Boron slurry cleaning method for N-type silicon wafer and solar cell

Abstract

The invention provides a boron slurry cleaning method for an N-type silicon wafer and a solar cell, and relates to the technical field of new energy. The boron slurry cleaning method comprises the following steps: putting an N-type original silicon wafer into a pre-cleaning solution, and pre-cleaning the N-type original silicon wafer to obtain a pre-cleaned N-type silicon wafer; boron slurry is printed on the surface of the pre-cleaned N-type silicon wafer, and high-temperature annealing treatment is carried out on the N-type silicon wafer printed with the boron slurry; putting the N-type silicon wafer subjected to high-temperature annealing treatment into an RAC solution for cleaning; putting the cleaned N-type silicon wafer into an alkaline etchant solution for secondary cleaning; and putting the N-type silicon wafer subjected to secondary cleaning into an acidic etchant solution for tertiary cleaning to obtain the N-type silicon wafer subjected to boron slurry cleaning. The boron slurry cleaning method provided by the embodiment of the invention is not limited by the boron concentration, the application scene is wide, the cleaning effect is not influenced by other ions in water, and the cleaning effect is stable.

Description

Technical Field

[0001] The invention relates to the field of new energy technology, and in particular to a boron slurry cleaning method for an N-type silicon wafer and a solar cell. Background Art

[0002] Crystalline silicon solar cells can be divided into P-type silicon wafers and N-type silicon wafers according to the type of doping elements. Among them, the preparation of PN junctions on N-type silicon wafers requires the use of boron sources for boron diffusion. Currently, boron sources include boron tribromide, boron chloride, boron slurry, etc. Boron slurry is widely used due to its low material cost, but the problem of difficulty in cleaning boron slurry is an important reason that limits the large-scale application of boron slurry.

[0003] At present, CH-99 boron removal ion exchange resin is usually used to adsorb boron on the surface of N-type silicon wafers. CH-99 resin has a functional group polyhydroxy amine that can form a complex with boron. Polyhydroxy amine can complex with boron to achieve the purpose of selective adsorption of boron.

[0004] However, the method of adsorbing boron on the surface of N silicon wafers by CH-99 resin is generally only applicable to scenarios with low boron concentrations. The adsorption effect of CH-99 resin is limited in scenarios with high boron concentrations. Moreover, the boron removal effect of this method is easily affected by other ions in water and the particle size of the resin. As a result, this method has limited application scenarios and unstable cleaning effects in actual applications. Summary of the invention

[0005] The present invention provides a boron slurry cleaning method for an N-type silicon wafer and a solar cell, so as to solve the problems in the related art of limited application scenarios and unstable cleaning effect when cleaning the surface of an N-type silicon wafer with boron slurry.

[0006] In order to solve the above problems, the technical solution of the present invention is implemented as follows:

[0007] An embodiment of the present invention provides a boron slurry cleaning method for an N-type silicon wafer, the method comprising:

[0008] Putting an N-type original silicon wafer into a pre-cleaning solution to pre-clean the N-type original silicon wafer to obtain a pre-cleaned N-type silicon wafer;

[0009] Printing boron paste on the surface of the pre-cleaned N-type silicon wafer, and performing high-temperature annealing treatment on the N-type silicon wafer printed with the boron paste;

[0010] The N-type silicon wafer after high temperature annealing is placed in a RAC solution for cleaning;

[0011] The cleaned N-type silicon wafer is placed in an alkaline etching solution for secondary cleaning;

[0012] The N-type silicon wafer after the second cleaning is placed in an acidic etching solution for three cleanings to obtain an N-type silicon wafer after cleaning with boron slurry.

[0013] Optionally, the pre-cleaning solution includes hydrogen peroxide and an alkaline solution; the concentration of the hydrogen peroxide is 1wt.% to 3wt.%;

[0014] The pre-cleaning time is 3 minutes to 5 minutes, and the pre-cleaning temperature is 25° C. to 30° C.

[0015] Optionally, the concentration of the alkaline solution is 0.5wt.% to 1wt.%; the alkaline solution includes potassium hydroxide solution or sodium hydroxide solution.

[0016] Optionally, printing boron paste on the surface of the pre-cleaned N-type silicon wafer includes:

[0017] Printing boron paste on any surface of the N-type silicon wafer using screen printing technology;

[0018] Wherein, the boron slurry includes a boron source, a silicon source and an organic binder; the proportion of the boron source in the boron slurry is 0.5wt.% to 40wt.%; the proportion of the silicon source in the boron slurry is 4.0wt.% to 75wt.%; the proportion of the organic binder in the boron slurry is 15wt.% to 85wt.%, and the sum of the proportions of the boron source, the silicon source and the organic solvent in the boron slurry is 100wt.%.

[0019] Optionally, the temperature of the high temperature annealing treatment is 900° C. to 1200° C., and the duration of the high temperature annealing treatment is 1 min to 3 min.

[0020] Optionally, the RAC solution includes RAC No. 1 solution and RAC No. 2 solution;

[0021] The step of placing the N-type silicon wafer after high temperature annealing into a RAC solution for cleaning comprises:

[0022] The N-type silicon wafer after high temperature annealing treatment is sequentially placed in the RAC No. 1 solution and the RAC No. 2 solution for cleaning; the cleaning temperature is 20° C. to 30° C., and the cleaning time is 5 min to 10 min.

[0023] Optionally, the duration of the secondary cleaning and / or the tertiary cleaning is 50 min to 60 min, and the temperature of the secondary cleaning and / or the tertiary cleaning is 50° C. to 60° C.

[0024] Optionally, the alkaline corrosion solution includes sodium hydroxide, potassium hydroxide and hydrogen peroxide; wherein the concentration of the sodium hydroxide and / or the potassium hydroxide is 10wt.% to 15wt.%, and the concentration of the hydrogen peroxide is 3wt.% to 5wt.%.

[0025] Optionally, the acidic corrosion solution includes at least one of hydrofluoric acid, nitric acid and hydrochloric acid; wherein the concentration of the hydrofluoric acid is 15wt.% to 20wt.%, and the concentration of the nitric acid is 10wt.% to 15wt.%.

[0026] An embodiment of the present invention further provides a solar cell, comprising an N-type silicon wafer obtained by using the boron slurry cleaning method for an N-type silicon wafer as described in any one of the above items.

[0027] In an embodiment of the present invention, the N-type original silicon wafer is pre-cleaned with a pre-cleaning solution; then, a boron paste is printed on the surface of the pre-cleaned N-type silicon wafer, and a PN junction is prepared in the N-type silicon wafer by high-temperature annealing the N-type silicon wafer printed with the boron paste; then, the N-type silicon wafer after the high-temperature annealing is sequentially placed in a RAC solution, an alkaline corrosion solution, and an acid corrosion solution for cleaning to obtain an N-type silicon wafer cleaned with the boron paste. The N-type silicon wafer boron slurry cleaning method provided in an embodiment of the present invention can clean N-type silicon wafers with different boron concentrations, is not limited by the boron concentration, and has a wider range of application scenarios. In addition, the boron slurry on the surface of the N-type silicon wafer is cleaned with a pre-cleaning solution, a RAC solution, an alkaline corrosion solution, and an acid corrosion solution, respectively, and the cleaning effect is not affected by other ions in the water, and the cleaning effect is more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0029] Figure 1 A flowchart showing a method for cleaning an N-type silicon wafer with boron slurry according to an embodiment of the present invention is shown;

[0030] Figure 2 A flowchart showing the steps of another method for cleaning an N-type silicon wafer with boron slurry according to an embodiment of the present invention is shown;

[0031] Figure 3 A comparison chart showing the results of cleaning an N-type silicon wafer surface with boron slurry according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. 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.

[0033] Reference Figure 1 , shows a flowchart of a method for cleaning an N-type silicon wafer with boron slurry according to an embodiment of the present invention, the method comprising steps 101 to 105:

[0034] Step 101: placing an N-type original silicon wafer into a pre-cleaning solution, and pre-cleaning the N-type original silicon wafer to obtain a pre-cleaned N-type silicon wafer.

[0035] Among them, the N-type original silicon wafer is a single crystal N-type original silicon wafer, the resistivity of the N-type original silicon wafer is 0.1Ω·cm to 0.4Ω·cm, and the thickness of the N-type original silicon wafer is 150μm to 170μm.

[0036] Specifically, before step 101, a single crystal N-type original silicon wafer with a resistivity of 0.1 Ω·cm to 0.4 Ω·cm and a thickness of 150 μm to 170 μm can be selected as the N-type original silicon wafer; then, step 101 is performed to put the N-type original silicon wafer into a pre-cleaning solution, and the N-type original silicon wafer is pre-cleaned with the pre-cleaning solution to obtain a pre-cleaned N-type silicon wafer; finally, the pre-cleaned N-type original silicon wafer can be further cleaned with deionized water to remove the pre-cleaning solution on the surface of the N-type original silicon wafer, and the N-type original silicon wafer cleaned with deionized water is placed in an oven for drying. The drying temperature can be 100° C. to 150° C.

[0037] It should be noted that the pre-cleaned N-type original silicon wafer is further cleaned with deionized water, specifically: the N-type silicon wafer is immersed in deionized water for 1 to 2 minutes; or the N-type silicon wafer is placed in flowing deionized water and continuously rinsed for 1 to 2 minutes; or the N-type silicon wafer is placed in deionized water and ultrasonically cleaned for 1 to 2 minutes, which is not specifically limited in the embodiment of the present invention.

[0038] In the embodiment of the present invention, by placing the N-type original silicon wafer into a pre-cleaning solution and pre-cleaning the N-type original silicon wafer, dirt on the surface of the N-type original silicon wafer can be removed, providing an N-type silicon wafer with a clean surface for step 102, which is conducive to the diffusion of boron atoms in the boron slurry into the N-type silicon wafer in step 102 to form a PN junction.

[0039] Step 102: printing boron paste on the surface of the pre-cleaned N-type silicon wafer, and performing high-temperature annealing treatment on the N-type silicon wafer printed with the boron paste.

[0040] The boron slurry may include a boron source, a silicon source and an organic binder. The boron source may be boron tribromide (BBr 3 ), boron chloride (BCl3), boron nitride (BN), etc., and the physical state of the boron source can be solid (such as powder) or liquid. The silicon source can be quartz sand, silane, silicon dioxide powder, etc., and the physical state of the silicon source can be solid.

[0041] Methods for printing boron paste on the surface of N-type silicon wafers include but are not limited to screen printing technology, 3D printing technology, and flexographic printing technology.

[0042] In an embodiment of the present invention, after obtaining the pre-cleaned N-type silicon wafer through step 101, boron paste can be printed on at least one surface of the pre-cleaned N-type silicon wafer; then, the N-type silicon wafer printed with the boron paste is subjected to high-temperature annealing treatment to diffuse the phosphorus atoms in the boron paste into the interior of the N-type silicon wafer to form a PN junction.

[0043] It should be noted that during the high temperature annealing process, some of the phosphorus atoms in the boron paste printed on the surface of the N-type silicon wafer will diffuse into the inside of the N-type silicon wafer to form a PN junction. After the high temperature annealing process, the other boron paste that has not diffused into the inside of the N-type silicon wafer needs to be cleaned through the cleaning operations of steps 103 to 105 to obtain the N-type silicon wafer after cleaning the boron paste.

[0044] Step 103: Place the N-type silicon wafer after high temperature annealing in a RAC solution for cleaning.

[0045] Specifically, after the N-type silicon wafer printed with the boron paste is subjected to high-temperature annealing treatment in step 102, the N-type silicon wafer is placed in a RAC solution for cleaning to preliminarily clean the boron paste on the surface of the N-type silicon wafer; then, the cleaned N-type silicon wafer is further cleaned with deionized water to remove the residual RAC solution on the surface of the N-type silicon wafer; finally, the N-type silicon wafer cleaned with deionized water is placed in an oven for drying.

[0046] It should be noted that, in the process of placing the N-type silicon wafer after high-temperature annealing treatment into the RAC solution for cleaning, only the surface of the N-type silicon wafer printed with boron paste can be placed in the RAC solution for cleaning, or the entire N-type silicon wafer can be immersed in the RAC solution for cleaning. The embodiment of the present invention does not make specific limitations on this.

[0047] In an embodiment of the present invention, the RAC solution may include at least one of a sulfuric acid / hydrogen peroxide mixed solution (Surfuric / Peroxide Mi, SPM), a hydrofluoric acid dilution solution (DHF), an ammonia and hydrogen peroxide mixed solution (RAC No. 1 solution, APM), and a hydrochloric acid and hydrogen peroxide mixed solution (RAC No. 1 solution, HPM). Among them, the SPM solution includes sulfuric acid and hydrogen peroxide, and the cleaning temperature is 120℃ to 150℃. The SPM solution has a high oxidation ability, which can oxidize the metal and dissolve it in the cleaning solution, and oxidize the organic matter into carbon dioxide and water; the DHF solution includes hydrofluoric acid, and the cleaning temperature is 20℃ to 25℃. The DHF solution can remove the oxide film on the surface of the N-type silicon wafer, and dissolve the metal attached to the oxide film to achieve the cleaning purpose; the RAC No. 1 solution includes ammonia water, hydrogen peroxide and water, and the cleaning temperature can be 20℃ to 30℃. The ammonia water in the RAC No. 1 solution can remove the glass in the boron slurry and the oxide film on the surface of the N-type silicon wafer, and dissolve the metal or organic particles attached to the oxide film; the RAC No. 2 solution includes hydrochloric acid, hydrogen peroxide and water, and the cleaning temperature can be 20℃ to 30℃. The RAC No. 2 solution can remove metals such as iron and zinc on the surface of the N-type silicon wafer.

[0048] In the case where the RAC solution includes a plurality of different types of solutions, the N-type silicon wafer after high-temperature annealing can be sequentially placed in the plurality of different types of solutions for cleaning.

[0049] Step 104: Place the cleaned N-type silicon wafer into an alkaline etching solution for secondary cleaning.

[0050] Specifically, after the N-type silicon wafer is cleaned with the RAC solution in step 103, the N-type silicon wafer may be placed in an alkaline etching solution for secondary cleaning to further clean the boron slurry remaining on the surface of the N-type silicon wafer, and at the same time, the oxide layer on the surface of the N-type silicon wafer is corroded to make the surface of the N-type silicon wafer present a polished structure; then, the N-type silicon wafer after the secondary cleaning is further cleaned with deionized water to remove the alkaline etching solution remaining on the surface of the N-type silicon wafer; finally, the N-type silicon wafer cleaned with deionized water is placed in an oven for drying.

[0051] In the embodiment of the present invention, the alkaline solution may be an alkaline mixed solution of sodium hydroxide and hydrogen peroxide, an alkaline mixed solution of potassium hydroxide and hydrogen peroxide, or an alkaline mixed solution of sodium hydroxide, potassium hydroxide and hydrogen peroxide.

[0052] The concentration of the alkaline solution and the duration of the secondary cleaning can be adjusted according to the cleaning effect. When the concentration of the alkaline solution is relatively high (e.g., 25 wt.%), the duration of the secondary cleaning can be relatively short (e.g., 30 s); when the concentration of the alkaline solution is relatively low (e.g., 5 wt.%), the duration of the secondary cleaning can be relatively long (e.g., 5 min). The embodiments of the present invention do not specifically limit this.

[0053] Step 105 , placing the N-type silicon wafer after the second cleaning into an acidic etching solution for three cleanings to obtain an N-type silicon wafer after the cleaning with boron slurry.

[0054] Specifically, after the N-type silicon wafer is cleaned with an alkaline etching solution in step 104, the N-type silicon wafer can be placed in an acidic etching solution for secondary cleaning to further clean the heavy metal ions and the like in the boron slurry remaining on the surface of the N-type silicon wafer. At the same time, since the surface of the N-type silicon wafer has a polished structure after the secondary cleaning with the alkaline solution in step 104, the surface of the N-type silicon wafer with a polished structure can be etched after the three cleaning operations in step 105 to optimize the reflectivity of the silicon wafer surface; thereafter, the N-type silicon wafer after the three cleanings is further cleaned with deionized water to remove the acidic etching solution remaining on the surface of the N-type silicon wafer; finally, the N-type silicon wafer cleaned with deionized water is placed in an oven for drying.

[0055] In the embodiment of the present invention, the acidic solution may be at least one of a hydrofluoric acid solution, a nitric acid solution or a hydrochloric acid solution.

[0056] The concentration of the acid solution and the duration of the three cleanings can be adjusted according to the cleaning effect. When the concentration of the acid solution is relatively high (e.g., 20 wt.%), the duration of the three cleanings can be relatively short (e.g., 40 s); when the concentration of the acid solution is relatively low (e.g., 8 wt.%), the duration of the three cleanings can be relatively long (e.g., 3 min). The embodiments of the present invention do not specifically limit this.

[0057] In an embodiment of the present invention, after cleaning with a RAC solution, most of the boron slurry on the surface of the N-type silicon wafer can be removed; thereafter, the cleaned N-type silicon wafer is placed in an alkaline corrosion solution for secondary cleaning, which can remove the oxide layer on the surface of the N-type silicon wafer and the silicon source in the residual boron slurry, and by corroding the surface of the N-type silicon wafer, the surface of the N-type silicon wafer presents a polished structure; finally, the N-type silicon wafer after the second cleaning is placed in an acidic corrosion solution for a third cleaning, which can remove the heavy metal ions and other components in the boron slurry remaining on the surface of the N-type silicon wafer, and the reflectivity of the surface of the N-type silicon wafer is optimized by corrosion with an acidic solution. While removing the boron slurry on the surface of the N-type silicon wafer, the reflectivity of the surface of the N-type silicon wafer is also optimized. Furthermore, the boron slurry cleaning method for N-type silicon wafers provided in an embodiment of the present invention has a simple cleaning process, can be used for tank cleaning equipment compatible with battery mass production machines, and has significant economic benefits.

[0058] Optionally, the pre-cleaning solution includes hydrogen peroxide and an alkaline solution; the concentration of the hydrogen peroxide is 1wt.% to 3wt.%; the pre-cleaning time is 3min to 5min, and the pre-cleaning temperature is 25°C to 30°C.

[0059] Optionally, the concentration of the alkaline solution is 0.5wt.% to 1wt.%; the alkaline solution includes potassium hydroxide solution or sodium hydroxide solution.

[0060] In an embodiment of the present invention, the pre-cleaning solution may be a mixed solution of potassium hydroxide solution and hydrogen peroxide, the pre-cleaning solution may be a mixed solution of sodium potassium hydroxide solution and hydrogen peroxide, or the pre-cleaning solution may be a mixed solution of sodium potassium hydroxide solution, potassium hydroxide solution and hydrogen peroxide.

[0061] It should be noted that the pre-cleaning temperature, pre-cleaning time and concentration of the alkaline solution can be adjusted according to the pre-cleaning effect. Specifically, when the pre-cleaning time is long or the pre-cleaning temperature is high, an alkaline solution with a lower concentration can be used; in order to shorten the pre-cleaning time, a higher pre-cleaning temperature and an alkaline solution with a higher concentration can be used, which is not specifically limited in the embodiments of the present invention.

[0062] Among them, in order to reduce the energy consumption during the boron slurry cleaning process of N-type silicon wafers and improve the simplicity of the cleaning process, a pre-cleaning temperature close to the ambient temperature (25°C to 30°C) can be adopted. At the same time, according to the expected pre-cleaning effect, the concentration of the alkaline solution (0.5wt.% to 1wt.%) and the pre-cleaning time (3min to 5min) are determined.

[0063] Optionally, the step 102 of printing the boron paste on the surface of the pre-cleaned N-type silicon wafer may include step 1021:

[0064] Step 1021 , printing boron paste on any surface of the N-type silicon wafer using screen printing technology.

[0065] Among them, the boron slurry includes a boron source, a silicon source and an organic binder; the proportion of the boron source in the boron slurry is 0.5wt.% to 40wt.%; the proportion of the silicon source in the boron slurry is 4.0wt.% to 75wt.%; the proportion of the organic binder in the boron slurry is 15wt.% to 85wt.%, and the sum of the proportions of the boron source, the silicon source and the organic solvent in the boron slurry is 100%.

[0066] In the embodiment of the present invention, the boron paste can be printed on any one of the two surfaces of the N-type silicon wafer.

[0067] The organic binder plays a role in uniformly dispersing the boron source and the silicon source to form a boron slurry. In an embodiment of the present invention, the organic binder may include an organic solvent and a resin, wherein the organic solvent accounts for 95wt.% to 99wt.%, the resin accounts for 1wt.% to 5wt.%, and the sum of the organic solvent and the resin in the organic binder is 100wt.%.

[0068] Specifically, the organic solvent can be at least one of diethylene glycol butyl ether acetate, alcohol ester dodecanol, terpineol, dimethyl adipate, N-methylpyrrolidone, dimethyl phthalate, and dimethyl terephthalate; the resin can be at least one of ethyl cellulose, hydroxyethyl cellulose, polyvinyl butyral (PVB), polyvinyl pyrrolidone, polyvinyl butyral ester, and acrylic resin.

[0069] Optionally, the temperature of the high temperature annealing treatment is 900° C. to 1200° C., and the duration of the high temperature annealing treatment is 1 min to 3 min.

[0070] In the embodiment of the present invention, the purpose of high temperature annealing is to accelerate the diffusion process of boron atoms in the boron paste on the surface of the N-type silicon wafer into the interior of the N-type silicon wafer. After the boron paste is printed on the surface of the pre-cleaned N-type silicon wafer in step 1021, the N-type silicon wafer printed with the boron paste can be transferred to a high temperature annealing device for high temperature annealing.

[0071] The duration of the high temperature annealing treatment can be determined according to the temperature of the high temperature annealing treatment. For example, when the high temperature annealing temperature is high, the high temperature annealing time can be appropriately shortened; when the high temperature annealing temperature is low, the high temperature annealing time can be appropriately extended. It should be noted that the higher high temperature annealing temperature and the lower high temperature annealing temperature here are annealing temperatures within a certain temperature threshold (for example, 900°C to 1200°C). When the high temperature annealing temperature is too high, there is a risk of overburning of the N-type silicon wafer; when the high temperature annealing temperature is too low, the speed of the boron atoms diffusing from the boron slurry to the N-type silicon wafer is too slow, resulting in too long execution time of step 102.

[0072] Optionally, the RAC solution includes RAC No. 1 solution and RAC No. 2 solution; the step 103 of placing the N-type silicon wafer after high temperature annealing into the RAC solution for cleaning may include step 1031:

[0073] Step 1031, placing the N-type silicon wafer after high temperature annealing treatment into the RAC No. 1 solution and the RAC No. 2 solution in sequence for cleaning.

[0074] The cleaning temperature is 20°C to 30°C, and the cleaning time is 5 min to 10 min.

[0075] Specifically, after obtaining the N-type silicon wafer after high temperature annealing treatment in step 102, firstly, the N-type silicon wafer after high temperature annealing treatment is placed in RAC No. 1 solution and washed at 20° C. to 30° C. for 5 min to 10 min; then, the N-type silicon wafer washed in RAC No. 1 solution is washed with deionized water to remove the RAC No. 1 solution remaining on the surface of the N-type silicon wafer; then, the N-type silicon wafer washed with deionized water is placed in RAC No. 2 solution and washed at 20° C. to 30° C. for 5 min to 10 min; then, the N-type silicon wafer washed in RAC No. 2 solution is washed with deionized water to remove the RAC No. 2 solution remaining on the surface of the N-type silicon wafer; finally, the N-type silicon wafer washed with deionized water is placed in an oven for drying.

[0076] It should be noted that the mass ratio of ammonia water, hydrogen peroxide and water in RAC No. 1 solution is 1:1:5; the mass ratio of hydrochloric acid, hydrogen peroxide and water in RAC No. 2 solution is 1:1:5.

[0077] In the embodiment of the present invention, most of the boron slurry on the surface of the N-type silicon wafer can be removed by washing with RAC No. 1 solution and RAC No. 2 solution in sequence; then, the cleaned N-type silicon wafer is placed in an alkaline corrosion solution and an acidic solution in sequence for secondary and tertiary washing, which removes the boron slurry on the surface of the N-type silicon wafer and optimizes the reflectivity of the surface of the N-type silicon wafer.

[0078] Optionally, the duration of the secondary cleaning and / or the tertiary cleaning is 50 min to 60 min, and the temperature of the secondary cleaning and / or the tertiary cleaning is 50° C. to 60° C.

[0079] Optionally, the alkaline corrosion solution includes sodium hydroxide, potassium hydroxide and hydrogen peroxide.

[0080] Wherein, the concentration of the sodium hydroxide and / or the potassium hydroxide is 10wt.% to 15wt.%, and the concentration of the hydrogen peroxide is 3wt.% to 5wt.%.

[0081] Optionally, the acidic corrosion solution includes at least one of hydrofluoric acid, nitric acid and hydrochloric acid.

[0082] Wherein, the concentration of the hydrofluoric acid is 15wt.% to 20wt.%, and the concentration of the nitric acid is 10wt.% to 15wt.%.

[0083] Reference Figure 2 , shows a flowchart of another method for cleaning an N-type silicon wafer with boron slurry according to an embodiment of the present invention, the method comprising steps 201 to 206:

[0084] Step 201: pre-cleaning.

[0085] Specifically, first, a single crystal N-type original silicon wafer with a resistivity of 0.4Ω·cm and a thickness of 170um is selected; then, the N-type original silicon wafer is pre-cleaned in a pre-cleaning solution to obtain a pre-cleaned N-type silicon wafer; finally, the pre-cleaned N-type silicon wafer is immersed in deionized water for 1 minute to remove the pre-cleaning solution on the surface of the N-type silicon wafer, and the N-type silicon wafer washed with deionized water is placed in an oven for drying at a drying temperature of 150°C.

[0086] The pre-cleaning solution includes sodium-potassium hydroxide solution and hydrogen peroxide, the concentration of the potassium hydroxide solution is 0.6 wt.%, and the concentration of the hydrogen peroxide is 2 wt.%. The pre-cleaning temperature is 30° C., and the pre-cleaning time is 3 minutes.

[0087] Step 202: Printing boron paste.

[0088] Specifically, after step 201, the boron paste is printed on any surface of the pre-cleaned N-type silicon wafer using screen printing technology.

[0089] Among them, the boron slurry includes a boron source, a silicon source and an organic binder; the proportion of the boron source in the boron slurry is 0.5wt.% to 40wt.%; the proportion of the silicon source in the boron slurry is 4.0wt.% to 75wt.%; the proportion of the organic binder in the boron slurry is 15wt.% to 85wt.%, and the sum of the proportions of the boron source, silicon source and organic solvent in the boron slurry is 100wt.%.

[0090] Step 203: high temperature annealing treatment.

[0091] Specifically, the N-type silicon wafer printed with the boron paste is subjected to high temperature annealing to obtain the N-type silicon wafer after high temperature annealing, wherein the temperature of the high temperature annealing is 900° C. and the duration of the high temperature annealing is 3 minutes.

[0092] Step 204: RAC solution cleaning.

[0093] Specifically, after obtaining the N-type silicon wafer after high-temperature annealing in step 203, firstly, the N-type silicon wafer after high-temperature annealing is placed in RAC No. 1 solution and washed at 30° C. for 10 minutes; then, the N-type silicon wafer washed in RAC No. 1 solution is immersed in deionized water for 2 minutes to remove the RAC No. 1 solution remaining on the surface of the N-type silicon wafer; then, the N-type silicon wafer washed with deionized water is placed in RAC No. 2 solution and washed at 30° C. for 10 minutes; then, the N-type silicon wafer washed in RAC No. 2 solution is immersed in deionized water for 2 minutes to remove the RAC No. 2 solution remaining on the surface of the N-type silicon wafer; finally, the N-type silicon wafer washed with deionized water is placed in an oven for drying, and the drying temperature may be 150° C. to obtain the N-type silicon wafer washed with RAC solution.

[0094] Step 205: cleaning with alkaline solution.

[0095] Specifically, first, the N-type silicon wafer after being cleaned with the RAC solution obtained in step 204 is placed in an alkaline solution for secondary cleaning; then, the N-type silicon wafer after the secondary cleaning is soaked in deionized water for 2 minutes to remove the alkaline solution on the surface of the N-type silicon wafer; finally, the N-type silicon wafer after being cleaned with deionized water is placed in an oven for drying, and the drying temperature can be 150°C.

[0096] The alkaline solution includes sodium hydroxide solution, potassium hydroxide solution and hydrogen peroxide. The concentration of the sodium hydroxide solution is 10wt.%, the concentration of the potassium hydroxide solution is 10wt.%, and the concentration of the hydrogen peroxide is 5wt.%.

[0097] The cleaning temperature of the alkaline solution is 60°C, and the cleaning time of the alkaline solution is 60 minutes.

[0098] Step 206: cleaning with an acidic solution.

[0099] Specifically, first, the N-type silicon wafer after being cleaned with the alkaline solution obtained in step 205 is placed in an acidic solution for three cleanings; then, the N-type silicon wafer after being cleaned three times is soaked in deionized water for 2 minutes to remove the acidic solution on the surface of the N-type silicon wafer; finally, the N-type silicon wafer after being cleaned with deionized water is placed in an oven for drying, and the drying temperature can be 150°C.

[0100] The acidic solution includes a hydrofluoric acid solution and a nitric acid solution. The concentration of the hydrofluoric acid solution is 15 wt.%, and the concentration of the nitric acid solution is 15 wt.%.

[0101] The cleaning temperature of the alkaline solution is 60°C, and the cleaning time of the alkaline solution is 60 minutes.

[0102] Reference Figure 3 , Figure 3 FIG. 2 shows a comparison of the results of cleaning the surface of an N-type silicon wafer with boron slurry according to an embodiment of the present invention. Figure 3 As shown, the method of using CH-99 boron removal ion exchange resin to adsorb boron on the surface of N-type silicon wafers still has a large amount of boron slurry residue on the surface of the obtained N-type silicon wafer (white spots in the picture), while the boron slurry cleaning method for N-type silicon wafers provided by the embodiment of the present invention has no obvious boron slurry residue on the surface of the obtained N-type silicon wafer. It can be seen that the boron slurry cleaning method for N-type silicon wafers provided by the embodiment of the present invention has a better boron slurry cleaning effect.

[0103] In summary, the boron slurry cleaning method for N-type silicon wafers provided in an embodiment of the present invention pre-cleans the N-type original silicon wafer with a pre-cleaning solution; then the boron slurry is printed on the surface of the pre-cleaned N-type silicon wafer, and a PN junction is prepared in the N-type silicon wafer by high-temperature annealing of the N-type silicon wafer printed with the boron slurry; then the N-type silicon wafer after the high-temperature annealing is sequentially placed in a RAC solution, an alkaline corrosion solution, and an acidic corrosion solution for cleaning to obtain an N-type silicon wafer after cleaning with the boron slurry. The boron slurry cleaning method for N-type silicon wafers provided in an embodiment of the present invention can clean N-type silicon wafers with different boron concentrations, is not limited by the boron concentration, and has a wider range of application scenarios. In addition, the boron slurry on the surface of the N-type silicon wafer is cleaned with a pre-cleaning solution, a RAC solution, an alkaline corrosion solution, and an acidic corrosion solution, respectively, and the cleaning effect is not affected by other ions in the water, and the cleaning effect is more stable.

[0104] An embodiment of the present invention further provides a solar cell, comprising an N-type silicon wafer obtained by using the boron slurry cleaning method for an N-type silicon wafer as described in any one of the above items.

[0105] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0106] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, a magnetic disk, or an optical disk), and includes a number of instructions for enabling a terminal (which can be a mobile phone, a computer, a server, an air conditioner, or a network device, etc.) to execute the methods described in each embodiment of the present invention.

[0107] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A boron slurry cleaning method for N-type silicon wafers, characterized in that: The method comprises: Putting an N-type original silicon wafer into a pre-cleaning solution to pre-clean the N-type original silicon wafer to obtain a pre-cleaned N-type silicon wafer; Printing boron paste on the surface of the pre-cleaned N-type silicon wafer, and performing high-temperature annealing treatment on the N-type silicon wafer printed with the boron paste; The N-type silicon wafer after high temperature annealing is placed in a RAC solution for cleaning; The cleaned N-type silicon wafer is placed in an alkaline etching solution for secondary cleaning; The N-type silicon wafer after the second cleaning is placed in an acidic etching solution for three cleanings to obtain an N-type silicon wafer after cleaning with boron slurry.

2. The method according to claim 1, characterized in that: The pre-cleaning solution includes hydrogen peroxide and an alkaline solution; the concentration of the hydrogen peroxide is 1wt.% to 3wt.%; The pre-cleaning time is 3 minutes to 5 minutes, and the pre-cleaning temperature is 25° C. to 30° C.

3. The method according to claim 2, characterized in that The concentration of the alkaline solution is 0.5wt.% to 1wt.%; the alkaline solution includes potassium hydroxide solution or sodium hydroxide solution.

4. The method according to claim 1, characterized in that: The printing of boron paste on the surface of the pre-cleaned N-type silicon wafer comprises: Printing boron paste on any surface of the N-type silicon wafer using screen printing technology; Wherein, the boron slurry includes a boron source, a silicon source and an organic binder; the proportion of the boron source in the boron slurry is 0.5wt.% to 40wt.%; the proportion of the silicon source in the boron slurry is 4.0wt.% to 75wt.%; the proportion of the organic binder in the boron slurry is 15wt.% to 85wt.%, and the sum of the proportions of the boron source, the silicon source and the organic solvent in the boron slurry is 100wt.%.

5. The method according to claim 1, characterized in that The temperature of the high temperature annealing treatment is 900° C. to 1200° C., and the duration of the high temperature annealing treatment is 1 min to 3 min.

6. The method according to claim 1, characterized in that The RAC solution includes RAC No. 1 solution and RAC No. 2 solution; The step of placing the N-type silicon wafer after high temperature annealing into a RAC solution for cleaning comprises: The N-type silicon wafer after high temperature annealing treatment is sequentially placed in the RAC No. 1 solution and the RAC No. 2 solution for cleaning; the cleaning temperature is 20° C. to 30° C., and the cleaning time is 5 min to 10 min.

7. The method according to claim 1, characterized in that The duration of the secondary cleaning and / or the tertiary cleaning is 50 min to 60 min, and the temperature of the secondary cleaning and / or the tertiary cleaning is 50° C. to 60° C.

8. The method according to claim 1, characterized in that The alkaline corrosion solution includes sodium hydroxide, potassium hydroxide and hydrogen peroxide; wherein the concentration of the sodium hydroxide and / or the potassium hydroxide is 10wt.% to 15wt.%, and the concentration of the hydrogen peroxide is 3wt.% to 5wt.%.

9. The method according to claim 1, characterized in that: The acidic etching solution includes at least one of hydrofluoric acid, nitric acid and hydrochloric acid; wherein the concentration of the hydrofluoric acid is 15wt.% to 20wt.%, and the concentration of the nitric acid is 10wt.% to 15wt.%.

10. A solar cell, characterized in that: The solar cell comprises an N-type silicon wafer obtained by the boron slurry cleaning method for an N-type silicon wafer according to any one of claims 1 to 9.

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