JP2006261180A - Method of manufacturing thin-film semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a thin-film semiconductor device which allows manufacturing of an electronic circuit device with improved performance by forming a polycrystalline silicon thin film having a dramatically larger grain diameter than the one manufactured by the conventional method. <P>SOLUTION: An amorphous silicon thin film 04a, 11a is formed in a desired thickness or above on a heterogeneous substrate 01, 09, and then continuous wave laser light 06, 13 is irradiated, scanning over the amorphous silicon thin film, to turn the amorphous silicon thin film into a polycrystalline silicon thin film 04b, 11b. Then, the polycrystalline silicon thin film is thinned to a desired thickness to form a polycrystalline silicon thin film 04b', 11b'. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a semiconductor element substrate such as a thin film solar cell, a TFT (Thin Film Transistor) substrate, or a semiconductor element (hereinafter collectively referred to as a thin film semiconductor device).

  In recent years, research on forming a crystalline silicon thin film on a non-conductive heterogeneous substrate such as a glass substrate has been actively conducted. The crystalline silicon thin film formed on this heterogeneous substrate can be used widely for TFTs, thin film solar cells and the like.

  A thin-film solar cell is formed by forming a crystalline silicon thin film having good crystallinity on an inexpensive substrate by a low-temperature process, and using this for a photoelectric conversion device, thereby reducing cost and improving performance. By using this crystalline silicon thin film for a solar cell, long-wavelength light that is not sensitive to solar cells made of amorphous silicon is not observed. Can also be converted into electrical energy. This technology is expected to be applicable not only to solar cells but also to photoelectric conversion elements such as optical sensors.

  A solar cell made of this crystalline silicon thin film generally uses a technique of directly depositing a crystalline silicon thin film by a plasma CVD method. It is known that a crystalline silicon thin film can be formed on a substrate at a low temperature by this method, and is said to be effective for cost reduction.

  In this plasma CVD method, the formation conditions are such that the silane source gas is diluted about 15 times or more with hydrogen, the pressure in the plasma reaction chamber is 1 Pa to 1000 Pa, the substrate temperature is 150 ° C. to 550 ° C., preferably 400 ° C. or less. By forming the film thickness within the range, the film is formed. Thereby, a crystalline silicon thin film is formed on the substrate. However, this method has made it difficult to form a polycrystalline silicon thin film having a large crystal grain size. In addition, the quality of the i layer, which is the basis of the power generation function, is drastically lowered when doping is performed to optimize the device structure. For these reasons, it has been difficult for a solar cell to achieve an efficiency greatly exceeding 10% with a single cell advantageous for cost reduction.

  On the other hand, various attempts to form crystalline silicon by laser scanning have been studied, and a method using a continuous wave laser is disclosed in JP-A-2001-351863 (Patent Document 1). This method forms amorphous silicon on a heterogeneous substrate, and melts and crystallizes into polycrystalline silicon by scanning a strip-like continuous light source, making it possible to grow long crystal grains in the scanning direction. .

When crystallization is performed using this continuous wave laser, it has been attempted to use a solid-state laser such as Nd: YAG or Nd: YVO ₄ . By using these solid-state lasers, it has become possible to significantly reduce running costs and at the same time form high-quality polycrystalline silicon.
JP 2001-351863 A

  However, even when a continuous wave laser is used, the crystal grain size of the polycrystalline silicon thin film is about 1 to 2 μm in width and about 10 μm in length. The size of the crystal grain is an important factor for determining the electrical characteristics of the device manufactured at that position, and it has been desired to form a crystal grain having a larger size.

  That is, in order to fabricate a circuit using an element with further improved electrical characteristics on the polycrystalline silicon thin film as described above, it is necessary to further increase the crystal grain size.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a thin film semiconductor device that can solve the above-described problems and can form a polycrystalline silicon thin film having a significantly larger particle size than conventional methods to constitute an electronic circuit device with improved performance. It is to provide.

  In order to achieve the above object, the present invention is configured as follows.

  The method of manufacturing a thin film semiconductor device according to the invention of claim 1 is characterized in that a silicon thin film is formed on a heterogeneous substrate to have a desired thickness or more, and the silicon thin film is crystallized by irradiating continuous wave laser light and scanning. Thereafter, the crystallized silicon thin film is thinned to a desired film thickness.

  According to a second aspect of the present invention, in the method of manufacturing a thin film semiconductor device according to the first aspect, a film thickness of the silicon thin film formed on the heterogeneous substrate is at least twice the desired film thickness. To do.

  According to a third aspect of the present invention, in the method for manufacturing a thin film semiconductor device according to the first aspect, the thickness of the silicon thin film formed on the heterogeneous substrate is not less than the desired thickness and not less than 500 nm. It is characterized by.

  According to a fourth aspect of the present invention, in the method of manufacturing a thin film semiconductor device according to any one of the first to third aspects, the wavelength of the continuous wave laser beam is 400 nm or more and 600 nm or less.

  According to a fifth aspect of the present invention, there is provided a method of manufacturing a thin film semiconductor device according to any one of the first to fourth aspects, wherein the crystallized silicon thin film is formed on the crystallized silicon thin film before the crystallized silicon thin film is thinned to a desired thickness. Further, a thin film layer is further formed, and the film is further thinned to a desired film thickness.

  The invention of claim 6 is the method of manufacturing a thin film semiconductor device according to claim 5, wherein the material constituting the thin film layer is any one of a photoresist, a semiconductor material, an inorganic insulating material, a metal material, and an organic material. It is characterized by that.

<Key points of the invention>
The present invention performs crystallization with a film thicker than a desired film thickness based on the new finding that the average crystal grain size increases as the film thickness to be crystallized increases. Thereafter, the desired film thickness is reduced. Further, a planarization step may be added after crystallization in order to eliminate the disadvantage that the unevenness of the surface becomes remarkable as the film thickness increases.

  Hereinafter, the gist of the present invention will be described in detail.

  FIG. 3 shows the dependence of the average crystal grain area on the thickness of the silicon thin film after crystallization by a continuous wave laser. Obviously, as the film thickness increases, the crystal grains become larger. In particular, the increase in crystal grain size is remarkable when the film thickness is 0.5 μm to 1 μm. It is known that the electrical characteristics, mobility, doping efficiency, etc. of the silicon thin film are improved as the crystal grains become larger. However, the optimum film thickness is determined according to the element and cannot be increased as much as possible. For example, TFTs are required to be as thin as about 50 nm. Therefore, in order to apply the above knowledge to device fabrication, it has been found that it is effective to form a thick film and thin it after crystallization.

  However, in crystallization by scanning with a continuous wave laser beam, the surface after melt crystallization is not flat, and unevenness occurs in the crystal plane when a cross section is taken in a direction perpendicular to the scanning direction. This surface profile is shown in FIG. In the figure, the left and right flat portions are portions that were not crystallized by laser. In particular, the unevenness became more prominent as the film thickness increased or the particle diameter increased. When the film thickness is reduced, the convex part is easily removed, so it could be used as it was, but in order to improve the performance and make the characteristics uniform, a more appropriate thin film was deposited and planarized. It was effective to make it thinner later.

  Next, the relationship between the configuration and effects of the present invention will be specifically described.

  In the manufacturing method according to the first aspect of the present invention, since the silicon thin film is formed on the heterogeneous substrate to have a desired film thickness or more, a silicon thin film having a large average grain size can be obtained. In addition, the silicon thin film is crystallized by irradiating and scanning with continuous wave laser light, and the resulting surface irregularities are removed by a flattening process to thin the silicon thin film to a desired thickness. Therefore, it is possible to form an electronic circuit device with improved performance by forming a polycrystalline silicon thin film having a significantly larger particle size than the conventional method.

  In the manufacturing method of the present invention, the film thickness of the silicon thin film formed on the heterogeneous substrate is preferably at least twice the desired film thickness. This is because the planarization process is facilitated, and a high-quality polycrystalline silicon thin film having a large grain size can be left. Since the minimum desired film thickness is 500 nm as shown in FIG. 3, the film thickness of the silicon thin film formed on the heterogeneous substrate is not less than the desired film thickness and not less than 500 nm. . Therefore, for example, when the desired film thickness is 1 μm, 1.5 μm, 2 μm, etc., it is preferable to set the thickness to 2 μm, 3 μm, 4 μm, etc., which is twice or more.

  The wavelength of the continuous wave laser beam is suitably 400 nm to 600 nm, which can reduce thermal damage to the underlying material, among wavelengths 400 nm to 900 nm that can be absorbed by the amorphous silicon thin film or the crystalline silicon thin film ( Claim 4).

In the manufacturing method according to the invention of claim 5, before the crystallized silicon thin film is thinned to a desired film thickness, a thin film layer is further formed on the crystallized silicon thin film, and the desired film thickness is formed thereon. Until thin. According to this, even when the film thickness is increased by increasing the film thickness, and the surface irregularities are conspicuous, an appropriate thin film layer is further deposited thereon to perform planarization. A flat thin film can be obtained.
As a material constituting the thin film layer, any one of a photoresist, a semiconductor material, an inorganic insulating material, a metal material, and an organic material can be used.

  According to the present invention, the following excellent effects can be obtained.

  According to the manufacturing method of the present invention, since a silicon thin film is formed on a different substrate with a desired thickness or more, a silicon thin film having a large average size of crystal grains can be obtained. The silicon thin film is crystallized by irradiating and scanning, and the resulting surface irregularities are removed by thinning the silicon thin film to a desired film thickness. An electronic circuit device with improved performance can be formed by forming a polycrystalline silicon thin film having a large diameter.

  According to another feature of the manufacturing method of the present invention, before the crystallized silicon thin film is thinned to a desired thickness, a thin film layer is further formed on the crystallized silicon thin film, and a desired layer is formed thereon. Reduce the film thickness. According to this, even if the film thickness is increased to increase the particle size, and even when the surface irregularities are conspicuous, an appropriate thin film layer is further deposited and flattened. Can be obtained.

  Hereinafter, embodiments of the present invention will be described focusing on examples. In addition, the following Examples show an example of this invention and this invention is not limited to these.

  FIG. 1 schematically shows a manufacturing process of a thin film semiconductor device in Example 1 of the present invention. FIG. 1 (a) shows crystallization of an amorphous silicon thin film having a desired thickness or more by laser irradiation. The figure which shows a process, (b) is a figure which shows the process of thinning the obtained polycrystalline silicon thin film by an etching, (c) is a figure which shows the process of forming an electrode. In this embodiment, an example applied to a photoelectric conversion element is shown.

In FIG. 1A, a rectangular glass substrate of 30 cm × 40 cm was prepared as the heterogeneous substrate 01, and a 200 nm SiN film was formed as the diffusion preventing layer 02. A refractory metal layer 03 was formed to a thickness of 100 nm on the substrate on which the diffusion prevention layer 02 was formed. On top of that, 3 μm of an amorphous silicon thin film 04a was formed by catalytic CVD. The film thickness of the amorphous silicon thin film 04a of 3 μm is a value thicker than the desired film thickness of 2 μm in this embodiment. The amorphous silicon thin film 04a was formed at a substrate temperature of 450 ° C. using a mixed gas of H ₂ containing SiH ₄ : 100 ccm and PH ₄ : 0.01 ccm. Under this condition, an amorphous silicon thin film containing an n-type dopant is formed.

Next, a laser beam 06 is irradiated from a 532 nm solid-state laser light source 05 based on the second harmonic of YVO ₄ , and a heterogeneous substrate (glass substrate) 01 is relatively scanned in the X direction so that the amorphous silicon thin film 04a. Crystallized. As a result, a polycrystalline silicon thin film 04b was formed. By irradiation with this laser beam 06, the amorphous silicon thin film 04a having a thickness of 3 μm was completely melted and crystallized. The silicon thin film melted and crystallized became a polycrystalline silicon thin film 04b having a large grain size laterally grown in the scanning direction.

  Here, the refractory metal layer 03 is a light absorption layer made of, for example, tungsten or molybdenum, and thereby lowers the irradiation energy density so that a wider area can be crystallized in a lump. The reason why the diffusion prevention layer 02 is provided is that the light absorption layer composed of the refractory metal layer 03 instantaneously becomes a temperature close to 2000 ° C. during melting, and impurities may be mixed into the amorphous silicon thin film 04a. It is for suppressing.

  Next, as shown in FIG. 1 (b), a polycrystalline silicon thin film 04b formed by scanning with a continuous wave laser beam formed with a desired film thickness (3 μm) or more as described above is then obtained. The film is thinned to a film thickness (2 μm) to obtain a polycrystalline silicon thin film 04b ′ having a film thickness of 2 μm.

  In this example, the 1 μm thick polycrystalline silicon thin film 04b was etched by sputter etching while introducing argon (Ar) gas. In this step, a polycrystalline silicon thin film 04b 'in which protrusions formed at the boundary of the laser scanning line were easily etched and the unevenness was relaxed was obtained.

When the average size of crystal grains was evaluated, when crystallized at a film thickness of 2 μm, the average crystal grain area was 500 μm ² , but when crystallized at a film thickness of 3 μm and thinned to 2 μm by etching as described above The average grain area was 700 μm ² or more.

Next, as shown in FIG. 1C, a p-type amorphous silicon thin film 07 having a thickness of 50 nm was formed on the 2 μm-thick polycrystalline silicon thin film 04b ′ by plasma CVD. This formation was performed using a mixed gas of H ₂ containing SiH ₄ : 50 ccm and B ₂ H ₆ : 0.1 ccm at a substrate temperature of 300 ° C.

  Further, a transparent electrode 08 made of an ITO film was formed to a thickness of 70 nm by sputtering.

  About the photoelectric conversion element produced by the above, the junction characteristic was investigated. As a result, the short-circuit probability when the sputter etching was not performed was 15%, but when the sputter etching was performed, it was 5% or less, which was a significant improvement.

  In this embodiment, the case of manufacturing one element is shown. However, it can be applied to a case where an integrated structure in which a base electrode and a transparent electrode are connected in series by a known mask vapor deposition method or a laser processing technique. Needless to say.

For the diffusion prevention layer 02, it was effective to use a SiO ₂ film, a ZnO film, a SnO ₂ film, an ITO film, a TiO ₂ film, a SiON film, or a laminated film thereof in addition to the SiN film. The heat resistance is greatly improved by increasing the film thickness to 1 μm or more, preferably 4 μm.

As the refractory metal layer 03, a metal having a melting point exceeding 1500 ° C., such as tantalum (Ta), molybdenum (Mo), tungsten (W), chromium (Cr), or an alloy thereof was effective. However, even if it is not a refractory metal, crystallization was possible if a conductive ZnO film, SnO ₂ film, ITO film, TiO ₂ film or the like was further formed thereon with a thickness of about 100 nm.

  In this embodiment, an example used for manufacturing a TFT will be described.

In FIG. 2, a 30 cm × 40 cm rectangular glass substrate was prepared as the heterogeneous substrate 09, and a SiO ₂ film (50 nm) / SiN film (50 nm) was formed as the diffusion preventing layer 10. On top of that, an amorphous silicon thin film 11a having a thickness of 500 nm or more was formed using a remote plasma CVD method. This formation was performed using a mixed gas of Ar containing SiH ₄ : 20 ccm at a substrate temperature of 400 ° C. Under this condition, an i-type (undoped) amorphous silicon thin film 11a is formed.

  Next, phosphorus was introduced into the amorphous silicon thin film 11a by ion implantation to form a source and a drain.

Thereafter, the laser beam 13 was irradiated from the 532 nm solid-state laser light source 12, and the crystal was crystallized by scanning relatively in the X direction. As a result, a polycrystalline silicon thin film 11b was formed. A second harmonic of Nd: YVO ₄ was used for the solid-state laser. A continuous wave was used for this laser. By irradiation with this laser beam 13, the amorphous silicon thin film 11a became a polycrystalline silicon thin film 11b having a large particle diameter laterally grown in the scanning direction.

  After crystallizing the silicon thin film as described above, in this embodiment, the thin film layer is further formed and then thinned as follows.

  That is, a photoresist film (not shown) was applied as the thin film layer, formed to a film thickness of 0.5 μm by heat treatment, and etched by sputtering to leave a 50 nm silicon thin film having a desired film thickness. As a result, a silicon thin film having a very large particle diameter was formed.

  Further, a gate insulating film was formed between the source and the drain, and a gate electrode was further formed thereon to complete the TFT structure.

  In the above embodiment, the catalytic CVD method and the remote plasma CVD method are used as the method for forming the amorphous silicon thin films 04a and 11a. However, as a method for forming the silicon thin film, any other method such as a low pressure thermal CVD method or a sputtering method may be used. Although doping is also shown for n-type using phosphorus (P), the method of the present invention can be used for p-type as well. Alternatively, an alloy film containing other elements, hydrogen, oxygen, nitrogen, carbon, germanium, or the like may be used. Furthermore, crystallization is further promoted by mixing elements having a catalytic action in crystallization of silicon such as nickel (Ni) and chromium (Cr). Furthermore, the silicon thin film is not limited to an amorphous silicon thin film, but may be a microcrystalline silicon thin film, a polycrystalline silicon thin film, or a mixture thereof. Rather, when the film thickness to be processed is thick, a film having a large crystal component with a small absorption coefficient is desirable.

  The laser light sources 05 and 12 may be continuous wave light sources having a required intensity. For example, a gas laser or a semiconductor laser can be used. The wavelength needs to be a wavelength that can be absorbed by the amorphous silicon thin film or the crystalline silicon thin film. Specifically, 400 nm to 900 nm can be used, but 400 nm to 600 nm is appropriate for reducing thermal damage to the base material. The laser beam may be a fundamental wave or a harmonic such as the second and third harmonics as long as it is within this wavelength range and sufficient light intensity can be obtained.

  Laser crystallization may be performed only on necessary portions, not on the entire surface. There are advantages in reducing the scanning range and shortening the processing time.

Moreover, as the material of the thin film layer formed after crystallization, photoresist is used in the above embodiment, but other materials such as semiconductor materials such as silicon and carbon, and insulating materials such as SiO ₂ , SiN, and Al ₂ O ₃ are used. A material, a metal material such as aluminum (Al) or copper (Cu), or an organic material such as a thermosetting resist can be used. As a method for forming the thin film layer, in addition to the coating method, a normal film forming method such as a CVD method, a sputtering method, a vapor deposition method, or a spray method can be used. Of course, as shown in the embodiments, it is desirable to use a material having a flattening effect and a film forming method that are formed by a coating method. That is, it is needless to say that a method of applying and drying a resist material such as a photoresist by a spinner as shown in the embodiments is particularly preferable. As a method of thinning the thin film layer, any means can be used as long as it can remove both silicon and the thin film thereon. Gas phase etching such as plasma etching or ion etching, or wet etching may be used, and mechanochemical etching or mechanical polishing may be used.

It is also effective to partially perform thin film formation of the thin film layer after crystallization and subsequent thinning by etching or the like. For example it is removed only necessary portions of the thin film formed of SiO ₂ and high-quality silicon thin film, not only the subsequent device formation is facilitated, features SiO ₂ film as a protective film in other regions There is merit to do.

FIG. 1 schematically shows a process for producing a crystalline silicon-based semiconductor device in Example 1 of the present invention. (A) shows forming an amorphous silicon thin film having a desired thickness or more by laser beam irradiation. The figure which shows the process of crystallizing, (b) is a figure which shows the process of thinning the obtained polycrystalline silicon thin film by an etching, (c) is a figure which shows the process of forming an electrode. It is a schematic diagram which shows the production first half of the crystalline silicon type semiconductor device in Example 2 of this invention. It is a figure which shows the dependence to the film thickness of the silicon thin film of the average crystal grain area after crystallization by a continuous wave laser. It is the surface profile of the silicon thin film which took the cross section in the direction orthogonal to the laser scanning surface after crystallization.

Explanation of symbols

01, 09 Dissimilar substrate 02, 10 Diffusion prevention layer 03 High melting point metal layer 04a, 11a Amorphous silicon thin film 04b, 11b Polycrystalline silicon thin film 04b 'Polycrystalline silicon thin film 05, 12 Solid-state laser light source 06, 13 Laser light 07 p Type amorphous silicon thin film 08 transparent electrode

Claims (6)

  A silicon thin film is formed on a heterogeneous substrate to have a desired thickness or more, and the silicon thin film is crystallized by irradiating and scanning with a continuous wave laser beam, and then the crystallized silicon thin film is thinned to a desired thickness. A method for manufacturing a thin film semiconductor device. In the manufacturing method of the thin film semiconductor device according to claim 1,
A method of manufacturing a thin film semiconductor device, wherein a film thickness of a silicon thin film formed on the heterogeneous substrate is at least twice the desired film thickness. In the manufacturing method of the thin film semiconductor device according to claim 1,
A method of manufacturing a thin film semiconductor device, wherein a thickness of a silicon thin film formed on the heterogeneous substrate is not less than the desired thickness and not less than 500 nm. In the manufacturing method of the thin film semiconductor device in any one of Claim 1 to 3,
A method of manufacturing a thin film semiconductor device, wherein the wavelength of the continuous wave laser beam is 400 nm or more and 600 nm or less. In the manufacturing method of the thin film semiconductor device according to claim 1,
Before thinning the crystallized silicon thin film to a desired film thickness, a thin film layer is further formed on the crystallized silicon thin film, and then the thin film semiconductor device is thinned to the desired film thickness. Manufacturing method. In the manufacturing method of the thin film semiconductor device according to claim 5,
A method for manufacturing a thin film semiconductor device, wherein the material constituting the thin film layer is any one of a photoresist, a semiconductor material, an inorganic insulating material, a metal material, and an organic material.

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