A method for preparing a flat-top pyramid velvet surface on the surface of single crystal silicon

Abstract

The invention discloses a method for preparing a flat-top pyramid velvet surface on the surface of a single crystal silicon, and relates to the field of production of a single crystal silicon solar cell sheet. The method is characterized in that the method comprises the following steps: step (1) texturing: adding an alkali solution, a texturing additive and water into a texturing tank in a certain proportion, heating the alkali solution to a certain temperature, placing a silicon wafer into the texturing tank for reaction for a certain period of time, and then taking the silicon wafer out and washing it with pure water; step (2) tower top flattening treatment: adding an alkali solution, a tower top flattening liquid and water into a flattening tank in a certain proportion, heating the alkali solution to a certain temperature, and then placing the silicon wafer into the flattening tank for reaction for a certain period of time to obtain a single crystal silicon wafer with a flat-top pyramid velvet surface; step (3) washing: washing the silicon wafer with pure water; step (4) drying: drying the silicon wafer with hot clean air having nitrogen passing therethrough; the invention adopts an alkali solution plus a tower top flattening liquid to replace the existing nitric acid hydrofluoric acid CP and ozone hydrofluoric acid CP, which is safer, more environmentally friendly and has lower cost.

Description

Technical Field

[0001] The invention relates to the field of production of monocrystalline silicon solar cell sheets, and in particular to a method for preparing a flat-top pyramid velvet surface on the surface of monocrystalline silicon. Background Art

[0002] In the production process of traditional monocrystalline silicon solar cells, the first step is texturing and cleaning, that is, the surface of the silicon wafer is etched by wet chemical etching to form a velvet structure with a pyramid structure, and the sunlight is reflected multiple times on the surface of the pyramid structure, thereby reducing the escape of light and increasing the absorption rate of sunlight, thereby increasing the current density of the solar cell and ultimately improving the photoelectric conversion efficiency of the solar cell; this structure is mainly formed by the principle of anisotropic corrosion of silicon by alkali.

[0003] However, for the new heterojunction (HJT) solar cells, due to their unique cell structure, a certain thickness of hydrogenated intrinsic amorphous silicon layer needs to be symmetrically deposited on the velvet surface on both sides of the silicon wafer. a-Si:H", this thin film layer can effectively passivate the silicon wafer and greatly reduce the carrier recombination rate. Therefore, for the manufacture of HJT cells, not only is it required that the pyramid velvet surface generated by the silicon wafer has a low reflectivity, but there are also special requirements for the microstructure of the pyramid surface; if the pyramid tip is too sharp, it will lead to The a-Si:H film layer is broken, which affects the coating quality. At the same time, due to the sharp tip of the tower, during the deposition of subsequent film layers, the tip discharge phenomenon may break through the previously deposited film layer, which will eventually lead to a reduction in the passivation effect, a reduction in the carrier lifetime, and a corresponding reduction in battery efficiency.

[0004] At the same time, the new BC battery process involves a more complicated process flow, which includes many mask layers. In the process, these film layers need to be patterned and opened with laser technology. In the laser patterning process, since the conventional pyramid has a sharp top and a significant height difference with the pyramid body, the top receives too much energy, which will cause uneven laser process opening, resulting in unclean subsequent cleaning and serious residue, which in turn affects the final battery efficiency.

[0005] The existing CP treatment method in the texturing process of heterojunction solar cells has the following disadvantages: nitric acid CP requires a large amount of nitric acid and hydrofluoric acid, and the reaction conditions are harsh and need to be kept at a low temperature (below 10°C) to achieve a good effect. At the same time, the use of a large amount of strong oxidizing acid and strong corrosive acid greatly increases the danger of the process and increases the cost of wastewater treatment; therefore, both in terms of safety and environmental protection, nitric acid CP is in urgent need of replacement. Ozone CP requires ozone and hydrofluoric acid. The use of ozone will affect the environment of the entire tank texturing machine. Ozone overflow will increase the ozone concentration in the texturing machine, which will seriously affect the texturing effect of the entire texturing machine, resulting in an abnormal increase in the reflectivity of the silicon wafer after texturing and unstable process. At the same time, the use of ozone requires an ozone machine, which requires high-frequency and high-voltage discharge to work, requires a large amount of electricity and is very dangerous, so it is not an ideal process. Summary of the invention

[0006] The present invention provides a method for preparing a flat-top pyramid velvet surface on the surface of a single crystal silicon wafer, so that a flat-top pyramid structure is formed on the single crystal silicon wafer. Since the top of the pyramid is flattened, the reflectivity of the silicon wafer is improved to a certain extent.

[0007] To achieve the purpose of the present invention, the present invention is implemented by the following technical solutions:

[0008] A method for preparing a flat-top pyramid velvet surface on the surface of single crystal silicon comprises the following steps:

[0009] Step (1): Velveting

[0010] Alkaline solution, texturing additives and water are added into the texturing tank in a certain proportion, heated to a certain temperature, and then the silicon wafer is placed into the texturing tank for a certain reaction time, and then taken out and washed with pure water;

[0011] Step (2): Tower top flattening

[0012] Alkaline solution, tower top flattening solution and water are added into the flattening tank in proportion, and after heating to a certain temperature, the silicon wafer treated in step (1) is placed into the flattening tank to react for a certain period of time to obtain a single crystal silicon wafer with a flat-top pyramid velvet surface;

[0013] Step (3): Washing

[0014] Wash the silicon wafer after the treatment in step (2) with pure water;

[0015] Step (4): Drying

[0016] The silicon wafer treated in step (3) is dried using hot clean air with nitrogen.

[0017] Further settings are as follows:

[0018] Preferably, in steps (1) and (2), the alkali solution is one or more of sodium hydroxide, potassium hydroxide, ammonia water, and TMAH.

[0019] Preferably, in step (1), the texturing tank is heated to 70-90° C. and maintained at this temperature; the silicon wafer reacts in the texturing tank for 5-8 minutes, and is washed with pure water for 2-5 minutes after texturing.

[0020] Preferably, in the texturing tank of step (1), the content of the texturing additive is 0.3-0.6% and the content of the alkali solution is 0.5-5% based on the total volume of the solution.

[0021] Preferably, in step (2), the tower top is leveled, and the tower top leveling liquid is a combination of various non-ionic surfactants such as polypeptide amide, polyethylene glycol, and hydroxypropyl methylcellulose.

[0022] Particularly preferably, in the embodiment of the present invention, the tower top leveling liquid is configured according to the following composition in weight percentage: 0.01-3.2% of polypeptide amide, 0.05-5.0% of polyethylene glycol, 0.10-8.5% of hydroxypropyl methylcellulose, and the remainder is pure water.

[0023] Preferably, in the leveling tank of step (2), the content of alkali solution is 0.2-2.5% based on the total volume of the solution, and the content of the leveling liquid at the top of the tower is 0.1-0.6%.

[0024] Preferably, in step (2), the top of the tower is flattened, and the reaction temperature of the silicon wafer in the flattening tank is 10-60° C. and the reaction time is 1-6 min.

[0025] Preferably, the washing time with pure water in step (3) is 2-6 minutes.

[0026] Preferably, nitrogen must be introduced during the drying process in step (4) to ensure that the silicon wafer will not be oxidized by hot air and to ensure effective passivation of the subsequently deposited hydrogenated amorphous silicon thin film layer.

[0027] Preferably, in step (4), the drying temperature is 50-80° C. and the drying time is 6-15 min.

[0028] The beneficial effects of the present invention are:

[0029] The present invention adopts alkaline solution plus tower top flattening liquid to replace the existing nitric acid hydrofluoric acid CP and ozone hydrofluoric acid CP, and obtains a single crystal silicon wafer with a flat-top pyramid velvet surface. The method has simple process control, is safer, and is more environmentally friendly. At the same time, because the flattening liquid is highly hydrophilic and easy to clean, the traditional pickling process can be omitted, and it has great compatibility with the existing machine tank body, does not need to be modified, and has lower cost.

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings and preferred embodiments of the specification. Of course, the embodiments of the present invention involved in the following description are usually only part of the embodiments of the present invention, rather than all of the embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the SEM image (cross section) of the pyramid structure of the single crystal silicon wafer prepared in Example 1 by normal alkali texturing.

[0032] Figure 2 This is the SEM image (plane) of the pyramid structure of the single crystal silicon wafer prepared in Example 1 by normal alkali texturing.

[0033] Figure 3 This is an SEM image (cross section) of the flat-top pyramid velvet surface after normal tower top flattening treatment in Example 2.

[0034] Figure 4 This is an SEM image (plane) of the flat-top pyramid velvet surface after normal tower top flattening treatment in Example 2.

[0035] Figure 5 This is an SEM picture (cross section) of the flat-topped pyramid velvet surface after flattening treatment after increasing the alkali solution concentration, temperature and time in Example 7.

[0036] Figure 6 This is the SEM picture (plane) of the flat-topped pyramid velvet surface after the flattening treatment in Example 7 after increasing the alkali solution concentration, temperature and time.

[0037] Figure 7 This is an SEM image (cross section) of the flat-top pyramid velvet surface after increasing the flattening treatment time in Example 10.

[0038] Figure 8 This is the SEM image (plane) of the flat-top pyramid velvet surface after the flattening treatment time is increased in Example 10. DETAILED DESCRIPTION

[0039] In the following examples, unless otherwise defined, all materials are known or commercially available.

[0040] In the embodiment of the present invention, the silicon wafer used is an externally purchased A-grade M10-sized gallium-doped P-type silicon wafer with a thickness of 150-10+20 μm.

[0041] In the embodiment of the present invention, the alkali solution is commercially available KOH with a concentration of 45%.

[0042] In the embodiment of the present invention, the texturing additive is not particularly limited, and a texturing additive with an existing typical formula may be used, or any commercially available texturing additive may be purchased, for example, the texturing additive produced by Shaoxing Guizhang New Energy Technology Co., Ltd.

[0043] In the embodiment of the present invention, the tower top leveling liquid is configured according to the following composition in weight percentage: 0.5% polypeptide amide, 2% polyethylene glycol, 5% hydroxypropyl methylcellulose, and the balance is pure water.

[0044] In the following embodiments of the present invention, the formulas of the texturing solution and the flattening bath solution have the following content percentages of the components: mass of the component in g / total volume of the solution in ml×100%.

[0045] Example 1

[0046] Step 1: Velveting

[0047] In a 45L texturing tank, prepare 40L of texturing liquid, heat the texturing liquid to 82°C, and then put the silicon wafer into the texturing tank to react for 6 minutes.

[0048] The formula of the velvet liquid is as follows:

[0049] Lye 2.5%

[0050] Texturing additive 0.6%

[0051] The balance is pure water.

[0052] Step 2: Wash

[0053] Wash the silicon wafer with pure water for 2 minutes;

[0054] Step 3: Drying

[0055] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0056] The dried silicon wafer was taken out for SEM testing, and the SEM images were as follows Figure 1 , Figure 2 As shown, Figure 1 is the cross section, Figure 2 They are all flat and have regular pyramid structures, with the top and bottom of the pyramids being relatively sharp.

[0057] Example 2

[0058] Step 1: Velveting

[0059] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0060] The formula of the velvet liquid is as follows:

[0061] Lye 2.5%

[0062] Texturing additive 0.5%

[0063] The balance is pure water.

[0064] Step 2: Flattening the top of the tower

[0065] Prepare 40L of flattening bath solution, heat the bath solution to 30°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 120 seconds;

[0066] The formula of the flattening bath is as follows:

[0067] Lye 0.45%

[0068] Top leveling liquid 0.4%

[0069] The balance is pure water.

[0070] Step 3: Wash

[0071] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0072] Step 4: Drying

[0073] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0074] The dried silicon wafer was taken out for SEM testing, and the SEM images were as follows: Figure 3 , Figure 4 As shown, Figure 3 is the cross section, Figure 4 It is flat, and you can see that a small part of the pyramid's top has been flattened.

[0075] Example 3

[0076] Step 1: Velveting

[0077] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0078] The formula of the velvet liquid is as follows:

[0079] Lye 2.5%

[0080] Texturing additive 0.5%

[0081] The balance is pure water.

[0082] Step 2: Flattening the top of the tower

[0083] Prepare 40L of flattening bath solution, heat the bath solution to 45°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 180 seconds.

[0084] The formula of the flattening bath is as follows:

[0085] Lye 0.45%

[0086] Top leveling liquid 0.4%

[0087] The balance is pure water.

[0088] Step 3: Wash

[0089] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0090] Step 4: Drying

[0091] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0092] Example 4

[0093] Step 1: Velveting

[0094] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0095] The formula of the velvet liquid is as follows:

[0096] Lye 2.5%

[0097] Texturing additive 0.5%

[0098] The balance is pure water.

[0099] Step 2: Flattening the top of the tower

[0100] Prepare 40L of flattening bath solution, heat the bath solution to 60°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 240 seconds.

[0101] The formula of the flattening bath is as follows:

[0102] Lye 0.45%

[0103] Top leveling liquid 0.4%

[0104] The balance is pure water.

[0105] Step 3: Wash

[0106] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0107] Step 4: Drying

[0108] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0109] Example 5

[0110] Step 1: Velveting

[0111] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0112] The formula of the velvet liquid is as follows:

[0113] Lye 2.5%

[0114] Texturing additive 0.5%

[0115] The balance is pure water.

[0116] Step 2: Flattening the top of the tower

[0117] Prepare 40L of flattening bath solution, heat the bath solution to 30°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 180 seconds.

[0118] The formula of the flattening bath is as follows:

[0119] Lye 0.55%

[0120] Top leveling liquid 0.4%

[0121] Step 3: Wash

[0122] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0123] Step 4: Drying

[0124] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0125] Example 6

[0126] Step 1: Velveting

[0127] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0128] The formula of the velvet liquid is as follows:

[0129] Lye 2.5%

[0130] Texturing additive 0.5%

[0131] The balance is pure water.

[0132] Step 2: Flattening the top of the tower

[0133] Prepare 40L of flattening bath solution, heat the bath solution to 45°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 240 seconds.

[0134] The formula of the flattening bath is as follows:

[0135] Lye 0.55%

[0136] Top leveling liquid 0.4%

[0137] The balance is pure water.

[0138] Step 3: Wash

[0139] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0140] Step 4: Drying

[0141] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0142] Example 7

[0143] Step 1: Velveting

[0144] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0145] The formula of the velvet liquid is as follows:

[0146] Lye 2.5%

[0147] Texturing additive 0.5%

[0148] The balance is pure water.

[0149] Step 2: Flattening the top of the tower

[0150] Prepare 40L of flattening bath solution, heat the bath solution to 60°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 120 seconds.

[0151] The formula of the flattening bath is as follows:

[0152] Lye 0.55%

[0153] Top leveling liquid 0.4%

[0154] The balance is pure water.

[0155] Step 3: Wash

[0156] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0157] Step 4: Drying

[0158] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0159] The dried silicon wafer was taken out and SEM test was performed. The SEM image was as follows Figure 5 , Figure 6 As shown, Figure 5 is the cross section, Figure 6 It is flat, and you can see that the top of the pyramid has been flattened more.

[0160] Example 8

[0161] Step 1: Velveting

[0162] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0163] The formula of the velvet liquid is as follows:

[0164] Lye 2.5%

[0165] Texturing additive 0.5%

[0166] The balance is pure water.

[0167] Step 2: Flattening the top of the tower

[0168] Prepare 40L of flattening bath solution, heat the bath solution to 30°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 240 seconds.

[0169] The formula of the flattening bath is as follows:

[0170] Lye 0.65%

[0171] Top leveling liquid 0.4%

[0172] Step 3: Wash

[0173] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0174] Step 4: Drying

[0175] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0176] Example 9

[0177] Step 1: Velveting

[0178] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0179] The formula of the velvet liquid is as follows:

[0180] Alkali solution (45% KOH) 2.5%

[0181] Texturing additive 0.5%

[0182] The balance is pure water.

[0183] Step 2: Flattening the top of the tower

[0184] Prepare 40L of flattening bath solution, heat the bath solution to 45°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 120 seconds.

[0185] The formula of the flattening bath is as follows:

[0186] Lye 0.65%

[0187] Top leveling liquid 0.4%

[0188] The balance is pure water.

[0189] Step 3: Wash

[0190] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0191] Step 4: Drying

[0192] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0193] Example 10

[0194] Step 1: Velveting

[0195] In a 45L texturing tank, prepare 40L of texturing liquid. After heating the texturing liquid to 82°C, put the silicon wafer into the texturing tank and react for 6 minutes, then take it out and wash the silicon wafer with pure water for 2 minutes.

[0196] The formula of the velvet liquid is as follows:

[0197] Lye 2.5%

[0198] Texturing additive 0.5%

[0199] The balance is pure water.

[0200] Step 2: Flattening the top of the tower

[0201] Prepare 40L of flattening bath solution, heat the bath solution to 60°C, and place the silicon wafer treated in the previous step into the flattening bath to react for 180 seconds.

[0202] The formula of the flattening bath is as follows:

[0203] Lye 0.65%

[0204] Top leveling liquid 0.4%

[0205] The balance is pure water.

[0206] Step 3: Wash

[0207] After taking out the silicon wafer processed in the previous step, wash the silicon wafer with pure water for 2 minutes.

[0208] Step 4: Drying

[0209] The silicon wafer was placed in a hot clean air (65°C) drying tank filled with nitrogen and dried for 12 minutes.

[0210] The dried silicon wafer was taken out for SEM testing, and the SEM images were as follows Figure 7 , Figure 8 As shown, Figure 7 is the cross section, Figure 8 It is a plane, the top of the pyramid is obviously flattened, and the cross-section appears to be a trapezoid.

[0211] Structure confirmation:

[0212] like Figures 1 to 8 As shown, Figure 1 , Figure 2 The cross-sectional view and plan view of the pyramid obtained by normal texturing in Example 1 are as follows: Figure 3 , Figure 4 The cross-sectional view and plan view of Example 2 after flattening are compared. Figure 1 and Figure 3 , we can clearly see: Figure 3 Each pyramid has its top flattened, further contrasting Figure 2 and Figure 4 , we can see the flattened platform of the spire; it can be proved that the method of the present invention can evenly flatten each pyramid spire. Figure 5 and Figure 6 To increase the SEM images of the alkali concentration and reaction temperature in the flattening process of step (2), compare Figure 2 and Figure 3 It can be clearly seen that the flattening degree of the pyramid tip is more significant, which indicates that the flattening process is greatly affected by alkali concentration and temperature; Figure 7 and Figure 8 contrast Figure 5 and Figure 6 In order to increase the SEM image of the alkali concentration and reaction time in the flattening process of step (2), it can be seen that Figure 7 and Figure 8 The flattening degree is greater and the reflectivity is also higher, indicating that the flattening process is also greatly affected by alkali concentration, reaction temperature and reaction time.

[0213] Performance Test:

[0214] The silicon wafers prepared in Examples 1-10 were subjected to weight loss and reflectivity tests, wherein: the weight loss was measured using an electronic analytical balance, and the reflectivity was measured using a D8 reflectivity meter. The test results are shown in Table 1.

[0215] Table 1

[0216]

[0217]

[0218] analyze:

[0219] (1) Combined with the examples in Table 1, compare Example 1 with Example 2, and Figure 1-Figure 4 , it can be seen that the top of the pyramid is obviously flattened; analysis shows that the reason for the formation of the pyramid top flattened structure in the present invention is: because the top flattening liquid forms a uniform film layer on the surface of the pyramid, it isolates the anisotropic corrosion of alkali and silicon, and also greatly reduces the reaction rate of alkali and silicon; at the same time, due to the tip effect of the pyramid top, the pyramid top can react with the alkali solution preferentially, and finally forms the pyramid top flattened structure.

[0220] (2) By comparing Example 4, Example 6 and Example 8, it can be seen that the effect of temperature on the flattening degree of the pyramid tip in step 2 is greater than the effect of alkali concentration on the flattening degree of the pyramid tip; by comparing Example 4, Example 7 and Example 10, it can be seen that the effect of alkali concentration on the flattening degree of the pyramid tip in step 2 is greater than the effect of reaction time on the flattening degree of the pyramid tip; in summary, the degree of influence of the reaction conditions in step 2 on the flattening structure of the pyramid tip is temperature>alkali concentration>reaction time from strong to weak.

[0221] It can be seen from the above embodiments that the present invention provides a new pyramid flattened velvet structure. The process adjustment window of the method is large, and the desired structure can be obtained under relatively mild reaction conditions, such as Example 2. Combined with the above table, it is not difficult to see that the reflectivity of a silicon wafer with a flat-top pyramid velvet surface on a single crystal silicon surface prepared by this process is positively correlated with the alkali concentration, reaction temperature and reaction time, among which temperature has the greatest influence on flattening.

Claims

1. A method for preparing a flat-top pyramid velvet surface on the surface of single crystal silicon, characterized in that: The steps include: Step (1): Velveting Alkaline solution, texturing additives and water are added into the texturing tank in a certain proportion, heated to a certain temperature, and then the silicon wafer is placed into the texturing tank for a certain reaction time, and then taken out and washed with pure water; Step (2): Tower top flattening Alkaline solution, tower top flattening solution and water are added into the flattening tank in proportion, and after heating to a certain temperature, the silicon wafer treated in step (1) is placed into the flattening tank to react for a certain period of time to obtain a single crystal silicon wafer with a flat-top pyramid velvet surface; Step (3): Washing Wash the silicon wafer after the treatment in step (2) with pure water; Step (4): Drying The silicon wafer treated in step (3) is dried using hot clean air with nitrogen.

2. The method for preparing a flat-topped pyramid velvet surface on a single crystal silicon surface according to claim 1, characterized in that: In steps (1) and (2), the alkali solution is selected from one or more of sodium hydroxide, potassium hydroxide, ammonia water, and TMAH.

3. The method for preparing a flat-topped pyramid velvet surface on a single crystal silicon surface according to claim 1, characterized in that: In step (1), the texturing tank is heated to 70-90°C, the silicon wafer reacts in the texturing tank for 5-8 minutes, and is washed with pure water for 2-5 minutes after texturing.

4. The method for preparing a flat-topped pyramid velvet surface on a single crystal silicon surface according to claim 1, characterized in that: In the texturing tank of step (1), the content of the texturing additive is 0.3-0.6% and the content of the alkali solution is 0.5-5% based on the total volume of the solution.

5. The method for preparing a flat-topped pyramid velvet surface on a single crystal silicon surface according to claim 1, characterized in that: In step (2), the tower top is leveled, and the tower top leveling liquid is a combination of polypeptide amide, polyethylene glycol, and hydroxypropyl methylcellulose.

6. The method for preparing a flat-topped pyramid velvet surface on the surface of single crystal silicon according to claim 1, characterized in that: In step (2), the tower top leveling liquid is prepared according to the following composition in weight percentage: 0.01-3.2% of polypeptide amide, 0.05-5.0% of polyethylene glycol, 0.10-8.5% of hydroxypropyl methylcellulose, and the remainder is pure water.

7. The method for preparing a flat-topped pyramid velvet surface on the surface of single crystal silicon according to claim 1, characterized in that: In the leveling tank of step (2), the content of alkali solution is 0.2-2.5% based on the total volume of the solution, and the content of the leveling liquid at the top of the tower is 0.1-0.6%.

8. The method for preparing a flat-topped pyramid velvet surface on the surface of single crystal silicon according to claim 1, characterized in that: In the tower top flattening treatment in step (2), the reaction temperature of the silicon wafer in the flattening tank is 10-60° C. and the reaction time is 1-6 min.

9. The method for preparing a flat-topped pyramid velvet surface on the surface of single crystal silicon according to claim 1, characterized in that: The washing time with pure water in step (3) is 2-6 minutes.

10. The method for preparing a flat-topped pyramid velvet surface on the surface of single crystal silicon according to claim 1, characterized in that: During the drying process of step (4), nitrogen is introduced, the drying temperature is 50-80° C., and the drying time is 6-15 min.

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