WO2013061648A1

WO2013061648A1 - Method for etching silicon substrate, etching solution for silicon substrate, and method for producing solar cell

Info

Publication number: WO2013061648A1
Application number: PCT/JP2012/064696
Authority: WO
Inventors: 裕介白柳; 吉田　育弘; 安永　望; 綾西山
Original assignee: 三菱電機株式会社
Priority date: 2011-10-28
Filing date: 2012-06-07
Publication date: 2013-05-02
Also published as: JP2015008167A

Abstract

A method for etching a silicon substrate, in which the surface of the silicon substrate is anisotropically etched by a wet etching process involving supplying an aqueous alkaline solution onto the surface of the silicon substrate, wherein the aqueous alkaline solution contains an alkylamine having a hydroxy group and a compound having both an amino group and a carboxyl group. According to the present invention, in the anisotropic etching of a silicon substrate with an alkaline etching solution, the etching of a silicon substrate can be achieved in such a manner that the stability of etching quality is excellent and the etching quality is good.

Description

Silicon substrate etching method, silicon substrate etching solution, and solar cell manufacturing method

The present invention relates to a silicon substrate etching method, a silicon substrate etching solution, and a solar cell manufacturing method.

In a solar power generation device, in order to absorb sunlight efficiently, it is necessary to penetrate the sunlight irradiated to the silicon substrate into the silicon substrate. That is, it is necessary to reduce the light reflectance on the surface of the silicon substrate as much as possible. For this reason, a texture is formed on the surface of the silicon substrate by etching. Here, the texture is a general term for minute irregularities formed on the surface of the silicon substrate. The texture is formed by etching using an alkaline etching solution obtained by adding an additive such as isopropyl alcohol to a hot alkaline aqueous solution. By using such an etchant, anisotropic etching in which etching does not proceed with respect to a specific crystal orientation occurs on the silicon substrate surface, and a minute pyramid structure composed of a stable (111) plane of silicon crystal is formed. Low reflectivity is realized.

JP 2010-074102 A JP 2010-135591 A JP 2011-139023 A

However, in the process of anisotropically etching silicon such as texture formation with an alkaline etchant, quality stability in mass production processes is often a problem. For example, the etching conditions change due to the change in the composition of the etching solution accompanying mass production or the contamination of the etching solution by metal ions brought into the etching solution from a silicon substrate or a member used for etching. For this reason, in the texture formation, an etching method and an etching solution capable of highly stable production are required.

As for the stabilization of the liquid composition of the etching solution, for example, as disclosed in Patent Document 1, measures such as substituting easily volatile components with low-volatile components are effective. In Patent Document 1, irregularities are formed on the surface of a silicon substrate by an etching solution containing water, an alkaline reagent, and an alcohol derivative.

Further, as a countermeasure against contamination of the etching solution by metal ions, for example, as disclosed in Patent Document 2, an etching solution to which hydroxyethylenediamine triacetic acid, which is a general chelating agent, is disclosed is disclosed. In Patent Document 2, an etching process is performed by immersing a silicon substrate in a silicon wafer etchant of an alkaline aqueous solution containing hydroxyethylenediaminetriacetic acid. By adding a general chelating agent such as hydroxyethylenediaminetriacetic acid, metal impurities such as Ni, Cu, and Fe on the surface of the silicon substrate after the etching treatment are reduced.

However, as a result of the examination of the effect of the chelating agent in the texture formation, the present inventors have found that the general chelating agent including the chelating agent shown in Patent Document 2 has a metal contamination of the silicon substrate after the texture formation. Although the reduction effect can be obtained, the metal ion cannot suppress the phenomenon that causes the deterioration of the quality such as the increase of the light reflectance of the texture and the occurrence of the defect in which the texture shape itself is not formed. It was found that it cannot be suppressed.

Further, by adding alkanolamine as shown in Patent Document 3 to the etching solution, it is possible to suppress the influence of metal ions or silicon dissolved in the etching solution to form a texture. However, in order to stably form a low-reflective texture in the mass production process, it is necessary to remove the influence of silicon dissolved in a further metal ion or etching solution.

The present invention has been made in view of the above, and in a silicon substrate anisotropic etching with an alkaline etchant, a silicon substrate etching method that is excellent in stability of etching quality and enables high-quality etching, and silicon substrate It aims at obtaining the manufacturing method of etching liquid of this, and a solar cell.

In order to solve the above-described problems and achieve the object, the silicon substrate etching method according to the present invention supplies an alkaline aqueous solution to the surface of the silicon substrate and anisotropically etches the surface of the silicon substrate by wet etching. A method for etching a silicon substrate, wherein the alkaline aqueous solution contains an alkylamine having a hydroxyl group and a compound having an amino group and a carboxyl group.

According to the present invention, in anisotropic etching of a silicon substrate with an alkaline etching solution, there is an effect that etching quality is stable and high-quality etching is possible.

FIG. 1 is a perspective view schematically showing an example of a wet etching process of a silicon substrate for forming a texture on the surface of the silicon substrate. FIG. 2 shows the concentration of alkylamine having a hydroxyl group when the silicon substrate is etched using an etching solution (Example 1) to which an alkylamine having a hydroxyl group and an aminocarboxylic acid are added as a chelating agent, and after the etching treatment. It is a characteristic view which shows the relationship with the light reflectance of the light of wavelength 700nm in a silicon substrate. FIG. 3 shows the concentration of aminocarboxylic acid and the silicon after the etching treatment when an etching solution (Example 2) in which an alkylamine having a hydroxyl group and an aminocarboxylic acid are added as a chelating agent is used. It is a characteristic view which shows the relationship with the light reflectance of the light of wavelength 700nm in a board | substrate. FIG. 4 shows the relationship between the total amount of silicon dissolved in the etching solution and the light reflectance at a wavelength of 700 nm of the silicon substrate after the etching treatment when the silicon substrate is etched using the etching solution of Example 1. FIG. FIG. 5 shows the concentration of organic amine when etching a silicon substrate using an etching solution (Example 3) in which an organic amine and an aminocarboxylic acid are added as a chelating agent, and the wavelength of 700 nm in the silicon substrate after the etching treatment. It is a characteristic view which shows the relationship with the light reflectivity of the light. FIG. 6 shows the relationship between the total amount of silicon dissolved in the etching solution and the light reflectance at a wavelength of 700 nm of the silicon substrate after the etching treatment when the silicon substrate is etched using the etching solution of Example 3. FIG. FIG. 7-1 is a cross-sectional view illustrating the solar power generation device manufactured using the substrate according to the first example. 7-2 is a top view of the solar power generation device manufactured using the substrate according to Example 1. FIG.

Embodiments of a silicon substrate etching method, a silicon substrate etching solution, and a solar cell manufacturing method according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably.

Embodiment 1 FIG.
In order to reduce the light reflectance on the surface of the silicon substrate, the present inventors have studied a wet etching process in which a texture is formed on the surface of the silicon substrate using an alkaline etching solution to which an additive has been added.

FIG. 1 is a perspective view schematically showing an example of a wet etching process of a silicon substrate for forming a texture on the surface of the silicon substrate. In order to form a texture on the surface of the silicon substrate, a wet etching process is performed by immersing the prepared silicon substrate 1 (FIG. 1A) in an alkaline etching solution 3 stored in an etching tank 2 (FIG. 1). 1 (b)). Thereby, the texture 6 is randomly formed on the surface of the silicon substrate 5 after the etching process (FIG. 1C).

Here, the alkaline etching solution 3 uses an alkaline aqueous solution in which a strong alkali reagent such as sodium hydroxide (NaOH), potassium hydroxide (KOH), trimethylammonium hydroxide (TMAH) is dissolved in water. The alkali concentration in the etching solution 3 is, for example, 0.5 wt% to 25 wt%. When the alkali concentration in the etching solution is less than 0.5 wt%, it is not preferable because the etching of silicon is difficult to proceed. When the alkali concentration in the etching solution exceeds 25 wt%, the texture itself is not easily formed, which is not preferable.

An additive is added to the etching solution 3 to moderately inhibit the etching reaction on the surface of the silicon substrate 1 and form a texture. As an additive added to the etching liquid 3, for example, an alcohol-based additive represented by the following chemical formula (1) is used.

X- (OH) n (1)
(X is a saturated or unsaturated hydrocarbon group having 4 to 7 carbon atoms, n is an integer of 1 or more, n <Cn)

Examples of such alcohol-based additives include isopropyl alcohol (IPA), normal propyl alcohol, ethylene glycol (EG), 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, 3-hexanol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1 , 5-hexanediol, 1,6-hexanediol, various hexanetriols and mixtures thereof can be used.

Further, as an additive to be added to the etching solution 3, a surfactant can also be used. The surfactant is preferably a nonionic surfactant, and preferably has a HLB (Hydrophile-Lipophile Balance) value of 10 or more. When the HLB value is less than 10, etching is excessively suppressed and it is difficult to form a good texture effective for reducing the light reflectance on the surface of the silicon substrate.

When any of the above-mentioned additives is used, the amount added to the etching solution 3 is preferably 0.05 g / L to 20 g / L, for example. When the amount added to the etching solution 3 is less than 0.05 g / L, no texture is formed on the surface of the silicon substrate. When the amount added to the etching solution 3 exceeds 20 g / L, the etching rate of silicon becomes too slow, which is not preferable.

The temperature of the etching solution 3 is preferably 40 ° C. to 100 ° C., for example, and more preferably 60 ° C. to 95 ° C. When the temperature of the etching solution 3 is less than 40 ° C., the etching time is too long, which is not preferable. When the temperature of the etching solution 3 exceeds 100 ° C., a pressurized container or the like may be required to store the etching solution 3, and further, the stability of the liquid composition of the etching solution 3 is caused by evaporation of the etching solution 3. It is easily damaged.

Etching time is, for example, 10 minutes to 60 minutes. When the etching time is less than 10 minutes, the etching of silicon does not proceed and the texture is not formed on the silicon substrate surface. When the etching time exceeds 60 minutes, the etching of silicon proceeds too much, which adversely affects texture formation.

In the wet etching process of the silicon substrate 1 with the alkaline etching liquid 3 containing the additive, the inventors have increased the amount of silicon dissolved in the etching liquid 3 due to the increase in the number of etching processes, Copper (Cu), iron (Fe), silver (Ag), calcium (Ca), manganese (Mg) and other metals derived from the above additives, phosphorus (P), boron (B) derived from silicon substrates It has been found that these adversely affect the quality of the texture 6 formed on the surface of the silicon substrate 5 after the etching process.

Silicon (Si) of the silicon substrate 1 reacts with an alkali such as sodium hydroxide (NaOH) in the liquid of the etching liquid 3 and is eluted in the liquid of the etching liquid 3, whereby the silicon substrate 5 after the etching treatment is dissolved. Texture 6 is formed on the surface. This etching reaction is represented by the following formula (2). At this time, hydrogen gas 4 is generated and silicate is deposited. Moreover, in order to activate this reaction more, it is necessary to carry out under the condition of high alkali or high temperature.

Si + 2OH ⁻ + 4H ₂ O → Si (OH) ₆ ² + + 2H ₂ ↑ (2)

The presence of the additive in the etching solution 3 inhibits the etching reaction of the formula (2) on the surface of the silicon substrate 1. More specifically, since the surface of the silicon substrate 1 is hydrophobic, the carbon chain portion of the additive which is a hydrophobic group is adsorbed on the surface of the silicon substrate 1 and inhibits the etching reaction of formula (2). By utilizing this inhibition reaction, the texture 6 can be randomly formed on the surface of the silicon substrate 5 after the etching process. The quality of the texture 6 formed on the surface of the silicon substrate 5 after the etching process varies depending on the material of the additive.

The inventors of the present invention clarified that the metal ions in the etching solution 3 and the silicon dissolved in the etching solution 3 have an adverse effect on the quality of the texture 6 in such etching. The addition of a chemical solution for suppression to the etching solution 3 was studied. As a result, the inventors added a combination of a compound having an amino group and a carboxyl group (aminocarboxylic acid), which is a general chelating agent, and an alkylamine having a hydroxyl group, to the alkaline etching solution 3 to produce a texture. It was found that the adverse effects of metal ions on the quality of silicon 6 and silicon dissolved in the etching solution 3 can be removed and suppressed. Thereby, the texture 6 with low light reflectance and high quality can be formed, and the occurrence of defects in the texture 6 can be suppressed. In addition, it was found that the texture was stably formed even when the etching solution was repeatedly used.

When the silicon substrate 1 is etched using the etching solution 3 contaminated with metal ions or dissolved silicon, the texture 6 formed on the silicon substrate 5 after the etching process has a dull ridge of the pyramid structure. The state where the flat surface of the pyramid is not formed occurs. In addition, a defect portion in which the pyramid itself is not formed frequently appears in the texture 6 formed on the silicon substrate 5 after the etching process. These causes are low fluidity gel-like substances generated due to additives such as metal ions existing in the solution of the etching solution 3, a silicate generated by the dissolution of the silicon substrate during etching, and alcohol. It is presumed that this is because the formation of the texture on the surface of the silicon substrate hinders texture formation.

When only a general chelating agent is used, such a phenomenon cannot be suppressed, and conversely, formation is promoted. A general chelating agent has a plurality of amino groups and carboxyl groups in the molecule. For this reason, it is difficult for a general chelating agent to supplement metal ions and silicates in the vicinity of the silicon substrate surface. Further, when a general chelating agent captures metal ions or silicates or diffuses in the vicinity of the surface of the silicon substrate, the fluidity of the gel material having low fluidity is further reduced.

In addition, when an alkylamine having a hydroxyl group is used as a chelating agent, unlike a general chelating agent, it has a high solubility in an etching solution 3 in a strong alkaline environment or an environment containing a high concentration of silicate. However, it does not promote the formation of a gel material having low fluidity, and can reduce the phenomenon of forming a gel material by interacting with metal ions or silicates. However, when only an alkylamine having a hydroxyl group is used, it is difficult to completely remove and suppress the influence of metal ions because the action of trapping metal ions present in the etching solution 3 is weak. is there.

On the other hand, by using aminocarboxylic acid, which is a general chelating agent, and alkylamine having a hydroxyl group in combination as a chelating agent, in a strong alkaline environment or an environment where a high concentration of silicate exists. A high concentration silicate formed by dissolution of the silicon substrate to form a chelate compound by binding the aminocarboxylic acid so as to enclose the metal ions present in the solution of the etching solution 3 is an alkylamine having a hydroxyl group. Are bound together to form a compound. Thereby, it can be removed and suppressed that metal ions or silicate adversely affects the quality of the texture 6 formed on the surface of the silicon substrate 5 after the etching process. Furthermore, by separating and capturing the metal ions and the silicate, it is possible to remove and suppress the generation of the low-fluidity gel substance generated due to the metal ions and the silicate. Therefore, by etching the silicon substrate 1 using the etching solution 3 to which aminocarboxylic acid and alkylamine having a hydroxyl group are added as a chelating agent, a texture 6 with low light reflectance and high quality is formed, and a pyramid is formed. It is possible to suppress the occurrence of defects in the texture 6 in which it is not formed.

In addition, the alkylamine having a hydroxyl group in the present embodiment has a property of low volatility in addition to high hydrophilicity, and has an advantage of low volatilization from the high temperature etching solution 3. Therefore, by adding an alkylamine having a hydroxyl group to the etching solution 3, a change in the composition of the etching solution 3 is suppressed even in a mass production process, and a highly stable texture can be formed. These effects can be obtained even in a low-stability etching solution that does not contain a low-volatile component or a highly decomposable component as in Patent Document 1.

Examples of the aminocarboxylic acid added to the etching solution 3 in the present embodiment include hydroxyethylenediaminetriacetic acid, EDTA (ethylenediaminetetraacetic acid), NTA (nitrilotriacetic acid), DTPA (diethylenetriaminepentaacetic acid), and picolinic acid. .

In the present embodiment, the alkylamine having a hydroxyl group added to the etching solution 3 has 6 or less carbon atoms per nitrogen atom and has a molecular structure having at least one hydroxyl group. When the number of carbon atoms is 7 or more with respect to one nitrogen atom, the hydrophilicity is deteriorated and it is difficult to dissolve in the etching solution 3, and the above-described effects cannot be obtained sufficiently.

Examples of such alkylamine having a hydroxyl group include methanolamine, ethanolamine, propanolamine, butanolamine, N-methylmethanolamine, N-methylethanolamine, N-ethylethanolamine, N-methyldimethanolamine, N-ethyldimethanolamine, N-propyldimethanolamine, N-butyldimethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-propyldiethanolamine, N-butyldiethanolamine, N-methyldipropanolamine, N- Ethyldipropanolamine, N-propyldipropanolamine, N-methyldibutanolamine, N-ethyldibutanolamine, N- (aminomethyl) methanolamine, N- (amino Methyl) ethanolamine, N- (aminomethyl) butanolamine, N- (aminoethyl) methanolamine, N- (aminoethyl) ethanolamine, N- (aminoethyl) propanolamine, N- (aminoethyl) butanolamine, N- (aminopropyl) methanolamine, N- (aminopropyl) ethanolamine, N- (aminopropyl) propanolamine, trimethanolamine, triethanolamine, etc., and isomers other than those listed above (same carbon number) And those having a straight chain or a side chain and / or those having different positions of hydroxyl groups and amino groups). The chelating agent is not limited to the above-described substances, and the bond between C and C may include a double bond or a triple bond in addition to a single bond.

The optimum amount of the alkylamine having a hydroxyl group in the etching solution 3 varies depending on the degree of metal contamination of the etching solution 3, but is preferably in the range of 0.01 wt% to 1.00 wt%. When the concentration of ethanolamine in the etching solution 3 is less than 0.01 wt%, the concentration is too small, so that the metal ions present in the solution of the etching solution 3 and the silicate produced by the dissolution of the silicon substrate during the etching The effect of reducing the light reflectance by the removal cannot be obtained sufficiently. When the concentration of ethanolamine in the etching solution 3 is higher than 1.00 wt%, the concentration is too high, and the ethanolamine functions to greatly inhibit the etching reaction on the surface of the silicon substrate 1, and is etched. The quality of the formed texture 6 is deteriorated.

Further, the optimum amount of aminocarboxylic acid added to the etching solution 3 varies depending on the degree of metal contamination of the etching solution 3, but is preferably in the range of 0.05 wt% to 0.80 wt%. When the concentration of the aminocarboxylic acid in the etching solution 3 is less than 0.05 wt%, the concentration is too low, so that the metal ions present in the solution of the etching solution 3 and the silicate produced by dissolving the silicon substrate during the etching The effect of reducing the light reflectance by the removal cannot be obtained sufficiently. When the concentration of the aminocarboxylic acid in the etching solution 3 is higher than 0.80 wt%, the concentration is too high, so that the aminocarboxylic acid functions to significantly inhibit the etching reaction on the surface of the silicon substrate 1, The quality of the texture 6 formed by etching is deteriorated.

When the addition concentration of the alkylamine having a hydroxyl group is 0.5 wt%, the ratio of the addition amount of the aminocarboxylic acid and the alkylamine having a hydroxyl group in the etching solution 3 is preferably a ratio of 2: 1 to 1:10. More preferably, it is 1: 1. When the ratio of the addition amount of aminocarboxylic acid and alkylamine having a hydroxyl group is higher than 2: 1, the aminocarboxylic acid is added excessively, so that the concentration of aminocarboxylic acid becomes too high and the aminocarboxylic acid becomes silicon. It acts to greatly hinder the etching reaction on the surface of the substrate 1 and deteriorates the quality of the texture 6 formed by etching. When the ratio of the addition amount of aminocarboxylic acid and alkylamine having a hydroxyl group is lower than 1:10, the effect of reducing light reflectance by removing metal ions in the etching solution with aminocarboxylic acid cannot be sufficiently obtained. .

Further, when the addition concentration of aminocarboxylic acid is 0.5 wt%, the ratio of the addition amount of alkylamine having a hydroxyl group and aminocarboxylic acid in the etching solution 3 is preferably a ratio of 2: 1 to 1:50, more Preferably, it is 1: 1. When the ratio of the addition amount of the alkylamine having a hydroxyl group and the aminocarboxylic acid is higher than 2: 1, the concentration of the alkylamine having a hydroxyl group becomes too high because the alkylamine having a hydroxyl group is excessively added. Alkylamine having a function of significantly hindering the etching reaction on the surface of the silicon substrate 1 deteriorates the quality of the texture 6 formed by etching. When the ratio of the added amount of alkylamine having a hydroxyl group and aminocarboxylic acid is lower than 1:50, the light reflection is caused by the removal of the silicate formed by dissolution of the silicon substrate during etching with the alkylamine having a hydroxyl group. The rate reduction effect cannot be obtained sufficiently.

In addition, the optimal ratio of the addition amount of the aminocarboxylic acid and the alkylamine having a hydroxyl group in the etching solution 3 varies depending on each additive concentration.

Next, the result of verifying the effect of adding the alkylamine having a hydroxyl group according to the present embodiment to the etching solution 3 will be described. FIG. 2 shows an etching solution 3 (Example 1) to which ethanolamine, which is an alkylamine having a hydroxyl group, and EDTA, which is an aminocarboxylic acid, are added as chelating agents. 5 is a characteristic diagram showing the relationship between the concentration (wt%) of ethanolamine when the silicon substrate is etched while changing the thickness and the light reflectance (%) of light having a wavelength of 700 nm in the silicon substrate 5 after the etching process. (Actually, the light reflectivity of a silicon substrate with a wavelength of 300 to 1200 nm is measured, and the light reflectivity of the silicon substrate is not fogged by other silicon substrates (= does not cross), so 700 nm is adopted as a typical wavelength.) . In addition, the quality of the texture 6 is so good that the light reflectance in the silicon substrate 5 after an etching process is low.

In the etching solution 3 used in Example 1, IPA as an additive was added to a 4.0 wt% NaOH aqueous solution at an addition amount of 10 g / L, and EDTA and ethanolamine were added as chelating agents. The concentration of EDTA was 0.5 wt%, and the concentration of ethanolamine was adjusted. Then, the silicon substrate 1 was etched under the conditions of the etching solution 3 temperature of 75 ° C. and the etching time of 20 minutes.

For comparison, when the silicon substrate 1 was etched using an etching solution (Comparative Example 1) prepared in the same manner as in Example 1 except that no alkylamine having a hydroxyl group and EDTA were added as chelating agents. FIG. 2 also shows the light reflectance (%) of light having a wavelength of 700 nm in the silicon substrate 5 after the etching process.

For comparison, in the silicon substrate 5 after the etching process when the silicon substrate 1 was etched with an etching solution (Comparative Example 2) prepared in the same manner as in Example 1 except that EDTA was not added. The light reflectance (%) of light having a wavelength of 700 nm is also shown in FIG. The etching conditions in Comparative Example 1 and Comparative Example 2 are the same as in Example 1.

By comparing Comparative Example 1 and Comparative Example 2 in FIG. 2, an alkylamine having a hydroxyl group is added as a chelating agent to the etching solution 3 (Comparative Example 2), and no etching agent is added at all. Compared with the case of using 3 (Comparative Example 1), the light reflectance is reduced, and the effect of improving the quality of the texture 6 formed on the silicon substrate 5 after the etching process can be obtained. On the other hand, when Example 1 and Comparative Example 2 were compared, ethanolamine which is an alkylamine having a hydroxyl group as a chelating agent and EDTA which is a general chelating agent were added in combination (Example 1). Compared with the case where only ethanolamine is added as a chelating agent (Comparative Example 2), the light reflectance is reduced, and the effect of further improving the quality of the texture 6 formed on the silicon substrate 5 after the etching treatment is obtained. Can get.

The reduction of the light reflectance in Example 1 is caused by the addition of a combination of EDTA and ethanolamine to the etching solution 3, and the metal ions existing in the etching solution 3 and the silicon substrate dissolved during the etching. This is due to the chelate effect that reduces the influence of the silicate by binding the silicate so as to enclose the silicate, and the effect of reducing the formation phenomenon of the gel substance.

From FIG. 2, in particular, in order to improve the quality of the texture 6 and lower the light reflectivity of the silicon substrate 5 after the etching process, the amount of ethanolamine added to the etching solution 3 containing 0.5 wt% EDTA. The total weight ratio is preferably 0.01 wt% to 1.00 wt%, more preferably 0.2 to 0.8 wt%. The amount of ethanolamine added is most preferably 0.5 wt%.

When the concentration of ethanolamine in the etching solution 3 containing 0.5 wt% of EDTA is less than 0.01 wt%, the concentration of ethanolamine is too small, and the silicon substrate is not etched during the etching existing in the solution of the etching solution 3. The effect of reducing the light reflectivity due to the chelate effect on the silicate produced by dissolution is not sufficiently obtained. When the concentration of ethanolamine in the etching solution 3 is higher than 1.00 wt%, the concentration of the chelating agent composed of ethanolamine and EDTA is too high, so that ethanolamine greatly affects the etching reaction on the surface of the silicon substrate 1. It acts to hinder the quality of the texture 6 formed by etching.

Next, the results of verifying the effect of adding the aminocarboxylic acid according to the present embodiment to the etching solution 3 will be described. FIG. 3 shows an etching solution 3 (Example 2) in which ethanolamine, which is an alkylamine having a hydroxyl group, and EDTA, which is an aminocarboxylic acid, are added as chelating agents, and the concentration of EDTA in the etching solution 3 (wt%). 5 is a characteristic diagram showing the relationship between the concentration (wt%) of EDTA when the silicon substrate is etched by changing the light reflectivity (%) of light having a wavelength of 700 nm in the silicon substrate 5 after the etching process.

In the etching solution 3 used in Example 2, IPA as an additive was added to a 4.0 wt% NaOH aqueous solution at an addition amount of 10 g / L, and EDTA and ethanolamine were added as chelating agents. The ethanolamine concentration was 0.5 wt%, and the EDTA concentration was adjusted. Then, the silicon substrate 1 was etched under the conditions of the etching solution 3 temperature of 75 ° C. and the etching time of 20 minutes.

For comparison, the silicon substrate 1 was etched using an etching solution (Comparative Example 1) prepared in the same manner as in Example 1 except that no alkylamine having a hydroxyl group and EDTA were added as chelating agents. FIG. 3 also shows the light reflectance (%) of light having a wavelength of 700 nm in the silicon substrate 5 after the etching process.

For comparison, the silicon substrate 5 after the etching process when the silicon substrate 1 was etched with an etching solution (Comparative Example 3) prepared in the same manner as in Example 2 except that ethanolamine was not added. 3 shows the light reflectance (%) of light having a wavelength of 700 nm. The etching conditions in Comparative Example 1 and Comparative Example 3 are the same as in Example 2.

In FIG. 3, by comparing Comparative Example 1 and Comparative Example 3, by adding EDTA as a chelating agent to the etching solution 3 (Comparative Example 3), the etching solution 3 to which no chelating agent is added is used. It can be seen that the quality of the texture 6 formed on the silicon substrate 5 after the etching process cannot be improved as compared with the case (Comparative Example 1). On the other hand, by comparing Example 2 and Comparative Example 3, when EDTA and ethanolamine were added in combination as a chelating agent (Example 2), compared to the case where only EDTA was added as a chelating agent ( Comparative Example 3) A reduction in light reflectance is observed.

From FIG. 3, in particular, in order to improve the quality of the texture 6 and lower the light reflectance of the silicon substrate 5 after the etching process, the amount of EDTA added is compared with the etching solution 3 containing 0.5 wt% of ethanolamine. The total weight ratio is preferably 0.05 wt% to 0.80 wt%, more preferably 0.1 to 0.8 wt%. The addition amount of EDTA is most preferably 0.5 wt%.

When the concentration of EDTA in the etching solution 3 containing 0.5% by weight of ethanolamine is less than 0.05% by weight, the concentration of EDTA is too low, and light reflection is caused by the removal of metal ions present in the solution of the etching solution 3. The effect of reducing the rate is not sufficiently obtained. When the concentration of EDTA in the etching solution 3 is higher than 0.8 wt%, the concentration of the chelating agent composed of ethanolamine and EDTA is too high, so that EDTA greatly inhibits the etching reaction on the surface of the silicon substrate 1. It works to degrade the quality of the texture 6 formed by etching.

In addition, although shown about the case where EDTA is used as ethanolamine and aminocarboxylic acid as an alkylamine which has a hydroxyl group here, also about alkylamine which has the above-mentioned hydroxyl groups other than ethanolamine, and the above-mentioned aminocarboxylic acid other than EDTA, It has been confirmed that the effect of reducing the light reflectance of the silicon substrate 5 after the etching treatment can be obtained in the same manner as described above. In addition, the range of the amount of the chelating agent according to this embodiment described above does not change even when the etching conditions such as the temperature of the etching solution 3, the etching time, the alkali concentration of the etching solution 3, and the additive concentration change. Confirmed.

Next, the result of verifying the influence of silicate generated in the etching solution 3 by etching the silicon substrate 1 will be described. When alkaline etching of the silicon substrate 1 is repeatedly performed with the etching solution 3, silicate (Si (OH) ₆ ²⁻ generated when silicon is dissolved in the etching solution 3 by the chemical reaction represented by the above formula (2). ) Increases as the amount of silicon dissolved in the etching solution 3 increases, and accumulates in the etching solution 3. Then, by increasing the concentration of silicate in the etching solution 3, a gel material having low fluidity is easily formed on the surface of the silicon substrate 1, and the texture 6 formed by etching with the etching solution 3 is improved. , Easy to adversely affect. Therefore, in order to suppress the influence of the silicate in the etching solution 3, the influence of the addition of the chelating agent according to the present embodiment to the etching solution 3 was verified.

FIG. 4 shows the total amount (g / L) of silicon dissolved in the etching solution 3 and the silicon substrate after the etching process when a plurality of silicon substrates 1 are etched using the etching solution of Example 1 described above. 5 is a characteristic diagram showing a relationship with light reflectance (%) at a wavelength of 700 nm. As the number of etching treatments increases, the amount of silicon dissolved in the etching solution 3 increases. The amount of silicon dissolved is calculated from the difference in weight before and after etching the silicon substrate 1. The concentrations of EDTA and ethanolamine in the etching solution 3 are each 0.5 wt%.

For comparison, the total amount of silicon dissolved in the etching solution (g / L) when the silicon substrate 1 is etched using the etching solution 3 of Comparative Example 1, Comparative Example 2, and Comparative Example 3 described above. 4 also shows the relationship between the light reflectance (%) at a wavelength of 700 nm of the silicon substrate 5 after the etching treatment. In addition, the density | concentration of the ethanolamine added to the etching liquid 3 in the comparative example 2 is 0.5 wt%. The concentration of EDTA added to the etching solution 3 in Comparative Example 3 is 0.5 wt%.

As can be seen from FIG. 4, when the etching solution of Comparative Example 1 to which no chelating agent is added is used, the light reflectance increases as the amount of silicon dissolved in the etching solution increases, and the quality of the texture 6 is poor. It has become. When the etching solution 3 of Comparative Example 3 to which EDTA is added is used, the light reflectance increases as the amount of silicon dissolved in the etching solution increases, although not as much as Comparative Example 1. On the other hand, when the etching solution of Comparative Example 2 to which ethanolamine, which is an alkylamine having a hydroxyl group, was added and Example 1 to which EDTA and ethanolamine were added in combination was used, the light reflectance was increased due to an increase in the amount of dissolved silicon. The increase is suppressed.

Such a tendency is caused by the addition of ethanolamine, which is an alkylamine having a hydroxyl group, to the silicate precipitated by dissolution of silicon in the etching solution 3, thereby forming a compound by bonding in enclosure. Is formed, indicating that the influence of silicate is suppressed. In addition, EDTA, which is an aminocarboxylic acid, also suppresses the influence of silicates, but not as much as alkylamines. However, the influence of silicate is further suppressed by using ethanolamine and EDTA in combination. Further, ethanolamine does not promote the formation of a gel material having low fluidity, and shows that the phenomenon of gel material formation is reduced by interacting with silicate. In addition, it was confirmed that the alkylamine having the above hydroxyl group other than ethanolamine and the above aminocarboxylic acid other than EDTA also have the effect of reducing the light reflectivity of the silicon substrate 5 after the etching treatment in the same manner as described above. ing.

In addition, since the alkylamine having a hydroxyl group in Embodiment 1 has a property of low volatility in addition to high hydrophilicity, and less volatilization from the high temperature etching solution 3, the etching solution 3 is also used in the mass production process. The liquid composition change is suppressed, and a highly stable texture can be formed.

Therefore, according to the first embodiment, it is possible to obtain the effects that the generation of defects is suppressed, the light reflectance is low, and the texture 6 having high quality can be stably formed.

Embodiment 2. FIG.
In the second embodiment, an organic amine having no hydroxyl group and an aminocarboxylic acid are used in order to improve the quality of the texture 6 by suppressing the influence of the metal ions in the etching solution 3 on the etching of the silicon substrate 1 on the etching. The case where it adds to the etching liquid 3 as a chelating agent is demonstrated.

Even when an organic amine having no hydroxyl group is added to the etching solution 3 instead of the alkylamine having a hydroxyl group as the chelating agent, the same effect as that obtained when an alkylamine having a hydroxyl group is added can be obtained. An organic amine having no hydroxyl group is also bonded to surround the free silicate and metal ions in the etching solution to form a compound, and the surface of the silicon substrate 5 after the metal ions and silicate are etched. It is possible to suppress adverse effects on the quality of the texture 6 formed on the surface.

When organic amines are more volatile than alkylamines having hydroxyl groups, the stability of the liquid composition may be slightly inferior, and although the effect of reducing the influence of metal ions is inferior, other chelating agents are present In this case, a sufficient effect can be obtained. That is, by making the etchant 3 coexist with an organic amine and an aminocarboxylic acid, the amount of metal ions and silicate dissolved in the etchant 3 is further reduced, which affects the quality of the texture 6 by the metal ions and silicate. The influence can be suppressed, and the texture 6 having a lower light reflectance and a higher quality can be formed.

In the case where a chelating agent is present in the etching solution 3, the metal ions are finally stabilized by the chelating agent. For this reason, even the weak stabilization effect due to the organic amine having no hydroxyl group contributes to temporary stabilization in the vicinity of the surface of the silicon substrate 1, so that the gel-like substance having low fluidity on the surface of the silicon substrate 1 can be obtained. Generation can be suppressed. Moreover, the organic amine which does not have a hydroxyl group can suppress the effect which a chelating agent interacts with a gel-like substance with low fluidity, and makes fluidity worse.

Further, as described in the first embodiment, by adding aminocarboxylic acid to the etching solution 3 as a chelating agent, a texture 6 having a low light reflectance and a high quality is formed, and defects in the texture 6 are suppressed. The

The aminocarboxylic acid added to the etching solution 3 as the chelating agent in the second embodiment is that shown in the first embodiment. The organic amine having no hydroxyl group added to the etching solution 3 in combination with the aminocarboxylic acid has a molecular structure having 6 or less carbon atoms per one nitrogen atom. When the number of carbon atoms is 7 or more with respect to one nitrogen atom, the hydrophilicity is poor and it is difficult to dissolve in the etching solution 3, and the effect of adding an organic amine having no hydroxyl group to the etching solution 3 is sufficient. I can't get it.

Examples of such organic amines having no hydroxyl group include tetramethylethylenediamine, tetraethylethylenediamine, methylaminomethylamine, methylaminoethylamine, methylaminopropylamine, methylaminobutylamine, ethylaminomethylamine, ethylaminoethylamine, and ethylamino. Propylamine, ethylaminobutylamine, propylaminomethylamine, propylaminoethylamine, propylaminopropylamine, butylaminomethylamine, butylaminoethylamine, pyridine, pyrrole, piperazine, pyrrolidine, piperidine, picoline, morpholine, methylmorpholine, diazabicyclo Ocran, diazabicyclononane, diazabicycloundecene, and other substances other than those listed above Body (position of a thing and / or amino group identical number of carbon atoms in the straight or side chain different) include. In addition to the substances described above, the bond between C and C may include a double bond or a triple bond in addition to a single bond.

The optimum amount of aminocarboxylic acid added in the etching solution 3 varies depending on the degree of metal contamination of the etching solution 3, but is preferably in the range of 0.05 wt% to 0.80 wt%, more preferably 0.5 wt%. is there. When the concentration of the aminocarboxylic acid in the etching solution 3 is less than 0.05 wt%, the chelating agent concentration is too low, so that the metal ions present in the solution of the etching solution 3 and the silicon substrate formed by dissolution of the silicon substrate during the etching. The effect of reducing the light reflectance by removing the acid salt cannot be obtained sufficiently. When the concentration of aminocarboxylic acid in the etching solution 3 is higher than 0.80 wt%, the chelating agent concentration is too high, so that the aminocarboxylic acid functions to significantly inhibit the etching reaction on the surface of the silicon substrate 1. Thus, the quality of the texture 6 formed by etching is deteriorated.

The optimum amount of the organic amine having no hydroxyl group in the etching solution 3 varies depending on the degree of metal contamination of the etching solution 3, but is preferably in the range of 0.05 wt% to 1.00 wt%, more preferably 0. 5 wt%. When the concentration of the organic amine not having a hydroxyl group in the etching solution 3 is less than 0.05 wt%, the concentration of the organic amine not having a hydroxyl group is too small, so that metal ions present in the solution of the etching solution 3 and silicon during etching The effect of reducing the light reflectivity due to the removal of the silicate formed by dissolving the substrate cannot be obtained sufficiently. When the concentration of the organic amine not having a hydroxyl group in the etching solution 3 is higher than 1.00 wt%, the concentration of the organic amine not having a hydroxyl group is too high. This significantly hinders the etching reaction in the above, and deteriorates the quality of the texture 6 formed by etching.

Next, the results of verifying the effect of adding an organic amine having no hydroxyl group according to the second embodiment to the etching solution 3 will be described. FIG. 5 shows the concentration of tetraethylenediamine (wt) in the etching solution 3 using the etching solution 3 (Example 3) to which tetraethylenediamine, which is an organic amine having no hydroxyl group, and EDTA, which is an aminocarboxylic acid, are added as chelating agents. %) Is a characteristic diagram showing the relationship between the concentration (wt%) of tetraethylenediamine when the silicon substrate is etched and the light reflectance (%) of light having a wavelength of 700 nm in the etched silicon substrate 5 It is.

Etching solution 3 used in Example 3 was prepared by adding 10 g / L of IPA as an additive to a 4.0 wt% NaOH aqueous solution and adding tetraethylenediamine and EDTA as chelating agents. The concentration of EDTA was 0.5 wt%, and the concentration of tetraethylenediamine was adjusted. Then, the silicon substrate 1 was etched under the conditions of the etching solution 3 temperature of 75 ° C. and the etching time of 20 minutes.

For comparison, when the silicon substrate 1 was etched using an etching solution (Comparative Example 1) prepared in the same manner as in Example 1 except that tetraethylenediamine and EDTA were not added as chelating agents, FIG. 5 also shows the light reflectance (%) of light having a wavelength of 700 nm in the silicon substrate 5 after the etching process.

For comparison, in the silicon substrate 5 after the etching process when the silicon substrate 1 was etched with an etching solution (Comparative Example 4) prepared in the same manner as in Example 3 except that EDTA was not added. The light reflectance (%) of light having a wavelength of 700 nm is also shown in FIG. The etching conditions in Comparative Example 1 and Comparative Example 4 are the same as in Example 3.

By comparing Comparative Example 1 and Comparative Example 4 in FIG. 5 and adding tetraethylenediamine as a chelating agent to the etching solution 3 (Comparative Example 4), the etching solution 3 to which no chelating agent is added is used. It can be seen that the quality of the texture 6 formed on the silicon substrate 5 after the etching process cannot be improved as compared with the case (Comparative Example 1). On the other hand, by comparing Example 3 with Comparative Example 4, when tetraethylenediamine and EDTA were added in combination as a chelating agent (Example 3), compared to the case where only tetraethylenediamine was added as a chelating agent, (Comparative example 4) Reduction of light reflectance is recognized.

From FIG. 5, in particular, in order to improve the quality of the texture 6 and reduce the light reflectance of the silicon substrate 5 after the etching process, the amount of tetraethylenediamine added is larger than that of the etching solution 3 containing 0.5 wt% EDTA. The total weight ratio is preferably 0.05 wt% to 1.00 wt%, more preferably 0.2 to 0.8 wt%. The addition amount of tetraethylenediamine is most preferably 0.5 wt%.

When the concentration of tetraethylenediamine in the etching solution 3 containing 0.5 wt% of EDTA is less than 0.05 wt%, the concentration of tetraethylenediamine is too low, so that the silicon substrate is removed during etching existing in the solution of the etching solution 3. The effect of reducing the light reflectivity due to the chelate effect on the silicate produced by dissolution is not sufficiently obtained. When the concentration of tetraethylenediamine in the etching solution 3 is larger than 1.00 wt%, the concentration of the chelating agent composed of tetraethylenediamine and EDTA is too high, so that tetraethylenediamine greatly affects the etching reaction on the surface of the silicon substrate 1. It acts to hinder the quality of the texture 6 formed by etching.

Here, the case where EDTA is used as the aminocarboxylic acid and tetraethylenediamine is used as the organic amine not having a hydroxyl group is shown. However, the above-mentioned aminocarboxylic acid other than EDTA and the above-mentioned hydroxylamine other than tetraethylenediamine are not present. In the same manner as above, it has been confirmed that the effect of reducing the light reflectance of the silicon substrate 5 after the etching treatment can be obtained. In addition, the range of the amount of the chelating agent according to this embodiment described above does not change even when the etching conditions such as the temperature of the etching solution 3, the etching time, the alkali concentration of the etching solution 3, and the additive concentration change. Confirmed.

Next, the results of verifying the influence of silicate generated in the etching solution 3 by etching the silicon substrate 1 using the etching solution 3 in the second embodiment will be described. FIG. 6 shows the total amount (g / L) of silicon dissolved in the etching solution 3 and the silicon substrate after the etching process when a plurality of silicon substrates 1 are etched using the etching solution of Example 3 above. 5 is a characteristic diagram showing a relationship with light reflectance (%) at a wavelength of 700 nm. As the number of etching treatments increases, the amount of silicon dissolved in the etchant increases. The amount of silicon dissolved is calculated from the difference in weight before and after etching the silicon substrate 1. The concentrations of EDTA and tetraethylenediamine in the etching solution 3 are each 0.5 wt%.

For comparison, the total amount (g / L) of silicon dissolved in the etching solution 3 and the etching treatment when the silicon substrate 1 is etched using the etching solution 3 of Comparative Example 1 and Comparative Example 4 described above. The relationship with the light reflectance (%) at a wavelength of 700 nm of the later silicon substrate 5 is also shown in FIG. In addition, the density | concentration of the tetraethylenediamine added to the etching liquid 3 in the comparative example 4 is 0.5 wt%.

As can be seen from FIG. 6, when the etching solution of Comparative Example 1 to which no chelating agent is added is used, the light reflectance increases as the amount of silicon dissolved in the etching solution 3 increases, and the quality of the texture 6 increases. It is getting worse. On the other hand, when the etching solution of Comparative Example 4 added with tetraethylenediamine, which is an organic amine having no hydroxyl group, and Example 3 added with a combination of tetraethylenediamine and EDTA was used, the light reflectance due to an increase in the amount of dissolved silicon The increase of is suppressed.

Such a tendency is due to the bond in the enclosure by adding tetraethylenediamine, which is an organic amine having no hydroxyl group, to the silicate precipitated by dissolution of silicon in the etchant 3. It shows that the compound is formed and that the effect of silicates is suppressed, although not as much as alkylamines with hydroxyl groups. Furthermore, by using tetraethylenediamine and EDTA in combination (Example 3), the influence of silicate is further suppressed. Further, it is shown that tetraethylenediamine does not promote the formation of a gel-like substance having low fluidity, but reduces the phenomenon that the gel-like substance is formed by interacting with silicate. In addition, it was confirmed that the organic amine having no hydroxyl group other than tetraethylenediamine and the aminocarboxylic acid other than EDTA also have the effect of reducing the light reflectance of the silicon substrate 5 after the etching treatment in the same manner as described above. Has been.

As described above, in the second embodiment, in the wet etching process in which a texture is formed on the surface of a silicon substrate using an alkaline etching solution to which an additive is added, an organic amine that does not have a hydroxyl group as a chelating agent in the etching solution. And the aminocarboxylic acid are added, the adverse effects of the metal ions, silicates, and low-fluid gel substances in the etching solution on texture formation can be removed and suppressed. Thereby, the texture 6 with low light reflectance and high quality can be formed, and the occurrence of defects in the texture 6 can be further suppressed.

Therefore, according to the second embodiment, it is possible to obtain the effects that the generation of defects is suppressed, the light reflectance is low, and the texture 6 having high quality can be stably formed.

In the above embodiment, it is described that the above-described chelating agent is added to the texture formation on the surface of the silicon substrate. However, the silicon substrate is anisotropically etched in addition to the texture formation. By adding the above-mentioned chelating agent, the anisotropic etching is improved.

Embodiment 3 FIG.
In Embodiment 3, a solar power generation device (solar cell) was manufactured using the silicon substrate 1 in which the texture was formed on the substrate surface by the wet etching process using the etching solution 3 described above. A P-type or N-type conductive silicon substrate is used as the silicon substrate 1, and an N-type or P-type semiconductor layer having a conductivity type opposite to the substrate is formed on the textured surface to form a PN junction. And made a solar cell. Below, the influence which the quality of the texture 6 formed in the surface of the silicon substrate 1 has on the power generation characteristic of a solar power generation device is demonstrated.

A wet etching process was performed to produce a silicon substrate 1 used in a solar power generation device. Etching solution 3 was added to a 4.0 wt% NaOH aqueous solution as an additive with an addition amount of IPA of 10 g / L, and EDTA and ethanolamine were combined as a chelating agent (Example 1 above), Alternatively, EDTA and tetraethylenediamine were added in combination (Example 3 above). The concentrations of EDTA, ethanolamine and tetraethylenediamine were each 0.5 wt%. Then, the silicon substrate 1 was etched under the conditions of the etching solution 3 temperature of 75 ° C. and the etching time of 20 minutes.

For comparison, the silicon substrate 1 was etched using an etching solution prepared in the same manner as in Example 1 (Comparative Example 1 above) except that EDTA and ethanolamine were not added as chelating agents.

For comparison, the silicon substrate 1 was etched with an etching solution prepared in the same manner as in Example 1 except that EDTA was not added as a chelating agent (Comparative Example 2 above).

For comparison, the silicon substrate 1 was etched using an etching solution (Comparative Example 3 described above) prepared in the same manner as in Example 1 except that ethanolamine was not added as a chelating agent.

For comparison, the silicon substrate 1 was etched with an etching solution (Comparative Example 4) prepared in the same manner as in Example 3 except that EDTA was not added as a chelating agent.

In the wet etching process, the silicon substrate 1 having a substrate size of 15 cm × 15 cm and a thickness of 200 μm was processed.

Next, a solar power generation device was manufactured using the silicon substrate 5 after the etching process of Example 1 (hereinafter, sometimes referred to as the silicon substrate 5) in which the wet etching process was completed as described above. FIGS. 7A and 7B are diagrams showing a solar power generation device manufactured using the silicon substrate 5 having a texture formed on the surface by the wet etching process described above, and FIG. 7-1 is a solar power generation device. FIG. 7-2 is a top view of the photovoltaic power generation apparatus. The solar power generation device shown in FIGS. 7-1 and 7-2 includes a silicon substrate 7 having an N layer 7a on the substrate surface, an antireflection film 8 formed on the light receiving surface side (surface) of the silicon substrate 7, A light receiving surface side electrode 9 formed on the light receiving surface side surface (front surface) of the silicon substrate 7 and a silicon substrate 7 and a back electrode 10 formed on the surface (back surface) opposite to the light receiving surface are provided.

The light receiving surface side electrode 9 includes a grid electrode 9a and a bus electrode 9b, and FIG. 7-1 shows a cross-sectional view in a cross section perpendicular to the longitudinal direction of the grid electrode 9a. And the 15 cm square solar power generation device is comprised for the silicon substrate using the silicon substrate 5 in which the texture 6 was formed by the wet etching process by the etching liquid 3 of Example 1 mentioned above.

Next, a process for manufacturing the solar power generation apparatus shown in FIGS. 7-1 and 7-2 using the above-described silicon substrate 5 will be described. In addition, since the process demonstrated here is the same as the manufacturing process of the solar power generation device using a general single crystal silicon substrate, it does not show in particular in figure.

The P-type silicon substrate 5 that has been subjected to the wet etching process of Example 1 described above is put into a thermal oxidation furnace and heated in the presence of phosphorus oxychloride (POCl ₃ ) vapor to form phosphorus glass on the surface of the silicon substrate 5. By forming, phosphorus is diffused in the silicon substrate, and an N layer 7 a which is an N-type conductive layer is formed on the surface layer of the silicon substrate 5.

Next, after removing the phosphorous glass layer of the silicon substrate 5 in a hydrofluoric acid solution, a silicon nitride film (SiN film) is formed as an antireflection film 8 by plasma CVD on the N layer 7a, and the formation area of the light receiving surface side electrode 9 Except for forming. The film thickness and refractive index of the antireflection film 8 are set to values that most suppress light reflection. Note that two or more layers having different refractive indexes may be stacked. The antireflection film 8 may be formed by a different film forming method such as a sputtering method.

Next, a paste mixed with silver is printed on the light receiving surface of the silicon substrate 5 in a comb shape by screen printing, and a paste mixed with aluminum is printed on the entire back surface of the silicon substrate 5 by screen printing, followed by a baking process. To form the light receiving surface side electrode 9 and the back surface electrode 10. As described above, the photovoltaic power generation apparatus shown in FIGS. 7-1 and 7-2 is manufactured as the photovoltaic power generation apparatus of the first embodiment.

Next, the produced solar power generation device was actually operated, and the power generation characteristics were measured and evaluated. As a result, photoelectric conversion efficiency η (%), open circuit voltage Voc (V), short circuit current Isc (mA / cm ² ), fill factor F.V. F. Is shown in Table 1.

Moreover, as a solar power generation device of Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, the above Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 were used. A 156 cm square solar power generation device was produced using a silicon substrate. And these solar power generation devices were actually operated, and the power generation characteristics were measured and evaluated. As a result, photoelectric conversion efficiency η (%), open circuit voltage Voc (V), short circuit current Isc (mA / cm ² ), fill factor F.V. F. Is also shown in Table 1.

As can be seen from Table 1, in the photovoltaic power generation apparatus according to Example 1, the photoelectric conversion efficiency η is 0.6% compared to Comparative Example 1, 0.4% compared to Comparative Example 2, and Comparative Example 3 Compared to 0.6%, the photoelectric conversion efficiency is improved. By adding a combination of EDTA and ethanolamine as chelating agents to the etchant 3, the reflection loss of the silicon substrate after the wet etching process is suppressed and the quality of the texture structure on the surface of the silicon substrate is enhanced. Therefore, by using the silicon substrate having a texture formed on the surface of the substrate by the wet etching method according to the first embodiment, the solar power generation device is configured to effectively suppress the reflection loss on the surface of the silicon substrate. It was found that it increased and contributed to the improvement of photoelectric conversion efficiency.

Further, as can be seen from Table 1, in the photovoltaic power generation apparatus according to Example 3, the photoelectric conversion efficiency η is 0.5% compared to Comparative Example 1, 0.5% compared to Comparative Example 3, and Comparative Example Compared to 4, the photoelectric conversion efficiency is improved. By adding a combination of EDTA and ethylenediamine as chelating agents to the etchant 3, the reflection loss of the silicon substrate after the wet etching process is suppressed and the quality of the texture structure on the silicon substrate surface is improved. Therefore, by using the silicon substrate having a texture formed on the surface of the substrate by the wet etching method according to Example 3, the solar power generation apparatus is configured to suppress the reflection loss on the surface of the silicon substrate as in Example 1. As a result, it was found that the short-circuit current increases and contributes to the improvement of photoelectric conversion efficiency.

In the photovoltaic power generation apparatus of the third embodiment, the PN junction is formed by the thermal diffusion method on the silicon substrate having the texture structure formed by the method of the first embodiment or the second embodiment, but instead of the thermal diffusion method. A thin film doped with impurities may be deposited on a silicon substrate having a texture structure to form a PN junction. For example, a heterojunction solar cell including an amorphous thin film in which an impurity having a conductivity opposite to that of the substrate is added on a crystal substrate may be used. The substrate may be N-type and an impurity added layer may be P-type.

As described above, the silicon substrate etching method according to the present invention is excellent in etching quality stability and useful for etching a silicon substrate capable of good quality etching.

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Etching tank 3 Etching liquid 4 Hydrogen gas 5 Silicon substrate after etching process 6 Texture 7 Semiconductor substrate 7a N layer 8 Antireflection film 9 Light-receiving surface side electrode

9a Grid electrode

9b Bus electrode 10 Back electrode

Claims

A method for etching a silicon substrate, comprising supplying an alkaline aqueous solution to the surface of the silicon substrate and anisotropically etching the surface of the silicon substrate by wet etching,
The alkaline aqueous solution contains an alkylamine having a hydroxyl group and a compound having an amino group and a carboxyl group;
A method for etching a silicon substrate.
The alkaline aqueous solution contains the alkylamine having a hydroxyl group in a range of 0.01 wt-1.00 wt% and the compound having an amino group and a carboxyl group in a range of 0.05 wt-0.80 wt%. thing,
The method for etching a silicon substrate according to claim 1.
The alkaline aqueous solution includes an alcohol additive represented by the following chemical formula (1) or a surfactant having an HLB value of 10 or more, and forms a texture on the surface of the silicon substrate;
The method for etching a silicon substrate according to claim 1, wherein:
X- (OH) n (1)
(X is a saturated or unsaturated hydrocarbon group having 4 to 7 carbon atoms, n is an integer of 1 or more, n <Cn)
A method for etching a silicon substrate, comprising supplying an alkaline aqueous solution to the surface of the silicon substrate and anisotropically etching the surface of the silicon substrate by wet etching,
The aqueous alkali solution contains a compound having an amino group and a carboxyl group and an organic amine not having a hydroxyl group;
A method for etching a silicon substrate.
The alkaline aqueous solution contains the compound having an amino group and a carboxyl group and the organic amine not having a hydroxyl group in a range of 0.05 wt% to 1.00 wt%;
The method of etching a silicon substrate according to claim 4.
The organic amine having no hydroxyl group is a compound having a molecular structure having 6 or less carbon atoms per nitrogen atom,
The method for etching a silicon substrate according to claim 4 or 5, wherein:
The alkaline aqueous solution includes an alcohol-based additive represented by the following chemical formula (2) or a surfactant having an HLB value of 10 or more, and forms a texture on the surface of the silicon substrate.
The method for etching a silicon substrate according to any one of claims 4 to 6, wherein:
X- (OH) n (2)
(X is a saturated or unsaturated hydrocarbon group having 4 to 7 carbon atoms, n is an integer of 1 or more, n <Cn)
An etchant for anisotropically etching the surface of the silicon substrate by supplying to the surface of the silicon substrate by wet etching,
Containing an alkylamine having a hydroxyl group as a main component of an alkaline aqueous solution and a compound having an amino group and a carboxyl group;
Etching solution for silicon substrate characterized by
An etchant for anisotropically etching the surface of the silicon substrate by supplying to the surface of the silicon substrate by wet etching,
Comprising an alkaline aqueous solution as a main component and a compound having an amino group and a carboxyl group and an organic amine not having a hydroxyl group;
Etching solution for silicon substrate characterized by
Forming a semiconductor layer having a conductivity type opposite to that of the silicon substrate on the conductive silicon substrate etched by the etching method according to any one of claims 1 to 7;
A method for manufacturing a solar cell.