Mask layer preparation method, monocrystalline silicon wafer and preparation method thereof, and solar cell

Abstract

The invention relates to a preparation method of a mask layer, a monocrystalline silicon wafer and a preparation method thereof, and a solar cell. According to the preparation method of the mask layer, the silicon nitride mask layer and / or the silicon oxide mask layer are / is formed on the monocrystalline silicon wafer by adopting a CVD (Chemical Vapor Deposition) process. Wherein a certain flow of silane and ammonia gas are introduced when the silicon nitride mask layer is prepared, deposition is carried out for a certain time under high-temperature and high-pressure conditions, deposition is carried out for a certain time under high-temperature, high-oxygen and high-pressure process conditions when the silicon oxide mask layer is prepared, the mask layer grows on the surface of the monocrystalline silicon wafer, and the mask layer has high density. The mask layer can tolerate long-time alkali washing, and the monocrystalline silicon below the mask layer after alkali washing is in an ideal suede state after alkali washing.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to a method for preparing a mask layer, a single crystal silicon wafer and a preparation method thereof, and a solar cell. Background Art

[0002] IBC battery, which refers to the interdigitated back contact battery, has its positive and negative electrodes arranged on the back, and the front is completely unobstructed, so it can increase the current of the battery; at the same time, the positive and negative electrodes on the back are densely arranged in interdigitated patterns, which reduces the carrier transmission distance, so the battery filling is also relatively high.

[0003] The back electrode design of the IBC cell is the same as the traditional crystalline silicon cell structure. Specifically, the back electrode design is to print silver paste on the N-type electrode and design a silver pad on the silver main grid line. Aluminum paste is printed on the P-type electrode. In order to make the P area more effectively increase reflection and increase the opening voltage, the P area needs to be prepared into a polished structure. Compared with the velvet structure, the reflected light increases after the long wave passes through the silicon substrate, thereby increasing the current.

[0004] The monocrystalline silicon wafer needs to form a mask layer first, and the monocrystalline silicon below the mask layer is in a velvet state after alkali washing. The non-mask area on the back of the monocrystalline silicon wafer is prepared to have a polishing effect, which can reduce the back recombination and increase the internal reflection of the battery; while the front and non-laser areas are prepared to have a velvet state, and the velvet state of the front needs to maintain good light absorption and low surface recombination. In order to clean the surface of the monocrystalline silicon wafer to a polishing effect, it is necessary to clean it in a specific alkali washing solution for a certain period of time, so a mask layer that can withstand alkali washing treatment is required. Summary of the invention

[0005] Based on this, it is necessary to provide a method for preparing a mask layer with good alkaline washing resistance, and further provide a single crystal silicon wafer and a preparation method, and further provide a solar cell.

[0006] A method for preparing a mask layer on a single crystal silicon wafer comprises the following steps:

[0007] Forming a silicon nitride mask layer and / or a silicon oxide mask layer on a single crystal silicon wafer using a CVD process;

[0008] The process parameters for forming the silicon nitride mask layer include:

[0009] The temperature is 400-450℃, the silane flow rate is 500-1500sccm, the ammonia flow rate is 5000-9000sccm, the power is 6000-9000w, the duty cycle is 30-50ms, the cycle is 40-60ms, the pressure is 300-500mtorr; the time is 300-400s;

[0010] The process parameters for forming the silicon oxide mask layer include:

[0011] The temperature is 800-1100°C, the pressure is 1500-1800 mbar, the oxygen flow rate is 3500-5000 sccm, the nitrogen flow rate is 500-2000 sccm, and the time is 3000-4200 s.

[0012] In one of the embodiments, before the step of coating the silicon nitride mask layer, the preparation method further comprises the step of pre-ventilating the CVD equipment;

[0013] The process parameters of the pre-ventilation include: temperature of 400-450°C, silane flow rate of 500-1500sccm, ammonia flow rate of 5000-9000sccm, power of 6000-9000w, duty cycle of 30-50ms, cycle of 40-60ms, pressure of 300-500mtorr; time of 50-100s.

[0014] In one of the embodiments, after the step of coating the silicon nitride mask layer, the preparation method further comprises the steps of evacuating and back-pressuring the CVD equipment;

[0015] The vacuuming process parameters include: temperature of 400-450°C, pressure of less than 30 mtorr, and time of 70-200 s;

[0016] The back pressure process parameters include: temperature of 400-450° C., nitrogen flow, flow rate of 10000-20000 sccm, pressure of 1000-1060 mtorr, and time of 70-200 s.

[0017] In one of the embodiments, after the step of coating the silicon oxide mask layer, the preparation method further comprises the steps of evacuating and back-pressuring the CVD equipment;

[0018] The vacuuming process parameters include: temperature of 800-1100°C, pressure of less than 30 mtorr, and time of 70-200 s;

[0019] The back pressure process parameters include: temperature of 800-1100° C., nitrogen flow, flow rate of 10000-20000 sccm, pressure of 1000-1060 mtorr, and time of 70-200 s.

[0020] In one of the embodiments, the thickness of the silicon nitride mask layer is 40-80 nm.

[0021] In one of the embodiments, the thickness of the silicon oxide mask layer is 4-10 nm.

[0022] A method for preparing a single crystal silicon wafer comprises the following steps:

[0023] Forming a mask layer on a single crystal silicon wafer according to the method for preparing a mask layer on a single crystal silicon wafer described in any of the above embodiments;

[0024] Performing laser processing on a set area on the single crystal silicon wafer on which the mask layer is formed, so as to remove the mask layer on the set area;

[0025] The single crystal silicon wafer treated by the laser is subjected to an alkali washing treatment to form a polished surface in the set area and a velvet surface in other areas.

[0026] In one embodiment, the alkaline washing solution used in the alkaline washing treatment comprises water, alkali and hydrogen peroxide, the pH value of the alkaline washing solution is 8-12, the mass fraction is 40%-49%, and the mass fraction of the hydrogen peroxide is 30%-36%.

[0027] In one embodiment, the alkali washing treatment time is 200s to 500s.

[0028] A single crystal silicon wafer is prepared by the preparation method described in any one of the above embodiments.

[0029] A solar cell comprises the above-mentioned single crystal silicon wafer.

[0030] In one embodiment, the solar cell is a TOPCon cell or an IBC cell.

[0031] Compared with the conventional scheme, the above-mentioned method for preparing the mask layer, the single crystal silicon wafer and the preparation method, and the solar cell have the following beneficial effects:

[0032] The method for preparing the mask layer adopts a CVD process to form a silicon nitride mask layer and / or a silicon oxide mask layer on a single crystal silicon wafer. When preparing the silicon nitride mask layer, a certain flow of silane and ammonia is introduced, and the deposition is carried out for a certain time under high temperature and high pressure conditions. When preparing the silicon oxide mask layer, the mask layer is deposited for a certain time under high temperature, high oxygen content and high pressure process conditions, and the mask layer grows on the surface of the single crystal silicon wafer. The mask layer has a high density and can withstand a long period of alkali washing, and the single crystal silicon under the mask layer after alkali washing is in an ideal velvet state after alkali washing. DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0034] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0035] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number or order of the indicated technical features.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0037] The present invention provides a method for preparing a mask layer on a single crystal silicon wafer, comprising the following steps:

[0038] A silicon nitride mask layer and / or a silicon oxide mask layer is formed on a single crystal silicon wafer by using a CVD process.

[0039] The process parameters for forming the silicon nitride mask layer include:

[0040] The temperature is 400-450°C, the silane flow rate is 500-1500sccm, the ammonia flow rate is 5000-9000sccm, the power is 6000-9000w, the duty cycle is 30-50ms, the cycle is 40-60ms, the pressure is 300-500mtorr; the time is 300-400s.

[0041] The method for preparing the mask layer adopts a CVD process to form a silicon nitride mask layer on a single crystal silicon wafer. When preparing the silicon nitride mask layer, a certain flow of silane and ammonia is introduced, and the deposition is carried out for a certain time under high temperature and high pressure conditions, and a mask layer grows on the surface of the single crystal silicon wafer. The mask layer has a high density and can withstand a long period of alkali washing, and the single crystal silicon under the mask layer after alkali washing is in an ideal velvet state after alkali washing.

[0042] In some of these examples, before the step of coating the silicon nitride mask layer, the method for preparing the mask layer on the single crystal silicon wafer further includes the step of pre-ventilating the CVD equipment;

[0043] The process parameters of pre-ventilation include: temperature of 400-450°C, silane flow rate of 500-1500sccm, ammonia flow rate of 5000-9000sccm, power of 6000-9000w, duty cycle of 30-50ms, cycle of 40-60ms, pressure of 300-500mtorr; time of 50-100s.

[0044] In some of the examples, after the step of coating the silicon nitride mask layer, the method for preparing the mask layer on the single crystal silicon wafer further includes the steps of evacuating and back-pressuring the CVD equipment.

[0045] The vacuuming process parameters include: temperature of 400-450° C., pressure of less than 30 mtorr, and time of 200 s.

[0046] The back pressure process parameters include: temperature of 400-450°C, nitrogen flow, flow rate of 10000-20000sccm, pressure of 1000-1060mtorr, and time of 70-200s.

[0047] In some examples, the process steps and parameters for preparing the silicon nitride mask layer include:

[0048] a) Entering the boat: temperature is 400-450°C, nitrogen is passed, the flow rate is 15000sccm, the pressure is 1060mtorr, and the time is 300-400s.

[0049] b) Heating: temperature is 400-450°C, nitrogen is passed, the flow rate is 15000sccm, the pressure is 1060mtorr, and the time is 500s.

[0050] c) Vacuuming: temperature is 400-450°C, pressure is 0, and time is 200s.

[0051] d) Pre-ventilation: temperature is 400-450°C, silane flow rate is 500-1500sccm, ammonia flow rate is 5000-9000sccm, power is 6000-9000w, duty cycle is 30-50ms, cycle is 40-60ms, pressure is 300-500mtorr; time is 50-100s.

[0052] e) Coating: temperature 400-450℃, silane flow rate 500-1500sccm, ammonia flow rate 5000-9000sccm, power 6000-9000w, duty cycle 30-50ms, cycle 40-60ms, pressure 300-500mtorr; time 300-400s.

[0053] f) Vacuuming: temperature is 400-450°C, pressure is 0, and time is 200s.

[0054] g) Back pressure: temperature 400-450°C, nitrogen flow, flow rate 15000sccm, pressure 1060mtorr, time 90s.

[0055] h) Leaving the boat: Pass nitrogen with a flow rate of 15000 sccm for 300-400 s.

[0056] In some of these examples, the thickness of the silicon nitride mask layer is 40-80 nm.

[0057] The process parameters for forming the silicon oxide mask layer include:

[0058] The temperature is 800-1100°C, the pressure is 1500-1800 mbar, the oxygen flow rate is 3500-5000 sccm, the nitrogen flow rate is 500-2000 sccm, and the time is 3000-4200 s.

[0059] The preparation method of the mask layer adopts CVD process to form a silicon oxide mask layer on a single crystal silicon wafer. Through high temperature, high oxygen content and high pressure process conditions for a certain period of time, a mask layer grows on the surface of the single crystal silicon wafer. The mask layer has a high density and can withstand a long period of alkali washing, and the single crystal silicon under the mask layer after alkali washing is in an ideal velvet state after alkali washing.

[0060] In some of the examples, after the step of coating the silicon oxide mask layer, the preparation method further includes the steps of evacuating and back-pressurizing the CVD equipment.

[0061] The vacuuming process parameters include: temperature of 800-1100°C, pressure of less than 30 mbar, and time of 70-200 s.

[0062] The back pressure process parameters include: temperature of 800-1100°C, nitrogen flow, flow rate of 10000-20000sccm, pressure of 1000-1060mbar, and time of 70-200s.

[0063] In some examples, the process steps and parameters for preparing the silicon oxide mask layer include:

[0064] a) Entering the boat: temperature is 800-1100°C, nitrogen is passed, the flow rate is 15000sccm, the pressure is 1060-2000mbar, and the time is 700s.

[0065] b) Heating: temperature is 800-1100°C, nitrogen is passed, the flow rate is 15000sccm, the pressure is 1060-2000mbar, and the time is 500s.

[0066] c) Vacuuming: temperature is 800-1100°C, pressure is 0, and time is 200s.

[0067] d) Oxidation: temperature is 800-1100°C, pressure is 1500-1800 mbar, oxygen flow rate is 3500-5000 sccm, nitrogen flow rate is 1000 sccm, and time is 3000-4200 s.

[0068] e) Vacuuming: temperature is 800-1100°C, pressure is 0, and time is 200s.

[0069] f) Back pressure: temperature 800-1100°C, nitrogen flow 15000sccm, pressure 1060-2000mbar, time 90s.

[0070] g) Leaving the boat: passing nitrogen at 15000 sccm for 700 s.

[0071] In some of these examples, the thickness of the silicon oxide mask layer is 4-10 nm.

[0072] Furthermore, the present invention also provides a method for preparing a single crystal silicon wafer, comprising the following steps:

[0073] Forming a mask layer on a single crystal silicon wafer according to any of the above-mentioned methods for preparing a mask layer on a single crystal silicon wafer;

[0074] Performing laser processing on a set area on the single crystal silicon wafer on which the mask layer is formed, so as to remove the mask layer on the set area;

[0075] The laser-treated single crystal silicon wafer is subjected to an alkali cleaning treatment to form a polished surface in a set area and a velvet surface in other areas.

[0076] Preferably, the alkaline cleaning solution used for the alkaline cleaning treatment matches the mask layer prepared by the above-mentioned preparation method. In some specific examples, the alkaline cleaning solution contains water, alkali, hydrogen peroxide and additives, the pH value of the alkaline cleaning solution is 8-12, and the mass fraction of hydrogen peroxide is 30%-36%. Furthermore, the alkaline cleaning solution contains additives, and the mass fraction of the additives is 10%-30%. Additives include surfactants, corrosion inhibitors, alkaline substances, antioxidants, bleaching agents, etc. The additive manufacturers are BP21V15 and BP63V01 of Shaoxing Tuobang New Energy Co., Ltd.

[0077] Optionally, the alkali cleaning treatment time is 200s to 500s. In some examples, the alkali cleaning treatment time is 250s to 450s. In some specific examples, the alkali cleaning treatment time is 200s, 250s, 300s, 350s, 400s, 450s, 500s, etc.

[0078] It can be understood that after the alkali cleaning treatment, the single crystal silicon wafer is also cleaned to remove the alkali.

[0079] In some specific examples, the cleaning process includes: water washing for 30-90 seconds, acid washing (hydrofluoric acid) for 90-180 seconds, water washing for 30-90 seconds, water washing for 30-90 seconds, slow pulling for 30-90 seconds, and drying for 300-800 seconds.

[0080] Furthermore, the present invention also provides a single crystal silicon wafer prepared by any of the preparation methods in the above examples.

[0081] Furthermore, the present invention also provides a solar cell, which includes the above-mentioned single crystal silicon wafer.

[0082] Optionally, the solar cell may be, but is not limited to, a TOPCon cell, an IBC cell, or the like.

[0083] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0084] Example 1

[0085] This embodiment provides a method for preparing a single crystal silicon wafer, comprising the following steps:

[0086] 1. After fine slicing and polishing processes, several silicon wafers to be processed are obtained.

[0087] 2. Form a silicon nitride mask layer on the silicon wafer to be processed by CVD process. The specific process steps and parameters include:

[0088] i) Entering the boat: temperature is 430°C, nitrogen is passed, the flow rate is 15000sccm, the pressure is 1060mtorr, and the time is 350s.

[0089] j) Heating: temperature is 430°C, nitrogen is passed, flow rate is 15000sccm, pressure is 1060mtorr, and time is 500s.

[0090] k) Vacuuming: temperature is 430°C, pressure is 0, and time is 200s.

[0091] l) Pre-ventilation: temperature is 430°C, silane flow rate is 1000 sccm, ammonia flow rate is:

[0092] 7500sccm, power 7500W, duty cycle 40ms, cycle 50ms, pressure 400mtorr; time 90s.

[0093] m) Coating: temperature 430°C, silane flow rate 1000sccm, ammonia flow rate 7500sccm, power 7500W, duty cycle 40ms, cycle 50ms, pressure 400mtorr; time 350s.

[0094] n) Vacuuming: temperature is 430°C, pressure is 0, and time is 200s.

[0095] o) Back pressure: temperature is 430°C, nitrogen is passed, flow rate is 15000sccm, pressure is 1060mtorr, and time is 90s.

[0096] p) Leaving the boat: Pass nitrogen with a flow rate of 15000 sccm for 350 s.

[0097] 3. Confirm the coating effect and record the film thickness, etc.

[0098] 4. According to the required pattern, laser processing is performed on a set area on the single crystal silicon wafer on which the mask layer is formed to remove the mask layer on the set area.

[0099] 5. Soak and clean the silicon nitride film with alkaline cleaning solution (including 250 liters of water, 7 liters of sodium hydroxide, 5 liters of hydrogen peroxide, and 2 liters of additives) to confirm the time of cleaning the silicon nitride film. The cleaning process is as follows: feeding, water washing, alkaline washing, water washing, acid washing, water washing, water washing, slow pulling, and drying.

[0100] Example 2

[0101] The steps of this embodiment are basically the same as those of Embodiment 1, except that in step 2, the coating process time is 450 seconds.

[0102] Example 3

[0103] This embodiment provides a method for preparing a single crystal silicon wafer, comprising the following steps:

[0104] 1. After fine slicing and polishing processes, several silicon wafers to be processed are obtained.

[0105] 2. Form a silicon oxide mask layer on the silicon wafer to be processed by CVD process. The specific process steps and parameters include:

[0106] h) Entering the boat: temperature is 1000°C, nitrogen is passed, the flow rate is 15000sccm, the pressure is 1060mbar, and the time is 700s.

[0107] i) Heating: temperature is 1000° C., nitrogen is passed through, flow rate is 15000 sccm, pressure is 1060 mbar, and time is 500 s.

[0108] j) Vacuuming: temperature is 1000°C, pressure is 0, and time is 200s.

[0109] k) Oxidation: temperature 1000° C., pressure 1650 mbar, oxygen flow rate 4000 sccm, nitrogen flow rate 1000 sccm, time 3500 s.

[0110] l) Vacuuming: temperature is 1000°C, pressure is 0, and time is 200s.

[0111] m) Back pressure: temperature 1000°C, nitrogen flow 15000 sccm, pressure 1060 mbar, time 90 s.

[0112] n) Leaving the boat: passing nitrogen at 15000 sccm for 700 s.

[0113] 3. Confirm the coating effect and record the film thickness, etc.

[0114] 4. According to the required pattern, laser processing is performed on a set area on the single crystal silicon wafer on which the mask layer is formed to remove the mask layer on the set area.

[0115] 5. Soak and clean the silicon oxide film with an alkaline cleaning solution (same as in Example 1) to confirm the time required to clean the silicon oxide film. The cleaning process is as follows: feeding, water washing, alkaline washing, water washing, acid washing, water washing, water washing, slow pulling, and drying.

[0116] Example 4

[0117] The steps of this embodiment are basically the same as those of embodiment 3, except that in step 5, the alkaline washing solution contains 250 liters of water, 10 liters of sodium hydroxide, 8 liters of hydrogen peroxide, and 3 liters of additives.

[0118] Example 5

[0119] The steps of this embodiment are basically the same as those of embodiment 3, except that in step 5, the alkaline washing solution contains 250 liters of water, 4 liters of sodium hydroxide, 3 liters of hydrogen peroxide, and 1 liter of additives.

[0120] Example 6

[0121] The steps of this embodiment are basically the same as those of embodiment 3, except that in step 5, the alkaline washing solution contains 250 liters of water, 4 liters of sodium hydroxide, 8 liters of hydrogen peroxide, and 3 liters of additives.

[0122] Example 7

[0123] The steps of this embodiment are basically the same as those of embodiment 3, except that in step 5, the alkaline washing solution contains 250 liters of water, 4 liters of sodium hydroxide, 8 liters of hydrogen peroxide, and 1 liter of additives.

[0124] Example 8

[0125] The steps of this embodiment are basically the same as those of embodiment 3, except that in step 5, the alkaline washing solution contains 250 liters of water, 10 liters of sodium hydroxide, 3 liters of hydrogen peroxide, and 1 liter of additives.

[0126] Comparative Example 1

[0127] In this comparative example, a mask layer is not plated on the single crystal silicon wafer, and after laser grooving, the wafer is directly cleaned with an alkaline cleaning solution.

[0128] Comparative Example 2

[0129] This comparative example provides a method for preparing a single crystal silicon wafer, comprising the following steps:

[0130] 1. After fine slicing and polishing processes, several silicon wafers to be processed are obtained.

[0131] 2. Form a silicon oxide mask layer on the silicon wafer to be processed by CVD process. The specific process steps and parameters include:

[0132] a) Entering the boat: temperature is 1000°C, nitrogen is passed, the flow rate is 15000sccm, the pressure is 1060mbar, and the time is 700s.

[0133] b) Heating: temperature is 1000° C., nitrogen is passed through, flow rate is 15000 sccm, pressure is 1060 mbar, and time is 500 s.

[0134] c) Vacuuming: temperature is 1000°C, pressure is 0, and time is 200s.

[0135] d) Oxidation: temperature 1000° C., pressure 400 mbar, oxygen flow rate 3000 sccm, nitrogen flow rate 1000 sccm, time 2700 s.

[0136] e) Vacuuming: temperature is 1000°C, pressure is 0, and time is 200s.

[0137] f) Back pressure: temperature 1000°C, nitrogen flow 15000 sccm, pressure 1060 mbar, time 90 s.

[0138] g) Leaving the boat: passing nitrogen at 15000 sccm for 700 s.

[0139] 3. Confirm the coating effect and record the film thickness, etc.

[0140] 4. According to the required pattern, laser processing is performed on a set area on the single crystal silicon wafer on which the mask layer is formed to remove the mask layer on the set area.

[0141] 5. Soak and clean the silicon oxide film with alkaline cleaning solution (formula 1) to confirm the cleaning time. The cleaning process is as follows: feeding, water washing, alkaline washing, water washing, acid washing, water washing, water washing, slow pulling, and drying.

[0142] Comparative Example 3

[0143] The steps of this comparative example are basically the same as those of comparative example 2, except that in step 2, the oxygen flow rate in the oxidation process is 4000 sccm.

[0144] Comparative Example 4

[0145] The steps of this comparative example are basically the same as those of comparative example 2, except that in step 2, the oxygen flow rate in the oxidation process is 5000 sccm.

[0146] Comparative Example 5

[0147] The steps of this comparative example are basically the same as those of comparative example 2, except that in step 2, the pressure in the oxidation process is 800 mbar.

[0148] Comparative Example 6

[0149] The steps of this comparative example are basically the same as those of comparative example 2, except that in step 2, the pressure in the oxidation process is 1600 mbar.

[0150] Comparative Example 7

[0151] The steps of this comparative example are basically the same as those of comparative example 2, except that in step 2, the oxidation process time is 1500s.

[0152] Comparative Example 8

[0153] The steps of this comparative example are basically the same as those of comparative example 2, except that in step 2, the oxidation process time is 3500s.

[0154] Comparative Example 9

[0155] The steps of this comparative example are basically the same as those of Example 3, except that in step 2, the oxidation process temperature is 650°C.

[0156] The appearance of the single crystal silicon wafers prepared in the above examples and comparative examples is shown in Table 1.

[0157] Table 1

[0158]

[0159]

[0160] In the above-mentioned embodiments 1 to 8, after the alkaline washing treatment, no black core is generated in the laser processed area of ​​the single crystal silicon wafer, the mask layer is in a normal state, and the silicon substrate under the mask is in a velvety state, indicating that under the high temperature, high pressure and high oxygen conditions, the mask layer grows with high density and can withstand alkaline washing for a long time.

[0161] It can be seen from Examples 4 to 8 that good cleaning effects can be achieved by adjusting the proportion of the components in the alkaline cleaning solution.

[0162] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0163] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a mask layer on a single crystal silicon wafer, characterized in that: The following steps are involved: Forming a silicon nitride mask layer and / or a silicon oxide mask layer on a single crystal silicon wafer using a CVD process; The process parameters for forming the silicon nitride mask layer include: The temperature is 400-450℃, the silane flow rate is 500-1500sccm, the ammonia flow rate is 5000-9000sccm, the power is 6000-9000w, the duty cycle is 30-50ms, the cycle is 40-60ms, the pressure is 300-500mtorr; the time is 300-400s; The process parameters for forming the silicon oxide mask layer include: The temperature is 800-1000°C, the pressure is 1500-1800 mbar, the oxygen flow rate is 3500-5000 sccm, the nitrogen flow rate is 500-2000 sccm, and the time is 3000-4200 s.

2. The method for preparing a mask layer on a single crystal silicon wafer according to claim 1, characterized in that: Before the step of coating the silicon nitride mask layer, the preparation method further comprises the step of pre-ventilating the CVD equipment; The process parameters of the pre-ventilation include: temperature of 400-450°C, silane flow rate of 500-1500sccm, ammonia flow rate of 5000-9000sccm, power of 6000-9000w, duty cycle of 30-50ms, cycle of 40-60ms, pressure of 300-500mtorr; time of 50-100s.

3. The method for preparing a mask layer on a single crystal silicon wafer according to claim 1 or 2, characterized in that: After the step of coating the silicon nitride mask layer, the preparation method further comprises the steps of evacuating and back-pressuring the CVD equipment; The vacuuming process parameters include: temperature of 400-450°C, pressure of less than 30 mtorr, and time of 70-200 s; The back pressure process parameters include: temperature of 400-450° C., nitrogen flow, flow rate of 10000-20000 sccm, pressure of 1000-1060 mtorr, and time of 70-200 s.

4. The method for preparing a mask layer on a single crystal silicon wafer according to claim 1, characterized in that: After the step of coating the silicon oxide mask layer, the preparation method further comprises the steps of evacuating and back-pressuring the CVD equipment; The vacuuming process parameters include: temperature of 800-1100°C, pressure of less than 30 mbar, and time of 70-200 s; The back pressure process parameters include: temperature of 800-1100° C., nitrogen flow, flow rate of 10000-20000 sccm, pressure of 1000-1060 mbar, and time of 70-200 s.

5. The method for preparing a mask layer on a single crystal silicon wafer according to claim 1, characterized in that: The thickness of the silicon nitride mask layer is 40-80 nm; and / or The thickness of the silicon oxide mask layer is 4-10 nm.

6. A method for preparing a single crystal silicon wafer, characterized in that: The following steps are involved: Forming a mask layer on a single crystal silicon wafer according to the preparation method of any one of claims 1 to 5; Performing laser processing on a set area on the single crystal silicon wafer on which the mask layer is formed, so as to remove the mask layer on the set area; The single crystal silicon wafer treated by the laser is subjected to an alkali washing treatment to form a polished surface in the set area and a velvet surface in other areas.

7. The method for preparing a single crystal silicon wafer according to claim 6, characterized in that: The alkaline washing solution used in the alkaline washing treatment comprises water, alkali and hydrogen peroxide. The pH value of the alkaline washing solution is 8-12, the mass fraction is 40%-49%, and the mass fraction of the hydrogen peroxide is 30%-36%.

8. The method for preparing a single crystal silicon wafer according to claim 6 or 7, characterized in that: The alkali washing treatment time is 200s to 500s.

9. A single crystal silicon wafer, characterized in that: It is prepared by the preparation method according to any one of claims 6 to 8.

10. A solar cell, characterized in that: A single crystal silicon wafer comprising the single crystal silicon wafer according to claim 9; Optionally, the solar cell is a TOPCon cell or an IBC cell.

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