N-type Czochralski silicon dopant co-doping method

Abstract

The invention discloses an N-type Czochralski monocrystalline silicon dopant co-doping method, and relates to the field of Czochralski monocrystalline silicon, and the method comprises the following operation steps: S1, determining the target resistivity of Czochralski monocrystalline silicon; s2, determining the concentration ratio of the first dopant to the second dopant; s3, determining the alloy concentration of the first dopant and the second dopant; s4, the alloy doping amount of the first doping agent and the second doping agent is calculated according to the segregation theory; s5, adding the first doping agent into the quartz crucible along with the silicon material in the last but one barrel of the re-feeding material; s6, adding a second doping agent into the quartz crucible along with the silicon material in the last barrel of re-feeding; and S7, completing doping, entering a subsequent crystal growth process, and controlling the concentration of the first dopant and the second dopant in the single crystal silicon rod to obtain the single crystal silicon rod with excellent resistivity range and resistance concentration ratio. And the growth length of the crystal can be greatly increased on the premise of keeping the resistivity range of the growth head and the growth tail of the crystal unchanged, so that the non-silicon cost of the crystal growth is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of Czochralski single crystals, and particularly to a method for co-doping N-type Czochralski single crystal silicon dopant. Background Technology

[0002] Improving photoelectric conversion efficiency is a perpetual theme in the photovoltaic industry. With the development of high-efficiency cell structures such as HJT and TOPcon, the crystalline silicon photovoltaic market is rapidly shifting from P-type to N-type, and the market demand for N-type silicon wafers is increasing rapidly. The main process parameters of the cell diffusion process—diffusion source concentration, temperature, pressure, and time—are basically stable and consistent. Under this premise, in order to further improve the photoelectric conversion efficiency of solar cells, it is necessary to further confirm the optimal matching range between silicon wafer resistivity and cell process. Higher silicon wafer resistivity will lead to an increase in cell series resistance, while lower resistivity will lead to a significant increase in Auger recombination of charge carriers. Both will reduce the photoelectric conversion efficiency of solar cells.

[0003] For mass-produced monocrystalline silicon wafers, a higher resistivity concentration of monocrystalline silicon rods will significantly improve the photoelectric conversion efficiency of downstream solar cells. Currently, the N-type monocrystalline silicon rods and wafers used in photovoltaic cells are mainly phosphorus-doped (P) monocrystalline silicon. The equilibrium segregation coefficient of phosphorus is 0.35, which is relatively small, resulting in a large difference in resistivity between the beginning and end of the N-type monocrystalline silicon rod. In the actual CZ crystal pulling process, in order to achieve a narrower resistivity range, the length of the crystal pulling rod is generally shortened. However, this will cause a significant increase in the non-silicon cost of crystal pulling.

[0004] Currently, the main dopant used in solar N-type monocrystalline silicon is phosphorus (P). Due to the small segregation coefficient of P, the concentration of impurities in the crucible increases rapidly as crystal growth progresses, leading to a rapid decrease in the resistivity of the crystal rod. In actual CZ crystal pulling, under a fixed crucible retention ratio, the resistivity of the produced monocrystalline silicon rod varies greatly from head to tail, resulting in poor resistivity concentration of the produced silicon wafer. This is not conducive to improving the overall photoelectric conversion efficiency at the cell end. At the same time, the poor concentration of photoelectric conversion efficiency of the cell results in a high proportion of inefficient output.

[0005] Therefore, it is necessary to propose an N-type Czochralski single-crystal silicon doping method to solve the above problems. Summary of the Invention

[0006] The main objective of this invention is to provide a method for co-doping N-type Czochralski single-crystal silicon with dopants, which can effectively solve the problems in the background art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for co-doping N-type Czochralski single-crystal silicon with dopant, comprising the following steps: S1: Determine the target resistivity of Czochralski single crystal silicon: Based on the size of the finished N-type Czochralski single crystal silicon, sample it, taking three pieces each from the head, middle and tail of the N-type Czochralski single crystal silicon, and marking them as discs. Then process them sequentially. Grind the discs with 28-42μm diamond abrasive, and then test the discs by grinding the upper and lower surfaces with 5-14μm alumina. Use the four-probe method to detect the resistance of the three discs. S2: Determine the concentration ratio of the first and second dopants: The concentration ratio of the first and second dopants is determined based on the target resistivity of the Czochralski single crystal silicon. S3: Determine the alloy concentrations of the first and second dopant elements: where the first dopant is phosphorus and the second dopant is arsenic. The formula for converting the resistivity of the first dopant to the dopant concentration is: The formula for converting the concentration of the first dopant to resistivity is: ; S4: Calculate the doping amount of the first and second dopant alloys according to the segregation theory: After calculating the doping amount of the first and second dopant alloys, prepare the first and second dopant based on the concentration and concentration ratio of the first and second dopant alloys; S5: When preparing N-type Czochralski single crystal silicon, the first dopant is added to the quartz crucible along with the silicon material in the second-to-last batch of the re-feeding batch. S6: Add the second dopant along with the silicon material to the quartz crucible in the last batch of re-feeding; S7: Complete the doping process and proceed to the subsequent crystal growth process to complete the co-doping of N-type Czochralski single crystal silicon dopant.

[0008] Preferably, in step S1, the device for the four-probe method is a 7075 digital voltmeter. The 7075 digital voltmeter is turned on, the current range for measurement is selected according to the resistivity range of the disc, and the measurement system is checked and recorded using a known resistivity sample.

[0009] Preferably, in step S1, when detecting resistance, the distance from the probe of the disc to the edge and thickness needs to be greater than three times the probe pitch, the geometric dimensions of the disc must meet the requirement of semi-infinite, the four probes need to have good ohmic contact with the disc, the contact point between the probe tip and the disc is hemispherical, the four probes are on the same straight line and the spacing is equal, and the current of the 7075 digital voltmeter remains constant during the measurement.

[0010] Preferably, in step S3, in the formula for converting the resistivity of the first dopant to the dopant concentration, p represents resistivity. The dopant concentration is for phosphorus. Where X is lgp, =-3.1083, =-3.2626, =1.2196, =-0.13923, =1.0265, =0.38755, =0.041833, in the formula for converting the concentration of the first dopant to resistivity, p is the resistivity. The dopant concentration is for phosphorus. y = (lg ), =-3.0769, =2.2108, =-0.62272, =-0.057501, =-0.68157, =0.19833, =-0.018376.

[0011] Preferably, in step S3, when the arsenic doping concentration in the N-type Czochralski single crystal silicon is less than 10... 19 cm- 3 When the concentration of the second dopant is converted to resistivity, the formula is: When the arsenic doping concentration is 10 19 cm- 3 -6 20 cm- 3 When the concentration of the second dopant is converted to resistivity, the formula is: lgp = -6633.667 + AX ​​+ BX 2 +CX 3 +DX 4 +EX 5 +FX 6 +GX 7 +HX 8 +JX 9 +KX 10 Where p is resistivity, Let X be the phosphorus dopant concentration, lgp, A = 768.2531, B = -25.77373, C = 0.9658177, D = -0.25643443, E = -8.888543 * 10 -4 F = 9.055838 * 10 -5 G = -1.776701 * 10 -6 H = 1.953279 * 10 -7 J = -5.754599 * 10 -9 K = -1.31657 * 10 -11 .

[0012] Beneficial effects Compared with the prior art, the present invention provides a method for co-doping N-type Czochralski single-crystal silicon with dopant, which has the following advantages: 1. This method of co-doping N-type Czochralski single-crystal silicon uses phosphorus and arsenic as the first and second dopants, respectively, while controlling the concentration and proportion of phosphorus and arsenic in the silicon melt. This significantly narrows the resistivity range of the produced crystal rod head while keeping the CZ pulling crucible ratio constant, thereby greatly improving the resistivity concentration of the produced silicon wafer. Under the premise of keeping the silicon wafer resistivity concentration requirement unchanged, the pulling length of N-type single crystal can be greatly extended, thereby significantly reducing the non-silicon cost of crystal growth. 2. This N-type Czochralski single-crystal silicon doping method, by controlling the concentrations of the first and second dopants in the single-crystal silicon rod, obtains a single-crystal silicon rod with excellent resistivity range and resistance concentration. While keeping the resistivity range at the beginning and end of crystal growth unchanged, the crystal growth length can be significantly increased, thereby significantly reducing the non-silicon cost of crystal growth; while keeping the crucible ratio of crystal growth unchanged, the resistance concentration of the produced crystal can be significantly increased, thereby obtaining higher energy conversion efficiency of photovoltaic cells. Attached Figure Description

[0013] Figure 1 This is a flowchart of the present invention; Figure 2 This is a theoretical segregation trend diagram of the resistivity of P-doped N-type single crystal and the concentration of impurities in the residue, according to the present invention. Detailed Implementation

[0014] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0015] like Figure 1 As shown, an N-type Czochralski single-crystal silicon doping method includes the following steps: S1: Determine the target resistivity of Czochralski single crystal silicon: Based on the size of the finished N-type Czochralski single crystal silicon, sample it, taking three pieces each from the head, middle and tail of the N-type Czochralski single crystal silicon, and marking them as discs. Then process them sequentially. Grind the discs with 28-42μm diamond abrasive, and then test the discs by grinding the upper and lower surfaces with 5-14μm alumina. Use the four-probe method to detect the resistance of the three discs. The equipment for the four-probe method is a 7075 digital voltmeter. The 7075 digital voltmeter is connected, and the current range is selected according to the resistivity range of the disc. The measurement system is checked using a known resistivity sample and the results are recorded. In step S1, when detecting resistance, the distance from the probes to the edge and thickness of the disc must be greater than three times the probe spacing. The geometric dimensions of the disc must be semi-infinite. The four probes must have good ohmic contact with the disc, the contact point between the probe tip and the disc is hemispherical, the four probes are on the same straight line with equal spacing, and the current of the 7075 digital voltmeter remains constant during measurement. S2: Determine the concentration ratio of the first and second dopants: The concentration ratio of the first and second dopants is determined based on the target resistivity of the Czochralski single crystal silicon. S3: Determine the alloy concentrations of the first and second dopant elements: where the first dopant is phosphorus and the second dopant is arsenic. The formula for converting the resistivity of the first dopant to the dopant concentration is: The formula for converting the concentration of the first dopant to resistivity is: ; In the formula for converting the resistivity of the first dopant to the dopant concentration, p is the resistivity. The dopant concentration is for phosphorus. Where X is lgp, =-3.1083, =-3.2626, =1.2196, =-0.13923, =1.0265, =0.38755, =0.041833, in the formula for converting the concentration of the first dopant to resistivity, p is the resistivity. The dopant concentration is for phosphorus. y = (lg ), =-3.0769, =2.2108, =-0.62272, =-0.057501, =-0.68157, =0.19833, =-0.018376; When the arsenic doping concentration in N-type Czochralski single crystal silicon is less than 10 19 cm- 3 When the concentration of the second dopant is converted to resistivity, the formula is: When the arsenic doping concentration is 10 19 cm- 3 -620 cm- 3 When the concentration of the second dopant is converted to resistivity, the formula is: lgp = -6633.667 + AX ​​+ BX 2 +CX 3 +DX 4 +EX 5 +FX 6 +GX 7 +HX 8 +JX 9 +KX 10 Where p is resistivity, Let X be the phosphorus dopant concentration, lgp, A = 768.2531, B = -25.77373, C = 0.9658177, D = -0.25643443, E = -8.888543 * 10 -4 F = 9.055838 * 10 -5 G = -1.776701 * 10 -6 H = 1.953279 * 10 -7 J = -5.754599 * 10 -9 K = -1.31657 * 10 -11 ; S4: Calculate the doping amount of the first and second dopant alloys according to the segregation theory: After calculating the doping amount of the first and second dopant alloys, prepare the first and second dopant based on the concentration and concentration ratio of the first and second dopant alloys; S5: When preparing N-type Czochralski single crystal silicon, the first dopant is added to the quartz crucible along with the silicon material in the second-to-last batch of the re-feeding batch. S6: Add the second dopant along with the silicon material to the quartz crucible in the last batch of re-feeding; S7: Complete the doping process and proceed to the subsequent crystal growth process to complete the co-doping of N-type Czochralski single crystal silicon dopant.

[0016] Specific Implementation 1: After determining the target resistance of crystal growth and the concentration ratio of the first and second dopants, the concentrations of the first and second dopant alloys used are confirmed. The amount of the first and second dopant alloys used is calculated based on the segregation theory. In order to minimize the impact of high-temperature volatilization of the dopants on the stability of the initial resistance control value, the first dopant alloy is added to the quartz crucible along with the silicon material in the second-to-last batch of the re-feeding process, and the second dopant alloy is added to the quartz crucible along with the silicon material in the last batch of the re-feeding process. After the dopant alloys are doped, the crystal growth process proceeds normally to the next stage. Specific Implementation Example 2: The equilibrium segregation coefficients (KO values) of different impurities in Si are shown in the table below: element KO element KO element KO element KO Boron (B) 0.8-0.9 Aluminum (Al) 0.002 Copper (Au) 0.0004 Oxygen (O) 1.25 Phosphorus (P) 0.35 Gallium (Ga) 0.008 Nickel (Ni) 0.000025 Carbon (C) 0.07 Arsenic (As) 0.3 Indium (In) 0.0004 Iron (Fe) 0.000008 Antimony (Sb) 0.023 Gold (Au) 0.000025 Manganese (Mn) 0.00001 The evaporation rate constants (Ev) of different impurities in silicon solution are shown in the table below: element Evaporation constant Ev / (cm / s) element Evaporation constant Ev / (cm / s) Boron (B) 5E-6 Copper (Au) 5E-5 Phosphorus (P) 1E-4 Iron (Fe) 2E-5 Antimony (Sb) 7E-2 Manganese (Mn) 2E-4 Arsenic (As) 5E-3 Gallium (Ga) 1E-3 Aluminum (Al) 1E-4 Indium (In) 5E-3 Calcium (Al) 1E-3 Currently, phosphorus (P) is the primary dopant used in N-type monocrystalline silicon for solar energy applications. Ignoring the effects of P volatilization at high temperatures, the theoretical resistance trend of P-doped N-type monocrystalline silicon is as follows, relating to the dopant impurity concentration in the remaining material within the crucible: Figure 2 As shown, the top line represents the concentration of residual impurities, and the bottom line represents the resistivity. Due to the small segregation coefficient of P element, the concentration of residual impurities in the crucible increases rapidly as crystal growth proceeds, which in turn leads to a rapid decrease in the resistivity of the crystal rod. In actual CZ crystal pulling, under the condition of a fixed crucible retention ratio, the resistivity of the produced single crystal silicon rod has a large range from head to tail, which results in poor resistivity concentration of the produced silicon wafer, which is not conducive to improving the overall photoelectric conversion efficiency at the battery end. At the same time, the concentration of photoelectric conversion efficiency of the battery is poor, and the proportion of inefficient output is relatively high. Group V elements phosphorus (P), arsenic (As), and antimony (Sb) can all be used as dopants for N-type single crystals. Among them, the segregation coefficient of arsenic (As) is relatively similar to that of phosphorus (P), which is currently the mainstream dopant. However, the theoretical evaporation rate of arsenic (As) in molten silicon is much faster than that of phosphorus (P), about 50 times faster. Based on the consistency of the segregation coefficients of phosphorus (P) and arsenic (As) in silicon and the difference in their evaporation rates, this invention selects phosphorus (P) and arsenic (As) as the first and second dopants of N-type single crystals, respectively. At the same time, the concentration and proportion of the first and second dopants in the silicon liquid are controlled. During the crystal growth process, the volatility of arsenic is utilized to significantly reduce the rate of concentration increase of residual impurities in the crucible due to segregation, thereby significantly reducing the rate of decrease in crystal resistivity. This invention uses phosphorus (P) and arsenic (As) as the first and second dopants for N-type single crystals, respectively, while controlling the concentration and proportion of phosphorus (P) and arsenic (As) in the silicon melt. This results in a significant narrowing of the resistivity range at the head of the produced crystal rod without changing the ratio of the CZ crystal pulling crucible, thereby significantly increasing the resistivity concentration of the produced silicon wafer. Under the premise of unchanged silicon wafer resistivity concentration requirements, the pulling length of N-type single crystals can be significantly extended, thereby significantly reducing the non-silicon costs of crystal growth.

[0018] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for co-doping N-type Czochralski single-crystal silicon, characterized in that: The procedure includes the following steps: S1: Determine the target resistivity of Czochralski single crystal silicon: Based on the size of the finished N-type Czochralski single crystal silicon, sample it, taking three pieces each from the head, middle and tail of the N-type Czochralski single crystal silicon, and marking them as discs. Then process them sequentially. Grind the discs with 28-42μm diamond abrasive, and then test the discs by grinding the upper and lower surfaces with 5-14μm alumina. Use the four-probe method to detect the resistance of the three discs. S2: Determine the concentration ratio of the first and second dopants: The concentration ratio of the first and second dopants is determined based on the target resistivity of the Czochralski single crystal silicon. S3: Determine the alloy concentrations of the first and second dopant elements: where the first dopant is phosphorus and the second dopant is arsenic. The formula for converting the resistivity of the first dopant to the dopant concentration is: The formula for converting the concentration of the first dopant to resistivity is: ; S4: Calculate the doping amount of the first and second dopant alloys according to the segregation theory: After calculating the doping amount of the first and second dopant alloys, prepare the first and second dopant based on the concentration and concentration ratio of the first and second dopant alloys; S5: When preparing N-type Czochralski single crystal silicon, the first dopant is added to the quartz crucible along with the silicon material in the second-to-last batch of the re-feeding batch. S6: Add the second dopant along with the silicon material to the quartz crucible in the last batch of re-feeding; S7: Complete the doping process and proceed to the subsequent crystal growth process to complete the co-doping of N-type Czochralski single crystal silicon dopant.

2. The method for co-doping N-type Czochralski single-crystal silicon according to claim 1, characterized in that: In step S1, the equipment for the four-probe method is a 7075 digital voltmeter. The 7075 digital voltmeter is turned on, the current range for measurement is selected according to the resistivity range of the disc, and the measurement system is checked and recorded using a known resistivity sample.

3. The method for co-doping N-type Czochralski single-crystal silicon according to claim 1, characterized in that: In step S1, when detecting resistance, the distance from the probe of the disc to the edge and thickness needs to be more than three times the probe pitch. The geometric dimensions of the disc must meet the requirement of semi-infinite. The four probes and the disc need to have good ohmic contact. The contact point between the probe tip and the disc is hemispherical. The four probes are on the same straight line and the spacing is equal. The current of the 7075 digital voltmeter remains constant during the measurement.

4. The method for co-doping N-type Czochralski single-crystal silicon according to claim 1, characterized in that: In step S3, in the formula for converting the resistivity of the first dopant to the dopant concentration, p represents the resistivity. The dopant concentration is for phosphorus. Where X is lgp, =-3.1083, =-3.2626, =1.2196, =-0.13923, =1.0265, =0.38755, =0.041833, in the formula for converting the concentration of the first dopant to resistivity, p is the resistivity. The dopant concentration is for phosphorus. y = (lg ), =-3.0769, =2.2108, =-0.62272, =-0.057501, =-0.68157, =0.19833, =-0.018376.

5. The method for co-doping N-type Czochralski single-crystal silicon according to claim 1, characterized in that: In step S3, when the arsenic doping concentration in the N-type Czochralski single crystal silicon is less than 10... 19 cm- 3 When the concentration of the second dopant is converted to resistivity, the formula is: When the arsenic doping concentration is 10 19 cm- 3 -6 20 cm- 3 When the concentration of the second dopant is converted to resistivity, the formula is: lgp = -6633.667 + AX ​​+ BX 2 +CX 3 +DX 4 +EX 5 +FX 6 +GX 7 +HX 8 +JX 9 +KX 10 Where p is resistivity, Let X be the phosphorus dopant concentration, lgp, A = 768.2531, B = -25.77373, C = 0.9658177, D = -0.25643443, E = -8.888543 * 10 -4 F = 9.055838 * 10 -5 G = -1.776701 * 10 -6 H = 1.953279 * 10 -7 J = -5.754599 * 10 -9 K = -1.31657 * 10 -11 .

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