TW201214548A - Texturing of multi-crystalline silicon substrates - Google Patents

Abstract

Etching solutions for etching and texturing of multi-crystalline silicon substrates, particularly for use as solar cells or photovoltaic devices are described. The solutions of the present invention provide more consistent and uniform texturing over the entire life of the solution, resulting in fewer discarded wafers, increased reliability and yield and lower costs. The etching solutions HF/HNO3/H2O solutions having silicon dissolved therein.

Description

201214548 VI. Description of the Invention: [Technical Field] The present invention relates to an improved chemical substance and method for use in a button pattern of a polycrystalline substrate which is particularly useful as a solar cell or a photovoltaic cell. [Prior Art] It is known to improve the efficiency of the device by reducing the reflectance of incident sunlight on solar cells and photovoltaic devices. A common method for reducing the reflectance is to use, for example, yttrium oxide, tantalum nitride or titanium oxide. Anti-Reflective Coating (ARC) Coating Shishi Substrate β However, these films exhibit a resonant structure that limits effectiveness to small angles and wavelength ranges, such that the reflectance becomes very dependent on the angle of incidence and wavelength of the light. Another way to reduce reflectivity and improve device efficiency is to wet the surface of the stone wafer using a wet chemical button to form a small structure that often has a tapered shape. These structures provide a higher level of light entrapment due to multiple scattering. Based on geometric optics, the button pattern should be made to be equal to or greater than the wavelength of the light of the incident light to reflect the incident light multiple times and thereby enhance the amount of absorption. For single crystal germanium substrates, the etching process is generally carried out using a mixture of potassium hydroxide (hydrazine) or sodium hydroxide (NaOH) and isopropanol (hydrazine) in deionized (DI) water as an etchant. IPA is added to mask a particular germanium site to prevent etching by the solution to thereby form a tapered structure. It has also been reported that the combination of ιρΑ with an aqueous alkaline glycol solution produces a more uniform cone etch on the highly polished stone (100) used in semiconductor electronic applications. However, alkaline etching solutions are generally not suitable for etching polycrystalline germanium substrates. This is because the etch rate of the alkaline solution is strongly dependent on the orientation of the crystal face exposed to the etched 156290.doc 201214548 solution. For example, the Si (111) oriented alkaline etch rate is less than 2 orders of magnitude lower than the other directional etch rates, such that the substrate is a (100) single crystal. The resulting structure appears to have ((1)) orientation. The four sides of the side wall are cones. This phenomenon is not true for the polycrystalline substrate, and 0 is that the enthalpy of each of the ruthenium grains in the substrate is different from each other and the reflectance cannot be easily obtained with a sufficient reduction in reflectance. Therefore, acid etching using a mixture of hydrofluoric acid and nitric acid (e.g., HF/HN〇3/H2〇) has been used to etch the polycrystalline germanium substrate. Isotropic etching does not rely on crystal orientation, but removes Shixia almost independently of the different orientations of the polycrystalline substrate. It has been found that as the etching solution ages, the uniformity and uniformity of the etched wafer are improved. Because the fresh etch solution does not provide a uniform and consistent etch, a large number of wafers may need to be discarded before the etch solution is added and it begins to provide acceptable uniformity and uniformity. Therefore, there is still a need in the art to further improve the etching of polycrystalline germanium substrates, particularly for use in solar cells and photovoltaic devices. In particular, there is still a need in the art to improve production consistency and performance throughout the life of the etching solution. SUMMARY OF THE INVENTION The present invention provides chemistries and methods for etching etches, particularly for use in solar cells or photovoltaic devices. The solution of the present invention provides a more consistent and uniform etched pattern throughout the lifetime, with the result that the number of discarded wafers is reduced at a lower level of 4 and thus increases reliability and yield. [Embodiment] The present invention relates to an improved chemical solution for etching etched substrates, particularly for use in solar cells or photovoltaic devices, 156290.doc 5? 201214548. The solution of the present invention provides a more consistent and uniform etch over the life of the solution. The poor uniformity of the surface structure when using a fresh etching solution can be at least partially attributed to the relatively low concentration of dissolved Si in the solution. As the surname solution is reused (or aged), the subsequently processed wafer exhibits a more consistent reflectance, which leads us to believe that the difference in results between the fresh solution and the aged solution is the amount of dissolved ruthenium in the etching solution. Caused by. A chemical reaction for achieving a uniform and consistent etch according to the present invention is summarized below. In detail, isotropic etching and etching using HF/HN〇3/H2〇 as an etching solution was carried out according to the following chemical sequence. 3Si+4HN03+12HF-»3SiF4+4N0+8H20 This reaction can be divided into the following two. First, the oxidation of Shi Xizhi 3Si+4HN03->3Si02+4H0+2H20 followed by Si-0 bond cleavage

Si02+4HF-»SiF4+2H20 is accompanied by the formation of a water-soluble complex [SiF6]2·S1F4+2HF—0 according to the following formula in order to maintain consistency and uniformity throughout the life of the etching solution, either at the beginning or in the etching solution When fresh, it is necessary to have sufficient Si-containing ions in the solution. Therefore, according to the present invention, the Si-containing ions are made part of the surname solution before the isotropic cooking for the first time to improve the generation of the polycrystalline stone. The present invention provides a higher concentration of Si-containing ions in the new 156290.doc 201214548 by dissolving Shi Xi in HFmN03. Alternatively, hexaic acid can be added to HF/HN03 to increase stability and consistency. However, the amount of excess dissolved hydrazine should be carefully monitored' because excessive dissolution of hydrazine can adversely affect the etch rate and quality. Therefore, according to the present invention, the concentration of ruthenium is maintained within the range of 4 to 3 Å g/l of etching solution. The effect of dissolving cerium in the etching solution of the polycrystalline ruthenium substrate according to the present invention is improved uniformity and uniformity. In particular, superior results were achieved compared to the use of etching solutions that did not have dissolved enthalpy. In particular, the etch solution of the present invention provides a more uniform and uniform etch of the polysilicon substrate over the life of the etch solution, resulting in fewer wafers being discarded. Therefore, with the present invention, reliability and productivity are increased and a lower cost is obtained. The structure formed using the etching solution of the present invention is uniform and uniform, and the resulting etched substrate is particularly suitable for use in solar cells and photovoltaic devices. Other embodiments and variations of the present invention are expected to be readily apparent to those skilled in the art in light of the foregoing description, and such embodiments and variations are also included in the scope of the invention as claimed in Within the scope of the invention. 156290.doc

Claims (1)

201214548 VII. Patent Application Range: 1. A wet chemical solution for etching a polycrystalline germanium substrate comprising a hf/hno3 solution having dissolved germanium. 2. The wet chemical solution of claim 1 'where the concentration of dissolved cesium is between 4 • g/Ι and 30 gA. 3. The wet chemical solution of claim 1 further comprising hexafluoroantimonic acid. 4. A method of etching a polycrystalline germanium substrate, comprising: engraving the substrate with a surnamed solution of HF/HNO3 having dissolved germanium. 5. The method of claim 4, wherein the dissolved cesium concentration is between 4 §/1 and 3 〇 g/1. 6. The method of claim 4, wherein the etching solution further comprises hexafluoroantimonic acid. 7. An etched polycrystalline germanium substrate formed by etching a polycrystalline germanium substrate using an etching solution comprising a HF/HNO3 solution having dissolved germanium. 8. The substrate of claim 7, wherein the dissolved hydrazine concentration is between 4 μ and % g/Ι. 9. The substrate of claim 7, wherein the etching solution further comprises hexafluoroantimonic acid. 0 156290.doc 201214548 IV. Designated representative diagram (1) The representative representative of the case is: (none) (2) Brief description of the component symbol ·· 5. If there is a chemical formula in this case, please disclose the chemical formula that best shows the characteristics of the invention: (none) 156290.doc