Monocrystalline silicon with high resistance concentration and crystal pulling process thereof

Abstract

The invention provides a crystal pulling process of monocrystalline silicon with high resistance concentration ratio, which comprises the following steps of: according to a preset initial furnace charge of polycrystalline silicon, performing crystal pulling on a formed silicon melt by using a polycrystalline silicon material and a dopant through an RCZ method, and growing to obtain a monocrystalline silicon crystal bar; the initial furnace feeding amount is M0, the unit is kilogram and meets the formula 1: M0 = (piLr2 * 2.33 / 10) / fsend, L is the length of a crystal bar, and the unit is meter; r is the radius of the crystal bar, and the unit is centimeter; fsend is the maximum solidification rate of a single crystal bar and meets the following formula 2; cs is the concentration of the dopant in the crystal bar, and C0 is the concentration of the dopant in the silicon melt in the initial crystal pulling stage; keff is the effective segregation coefficient of the dopant, K is the mass transfer coefficient of the dopant, and v is the crystal pulling rate. The whole crystal pulling process is stable, easy to control and high in operability; the obtained crystal bar is stable in quality, and the head resistivity hit rate of different crystal bars is high. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic single crystal silicon, and in particular to single crystal silicon with high resistance concentration and a crystal pulling process thereof. Background Art

[0002] In the photovoltaic field, monocrystalline silicon solar cells have a high photoelectric conversion efficiency. Among them, the cost of preparing monocrystalline silicon by the CZ method (CZ method) is relatively low. The main process is to first place high-purity polycrystalline silicon raw materials in a quartz crucible and heat and melt them, and then insert the monocrystalline silicon seed crystal into the melt surface. After the seed crystal and the melt are melted, the seed crystal is pulled upward. The crystal will grow at the lower end of the seed crystal, and gradually grow to form a crystal rod as the seed crystal is pulled. At present, the multiple feeding and repeated CZ single crystal method (RCZ) is the mainstream method for growing photovoltaic monocrystalline silicon crystals. It is improved by adding a feeding device on the basis of the batch CZ method. The RCZ method keeps the crucible at a high temperature after each pulling of the silicon crystal rod, and adds the polycrystalline silicon particle raw material to the remaining silicon melt in the crucible through the feeding device for melting for the next crystal rod pulling.

[0003] The RCZ method can further reduce production costs, but due to the influence of segregation, the concentration of dopants (IIIA, IVA, VA elements) in the crystal rod usually shows a trend of "low at the head and high at the tail", resulting in a corresponding trend of "high at the head and low at the tail" in the resistivity distribution of the crystal rod. On the other hand, the resistivity of silicon wafers is one of the important factors affecting the output power and efficiency of solar cells; too high a resistivity of silicon wafers will increase the series resistance, while too low a resistivity will increase the carrier Auger recombination loss.

[0004] In order to narrow the resistivity distribution of the head and tail of the crystal rod, the existing technical solutions mainly focus on the adjustment of the crystal pulling process and element doping. For example, the Chinese patent document with the publication number CN 114540950 A discloses a method for growing n-type CZ single crystal silicon by reducing the furnace pressure, which first places polycrystalline silicon material and n-type dopant in a quartz crucible, heats to stable molten silicon in an argon atmosphere, introduces seed crystals therein, and then enters the equal diameter growth stage after necking and shouldering. In this middle and late stages, the crystal pulling rate is kept unchanged, the argon gas pressure in the single crystal furnace is reduced, and the vacuum degree in the furnace is increased to an appropriate value and maintained until the CZ single crystal silicon growth is completed. The method of reducing furnace pressure to pull crystals mainly reduces the resistance ratio of the head and tail of the crystal rod by reducing the furnace pressure in the late equal diameter stage and increasing the volatilization rate of the dopant. However, this method requires a large reduction in furnace pressure, easily destroys the stability of the solid-liquid interface, and increases the wire breakage rate. It is also complicated to operate and is not very operable in photovoltaic single crystal silicon crystal rods. Summary of the invention

[0005] In view of the problem that the resistance distribution of the head and tail of the crystal rod produced by the existing RCZ method is wide and the operability is poor, the present invention provides a single crystal silicon with high resistance concentration and a crystal pulling process thereof. The single crystal silicon crystal pulling method is easy to operate, can effectively narrow the resistance ratio of the crystal rod head and tail, reduce the output power fluctuation of the photovoltaic cell, and thus improve the efficiency of the photovoltaic cell and the module.

[0006] The present invention provides a single crystal silicon pulling process with high resistance concentration, comprising the following steps:

[0007] According to the preset initial amount of polysilicon put into the furnace, the polysilicon material and the dopant are used to pull the formed silicon melt through the RCZ method to grow a single crystal silicon ingot;

[0008] The initial furnace quantity is M 0 , in kilograms, satisfies the following formula 1:

[0009] M 0 =(πLr 2 ×2.33 / 10)÷f send Formula 1;

[0010] In formula 1, L is the length of the crystal rod, in meters; r is the radius of the crystal rod, in centimeters;

[0011] f send is the maximum solidification rate of a single crystal rod, satisfying the following formula 2:

[0012]

[0013] In formula 2, C s is the concentration of dopant in the crystal rod, C 0 K is the concentration of dopants in the silicon melt at the initial stage of crystal pulling; eff is the effective segregation coefficient of the dopant, K is the mass transfer coefficient of the dopant, and v is the crystal pulling rate.

[0014] In some embodiments of the present invention, the initial amount of the raw materials put into the furnace is above 880 kg. Furthermore, the initial amount of the raw materials put into the furnace is between 880 kg and 1100 kg.

[0015] In some embodiments of the present invention, the crystal pulling rate is 0.6-1.8 mm / min.

[0016] Furthermore, the crystal pulling rate includes a first crystal pulling rate at one end and a second crystal pulling rate at the other end, the first crystal pulling rate is 1.2-1.8 mm / min, and the second crystal pulling rate is 0.6-1.0 mm / min.

[0017] In some embodiments of the present invention, the dopant is an n-type dopant, the furnace atmosphere of the RCZ method is argon, and the crystal pulling furnace pressure is 10-15 torr.

[0018] Furthermore, the dopant is a phosphorus-containing substance, and the crystal pulling furnace pressure of the RCZ method is 11 to 13 torr.

[0019] In some embodiments of the present invention, the crucible retention rate of the RCZ method is 40-45%.

[0020] The present invention provides a single crystal silicon ingot, which is obtained according to the above-mentioned crystal pulling process and has a resistance range of 0.8 to 1.3 Ω.cm.

[0021] In some embodiments of the present invention, the single crystal silicon ingot has a diameter of 60 to 600 mm and a length of 200 to 400 cm.

[0022] Under the commonly used crystal pulling process, the length of a single crystal silicon ingot is about 3 meters, and the resistance ratio between the head and tail of the ingot is greater than 2.5. In order to narrow the resistivity distribution between the head and tail of the ingot, it is generally necessary to shorten the ingot length, which will increase the cost of crystal pulling.

[0023] Compared with the prior art, the present invention increases the preset initial furnace input amount according to the solidification rate of the crystal rod, and uses the RCZ method to grow single crystal silicon without involving process changes. The present invention does not need to shorten the length of the crystal rod, the process is simple, and the cost is low. The resistivity of the entire crystal rod can be concentrated near the resistivity that is most suitable for the battery process (that is, at this resistivity, the output power and efficiency of the battery cell are optimal), and the resistivity hit rate of different crystal rod heads is greater than 95%, thereby effectively reducing the fluctuation of the battery cell output power and increasing the efficiency of the battery cell and the module. It can be seen that the whole process of crystal pulling of the present invention is stable, easy to control, and highly operable. The crystal rod obtained by the present invention has stable quality and a high resistivity hit rate of different crystal rod heads.

[0024] In addition, the method of the present invention does not involve multi-element doping, which facilitates the cleaning and control of circulating materials and the recovery and utilization of argon gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Some specific principles and operation steps of the embodiments of the present invention are shown in the figure;

[0026] Figure 2 is a curve showing the relationship between the length and resistivity of a phosphorus-doped crystal rod according to some embodiments of the present invention;

[0027] Figure 3 1 is a curve showing the relationship between the length and resistivity of the phosphorus-doped crystal rod in Examples 1-3. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Unless otherwise defined, all professional terms used hereinafter have the same meaning as those skilled in the art generally understand. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0029] The present invention provides a high resistance concentration single crystal silicon crystal pulling process, comprising the following steps:

[0030] According to the preset initial amount of polysilicon put into the furnace, the polysilicon material and the dopant are used to pull the formed silicon melt through the RCZ method to grow a single crystal silicon ingot;

[0031] The initial furnace quantity is M 0 , in kilograms, satisfies the following formula 1:

[0032] M 0 =(πLr 2 ×2.33 / 10)÷f send Formula 1;

[0033] In formula 1, L is the length of the crystal rod, in meters; r is the radius of the crystal rod, in centimeters;

[0034] f send is the maximum solidification rate of a single crystal rod, satisfying the following formula 2:

[0035]

[0036] In formula 2, C s is the concentration of dopant in the crystal rod, C 0 K is the concentration of dopants in the silicon melt at the initial stage of crystal pulling; eff is the effective segregation coefficient of the dopant, K is the mass transfer coefficient of the dopant, and v is the crystal pulling rate.

[0037] The present invention mainly provides a RCZ (repeated direct-pull single crystal method with multiple feeding) process, which is easy to operate, can effectively narrow the head-tail resistance ratio of the crystal rod, reduce the output power fluctuation of the photovoltaic cell, and thus improve the efficiency of the photovoltaic cell and the module.

[0038] See also Figure 1 Some specific principles and operation steps of the embodiments of the present invention include: determining the solidification rate cutoff value (i.e., the maximum solidification rate) according to the target resistivity range, calculating the initial feed amount according to the maximum solidification rate, the crystal rod size, and the target crystal rod length, and then performing crystal pulling verification, and correcting the solidification rate-resistivity curve, and then performing crystal pulling application again.

[0039] For example, the maximum coagulation rate f is calculated based on the target resistivity of 1.3 Ω·cm. send , and the resistivity of the crystal rod is calculated according to the concentration of the dopant in the crystal rod, and the solidification rate-resistivity relationship curve is drawn. The results are shown in Figure 2 (Theoretical curve obtained according to Sheil equation). Figure 2 The relationship between the resistivity of phosphorus-doped crystal rod and the solidification rate, where the crystal pulling furnace pressure is 12torr. It is preliminarily believed that the axial distribution of dopants in silicon single crystals conforms to the Sheil equation, that is:

[0040]

[0041] Among them, f s is the solidification rate of silicon melt, representing the instantaneous solidification rate at any moment in the crystal pulling process, f s =Crystal rod weight / total amount of silicon material; C s is the concentration of dopant in the crystal rod (unit: atoms / cm 3 ), C 0 is the concentration of dopants in the silicon melt at the initial stage of crystal pulling (unit: atoms / cm 3 ), K eff is the effective segregation coefficient of the dopant; X = K / v, K is the mass transfer coefficient of the dopant, v is the pulling speed of the crystal rod; f send It is the solidification rate of the crystal rod at the end of single crystal rod growth, that is, the solidification rate corresponding to the target resistivity, representing the maximum solidification rate at the end of crystal pulling.

[0042] According to Sheil's formula, the head-to-tail resistance ratio of the crystal rod is only related to the crucible retention rate or the crystal rod solidification rate.

[0043] Then, according to the target crystal rod radius r / cm and crystal rod length L / m in formula 1, the target crystal rod weight M / kg is calculated, that is: πLr 2 ×2.33 / 10; then according to the target crystal rod weight M / kg, maximum solidification rate f send , calculate the initial furnace quantity M 0 , that is: M 0 =M / f send .

[0044] An experimental verification is carried out based on the initial furnace charge obtained, and the solidification rate-resistivity relationship curve obtained from the experiment is compared with the solidification rate-resistivity relationship curve drawn by the above measurement. If the result is consistent with the calculated value, crystal pulling is carried out. If it does not meet the requirements, the solidification rate-resistivity curve is refitted according to the experimental results.

[0045] Finally, the furnace loading amount is determined based on the fitted Sheil equation, the target resistivity range, the crystal rod length and the radius, and single crystal silicon is grown using the RCZ method.

[0046] The present invention is based on the application and modification of the Sheil formula. After the target resistivity range is known, the Sheil formula can be used to calculate the target condensation rate or crucible retention rate. When the crucible retention rate is fixed, the length of the crystal rod can be increased by simply increasing the feed amount.

[0047] In some embodiments of the present invention, a method for ensuring the length of a crystal rod by increasing the amount of material fed is provided under the condition of fixing the resistivity / resistance ratio of the head and tail of the crystal rod, and the specific steps include: 1. Calculating the crucible retention rate according to the target resistivity range and Sheil formula, the crucible retention rate = (1-solidification rate) * 100%, and drawing a resistivity range VS crucible retention rate curve; 2. Calculating the feed amount according to the crucible retention rate and the target crystal rod size and length; 3. Crystal pulling verification, measuring the head and tail resistivity and the head and tail resistance ratio of the crystal rod; 4. Correcting (re-fitting) the resistivity range VS crucible retention rate curve according to the verification result, the crucible retention rate of the RCZ method is 40-45%; 5. According to the corrected (re-fitted) curve, after the head and tail resistance of the crystal rod is known, calculating the feed amount and carrying out the crystal pulling process.

[0048] In some embodiments, the initial amount of furnace charge is above 880 kg, for example, 880 kg, 900 kg, 1000 kg, 1100 kg, etc.

[0049] Compared with the conventional method for narrowing the resistivity, the method of the embodiment of the present invention does not involve process changes and is easy to operate. In some embodiments, the crystal pulling rate is 0.6 to 1.8 mm / min. Further, the crystal pulling rate includes a first crystal pulling rate at one end and a second crystal pulling rate at the other end, the first crystal pulling rate is 1.2 to 1.8 mm / min, and the second crystal pulling rate is 0.6 to 1.0 mm / min.

[0050] The dopant involved in the process of the embodiment of the present invention is generally an n-type dopant, such as phosphorus and arsenic, which makes the doped silicon into an n-type material (electrons are the majority carriers); the doping concentration is 4×10 19 ~10×10 19 atm / cm 3 (atm / cm 3 It is an atomic concentration unit, which indicates the number of dopant atoms contained in a unit volume of silicon melt. It does not involve multi-element doping, which is convenient for recycling material cleaning and control and argon recycling. The furnace atmosphere of the RCZ method is argon, and the crystal pulling furnace pressure can be 10 to 15 torr, and further 11 to 13 torr.

[0051] The present invention provides a single crystal silicon ingot, which is obtained according to the above-mentioned crystal pulling process, and has a resistance range of 0.8 to 1.3 Ω.cm. In some embodiments, the diameter of the single crystal silicon ingot is 60 to 600 mm, further 200 to 300 mm, and the length can be 200 to 400 cm.

[0052] The embodiment of the present invention regulates the resistivity distribution of the crystal rod by controlling the feeding amount, and has the advantages of simple operation, stable crystal rod quality, narrow resistivity distribution of the crystal rod, high resistivity hit rate of different crystal rod heads, moderate crucible retention rate, and convenient cleaning of circulating materials.

[0053] In order to better illustrate the present invention, the following examples are further illustrated. Unless otherwise specified, the various reagents and raw materials used in the present invention are all commercially available products or products that can be prepared by recognized methods.

[0054] Examples 1-3

[0055] Using phosphorus as the dopant and the target resistivity of 1.3Ω·cm, the maximum solidification rate f is calculated. send , and the resistivity of the crystal rod is calculated according to the concentration of the dopant in the crystal rod, and the solidification rate-resistivity relationship curve is drawn. The relationship between the length of the phosphorus-doped crystal rod and the resistivity is shown in Figure 2 As shown, the calculation formula is as follows.

[0056] ρ=6.242×10 18 / C s ×10 Z’ ; C s is the atomic concentration of the doping element in the remaining silicon melt (atm / cm 3 ), Z' is the resistivity, y=(log 10 N1)-16;

[0057]

[0058] Among them, A' 0 =-3.0769, A' 1 =2.2108, A' 2 =-0.62272, A' 3 =0.057501, B' 1 =-0.68157, B' 2 =0.89133, B' 3 =-0.018376.

[0059] It is preliminarily believed that the axial distribution of dopants in silicon single crystals conforms to the Sheil equation, namely:

[0060]

[0061] Among them, f s is the solidification rate of silicon melt, f s =Crystal rod weight / total amount of silicon material; C s is the concentration of dopant in the crystal rod, C 0 is the concentration of dopants in the silicon melt at the initial stage of crystal pulling, K eff is the effective segregation coefficient of the dopant; X = K / v, K is the mass transfer coefficient of the dopant, v is the pulling speed of the crystal rod; f send is the solidification rate of the crystal rod at the end of the growth of a single crystal rod.

[0062] Then, according to the target crystal rod radius r / cm and crystal rod length L / m in formula 1, the target crystal rod weight M / kg is calculated, that is: πLr 2 ×2.33 / 10; then according to the target crystal rod weight M / kg, maximum solidification rate f send , calculate the initial furnace quantity M 0 , that is: M 0 =M / f send The initial loading amounts of Examples 1-3 are 880 kg, 1000 kg, and 1100 kg, respectively.

[0063] According to the obtained initial furnace input amount, experimental verification was carried out, and the solidification rate-resistivity relationship curve obtained by the experiment was compared with the solidification rate-resistivity relationship curve drawn by the above measurement. The result was consistent with the calculated value, and the crystal pulling application was carried out, and the RCZ method was used to grow single crystal silicon. The crystal pulling process is a common and well-known process flow in the industry, and it is not necessary to elaborate on it here.

[0064] The crystal pulling process includes: 880kg, 1000kg, 1100kg furnace load, crystal rod diameter is 300mm, crystal head pulling speed is 1.8mm / min, tail pulling speed is 0.9mm / min, crystal pulling furnace pressure is 12torr; the total furnace load is 3500kg. The relationship between phosphorus-doped crystal rod length and resistivity can be found in Figure 3 .

[0065] Table 1 Crystal pulling process parameters of Examples 1-3

[0066] Furnace quantity / kg 880 1000 1100 Head resistivity / (Ω.cm) 1.3 1.3 1.3 Tail resistivity / (Ω.cm) 0.8 0.8 0.8 Crystal rod length / cm 297 339 373 Crumb retention rate / % 44.1 43.8 43.8

[0067] Figure 3 As shown in Table 1, under the fixed target resistance range (0.8-1.2Ω.cm) and crystal rod size (diameter 300mm), by adjusting the furnace loading, the crystal rod length can be quantitatively controlled, and the crucible retention rate is moderate. If the furnace loading is less than 880kg, the length of the obtained crystal rod is shorter in the same head and tail resistivity range, resulting in low production efficiency.

[0068] It can be seen from the above embodiments that the present invention increases the preset initial furnace input according to the solidification rate of the crystal rod, and uses the RCZ method to grow single crystal silicon without involving process changes. The present invention does not need to shorten the length of the crystal rod, the process is simple, and the cost is low. The resistivity of the entire crystal rod can be concentrated near the resistivity that is most suitable for the battery process (that is, at this resistivity, the output power and efficiency of the battery cell are optimal), and the resistivity hit rate of different crystal rod heads is greater than 95%, thereby effectively reducing the fluctuation of the battery cell output power and increasing the efficiency of the battery cell and the module. The head resistivity hit rate is defined as the ratio of the number of crystal rods with qualified head resistivity (within the target resistivity range) to the total number of crystal rods pulled after resistivity measurement (the measurement method is a commonly known method in the industry).

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for pulling single crystal silicon with high resistance concentration, characterized in that: The following steps are involved: According to the preset initial amount of polysilicon put into the furnace, the polysilicon material and the dopant are used to pull the formed silicon melt through the RCZ method to grow a single crystal silicon ingot; The initial furnace loading amount is M0, in kilograms, and satisfies the following formula 1: M0=(πLr 2 ×2.33 / 10)÷f send Formula 1; In formula 1, L is the length of the crystal rod, in meters; r is the radius of the crystal rod, in centimeters; f send is the maximum solidification rate of a single crystal rod, satisfying the following formula 2: In formula 2, C s is the concentration of dopants in the crystal rod, C0 is the concentration of dopants in the silicon melt at the initial stage of crystal pulling; K eff is the effective segregation coefficient of the dopant, K is the mass transfer coefficient of the dopant, and v is the crystal pulling rate.

2. The crystal pulling process according to claim 1, characterized in that: The initial furnace loading amount is more than 880 kg.

3. The crystal pulling process according to claim 2, characterized in that: The initial amount of the furnace is 880-1100 kg.

4. The crystal pulling process according to any one of claims 1 to 3, characterized in that: The crystal pulling rate is 0.6-1.8 mm / min.

5. The crystal pulling process according to claim 4, characterized in that: The crystal pulling rate includes a first crystal pulling rate at one end and a second crystal pulling rate at the other end, the first crystal pulling rate is 1.2-1.8 mm / min, and the second crystal pulling rate is 0.6-1.0 mm / min.

6. The crystal pulling process according to any one of claims 1 to 3, characterized in that: The dopant is an n-type dopant, the atmosphere in the furnace of the RCZ method is argon, and the crystal pulling furnace pressure is 10 to 15 torr.

7. The crystal pulling process according to claim 6, characterized in that: The dopant is a phosphorus-containing substance, and the crystal pulling furnace pressure of the RCZ method is 11 to 13 torr.

8. The crystal pulling process according to claim 7, characterized in that: The crucible retention rate of the RCZ method is 40-45%.

9. A single crystal silicon ingot, characterized in that: It is manufactured by the crystal pulling process according to any one of claims 1 to 8, and the resistance range is 0.8 to 1.3 Ω.cm.

10. The single crystal silicon ingot according to claim 9, characterized in that: The single crystal silicon ingot has a diameter of 60 to 600 mm and a length of 200 to 400 cm.

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