Method for improving resistivity distribution uniformity of silicon single crystal rod

Abstract

The invention discloses a method for improving resistivity distribution uniformity of a single crystal silicon rod, and belongs to the technical field of photovoltaic material production, and the method comprises the following steps: (1) preparing a multi-element master alloy which comprises a ternary master alloy or a quaternary master alloy and the like; (2) calculating the doping concentration of the multi-element mother alloy in the silicon raw material according to the target monocrystalline silicon rod parameter, wherein the target monocrystalline silicon rod parameter comprises the resistivity rho of the head of the target monocrystalline silicon rod; and (3) feeding the silicon raw material and the multi-element master alloy according to the calculated doping concentration of the multi-element master alloy, and preparing the silicon single crystal rod with good resistivity distribution uniformity by using a multi-feeding and multi-pulling method. Besides, a second movable auxiliary chamber is further arranged in a conventional single crystal furnace device, after drawing of the single crystal rod is completed in the main heating chamber, the next cooling process is performed in the first auxiliary chamber and the second movable auxiliary chamber in sequence, the heat preservation waiting time of the main heating chamber is shortened, and the crystal pulling efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic material production, and in particular to a method for improving the resistivity distribution uniformity of a single crystal silicon rod. Background Art

[0002] Currently, silicon solar cells, typically based on single crystal silicon, still dominate the photovoltaic industry. The repetitively charged zone (RCZ) method is one of the mainstream techniques for producing single crystal silicon. This method, a modified Czochralski method, involves retaining some molten silicon during the pulling process to maintain a high crucible temperature. Silicon material is then added to the crucible via a doping device to pull the next silicon rod. During the RCZ method for producing single crystal silicon, the use of a master alloy as a dopant effectively adjusts the concentration of donor or acceptor impurities in the silicon melt, ensuring the grown silicon single crystal has the desired resistivity specifications. Master alloy doping involves pre-preparing a highly doped silicon alloy (such as boron-silicon or phosphorus-silicon) and then feeding it in small chunks into the silicon melt. Master alloy doping offers the following advantages: it avoids segregation caused by density differences between the dopant and the silicon melt, reduces dopant volatilization losses, and allows for precise control of dopant concentration. However, due to the segregation coefficient of dopants in silicon, the dopant concentration in a single-crystal silicon rod exhibits a "low at the head and high at the tail" distribution, corresponding to a "high at the head and low at the tail" resistivity distribution. The resistivity of silicon wafers significantly impacts the performance of silicon solar cells. Therefore, narrowing the resistivity distribution range of single-crystal silicon rods and improving their longitudinal resistivity uniformity are crucial.

[0003] Chinese patent publication CN105755533A discloses a method for producing high-resistance silicon single crystals using the Czochralski method. The method first produces several master alloy samples with a resistivity of 0.015 to 0.020 Ω / cm. These master alloy samples are then used to produce high-resistance silicon single crystals using the Czochralski method. This invention achieves stable growth of high-resistance silicon single crystals by precisely controlling the resistivity of each small batch of master alloys, increasing the doping level, and reducing errors in calculation and weighing of the master alloys. The method achieves a resistivity of 300 Ω / cm for P-type single crystals, with a radial resistivity uniformity of less than 3%. However, this method has high process requirements and suffers from the problem of crucibles being unable to be reused due to cracking during cooling.

[0004] Chinese patent publication CN115506018A discloses a method for drawing single crystal silicon using the RCZ method. This method, on the one hand, adjusts the amount of alloy added during the drawing of the n-1th rod to reduce the alloy concentration deposited at the bottom of the crucible, thereby preventing an increase in the alloy content of the single crystal silicon rod during the drawing of the n-1th rod, which would result in a decrease in resistivity and ensure stable performance of multiple single crystal silicon rods during the drawing process. On the other hand, when drawing the nth rod, the diameter of the nth rod is increased, the drawing length of the n-1th rod is adjusted, and the amount of silicon material re-feed and alloy addition are controlled during the drawing of the nth rod to comprehensively reduce the alloy concentration during the drawing of the nth rod, so that the resistivity of the nth rod matches the diameter of the nth rod, meeting the requirements of use. However, this invention also suffers from the problem of high control precision of process parameters.

[0005] In addition, in the traditional RCZ technology, the main heating chamber for single crystal silicon is equipped with a sub-chamber. After a single crystal silicon rod is pulled, it needs to be pulled into the sub-chamber for cooling, and the cooling time takes several hours. During this process, the next single crystal silicon cannot be pulled. The main heating chamber is idle and the power supply cannot be interrupted during this period, otherwise the temperature of the furnace body cannot be maintained, which is not conducive to the pulling of the next single crystal silicon rod. Therefore, the preparation efficiency of single crystal silicon is low and the power resources are wasted. In other words, improving the preparation efficiency of single crystal silicon in RCZ technology is also the key to process improvement. Summary of the Invention

[0006] In order to address the deficiencies in the above-mentioned prior art, the present invention provides a method for improving the resistivity distribution uniformity of a single crystal silicon rod and a method for improving the crystal pulling efficiency.

[0007] The specific technical solutions adopted are as follows:

[0008] A method for improving the resistivity distribution uniformity of a single crystal silicon rod comprises the following steps:

[0009] (1) preparing a multi-element master alloy XY-Si, XZ-Si, YZ-Si or XYZ-Si, wherein X is selected from at least one of boron, aluminum and gallium, Y is selected from at least one of phosphorus, arsenic and antimony, and Z is selected from at least one of germanium, nitrogen and carbon;

[0010] (2) calculating the doping concentration of the multi-element master alloy in the silicon raw material based on target single crystal silicon rod parameters, wherein the target single crystal silicon rod parameters include the target single crystal silicon rod head resistivity ρ;

[0011] x represents the specific position of the target single crystal silicon rod, ρ(x) represents the resistivity at x, N net (x) represents the net carrier concentration at x, μ majrepresents the mobility of majority carriers (when silicon is p-type, it is the mobility of holes, when silicon is n-type, it is the mobility of electrons), q represents the charge, then:

[0012] ρ(x)=qN net (x)μ maj ;

[0013]

[0014] Among them, N net (x) is the sum of the contributions of all doping elements except Si in the multi-element master alloy, n represents the number of element types of X acceptor elements and Y donor elements in the multi-element master alloy, and the contribution of the i-th doping element is k i is the segregation coefficient of the i-th doping element in silicon, C i is the doping concentration of the i-th doping element. When the doping element is Y donor element, When the doping element is an X acceptor element, For the Z element in the multi-element master alloy, its contribution is 0; according to N net (x) calculating the theoretical doping concentration of each doping element in the multi-element master alloy;

[0015] (3) According to the theoretical doping concentration calculated in step (2), silicon raw material and multi-element master alloy are added to the crucible of the main heating chamber of the single crystal furnace, and a single crystal silicon rod with good resistivity distribution uniformity is prepared by a multiple feeding and pulling method.

[0016] The present invention adopts a multi-component master alloy for doping to precisely control the doping concentration. The multi-component master alloy can also realize compensation doping. Specifically, compensation doping is achieved by simultaneously introducing donor and acceptor impurities into the multi-component master alloy, utilizing the charge neutralization effect of the two, and precisely regulating the net carrier concentration, thereby narrowing the resistivity distribution range.

[0017] Specifically, in step (1), the multi-component master alloy is prepared by a melting method, a powder metallurgy method or a vapor deposition method.

[0018] Furthermore, the process of preparing the multi-component master alloy by melting method is as follows: adding the doping element powder into the high-purity silicon melt, and preparing the multi-component master alloy by Czochralski method or casting method.

[0019] Furthermore, the process of preparing the multi-element master alloy by powder metallurgy is as follows: silicon powder is mixed with doping element powder, and the multi-element master alloy is formed by high-temperature sintering or hot pressing.

[0020] Furthermore, the process of preparing the multi-component master alloy by vapor deposition is as follows: depositing a doping layer on a silicon substrate by chemical vapor deposition (CVD) or physical vapor deposition (PVD), and then performing high-temperature diffusion to prepare the multi-component master alloy.

[0021] Preferably, in step (3), the feeding amount of the silicon raw material is determined according to the parameters of the target single crystal silicon rod, the feeding amount of the silicon raw material is calculated by the following formula, and the doping amount of the multi-element master alloy is further determined, and the feeding is performed according to the corresponding feeding amount and doping amount;

[0022]

[0023] Among them, m Si is the feeding amount of silicon raw material; ρ Si is the density of the target single crystal silicon rod; D and L are the diameter and length of the target single crystal silicon rod respectively, and m0 is the reserved tail silicon mass.

[0024] Specifically, the process flow of the multiple-feed re-pulling method includes: vacuuming, leak detection, heating and melting. After the melting is completed, cooling and stabilization, crystal induction, shoulder release, shoulder rotation, equal diameter growth, and finishing are carried out to pull the first single crystal rod, and the single crystal rod is pulled to the sub-chamber of the single crystal furnace for cooling. At the same time, the remaining melt in the main heating chamber of the single crystal furnace is given a certain power for insulation; then the re-feed device is loaded with re-feed material to continue adding silicon raw material and multi-element master alloy to the main heating chamber of the single crystal furnace, and the above steps are repeated until the last single crystal silicon rod is prepared.

[0025] Preferably, the single crystal furnace sub-chamber includes a first sub-chamber and a second movable sub-chamber. After the single crystal rod is pulled in the main heating chamber of the single crystal furnace, the next cooling process is carried out in the first sub-chamber and the second movable sub-chamber respectively, thereby reducing the insulation waiting time of the main heating chamber of the single crystal furnace.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention accurately calculates the doping concentration of a specific multi-component master alloy in a silicon raw material based on the target single crystal silicon rod parameters, thereby enabling the multi-component master alloy to simultaneously achieve compensatory doping, thereby narrowing the resistivity distribution range.

[0028] (2) The present invention applies the second movable sub-chamber to the RCZ technology, which can effectively improve the pulling efficiency of single crystal silicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a single crystal furnace equipped with a second movable sub-chamber.

[0030] Figure numerals: 1 is the first exhaust hole, 2 is the main heating chamber, 3 is the main heating chamber gate valve, 4 is the first sub-chamber gate valve, 5 is the first sub-chamber, 6 is the crystal lifting device, 7 is the first manipulator, 8 is the connecting device, 9 is the second exhaust hole, 10 is the feeding hole, 11 is the second movable sub-chamber, 12 is the second manipulator, 13 is the movable trolley, 14 is the supporting foot, and 15 is the wheel.

[0031] Figure 2 This is a resistivity distribution diagram of n-type single crystal silicon produced by doping and pulling with different multi-element master alloys in an embodiment of the present invention.

[0032] Figure 3 This is a resistivity distribution diagram of p-type single crystal silicon produced by doping and pulling with different multi-element master alloys in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the objects, features and advantages of the present invention more clearly understood, a detailed description is given below using specific embodiments. In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0034] Example 1

[0035] In this embodiment, the method for improving the resistivity distribution uniformity of a single crystal silicon rod includes the following steps:

[0036] (1) The method for preparing the multi-element master alloy is a melting method, in which silicon powder is mixed with doping element powder and formed into a multi-element master alloy by high-temperature sintering or hot pressing. Finally, seven kinds of master alloys, namely P-Si, P-Ga-Si, P-Al-Si, B-Si, BP-Si, B-Ga-P-Si, and B-Al-P-Si, are prepared;

[0037] (2) The doping concentration of the multi-element master alloy in the silicon raw material is calculated based on the target single crystal silicon rod parameters. The calculation formula for the resistivity ρ(x) at a specific position of the single crystal silicon rod pulled by the RCZ method is as follows:

[0038] ρ(x)=qN net (x)μ maj Formula 1

[0039] In formula 1, x represents the specific position of the target single crystal silicon rod, ρ(x) represents the resistivity at x, and N net (x) represents the net carrier concentration at x (taking P-Ga-Si ternary master alloy as an example, Nnet (x) calculated according to formula 2), μ maj is the mobility of majority carriers (when silicon is p-type, it is the mobility of holes, when silicon is n-type, it is the mobility of electrons), q represents the charge;

[0040] Specifically, taking P-Ga-Si ternary master alloy as an example,

[0041]

[0042] Correspondingly, k P and k Ga are the segregation coefficients of P and Ga in silicon, C P and C Ga are the doping concentrations of P and Ga in the silicon raw material, respectively. In the multi-element master alloy or XY-Si, XZ-Si, YZ-Si or XYZ-Si (wherein X is boron, aluminum or gallium; Y is phosphorus, arsenic or antimony; and Z is germanium, nitrogen or carbon), the dopant contained in Z is generally not electrically active. Its function is usually to regulate defects or mechanical properties in single crystal silicon. Its effect on resistivity is generally ignored because the term related to the Z element should not be included in the calculation of Formula 2 by analogy, and the concentration distribution of the Z element needs to be calculated separately.

[0043] For the preset target single crystal silicon rod head resistivity, C can be estimated according to Equation 1 and Equation 2. P and C Ga The doping concentration of the multi-element master alloy in the silicon raw material can be obtained by using the value of N. For other cases such as XY-Si, XZ-Si, YZ-Si and XYZ-Si, the doping concentration of the multi-element master alloy in the silicon raw material can be obtained by using the formula 2 and N. net The calculation method of (x) is analogous.

[0044] Here, we take P-Si, P-Ga-Si, P-Al-Si, B-Si, BP-Si, B-Ga-P-Si, and B-Al-P-Si as examples, and set the target single crystal silicon head resistivity to 10Ωcm. The calculation shows that for P-Si master alloy doping, C P The value is 1.23×10 15 cm -3 ; For P-Ga-Si master alloy doping, C P The value is 2.03×10 15 cm -3 , C Ga The value is 3.49×10 16 cm -3 ; For P-Al-Si master alloy doping, C P The value is 2.01×10 15 cm -3 , CAl The value is 1.36×10 17 cm -3 ; For B-Si master alloy doping, C B The value is 1.56×10 15 cm -3 ; For BP-Si master alloy doping, C B The value is 1.88×10 15 cm -3 , C P The value is 7.24×10 14 cm -3 ; For B-Ga-P-Si master alloy doping, C B The value is 2.39×10 15 cm -3 , C Ga The value is 2.74×10 16 cm -3 , C P The value is 2.51×10 15 cm -3 ; For B-Al-P-Si master alloy doping, C B The value is 2.38×10 15 cm -3 , C Al The value is 1.06×10 17 cm -3 , C P The value is 2.49×10 15 cm -3 .

[0045] (3) Determining the feed amount of silicon raw material based on the parameters of the target single crystal silicon rod. The feed amount of silicon raw material is specifically calculated by Formula 3. The doping amount of the multi-component master alloy is further determined by the doping concentration of the multi-component master alloy calculated in the above steps. Feeding is performed according to the corresponding feed amount and doping amount.

[0046]

[0047] Among them, m Si is the feeding amount of silicon raw material; ρ Si is the density of the target single crystal silicon rod; D and L are the diameter and length of the target single crystal silicon rod respectively, and m0 is the reserved tail silicon mass.

[0048] Subsequently, a multiple-feed and re-pulling method is used to prepare a single crystal silicon rod with good resistivity distribution uniformity. The process flow of the multiple-feed and re-pulling method includes: vacuuming, leak detection, heating and melting. After the melting is completed, cooling and stabilization, crystal induction, shoulder release, shoulder rotation, equal diameter growth, and finishing are carried out to pull the first single crystal rod. The single crystal rod is pulled to the sub-chamber of the single crystal furnace for cooling, and at the same time, the remaining melt in the main heating chamber of the single crystal furnace is given a certain power for insulation; then the re-feed device is loaded with re-feed material to continue adding silicon raw material and multi-element master alloy to the main heating chamber of the single crystal furnace, and the above steps are repeated until the last single crystal silicon rod is prepared.

[0049] Furthermore, the single crystal furnace sub-chamber includes a first sub-chamber and a second movable sub-chamber. After the single crystal rod is pulled in the main heating chamber of the single crystal furnace, the next cooling process is carried out in the first sub-chamber and the second movable sub-chamber in sequence, thereby reducing the insulation waiting time of the main heating chamber of the single crystal furnace. Specifically, the schematic diagram of the single crystal furnace equipped with the second movable sub-chamber is shown as follows: Figure 1 As shown, when the main heating chamber 2 completes the pulling of the first single crystal silicon rod, the single crystal silicon rod is then pulled into the first sub-chamber 5 using the crystal lifting device 6. The trolley 13 (with wheels 15) loaded with the second movable sub-chamber 11 is moved to the vicinity of the main heating chamber 2. The support legs 14 are lowered, the main heating chamber gate valve 3 and the first sub-chamber gate valve 4 are closed, and argon is filled between the two valves through the second exhaust hole 9 until it reaches atmospheric pressure. The connecting device 8 between the main heating chamber 2 and the first sub-chamber 5 is released, and the first sub-chamber 5 is removed from the main heating chamber 2 using the first manipulator 7. At the same time, the second movable sub-chamber 11 is installed on the main heating chamber and fastened using the second manipulator 12. The gate valve of the second movable sub-chamber is opened, and argon is then filled in after evacuation. At the same time, re-feeding is carried out into the main heating chamber from the feeding hole 10. After the feeding is completed, the air pressure of the second movable sub-chamber 11 is adjusted to be consistent with that of the main heating chamber 2. Finally, the main heating chamber gate valve 3 is opened to pull the next single crystal silicon rod. A first exhaust hole 1 connected to the external exhaust system is provided on the furnace wall 2, which is the exhaust outlet of the inert gas. And so on, until the last single crystal silicon rod is prepared.

[0050] Figure 2 The longitudinal distribution of resistivity in single crystal silicon rods obtained by doping n-type silicon with three master alloys: P-Si, P-Ga-Si, and P-Al-Si is shown in the figure. It can be seen that compared with binary master alloy doping, the resistivity distribution range obtained by compensatory doping with ternary master alloys is narrower, and the effects of compensatory doping with P-Ga-Si and P-Al-Si on the resistivity distribution are very similar.

[0051] Figure 3The longitudinal resistivity distribution of p-type silicon single crystal silicon rods obtained by doping with four master alloys: B-Si, BP-Si, B-Ga-P-Si, and B-Al-P-Si. Compensatory doping with ternary master alloys can narrow the longitudinal resistivity distribution. Furthermore, compared to ternary master alloy compensatory doping, quaternary master alloy doping with B-Ga-P-Si and B-Al-P-Si can further narrow the longitudinal resistivity distribution, maintaining the resistivity at a preset level of around 10Ωcm from the tip to the 60% position of the entire single crystal silicon rod.

[0052] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for improving the resistivity distribution uniformity of a single crystal silicon rod, characterized in that: The following steps are involved: (1) preparing a multi-element master alloy XY-Si, XZ-Si, YZ-Si or XYZ-Si, wherein X is selected from at least one of boron, aluminum and gallium, Y is selected from at least one of phosphorus, arsenic and antimony, and Z is selected from at least one of germanium, nitrogen and carbon; (2) calculating the doping concentration of the multi-element master alloy in the silicon raw material based on target single crystal silicon rod parameters, wherein the target single crystal silicon rod parameters include the target single crystal silicon rod head resistivity ρ; x represents the specific position of the target single crystal silicon rod, ρ(x) represents the resistivity at x, N net (x) represents the net carrier concentration at x, μ maj represents the mobility of majority carriers, q represents the charge, then: ρ(x)=qN net (x)μ maj ; Among them, N net (x) is the sum of the contributions of all doping elements except Si in the multi-element master alloy, n represents the number of element types of X acceptor elements and Y donor elements in the multi-element master alloy, and the contribution of the i-th doping element is k i is the segregation coefficient of the i-th doping element in silicon, C i is the doping concentration of the i-th doping element. When the doping element is Y donor element, When the doping element is an X acceptor element, For the Z element in the multi-element master alloy, its contribution is 0; according to N net (x) calculating the theoretical doping concentration of each doping element in the multi-element master alloy; (3) According to the theoretical doping concentration calculated in step (2), silicon raw material and multi-element master alloy are added to the crucible of the main heating chamber of the single crystal furnace, and a single crystal silicon rod with good resistivity distribution uniformity is prepared by a multiple feeding and pulling method.

2. The method for improving the resistivity distribution uniformity of a single crystal silicon rod according to claim 1, characterized in that: In step (1), the multi-component master alloy is prepared by a melting method, a powder metallurgy method or a vapor deposition method.

3. The method for improving the resistivity distribution uniformity of a single crystal silicon rod according to claim 2, characterized in that: The process of preparing a multi-element master alloy by melting is as follows: adding doping element powder to a high-purity silicon melt, and preparing the multi-element master alloy by a Czochralski method or a casting method.

4. The method for improving the resistivity distribution uniformity of a single crystal silicon rod according to claim 2, wherein: The process of preparing a multi-element master alloy by powder metallurgy is as follows: silicon powder is mixed with doping element powder, and the multi-element master alloy is formed by high-temperature sintering or hot pressing.

5. The method for improving the resistivity distribution uniformity of a single crystal silicon rod according to claim 2, characterized in that: The process of preparing a multi-component master alloy by vapor deposition is as follows: depositing a doping layer on a silicon substrate by chemical vapor deposition or physical vapor deposition, and then performing high-temperature diffusion to prepare the multi-component master alloy.

6. The method for improving the resistivity distribution uniformity of a single crystal silicon rod according to claim 1, characterized in that: In step (3), the feeding amount of silicon raw material is determined according to the parameters of the target single crystal silicon rod. The feeding amount of silicon raw material is calculated by the following formula, and the doping amount of the multi-element master alloy is further determined. The feeding is carried out according to the corresponding feeding amount and doping amount; Among them, m Si is the feeding amount of silicon raw material; ρ Si is the density of the target single crystal silicon rod; D and L are the diameter and length of the target single crystal silicon rod respectively, and m0 is the reserved tail silicon mass.

7. The method for improving the resistivity distribution uniformity of a single crystal silicon rod according to claim 1, wherein: The process flow of the multiple-feed re-pulling method includes: vacuuming, leak detection, heating and melting. After melting, cooling and stabilization, crystal induction, shoulder release, shoulder rotation, equal diameter growth, and finishing are carried out to pull the first single crystal rod, which is then pulled to the sub-chamber of the single crystal furnace for cooling. At the same time, the remaining melt in the main heating chamber of the single crystal furnace is given a certain power for insulation; then the re-feed device is loaded with re-feed material to continue adding silicon raw material and multi-element master alloy to the main heating chamber of the single crystal furnace, and the above steps are repeated until the last single crystal silicon rod is prepared.

8. The method for improving the resistivity distribution uniformity of a single crystal silicon rod according to claim 7, characterized in that: The single crystal furnace sub-chamber includes a first sub-chamber and a second movable sub-chamber. After the single crystal rod is pulled in the main heating chamber of the single crystal furnace, the next cooling process is carried out in the first sub-chamber and the second movable sub-chamber respectively, thereby reducing the insulation waiting time of the main heating chamber of the single crystal furnace.

Images