CN108400201A - A kind of lithographic method of polysilicon surface pyramid matte - Google Patents

Abstract

The present invention relates to a kind of lithographic methods of polysilicon surface pyramid matte, include the following steps：Polysilicon chip surface clean and damaging layer removal, the cleaning of polysilicon chip surface acid etch, polysilicon chip surface alkaline etching and silicon chip.The present invention is etched the preferable pyramid shape suede structure of pattern in polysilicon surface and is achieved good anti-reflective effect using acid+alkali two-step etching method.The average reflectance of polysilicon with pyramid shape matte is 11%.Compared to other lithographic methods, method of the present invention only with acid combined with alkali, without any additive, simple for process, easy to operate, controllability is good and pollution-free, is adapted to commercialization mode of manufacture.

Description

A kind of etching method of pyramid suede surface on polysilicon surface

technical field

The invention belongs to the field of surface structure treatment of polycrystalline silicon solar cells, and in particular relates to an etching method for the surface pyramid suede of a polycrystalline silicon wafer cut by mortar.

Background technique

Due to the depletion of fossil energy, it is urgent to find alternative energy to meet the needs of social development. The new energy industry dominated by the photovoltaic industry has been paid more and more attention by people for its advantages of no pollution and huge output. Especially in recent years, the solar cell industry has achieved rapid development. However, in commercial solar cell products, crystalline silicon (single crystal, polycrystalline, microcrystalline) solar cells account for the largest market share, nearly 90% of the market share. Due to the wide range of sources of materials for polycrystalline silicon solar cells, manufacturing The cost is lower, therefore, polycrystalline silicon solar cell technology has far surpassed monocrystalline and microcrystalline solar cells. To sum up, improving the efficiency of polycrystalline silicon solar cells is of great strategic significance for solving the energy crisis and environmental pollution.

There are many ways to improve polysilicon solar cells, and etching anti-reflection texture on the surface of polysilicon is the simplest and most effective way. Various anti-reflection textures can effectively reduce the surface reflection of solar cells rate, increase the light absorption, and then improve the photoelectric conversion efficiency.

In order to obtain a good textured structure on the surface of crystalline silicon solar cells to achieve a better anti-reflection effect, people have tried many methods, forming wet etching based on acid or lye and mechanical processing. dry etching. Commonly used methods include mechanical grooving, laser etching, and reactive ion etching (RIE). Although dry etching can obtain lower surface reflectivity, this method causes serious mechanical damage to the surface of the silicon wafer, and its yield is relatively low, and the dry etching process is relatively complicated, resulting in poor economic efficiency.

Due to the different crystal orientations on the surface of polysilicon, simple alkali etching cannot form a uniform and dense textured structure on the surface of polysilicon. However, the pit-like suede surface formed by acid etching cannot effectively reduce the reflectivity. Therefore, it is of great significance to find a simple and convenient etching method to etch a dense and uniform textured structure on the surface of polysilicon.

Contents of the invention

In view of the above problems, the invention provides a method for etching the pyramid textured surface of a polysilicon wafer, which is simple, convenient, and low in cost. The acid method and the alkali method are combined to successfully etch the pyramid textured surface on the polysilicon surface. , significantly improving the light absorption capacity of the polysilicon surface.

Technical solution: In order to achieve the above object, a method for etching a pyramid textured surface on a polysilicon surface of the present invention comprises the following steps:

Cleaning the surface of the polycrystalline silicon wafer and removing the damaged layer: cleaning the polycrystalline silicon wafer with deionized water and then placing it in a certain concentration of HF to remove the mechanically damaged layer on the surface;

Acid etching on the surface of the polycrystalline silicon wafer: configure an acid etching solution, place the configured acid etching solution under an ice bath for a period of time, then float the polycrystalline silicon wafer on the surface of the acid etching solution for etching for a period of time, Cleaning after etching;

Alkali etching on the surface of polycrystalline silicon wafers: configure an alkaline etching solution, place the configured alkaline etching solution in a water bath for a period of time, and then immerse the acid-etched polycrystalline silicon wafer in the alkaline etching solution for a period of etching. time;

Silicon wafer cleaning: After the alkali etching is completed, the polycrystalline silicon wafer is cleaned with a certain concentration of HF and then cleaned with deionized water.

In the above solution, the concentration of HF in the removal of the damaged layer is 5%, and the light etching time of the polysilicon wafer in the acid etching solution in the HF solution is 2-3 minutes.

In the above solution, the acid etching solution is a mixture of HF and HNO ₃ ; the volume ratio of HF and HNO ₃ is HF (40%):HNO ₃ (65-68%)=1:5.

In the above solution, the acid etching solution is placed in the ice bath for 15 minutes, and the etching time for the polycrystalline silicon wafer in the acid etching solution is 2 minutes.

In the above scheme, the alkaline etching solution is 0.5 mol/L NaOH solution.

In the above solution, the alkali etching solution is placed in a water bath at 50°C for 20-30 minutes, and the polycrystalline silicon wafer is etched in the alkali etching solution for 25-40 minutes.

In the above solution, the etching time of the polycrystalline silicon wafer in the alkaline etching solution is 40 minutes.

In the above solution, after the alkali etching of the polysilicon sheet is completed, it is cleaned with HF with a concentration of 5% to 8%.

Due to the adoption of the above-mentioned technical solution, compared with the prior art, the present invention has the following advantages:

1. In the present invention, the polycrystalline silicon wafer has no selective anisotropy to acid etching, so after acid etching, the surface of the silicon wafer is covered with a large number of corrosion pits, and the edges and corners between these corrosion pits are pyramid suede surface etched by alkali solution Nucleation conditions are provided. With the prolongation of the time of the polysilicon wafer in the alkali etching solution, the surface of the polysilicon is etched with a good pyramid texture. When the etching time of the polysilicon wafer in the alkali solution is 40min, the polysilicon The surface is covered by a large number of pyramids.

2. The present invention combines the existing acid etching and alkali etching technology to obtain the etching method of the pyramid textured surface on the polysilicon surface through a large number of experiments, and adopts the first acid etching solution to etch the silicon wafer surface to form a pit-shaped textured surface After cleaning, the pyramid structure is further etched in an alkali etching solution, and finally a pyramid texture structure more suitable for crystalline silicon solar cells is obtained. After testing, in sunlight with a wavelength of 300nm-1000nm, the average reflectance of the surface of the polycrystalline silicon prepared by the present invention is 11%, and the efficiency of the prepared complete polycrystalline silicon solar cell is also close to 18%.

3. The preparation method of the present invention is simple and easy to implement, has good compatibility with the existing industrial production process, and does not need to add any additives, effectively reducing the operating cost of the experiment. Suitable for promotional applications.

Description of drawings

Fig. 1 is a low-magnification scanning electron micrograph (scale bar is 30 μm) of a pyramid-like textured structure obtained under the condition of etching for 40 minutes according to the method provided by the implementation of the present invention.

Fig. 2 is a high-magnification scanning electron micrograph (scale bar is 3 μm) of a pyramid-like textured structure obtained under the condition of etching for 40 minutes according to the method provided by the implementation of the present invention.

Fig. 3 is a picture of the original silicon wafer and the reflectance measured by the method under the conditions of etching for 25 minutes, 35 minutes and 40 minutes.

Fig. 4 is a low-magnification scanning electron micrograph (scale bar is 30 μm) of the textured structure obtained under the condition of etching for 25 minutes according to the method provided by the implementation of the present invention.

Fig. 5 is a low-magnification scanning electron micrograph (scale bar is 30 μm) of the textured structure obtained under the condition of etching for 35 minutes according to the method provided by the implementation of the present invention.

Detailed ways

Below in conjunction with embodiment the present invention will be further described. The method for etching the pyramid texture on the polysilicon surface of the present invention adopts the method of acid+alkali corrosion, and by adjusting the etching time, the pyramid texture with better shape can be etched on the polysilicon surface.

The method for etching pyramid suede on the surface of polycrystalline silicon according to the present invention is realized through the following steps: cleaning the surface of polycrystalline silicon wafers and removing damaged layers, acid etching the surface of polycrystalline silicon wafers, alkali etching the surface of polycrystalline silicon wafers, and cleaning silicon wafers.

Surface cleaning of polycrystalline silicon wafers and removal of damaged layers: firstly, the polycrystalline silicon wafers are cleaned with deionized water in order to remove dust and impurities on the surface of the silicon wafers, and then the washed polycrystalline silicon wafers are cleaned with ethanol to remove oil stains on the surface of the silicon wafers. Afterwards, immerse the silicon wafer in a certain concentration of HF and clean it for 2 to 3 minutes to remove the mechanical damage layer on the surface of the silicon wafer, and then use a large amount of deionized cleaning to remove the residual HF on the surface of the silicon wafer several times. Wherein, the HF concentration for cleaning the silicon wafer is 5%, and after the cleaning is completed, a large amount of deionized water is used for cleaning to remove excess HF.

Acid etching on the surface of polycrystalline silicon wafers: prepare acid etching solution, prepare an appropriate amount of acid solution according to the ratio of volume ratio HF:HNO ₃ =1:5, and then place the acid etching solution in an ice bath environment for 15 minutes to reduce the amount of acid solution temperature. Float the cleaned silicon wafer on the surface of the acid etching solution for the first step of etching, and the etching time is 2 minutes. Then, the etched polysilicon wafer was cleaned with 5% NaOH solution to remove residual acid solution on the surface of the silicon wafer, then cleaned with a large amount of deionized water, and finally dried with nitrogen flow. Wherein the concentration of HF in the acid etching solution is 40%, the concentration of HN0 ₃ is 65%-68%, and no additives are added during the etching process.

Alkali etching on the surface of polycrystalline silicon wafers: configure 0.5mol/L NaOH solution as an alkali etching solution, and then place the alkali etching solution in a water bath at 50°C for 20-30 minutes to stabilize the temperature of the alkali etching solution at 50°C , and then immerse the acid-etched silicon wafer in alkali solution, and the etching time is 25-40 minutes.

Cleaning of the silicon wafer: After the etching is completed, the lye remaining on the surface of the silicon wafer is firstly cleaned with 5%-8% HF, then cleaned with deionized water, and finally blown dry with nitrogen flow.

Embodiment one:

A kind of etching method of pyramid textured surface on polysilicon surface comprises the following steps:

Surface cleaning of polysilicon wafers and removal of damaged layers: cut polysilicon wafers into 1cm ² size, clean the cut polysilicons with 5% HF and lightly etch them for 2-3 minutes to remove the mechanical damage layer on the surface.

Acid etching on the surface of polycrystalline silicon wafers: configure an acid etching solution with a volume ratio of HF:HNO ₃ =1:5, place the acid etching solution in an ice bath environment for 15 minutes, reduce the temperature of the etching solution, and then place the cleaned The polycrystalline silicon wafer is etched on the surface of the acid solution for 2 minutes, and then the acid etched polycrystalline silicon wafer is cleaned with a 5% NaOH solution to remove the residual acid solution on the surface of the silicon wafer, and then cleaned with a large amount of deionized water , and finally blow dry with nitrogen stream.

Alkali etching on the surface of polysilicon wafers: first prepare 5mol/L NaOH solution, place it in a water bath at 50°C for 20 to 30 minutes, make the temperature reach the set 50°C condition, and immerse the polysilicon wafer after acid etching Etched in alkaline etching solution for 40min.

Cleaning of silicon wafers: Clean the etched polysilicon wafers with 5% HF solution, then wash them with a large amount of deionized water to completely remove the residual acid or lye on the surface of the silicon wafers, and finally dry them with nitrogen flow. The SEM images of the finally formed silicon surface are shown in Figures 1 and 2, the polysilicon surface is covered by a large number of pyramids.

Embodiment two:

A kind of etching method of pyramid textured surface on polysilicon surface comprises the following steps:

Surface cleaning of polysilicon wafers and removal of damaged layer: cut the polysilicon wafers into 1cm ² size, clean the cut polysilicon and lightly corrode it with 5% HF for 2-3 minutes to remove the mechanical damage layer on the surface.

Acid etching on the surface of polycrystalline silicon wafers: Prepare an acid etching solution with a volume ratio of HF:HNO ₃ =1:5, place it in an ice bath environment for 15 minutes, reduce the temperature of the etching solution, and then float the cleaned polycrystalline silicon wafers Etching is performed on the surface of the acid solution for 2 minutes. Finally, the acid-etched polysilicon wafer is cleaned with a 5% NaOH solution to remove residual acid solution on the surface of the silicon wafer, then cleaned with a large amount of deionized water, and finally blown dry with a nitrogen stream.

Alkali etching on the surface of polycrystalline silicon wafers: first prepare 5mol/L NaOH solution, place it in a water bath at 50°C for 20-30min, and make the temperature reach the set 50°C condition. The acid-etched polysilicon wafer was immersed in an alkali etching solution and etched for 25 minutes.

Cleaning of silicon wafers: Clean the etched polysilicon wafers with 5% HF solution, then wash them with a large amount of deionized water to completely remove the residual acid or lye on the surface of the silicon wafers, and finally dry them with nitrogen flow. The SEM image of the finally formed silicon surface is shown in Figure 4. It can be seen from the figure that after the polysilicon wafer is etched in alkaline etching solution for 25 minutes, the depth of the pit-like structure on the surface decreases, but small pyramid nuclei appear on the ridges of the pit-like structure. This is due to the anisotropy of lye to polysilicon.

Embodiment three:

A kind of etching method of pyramid textured surface on polysilicon surface comprises the following steps:

Surface cleaning of polysilicon wafers and removal of damaged layer: cut the polysilicon wafers into 1cm ² size, clean the cut polysilicon and lightly corrode it with 5% HF for 2-3 minutes to remove the mechanical damage layer on the surface.

Acid etching on the surface of the polycrystalline silicon wafer: Prepare an etching solution with a volume ratio of HF:HNO ₃ =1:5, place it in an ice bath environment for 15 minutes, and lower the temperature of the etching solution. Then float the cleaned polysilicon wafer on the surface of the acid solution for etching for 2 minutes. Finally, the acid-etched polysilicon wafer is cleaned with a 5% NaOH solution to remove residual acid solution on the surface of the silicon wafer, then cleaned with a large amount of deionized water, and finally blown dry with a nitrogen stream.

Alkali etching on the surface of polycrystalline silicon wafers: first prepare 5mol/L NaOH solution, place it in a water bath at 50°C for 20-30min, and make the temperature reach the set 50°C condition. The acid-etched polysilicon wafer was immersed in an alkali etching solution and etched for 35 minutes.

Cleaning of silicon wafers: Clean the etched polysilicon wafers with 5% HF solution, then wash them with a large amount of deionized water to completely remove the residual acid or lye on the surface of the silicon wafers, and finally dry them with nitrogen flow. The SEM image of the finally formed silicon surface is shown in Figure 5. It can be seen from the figure that as time goes on, the pyramid-shaped nuclei on the polysilicon surface begin to grow and overlap each other.

It can be seen from FIG. 1 , FIG. 3 , FIG. 4 and FIG. 5 that the method provided by the implementation of the present invention can obtain a better pyramid texture on the polysilicon surface and obviously reduce the reflectivity. And as the etching time changes, the morphology of the polysilicon surface also changes. When the etching time is 25 minutes, pyramidal nuclei appear on the polysilicon surface. When the etching time is extended to 35 minutes, the pyramidal nuclei begin to grow. And become dense, further extend the time to 40min, the pyramids grow further and separate from each other. From the reflectance comparison in Figure 3, we can also see that the reflectance is the lowest when the etching time is 40 minutes. It shows that the pyramid structure can play a good role in reducing the reflectivity. In addition, the method of the present invention is novel and simple compared with other existing methods for etching polysilicon, and does not need to add any additives during the reaction process, which effectively reduces the cost of experimental operations. Therefore, it has good application and development prospects.

The above is a detailed description of the embodiments of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be It is regarded as the protection scope of the present invention.

Claims (8)

1. a kind of etching method of polysilicon surface pyramid suede is characterized in that, comprises the following steps: Cleaning the surface of the polycrystalline silicon wafer and removing the damaged layer: cleaning the polycrystalline silicon wafer with deionized water and then placing it in a certain concentration of HF to remove the mechanically damaged layer on the surface; Acid etching on the surface of the polycrystalline silicon wafer: configure an acid etching solution, place the configured acid etching solution under an ice bath for a period of time, then float the polycrystalline silicon wafer on the surface of the acid etching solution for etching for a period of time, Cleaning after etching; Alkali etching on the surface of polycrystalline silicon wafers: configure an alkaline etching solution, place the configured alkaline etching solution in a water bath for a period of time, and then immerse the acid-etched polycrystalline silicon wafer in the alkaline etching solution for a period of etching. time; Silicon wafer cleaning: After the alkali etching is completed, the polycrystalline silicon wafer is cleaned with a certain concentration of HF and then cleaned with deionized water. 2. the preparation method of polysilicon surface pyramid suede structure according to claim 1 is characterized in that, the concentration of HF is 5% in the removal of described damage layer, and the HF solution of described polysilicon chip in acid etching solution The light etching time in the medium is 2~3min. 3. the preparation method of polysilicon surface pyramid structure according to claim 1, is characterized in that, described acid etching solution is HF and HNO ₃ mixed solution; HF and HNO ₃ volume ratios are HF:HNO ₃ = 1:5. 4. according to the preparation method of claim 1 or 3 described polycrystalline silicon surface pyramid structures, it is characterized in that, the time that described acid etching solution is placed on ice bath is 15min, and the time of described polycrystalline silicon sheet in acid etching solution The etching time is 2min. 5. the preparation method of polysilicon surface pyramid textured structure according to claim 1, is characterized in that, described alkaline etching solution is the NaOH solution of 0.5mol/L. 6. according to the preparation method of claim 1 or 5 described polycrystalline silicon surface pyramid suede structure, it is characterized in that, the time that described alkaline etching solution is placed in the water bath of 50 ℃ is 20～30min, and described polycrystalline silicon sheet The etching time in the alkali etching solution is 25-40 minutes. 7. the preparation method of polysilicon surface pyramid textured structure according to claim 6 is characterized in that, the etching time of described polysilicon sheet in alkaline etching solution is 40min. 8 . The method for preparing the pyramid textured structure on the surface of polysilicon according to claim 1 , wherein the polysilicon sheet is etched with HF with a concentration of 5% to 8% for cleaning after alkali etching.