JP4243002B2 - Semiconductor thin film and method of forming the same, amorphous Si solar cell using semiconductor thin film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor thin film and a method for forming the same, and an amorphous Si solar cell using the semiconductor thin film, and more specifically, a semiconductor thin film for forming a Si thin film on a substrate, a method for forming the same, and an amorphous Si solar using the semiconductor thin film. It relates to batteries.
[0002]
[Prior art]
Conventionally, it has been known that, in a method for forming a semiconductor thin film used particularly in an amorphous Si solar cell, the conversion efficiency of the solar cell is increased by forming islands by growing crystals into islands. Such a method for manufacturing a semiconductor thin film is disclosed in the following publications.
[0003]
For example, in Japanese Patent Laid-Open No. 01-110777, a step of sequentially forming a thin film of a high melting point metal and a thick film of a low melting point metal on an insulating substrate or a conductive substrate, A method for producing a semiconductor polycrystalline film, comprising: depositing semiconductor microcrystal grains; and heating the substrate to a temperature equal to or higher than a melting point of the low-melting-point metal and gradually cooling the substrate. Disclosed.
[0004]
In Japanese Patent Laid-Open No. 03-280420, a silicon thin film layer is formed on a glass substrate, tin fine particles are dispersed in an organic solvent, and a paste is applied on the silicon thin film as much as possible. Disclosed is a semiconductor thin film characterized by annealing after heating as described above.
[0005]
In Japanese Patent Laid-Open No. 05-294793, when a thin film diamond is vapor-phase synthesized on a substrate, at least one intermediate layer is formed in a predetermined region of the substrate surface, and fine powder diamond is pressed into the intermediate layer surface, Disclosed is a method for producing a thin film diamond characterized by growing a diamond thin film using the fine powder diamond as a nucleus.
[0006]
Japanese Patent Application Laid-Open No. 06-140327 discloses a silicon thin film formed on a substrate on which nuclei of microcrystalline silicon are formed.
[0007]
Japanese Patent Application Laid-Open No. 07-297122 discloses a semiconductor device in which an active region made of a crystalline Si thin film is formed on a substrate having an insulating surface, the active region being an amorphous Si thin film. In addition, a semiconductor device is disclosed which is formed by crystal growth by performing heat treatment and laser light or intense light irradiation.
[0008]
[Problems to be solved by the invention]
However, the conventional method is not economical because a flat thin film is once formed and then an island is formed by a method such as etching or laser annealing, which requires a large number of steps and increases manufacturing costs. Further, impurities may be mixed into the semiconductor thin film during the etching process or annealing process. Further, in the conventional method, since the crystallization rate of the Si thin film is low, there is a problem that the conversion efficiency is low when used for an amorphous Si solar cell, for example.
[0009]
Therefore, an object of the present invention is to provide a new and improved method for forming a semiconductor thin film capable of obtaining a semiconductor thin film having a high crystallization rate by a simple process and preventing contamination of impurities, The object is to provide an amorphous Si solar cell with high conversion efficiency.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is a method for forming a semiconductor thin film on which a Si thin film is formed on a substrate, the metal paste comprising a metal organic material containing In and Sn on the substrate. And a step of baking the substrate coated with the metal paste at a predetermined temperature for a predetermined time to form crystal nuclei; And a step of depositing the Si thin film on the substrate on which the crystal nuclei have been formed. When the coating thickness of the metal paste is 0.25 μm or less, crystal nuclei are not generated in the firing step, and when the thickness is 0.5 μm or more, the grain size of the crystal nuclei after firing becomes too large, 1 μm or more. Therefore, it is not preferable.
[0011]
In the invention described in this section, submicron crystal nuclei can be formed on a substrate even by firing at a relatively low temperature. Therefore, when a Si thin film is formed on a crystal nucleus by, for example, plasma CVD, the Si thin film has, for example, crystal nuclei. As a starting point, an island is formed by columnar growth, and a Si thin film having a high crystallization rate can be obtained. As a result, if an amorphous Si solar cell, for example, is fabricated on a Si thin film having a high crystallization rate, high conversion efficiency can be obtained. Furthermore, since an etching process and a laser annealing process are not required, a high-performance Si thin film can be manufactured with a simple manufacturing process. The crystal grain size of the Si thin film can be easily controlled by changing conditions such as the heat treatment time.
[0012]
Further, as in the invention described in claim 2, if the baking temperature is set in a temperature range of 250 to 400 ° C., organic substances in the metal paste fly to form crystal nuclei having good adhesion to the substrate. can do. Further, as in the invention described in claim 3, if the firing time is configured to be in the time range of 45 to 90 minutes, the organic substance in the metal paste will fly to form crystal nuclei having good adhesion to the substrate. can do.
[0013]
Further, as in the invention described in claim 4, if the firing is performed at a vacuum of 10 ⁻⁵ Pa or less, the organic substance in the metal paste will fly and crystal nuclei having good adhesion to the substrate will be formed. Can be formed.
[0020]
In the invention described in this section, high conversion efficiency can be obtained if, for example, an amorphous Si solar cell is fabricated on a Si thin film having a high crystallization rate.
[0026]
In the invention described in this section, since an amorphous Si solar cell is fabricated on a Si thin film having a high crystallization rate, high conversion efficiency can be obtained.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, components having the same function and configuration are denoted by the same reference numerals, and redundant description is omitted.
[0028]
Hereinafter, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional process diagram illustrating a method for forming a semiconductor thin film according to the present embodiment.
[0029]
First, as shown in FIG. 1A, for example, a metal paste 102 made of a metal organic material (MO), a thickener, and an organic solvent is formed on a SiO 2 substrate 100 with a thick film of, for example, 0.25 to 0.5 μm. Apply. At this time, one or more kinds of elements such as Si, Sn, Ag, Au, Ni, Co, and Pt can be used as the metal element.
[0030]
At this time, if the metal paste 102 has a film thickness of about 0.3 μm, for example, the submicron nuclei are evenly distributed on the SiO 2 substrate 100 in the subsequent baking step, which is particularly preferable. On the other hand, if the film thickness is 0.25 μm or less, crystal nuclei are not generated in the firing step, and if the film thickness is 0.5 μm or more, the grain size of the crystal nuclei after firing becomes too large, 1 μm or more.
[0031]
Next, as shown in FIG. 1B, the SiO 2 substrate 100 coated with the metal paste 102 is baked in a temperature range of 250 to 400 ° C., for example. That is, at a temperature of 250 ° C. or lower, organic substances in the metal paste 102 do not fly and crystal nuclei are not formed. Further, a temperature of 400 ° C. or higher is not preferable because the generated crystal nucleus is easily peeled off because the adhesion between the generated crystal nucleus and the SiO 2 substrate 100 is poor.
[0032]
Note that the metal paste 102 is preferably fired at a vacuum degree of 10 ⁻⁵ Pa or higher, because organic substances in the metal paste 102 do not fly and crystal nuclei are not generated at a vacuum degree of 10 ⁻⁵ Pa or lower.
[0033]
Moreover, it is preferable that the baking time of the metal paste 102 is 45 to 90 minutes. When the time is shorter than 45 minutes, the organic matter in the metal paste 102 does not fly completely and nuclei are not generated. When the time is longer than 90 minutes, the adhesion between the generated crystal nuclei and the SiO 2 substrate 100 is poor. Is not preferred because it tends to peel off.
[0034]
When the metal paste 102 is baked under the above conditions, submicron crystal nuclei are formed on the surface of the SiO 2 substrate 100.
[0035]
Next, as shown in FIG. 1C, a Si thin film 104 is formed on the SiO 2 substrate 100 on which crystal nuclei are formed by, for example, plasma CVD. At this time, the Si thin film 104 grows in a columnar shape starting from the crystal nucleus to form an island, and the Si thin film 104 having a crystallization rate of about 60% to about 95% is formed.
[0036]
Furthermore, an amorphous Si solar cell is fabricated on the Si thin film 104 having a high crystallization rate. As a result, it is possible to obtain higher conversion efficiency than that of the conventional amorphous Si solar cell.
[0037]
In this embodiment, submicron crystal nuclei can be formed on a substrate even at relatively low temperature firing. Therefore, when a Si thin film is formed on the crystal nuclei by, for example, a plasma CVD method, the Si thin film starts at the crystal nuclei, for example. As described above, an island is formed by columnar growth, and a Si thin film having a high crystallization rate can be obtained. As a result, if an amorphous Si solar cell, for example, is fabricated on a Si thin film having a high crystallization rate, high conversion efficiency can be obtained. Furthermore, since an etching process and a laser annealing process are not required, a high-performance Si thin film can be manufactured with a simple manufacturing process. The crystal grain size of the Si thin film can be easily controlled by changing conditions such as the heat treatment time.
[0038]
( Reference Example 1 )
In the embodiment, using a metal paste comprising a metal organic material to form crystal nuclei, although the growth starting point of a high crystallization ratio Si thin film, in the present embodiment, a discontinuous Si crystal film Si thin A method for starting growth will be described.
[0039]
Hereinafter, a method for forming a semiconductor thin film according to this reference example will be described with reference to FIG. FIG. 2 is a cross-sectional process diagram illustrating a method of forming a semiconductor thin film according to this reference example .
[0040]
First, as shown in FIG. 2A, a discontinuous amorphous Si thin film 202 is formed on a SiO2 substrate 200 by a sputtering method, for example, with a film thickness of, for example, 50 to 100 mm. At this time, when the film thickness is 50 mm or less, it is difficult to control the island density at the time of film formation, and when the film thickness is 100 mm or more, it becomes a continuous film.
[0041]
Next, as shown in FIG. 2B, the SiO 2 substrate 200 on which the discontinuous amorphous Si thin film 202 is formed is heat-treated at a temperature of, for example, 1,000 to 1,200 ° C. 204 is formed. As shown in FIG. 3, the discontinuous crystalline Si thin film 204 is in a state where crystals having a diameter of several tens to several hundreds of nanometers exist in amorphous Si.
[0042]
At this time, the amorphous Si thin film 202 is not crystallized at a temperature of 1,000 ° C. or lower, and a temperature of 1,200 ° C. or higher is not preferable from the viewpoint of furnace temperature limit, energy consumption, and high cost. The heat treatment of the amorphous Si thin film 202 is preferably performed in an inert gas or reducing gas atmosphere. In an oxidizing gas atmosphere, the amorphous Si thin film 202 is oxidized and becomes a SiO 2 film, which is not preferable.
[0043]
Next, as shown in FIG. 2C, an Si thin film 206 is formed on the SiO 2 substrate 200 on which the discontinuous crystalline Si thin film 204 is formed, for example, by a plasma CVD method. At this time, the Si thin film 206 is grown in a columnar shape starting from the discontinuous crystalline Si thin film 204 to form islands, and the Si thin film 206 having a crystallization rate of about 60% to about 95% is formed.
[0044]
Further, an amorphous Si solar cell is fabricated on the Si thin film 206 having a high crystallization rate. As a result, it is possible to obtain higher conversion efficiency than that of the conventional amorphous Si solar cell.
[0045]
In the invention described in this section, a discontinuous crystalline Si thin film is formed on the substrate by a predetermined heat treatment. When a Si thin film is formed on the substrate by, for example, plasma CVD, the Si thin film becomes crystalline Si. Since the island is formed by columnar growth starting from the thin film, a Si thin film having a high crystallization rate can be formed. As a result, when an amorphous Si solar cell is manufactured, high conversion efficiency can be obtained. As a result, if an amorphous Si solar cell, for example, is fabricated on a Si thin film having a high crystallization rate, high conversion efficiency can be obtained. In addition, since no elements other than Si, H, and Ar are used, there is very little contamination of impurities. Furthermore, since an etching process and a laser annealing process are not required, a high-performance Si thin film can be manufactured with a simple manufacturing process. The crystal grain size of the Si thin film can be easily controlled by changing conditions such as the heat treatment time.
[0046]
( Reference Example 2 )
In this embodiment, a configuration in which metal nuclei are formed on a substrate in order to obtain a growth starting point for obtaining a Si thin film having a high crystallization rate will be described. Hereinafter, a method for forming a semiconductor thin film according to this reference example will be described with reference to FIG. FIG. 4 is a cross-sectional process diagram illustrating a method for forming a semiconductor thin film according to the present reference example .
[0047]
First, as shown in FIG. 4A, a discontinuous metal film 302 of 50 to 100 mm is formed on, for example, a SiO 2 substrate 300 by, eg, sputtering. At this time, if the film thickness is 50 mm or less, it is difficult to control the island density at the time of forming the Si film. The metal element used at this time is not limited as long as it is a metal that does not adversely affect subsequent processes.
[0048]
Next, as shown in FIG. 4B, a Si thin film 304 is formed on the SiO 2 substrate 300 on which the metal cores 302 are formed, for example, by plasma CVD. At this time, the Si thin film 304 grows in a columnar shape starting from the metal nucleus 302 to form islands, and the Si thin film 304 with a crystallization rate of about 60% to about 95% is formed.
[0049]
Furthermore, an amorphous Si solar cell is fabricated on a high crystallization rate Si thin film. As a result, it is possible to obtain higher conversion efficiency than that of the conventional amorphous Si solar cell.
[0050]
The preferred embodiment and the reference example according to the present invention have been described above, but the present invention is not limited to such a configuration. A person skilled in the art can envision various modifications and changes within the scope of the technical idea described in the claims. The modifications and changes are also within the technical scope of the present invention. It is understood that it is included in
[0051]
The preferred embodiment according to the present invention has been described above, but the present invention is not limited to such a configuration. A person skilled in the art can envision various modifications and changes within the scope of the technical idea described in the claims. The modifications and changes are also within the technical scope of the present invention. It is understood that it is included in
[0052]
【Example】
Since the semiconductor thin film (Si thin film) is formed based on the above embodiment, a specific description will be given based on a comparative example.
[0053]
First, on a 7059 glass substrate, a metal paste having a composition of In, Sn organic matter (MO) 10 wt%, thickener 2.3 wt%, organic solvent 87.3% and viscosity of 23,000 cps Using a printing press, the coating was performed under the conditions of clearance: 0.9 mm, printing pressure: 1.75 Kg / f, squeegee angle: 70 degrees, squeegee speed: 80 mm / second, and coating thickness after coating and drying: 0.3 μm. .
[0054]
Next, the metal paste coated substrate was fired under firing conditions: firing temperature: 370 ° C., atmosphere: vacuum degree 10 ⁻⁵ Pa, firing time: 60 minutes. After firing, it was confirmed that the submicron crystal nuclei were uniformly distributed on the substrate.
[0055]
Next, the substrate temperature is 330 ° C., the discharge power is 33.5 mW / cm2, the source gas dilution ratio is 1/40, the source gas is SiH4, the diluent gas is H2, and the discharge gas pressure is 0.1 Torr. A Si thin film was formed on the baked substrate by plasma CVD. It was confirmed that the Si thin film grew columnarly.
[0056]
As described above, the crystallization rate of the Si thin film formed by the plasma CVD method was 90%. In addition, an amorphous Si solar cell was fabricated using the Si thin film having a high crystallization rate according to this example, and the conversion efficiency of the solar cell was measured under the condition of air mass 1.5 by a solar simulator. As a result, the conversion efficiency of the amorphous Si solar cell was 10%.
[0057]
( Reference Example 3 )
First, a film is formed on a 7059 glass substrate by a sputtering method under a film formation temperature of 150 ° C., a discharge power of 10 mA * 40 kV, a discharge gas pressure of 10 ⁻³ Pa, and a target of Cu (4N). did. As a result of surface observation, a Cu island was formed as shown in FIG. FIG. 5 is an SEM photograph of the Cu island photographed at a magnification of 10,000.
[0058]
Next, the substrate on which the Cu island is formed is formed under the following film forming conditions: substrate temperature: 330 ° C., discharge power: 33.5 mW / cm2, source gas dilution ratio: 1/40, discharge gas pressure: 0.1 Torr. A Si thin film was formed by plasma CVD.
[0059]
As described above, the crystallization rate of the Si thin film formed by the plasma CVD method was 90%. In addition, an amorphous Si solar cell was fabricated using the Si thin film having a high crystallization rate according to this example, and the conversion efficiency of the solar cell was measured under the condition of air mass 1.5 by a solar simulator. As a result, the conversion efficiency of the amorphous Si solar cell was 10%.
[0060]
(Comparative Example 1)
First, on a 7059 glass substrate, a substrate temperature: 330 ° C., discharge power: 33.5 mW / cm2, source gas dilution ratio: 1/40, discharge gas pressure: 0.1 Torr by a plasma CVD method under film formation conditions, A Si thin film was formed. As a result of measuring the crystallization rate of the deposited Si thin film, the crystallization rate was 40%. Moreover, using this Si thin film, an amorphous Si solar cell was produced, and the conversion efficiency of the solar cell was measured with a solar simulator under the condition of air mass 1.5. As a result, the conversion efficiency of the amorphous Si solar cell was 7%.
[0061]
As shown above, the conversion efficiency of the amorphous Si solar cell obtained in the example is about 1.4 times higher than that of the conventional amorphous Si solar cell shown in the conventional example. I was able to.
[0062]
【The invention's effect】
Since a film having various nuclei can be formed on the substrate, if a Si thin film is formed thereon, islands are formed by growing various nuclei as growth starting points, thereby obtaining a Si film having a high crystallization rate. be able to. As a result, high conversion efficiency can be obtained when an amorphous Si solar cell is manufactured using a Si thin film having a high crystallization rate.
[Brief description of the drawings]
1 is a cross-sectional process drawing illustrating a method of forming a semiconductor thin film according to the present embodiment.
2 is a cross-sectional process diagram illustrating a method of forming a semiconductor thin film according to Reference Example 1. FIG.
3 is a schematic diagram showing a crystal image of a discontinuous crystalline Si thin film according to Reference Example 1. FIG.
4 is a cross-sectional process diagram illustrating a method of forming a semiconductor thin film according to Reference Example 2. FIG.
FIG. 5 is a SEM photograph of the Cu island formed in Reference Example 3 taken at a magnification of 10,000.

Claims (4)

A method for forming a semiconductor thin film on which a Si thin film is formed on a substrate,
Applying a metal paste made of a metal organic material containing In and Sn on the substrate in a thickness of more than 0.25 μm and less than 0.5 μm;
Firing the substrate coated with the metal paste at a predetermined temperature for a predetermined time to form crystal nuclei;
Depositing the Si thin film on the substrate on which the crystal nuclei are formed;
A method for forming a semiconductor thin film, comprising: The method for forming a semiconductor thin film according to claim 1, wherein the baking temperature is in a temperature range of 250 to 400 ° C. 3. The method for forming a semiconductor thin film according to claim 1, wherein the baking time is in a time range of 45 to 90 minutes. 4. The method for forming a semiconductor thin film according to claim 1, wherein the baking is performed at a vacuum degree of 10 ⁻⁵ Pa or less. ⁵ .

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