CN112359415A - Manufacturing process of solar P-type polycrystalline silicon wafer - Google Patents

Manufacturing process of solar P-type polycrystalline silicon wafer Download PDF

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CN112359415A
CN112359415A CN202011317073.5A CN202011317073A CN112359415A CN 112359415 A CN112359415 A CN 112359415A CN 202011317073 A CN202011317073 A CN 202011317073A CN 112359415 A CN112359415 A CN 112359415A
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silicon
circulating
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silicon material
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CN112359415B (en
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刘振东
刘笑笑
晁军峰
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Anyang Institute of Technology
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B28/00—Production of homogeneous polycrystalline material with defined structure
    • C30B28/04—Production of homogeneous polycrystalline material with defined structure from liquids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28D—WORKING STONE OR STONE-LIKE MATERIALS
    • B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/06—Silicon

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Abstract

The invention discloses a manufacturing process of a solar P-type polycrystalline silicon wafer, which comprises the following production process steps: (1) preparing raw materials; (2) preparing a P-type silicon ingot; (3) cutting and squaring a silicon ingot; (4) cutting and cleaning a silicon wafer; the raw materials used include: primary silicon material with the purity of 6N, circulating silicon material and gallium dopant; the circulating silicon material comprises a circulating silicon plate, a circulating silicon block, a circulating silicon wafer and circulating silicon powder. The method comprises the steps of removing impurities from a circulating silicon material before use, purifying, filling the circulating silicon material at the edge of a crucible during ingot casting, filling a gallium-doped primary silicon material at the center of the crucible, gradually reducing the doping concentration of gallium in the primary silicon material from the bottom of the crucible to the top of the crucible, enabling the concentration of gallium at the top to be zero, then placing the crucible filled with the silicon material in a microwave sintering furnace, and taking the crucible out of the furnace after heating, heat preservation and cooling under the protection of argon gas to obtain the P-type silicon ingot with uniform gallium doping. The invention makes full use of the circulating silicon material, and the prepared silicon chip has stable quality.

Description

Manufacturing process of solar P-type polycrystalline silicon wafer
Technical Field
The invention particularly relates to a manufacturing process of a solar P-type polycrystalline silicon wafer, and belongs to the technical field of semiconductor materials.
Background
The photoelectric conversion efficiency of the solar cell is closely related to the quality of the solar silicon wafer, and the purity of the silicon wafer is generally required to be not lower than 6N (99.9999%). The manufacturing process of the polycrystalline silicon wafer generally comprises ingot casting, squaring, slicing, detecting, packaging and the like, and a large amount of circulating silicon materials are generated in the process, wherein the circulating silicon materials comprise top skin, low skin, side skin and the like which are cut off in the cutting process of a silicon ingot, and the top skin, the low skin, the side skin and the like are generally in a thin plate shape (a circulating silicon plate and a silicon block), and the impurity element content of the parts is higher than the impurity content of primary silicon; fragments of damaged monocrystalline silicon pieces or polycrystalline silicon pieces and the like are incomplete; and thirdly, silicon mud generated by slicing. Because the high-purity silicon material is expensive, in order to save raw materials, the recycled silicon material is used for replacing part of the primary silicon material and is used as a part of a new ingot, so that the manufacturing cost can be obviously saved. However, these recycled silicon materials have relatively many impurities, and how to reasonably utilize the recycled silicon materials to produce qualified polycrystalline silicon wafers is a subject to be researched.
Polycrystalline silicon wafers can be classified into P-type silicon wafers and N-type silicon wafers according to the dopant. The P-type silicon wafer has dopant comprising boron (B) and gallium (Ga), resistivity of 0.5-1.5 Ω & cm, and dopant concentration of 0.8 ppmw. Because the solar cell prepared by the B-doped P-type silicon wafer has a B-O complex and further causes a light-induced attenuation phenomenon, the dopant of the current P-type silicon wafer is gradually replaced by Ga element from the traditional B element. The gallium-doped solar cell has no B-O complex, the light-induced attenuation phenomenon is greatly reduced, the performance of the gallium-doped solar cell is superior to that of a boron-doped solar cell, and the P-type silicon wafer with the Ga dopant has wide market value and application prospect. Since the melting point (29.8 ℃) of Ga is lower than that of Si (1410 ℃) and the atomic radius (125 pm) is larger than that of Si (118 pm), the segregation coefficient of Ga in the Si melt is far less than 1 and about 0.008, the low segregation coefficient is not favorable for uniform distribution of Ga in the silicon ingot, and how to uniformly distribute Ga in the silicon ingot along the longitudinal direction is also a subject to be researched.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a manufacturing process of a solar P-type polycrystalline silicon wafer, and aims to solve the problems of secondary utilization of a circulating silicon material and how to uniformly distribute gallium in the silicon wafer.
The technical scheme of the invention is as follows: a manufacturing process of a solar P-type polycrystalline silicon wafer comprises the following production process steps: (1) preparing raw materials; (2) preparing a P-type silicon ingot; (3) cutting and squaring a silicon ingot to obtain a square ingot; (4) cutting the square ingot into silicon chips, cleaning and detecting;
the raw materials used include: primary silicon material with the purity of 6N, circulating silicon material and gallium dopant; the circulating silicon material comprises a circulating silicon plate, a circulating silicon block, a circulating silicon wafer and circulating silicon powder;
wherein the circulating silicon material is subjected to impurity removal and purification treatment before use, and the impurity removal and purification method adopts one or more of the following methods: sand blasting, magnetic separation, microwave carbonization, supercritical water rinsing, acid washing and alkali washing;
the preparation process of the P-type silicon ingot comprises the following steps: preparing a crucible, coating an SiN film on the inner wall of the crucible, paving and filling primary monocrystalline silicon with a certain thickness at the bottom of the crucible, filling the edge of the crucible with a circulating silicon material, filling the center of the crucible with a primary gallium-doped silicon material, wherein the doping concentration of gallium in the primary silicon material is gradually reduced from the bottom of the crucible to the top of the crucible, and the concentration of gallium at the top is zero, then placing the crucible filled with the silicon material in a microwave sintering furnace, and taking the crucible out of the furnace after heating, heat preservation and cooling under the protection of argon gas to obtain the gallium-doped P-type silicon ingot.
Further, in the preparation process of the silicon ingot, the microwave sintering furnace heats the silicon material by using microwaves, the microwave frequency is 2.45GHz +/-25 MHz, the heating rate is 26 ℃/min, the silicon material is heated to 1550 ℃ and then is kept warm for 120min, then the temperature of the silicon material is gradually reduced, the growth rate of the silicon ingot is controlled to be 1 cm/h, the silicon ingot is cooled to 450 ℃ within 12h after the ingot growth is completed, the cooling rate is 0.7 ℃/min, the cooling is continued, the temperature of the silicon ingot is kept at 420 ℃ for 16min, then the temperature of the silicon ingot is reduced to 60 ℃ within 1.5 h, and then the silicon ingot is taken out of the furnace.
Furthermore, the doping concentration of the primary silicon material gallium in the center of the crucible is doped according to a square gradient method. The specific method comprises the following steps: uniformly mixing required gallium (with the purity of 6N) and 1kg of primary silicon powder to form a doping material, uniformly dividing the doping material into a plurality of equal parts, uniformly dividing the primary silicon material with the required weight into a plurality of equal parts, and doping the silicon material with the doping material added in each part in a mode of increasing from the top to the bottom in a manner of being in direct proportion to the square of a natural number.
Furthermore, the method for removing the impurities on the surface of the circulating silicon plate adopts a sand blasting method, SiC powder with the diameter of 10-46 microns is used for scanning the surface of the circulating silicon plate point by point under the high pressure of 0.7MPa, and whether the content of the impurities on the surface of the circulating silicon plate exceeds the standard or not is judged according to the color of the reflected particle flow.
Further, organic impurities (except epoxy resin and other impurities) in the circulating silicon material are removed by a microwave carbonization method, the circulating silicon material is placed into a quartz crucible and then placed into a microwave carbonization furnace, the rotation speed of the crucible is 6rpm/h, and the heating rate is 5 ℃/min. Setting different temperatures according to organic components, preserving heat for 0.5h, and then circulating the silicon material to naturally cool and discharge. If the recycled silicon material contains the epoxy resin and other stick glue and the curing agent, the epoxy resin is not suitable for being removed by a carbonization method, because the epoxy resin has high burning point and large energy consumption, and the stick glue and the curing agent are carbonized at high temperature, so that an oxide film is easily generated on the surface of the silicon material. If the surface of the circulating silicon material is adhered with the viscose glue, the curing agent and the like, the circulating silicon material is separated from the silicon material in hot water at the temperature of 56-100 ℃ under the assistance of weak acid substances such as acetic acid, lactic acid, citric acid and the like, and the ratio of the weak acid to the deionized water is set to be 1: 2; if hydrochloric acid is used for assisting the separation, the concentration of the hydrochloric acid is not more than 0.5M. The pressure of the microwave carbonization furnace, the temperature in the furnace, the concentration of the auxiliary acid liquid and the degumming time can also be determined according to the structure of organic matters such as epoxy resin. Setting the pressure in the furnace to be 1-2 atmospheric pressure, setting the temperature in the furnace to be 56-120 ℃, setting the degumming time to be 15 min-2 h, and setting the mass ratio of weak acid to deionized water to be 1: 2; if hydrochloric acid is used for assisting the separation, the concentration of the hydrochloric acid is not more than 0.5M.
Further, removing metal impurities in the circulating silicon wafer by adopting an acid washing method, wherein the acid washing solution is 2mol/L H2O21mol/L HF, 0.5 mol/L buffer, wherein the buffer is glycerol or ethylene glycol.
Further, in the cutting and squaring process of the silicon ingot, a diamond wire saw is used for cutting the silicon ingot, the lubricant is mortar, the surface coating of the diamond wire saw is in a threaded shape, the mortar is a mixed solution of SiC abrasive particles and polyethylene glycol, and the mass ratio of SiC to polyethylene glycol is 1: 1; the surface of the cut square ingot is polished by a grinder, and deionized water is used as a lubricant.
Furthermore, the equipment used for cutting the silicon wafer is a numerical control slicer. The fixed order of the square ingots is as follows: crystal support, blue viscose, PPC resin plate, purple viscose and square ingot. The square ingot is compacted for 3 hours by the weight of the square ingot, so that all parts are firmly adhered, and smooth implementation of silicon wafer cutting is facilitated. Cutting steel wire phi 57 mu m, wherein the cutting fluid is a mixture of deionized water and polyethylene glycol, the mass ratio is 1: 1, the cutting rate is 1.49 mm/min, and the size of the silicon wafer is 157mm multiplied by 0.18 mm. And then manually sorting, removing the silicon wafers with defects, washing by deionized water, drying and the like, and entering the next procedure.
And removing photoresist from the silicon wafer and detecting. Separating the silicon wafer from the crystal support, the sticky stick glue and the PPC resin plate at 56 ℃ in an attempt to ensure that the curvature of the silicon wafer is not influenced by the temperature; the crystal support, the viscose glue and the PPC resin plate were separated by boiling with boiling water (100 ℃). According to the indexes of the silicon wafer such as size, thickness, line mark, TTV (thickness variation of the silicon wafer), resistivity, collapse, chromatic aberration and the like, intelligent control and manual supervision are realized to classify, screen, pack and store the silicon wafer, and reasonable utilization of resources is realized.
Furthermore, in the cleaning procedure of the silicon wafer, a megasonic cleaning machine is adopted, the concentration of a cleaning agent is 1.5-3%, and the cleaning agent comprises an aqueous solution of one or more mixed substances in the following components: 0.1-0.3% of EDTA, 0.2-0.6% of fatty alcohol-polyoxyethylene ether, 0.2-0.6% of polyoxyethylene octylphenol ether-10, 0.3-0.6% of coconut oil fatty acid diethanolamide and 0.3-0.5% of triethanolamine; the pH of the detergent solution may be adjusted with sodium tripolyphosphate.
Has the advantages that: the impurities of the circulating silicon material are effectively removed and purified by adopting various methods, the circulating silicon material after being removed and purified is placed at the edge of the side part of the crucible, the primary high-purity silicon material is contained in the center of the crucible, the outer surface of the prepared silicon ingot is mainly the circulating silicon material, the core of the silicon ingot is mainly the primary silicon material, and the top surface, the bottom surface and the side surface of the prepared silicon ingot can be cut off when the silicon ingot is cut in a squaring way, so that the circulating silicon material can not obviously influence the quality of the finally obtained silicon wafer, and the consumption of the primary silicon material is reduced because the circulating silicon material is fully utilized, thereby obviously saving the production cost; meanwhile, because the segregation coefficient of gallium in silicon is small, gallium tends to be enriched towards the top of a silicon ingot when silicon is solidified and crystallized. According to the invention, by adopting a gradient distribution method that the doping concentration of gallium is gradually reduced from the bottom to the top when the primary silicon material is added in the center of the crucible, and simultaneously matching with specific process parameters of heating, heat preservation, cooling and the like of the microwave sintering furnace, gallium elements can be uniformly distributed in a silicon ingot, and the consistent stability of the performance of the prepared silicon wafer is further ensured. In addition, the microwave sintering furnace is adopted to heat the silicon material in the ingot casting process, the temperature rising speed is high, the silicon material is heated uniformly, impurities on the crucible wall are not easy to diffuse into the ingot casting, and the grain growth tends to be more consistent. The heat loss is less, compared with the conventional resistance furnace, the temperature is raised to the same value, the energy is saved by over 40 percent, and the energy-saving effect is obvious.
Detailed Description
The invention provides a manufacturing process of a solar P-type polycrystalline silicon wafer, which comprises the following production procedures: firstly, impurity removal and purification of a circulating silicon material; preparing a P-type silicon ingot; cutting a silicon ingot; cutting, cleaning, removing glue and detecting the silicon wafer.
The material for the solar P-type silicon ingot prepared by the invention comprises the following components: native silicon (purity 6N); secondly, circulating the silicon material; ③ gallium (Ga) as a dopant.
The recycled silicon material refers to: top skin, low skin and side skin of the silicon ingot cut in the cutting process are generally thin plates (circulating silicon plates), and the impurity element content of the parts is higher and far higher than the impurity content of primary silicon; defective monocrystalline silicon pieces or polycrystalline silicon pieces, etc.; ③ silicon powder purified from the silicon mud, and the like. In order to save raw materials, the recycled silicon material is used for replacing part of the primary silicon material and is placed at the edge of the quartz crucible to be used as the edge material of a new ingot.
One of the impurity removal methods of the circulating silicon material comprises the following steps: the circulating silicon plate was placed in the sandblaster cabinet (dark) using high pressure (P = 0.7 MP)a) Scanning the surface of the circulating silicon plate point by SiC powder (with the diameter of 10-46 mu m), and judging the circulating silicon plate according to the color of the reflected SiC particle flowWhether the surface impurity content exceeds the standard or not. If the reflective SiC particle flow is red, the impurity content of the part is high, and the fixed-point continuous injection is carried out until the reflective SiC particle flow is white.
And the second impurity removal method of the circulating silicon material comprises the following steps: the recycled silicon material (defective monocrystalline silicon pieces, polycrystalline silicon pieces, solar energy silicon pieces and the like) may be mixed with metal impurities such as diamond wires, iron nails, staples and the like, and is removed by magnetic separation.
One method for removing organic impurities by circulating silicon materials comprises the following steps: the recycled silicon material may contain organic impurities such as oil, plastic fragments, etc., which must be removed as ingot starting material. By thermogravimetric analysis, the maximum endotherm point was at 390 ℃, with the greatest loss of sample mass. The safety factor is determined according to about 30 percent, the carbonization temperature for removing organic matters by using a microwave carbonization furnace is set to be 500 ℃, the furnace core is a quartz crucible, the rotation speed is 6rpm/h, the heating rate is 5 ℃/min, the temperature is kept for 0.5h, and then the furnace is naturally cooled. The purpose is to fully oxidize the organic matters and generate oxide overflow.
The second method for removing organic impurities by circulating silicon materials comprises the following steps: and rinsing and circulating the silicon material organic matters by using a supercritical water reactor. Organic matter is miscible with supercritical water, O2、N2Gases such as CO can also be dissolved in supercritical water at any ratio. Under the conditions of 374.3 ℃ and 25 MPa, oxygen-free deionized water is converted into supercritical water. At 500 ℃, the ionization degree of supercritical water is weakest, and the ability of silicon to dissolve in supercritical water is suppressed. The recovery rate after rinsing the circulating silicon material can reach 95%, and the organic matter removal rate of silicon can reach more than 99.9%. The rinsing time is short, the efficiency of removing silicon organic matters is greatly improved, and the energy consumption of the system is reduced. When the content of the silicon organic matter exceeds 2%, the heat generated by the supercritical water oxidation of the organic matter can maintain the rinsing process without additionally supplying heat to the system. Meanwhile, supercritical water can also dissolve SiO on the surface of the silicon material2A film.
And (5) cleaning the circulating silicon wafer. With 2mol/L of H2O2The silicon material is mixed with 1mol/L HF for rinsing cycle. To reduce H2O2The heating temperature is not easy to be higher than 58 ℃. Magnetic stirring rate 600rpm. After 2 hours, the purity of the circulating silicon material can reach more than 99.999 percent, and the impurity removal effect of hydrogen peroxide is far better than that of other pickling solutions especially for copper ions which are not dissolved in the pickling solutions. In an acidic environment, H2O2Has strong oxidizing ability and can oxidize metal impurities remained in various circulating silicon materials. In order to reduce the loss of silicon material, glycerin or ethylene glycol may be added during the pickling process, and its concentration is set to 0.5 mol/L. Followed by rinsing with flowing ultrasonic deionized water for about 80S until the rinse water conductivity < 1000 μ S/cm, pH = 7. And finally, drying the circulating silicon wafer by using compressed air.
And (5) cleaning the circulating silicon block. Performing alkali washing with 2M NaOH solution for 0.5h, and then performing acid washing with mixed solution of HCl 36 wt%: 40% HF = 1: 1 for 0.5h, wherein the concentration of the mixed acid washing solution is 2M. Followed by rinsing with running ultrasonic deionized water for 80 seconds until the conductivity of the rinse water is less than 23 mus/cm. And finally, circulating the silicon block and drying by using compressed air.
Preparing a P-type silicon ingot: and sintering the silicon material to 1550 ℃ in an argon environment by adopting a microwave sintering furnace, wherein the microwave frequency is 2.45GHz +/-25 MHz. The heating speed is 26 ℃/min, the temperature is kept for 120min, the temperature is raised and lowered, the whole process is protected by argon and cooled, and the purity of the argon is 4N (99.99%). The argon gas serves to prevent the silicon material from being oxidized during the heating process. The temperature of the microwave sintering furnace is controlled by an intelligent control system, and the temperature is measured by infrared rays. The microwave generated by the microwave sintering furnace diffracts (diffracts) inside the silicon material to heat the silicon material simultaneously, so that the heating speed is high and the heat loss is small. Compared with a resistance furnace, the temperature is raised to the same level, and the energy can be saved by over 40 percent. Meanwhile, the silicon material is heated uniformly, impurities on the crucible wall are not easy to enter the silicon ingot, the crystal growth is consistent, the resistivity is consistent, the minority carrier lifetime is long, the crystal grain boundary is few, and the crystal grain is large.
The working principle of the microwave sintering furnace is as follows: when electromagnetic waves generated by the microwave sintering furnace are radiated to the silicon material, the movement of intrinsic carriers in the silicon material changes along with the change of the microwave field, which is similar to the friction phenomenon, so that the temperature of the silicon material is increased.
Before silicon materials are loaded into a quartz crucible, a layer of SiN film is coated on the inner wall of the crucible by a robot, and the thickness of the SiN film is about 1 mm. In order to have a sharp boundary of impurities when the ingot is cut, the SiN coating is 2 cm from the upper edge of the crucible. When the silicon material is added into the crucible, the dopant (solid gallium) is mixed with the powder silicon, the adding amount is gradually reduced from the bottom to the top, and the concentration of the solid gallium at the uppermost end is zero. The purity of solid gallium needs to reach 6N.
Quartz naturally softens at 1200 ℃ and needs to be reinforced by a graphite plate at the back of the quartz crucible. Since the solid density of silicon is 2.33 g/cm3Liquid density of 2.42 g/cm3After the silicon material is melted, the liquid silicon sinks, and the solid silicon floats upwards. Whether the silicon material is completely melted or not can be tested by a laser range finder at a lookout port at the top of the microwave sintering furnace.
And cutting the silicon ingot into square ingots. The used equipment is a silicon ingot squarer, the squaring speed is 2 mm/min, the squaring line phi is 0.3 mm, and the line tension is 98.0N; the silicon ingot is cut off by a numerical control diamond wire cutting machine, and the cutting line phi is 0.42 mm. The lubricant is mortar, the mortar is prepared from abrasive particles SiC and cutting fluid polyethylene glycol, and the mass is 1: 1, magnetically stirring for 1 h at a stirring speed of 600 rpm.
The cutting line of the silicon ingot is a diamond wire saw, and the surface coating of the diamond wire saw is in a thread shape, so that the cutting force of the diamond wire saw is increased. The cut square ingot quality detection is tested by adopting a minority carrier lifetime tester, an electrical resistivity tester and an infrared flaw detector, the minority carrier lifetime is required to be 5.3-5.8 microseconds, the electrical resistivity is 0.5-1.5 Ω & cm, the oxygen content is less than 10 ppma, the carbon content is less than 5 ppma, and no crack, no edge collapse and no abnormal point appear. And (4) cutting off unqualified areas in the square ingot by adopting intelligent control, and using the unqualified areas as a circulating silicon material as a scrap leather material in the next round of ingot casting preparation.
The square ingots are required to have uniform crystalline phase, consistent size and consistent crystal orientation. And judging the conductivity type of the square ingot by using a P/N type tester.
Polishing the surface of the square ingot by using a grinding wheel machine, using deionized water as a lubricant, and chamfering corners by using a chamfering machine.
And cutting the silicon wafer by using a phi 57 mu m gold steel wire. The cutting fluid is a mixed solution of deionized water, polyethylene glycol and mass ratio of 1: 1.
And (5) cleaning the silicon wafer. Cleaning with a megasonic cleaner, and drying with tunnel purified hot air. The negative pressure cleaning agent filter is arranged in the cleaning cavity, so that the cleanliness of the cleaning agent is high, and no pollution ions are generated. The concentration of the cleaning agent is 1.5-3%. The megasonic cleaner can completely clean the silicon wafer with complicated shape, dead corners and dirt in hidden holes, thereby achieving the best cleaning effect.
The silicon wafer surface cleaner comprises (i) 0.1-0.3% of EDTA (ethylene diamine tetraacetic acid) for removing some metal ions; 0.2-0.6% fatty alcohol-polyoxyethylene ether which is a nonionic surfactant and has the performances of emulsifying, foaming, decontaminating and dispersing impurity elements; ③ 0.2 to 0.6 percent of polyoxyethylene octyl phenol ether-10, which has the characteristics of excellent level dyeing, emulsification, wax prevention, corrosion inhibition, wetting, diffusion, antistatic property, etc.; or 0.3 to 0.6 percent of coconut oil fatty acid diethanolamide, which belongs to a nonionic surfactant, is easy to dissolve in water and has good functions of foaming, foam stabilization, penetration decontamination, hard water resistance and the like; 0.3-0.5% triethanolamine, which is alkalescent and can react with inorganic acid or organic acid to generate salt; sixthly, deionized water; the pH value of the solution can be adjusted by sodium tripolyphosphate. The components of the cleaning agent can be properly adjusted according to different components and contents of the pollution elements on the surface of the silicon wafer.
Example (b):
the first step is as follows: and preparing a P-type circulating silicon material. The circulating silicon material contains metal impurities such as hair, staple, diamond wire and the like, and organic impurities such as stick glue, plate glue, resin plate and the like. Magnetic separation, hot water degumming, carbonization, 20% HF corrosion, 25% HCl and 30% H2O2Mixed liquor acid washing, water isolation, 12% NaOH alkali washing and the like, then neutralizing residual liquid on the surface of the fragments by using HCl with proper concentration, ultrasonically rinsing by using deionized water and the like, and finally rinsing with water with the conductivity of 936 mu S/cm and the pH = 7.01. And drying the silicon chips at 105 ℃ by a microwave heating furnace, manually sorting and the like, and packaging and warehousing the crushed silicon chips without impurities. The manual separation is mainly used for screening non-silicon impurities such as stones which cannot be treated by acid washing, alkali washing and other procedures and are not treated.
The second step is that: and preparing the P-type polycrystalline silicon ingot by using a microwave sintering furnace. A G6 quartz crucible having a length, width, and height of 104 cm × 104 cm × 54 cm was prepared, and a SiN film was applied to the inside of the crucible and dried. Primary monocrystalline silicon with the thickness of 2 cm is paved and filled at the bottom of the quartz crucible, so that the crystalline phase area of the silicon wafer is increased, and the minority carrier lifetime of the silicon wafer is prolonged as much as possible under the condition of uniform crystalline phase. The edge of the crucible is filled with a circulating silicon plate, and large and small silicon materials are mixed, so that the heat conduction efficiency of the silicon materials is increased, and the microwave transmission of a sintering furnace is facilitated. The center of the crucible is filled with a gallium-doped primary silicon material. 800kg of primary silicon material, 0.7g of pure gallium and the rest 60 kg of the primary silicon material are circulating silicon materials. The gallium concentration in the primary silicon material at the center of the crucible is gradually reduced from the bottom of the crucible to the top of the crucible, and the gallium concentration at the top is zero. Because the addition amount of gallium is too small, for convenient operation, doping is carried out according to a square gradient method, and the specific method for mixing and adding solid gallium and silicon powder comprises the following steps: uniformly mixing 0.7g of required gallium with 1kg of primary silicon powder, and then uniformly dividing into 140 parts of doping materials, wherein each part of doping materials is 7.148g (containing 0.005g of gallium); evenly dividing 800kg of primary silicon material into 8 parts, each part being 100kg, uniformly mixing each part of primary silicon material with a certain part of doping material, gradually feeding the materials from the bottom to the top when feeding the materials into a crucible, doping the doping material in each part of silicon material in a mode of increasing the parts from the top to the bottom, wherein the increasing mode of the parts of the doping material is in direct proportion to the flat placement of natural numbers, and the specific doping formula is shown in table 1:
Figure 339215DEST_PATH_IMAGE002
and then heating the silicon material to 1550 ℃ under the protection of 99.99% Ar gas environment, wherein the heating rate is 27 ℃/min, and the heat preservation time is 120 min. Then the silicon material is gradually cooled to 950-980 ℃, and the growth rate of the silicon ingot is 1 cm/h. Then the silicon ingot is cooled to 450 ℃ within 12h, and the cooling rate is 0.7 ℃/min. In order to avoid cracks in the silicon ingot during rapid cooling, the silicon ingot was held at 420 ℃ for 16 min. Then cooling the silicon ingot to 60 ℃ within 1.5 h, and discharging. The quality detection result of the silicon ingot by the infrared flaw detector shows that no cracks are found to be hidden in the silicon ingot. And (3) detecting the height, the resistivity and the minority carrier lifetime of the silicon ingot after discharging, wherein the height of the silicon ingot is 365mm, and the data of the resistivity and the minority carrier lifetime are shown in tables 2 and 3. The maximum value of the resistivity at a position 30 mm from the bottom of the silicon ingot is 1.47 omega cm,the minimum value of the resistivity at a position 35 mm from the top is 0.64 omega cm, and the qualified proportion between 0.5 and 1.5 omega cm is 96.7 percent. By theoretical calculation and experimental tests, the diffusion coefficient of gallium in molten silicon is 2.08 × 10-5 cm2·s-1A mobility coefficient of 2.66X 10 in molten silicon-6 m·s-1. According to the invention, the diffusion distribution effect and the segregation effect of gallium in the molten silicon are interacted together by the square gradient method, so that the Ga is more uniformly doped in the silicon ingot along the longitudinal direction, the resistivity of the silicon ingot is more uniformly distributed along the longitudinal direction, and the quality requirement of solar-grade polycrystalline silicon on the silicon ingot is better met.
The third step: and cutting the silicon ingot. And cutting the silicon ingot with the volume of 101cm multiplied by 36.5cm into 36 square ingots by a silicon ingot squarer, wherein the diamond wire saw phi is 0.3 mm, and the cutting rate is 2 mm/min. The surface of the square ingot is ground by a numerical control flour-milling machine, and the lubricant is deionized water. The P/N type tester judges that the conductivity type of the square ingot is P type, the resistivity of each point of the square ingot is between 0.5 and 1.5 omega cm, and the minority carrier lifetime is between 5.34 and 5.71 mu s. The minority carrier lifetime and the resistivity of the square ingot can be scanned point by point, and areas which do not meet the quality requirement are cut off by a numerical control diamond wire cutting machine and recycled as recycled materials.
The fourth step: and (5) cutting the silicon wafer. The equipment used is a numerical control slicer. The fixed order of the square ingots is as follows: crystal support, blue viscose, PPC resin plate, purple viscose and square ingot. The square ingot is compacted for 3 hours by the weight of the square ingot, so that all parts are firmly adhered, and smooth implementation of silicon wafer cutting is facilitated. Cutting steel wire phi 57 mu m, wherein the cutting fluid is a mixture of deionized water and polyethylene glycol, the mass ratio is 1: 1, the cutting rate is 1.49 mm/min, and the silicon wafer size is 157mm multiplied by 0.18 mm. And then manually sorting, removing the silicon wafers with defects, washing by deionized water, drying and the like, and entering the next procedure.
The fifth step: and removing photoresist from the silicon wafer and detecting. Separating the silicon wafer from the crystal support, the sticky stick glue and the PPC resin plate at 56 ℃ in an attempt to ensure that the curvature of the silicon wafer is not influenced by the temperature; the crystal support, the viscose glue and the PPC resin plate were separated by boiling with boiling water (100 ℃). According to the indexes of the silicon wafer such as size, thickness, line mark, TTV (thickness variation of the silicon wafer), resistivity, collapse, chromatic aberration and the like, intelligent control and manual supervision are realized to classify, screen, pack and store the silicon wafer, and reasonable utilization of resources is realized.
Comparative example: 800kg of primary silicon material, 0.7g of pure gallium and the rest of about 60 kg of pure gallium are used as circulating silicon materials, and the difference from the embodiment is that: the primary silicon material and the gallium dopant are mixed uniformly by a conventional process, and are not doped in a gradient manner in a crucible, and other steps are the same as those in example 1. The resistivity and minority carrier lifetime of the prepared silicon ingot were measured, and the results are shown in table 4, where it is seen that the resistivity at a position 30 mm from the bottom of the silicon ingot was 2.07. omega. cm, the resistivity at a position 35 mm from the top was 0.34. omega. cm, and the acceptable ratio between 0.5 and 1.5. omega. cm was 57.1%. It can be seen that the resistivity distribution of the silicon ingot in the longitudinal direction in the comparative example is broad and is significantly less concentrated than the distribution in example 1, the acceptable availability of the silicon ingot is not as high as that in example 1, and the minority carrier lifetime is not as long as that in the example. After the silicon ingot is cut into silicon wafers, the yield and the quality of qualified silicon wafers are not as high as those of the embodiment. Therefore, the invention has obvious beneficial effects after implementation and is worthy of industrial use.
Figure 849830DEST_PATH_IMAGE004
Figure DEST_PATH_IMAGE006
Figure DEST_PATH_IMAGE008

Claims (8)

1. A manufacturing process of a solar P-type polycrystalline silicon wafer comprises the following production process steps: (1) preparing raw materials; (2) preparing a P-type silicon ingot; (3) cutting and squaring a silicon ingot to obtain a square ingot; (4) cutting the square ingot into silicon chips, cleaning and detecting; the method is characterized in that:
the raw materials used include: primary silicon material with the purity of 6N, circulating silicon material and gallium dopant; the circulating silicon material comprises a circulating silicon plate, a circulating silicon block, a circulating silicon wafer and circulating silicon powder;
the circulating silicon material is subjected to impurity removal and purification treatment before use, and the impurity removal and purification method adopts one or more of the following methods: sand blasting, magnetic separation, microwave carbonization, supercritical water rinsing, acid washing and alkali washing;
the preparation process of the P-type silicon ingot comprises the following steps: preparing a crucible, coating an SiN film on the inner wall of the crucible, paving and filling primary monocrystalline silicon with a certain thickness at the bottom of the crucible, filling the edge of the crucible with a circulating silicon material, filling the center of the crucible with a primary gallium-doped silicon material, wherein the doping concentration of gallium in the primary silicon material is gradually reduced from the top of the crucible to the bottom of the crucible, the concentration of gallium at the top is zero, then placing the crucible filled with the silicon material in a microwave sintering furnace, and taking the crucible out of the furnace after heating, heat preservation and cooling under the protection of argon gas to obtain the gallium-doped P-type silicon ingot.
2. The process for manufacturing a solar P-type polycrystalline silicon wafer according to claim 1, wherein the process comprises the following steps: in the preparation process of the silicon ingot, the microwave sintering furnace adopts microwave to heat the silicon material, the microwave frequency is 2.45GHz +/-25 MHz, the heating rate is 26 ℃/min, the silicon material is heated to 1550 ℃ and then is kept warm for 120min, then the temperature of the silicon material is gradually reduced, the growth rate of the silicon ingot is controlled to be 1 cm/h, the silicon ingot is cooled to 450 ℃ within 12h after the ingot growth is finished, the temperature reduction rate is 0.7 ℃/min, the cooling is continued, the temperature of the silicon ingot is kept at 420 ℃ for 16min, then the temperature of the silicon ingot is reduced to 60 ℃ within 1.5 h, and then the silicon ingot is taken out of.
3. The process for manufacturing a solar P-type polycrystalline silicon wafer according to claim 1, wherein the process comprises the following steps: the doping concentration of gallium in the primary silicon material at the center of the crucible is doped according to a square gradient method, and the specific method for mixing and adding the solid gallium and the silicon powder comprises the following steps: uniformly mixing the required gallium with 1kg of primary silicon powder, uniformly dividing into a certain part of doping materials, uniformly dividing the required weight of primary silicon material into a plurality of parts, adding a certain part of doping materials into each part of primary silicon material, uniformly mixing, gradually feeding from the bottom to the top when feeding into a crucible, doping the parts of doping materials added into each part of primary silicon material in a mode of increasing from top to bottom, wherein the increasing mode of the part number of the doping materials is in direct proportion to the flat placement of natural numbers.
4. The process for manufacturing a solar P-type polycrystalline silicon wafer according to claim 1, wherein the process comprises the following steps: and removing impurities on the surface of the circulating silicon plate by adopting a sand blasting method, scanning the surface of the circulating silicon plate point by utilizing SiC powder with the diameter of 10-46 micrometers under the high pressure of 0.7MPa, and judging whether the content of the impurities on the surface of the circulating silicon plate exceeds the standard or not according to the color of the reflected particle flow.
5. The process for manufacturing a solar P-type polycrystalline silicon wafer according to claim 1, wherein the process comprises the following steps: removing organic impurities except epoxy resin in the circulating silicon material by adopting a microwave carbonization method, putting the circulating silicon material into a quartz crucible, then putting the quartz crucible into a microwave carbonization furnace, setting the crucible rotation speed at 6rpm/h, the heating rate at 5 ℃/min, setting the carbonization temperature according to the type of the organic impurities, preserving the heat for 0.5h, and then naturally cooling and discharging the silicon material out of the furnace.
6. The process for manufacturing a solar P-type polycrystalline silicon wafer according to claim 1, wherein the process comprises the following steps: removing metal impurities in the circulating silicon wafer by adopting an acid washing method, wherein the acid washing solution is 2mol/L H2O21mol/L HF, 0.5 mol/L buffer, wherein the buffer is glycerol or ethylene glycol.
7. The process for manufacturing a solar P-type polycrystalline silicon wafer according to claim 1, wherein the process comprises the following steps: in the cutting and squaring procedure of the silicon ingot, a diamond wire saw is used for cutting the silicon ingot, a lubricant is mortar, a surface coating of the diamond wire saw is in a threaded shape, the mortar is a mixed solution of SiC abrasive particles and polyethylene glycol, and the mass ratio of SiC to polyethylene glycol is 1: 1; the surface of the cut square ingot is polished by a grinder, and deionized water is used as a lubricant.
8. The process for manufacturing a solar P-type polycrystalline silicon wafer according to claim 1, wherein the process comprises the following steps: in the cleaning procedure of the silicon wafer, a megasonic cleaning machine is adopted, the concentration of a cleaning agent is 1.5-3%, and the cleaning agent comprises an aqueous solution of one or more mixed substances in the following components: 0.1-0.3% of EDTA, 0.2-0.6% of fatty alcohol-polyoxyethylene ether, 0.2-0.6% of polyoxyethylene octylphenol ether-10, 0.3-0.6% of coconut oil fatty acid diethanolamide and 0.3-0.5% of triethanolamine; the pH of the detergent solution may be adjusted with sodium tripolyphosphate.
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