JP2012134525A - Manufacturing method for photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: a catalyst material used for crystallization is not a favorable material in a crystalline silicon film so that the concentration thereof needs to be as low as possible after the crystallization; and when silicon has many defect levels, photo-produced carriers are trapped in the defect level and disappear to deteriorate the photoelectric conversion characteristics; and to crystallize silicon with the catalyst material and improve the characteristics of a photoelectric conversion device by removing the catalyst material that has become unnecessary after the crystallization.SOLUTION: A catalyst element remaining in a first semiconductor film after crystallization is gathered in a second semiconductor film containing a rare gas element in a manner that the second semiconductor film is formed on the first semiconductor film and second heat treatment is performed thereon. In other words, a strain field is formed by forming the second semiconductor film containing a rare gas element, and the strain field is used as a gettering site. Since a rare gas element does not basically bond with another atom, a strain field can be formed by inserting a rare gas element between lattices in the semiconductor film.

Description

  The present invention relates to a photoelectric conversion device formed on a substrate and having a photoelectric conversion layer formed of a crystalline silicon film, and a manufacturing method thereof.

  A photoelectric conversion device can be manufactured using various semiconductor materials and organic compound materials, but silicon is mainly used industrially. Photoelectric conversion devices using silicon can be classified into bulk photoelectric conversion devices using single crystal silicon or polycrystalline silicon wafers, and thin film photoelectric conversion devices in which a silicon film is formed on a substrate. A bulk type photoelectric conversion device requires a semiconductor substrate (such as a silicon wafer) like an LSI (Large Scale Integrated circuit) and the production capacity is limited by its supply capability. On the other hand, a thin film photoelectric conversion device uses a semiconductor film formed on a predetermined substrate, and thus has a high potential production capacity.

At present, photoelectric conversion devices using amorphous silicon have been put into practical use. However, conversion efficiency is lower than photoelectric conversion devices using single crystal silicon or polycrystalline silicon, and there are problems such as light degradation. Therefore, it is limited to the use of products with low power consumption such as a calculator.
In application development based on the assumption of a photovoltaic power generation system, development of a photoelectric conversion device using a silicon film obtained by crystallizing an amorphous silicon film (hereinafter referred to as a crystalline silicon film) is being actively conducted. .

  As a method for forming a crystalline silicon film, there are a melt recrystallization method and a solid phase growth method. In both cases, amorphous silicon is formed on a substrate and recrystallized to form a crystalline silicon film. In any case, the substrate is required to withstand the crystallization temperature of silicon, and materials that can be used as the substrate are limited. In particular, in the melt recrystallization method, the substrate is limited to a material that can withstand 1412 ° C., which is the melting point of silicon.

  The solid-phase growth method is a method in which an amorphous silicon film is formed on a substrate and is then crystallized by heat treatment. Usually, the amorphous silicon film hardly crystallizes at a temperature of 500 ° C. or lower, and it is practically necessary to heat it at 600 ° C. or higher. For example, when an amorphous silicon film formed by vapor deposition is heated to be crystallized, if the heating temperature is 600 ° C., 10 hours are required. On the other hand, a heating time of 100 hours or more is required at a heating temperature of 550 ° C.

  For this reason, a substrate for forming a crystalline silicon film is required to have high heat resistance. Accordingly, it is preferable to use quartz, carbon, or a ceramic material for the substrate, but it is understood that these substrates are not necessarily suitable for the purpose of reducing the manufacturing cost. Originally, it is considered desirable to use a substrate that is distributed in large quantities in the market and that is inexpensive. However, for example, Corning's # 7059 glass substrate which is often used generally has a strain point of 593 ° C., and the conventional crystallization technique cannot be used because the substrate undergoes large deformation. In addition, since a substrate which is essentially a different substance from silicon is used, a single crystal film cannot be obtained even if crystallization is performed simply by heat treatment, and only a polycrystalline film can be obtained. Even with such a polycrystalline film, it is difficult to increase the grain size, which is a limiting factor for improving the efficiency of the photoelectric conversion device.

  As a method for solving the above problems, Japanese Patent Application Laid-Open No. 7-58338 discloses a technique for performing crystallization by adding a trace amount of a catalytic element as a catalyst material in order to promote crystallization at a low temperature. According to the published patent publication, it is possible to lower the heat treatment temperature and shorten the treatment time. For example, when the heating temperature is set to 550 ° C., it has been confirmed that crystallization is caused by heat treatment for 4 hours. It is described that nickel (Ni), iron (Fe), cobalt (Co), platinum (Pt), or a compound of silicon and the like is suitable as a catalyst element as a catalyst.

However, since all of the catalyst materials used for promoting crystallization are materials that are inherently undesirable for crystalline silicon, it is desirable that the concentration be as low as possible after crystallization. The concentration of the catalyst material necessary to promote crystallization is in the range of 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ²⁰ / cm ³ or less. However, even when the concentration is relatively low, an element suitable as a catalyst material is a metal. Therefore, when it is incorporated into silicon, it forms a defect level and has important characteristics for a photoelectric conversion device, such as carrier lifetime. It is clear that this will be reduced.

  By the way, it is thought that the operation principle of the photoelectric conversion device manufactured by forming the PN junction is roughly as follows. The photoelectric conversion device absorbs light and generates electron / hole carriers by the energy of the absorbed light. The generated carrier drifts due to the junction electric field and diffusion causes electrons to move to the n-layer side and holes to move to the p-layer side. If there are many defect levels in silicon, trapped at the defect level in the middle. And disappears. That is, the photoelectric conversion characteristics are deteriorated. The time from the generation and disappearance of electrons / holes is called the lifetime, or lifetime, and it is desirable that this value be larger in the photoelectric conversion device. Therefore, it is essential that the number of impurity elements that generate defect levels in silicon is minimized.

  An object of the present invention is to obtain the photoelectric conversion device having excellent photoelectric conversion characteristics by taking advantage of the crystallization of silicon by the catalyst material and removing the unnecessary catalyst material after crystallization. is there.

  In order to solve the above problems, a method for manufacturing a photoelectric conversion device according to the present invention includes a first step of forming a first semiconductor film having an amorphous structure, and a crystal formed in the semiconductor film having an amorphous structure. A second step of forming a first semiconductor film having a crystal structure by a first heat treatment by adding a catalyst element that promotes the formation of the catalyst, and a rare gas element is included on the first semiconductor film having the crystal structure A third step of forming the second semiconductor film, a fourth step of moving the catalytic element to the second semiconductor film by a second heat treatment, and a fifth step of removing the second semiconductor film. It is characterized by having these processes.

  By adding a catalytic element that promotes crystallization to the first semiconductor film having an amorphous structure and performing the first heat treatment, the heating temperature required for crystallization can be made lower than before. it can. As the catalyst element, one or more selected from Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au can be used.

Then, the catalyst element remaining in the first semiconductor film after crystallization forms a second semiconductor film containing a rare gas element thereon, and is subjected to a second heat treatment, whereby the second semiconductor film is formed. It can be moved to a membrane and concentrated. That is, secondly, by adding a rare gas element to the semiconductor film, a strain field can be formed and used as a gettering site.
Since the rare gas element basically does not form a bond with other atoms, it can be inserted between the lattices in the semiconductor film, thereby forming a strain field.

  The gettering technique is well known as an integrated circuit manufacturing technique using a silicon single crystal substrate. The gettering technology uses extrinsic gettering to give a gettering effect by applying a strain field and chemical action to the silicon substrate from the outside, and a strain field of lattice defects involving oxygen generated inside the wafer. There is intrinsic gettering. The extrinsic gettering includes a method of mechanically damaging the back surface of the silicon substrate (an opposite surface on which elements are formed), a method of forming a polycrystalline silicon film, and a method of diffusing phosphorus. There is also a gettering technique in which a strain field is formed by secondary lattice defects formed by ion implantation. Although the detailed mechanism of gettering is not necessarily clarified uniformly, when heat treatment is performed as described above, a phenomenon in which a metal element precipitates in a region where a strain field is formed is actively used. It is what.

In order to remove the second semiconductor film formed over the first semiconductor film with high selectivity after the gettering, a barrier layer is preferably formed over the first semiconductor film.
The barrier layer may be formed by treating the first semiconductor film with ozone water to form chemical oxide or oxidizing the surface by plasma treatment. Further, it may be formed by irradiating ultraviolet rays in an atmosphere containing oxygen to generate ozone and oxidize the surface.

  The second semiconductor film is formed by sputtering or plasma CVD. A rare gas element can be taken into the second semiconductor film by adding a rare gas to the sputtering gas or adding a rare gas to the reaction gas. Further, after the formation of the film, it may be added by an ion implantation method or an ion doping method. As the rare gas element, one selected from He, Ne, Ar, Kr, and Xe is used.

  The first heat treatment and the second heat treatment are a rapid thermal anneal (RTA) method using a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, and a high pressure mercury lamp as heating means. Or furnace annealing using an electric furnace. In the present invention, the gettering can be accomplished by a short heat treatment such as the RTA method because the catalyst element only needs to be moved by the thickness of the semiconductor film.

  In a method for manufacturing a photoelectric conversion device according to the present invention, a crystalline silicon film is formed at a lower heat treatment temperature than before by using a catalyst material such as nickel in a step of crystallizing an amorphous silicon film by heat treatment. Obtainable. In addition, the concentration of the catalyst material remaining in the obtained crystalline silicon film can be lowered. As a result, a photoelectric conversion device having an excellent photoelectric conversion characteristic can be obtained using an inexpensive glass substrate.

1 is a schematic view of a method for manufacturing a photoelectric conversion device of the present invention. 1 is a schematic view of a method for manufacturing a photoelectric conversion device of the present invention. The figure which shows an example of the cross-section of the photoelectric conversion apparatus of this invention The figure which shows an example of the cross-section of the photoelectric conversion apparatus of this invention 1 is a schematic view of a method for manufacturing a photoelectric conversion device of the present invention. The graph which shows the density | concentration distribution of the argon added to the crystalline silicon film by the ion doping method. The graph which shows the density | concentration distribution of the nickel added to the crystalline silicon film, and shows the change before and behind heat processing.

[Embodiment 1] A catalytic element for promoting crystallization of silicon is formed in close contact with an amorphous silicon film, the amorphous silicon film is crystallized by heat treatment, and the catalytic element remaining after crystallization is removed. A method for manufacturing the photoelectric conversion device by removing it from the crystalline silicon film will be described with reference to FIGS.

In FIG. 1, a silicon oxide film 102 is formed to a thickness of 0.3 μm as a base film on a glass substrate 101 (for example, 1737 glass substrate manufactured by Corning). The silicon oxide film 102 may be formed by a plasma CVD method using methyl tetrasilicate (TEOS) as a raw material, but may be formed by a sputtering method as another method.
Next, an amorphous silicon film (amorphous silicon film) 103 is formed by a plasma CVD method using silane gas as a raw material.

  The amorphous silicon film 103 may be formed by a low pressure thermal CVD method, a sputtering method, or a vacuum evaporation method in addition to the plasma CVD method. The amorphous silicon film 103 may be a genuine amorphous silicon film to which no periodic group 13 or 15 element is intentionally added, and boron (B) is added in an amount of 0.001 to 0.1 atomic%. An amorphous silicon film may be formed. The thickness of the amorphous silicon film 103 is 1 to 20 μm, preferably 5 to 10 μm. (Fig. 1 (A))

  Next, the substrate is immersed in an aqueous solution in which hydrogen peroxide and ammonia are mixed and kept at 70 ° C. for 5 minutes to form an oxide film (not shown) on the surface of the amorphous silicon film 103. This oxide film is formed in order to improve the wettability in the subsequent application step of the nickel acetate solution. Further, a nickel acetate solution is applied to the surface of the amorphous silicon film 103 by spin coating. Thus, nickel serving as a catalyst element is dispersed on the surface of the amorphous silicon film 103. Nickel acts as a catalyst for promoting crystallization when the amorphous silicon film 103 is crystallized.

  Next, in the nitrogen atmosphere, the hydrogen in the amorphous silicon film 103 is released by holding at 450 ° C. for 1 hour. This is because the threshold energy for subsequent crystallization is lowered by intentionally forming a dangling bond in the amorphous silicon film 103. After that, the amorphous silicon film 103 is crystallized by performing heat treatment at 500 to 600 ° C., preferably 550 ° C. for 4 to 8 hours in a nitrogen atmosphere, so that the crystalline silicon film 104 is formed. . The reason why the temperature during the crystallization could be set to 550 ° C. was due to the catalytic action of nickel. The crystalline silicon film 104 contains 0.001 atomic% to 5 atomic% of hydrogen. During the heat treatment, nickel forms silicide and diffuses in the silicon, thereby causing crystallization to proceed.

  As other heat treatment methods, an RTA method using a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, a high pressure mercury lamp, or the like is employed. When the RTA method is used, the lamp light source for heating is turned on for 1 to 60 seconds, preferably 30 to 60 seconds, and this is repeated 1 to 10 times, preferably 2 to 6 times. The emission intensity of the lamp light source is arbitrary, but the semiconductor film is instantaneously heated to 600 to 1000 ° C., preferably about 650 to 750 ° C. Even if the temperature suddenly becomes high, a lamp light source is selected, and the wavelength band of the emitted electromagnetic wave is set to an appropriate one (that is, a wavelength band having a high absorption coefficient of the semiconductor film). Preferential heating is possible. Therefore, the substrate 101 itself is not distorted and deformed. For example, a halogen lamp having a spectral peak in a wavelength band longer than 600 nm is suitable for heating an amorphous silicon film. In this manner, the crystalline silicon film 104 can be obtained even when the semiconductor film having an amorphous structure is crystallized.

Thus, the crystalline silicon film 104 can be formed on the glass substrate 101. Next, as shown in FIG. 1B, an amorphous silicon film 105 containing a rare gas element is formed over the crystalline silicon film 104. A typical example is an amorphous silicon film containing argon as a rare gas element at a concentration of 1 × 10 ¹⁹ to 1 × 10 ²² / cm ³ , and has a thickness of 0.05 to 0.1 μm by sputtering. Form. In the sputtering method, high-purity silicon is used as a target, and an amorphous silicon film is formed using argon or argon and hydrogen as sputtering gases. In order to contain a large amount of argon in the film, it is essential to control the pressure during film formation. Although detailed conditions depend on the apparatus to be used, the argon content can be increased by setting the pressure during film formation to 0.2 to 1 Pa and relatively slowing the film formation rate.

  Of course, the applicable rare gas element is not limited to argon, and helium, krypton, neon, and xenon may also be used. The manufacturing method of the amorphous silicon film 105 is not limited to the sputtering method, and a plasma CVD method or a vapor deposition method can be used as long as the amorphous silicon film 105 contains a rare gas element at a similar concentration.

Thereafter, the amorphous silicon film 105 containing a rare gas element becomes a gettering site by performing heat treatment in a nitrogen atmosphere at 450 to 800 ° C., preferably 550 ° C. for 1 to 4 hours using an electric furnace. The concentration of the catalyst element (here, nickel) contained in the crystalline silicon film 104 can be 2 × 10 ¹⁸ / cm ³ or less. At this time, the catalyst element moves in the direction of the arrow shown in FIG. 1B and is concentrated in the amorphous silicon film 105 containing a rare gas element.

When the RTA method is used, the lamp light source for heating is turned on for 1 to 60 seconds, preferably 30 to 60 seconds, and this is repeated 1 to 10 times, preferably 2 to 6 times.
The emission intensity of the lamp light source is arbitrary, but the semiconductor film is instantaneously heated to 600 to 1000 ° C., preferably about 700 to 750 ° C.

Thereafter, the amorphous semiconductor film 107 is removed by etching. As an etching method, dry etching using NF ₃ or CF ₄ or dry etching without using plasma with ClF ₃ is performed. Alternatively, wet etching with an alkaline solution such as an aqueous solution containing hydrazine or tetraethylammonium hydroxide (chemical formula (CH ₃ ) ₄ NOH) can be performed.

  By this etching process, the surface of the crystalline silicon film 104 is exposed. An n-type crystalline silicon film 106 is formed on this surface. The n-type crystalline silicon film 106 may be formed using a plasma CVD method, or may be formed using a low pressure thermal CVD method. The n-type crystalline silicon film 106 is preferably formed to a thickness of 0.02 to 0.2 μm, but typically is formed to a thickness of 0.1 μm. Next, a transparent electrode 107 is formed on the n-type crystalline silicon film 106. The transparent electrode 107 is formed of indium tin oxide alloy (ITO) with a thickness of 0.08 μm by sputtering. (Figure 1 (C))

  Next, a step of providing extraction electrodes 108 and 109 is performed. In providing the extraction electrodes 108 and 109, as shown in FIG. 1E, a part of the transparent electrode 107, the n-type crystalline silicon 105, and the crystalline silicon 103 is removed. Then, a metal film such as aluminum or silver is formed by sputtering or vacuum deposition to provide a positive electrode 108 on the crystalline silicon film 104, and a negative electrode 109 is formed on the transparent electrode 106. The extraction electrodes 108 and 109 can be formed using aluminum, silver, silver paste, or the like.

  Further, when the extraction electrodes 108 and 109 are provided and then heat-treated at 150 ° C. to 300 ° C. for several minutes, the adhesion between the crystalline silicon film 104 and the silicon oxide film 102 of the base film is improved, and good electrical characteristics are obtained. can get. Specifically, heat treatment is preferably performed at 200 ° C. for 30 minutes in an nitrogen atmosphere using an oven. Through the above steps, a photoelectric conversion device can be obtained.

[Embodiment Mode 2] In this embodiment mode, in a method for manufacturing a photoelectric conversion device, a rare gas element is ionized on the surface of a crystalline silicon film in a step of removing a catalytic element that promotes crystallization of silicon after crystallization. A method of adding by using an implantation method or an ion doping method is employed.

In FIG. 2, a silicon oxide film 202 is formed as a base film on a glass substrate 201 to a thickness of 0.3 μm. This silicon oxide film is formed by a plasma CVD method using methyl tetrasilicate (TEOS) as a raw material, but can also be formed by a sputtering method as another method. Next, the amorphous silicon film 203 is formed by a plasma CVD method using silane gas as a raw material. Next, the substrate is immersed in perhydro ammonia and kept at 70 ° C. for 5 minutes to form an oxide film (not shown) on the surface of the amorphous silicon film 203.
A nickel acetate solution is applied to the surface of the amorphous silicon film 203 by spin coating. The nickel element functions as an element that promotes crystallization when the amorphous silicon film 203 is crystallized.

  Next, hydrogen in the amorphous silicon film 203 is desorbed by holding at 450 ° C. for 1 hour in a nitrogen atmosphere. Then, by performing a heat treatment at 550 ° C. for 4 to 8 hours in a nitrogen atmosphere, the amorphous silicon film 203 is crystallized to obtain a crystalline silicon film 204. The steps up to here are performed in the same manner as in the first embodiment.

Thereafter, a rare gas element is added to the crystalline silicon film 204 by an ion doping method. Argon is used as the rare gas element, and the dose may be 1 × 10 ¹⁴ to 1 × 10 ¹⁷ / cm ² , but typically 2 × 10 ¹⁵ / cm ² and the acceleration voltage is 10 keV. By this doping process, a region 205 containing argon at a concentration of 1 × 10 ¹⁸ / cm ³ or more is formed in a region 205 having a depth of about 0.1 μm from the surface of the crystalline silicon film 204. (Fig. 2 (B))

Thereafter, heat treatment is performed to getter the nickel remaining in the crystalline silicon film 204. In the case of using an electric furnace, the heat treatment temperature is 500 to 800 ° C., preferably 550 ° C. for 1 to 4 hours in a nitrogen atmosphere. It can also be performed by the RTA method. In the region 205 into which the rare gas is injected, the crystal is broken and has an amorphous structure. A strain field is formed in this region 205 by injecting argon larger than the atomic radius of silicon, and can be a gettering site. With the heat treatment, nickel in the crystalline silicon film 204 moves to this region 205, and the concentration of nickel element in the crystalline silicon film 204 can be 2 × 10 ¹⁸ / cm ³ or less.

FIG. 6 shows a rare gas element formed by applying an ion doping method to a crystalline silicon film obtained by applying a 100 ppm nickel acetate solution to a 300 nm amorphous silicon film and crystallizing it at 550 ° C. for 4 hours. As a result, the argon distribution was measured by secondary ion mass spectrometry when argon was implanted at an acceleration voltage of 10 keV and a dose of 2 × 10 ¹⁵ / cm ² . Argon is implanted to a depth of about 80 nm from the surface of the crystalline silicon film, and its concentration is 1 × 10 ¹⁸ / cm ³ or more. FIG. 6 also shows a profile after the same sample is heated at 550 ° C. for 4 hours, but the argon concentration distribution hardly changes. Further, since the content in the film is not changed, it is understood that the film is not re-released outside the film at this temperature. The fact that argon is not redistributed by heat treatment means that the gettering site can be stably maintained, and if the argon-added region is removed as will be shown later, no adverse effect is left on the crystalline silicon film. Is shown.

FIG. 7 shows data obtained by measuring the nickel concentration distribution in the same sample by secondary ion mass spectrometry. The nickel concentration in the film is 5 × 10 ¹⁸ / cm ³ to 1 after heat treatment at 550 ° C. for 4 hours. It is reduced to × 10 ¹⁸ / cm ³ . The reduced nickel moves to a region to which argon is added (region having a depth of about 80 nm from the surface of the crystalline silicon film), and the concentration of the region is 1.2 × 10 ¹⁹ / cm ³ to 6 in peak value. × 10 ¹⁹ / cm ³ increased. Thus, the data of FIG. 7 clearly shows the effect of gettering with argon. Of course, the effect of such gettering is not limited to argon, and the same effect can be obtained by using other rare gas elements.

  Further, the region 205 to which argon is added at a high concentration is not recrystallized by this heat treatment. Therefore, the strain field remains as it is, and it is a good gettering site for the purpose of gettering.

Therefore, it is necessary to remove this region 205 in order to complete the photoelectric conversion device. The etching method may be performed in the same manner as in the first embodiment. After removing about 0.1 μm from the surface of the crystalline silicon film 204, the n-type crystalline silicon film 206 is formed.
The n-type crystalline silicon film 206 may be formed using a plasma CVD method, or may be formed using a low pressure thermal CVD method. The n-type crystalline silicon film 206 is preferably formed with a thickness of 0.02 to 0.2 μm, but typically is formed with a thickness of 0.1 μm. Further, a transparent electrode 107 is formed. The transparent electrode 106 is formed of indium tin oxide alloy (ITO) with a thickness of 0.08 μm by sputtering. (Fig. 2 (C)
)

  Then, in order to form the extraction electrodes 208 and 209, as shown in FIG. 2D, the transparent electrode 207, the n-type crystalline silicon film 206, and the crystalline silicon 204 are partially removed to obtain crystalline silicon. The surface of the film 204 is partially exposed. Then, a metal film such as aluminum or silver is formed by sputtering or vacuum vapor deposition, a positive electrode 208 is provided on the crystalline silicon film 204, and a negative electrode 209 is formed on the transparent electrode 207.

  Further, after the extraction electrodes 208 and 209 are provided, when heat treatment is performed at 150 ° C. to 300 ° C. for several minutes, the adhesion between the crystalline silicon film 204 and the silicon oxide film 202 as the base film is improved, and good electrical characteristics are obtained. can get. In this example, an oven was used and heat treatment was performed in a nitrogen atmosphere at 200 ° C. for 30 minutes. Through the above steps, the photoelectric conversion device can be completed.

[Embodiment Mode 3] An example of a mode in which an amorphous silicon film formed as a gettering site on a crystalline silicon film formed using a catalytic element is selectively removed will be described.

  In FIG. 5A, a silicon oxide film 502 is formed to a thickness of 0.3 μm as a base film over a substrate 501 in the same manner as in Embodiment Mode 1. Next, an amorphous silicon film is formed by a plasma CVD method using silane gas as a raw material, and a crystalline silicon film 503 is formed by introducing a catalytic element and crystallizing. The steps up to here are performed in the same manner as in the first embodiment.

  Next, a barrier layer 504 is formed on the surface of the crystalline silicon film 503. The barrier layer may use chemical oxide formed by treatment with ozone water. Similarly, chemical oxide can be formed by treatment with an aqueous solution in which sulfuric acid, hydrochloric acid, nitric acid or the like and hydrogen peroxide are mixed. As another method, the oxidation treatment may be performed by generating ozone by plasma treatment in an oxidizing atmosphere or ultraviolet irradiation in an oxygen-containing atmosphere. Alternatively, a thin oxide film may be formed by heating to about 200 to 350 ° C. using a clean oven to form a barrier layer. Alternatively, a barrier layer may be formed by depositing an oxide film of about 1 to 5 nm by plasma CVD, sputtering, vapor deposition, or the like.

  Thereafter, an amorphous silicon film 505 containing a rare gas element is formed over the barrier layer 504. This may be formed as in the first embodiment. Alternatively, after an amorphous silicon film is formed, a rare gas element may be added by an ion implantation method or an ion doping method as described in Embodiment Mode 2. This amorphous silicon film 505 is used as a gettering site.

  Then, heat treatment is performed in order to getter the catalyst element remaining in the crystalline silicon film 503. Heat treatment is performed at 500 to 800 ° C., preferably 550 ° C. for 1 to 4 hours in a nitrogen atmosphere. Alternatively, the lamp light source for heating is turned on for 1 to 60 seconds, preferably 30 to 60 seconds by the RTA method, and this is repeated 1 to 10 times, preferably 2 to 6 times. The emission intensity of the lamp light source is arbitrary, but the semiconductor film is instantaneously heated to 600 to 1000 ° C., preferably about 700 to 750 ° C.

Thereafter, the amorphous silicon film 505 is selectively etched and removed. As an etching method, dry etching without using plasma with ClF ₃ or wet etching with an alkaline solution such as an aqueous solution containing hydrazine or tetraethylammonium hydroxide (chemical formula (CH ₃ ) ₄ NOH) can be performed. At this time, the barrier layer 504 functions as an etching stopper. Further, the barrier layer 504 may be subsequently removed with hydrofluoric acid.

Thus, the catalytic element in the crystalline silicon film 503 is gettered to the amorphous silicon film 505 to which the rare gas element is added, and the concentration of the catalytic element in the crystalline silicon film 503 is 2 × 10 ¹⁸ / cm ^3. It can be as follows.

  An n-type crystalline silicon film 506 is formed on this surface. The n-type crystalline silicon film 506 may be formed using a plasma CVD method or may be formed using a low pressure thermal CVD method. The n-type crystalline silicon film 506 is formed with a thickness of 0.02 to 0.2 μm. Next, an indium tin oxide alloy (ITO) having a thickness of 0.08 μm is formed on the n-type crystalline silicon film 506 as a transparent electrode 507 by sputtering. (Fig. 5 (B))

  Further, a step of providing extraction electrodes 508 and 509 is performed. In providing the extraction electrodes 508 and 509, as shown in FIG. 5C, the transparent electrode 507, the n-type crystalline silicon 506, and part of the crystalline silicon film 503 are removed. Then, a metal film such as aluminum or silver is formed by sputtering or vacuum deposition, and a positive electrode 508 is provided on the crystalline silicon film 503, and a negative electrode 509 is formed on the transparent electrode 506. The extraction electrodes 508 and 509 can be formed using aluminum, silver, silver paste, or the like.

  Further, when the extraction electrodes 508 and 509 are provided and then heat-treated at 150 ° C. to 300 ° C. for several minutes, the adhesion between the crystalline silicon film 503 and the silicon oxide film 502 as the base film is improved, and good electrical characteristics are obtained. can get. In this example, an oven was used and heat treatment was performed in a nitrogen atmosphere at 200 ° C. for 30 minutes. Through the above steps, the photoelectric conversion device can be completed. Note that the structure of this embodiment can be combined with Embodiment 1 or Embodiment 2.

[Embodiment Mode 4] In this embodiment mode, an anisotropic etching process is performed on the surface of a crystalline silicon film in the process of the photoelectric conversion device described in Embodiment Modes 1 to 3, as shown in FIG. An example in which the surface of the I layer of the photoelectric conversion device is made uneven is shown. A technique for making the surface uneven and reducing the surface reflection of the photoelectric conversion device is called texture processing.

  A silicon oxide film having a thickness of 0.3 μm was formed as a base film 302 on a glass substrate (for example, Corning 7959 glass substrate) 301. This silicon oxide film is formed by a plasma CVD method using methyl tetrasilicate (TEOS) as a raw material, but can also be formed by a sputtering method as another method. Next, an amorphous silicon film was formed by plasma CVD. In addition to the plasma CVD method, the amorphous silicon film may be formed by using a low pressure thermal CVD method, a sputtering method, or a vacuum evaporation method. The amorphous silicon film may be a substantially genuine amorphous silicon film or an amorphous silicon film to which boron (B) is added in an amount of 0.001 to 0.1%. The thickness of the amorphous silicon film is 20 μm. Of course, this thickness may be a thickness required by the practitioner.

Then, heat treatment is performed to form a crystalline silicon film 303. In the crystalline silicon film 303, the concentration of the catalytic element introduced during the crystallization process is reduced to 2 × 10 ¹⁸ / cm ³ or less by the gettering process of the present invention.

  After the gettering process is finished, a texture process is applied to the surface of the crystalline silicon film 303. The texture treatment can be performed using an aqueous solution of hydrazine or sodium hydroxide. The case where sodium hydroxide is used is shown below.

  The texture treatment is performed by heating an aqueous solution having a sodium hydroxide concentration of 2% to 80 ° C. Under this condition, the etching rate of the crystalline silicon film 303 used in this embodiment is about 1 μm / min. Etching is performed for 5 minutes, and then immersed in boiling water to stop the reaction instantly, and further washed thoroughly with running water. When the surface of the crystalline silicon film 303 after the texture treatment is observed with an electron microscope, unevenness of about 0.1 to 5 μm can be observed although it is random.

  An n-type crystalline silicon film 304 is formed on this surface. The n-type crystalline silicon film 304 may be formed using a plasma CVD method, or may be formed using a low pressure thermal CVD method. The n-type crystalline silicon film 304 is preferably formed to a thickness of 0.02 to 0.2 μm, but in this embodiment, it is formed to a thickness of 0.1 μm.

Next, a transparent electrode 305 is formed on the n-type crystalline silicon film 304. The transparent electrode 305 is formed of indium tin oxide alloy (ITO) with a thickness of 0.08 μm by sputtering. Finally, a step of providing an extraction electrode is performed. In providing the extraction electrode, after removing a part of the transparent electrode, n-type crystalline silicon, and crystalline silicon film 303 so as to have the structure shown in FIG. A positive electrode 306 is provided on the crystalline silicon film 303.
The extraction electrode 306 can be formed using aluminum, silver, silver paste, or the like formed by a sputtering method or a vacuum evaporation method. Furthermore, when the electrode 306 is provided and then heat-treated at 150 ° C. to 300 ° C. for several minutes, the adhesion between the crystalline silicon film 303 and the base film 302 is improved, and good electrical characteristics are obtained. In this example, an oven was used and heat treatment was performed in a nitrogen atmosphere at 200 ° C. for 30 minutes. Through the above steps, a photoelectric conversion device having a texture structure on the surface can be obtained. Note that the structure of this embodiment mode can be freely combined with Embodiment Modes 1 to 3.

[Embodiment 5] In this example, a film made of a catalytic element for promoting crystallization of silicon is formed on a substrate as shown in FIG. 4, and an amorphous silicon film is adhered to the film made of the catalytic element. In this technique, the amorphous silicon film is crystallized by heat treatment, and after the crystallization, the catalyst element diffused in the crystalline silicon film is removed to manufacture a photoelectric conversion device.

  First, a film of a catalytic element that promotes crystallization of silicon is formed on a substrate. Typically, nickel is used as the catalyst element. First, a silicon oxide film having a thickness of 0.3 μm is formed as a base film 402 on a glass substrate (eg, Corning 7059 glass substrate) 401. This silicon oxide film is formed by a plasma CVD method using methyl tetrasilicate (TEOS) as a raw material, but can also be formed by a sputtering method as another method. Next, a nickel film 407 is formed on the substrate. The nickel film is formed to a thickness of 0.1 μm using a pure nickel tablet by electron beam vacuum deposition. Next, an amorphous silicon film (amorphous silicon film) is formed by plasma CVD. In addition to the plasma CVD method, the amorphous silicon film may be formed by using a low pressure thermal CVD method, a sputtering method, or a vacuum evaporation method. The amorphous silicon film may be an amorphous silicon film to which no element of Group 13 or 15 of the periodic table is added, or amorphous silicon to which 0.001 to 0.1 atomic% of boron (B) is added. It may be a film. The thickness of the amorphous silicon film is 10 μm. Of course, this thickness may be a thickness required by the practitioner.

  Next, hydrogen in the amorphous silicon film is desorbed by holding at 450 ° C. for 1 hour in a nitrogen atmosphere. This is because the threshold energy for subsequent crystallization is lowered by intentionally forming a dangling bond in the amorphous silicon film. Then, the amorphous silicon film is crystallized by performing a heat treatment at 550 ° C. for 4 to 8 hours in a nitrogen atmosphere, whereby a crystalline silicon film 403 is obtained. The reason why the temperature at the time of crystallization can be set to 550 ° C. is due to the action of nickel element. The crystallized crystalline silicon film 403 contains hydrogen at a rate of 0.001 atomic% to 5 atomic%. Crystallization proceeds as a part of nickel element diffuses from the nickel film 407 into the silicon film. Thus, the crystalline silicon film 403 can be formed over the glass substrate.

  Thereafter, a gettering site is formed in order to perform gettering. The gettering site can be formed with an amorphous silicon film containing a rare gas element, or a region where a rare gas element is implanted into the crystalline silicon film 403 may be formed. Thereafter, gettering is performed by heat treatment, and the gettering sites that are no longer needed are removed by etching.

  As a result, the surface of the crystalline silicon film 403 is exposed on the main surface of the substrate 401. An n-type crystalline silicon film 404 is formed on this surface. Next, a transparent electrode 405 is formed on the n-type crystalline silicon film 404 by sputtering to form an indium tin oxide alloy (ITO) having a thickness of 0.08 μm. Finally, a process of providing the extraction electrode 406 is performed, whereby the photoelectric conversion device can be completed. Note that the structure of this embodiment mode can be freely combined with Embodiment Modes 1 to 4.

Claims (6)

Forming a first amorphous silicon film;
Adding a catalyst element for promoting crystallization to the first amorphous silicon film, and forming a crystalline silicon film by a first heat treatment;
Forming a second amorphous silicon film containing argon at a concentration of 1 × 10 ¹⁹ to 1 × 10 ²² / cm ^{3 on} the crystalline silicon film;
By the second heat treatment, the catalyst element is moved to the second amorphous silicon film,
Removing the second amorphous silicon film;
A method for manufacturing a photoelectric conversion device, comprising forming an n-type crystalline silicon film over the crystalline silicon film. Forming a first amorphous silicon film;
Adding a catalyst element for promoting crystallization to the first amorphous silicon film, and forming a crystalline silicon film by a first heat treatment;
Forming a barrier layer on the surface of the crystalline silicon film;
Forming a second amorphous silicon film containing argon at a concentration of 1 × 10 ¹⁹ to 1 × 10 ²² / cm ³ on the barrier layer;
By the second heat treatment, the catalyst element is moved to the second amorphous silicon film,
Removing the second amorphous silicon film;
Removing the barrier layer;
A method for manufacturing a photoelectric conversion device, comprising forming an n-type crystalline silicon film over the crystalline silicon film. In claim 1 or claim 2,
The second amorphous silicon film is formed by a sputtering method in which a gas containing argon is used as a sputtering gas and a pressure during film formation is 0.2 to 1 Pa. Manufacturing method. In any one of Claims 1 thru | or 3,
In the method for manufacturing a photoelectric conversion device, the second heat treatment is performed at 600 ° C. to 1000 ° C. In any one of Claims 1 thru | or 4,
The method for manufacturing a photoelectric conversion device, wherein the second heat treatment is performed by an RTA method. In any one of Claims 1 thru | or 5,
The method for manufacturing a photoelectric conversion device, wherein the second amorphous silicon film is removed by wet etching.

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