CN105070772A - Wet chemical method of preparing uniform reverse pyramid textured structures on the surface of a monocrystalline silicon - Google Patents

Abstract

The invention discloses a wet chemical method for preparing uniform inverted pyramid suede on the surface of single crystal silicon, which is used to prepare uniform inverted pyramid suede on the surface of large-size single crystal silicon wafers. The wet chemical method comprises the following steps: 1 ) Place the monocrystalline silicon wafer in the deposition solution for deposition treatment; 2) Place the silicon wafer after particle deposition treatment in the etching solution for etching treatment; 3) Place the etched silicon wafer in the Anisotropic etching treatment in alkaline solution; 4) Cleaning with acid solution to remove the metal on the surface of the silicon wafer. The invention can prepare a uniform inverted pyramid textured surface on the surface of a large-size single crystal silicon wafer. The invention does not need to pre-etch the surface of the silicon wafer, and realizes the uniform control of the size and distribution of the hole structure through the control of the metal deposition stage, and finally realizes the large-area uniform distribution of the inverted pyramid structure, which is simple and effective.

Description

A Wet Chemical Method for Fabricating Uniform Inverted Pyramid Texture on Single Crystal Silicon Surfaces

technical field

The invention relates to a wet chemical method for preparing uniform inverted pyramid suede on the surface of single crystal silicon.

Background technique

For crystalline silicon photovoltaic cells, increasing the light absorption of silicon wafers as much as possible is an important link to improve the conversion efficiency of solar cells. Depositing anti-reflection coatings on the surface of crystalline silicon solar cells and texturing the surface of silicon wafers are commonly used methods to increase the light absorption of cells. For monocrystalline silicon photovoltaic cells, the currently widely used production process is to etch randomly distributed positive pyramid-like textured structures on the surface of silicon wafers by means of alkaline etching. Compared with the positive pyramid texture, there are actually many other silicon wafer surface textures that can increase light absorption, such as circular hole texture, honeycomb texture, inverted pyramid texture and so on. Among them, the inverted pyramid texture can not only obtain lower reflectivity and be adopted by some high-efficiency cell structures, but also, after theoretical calculation, the silicon wafer with the inverted pyramid texture surrounded by four <111> crystal planes is less than The surface area is 1.7 times that of the non-textured silicon wafer, which is the smallest among various textured structures. The PN junction of crystalline silicon cells is formed along the textured surface, so the small surface area can reduce the recombination probability of photogenerated carriers, which is conducive to the improvement of cell efficiency. The PERL battery with an efficiency of 25% adopts this inverted pyramid structure. Therefore, this structure is more suitable for high-efficiency crystalline silicon cells.

There are many wet chemical technologies for preparing inverted pyramid texture or similar light-trapping structures on single crystal silicon wafers, mainly including optical imprinting technology and etching technology. The optical imprinting technology is to first coat the mask glue on the surface of the silicon wafer, and then perform photolithography to remove part of the mask glue to obtain a pattern, and then perform chemical etching to obtain a regular inverted pyramid structure suede. This approach has been used by UNSW's Photovoltaics Laboratory to make a variety of high-efficiency solar cells. However, this method has not been able to be mass-produced due to the need to apply a mask and remove the mask structure, the steps are complicated and the cost is high. Etching technology mainly uses metal-catalyzed methods to prepare porous silicon holes and groove structures, which are generally used to manufacture black silicon textured surfaces, and improve battery efficiency by reducing reflectivity. However, since the size of porous silicon holes and trenches is generally between 100-300 nanometers, and the depth of the diffusion junction is 200-300 nanometers, a large number of diffusion dead layers are generated on the surface of black silicon, and the strong recombination effect of the dead layers is greatly improved. The improvement of efficiency is limited, so the method of making black silicon from single crystal has not been applied to the battery production line. So far, the use of metal catalysis to produce large-area monocrystalline silicon wafer inverted pyramid suede is still blank, which is the technological commanding height pursued by photovoltaic companies.

Contents of the invention

The present invention first proposes a wet chemical method capable of preparing a uniform inverted pyramid texture on the surface of single crystal silicon, and can prepare a uniform inverted pyramid texture on the surface of a large-size single crystal silicon wafer (156mm×156mm). The invention does not need to pre-etch the surface of the silicon wafer, and realizes uniform control of the size and distribution of the hole structure through the control of the metal deposition stage, and finally realizes the large-area uniform distribution of the inverted pyramid structure, which is simple and effective.

In order to achieve the above object, the technical solution of the present invention is to design a kind of wet chemical method for preparing uniform inverted pyramid textured surface on the surface of monocrystalline silicon, which is used to prepare uniform inverted pyramid textured surface on the surface of large-scale single crystal silicon wafer, said A large-sized single crystal silicon wafer is a single crystal silicon wafer not smaller than 156mm×156mm, and the wet chemical method includes the following steps:

1) Place the monocrystalline silicon wafer in the deposition solution for deposition treatment, and deposit metal nanoparticles on the surface of the silicon wafer;

2) Place the silicon wafer after particle deposition treatment in an etching solution for etching treatment, and etch a nano-comb-shaped hole array on the surface of the silicon wafer;

3) Place the etched silicon wafer in an alkaline solution for anisotropic etching, etch a suede surface with a uniform inverted pyramid structure on the surface of the silicon wafer, and each inner wall of the inverted pyramid structure is <111 >Crystal plane;

4) Wash with acid to remove the metal on the surface of the silicon wafer.

Preferably, the process of preparing a uniform inverted pyramid texture on the surface of the large-size single crystal silicon wafer is carried out at a low temperature, and the low temperature is 12-40°C.

Preferably, in the deposition solution, on the basis of metal ions and hydrofluoric acid, an appropriate amount of sodium chloride and polyvinylpyrrolidone are added; the molecular weight of the polyvinylpyrrolidone is 3000-50000; the metal The ions are one or more of gold, silver, nickel, zinc, and tin ions.

Preferably, the metal ions are mainly provided by metal salts mixed into the deposition solution, and the metal salts are complex salts or silver sulfate.

Preferably, the deposition solution is formulated with 0.05% to 1% of hydrofluoric acid, 0.002% to 0.1% of complex salt or silver sulfate, 0.001% to 2% of polyvinylpyrrolidone, 0.001% to 3% of Sodium chloride; Wherein, described percentage is mass percent, and described complex salt is the thiosulfate of silver.

Preferably, the etching solution is formulated with 20%-40% hydrofluoric acid and 5%-20% hydrogen peroxide; wherein, the percentages are mass percentages.

Preferably, the alkali in the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, sodium carbonate, sodium bicarbonate; the concentration of the alkali in the alkaline solution is 3 ~12%.

Preferably, the temperature of the deposition treatment is 12-40° C., and the time is 5-60 minutes.

Preferably, the reaction temperature of the etching treatment is 12-22° C., and the time is 2-10 minutes.

Preferably, the temperature of the anisotropic etching treatment is 20-40° C., and the time is 5-15 minutes.

In the present invention, in the first deposition stage, a special deposition solution is used for the deposition of metal nanoparticles on the silicon surface. The present invention changes the concentration of charged ions in the solution by adding polyvinylpyrrolidone (molecular weight: 3000-50000) and sodium chloride with a specific molecular structure in the deposition solution, thereby controlling the aggregation degree of the metal nanoparticles at the initial stage of formation and the degree of dispersion among the particles . In addition, since polyvinylpyrrolidone is a multidentate ligand, the lactyl group contained in its molecular structure can combine with metal ions through coordination, and at the same time play a role in steric hindrance and control the growth morphology of the metal. In addition, polyvinylpyrrolidone can be used as a surfactant, which is easy to adsorb on the silicon surface. Chloride ions have the function of promoting the aggregation of metal atoms during the growth process. It can use the skeleton structure of polyvinylpyrrolidone to promote clusters of metal atoms at each growth point, thereby increasing the degree of aggregation and increasing the size of metal nanoparticles. And hydrofluoric acid can make the reduction reaction chain of metal continue for a certain period of time, and promote the success of deposition. In the end, the metal nanoparticles deposited on the surface of the silicon wafer are more uniformly distributed, with larger particle sizes and smaller particle size differences.

In the second etching stage, the present invention makes full use of the metal nanoparticles deposited on the surface of the silicon wafer, cooperates with hydrofluoric acid and hydrogen peroxide to etch the single crystal silicon, and etches a nano-comb-shaped hole array on the surface of the silicon wafer. . The pore size of each pore, as well as the distribution of the pores on the surface of the silicon wafer, are directly related to the metal nanoparticles. Due to the metal nanoparticles, the distribution is more uniform, the particle size is larger, and the particle size difference is smaller; therefore, the etched nano-comb hole array is more uniform, the pore size is larger, and the pore size difference is smaller.

In the anisotropic etching stage of the third step, the present invention can also make full use of the nano-comb-shaped hole array etched on the surface of the silicon chip, cooperate with an alkali solution to further etch the single crystal silicon, and use the nano-comb-shaped hole Based on the array, a conical pit (inverted pyramid structure) is etched on the surface of the silicon wafer. The shape of the conical pits, as well as the distribution of the conical pits on the surface of the silicon wafer, are directly related to the nanocomb hole array. Due to the nano-comb hole array, the distribution is more uniform, the pore size is larger, and the difference in pore size is smaller; therefore, the distribution of the etched conical pits is more uniform. Moreover, due to the larger diameter of the nano-comb-shaped holes, the depth of the nano-comb-shaped holes does not need to be very deep to successfully etch larger-sized tapered pits during the process of etching the tapered pits, and the weight reduction rate of the silicon wafer can be reduced accordingly.

In the fourth cleaning stage of the present invention, hydrochloric acid solution (concentration range is 20% to 36%) or nitric acid solution (concentration range is 30% to 70%) is used to soak and clean for 15 to 20 minutes at a room temperature of 10 to 20°C to remove Residual metal nanoparticles on the surface of a silicon wafer.

Finally, as mentioned above, the present invention divides the surface texture treatment of single crystal silicon into four steps in sequence, and the treatment process of each step is controllable. The result obtained in the previous step is the basis for the subsequent treatment. Positive combined effect.

The present invention has following characteristics:

In the present invention, at the initial stage of formation of the metal nanoparticles, the degree of aggregation and the degree of dispersion among the particles are optimally controlled, thereby ensuring the controllability of the etched morphology from the source.

The composite suede structure prepared by the invention is more uniform.

In the anisotropic etching stage, by compounding the alkali solution, the present invention can realize the fine adjustment of the cone angle of the conical pit, so as to adapt to the etching of nano-comb-shaped holes with different depths, so that the depth of the nano-comb-shaped holes is not deep In the anisotropic etching stage, it is not merged but remains as a small-sized inverted pyramid structure, which can adapt to the trend of decreasing thickness of monocrystalline silicon wafers in existing photovoltaic technology.

The invention is particularly beneficial to prepare a conical pit structure with a larger size aperture, which is very useful for matching the subsequent diffusion and silk screen process and improving battery efficiency.

The invention can control the weight loss rate while preparing suitable inverted pyramid suede, which is very effective for thin crystal silicon wafers.

Detailed ways

The specific implementation of the present invention will be further described below in conjunction with the examples. The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

The invention provides a wet chemical method for preparing a uniform inverted pyramid texture on the surface of single crystal silicon, which is used to prepare a uniform inverted pyramid texture on the surface of a large-size single crystal silicon chip, and the large-size single crystal silicon chip is not less than 156mm * 156mm monocrystalline silicon wafer, described wet chemical method comprises the following steps:

1) Place the monocrystalline silicon wafer in the deposition solution for deposition treatment, and deposit metal nanoparticles on the surface of the silicon wafer; the deposition solution, on the basis of adding metal ions and hydrofluoric acid, also adds an appropriate amount of sodium chloride and polyvinylpyrrolidone; the molecular weight of the polyvinylpyrrolidone is 3000-50000; the metal ion is one or more of gold, silver, nickel, zinc, tin ions; the metal ion is mainly composed of The metal salt in the deposition solution is provided, and the metal salt is a complex salt or silver sulfate;

2) Place the silicon chip after the particle deposition treatment in an etching solution for etching treatment, and etch a nano-comb-shaped hole array on the surface of the silicon chip; the etching solution is mixed with an appropriate amount of hydrofluoric acid and hydrogen peroxide ;

3) Place the etched silicon wafer in an alkaline solution for anisotropic etching, etch a suede surface with a uniform inverted pyramid structure on the surface of the silicon wafer, and each inner wall of the inverted pyramid structure is <111 > crystal face; the alkali in the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, sodium carbonate, sodium bicarbonate;

4) Cleaning with acid solution to remove the metal on the surface of the silicon wafer;

The entire process of preparing a uniform inverted pyramid texture on the surface of the large-size single crystal silicon wafer is carried out at low temperature, and the low temperature is 12-40°C.

In some/some optional embodiments, the deposition solution is formulated with 0.05% to 1% of hydrofluoric acid, 0.002% to 0.1% of complex salt or silver sulfate, and 0.001% to 2% of polyvinylpyrrolidone , 0.001% to 3% of sodium chloride; wherein, the percentage is a mass percentage, and the complex salt is silver thiosulfate;

In some/some optional embodiments, the etching solution is formulated with 20%-40% hydrofluoric acid and 5%-20% hydrogen peroxide; wherein, the percentages are mass percentages.

In some/some optional embodiments, the alkali concentration in the alkali solution is 3-12%.

In some/some optional embodiments, the temperature of the deposition treatment is 12-40° C., and the time is 5-60 minutes.

In some/some optional embodiments, the reaction temperature of the etching treatment is 12-22° C., and the time is 2-10 minutes.

In some/some optional embodiments, the temperature of the anisotropic etching treatment is 20-40° C., and the time is 5-15 minutes.

In some/some optional embodiments, the specific steps of cleaning and removing the metal on the surface of the silicon wafer with acid solution are: using hydrochloric acid solution (with a concentration range of 20% to 36%) or nitric acid solution ( The concentration range is 30%~70%) soaking and cleaning for 15~20 minutes to remove the residual metal nanoparticles on the surface of the silicon wafer.

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

Claims (10)

1. A wet chemical method for preparing a uniform inverted pyramid texture on the surface of monocrystalline silicon, which is used to prepare a uniform inverted pyramid texture on the surface of a large-sized monocrystalline silicon wafer, and the size of the large-sized monocrystalline silicon wafer is not less than 156mm×156mm The monocrystalline silicon wafer, it is characterized in that, described wet chemical method comprises the steps: 1) Place the monocrystalline silicon wafer in the deposition solution for deposition treatment, and deposit metal nanoparticles on the surface of the silicon wafer; 2) Place the silicon wafer after particle deposition treatment in an etching solution for etching treatment, and etch a nano-comb-shaped hole array on the surface of the silicon wafer; 3) Place the etched silicon wafer in an alkaline solution for anisotropic etching, etch a suede surface with a uniform inverted pyramid structure on the surface of the silicon wafer, and each inner wall of the inverted pyramid structure is <111 >Crystal plane; 4) Wash with acid to remove the metal on the surface of the silicon wafer. 2. prepare the wet chemical method of uniform inverted pyramid textured surface on monocrystalline silicon surface according to claim 1, it is characterized in that, the described process of uniform inverted pyramid textured surface is prepared at low temperature on large-scale single crystal silicon chip surface The low temperature is 12-40°C. 3. according to claim 2, prepare the wet chemical method of even inverted pyramid suede on the surface of single crystal silicon, it is characterized in that, described deposition solution, on the basis that has been mixed with metal ion and hydrofluoric acid, also adds An appropriate amount of sodium chloride and polyvinylpyrrolidone; the molecular weight of the polyvinylpyrrolidone is 3000-50000; the metal ion is one or more of gold, silver, nickel, zinc and tin ions. 4. according to claim 3, prepare the wet chemical method of even inverted pyramid suede on the surface of monocrystalline silicon, it is characterized in that, described metal ion is mainly provided by the metal salt that is mixed in the deposition solution, and described metal salt is complex salt or silver sulfate. 5. the wet chemical method for preparing evenly inverted pyramid suede on the surface of monocrystalline silicon according to claim 4, is characterized in that, described deposition solution has joined the hydrofluoric acid of 0.05%～1%, 0.002%～0.1 % of complex salt or silver sulfate, 0.001% to 2% of polyvinylpyrrolidone, and 0.001% to 3% of sodium chloride; wherein, the percentage is a mass percentage, and the complex salt is silver thio Sulfates. 6. the wet chemical method of preparing evenly inverted pyramid suede on the surface of monocrystalline silicon according to claim 5, is characterized in that, described etching solution has joined the hydrofluoric acid of 20%～40%, 5%～ 20% hydrogen peroxide; Wherein, said percentage is mass percentage. 7. according to claim 6, prepare the wet chemical method of even inverted pyramid suede on the surface of monocrystalline silicon, it is characterized in that, the alkali in the described alkali solution is sodium hydroxide, potassium hydroxide, tetramethyl hydroxide One or more of ammonium, sodium carbonate and sodium bicarbonate; the concentration of alkali in the alkali solution is 3-12%. 8 . The wet chemical method for preparing a uniform inverted pyramid texture on the surface of single crystal silicon according to claim 7 , wherein the temperature of the deposition treatment is 12-40° C. and the time is 5-60 minutes. 9 . The wet chemical method for preparing a uniform inverted pyramid texture on the surface of single crystal silicon according to claim 8 , wherein the reaction temperature of the etching treatment is 12-22° C. and the time is 2-10 minutes. 10. the wet chemical method of preparing uniform inverted pyramid textured surface on the surface of single crystal silicon according to claim 9, is characterized in that, the temperature of described anisotropic etching treatment is 20～40 ℃, and the time is 5～15min .