Etching solution for etching back copper seed layer and preparation method and application thereof

Abstract

The invention belongs to the technical field of solar cells, and provides an etching solution for copper seed layer etch-back and a preparation method and application thereof. The etching liquid for etching back the copper seed layer is prepared from the following components in parts by mass: 1.5 to 2.5 parts of potassium hydrogen persulfate composite salt, 0.8 to 1.2 parts of concentrated sulfuric acid, 0.02 to 0.03 part of benzimidazole compound, 0.01 to 0.02 part of organic sulfur compound and 100 parts of water. According to the etching solution for etching back the copper seed layer, a compound corrosion inhibitor benzimidazole compound and an organic sulfur compound are introduced into a potassium hydrogen persulfate compound salt etching solution system, so that full-coverage protection on the surface of a copper electrode can be realized, and the lateral erosion phenomenon of an acidic corrosive agent on the copper electrode of a solar cell can be effectively inhibited; and the corrosion inhibition capability of a copper electrode can be improved, and selective adsorption protection can be provided for a silicon-based solar cell copper grid line.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly relates to an etching solution for copper seed layer etchback, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, heterojunction (HJT) solar cells have become the focus of the industry due to their excellent passivation performance, high conversion efficiency, and the advantage of low-temperature processing. In terms of the metal electrodes used in such solar cells, copper, as a metal with low cost and low resistivity, has become an ideal choice to replace traditional silver electrodes. Copper plating is an ideal alternative solution for the electrodes of diffused solar cells, which has high conductivity and narrow electrode shadow loss. Therefore, by adopting electroplated copper grid lines, not only can the production cost be reduced, but also the grid line width can be reduced, thereby reducing the light-shielding area and improving the cell efficiency. Currently, the preparation process of copper-plated electrodes includes steps such as depositing a copper seed layer, electrode patterning, electroplating a copper electrode, and etchback of the seed layer. Among them, the etchback of the seed layer adopts a wet etching process, and the purpose is to remove the residual copper seed layer to achieve the selective formation of the electrode. However, in the actual process of copper seed layer etchback, the etching solution will cause bottom side etching (undercut) when etching the seed layer, resulting in defects such as pinholes and pits on the surface of the copper electrode due to uneven etching. These defects not only seriously affect the adhesion between the copper electrode and the battery substrate material, but also have an adverse effect on the cell efficiency. The reason for this is the inherent isotropic characteristic of wet etching, which causes copper to undergo lateral erosion while etching longitudinally, thereby forming an undercut effect, significantly weakening the bonding force between the copper grid and the battery base layer and the electrode contact stability.

[0003] Currently, the photovoltaic industry mostly uses a potassium peroxymonosulfate composite salt solution system as the etching solution for copper seed layer etchback. This system mainly includes a mixed solution of potassium peroxymonosulfate composite salt (KHSO5·0.5KHSO4·0.5K2SO4) and concentrated sulfuric acid (H2SO4), which has good stability under acidic conditions. However, during the copper electroplating process, copper growth tends to preferentially grow along low-energy crystal planes, and the lateral growth rate is slower, resulting in high-energy crystal planes or non-ideal orientations being retained on the sidewalls, thereby causing dislocation or grain boundary enrichment on the sidewalls of the copper electrode. The atoms on the high-energy crystal planes of the sidewalls have weak bonding and are more easily attacked by etchants (such as KHSO5 / H2SO4), further amplifying the defect density, and thus the bottom side etching phenomenon is more serious.

[0004] Therefore, it is of great significance to provide an etching solution that can effectively inhibit the side etching phenomenon while ensuring efficient etching to thoroughly remove the residual copper seed layer. Summary of the Invention

[0005] In view of this, the present invention provides an etching solution for copper seed layer etch-back, its preparation method and application, so as to solve the problem that it is difficult to inhibit the side etching phenomenon while removing the residual copper seed layer with the existing etching solution.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides an etching solution for copper seed layer etch-back, comprising the following components in parts by mass: Potassium peroxymonosulfate compound 1.5 - 2.5 parts, concentrated sulfuric acid 0.8 - 1.2 parts, benzimidazole compound 0.02 - 0.03 parts, organic sulfur compound 0.01 - 0.02 parts, water 100 parts.

[0007] Preferably, the benzimidazole compound includes one or more of 5-methylbenzimidazole, benzotriazole, 2-mercaptobenzimidazole and 5-chlorobenzimidazole; the organic sulfur compound includes one or more of thiourea, 2,5-dimercapto-1,3,4-thiadiazole and sodium dimethyldithiocarbamate.

[0008] Preferably, the mass concentration of sulfuric acid in the etching solution for copper seed layer etch-back is 0.75 - 1.20%.

[0009] The present invention also provides a preparation method of the above-mentioned etching solution for copper seed layer etch-back, comprising the following steps: Mix potassium peroxymonosulfate compound, concentrated sulfuric acid, benzimidazole compound, organic sulfur compound and water to obtain the etching solution for copper seed layer etch-back.

[0010] The present invention also provides an application of the etching solution for copper seed layer etch-back prepared by the above preparation method in removing the residual copper seed layer of a copper grid heterojunction solar cell, and the method of the application comprises the following steps: Immerse the electroplated copper cell wafer into the etching solution for copper seed layer etch-back for reaction to complete the removal of the residual copper seed layer of the copper grid heterojunction solar cell.

[0011] Preferably, the temperature of the reaction is 24 - 28 °C and the time is 80 - 100 s.

[0012] It can be seen from the above technical solutions that compared with the prior art, the beneficial effects of the present invention are as follows: In the present invention, a composite corrosion inhibitor, namely benzimidazole compound and organic sulfur compound, is introduced into the potassium peroxymonosulfate composite salt etching solution system. During the back-etching process of the copper seed layer, the N atom in the benzimidazole compound is preferentially adsorbed on the active crystal plane of the side wall of the copper electrode, while the S atom in the organic sulfur compound occupies the area not covered by the benzimidazole compound (such as grain boundaries or defect sites), forming a synergistic protective layer with the benzimidazole compound to achieve full coverage protection of the copper electrode surface. It can effectively inhibit the side-etching phenomenon of the acidic etchant on the copper electrode of the solar cell, and can also improve the corrosion inhibition ability of the copper electrode, providing selective adsorption protection for the copper grid line of the silicon-based solar cell. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0014] Figure 1 It is a cross-sectional view of the copper electrode of the battery wafer after removing the residual copper seed layer by the etching solution for back-etching the copper seed layer prepared in Example 1 of the present invention; Figure 2 It is a cross-sectional view of the copper electrode of the battery wafer after removing the residual copper seed layer by the etching solution for back-etching the copper seed layer prepared in Comparative Example 1 of the present invention. Detailed Embodiments

[0015] The present invention provides an etching solution for back-etching a copper seed layer, which comprises the following components in parts by mass: 1.5 - 2.5 parts of potassium peroxymonosulfate composite salt, 0.8 - 1.2 parts of concentrated sulfuric acid, 0.02 - 0.03 parts of benzimidazole compound, 0.01 - 0.02 parts of organic sulfur compound, and 100 parts of water.

[0016] In the present invention, the potassium peroxymonosulfate composite salt is preferably 1.8 - 2.3 parts, more preferably 1.9 - 2.1 parts, and still more preferably 2.0 parts; the concentrated sulfuric acid is preferably 0.85 - 1.1 parts, more preferably 0.9 - 1.05 parts, and still more preferably 1.0 parts; the benzimidazole compound is preferably 0.022 - 0.028 parts, more preferably 0.023 - 0.026 parts, and still more preferably 0.025 parts; the organic sulfur compound is preferably 0.012 - 0.018 parts, more preferably 0.013 - 0.017 parts, and still more preferably 0.015 parts.

[0017] In the present invention, the benzimidazole compounds include one or more of 5-methylbenzimidazole, benzotriazole, 2-mercaptobenzimidazole, and 5-chlorobenzimidazole, preferably 5-methylbenzimidazole; the organic sulfur compounds include one or more of thiourea, 2,5-dimercapto-1,3,4-thiadiazole, and sodium dimethyldithiocarbamate, preferably thiourea.

[0018] In the present invention, the mass concentration of sulfuric acid in the etchant for copper seed layer etch-back is 0.75 - 1.20%, preferably 0.80 - 1.15%, further preferably 0.85 - 1.10%, and more preferably 0.90 - 1.0%.

[0019] In the present invention, the mass concentration of concentrated sulfuric acid is preferably 98%.

[0020] In the present invention, the benzimidazole compounds and organic sulfur compounds in the etchant for copper seed layer etch-back act as corrosion inhibitors and can effectively inhibit the corrosion of the metal surface in the corrosive medium.

[0021] The present invention also provides a preparation method of the above-mentioned etchant for copper seed layer etch-back, which includes the following steps: Mix potassium peroxymonosulfate compound, concentrated sulfuric acid, benzimidazole compounds, organic sulfur compounds, and water to obtain the etchant for copper seed layer etch-back.

[0022] The present invention also provides an application of the etchant for copper seed layer etch-back prepared by the above-mentioned preparation method in removing the residual copper seed layer of a copper grid heterojunction solar cell. The method of the application includes the following steps: Immerse the electroplated copper cell wafer into the etchant for copper seed layer etch-back for reaction to complete the removal of the residual copper seed layer of the copper grid heterojunction solar cell.

[0023] In the present invention, the temperature of the reaction is 24 - 28°C, preferably 25 - 27°C, and more preferably 26°C; the time of the reaction is 80 - 100 s, preferably 82 - 96 s, further preferably 85 - 92 s, and more preferably 90 s.

[0024] In the present invention, after the reaction is completed, it preferably further includes an operation of rinsing with water to make the surface of the cell wafer free of residual etchant.

[0025] The following combines examples to detail the technical solutions provided by the present invention, but they cannot be construed as limiting the protection scope of the present invention.

[0026] Example 1

[0027] Mix 2 parts of potassium monopersulfate compound salt (Sinopharm Group, analytical pure, 500 g / bottle, CAS: 70693-62-8), 1 part of concentrated sulfuric acid with a mass concentration of 98%, 0.025 part of 5-methylbenzimidazole, 0.015 part of thiourea, and 100 parts of deionized water to obtain an etchant for copper seed layer etching-back. Among them, the mass concentration of sulfuric acid in the etchant for copper seed layer etching-back is 0.95%.

[0028] Example 2

[0029] Mix 1.5 parts of potassium monopersulfate compound salt (the same as in Example 1), 0.8 part of concentrated sulfuric acid with a mass concentration of 98%, 0.02 part of 5-methylbenzimidazole, 0.01 part of thiourea, and 100 parts of deionized water to obtain an etchant for copper seed layer etching-back. Among them, the mass concentration of sulfuric acid in the etchant for copper seed layer etching-back is 0.77%.

[0030] Example 3

[0031] Mix 2.5 parts of potassium monopersulfate compound salt (the same as in Example 1), 1.2 parts of concentrated sulfuric acid with a mass concentration of 98%, 0.03 part of 5-methylbenzimidazole, 0.02 part of thiourea, and 100 parts of deionized water to obtain an etchant for copper seed layer etching-back. Among them, the mass concentration of sulfuric acid in the etchant for copper seed layer etching-back is 1.16%.

[0032] Comparative Example 1 Mix 2 parts of potassium monopersulfate compound salt (the same as in Example 1), 1 part of concentrated sulfuric acid with a mass concentration of 98%, and 100 parts of deionized water to obtain an etchant for copper seed layer etching-back. Among them, the mass concentration of sulfuric acid in the etchant for copper seed layer etching-back is 0.95%.

[0033] Experimental Example Immerse the electroplated copper solar cells into the etchants for copper seed layer etching-back prepared in Example 1 and Comparative Example 1 respectively, react at a temperature of 25 °C for 90 s, and after the reaction is completed, rinse with deionized water until there is no residual etchant on the surface of the solar cells, to complete the removal of the residual copper seed layer of the copper grid heterojunction solar cells.

[0034] After testing, after the solar cells immersed in the etchant for copper seed layer etching-back prepared in Example 1 complete the removal of the residual copper seed layer, the contact angle between the surface of the solar cells and water is 68.5º. After the solar cells immersed in the etchant for copper seed layer etching-back prepared in Comparative Example 1 complete the removal of the residual copper seed layer, the contact angle between the surface of the solar cells and water is 46.5º.

[0035] Figure 1Cross-sectional view of the copper electrode after removing the residual copper seed layer from the solar cell immersed in the etchant for copper seed layer etching prepared in Example 1. After measurement, the undercut value is: 16.60 - 16.06 = 0.54 μm.

[0036] Figure 2 Cross-sectional view of the copper electrode after removing the residual copper seed layer from the solar cell immersed in the etchant for copper seed layer etching prepared in Comparative Example 1. After measurement, the undercut value is: 17.78 - 13.70 = 4.08 μm.

[0037] In summary, it can be seen that in the seed layer etching process of the copper electrode of the solar cell, the etchant for copper seed layer etching prepared in Example 1 of the present invention can well balance the two key problems of side etching of the copper electrode and complete removal of the residual copper seed layer. While the copper seed layer is selectively removed, the corrosion of the copper electrode can be greatly reduced. Compared with the conventional process, a better corrosion inhibition effect is obtained on the surface of the copper electrode, the surface is smoother, and the contact angle with water is greatly increased, indicating that the corrosion defects are greatly reduced and the smoothness is significantly improved. At the same time, compared with the etchant without corrosion inhibitor, when using the etchant for copper seed layer etching prepared in Example 1 of the present invention to remove the residual copper seed layer of the copper grid heterojunction solar cell, the undercut value can be reduced from 4.08 microns to 0.54 microns, that is, the side etching phenomenon of the copper electrode is also greatly improved.

[0038] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An etching solution for copper seed layer etchback, characterized in that, It comprises components in the following parts by mass: 1.5 - 2.5 parts of potassium peroxymonosulfate compound salt, 0.8 - 1.2 parts of concentrated sulfuric acid, 0.02 - 0.03 parts of benzimidazole compound, 0.01 - 0.02 parts of organic sulfur compound, and 100 parts of water.

2. An etching solution for copper seed layer etchback, according to claim 1, characterized in that The benzimidazole compound includes one or more of 5 - methylbenzimidazole, benzotriazole, 2 - mercaptobenzimidazole, and 5 - chlorobenzimidazole; The organic sulfur compound includes one or more of thiourea, 2,5 - dimercapto - 1,3,4 - thiadiazole, and sodium dimethyldithiocarbamate.

3. An etching solution for copper seed layer etchback, according to claim 2, characterized in that, The mass concentration of sulfuric acid in the etchant for copper seed layer back - etching is 0.75 - 1.20%.

4. The preparation method of an etching solution for copper seed layer etchback according to any one of claims 1 to 3, characterized in that, It includes the following steps: Mix potassium peroxymonosulfate compound salt, concentrated sulfuric acid, benzimidazole compound, organic sulfur compound, and water to obtain the etchant for copper seed layer back - etching.

5. Use of the etching solution for copper seed layer etchback prepared by the preparation method according to claim 4 in removing the residual copper seed layer of a copper grid heterojunction solar cell, characterized in that, The application method includes the following steps: Immerse the electroplated copper cell in the etchant for copper seed layer back - etching to react and complete the removal of the residual copper seed layer of the copper grid heterojunction solar cell.

6. Use of the etching solution for copper seed layer etchback in removing the residual copper seed layer of a copper grid heterojunction solar cell, characterized in that, The temperature of the reaction is 24 - 28 °C, and the time is 80 - 100 s.

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