A method of anisotropic etching of crystalline silicon

Abstract

The application discloses a crystal silicon anisotropic etching method, belongs to the technical field of new materials, and can be used for preparing a micro-nano scale pyramid structure on a crystal silicon surface. The method is simple and easy to implement, does not need to add a strong oxidant such as hydrogen peroxide or copper ions in a hydrofluoric acid etching solution, has low cost, and the prepared large-area micro-nano scale pyramid suede has the same pyramid suede structure as that generated by industrial alkali etching and has excellent light absorption performance.

Description

Technical Field

[0001] This invention relates to an anisotropic etching method for crystalline silicon, belonging to the field of new materials technology. Background Technology

[0002] The fabrication of pyramidal textures on crystalline silicon surfaces plays a crucial role in improving the photoelectric conversion efficiency of crystalline silicon photovoltaic devices. For nearly half a century, the etching methods for creating pyramidal structures on crystalline silicon surfaces have primarily relied on alkaline solutions such as sodium hydroxide, potassium hydroxide, and tetramethylammonium hydroxide [see: Chinese Patent CN201310562781.9] or tetramethylammonium hydroxide etching solution [see: Chinese Patent ZL200410017032.9]. Using precious metals such as silver or gold as catalysts, highly anisotropic etching of silicon can also be achieved in hydrofluoric acid containing oxidants, allowing for the fabrication of large-area silicon nanowires and other micro / nano structures on the silicon surface [see: Chinese Patent ZL02104179.2; Chinese Patent Application No. ZL200510011753.3]. Researchers have used a mixed etching solution of copper nitrate, hydrogen peroxide, and hydrofluoric acid to etch an inverted pyramid textured structure onto the surface of crystalline silicon [see: Y. Wang, LX Yang, YPLiu, ZX Mei, W. Chen, JQ Li, HL Liang, A. Kuznetsov, XL Du, Maskless inverted pyramid texturization of silicon. Sci. Rep., 2015, 5, 10843]. During the etching process, a large amount of copper is deposited on the silicon surface, and the resulting inverted pyramid surface is rough. In recent years, we have invented an anisotropic wet etching method for crystalline silicon. Hydrofluoric acid containing soluble copper salts can anisotropically etch crystalline silicon, forming a large-area positive pyramid textured structure on the surface of crystalline silicon (100). This method does not require the addition of oxidants such as hydrogen peroxide or nitric acid and is simple and easy to implement [see: Chinese Patent ZL201710127031.7]. However, the above methods result in a large amount of metallic copper particles being deposited on the surface of the crystalline silicon during the etching process. Summary of the Invention

[0003] The purpose of this invention is to provide an anisotropic etching method for crystalline silicon. This method utilizes a hydrofluoric acid solution containing ferric chloride to anisotropically etch crystalline silicon, enabling the fabrication of large-area positive pyramid array structures on the surface of crystalline silicon (100). This method does not require the addition of copper ions or other oxidizing agents such as hydrogen peroxide or nitric acid, making it safe, simple, and easy to operate. Because the acidic etching solution does not contain easily deposited copper and silver ions, the pyramid surfaces prepared using this method are smooth, free of metal particle deposition, and have an average reflectivity of 5%–15%, showing promising applications in photovoltaics and other fields.

[0004] This invention proposes an anisotropic etching method for crystalline silicon, characterized by the following steps:

[0005] (1) Place the cleaned crystalline silicon wafer into a container containing a mixed solution of ferric chloride and hydrofluoric acid, and react at 20-80℃ for 1-24 hours. Then, immerse the etched crystalline silicon wafer in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove the residual metal ions on the surface.

[0006] The crystalline silicon wafers used in the above steps are monocrystalline and polycrystalline silicon wafers, with ferric chloride concentration of 0.005-1.0 mol / L and hydrofluoric acid concentration of 0.5-20.0 mol / L. Attached Figure Description

[0007] Figure 1 This is a topographic image of a pyramidal structure prepared on a single-crystal silicon (100) crystal plane according to the present invention. Detailed Implementation

[0008] This invention utilizes anisotropic etching of crystalline silicon with a hydrofluoric acid solution containing ferric chloride to fabricate pyramids on the surface of crystalline silicon (100). The invention is further illustrated below with reference to specific examples:

[0009] Example 1

[0010] The cleaned monocrystalline silicon wafer is placed in a polytetrafluoroethylene container containing a mixed solution of 0.005 mol / L ferric chloride and 3.0 mol / L hydrofluoric acid and reacted at 50°C for 60 minutes to obtain a pyramidal textured surface on the crystalline silicon. Then, the etched crystalline silicon wafer is immersed in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove residual metal ions from the surface.

[0011] Example 2

[0012] The cleaned monocrystalline silicon wafer is placed in a polytetrafluoroethylene container containing a mixed solution of 0.01 mol / L ferric chloride and 5.0 mol / L hydrofluoric acid and reacted at 25°C for 5 hours to obtain a pyramidal textured surface on the crystalline silicon. Then, the etched crystalline silicon wafer is immersed in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove residual metal ions from the surface.

[0013] Example 3

[0014] The cleaned monocrystalline silicon wafer is placed in a polytetrafluoroethylene container containing a mixed solution of 0.1 mol / L ferric chloride and 5.0 mol / L hydrofluoric acid and reacted at 25°C for 10 hours to obtain a pyramidal textured surface on the crystalline silicon. Then, the etched crystalline silicon wafer is immersed in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove residual metal ions from the surface.

[0015] Example 4

[0016] The cleaned monocrystalline silicon wafer is placed in a polytetrafluoroethylene container containing a mixed solution of 0.2 mol / L ferric chloride and 10.0 mol / L hydrofluoric acid and reacted at 25°C for 20 hours to obtain a pyramidal textured surface on the crystalline silicon. Then, the etched crystalline silicon wafer is immersed in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove residual metal ions from the surface.

[0017] Example 5

[0018] The cleaned monocrystalline silicon wafer is placed in a polytetrafluoroethylene container containing a mixed solution of 0.5 mol / L ferric chloride and 10.0 mol / L hydrofluoric acid and reacted at 25°C for 24 hours to obtain a pyramidal textured surface on the crystalline silicon. Then, the etched crystalline silicon wafer is immersed in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove residual metal ions from the surface.

[0019] Example 6

[0020] The cleaned monocrystalline silicon wafer is placed in a polytetrafluoroethylene container containing a mixed solution of 1.0 mol / L ferric chloride and 20.0 mol / L hydrofluoric acid and reacted at 25°C for 12 hours to obtain a pyramidal textured surface on the crystalline silicon. Then, the etched crystalline silicon wafer is immersed in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove residual metal ions from the surface.

[0021] Example 7

[0022] The cleaned monocrystalline silicon wafer is placed in a polytetrafluoroethylene container containing a mixed solution of 0.1 mol / L ferric chloride and 20.0 mol / L hydrofluoric acid and reacted at 25°C for 12 hours to obtain a pyramidal textured surface on the crystalline silicon. Then, the etched crystalline silicon wafer is immersed in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove residual metal ions from the surface.

[0023] The specific embodiments described above are merely illustrative and not intended to limit the invention. Any person skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the claims, and such modifications or alterations shall all fall within the protection scope of this invention.

Claims

1. A method of anisotropic etching of crystalline silicon, characterized in that, include: Place the cleaned crystalline silicon wafer into a container containing a mixed solution of ferric chloride and hydrofluoric acid, and react at 20-80℃ for 1-24 hours. Then, immerse the etched crystalline silicon wafer in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to remove residual metal ions from the surface. The concentration of ferric chloride is 0.005-1.0 mol / L, and the concentration of hydrofluoric acid is 0.5-20.0 mol / L. The above method uses a hydrofluoric acid solution containing ferric chloride to anisotropically etch crystalline silicon, thereby preparing a large-area positive pyramid array structure on the surface of crystalline silicon. It does not require the addition of copper ions or other oxidants, and is safe, simple and easy to operate. Since the acidic etching solution does not contain easily deposited copper and silver ions, the surface of the pyramid prepared by etching is smooth and free of metal particle deposition, with an average reflectivity of 5% to 15%, which can be applied to optoelectronic devices.

2. The anisotropic etching method for crystalline silicon according to claim 1, wherein the crystalline silicon wafer is a monocrystalline or polycrystalline silicon wafer.

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