A method for improving uniformity of silicon wafers

Abstract

The invention relates to the field of semiconductor equipment technology, and proposes a method for improving the uniformity of silicon wafers. A method for improving the uniformity of silicon wafers, wherein silicon wafers are placed in an alkali polishing tank, and each batch of silicon wafers is taken out after alkali polishing; during the alkali polishing process of 1 to 50 batches of silicon wafers, the amount of sodium hydroxide replenished is 248 mL / L to 253 mL / L; during the alkali polishing process of 51 to 100 batches of silicon wafers, the amount of sodium hydroxide replenished is 242 mL / L to 248 mL / L; during the alkali polishing process of 101 to 170 batches of silicon wafers, the amount of sodium hydroxide replenished is 238 mL / L to 242 mL / L; during the alkali polishing process of 171 to 300 batches of silicon wafers, the amount of sodium hydroxide replenished is 230 mL / L to 240 mL / L. This method can ensure the uniformity of the oxide layer and achieve the effect of effective control of the thickness in the alkali polishing process.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor equipment, and in particular to a method for improving the uniformity of a silicon wafer. Background Art

[0002] In the TOPCon solar cell structure, the tunneling layer refers to a very thin silicon oxide layer (SiOx), which is usually about 1-2 nanometers thick. This layer of material uses the quantum tunneling effect to achieve the transmission of electrons and effectively prevents the recombination of holes, thereby achieving the purpose of passivating the back of the solar cell. Before preparing the tunneling layer, there will be a layer of SiO2 layer on the back that is naturally formed after polishing. The uniformity of the oxide layer directly affects the uniformity of the tunneling layer. In the existing N-type TOPCON battery back alkaline polishing process, the main functional tanks are: pre-cleaning / alkaline polishing / post-cleaning / acid washing / slow pulling / drying tanks. In the alkaline polishing process, hydrofluoric acid and hydrochloric acid are mostly used for treatment, and pure hydrochloric acid is also used for treatment. In the pure hydrochloric acid treatment method, the dehydration of the silicon wafer is poor after being pulled too slowly, and the silicon reacts quickly with oxygen when exposed to the air, so the uniformity and thickness of the naturally generated oxide layer cannot be well controlled. If the uniformity of the oxide layer is poor, it will lead to poor photoelectric conversion efficiency, large carrier recombination losses, accelerated battery aging and increased failure rate. If the thickness of the oxide layer cannot be stably controlled, when the thickness is too thick, it will lead to poor photoelectric conversion efficiency, large carrier recombination losses, and affected contact resistance. When the thickness is too thin, it will lead to increased interface state density, poor passivation effect, excessive tunneling effect and serious structural stability problems. Summary of the invention

[0003] The object of the present invention is to provide a method for improving the uniformity of silicon wafers, which can ensure the uniformity of the oxide layer and achieve the effect of effectively controlling the thickness in the alkali polishing process.

[0004] To solve the above problems, the technical solution adopted by the present invention is:

[0005] The present invention provides a method for improving the uniformity of silicon wafers, wherein silicon wafers are placed in an alkali polishing tank, and each batch of silicon wafers is taken out after alkali polishing;

[0006] During the alkaline polishing process of 1 to 50 batches of silicon wafers, the replenishment volume of sodium hydroxide was 248 mL / L to 253 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0007] During the alkaline polishing process of batches 51 to 100 of silicon wafers, the replenishment volume of sodium hydroxide was 242 mL / L to 248 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0008] During the alkaline polishing process of silicon wafer batches 101 to 170, the replenishment volume of sodium hydroxide was 238 mL / L to 242 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0009] During the alkaline polishing process of batches 171 to 300 of silicon wafers, the replenishment amount of sodium hydroxide was 230 mL / L to 240 mL / L, and the replenishment amount of deionized water was 190 mL / min.

[0010] In some embodiments of the present invention, the above method comprises the following steps:

[0011] Pre-cleaning: Place the silicon wafer in the pre-cleaning tank to clean the dirt on the surface of the silicon wafer;

[0012] Alkali polishing: Place the silicon wafers into the alkaline polishing tank and take out each batch of silicon wafers after alkaline polishing;

[0013] Post-cleaning: Place the silicon wafer in the post-cleaning tank and clean the surface of the silicon wafer again;

[0014] Pickling: Place the silicon wafer in a pickling tank and clean it with hydrochloric acid and deionized water;

[0015] Slow pulling: Place the silicon wafer into a slow pulling tank, inject solution into the tank, sink the silicon wafer to the bottom of the tank and then pull it up;

[0016] Drying: Place the silicon wafer in a drying tank and dry it at 80°C to 100°C. Adjust the opening angle of the air inlet valve of the drying tank to 40° to 50°.

[0017] Among them, in the alkali polishing step, during the alkali polishing process of 1 to 50 batches of silicon wafers, the replenishing amount of sodium hydroxide is 248 mL / L to 253 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 51 to 100 batches of silicon wafers, the replenishing amount of sodium hydroxide is 242 mL / L to 248 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 101 to 170 batches of silicon wafers, the replenishing amount of sodium hydroxide is 238 mL / L to 242 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 171 to 300 batches of silicon wafers, the replenishing amount of sodium hydroxide is 230 mL / L to 240 mL / L, and the replenishing amount of deionized water is 190 mL / min.

[0018] In some embodiments of the present invention, the concentration of sodium hydroxide in the alkali polishing step is 46% to 48%.

[0019] In some embodiments of the present invention, the silicon wafer cleaning in the above-mentioned pre-cleaning step is specifically to place the silicon wafer in a cleaning solution 1 and clean it for 60 s to 120 s, wherein the cleaning solution 1 comprises cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of (140-145): (470-480): (3.4-3.8): (17-18).

[0020] In some embodiments of the present invention, the silicon wafer cleaning in the above-mentioned pre-cleaning step is specifically to place the silicon wafer in a cleaning solution 2 and clean it for 60 s to 120 s, wherein the cleaning solution 2 comprises cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of (140-145): (470-480): (2-2.2): (17-18).

[0021] In some embodiments of the present invention, the pickling time of the pickling step is 60 s to 120 s, and the volume ratio of hydrochloric acid to deionized water is (2.2 to 2.8):495.

[0022] In some embodiments of the present invention, the above slow pulling is specifically to fill the slow pulling tank with solution and keep the solution injected, sink the silicon wafer to the bottom of the tank and then pull it up, the solution includes deionized water with a ratio of cold water to hot water of 2:1, the solution temperature is 37°C to 43°C, and the solution conductivity is 3 10 μS / cm~5 10 μS / cm, and the time for the silicon wafer to sink to the bottom of the groove and then be pulled up is 90 to 110 seconds.

[0023] In some embodiments of the present invention, the drying gas is nitrogen, and the nitrogen gas flow rate is 1900 m 3 / h~2100m 3 / h, and the drying temperature is 80℃~100℃.

[0024] In some embodiments of the present invention, the alkali polishing treatment time of each batch of silicon wafers is 150 s to 180 s.

[0025] Compared with the prior art, the invention of the present invention has at least the following advantages or beneficial effects:

[0026] The present invention can improve the uniformity of the tower base on the back of the silicon wafer by improving the amount of alkali solution added, so that the oxide layer produced by the silicon wafer during the pickling reaction can be more uniform. Specifically, since the reaction of Si and alkali will occur during the alkali polishing process, the reaction equation is 2NaOH+Si+H2O=Na2SiO3+2H2, so as to corrode the back pyramid to form the back tower base, and the alkali in the solution will be consumed during the reaction. The inventors found that with the increase of the reaction batches, the alkali content in the solution is also constantly changing, resulting in the reaction of alkali and Si changing all the time. If the amount of addition remains unchanged, the alkali concentration in the solution will also change accordingly. Based on this, the inventors found after research that by adjusting the amount of sodium hydroxide replenishment of different batches, the alkali content in the solution can be maintained in a relatively balanced state, so that the reaction of alkali and Si is always maintained in a relatively balanced state, so as to achieve the effect of balanced control of the corrosion of the back pyramid, form a uniform tower base, and thus obtain each batch of silicon wafers with good uniformity.

[0027] In addition, the present invention improves the opening angle of the air intake valve of the drying tank, thereby making the drying tank body basically closed. The inventors found that silicon wafers in a wet state react with oxygen in the air to generate an oxide layer faster than in a dry state. By changing the angle to 40° to 50°, the air intake becomes smaller, which directly affects the air circulation in the drying tank body, maintains the minimum temperature in the drying tank at a higher level, makes silicon wafers easier to dry, and makes the oxide layer thickness easier to control and more stable, thereby improving uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0029] Figure 1 This is a picture of a silicon wafer product after being processed in Example 1 of the present invention;

[0030] Figure 2 This is a picture of a silicon wafer product after being processed in Comparative Example 1 of the present invention;

[0031] Figure 3 This is a picture of a silicon wafer product after being processed in Comparative Example 2 of the present invention;

[0032] Figure 4 This is a picture of the silicon wafer product after being processed in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0034] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0035] The present invention provides a method for improving the uniformity of silicon wafers, wherein silicon wafers are placed in an alkali polishing tank, and each batch of silicon wafers is taken out after alkali polishing;

[0036] During the alkaline polishing process of 1 to 50 batches of silicon wafers, the replenishment volume of sodium hydroxide was 248 mL / L to 253 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0037] During the alkaline polishing process of batches 51 to 100 of silicon wafers, the replenishment volume of sodium hydroxide was 242 mL / L to 248 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0038] During the alkaline polishing process of silicon wafer batches 101 to 170, the replenishment volume of sodium hydroxide was 238 mL / L to 242 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0039] During the alkaline polishing process of batches 171 to 300 of silicon wafers, the replenishment amount of sodium hydroxide was 230 mL / L to 240 mL / L, and the replenishment amount of deionized water was 190 mL / min.

[0040] The present invention can improve the uniformity of the tower base on the back of the silicon wafer by improving the amount of alkali solution added, so that the oxide layer produced by the silicon wafer during the pickling reaction can be more uniform. Specifically, since the reaction of Si and alkali will occur during the alkali polishing process, the reaction equation is 2NaOH+Si+H2O=Na2SiO3+2H2, so as to corrode the back pyramid to form the back tower base, and the alkali in the solution will be consumed during the reaction. The inventors found that with the increase of the reaction batches, the alkali content in the solution is also constantly changing, resulting in the reaction of alkali and Si changing all the time. If the amount of addition remains unchanged, the alkali concentration in the solution will also change accordingly. Based on this, the inventors found after research that by adjusting the amount of sodium hydroxide replenishment of different batches, the alkali content in the solution can be maintained in a relatively balanced state, so that the reaction of alkali and Si is always maintained in a relatively balanced state, so as to achieve the effect of balanced control of the corrosion of the back pyramid, form a uniform tower base, and thus obtain each batch of silicon wafers with good uniformity.

[0041] In some embodiments of the present invention, the above method comprises the following steps:

[0042] Pre-cleaning: Place the silicon wafer in the pre-cleaning tank to clean the dirt on the surface of the silicon wafer;

[0043] Alkali polishing: Place the silicon wafers into the alkaline polishing tank and take out each batch of silicon wafers after alkaline polishing;

[0044] Post-cleaning: Place the silicon wafer in the post-cleaning tank and clean the surface of the silicon wafer again;

[0045] Pickling: Place the silicon wafer in a pickling tank and clean it with hydrochloric acid and deionized water;

[0046] Slow pulling: Place the silicon wafer into a slow pulling tank, inject solution into the tank, sink the silicon wafer to the bottom of the tank and then pull it up;

[0047] Drying: Place the silicon wafer in a drying tank and dry it at 80°C to 100°C. Adjust the opening angle of the air inlet valve of the drying tank to 40° to 50°.

[0048] Among them, in the alkali polishing step, during the alkali polishing process of 1 to 50 batches of silicon wafers, the replenishing amount of sodium hydroxide is 248 mL / L to 253 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 51 to 100 batches of silicon wafers, the replenishing amount of sodium hydroxide is 242 mL / L to 248 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 101 to 170 batches of silicon wafers, the replenishing amount of sodium hydroxide is 238 mL / L to 242 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 171 to 300 batches of silicon wafers, the replenishing amount of sodium hydroxide is 230 mL / L to 240 mL / L, and the replenishing amount of deionized water is 190 mL / min.

[0049] In addition, the present invention improves the opening angle of the air intake valve of the drying tank, thereby making the drying tank body basically closed. The inventors found that silicon wafers in a wet state react with oxygen in the air to generate an oxide layer faster than in a dry state. By changing the angle to 40° to 50°, the air intake becomes smaller, which directly affects the air circulation in the drying tank body, maintains the minimum temperature in the drying tank at a higher level, makes silicon wafers easier to dry, and makes the oxide layer thickness easier to control and more stable, thereby improving uniformity.

[0050] In some embodiments of the present invention, the concentration of sodium hydroxide in the alkali polishing step is 46% to 48%.

[0051] In some embodiments of the present invention, the silicon wafer cleaning in the pre-cleaning step is specifically to place the silicon wafer in a cleaning solution 1 for cleaning for 60 s to 120 s, wherein the cleaning solution 1 comprises cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of (140-145): (470-480): (3.4-3.8): (17-18). By adjusting the ratio of hot and cold water, the hot and cold mixed mixture can mix the chemicals added to the tank more evenly than single cold water or hot water, thereby improving the uniformity of the silicon wafer.

[0052] The temperature of the hot deionized water is 100°C to 110°C.

[0053] The hydrogen peroxide in the cleaning solution 1 has strong oxidizing properties and can oxidize organic matter on the surface of the silicon wafer, and the sodium hydroxide can dissolve the oxidation product. The organic film on the surface of the silicon wafer is removed by this oxidation and dissolution method, and the organic pollution on the surface of the silicon wafer is removed by sodium hydroxide. The combination of the above-mentioned raw materials can effectively improve the removal effect of impurities on the surface of the silicon wafer.

[0054] In some embodiments of the present invention, the silicon wafer cleaning in the pre-cleaning step is specifically to place the silicon wafer in a cleaning solution 2 for cleaning for 60 s to 120 s, wherein the cleaning solution 2 comprises cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of (140-145): (470-480): (2-2.2): (17-18). By adjusting the ratio of hot and cold water, the desired temperature can be reached more quickly than simply heating, and the uniformity of silicon wafer processing can also be improved.

[0055] The temperature of the hot deionized water is 100°C to 110°C.

[0056] In some embodiments of the present invention, the pickling time of the pickling step is 60 s to 120 s, and the volume ratio of hydrochloric acid to deionized water is (2.2 to 2.8): 495. The residual alkali solution remaining on the surface of the silicon wafer can be neutralized by pickling.

[0057] In some embodiments of the present invention, the above slow pulling is specifically to fill the slow pulling tank with solution and keep the solution injected, sink the silicon wafer to the bottom of the tank and then pull it up, the solution includes deionized water with a ratio of cold water to hot water of 2:1, the solution temperature is 37°C to 43°C, and the solution conductivity is 3 10 μS / cm~5 10 μS / cm, and the time for the silicon wafer to sink to the bottom of the groove and then be pulled up is 90 s to 110 s.

[0058] The slow pulling process can pre-dehydrate the surface of the silicon wafer, and the temperature of the solution is selected to be 37°C to 43°C so that the surface tension becomes larger and the adsorption force becomes smaller, making it easier to remove impurities and residual acid that have been desorbed from the surface, thus preparing for drying the silicon wafer.

[0059] In some embodiments of the present invention, the drying gas is nitrogen, and the nitrogen gas flow rate is 1900 m 3 / h~2100m 3 / h, and the drying temperature is 80℃~100℃.

[0060] In some embodiments of the present invention, the alkali polishing treatment time of each batch of silicon wafers is 150 s to 180 s.

[0061] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0062] Example 1

[0063] A method for improving uniformity of a silicon wafer comprises the following steps:

[0064] Pre-cleaning: Place the silicon wafer in the pre-cleaning tank and clean the silicon wafer with cleaning solution 1 (cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of 140:480:3.4:17.1) for 60 seconds, then take it out;

[0065] Alkali polishing: Put the silicon wafers into the alkaline polishing tank, and take out each batch of silicon wafers after 150s of alkaline polishing;

[0066] During the alkaline polishing process of 1 to 50 batches of silicon wafers, the replenishment volume of sodium hydroxide (concentration 46%) was 248 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0067] During the alkaline polishing process of batches 51 to 100 of silicon wafers, the replenishment volume of sodium hydroxide (concentration 46%) was 242 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0068] During the alkaline polishing process of silicon wafer batches 101 to 170, the replenishment volume of sodium hydroxide (concentration 46%) was 238 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0069] During the alkaline polishing process of silicon wafer batches 171 to 300, the replenishment volume of sodium hydroxide (concentration 46%) was 230 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0070] Post-cleaning: Place the silicon wafer in the post-cleaning tank and put it into cleaning solution 2 (cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of 140:480:2:17) to clean the surface of the silicon wafer again for 60 seconds;

[0071] Pickling: Place the silicon wafer in a pickling tank, mix hydrochloric acid and deionized water in a volume ratio of 2.3:495, and rinse for 60 seconds;

[0072] Slow pull: Fill the slow pull tank with 520L of solution and keep the solution injected, sink the silicon wafer to the bottom of the tank and then pull it up. The solution includes deionized water with a ratio of cold water to hot water of 2:1. The solution temperature is 38°C and the solution conductivity is 4 10 μS / cm, the time for the silicon wafer to sink to the bottom of the groove and then be pulled up is 100s

[0073] Drying: Place the silicon wafer in a drying tank and place it in a nitrogen gas flow rate of 2000m 3 / h, dry the silicon wafers at 100°C, and adjust the opening angle of the air inlet valve of the drying tank to 45°.

[0074] Example 2

[0075] A method for improving uniformity of a silicon wafer comprises the following steps:

[0076] Pre-cleaning: Place the silicon wafer in the pre-cleaning tank and clean the silicon wafer for 80 seconds using cleaning solution 1 (cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of 143:475:3.6:18), then take it out;

[0077] Alkali polishing: Put the silicon wafers into the alkaline polishing tank, and take out each batch of silicon wafers after 170s of alkaline polishing;

[0078] During the alkaline polishing process of 1 to 50 batches of silicon wafers, the replenishment volume of sodium hydroxide (concentration 47%) was 250 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0079] During the alkaline polishing process of batches 51 to 100 of silicon wafers, the replenishment volume of sodium hydroxide (concentration 47%) was 246 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0080] During the alkaline polishing process of silicon wafer batches 101 to 170, the replenishment volume of sodium hydroxide (concentration 47%) was 240 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0081] During the alkaline polishing process of silicon wafer batches 171 to 300, the replenishment volume of sodium hydroxide (concentration 47%) was 235 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0082] Post-cleaning: Place the silicon wafer in the post-cleaning tank and put it into cleaning solution 2 (cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of 145:475:2.1:17.5) to clean the surface of the silicon wafer again for 100 seconds;

[0083] Pickling: Place the silicon wafer in a pickling tank, mix hydrochloric acid and deionized water in a volume ratio of 2.6:495, and rinse for 90 seconds;

[0084] Slow pull: Fill the slow pull tank with 520L of solution and keep the solution injected, sink the silicon wafer to the bottom of the tank and then pull it up. The solution includes deionized water with a ratio of cold water to hot water of 2:1. The solution temperature is 37°C and the solution conductivity is 3 10 μS / cm, the time for the silicon wafer to sink to the bottom of the groove and then be pulled up is 90s

[0085] Drying: Place the silicon wafer in a drying tank and heat it with nitrogen gas flow rate of 1900m 3 / h, dry the silicon wafers at 80°C, and adjust the opening angle of the air inlet valve of the drying tank to 40°.

[0086] Example 3

[0087] A method for improving uniformity of a silicon wafer comprises the following steps:

[0088] Pre-cleaning: Place the silicon wafer in the pre-cleaning tank and clean the silicon wafer for 120 seconds using cleaning solution 1 (cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of 145:480:3.8:17), then take it out;

[0089] Alkali polishing: put the silicon wafers into the alkali polishing tank, and take out each batch of silicon wafers after 180s of alkali polishing;

[0090] During the alkaline polishing process of 1 to 50 batches of silicon wafers, the replenishment volume of sodium hydroxide (concentration 48%) was 248 to 253 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0091] During the alkaline polishing process of batches 51 to 100 of silicon wafers, the replenishment volume of sodium hydroxide (concentration 48%) was 248 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0092] During the alkaline polishing process of silicon wafer batches 101 to 170, the replenishment volume of sodium hydroxide (concentration 48%) was 242 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0093] During the alkaline polishing process of silicon wafer batches 171 to 300, the replenishment volume of sodium hydroxide (concentration 48%) was 240 mL / L, and the replenishment volume of deionized water was 190 mL / min;

[0094] Post-cleaning: Place the silicon wafer in the post-cleaning tank and place it in cleaning solution 2 (cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of 145:480:2.2:17) to clean the surface of the silicon wafer again for 120 seconds;

[0095] Pickling: Place the silicon wafer in a pickling tank, mix hydrochloric acid and deionized water in a volume ratio of 2.8:495, and rinse for 120 seconds;

[0096] Slow pull: Fill the slow pull tank with 520L of solution and keep the solution injected, sink the silicon wafer to the bottom of the tank and then pull it up. The solution includes deionized water with a ratio of cold water to hot water of 2:1. The solution temperature is 43°C and the solution conductivity is 5 10 μS / cm, the time for the silicon wafer to sink to the bottom of the groove and then be pulled up is 110s

[0097] Drying: Place the silicon wafer in a drying tank and place it in a nitrogen gas flow rate of 2100m 3 / h, dry the silicon wafers at 100°C, and adjust the opening angle of the air inlet valve of the drying tank to 50°.

[0098] Comparative Example 1

[0099] This comparative example is basically the same as Example 1, except that: in the alkali polishing step, during the alkali polishing process of 1 to 300 batches of silicon wafers, the replenishing amount of sodium hydroxide is 245 mL / L.

[0100] Comparative Example 2

[0101] This comparative example is basically the same as Example 1, except that the opening angle of the air inlet valve in the drying step is 90°.

[0102] Comparative Example 3

[0103] This comparative example is basically the same as Example 1, except that: in the alkaline polishing step, during the alkaline polishing process of 1 to 300 batches of silicon wafers, the replenishing amount of sodium hydroxide is 245 mL / L; and the opening angle of the air inlet valve in the drying step is 90°.

[0104] (I) The silicon wafers of Example 1 and Comparative Examples 1 to 3 were inspected by 3D testing instrument Zeta. The results are as follows: Figure 1 to Figure 4 shown.

[0105] observe Figure 1 to Figure 4 , it can be seen that Figure 1 The size and uniformity of the tower base remain consistent, and the uniformity of the tower base morphology improves, all between 8.20μm and 8.48μm; Figure 2 The tower base is obviously more irregular in shape, and the size is between 8.32μm and 8.87μm; Figure 3 The base of the tower is between 7.78μm and 8.41μm, and there are also many irregular bases; Figure 4 Although the tower base is Figures 2-3 The size of the tower base is between 7.47 μm and 9.81 μm. Based on the above figures, it can be seen that under the scheme of Example 1, adjusting the flow rate of sodium hydroxide in batches can effectively improve the uniformity of the silicon wafer.

[0106] (ii) The temperature of the main tank of the drying tank during the drying steps of Example 1 and Comparative Example 2 was detected using the temperature measurement device provided in the drying tank of the Jiejia Chuang machine.

[0107] Six drying tanks are used for both Example 1 and Comparative Example 2 to increase the output of silicon wafers. The lowest temperature of each tank used in Example 1 is lower than the lowest temperature of each tank used in Comparative Example 2, and the temperature rise curve is more stable. This is due to the principle of the formation of the oxide layer in the drying tank: the drying tank is in a basically closed state, and the formation of the oxide layer is that the silicon wafer in a wet state reacts with oxygen in the air to form an oxide layer faster than in a dry state. Therefore, under the valve angle of Example 1, the lowest temperature is low, the curve is more stable, the silicon wafer is dried faster and more stably, and the formation of the oxide layer is more stable and controllable.

[0108] (III) The natural oxide layer thickness and range of silicon wafers at the front / middle / back positions of the flower basket were tested for two polishing grooves of the same batch of Example 1 and Comparative Example 1. The oxide layer thickness of a silicon wafer was tested at five points, and the average was taken as the natural oxide layer thickness. The range was taken as the maximum and minimum difference between the oxide layers at the five test points of the same silicon wafer. The results of Example 1 are shown in Table 1, and the results of Comparative Example 1 are shown in Table 2.

[0109] Table 1

[0110] sample Location Temperature / ℃ humidity Natural oxide layer thickness / μm Range / μm 1 slot forward 33.4 24 0.6082 0.1180 middle 33.4 24 0.6143 0.1179 back 33.4 24 0.6615 0.1667 2 slots forward 33.8 24 0.5330 0.1144 middle 33.8 24 0.6002 0.0583 back 33.8 24 0.6266 0.0754

[0111] Table 2

[0112] sample Location Temperature / ℃ humidity Natural oxide layer thickness / μm Range / μm 1 slot forward 34.3 23 0.6661 0.2025 middle 34.3 23 0.6337 0.1058 back 34.3 23 0.6015 0.1801 2 slots forward 34 25 0.6616 0.1666 middle 34 25 0.6776 0.1358 back 34 25 0.6954 0.2113

[0113] From Table 1 and Table 2, it can be seen that the silicon wafer of Example 1 has better uniformity and lower range.

[0114] In summary, the present invention can improve the uniformity of the tower base on the back of the silicon wafer by improving the amount of alkali solution added, so that the oxide layer generated by the silicon wafer during the pickling reaction can be more uniform.

[0115] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for improving the uniformity of a silicon wafer, characterized in that: Place the silicon wafers in the alkaline polishing tank and take out each batch of silicon wafers after alkaline polishing; During the alkaline polishing process of 1 to 50 batches of silicon wafers, the replenishment volume of sodium hydroxide was 248 mL / L to 253 mL / L, and the replenishment volume of deionized water was 190 mL / min; During the alkaline polishing process of 51 to 100 batches of silicon wafers, the replenishment volume of sodium hydroxide was 242 mL / L to 248 mL / L, and the replenishment volume of deionized water was 190 mL / min; During the alkaline polishing process of silicon wafer batches 101 to 170, the replenishment volume of sodium hydroxide was 238 mL / L to 242 mL / L, and the replenishment volume of deionized water was 190 mL / min; During the alkaline polishing process of batches 171 to 300 of silicon wafers, the replenishment amount of sodium hydroxide was 230 mL / L to 240 mL / L, and the replenishment amount of deionized water was 190 mL / min.

2. A method for improving uniformity of silicon wafers according to claim 1, characterized in that: The steps include: Pre-cleaning: Place the silicon wafer in the pre-cleaning tank to clean the dirt on the surface of the silicon wafer; Alkali polishing: Place the silicon wafers into the alkaline polishing tank and take out each batch of silicon wafers after alkaline polishing; Post-cleaning: Place the silicon wafer in the post-cleaning tank and clean the surface of the silicon wafer again; Pickling: Place the silicon wafer in a pickling tank and clean it with hydrochloric acid and deionized water; Slow pulling: Place the silicon wafer into a slow pulling tank, inject solution into the tank, sink the silicon wafer to the bottom of the tank and then pull it up; Drying: Place the silicon wafer in a drying tank and dry it at 80°C to 100°C. Adjust the opening angle of the air inlet valve of the drying tank to 40° to 50°. Among them, in the alkali polishing step, during the alkali polishing process of 1 to 50 batches of silicon wafers, the replenishing amount of sodium hydroxide is 248 mL / L to 253 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 51 to 100 batches of silicon wafers, the replenishing amount of sodium hydroxide is 242 mL / L to 248 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 101 to 170 batches of silicon wafers, the replenishing amount of sodium hydroxide is 238 mL / L to 242 mL / L, and the replenishing amount of deionized water is 190 mL / min; during the alkali polishing process of 171 to 300 batches of silicon wafers, the replenishing amount of sodium hydroxide is 230 mL / L to 240 mL / L, and the replenishing amount of deionized water is 190 mL / min.

3. A method for improving uniformity of silicon wafers according to claim 1 or 2, characterized in that: The volume concentration of sodium hydroxide in the alkali polishing step is 46% to 48%.

4. A method for improving uniformity of silicon wafers according to claim 2, characterized in that: The silicon wafer cleaning in the pre-cleaning step is specifically to place the silicon wafer in a cleaning solution 1 and clean it for 60 s to 120 s. The cleaning solution 1 includes cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of (140-145): (470-480): (3.4-3.8): (17-18).

5. The method for improving uniformity of silicon wafers according to claim 2, characterized in that: The silicon wafer cleaning in the pre-cleaning step is specifically to place the silicon wafer in a cleaning solution 2 for cleaning for 60 s to 120 s, wherein the cleaning solution 2 comprises cold deionized water, hot deionized water, sodium hydroxide and hydrogen peroxide in a volume ratio of (140-145):(470-480):(2-2.2):(17-18).

6. A method for improving uniformity of silicon wafers according to claim 2, characterized in that: The pickling time of the pickling step is 60 s to 120 s, and the volume ratio of hydrochloric acid to deionized water is (2.2 to 2.8):

495.

7. The method for improving uniformity of silicon wafers according to claim 2, characterized in that: The slow pulling is specifically to fill the slow pulling tank with solution and keep the solution injected, sink the silicon wafer to the bottom of the tank and then pull it up, the solution includes deionized water with a ratio of cold water to hot water of 2:1, the solution temperature is 37°C to 43°C, and the solution conductivity is 3 10 μS / cm~5 10 μS / cm, and the time for the silicon wafer to sink to the bottom of the groove and then be pulled up is 90 s to 110 s.

8. The method for improving uniformity of silicon wafers according to claim 2, characterized in that: The drying gas is nitrogen, and the nitrogen flow rate is 1900 m 3 / h~2100m 3 / h, and the drying temperature is 80℃~100℃.

9. A method for improving uniformity of silicon wafers according to claim 1 or 2, characterized in that: The alkali polishing treatment time for each batch of silicon wafers is 150 s to 180 s.

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