Preparation method of high-efficiency ultrathin silicon wafer and high-efficiency ultrathin silicon wafer prepared by same

Abstract

The invention provides a preparation method of an ultrathin silicon wafer and the ultrathin silicon wafer prepared by the preparation method. By mixing the antimony element and the rare earth element, on one hand, the mechanical strength of the silicon wafer can be improved, and the silicon wafer is assisted to be thinned; narrowing the longitudinal resistivity distribution of the crystal bar; and on the other hand, the absorption and utilization of the solar cell on ultraviolet and infrared spectrums can be increased, so that the photoelectric conversion efficiency of the solar cell is improved. Further, from the end of drawing of a single monocrystalline silicon rod to the beginning of drawing of a next crystal rod, the loss amount of the antimony element is detected in real time, and compensation is performed in time during re-feeding, so that the stable quality of the crystal rod is guaranteed. The mechanical performance of the silicon wafer and the photoelectric conversion efficiency of the silicon wafer are both improved, and thinning of the silicon wafer and cost reduction of the obtained battery piece are facilitated; due to volatilization and segregation effects of the antimony element, resistance distribution at the head and the tail of the crystal bar is narrow, and recycling of the head and the tail is facilitated. The method provided by the invention is simple and easy to obtain, and is more suitable for batch popularization.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar silicon wafers, and relates to a method for preparing an ultra-thin silicon wafer and the ultra-thin silicon wafer prepared therefrom, and in particular to a method for preparing a high-efficiency ultra-thin silicon wafer and the high-efficiency ultra-thin silicon wafer prepared therefrom. Background Art

[0002] Crystalline silicon usually absorbs sunlight with a wavelength of 400 to 1100nm. However, the wavelength of sunlight reaching the ground covers 200 to 2500nm. Therefore, the utilization rate of ultraviolet and short-wave infrared light by crystalline silicon is very low, which limits the improvement of crystalline silicon efficiency. In order to increase the photoelectric conversion efficiency of silicon wafers, technical researchers have explored a large number of quantum dot preparation methods and materials. Among them, rare earth element quantum dots have become one of the important alternative materials for increasing the photoelectric conversion efficiency of silicon wafers due to their high quantum efficiency, simple manufacturing process, and no effect on the electrical properties of crystalline silicon cells. At the same time, thinning and high efficiency are the main development trends of current solar N-type silicon wafers. However, under the same process and raw material conditions, thinning silicon wafers will inevitably lead to a decrease in the mechanical strength of silicon wafers. On the one hand, thinning silicon wafers will bring the risk of increased fragmentation rate in the slicing process. On the other hand, in the high-temperature process of N-type cells, silicon wafers will be warped and fragmented, reducing the yield rate. Studies have shown that in the silicon lattice, 95% of oxygen exists in the interstitial state. Interstitial oxygen can "pin dislocations" and reduce dislocation slip, which has a great impact on the internal impurity ability, mechanical strength, and resistivity of silicon wafers. Antimony doping can be used to inhibit the diffusion of interstitial oxygen atoms and oxygen precipitation in single crystal silicon. Therefore, antimony doping can increase the mechanical strength of silicon wafers and promote further thinning of N-type silicon wafers.

[0003] Some antimony doping technical solutions have also been disclosed in existing research, such as patent CN117702269 A discloses an antimony-doped N-type single crystal silicon wafer and doping technology. Through antimony doping and matching doping process, the minority carrier lifetime of silicon wafers can be effectively improved, the resistance distribution of the head and tail of the crystal rod can be narrowed, and the mechanical strength of silicon wafers can be improved. However, due to the nature of single crystal silicon itself, this technology cannot increase the absorption of ultraviolet light and short-wave infrared light by silicon wafers, and therefore cannot fundamentally break through the efficiency limit of single crystal silicon. For example, patent CN102832267A discloses a rare earth element doped silicon wafer. The invention obtains single crystal / polycrystalline silicon containing up-converted light emitting quantum dots by doping rare earth elements or their oxides and combining annealing process. This technology can increase the absorption efficiency of silicon wafers to infrared spectra, thereby improving the efficiency of solar cells. Similarly, patent CN102828242A proposes doping rare earth elements or their oxides to improve the absorption utilization rate of silicon wafers to ultraviolet spectra, thereby improving the efficiency of solar cells. However, the above two inventions cannot improve the mechanical properties of silicon wafers, and do not solve the problem of high fragmentation rate caused by thinning of silicon wafers.

[0004] Moreover, in the current related technical research, the antimony doping is mostly concentrated in the initial silicon material investment stage, and the precise doping of volatile elements lacks the calculation and measurement method of the volatile dopant in the remaining silicon melt in the reinvestment stage, and it is impossible to accurately control the compensation amount of volatile dopant in the reinvestment stage. Antimony is highly volatile. When it is impossible to measure the volatilization loss of antimony in time and accurately compensate for the dopant, it will cause large differences in antimony content between crystal rods and large fluctuations in crystal rod quality.

[0005] Therefore, it is urgent to find a more suitable way to break through the above-mentioned problems existing in existing materials and preparation methods, which has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing an ultra-thin silicon wafer and an ultra-thin silicon wafer prepared therefrom, in particular, a method for preparing an efficient ultra-thin silicon wafer. The silicon wafer prepared by the preparation method provided by the present invention takes into account both the improvement of mechanical properties and the improvement of the photoelectric conversion efficiency of the silicon wafer, which is conducive to the thinning of the silicon wafer and the cost reduction and efficiency increase of the obtained solar cell, and has a simple process, good controllability, strong operability, and is more suitable for industrial promotion and application.

[0007] The present invention provides a method for preparing an ultra-thin silicon wafer, comprising the following steps:

[0008] 1) Using polycrystalline silicon material doped with phosphorus, antimony and rare earth sources as silicon rod raw materials, and preparing single crystal silicon rods by multiple feeding and pulling method under protective atmosphere;

[0009] 2) completing the previous single crystal silicon rod pulling, and recording the curve of the antimony element concentration C in the protective atmosphere changing with time t during the single crystal silicon rod pulling process, and performing a linear fit again to obtain the slope k of the fitted curve;

[0010] 3) Measure the resistivity of the tail end of the previous single crystal silicon rod, calculate the concentration N1 of the antimony element in the remaining silicon liquid, and then calculate the compensation amount of the antimony element in the reinvestment stage based on the concentration of the antimony element in the remaining silicon melt and the slope k of the fitting curve;

[0011] 4) Re-dosing silicon material, completing antimony element supplementation according to the compensation amount of antimony element obtained in the above steps, and pulling the crystal rod to obtain a single crystal silicon rod;

[0012] 5) Cutting the single crystal silicon rod obtained in the above steps to obtain silicon wafers.

[0013] Preferably, the polysilicon material comprises N-type polysilicon dense material;

[0014] The doping concentration ratio of the phosphorus element to the antimony element is 5:(1-3);

[0015] The doping concentration ratio of the phosphorus element to the rare earth source is 5:(0.5-1).

[0016] Preferably, the rare earth source comprises rare earth and / or rare earth oxide;

[0017] The rare earth includes one or more of erbium, promethium, gadolinium, holmium, thulium and samarium;

[0018] The atomic concentration of phosphorus in the silicon rod raw material is greater than or equal to 4×10 19 ~10×10 19 atom / cm 3 .

[0019] Preferably, the detection method of the antimony element concentration in the protective atmosphere includes detection by inductively coupled plasma emission spectroscopy;

[0020] The first linear fitting curve is C=kt+b;

[0021] Where C is the antimony concentration in the protective atmosphere (atom / cm 3 ), k is the slope of the fitting curve, b is the fitting constant, and t is the time (hours).

[0022] Preferably, in step 3), the formula for calculating the concentration of antimony element in the remaining silicon melt is as shown in formula (1) and formula (2):

[0023] ρ=6.242×10 18 / N1×10 Z’ (1);

[0024] Where ρ is the resistivity of the end skin of the crystal rod (Ω·cm), N1 is the concentration of antimony in the remaining silicon melt (atom / cm 3 ), y=(log 10 N1)-16;

[0025]

[0026] Among them, A'0=-3.0769, A'1=2.2108, A'2=-0.62272, A'3=0.057501, B'1=-0.68157, B'2=0.19833, B'3=-0.018376.

[0027] Preferably, the calculation formula for the compensation amount of antimony element in the reinvestment stage is as shown in formula (3):

[0028] Δw=N×W+k×Δt-N1W1 (3)

[0029] Wherein, Δw is the compensation amount of antimony element in the reinvestment stage; N is the antimony element concentration in silicon melt at the target resistivity (atom / cm 3 ); W is the total volume of silicon melt after re-injection (cm 3 ), k is the slope of the fitted curve; Δt is the interval time (hours) from the end of the previous crystal ingot pulling to the start of this crystal ingot seeding; N1 is the antimony concentration in the silicon melt at the end of the previous crystal ingot pulling (atom / cm 3 ); W1 is the remaining silicon melt volume at the end of the previous crystal rod pulling (cm 3 ).

[0030] Preferably, the previous single crystal silicon rod pulling includes the first to seventh times of multiple feedings in a single furnace;

[0031] The diameter of the single crystal silicon rod is 250-350 mm;

[0032] The length of the single crystal silicon rod is 2000-4000 mm.

[0033] Preferably, the silicon wafer is a single crystal silicon wafer;

[0034] The thickness of the silicon wafer is 80 to 100 μm;

[0035] When the number of times of re-injection of the silicon material is 7, the prepared single crystal silicon rod can be cut to obtain a silicon slice with the thickness.

[0036] The present invention also provides an ultra-thin silicon wafer, which is obtained by cutting a single crystal silicon rod prepared by the preparation method described in any one of the above technical solutions.

[0037] Preferably, the length of the single crystal silicon rod is greater than or equal to 2.0 m;

[0038] The number of single crystal silicon rods pulled from a single furnace is greater than or equal to 6;

[0039] The head resistance hit rate of single-furnace single-crystal silicon rods is greater than or equal to 95%.

[0040] The difference in head resistivity between the single crystal silicon rods in the single furnace is less than or equal to 20%;

[0041] The thickness of the silicon wafer is 80-100 μm.

[0042] The present invention provides a method for preparing an ultra-thin silicon wafer, comprising the following steps: firstly, doping phosphorus element, antimony element and rare earth source into polycrystalline silicon material as silicon rod raw material, and preparing single crystal silicon rod by multiple feeding and re-pulling method under protective atmosphere; then completing the pulling of the previous single crystal silicon rod, and recording the variation curve of antimony element concentration C in the protective atmosphere with time t during the pulling process of the single crystal silicon rod, and performing a linear fitting to obtain the slope k of the fitted curve; then measuring the resistivity of the edge skin of the tail end of the previous single crystal silicon rod, calculating the concentration N1 of antimony element in the remaining silicon liquid, and then calculating the compensation amount of antimony element in the re-feeding stage based on the concentration of antimony element in the remaining silicon melt and the slope k of the fitted curve; then re-feeding silicon material, completing the antimony element supplementary doping according to the compensation amount of antimony element obtained in the above steps, and pulling the crystal rod to obtain the single crystal silicon rod; finally, cutting the single crystal silicon rod obtained in the above steps to obtain a silicon wafer. Compared with the prior art, the present invention believes that relying solely on rare earth element doping cannot effectively improve the mechanical strength of silicon wafers, is not conducive to silicon wafer thinning, and therefore has no effect on reducing the cost of silicon wafers. However, due to the nature of single crystal silicon itself, relying solely on antimony element doping cannot increase the absorption and utilization efficiency of silicon wafers for ultraviolet and infrared spectra, and cannot fundamentally break through the efficiency limit of single crystal silicon. At the same time, after the pulling of a single single crystal silicon rod (crystal rod) is completed, the next crystal rod begins to be pulled, which requires the cooling of the crystal rod, the re-investment of silicon materials, and the chemical process, which takes 8 to 15 hours. During this process, the antimony element is continuously lost. However, the loss of antimony elements cannot be detected in real time, resulting in uncertainty in the calculation of the compensation amount of antimony in the re-investment stage, resulting in instability and unevenness in the crystal quality.

[0043] Based on this, the present invention creatively designs a method for preparing ultra-thin silicon wafers with specific steps. First, by mixing antimony elements with rare earth elements, on the one hand, the mechanical strength of the silicon wafer can be improved, and the silicon wafer thinning can be assisted; the longitudinal resistivity distribution of the crystal rod can be narrowed; on the other hand, the absorption and utilization of the ultraviolet and infrared spectra of the solar cell can be increased, thereby improving the photoelectric conversion efficiency of the solar cell. Secondly, after the pulling of a single single crystal silicon rod is completed, and before the next crystal rod starts the pulling process, the loss of antimony elements is detected in real time, and timely compensation is made during the re-investment to ensure the stability of the crystal rod quality.

[0044] The present invention takes into account both the improvement of the mechanical properties of silicon wafers and the improvement of the photoelectric conversion efficiency of silicon wafers, which is conducive to the thinning of silicon wafers and the cost reduction of the resulting solar cells; and due to the volatilization and segregation effect of the antimony element, the resistance distribution of the head and tail of the crystal rod is narrow, which is conducive to the recycling of the head and tail materials. The method provided by the present invention is simple and easy to obtain, has good controllability, strong operability, and is more suitable for mass promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The invention provides a device for testing the volatilization rate of antimony elements. DETAILED DESCRIPTION

[0046] In order to further understand the present invention, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all 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.

[0047] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0048] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure raw materials or raw materials with conventional purity in the field of single crystal silicon rod or silicon wafer preparation.

[0049] The present invention provides a method for preparing an ultra-thin silicon wafer, comprising the following steps:

[0050] 1) Using polycrystalline silicon material doped with phosphorus, antimony and rare earth sources as silicon rod raw materials, and preparing single crystal silicon rods by multiple feeding and pulling method under protective atmosphere;

[0051] 2) completing the previous single crystal silicon rod pulling, and recording the curve of the antimony element concentration C in the protective atmosphere changing with time t during the single crystal silicon rod pulling process, and performing a linear fit again to obtain the slope k of the fitted curve;

[0052] 3) Measure the resistivity of the tail end of the previous single crystal silicon rod, calculate the concentration N1 of the antimony element in the remaining silicon liquid, and then calculate the compensation amount of the antimony element in the reinvestment stage based on the concentration of the antimony element in the remaining silicon melt and the slope k of the fitting curve;

[0053] 4) Re-dosing silicon material, completing antimony element supplementation according to the compensation amount of antimony element obtained in the above steps, and pulling the crystal rod to obtain a single crystal silicon rod;

[0054] 5) Cutting the single crystal silicon rod obtained in the above steps to obtain silicon wafers.

[0055] The present invention firstly adopts polysilicon material doped with phosphorus element, antimony element and rare earth source as silicon rod raw material, and prepares single crystal silicon rod by multiple feeding and multiple pulling method under protective atmosphere.

[0056] In the present invention, the polysilicon material preferably includes N-type polysilicon dense material.

[0057] In the present invention, the doping concentration ratio of the phosphorus element to the antimony element is preferably 5:(1-3), more preferably 5:(1.4-2.6), and more preferably 5:(1.8-2.2).

[0058] In the present invention, in the present invention, the doping concentration ratio of the phosphorus element to the rare earth source is preferably 5:(0.5-1), more preferably 5:(0.6-0.9), and more preferably 5:(0.7-0.8).

[0059] In the present invention, the rare earth source preferably includes rare earth and / or rare earth oxide, more preferably rare earth or rare earth oxide.

[0060] In the present invention, the rare earth preferably includes one or more of erbium, promethium, gadolinium, holmium, thulium and samarium, and more preferably erbium, promethium, gadolinium, holmium, thulium or samarium.

[0061] In the present invention, the atomic concentration of phosphorus in the silicon rod raw material is preferably greater than or equal to 4×10 19 ~10×10 19 atom / cm 3 , more preferably 5×10 19 ~9×10 19 atom / cm 3 , more preferably 6×10 19 ~8×10 19 atom / cm 3 .

[0062] The present invention completes the previous single crystal silicon rod pulling again, and records the variation curve of the antimony element concentration C in the protective atmosphere with time t during the single crystal silicon rod pulling process, and then performs a linear fitting to obtain the fitting curve slope k.

[0063] In the present invention, the method for detecting the antimony element concentration in the protective atmosphere preferably includes detecting by inductively coupled plasma emission spectroscopy.

[0064] In the present invention, the first-order linear fitting curve is preferably C=kt+b.

[0065] In the present invention, C is preferably the antimony element concentration (atom / cm 3 ), k is preferably the slope of the fitted curve, b is preferably the fitted constant, and t is preferably time (hours).

[0066] The present invention then measures the resistivity of the tail end of the previous single crystal silicon rod, calculates the concentration N1 of the antimony element in the remaining silicon liquid, and then calculates the compensation amount of the antimony element in the reinvestment stage based on the concentration of the antimony element in the remaining silicon melt and the slope k of the fitting curve.

[0067] In the present invention, in step 3), the formula for calculating the concentration of antimony element in the remaining silicon melt is preferably as shown in formula (1) and formula (2):

[0068] ρ=6.242×10 18 / N1×10 Z’ (1);

[0069] Wherein, ρ is preferably the resistivity of the end skin of the crystal rod (Ω·cm), N1 is preferably the concentration of antimony in the remaining silicon melt (atom / cm 3 ), y=(log 10 N1)-16;

[0070]

[0071] Among them, A'0=-3.0769, A'1=2.2108, A'2=-0.62272, A'3=0.057501, B'1=-0.68157, B'2=0.19833, and B'3=-0.018376 are preferred.

[0072] In the present invention, the calculation formula of the compensation amount of antimony element in the reinvestment stage is preferably as shown in formula (3):

[0073] Δw=N×W+k×Δt-N1W1 (3)

[0074] Among them, Δw is preferably the compensation amount of antimony element in the re-investment stage; N is the antimony element concentration in the silicon melt at the target resistivity; W is the total volume of the silicon melt after re-investment (cm 3 ), k is the slope of the fitted curve; Δt is the interval time (hours) from the end of the previous crystal ingot pulling to the start of this crystal ingot seeding; N1 is the antimony concentration in the silicon melt at the end of the previous crystal ingot pulling (atom / cm 3 ); W1 is the remaining silicon melt volume at the end of the previous crystal rod pulling (cm 3 ).

[0075] In the present invention, at a set target resistivity ρ, based on equations (1) and (2), the concentration N of the volatile dopant in the silicon melt can be calculated, where W is the total volume of the silicon melt after re-dosing.

[0076] The present invention then re-doses silicon material, completes antimony element supplementation according to the compensation amount of antimony element obtained in the above steps, and performs crystal rod pulling to obtain a single crystal silicon rod.

[0077] In the present invention, the previous single crystal silicon rod pulling preferably includes the first to seventh times of multiple charging in a single furnace, more preferably the second to sixth times, and more preferably the third to fifth times. The first charging refers to the initial charging.

[0078] In the present invention, the diameter of the single crystal silicon rod is preferably 250-350 mm, more preferably 270-330 mm, and more preferably 290-310 mm.

[0079] In the present invention, the length of the single crystal silicon rod is preferably 2000-4000 mm, more preferably 2400-3600 mm, and more preferably 2800-3200 mm.

[0080] Finally, the present invention cuts the single crystal silicon rod obtained in the above steps to obtain silicon wafers.

[0081] In the present invention, the silicon wafer is preferably a single crystal silicon wafer.

[0082] In the present invention, the thickness of the silicon wafer is preferably 80 to 100 μm, more preferably 84 to 96 μm, and even more preferably 88 to 92 μm.

[0083] In the present invention, when the number of times of re-injection of the silicon material is preferably 7 times, the prepared single crystal silicon rod can be cut to obtain a silicon wafer having the above thickness.

[0084] The present invention provides an ultra-thin silicon wafer, which is obtained by cutting a single crystal silicon rod prepared by the preparation method described in any one of the above technical solutions.

[0085] In the present invention, the length of the single crystal silicon rod is preferably greater than or equal to 2.0 m, more preferably greater than or equal to 2.5 m, and more preferably greater than or equal to 3.0 m.

[0086] In the present invention, the number of single crystal silicon rods pulled in a single furnace is preferably greater than or equal to 6, more preferably greater than or equal to 7, and more preferably greater than or equal to 8.

[0087] In the present invention, the head resistance hit rate of the single-furnace single-crystal silicon rods is preferably greater than or equal to 95%, more preferably greater than or equal to 96%, and more preferably greater than or equal to 97%.

[0088] In the present invention, the difference in head resistivity between the single crystal silicon rods in a single furnace is preferably less than or equal to 20%, more preferably less than or equal to 19%, and more preferably less than or equal to 18%.

[0089] In the present invention, the thickness of the silicon wafer is preferably 80 to 100 μm, more preferably 84 to 96 μm, and even more preferably 88 to 92 μm.

[0090] The present invention is to complete and refine the overall technical solution, better ensure the structure and characteristics of the single crystal silicon rod prepared by the multiple feeding and pulling method, ensure the stability of the crystal rod quality, further improve the mechanical strength and photoelectric conversion efficiency of the silicon wafer, and reduce the thickness of the silicon wafer. The preparation method of the above-mentioned high-efficiency ultra-thin silicon wafer and the high-efficiency ultra-thin silicon wafer prepared by the method may specifically include the following contents:

[0091] The high-efficiency ultra-thin silicon wafer of the present invention is prepared according to the following method:

[0092] Step 1, doping phosphorus, antimony and rare earth elements as dopants into the N-type polysilicon dense material, wherein the concentration ratio of phosphorus, antimony and rare earth elements is 5:(1-3):(0.5-1), wherein the concentration of phosphorus is greater than 4×10 19 / cm 3 The rare earth element is one or more of erbium (Er), promethium (Pm), gadolinium (Gd), holmium (Ho), thulium (Tm) or samarium (Sm) and their corresponding oxides.

[0093] Step 2, preparing single crystal silicon rods by multiple feeding and pulling method, with argon as the protective gas in the furnace.

[0094] Step 3: After the last crystal rod pulling is completed, open the monitoring valve (such as Figure 1 According to the national standard HJ 777-2015, the antimony content in argon was detected by inductively coupled plasma emission spectrometry. The detection time t (hours) and the antimony concentration C (atom / cm 3 ). Draw the curve of the concentration of antimony in argon gas changing with time at this stage. Make a linear fit to the curve (i.e. C=kt+b, where k is the slope of the fitted curve, representing the volatilization rate of antimony at this stage, and b is the fitting constant). Close the monitoring valve.

[0095] See also Figure 1 , Figure 1 The invention provides a device for testing the volatilization rate of antimony elements.

[0096] Step 4, measuring the resistivity of the skin at the tail end of the previous crystal rod, and calculating the concentration of antimony in the remaining silicon liquid, the calculation method is shown in Formula 1 and Formula 2.

[0097] ρ=6.242×10 18 / N1×10 Z’ (Formula 1)

[0098] Where ρ is the resistivity (Ω·cm), N1 is the dopant concentration (atom / cm 3 ), y=(log 10 N1)-16.

[0099]

[0100] Among them, A'0=-3.0769, A'1=2.2108, A'2=-0.62272, A'3=0.057501, B'1=-0.68157, B'2=0.19833, B'3=-0.018376.

[0101] Step 5, calculate the antimony element compensation amount according to formula 3.

[0102] Δw=N×W+k×Δt-N1W1 (Formula 3).

[0103] Where Δw is the compensation amount of volatile dopants in the re-investment stage, and the concentration of volatile dopants in the silicon melt (atom / cm 3 ), W is the total volume of silicon melt after re-injection (cm 3 ), Δt is the interval time (hours) from the end of the previous crystal ingot pulling to the start of the current crystal ingot seeding, k is the volatilization rate of antimony in the silicon melt during this time period, obtained by the method in step 3, and N1 is the concentration of volatile dopants in the remaining silicon melt after the previous crystal ingot pulling is completed (atom / cm 3 ), W1 is the total volume of the remaining silicon melt after the previous crystal rod pulling is completed (cm 3 ). The calculation methods of N and N1 are shown in formulas 1 and 2.

[0104] Step 6, complete 7 times of silicon material re-injection, antimony element supplementation and crystal rod pulling.

[0105] Step 7, cutting the obtained silicon rod with tungsten diamond wire, and the obtained silicon wafer has a thickness of 80 to 100 μm.

[0106] The present invention provides a high-efficiency ultra-thin single crystal silicon wafer, which is doped with phosphorus, antimony and rare earth elements at the same time, and the antimony volatilization loss amount is monitored and calculated from the end of the previous crystal rod pulling to the seeding of the next crystal rod, and a calculation method for the antimony element compensation amount from the end of the previous crystal rod pulling to the seeding of the next crystal rod is designed. The crystal rod pulled by the present invention is characterized in that the resistance hit rate of the crystal rod head is greater than 95%, and the head resistivity difference between the crystal rods is within 20%.

[0107] The above content of the present invention provides a method for preparing an efficient ultra-thin silicon wafer and the prepared efficient ultra-thin silicon wafer. The method for preparing an ultra-thin silicon wafer with specific steps designed by the present invention firstly mixes antimony elements with rare earth elements, which can improve the mechanical strength of the silicon wafer and assist in thinning the silicon wafer; narrow the longitudinal resistivity distribution of the crystal rod; on the other hand, it can increase the absorption and utilization of the ultraviolet and infrared spectra of the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell. Secondly, after the pulling of a single single crystal silicon rod is completed and before the pulling process of the next crystal rod begins, the loss of antimony elements is detected in real time, and timely compensation is made during re-investment to ensure the stable quality of the crystal rod.

[0108] The present invention takes into account both the improvement of the mechanical properties of silicon wafers and the improvement of the photoelectric conversion efficiency of silicon wafers, which is conducive to the thinning of silicon wafers and the cost reduction of the resulting solar cells; and due to the volatilization and segregation effect of the antimony element, the resistance distribution of the head and tail of the crystal rod is narrow, which is conducive to the recycling of the head and tail materials. The method provided by the present invention is simple and easy to obtain, has good controllability, strong operability, and is more suitable for mass promotion.

[0109] In order to further illustrate the present invention, a method for preparing an ultra-thin silicon wafer and the ultra-thin silicon wafer prepared therefrom are described in detail below in conjunction with embodiments. However, it should be understood that these embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following embodiments.

[0110] Example

[0111] By adopting the preparation method provided by the present invention, single crystal silicon rods doped with phosphorus, antimony and rare earth sources are prepared according to the conventional RCz process, each group of crystal rods are cut into 10,000 ultra-thin silicon wafers through a slicing process, and a conventional TOPcon cell preparation process is used to prepare TOPcon cells.

[0112] As a comparison group, the preparation method provided by the present invention was adopted to pull phosphorus-doped crystal rods of the same specification, and the TOPcon cells of the same specification were made through the same slicing and cell processing technology.

[0113] Compare the increase in resistivity concentration in the range of 0.7 to 1.4Ω·cm, the decrease in silicon wafer fragmentation rate in the battery process relative to the control group, and the increase in battery cell efficiency relative to the control group.

[0114] The crystal rods prepared in the embodiments of the present invention are statistically analyzed, see Table 1, which shows the parameters of the crystal rods prepared in the embodiments of the present invention.

[0115] Table 1

[0116]

[0117] The above is a detailed introduction to a method for preparing a high-efficiency ultra-thin silicon wafer provided by the present invention and the high-efficiency ultra-thin silicon wafer prepared therefrom. The principles and implementation methods of the present invention are described in detail using specific examples herein. The description of the above embodiments is only used to help understand the method and its core ideas of the present invention, including the best mode, and also enables any technician in the field to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in the technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing an ultra-thin silicon wafer, characterized in that: The following steps are involved: 1) Using polycrystalline silicon material doped with phosphorus, antimony and rare earth sources as silicon rod raw materials, and preparing single crystal silicon rods by multiple feeding and pulling method under protective atmosphere; 2) completing the previous single crystal silicon rod pulling, and recording the curve of the antimony element concentration C in the protective atmosphere changing with time t during the single crystal silicon rod pulling process, and performing a linear fit again to obtain the slope k of the fitted curve; 3) Measure the resistivity of the tail end of the previous single crystal silicon rod, calculate the concentration N1 of the antimony element in the remaining silicon liquid, and then calculate the compensation amount of the antimony element in the reinvestment stage based on the concentration of the antimony element in the remaining silicon melt and the slope k of the fitting curve; 4) Re-dosing silicon material, completing antimony element supplementation according to the compensation amount of antimony element obtained in the above steps, and pulling the crystal rod to obtain a single crystal silicon rod; 5) Cutting the single crystal silicon rod obtained in the above steps to obtain silicon wafers.

2. The preparation method according to claim 1, characterized in that: The polysilicon material includes N-type polysilicon dense material; The doping concentration ratio of the phosphorus element to the antimony element is 5:(1-3); The doping concentration ratio of the phosphorus element to the rare earth source is 5:(0.5-1).

3. The preparation method according to claim 1, characterized in that: The rare earth source includes rare earth and / or rare earth oxide; The rare earth includes one or more of erbium, promethium, gadolinium, holmium, thulium and samarium; The atomic concentration of phosphorus in the silicon rod raw material is greater than or equal to 4×10 19 ~10×10 19 atom / cm 3 .

4. The preparation method according to claim 1, characterized in that: The detection method of the antimony element concentration in the protective atmosphere includes detection by inductively coupled plasma emission spectrometry; The first linear fitting curve is C=kt+b; Where C is the antimony concentration in the protective atmosphere (atom / cm 3 ), k is the slope of the fitting curve, b is the fitting constant, and t is the time (hours).

5. The preparation method according to claim 1, characterized in that: In the step 3), the formula for calculating the concentration of antimony element in the remaining silicon melt is as shown in formula (1) and formula (2): p=6.242×10 18 / N1×10 Z’ (1); Where ρ is the resistivity of the end skin of the crystal rod (Ω·cm), N1 is the concentration of antimony in the remaining silicon melt (atom / cm 3 ), y=(log 10 N1)-16; Among them, A'0=-3.0769, A'1=2.2108, A'2=-0.62272, A'3=0.057501, B'1=-0.68157, B'2=0.19833, B'3=-0.018376.

6. The preparation method according to claim 5, characterized in that: The calculation formula for the compensation amount of antimony element in the reinvestment stage is shown in formula (3): Δw=N×W+k×Δt-N1W1 (3) Wherein, Δw is the compensation amount of antimony element in the reinvestment stage; N is the antimony element concentration in silicon melt at the target resistivity (atom / cm 3 ); W is the total volume of silicon melt after re-injection (cm 3 ), k is the slope of the fitted curve; Δt is the interval time (hours) from the end of the previous crystal ingot pulling to the start of this crystal ingot seeding; N1 is the antimony concentration in the silicon melt at the end of the previous crystal ingot pulling (atom / cm 3 ); W1 is the remaining silicon melt volume at the end of the previous crystal rod pulling (cm 3 ).

7. The preparation method according to claim 1, characterized in that: The previous single crystal silicon rod pulling includes the first to seventh times of multiple feedings in a single furnace; The diameter of the single crystal silicon rod is 250-350 mm; The length of the single crystal silicon rod is 2000-4000 mm.

8. The preparation method according to claim 1, characterized in that: The silicon wafer is a single crystal silicon wafer; The thickness of the silicon wafer is 80 to 100 μm; When the number of times of re-injection of the silicon material is 7, the prepared single crystal silicon rod can be cut to obtain a silicon slice with the thickness.

9. An ultra-thin silicon wafer, characterized in that: The silicon wafer is obtained by cutting a single crystal silicon rod prepared by the preparation method according to any one of claims 1 to 8.

10. The ultra-thin silicon wafer according to claim 9, characterized in that: The length of the single crystal silicon rod is greater than or equal to 2.0 m; The number of single crystal silicon rods pulled from a single furnace is greater than or equal to 6; The head resistance hit rate of single-furnace single-crystal silicon rods is greater than or equal to 95%. The difference in head resistivity between the single crystal silicon rods in the single furnace is less than or equal to 20%; The thickness of the silicon wafer is 80-100 μm.

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