necessary image information can be captured by operating the operation switch 2004. An image captured by the camera unit 2002 is captured from the image receiving unit 2003 into the apparatus.
[0182]
FIG. 8B shows a display device called a head mounted display. This apparatus has a function of displaying an image at a location several cm in front of the eyes with two active matrix liquid crystal displays 2102 attached to a main body 2101 on the head. With this device, images can be seen in a pseudo-experienced manner.
[0183]
FIG. 8C shows a car navigation system. This device has a function of measuring a position using a signal from an artificial satellite received by an antenna 2204. Then, the measured position is displayed on the active matrix type liquid crystal display device 2202. Selection of information to be displayed is performed by the operation switch 2203.
[0184]
Note that an active matrix EL display device can be used instead of the liquid crystal display device.
[0185]
FIG. 8D illustrates an example of a mobile phone. In this apparatus, an antenna 2306 is provided in a main body 2301, and an audio input unit 2303 and an audio input unit 2302 are provided.
[0186]
When making a call, the operation switch 2305 is operated. Various kinds of image information are displayed on the display device 2304. As a portable display device, an active matrix liquid crystal display device or an active matrix EL display device is used.
[0187]
FIG. 8E illustrates a portable video camera. This apparatus has a function of storing an image captured from the image receiving unit 2406 on a magnetic tape stored in the main body 2401.
[0188]
Various digital processes are performed on the image in the integrated circuit 2407. This integrated circuit 2407 may be configured by combining conventional IC chips, or may be configured by using a TFT as disclosed in this specification. Moreover, you may comprise by those combination.
[0189]
An image received by the image receiving unit 2406 and an image stored on an internal magnetic tape are displayed on an active matrix liquid crystal display device 2402. The operation of the apparatus is performed by an operation switch 2404. In addition, the power of the apparatus is provided by the battery 2405.
[0190]
FIG. 8F illustrates a projection display device. This apparatus has a function of displaying an image projected from the main body 2501 on a screen.
[0191]
The main body 2501 includes a light source 2502, an active matrix liquid crystal display device 2503 that optically modulates light from the light source and forms an image, and an optical system 2504 for projecting an image.
[0192]
The liquid crystal display device can be used in either a transmission type or a reflection type except for the device shown in FIG.
[0193]
【The invention's effect】
When a nine-stage ring oscillator was configured by combining PTFT and NTFT obtained by utilizing the invention disclosed in this specification, it was possible to oscillate at 400 MHz or higher.
[0194]
In general, in consideration of designing an actual circuit with about 10% of the oscillation frequency of the ring oscillator, a circuit that operates at a frequency of about 40 MHz can be configured with the TFT.
[0195]
In this manner, by using the invention disclosed in this specification, a thin film transistor that can form a circuit that requires high-speed operation (generally operating speed of several tens of MHz or more) can be obtained.
[0196]
In particular, with respect to the S value, a characteristic comparable to that of a MOS transistor manufactured using a single crystal silicon wafer of 100 (mV / dec) or less can be obtained.
[0197]
By utilizing the invention disclosed in this specification, a structure in which circuits requiring various high-speed operations are integrated with TFTs over the same substrate can be provided. In addition, a manufacturing method thereof can be provided.
[Brief description of the drawings]
FIGS. 1A to 1C illustrate a manufacturing process of a thin film transistor. FIGS.
FIGS. 2A and 2B illustrate a manufacturing process of a thin film transistor. FIGS.
FIG. 3 illustrates a manufacturing process of a thin film transistor.
4A and 4B illustrate a manufacturing process of a thin film transistor.
FIGS. 5A and 5B illustrate a manufacturing process of a thin film transistor. FIGS.
FIG. 6 is an electron micrograph showing a silicon thin film.
FIG. 7 is an electron micrograph showing a silicon thin film.
FIG. 8 is a diagram showing an outline of various semiconductor devices using TFTs.
FIG. 9 is a schematic diagram showing a state of crystal growth.
[Explanation of symbols]
201 Quartz substrate 202 Base film (silicon oxide film)
203 Amorphous silicon film 204 Mask made of silicon oxide film 205 Openings formed in the mask (nickel element introduction region)
206 Nickel element 207 held in contact with the substrate 207 Crystal growth direction 208 Crystalline silicon film 209 Thermal oxide film 210 Silicon film pattern 211 constituting the active layer Thermal oxide film 304 Silicon oxide film (CVD) Oxide film)
305 Pattern made of aluminum film 306 Resist mask 307 Gate electrode 308 Porous anodic oxide film 309 Anodized film 310 having a dense film quality Residual silicon oxide film 311 Source region 312 Low concentration impurity region 313 Channel region 314 Low concentration impurity Region 315 Drain region 316 Interlayer insulating film 317 Source electrode 318 Drain electrode

Claims (12)

Forming an amorphous silicon film over a substrate having an insulating surface;
Selectively introducing a metal element for promoting crystallization of silicon into a part of the amorphous silicon film;
Heat treatment is performed to cause crystal growth in a direction parallel to the substrate from the region where the metal element is selectively introduced toward another region,
Forming a first thermal oxide film by heat treatment in an oxidizing atmosphere containing a halogen element;
Removing the first thermal oxide film;
Forming a second thermal oxide film by heat treatment in an oxidizing atmosphere containing a halogen element;
A method for manufacturing a semiconductor device, wherein the finally obtained silicon film is thinner than the second thermal oxide film. Forming an amorphous silicon film over a substrate having an insulating surface;
Selectively introducing a metal element for promoting crystallization of silicon into a part of the amorphous silicon film;
Heat treatment is performed to cause crystal growth in a direction parallel to the substrate from the region where the metal element is selectively introduced toward another region,
Forming a first thermal oxide film by heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element;
Removing the first thermal oxide film;
A second thermal oxide film is formed by heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element;
A method for manufacturing a semiconductor device, wherein the finally obtained silicon film is thinner than the second thermal oxide film. Forming an amorphous silicon film over a substrate having an insulating surface;
Selectively introducing a metal element for promoting crystallization of silicon into a part of the amorphous silicon film;
Heat treatment is performed to cause crystal growth in a direction parallel to the substrate from the region where the metal element is selectively introduced toward another region,
Forming a first thermal oxide film by heat treatment in an oxidizing atmosphere containing a halogen element;
Removing the first thermal oxide film;
Forming a second thermal oxide film by heat treatment in an oxidizing atmosphere containing a halogen element;
A method for manufacturing a semiconductor device, wherein the finally obtained silicon film has a thickness less than a total thickness of the first thermal oxide film and the second thermal oxide film. Forming an amorphous silicon film over a substrate having an insulating surface;
Selectively introducing a metal element for promoting crystallization of silicon into a part of the amorphous silicon film;
Heat treatment is performed to cause crystal growth in a direction parallel to the substrate from the region where the metal element is selectively introduced toward another region,
Forming a first thermal oxide film by heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element;
Removing the first thermal oxide film;
A second thermal oxide film is formed by heat treatment at 800 ° C. to 1100 ° C. in an oxidizing atmosphere containing a halogen element;
A method for manufacturing a semiconductor device, wherein the finally obtained silicon film has a thickness less than a total thickness of the first thermal oxide film and the second thermal oxide film. In any one of Claims 1 thru | or 4 ,
A method for manufacturing a semiconductor device, wherein nickel (Ni) is used as a metal element that promotes crystallization of silicon. In any one of Claims 1 thru | or 4 ,
One or more kinds of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au are used as a metal element that promotes crystallization of silicon. A method for manufacturing a semiconductor device. An information terminal manufactured by the method according to claim 1 and having an active matrix liquid crystal display device or an active matrix EL display device in a display portion. A head-mounted display manufactured by the method according to claim 1 and having an active matrix liquid crystal display device in a display portion. A car navigation device manufactured by the method according to claim 1 and having an active matrix liquid crystal display device or an active matrix EL display device in a display portion. A cellular phone manufactured by the method according to claim 1 and having an active matrix liquid crystal display device or an active matrix EL display device in a display portion. A video camera manufactured by the method according to claim 1 and having an active matrix liquid crystal display device in a display portion. A projection display device manufactured by the method according to claim 1 and having an active matrix liquid crystal display device in a display portion.

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