Crystal pulling method for reducing longitudinal oxygen content of monocrystalline silicon rod

Abstract

The invention provides a crystal pulling method for reducing the longitudinal oxygen content of a monocrystalline silicon rod, and belongs to the technical field of monocrystalline silicon, the crystal pulling method comprises an equal-diameter early-stage process, an equal-diameter middle-stage process and an equal-diameter later-stage process which are carried out in sequence, and the equal-diameter middle-stage process is divided into a first equal-diameter middle-stage process and a second equal-diameter middle-stage process; in the equal-diameter early-stage process and the first equal-diameter middle stage, crucible rotation, crystal rotation, furnace pressure and argon flow of crystal bars with different lengths are all unchanged, and the stability of the liquid level of a silicon solution in the drawing process of the crystal bars is guaranteed; in the second equal-diameter middle stage, the furnace pressure in the second equal-diameter middle stage is smaller than that in the first equal-diameter middle stage, and crucible rotation, crystal rotation and argon flow are not changed, so that the furnace pressure is gradually reduced in the whole equal-diameter growth process, and the crystal growth stability is ensured; in the equal-diameter later-stage process, the furnace pressure of the equal-diameter later-stage process is smaller than that of the second equal-diameter middle-stage process, the argon flow of the equal-diameter later-stage process is gradually increased, crucible rotation and crystal rotation are not changed, and the oxygen content of the tail of the crystal bar is greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of single crystal silicon, and in particular to a crystal pulling method for reducing the longitudinal oxygen content of a single crystal silicon rod. Background Art

[0002] There are many methods for preparing single crystal silicon, such as the Czochralski method, the zone melting method, the flame melting method, the hydrothermal method, etc. Among them, the Czochralski method is the most common. The Czochralski method is also called the CZ method, abbreviated as CZ method. The process can be divided into material chemical process, crystal seeding process, necking process, shoulder release process, shoulder rotation process, equal diameter early process, equal diameter mid-term process, equal diameter late process, and finishing process. This method has relatively low production cost and can be mass-produced. It is widely used in the single crystal preparation process.

[0003] Currently, in the process of pulling single crystal silicon by the direct pulling method, the set values ​​of the furnace pressure and the argon flow rate are constant throughout the pulling process, and the set values ​​of the furnace pressure and the argon flow rate are a certain value within a limited range, for example, the limited range of the furnace pressure is 1KPa-6KPa, and the limited range of the argon flow rate is 40-100slmp. However, since the silicon solution is in a high temperature and low pressure environment, and the power of the material processing step is relatively large, the temperature of the silicon solution will reach about 1430°C. At this time, microbubbles will be generated on the surface of the quartz crucible. The microbubbles contain oxygen impurities and continue to grow. Eventually, the microbubbles will rupture and release oxygen impurities, so that the oxygen impurities flow to the solid-liquid interface of the single crystal with the silicon liquid. At the same time, since the set value of the furnace pressure remains unchanged throughout the equal-diameter process, and the heating power of the single crystal furnace needs to gradually increase in the later stage of equal-diameter to accelerate the reaction rate of the quartz crucible and the molten silicon, this will cause the oxygen content at the tail of the single crystal silicon rod to increase, and the oxygen content at the tail will be higher than that at the head, and the longitudinal oxygen content of the entire crystal rod will be higher. Summary of the invention

[0004] In view of this, in order to address the above shortcomings, it is necessary to propose a crystal pulling method for reducing the longitudinal oxygen content of a single crystal silicon rod, so as to solve the technical problem of high longitudinal oxygen content of the crystal rod.

[0005] A crystal pulling method for reducing the longitudinal oxygen content of a single crystal silicon rod, comprising an equal diameter early stage process, an equal diameter middle stage process, and an equal diameter late stage process performed in sequence, wherein the equal diameter middle stage process is divided into a first equal diameter middle stage and a second equal diameter middle stage; In the above-mentioned pre-diameter equalization process and the first mid-diameter equalization process, the crucible rotation, crystal rotation, furnace pressure and argon gas flow rate of the crystal rods of different lengths remain unchanged; In the second equal-diameter mid-stage, the furnace pressure in the second equal-diameter mid-stage is less than the furnace pressure in the first equal-diameter mid-stage, and the crucible rotation, crystal rotation, and argon gas flow rate remain unchanged; In the equal-diameter late stage process, the furnace pressure of the equal-diameter late stage process is lower than the furnace pressure of the second equal-diameter mid stage process, the argon gas flow rate of the equal-diameter late stage process increases gradually, and the crucible rotation and the crystal rotation remain unchanged.

[0006] Preferably, the first mid-stage equal-diameter process is a period from the beginning of pulling the crystal rod of the mid-stage equal-diameter process to 30%-35% of the overall crystal rod length of the mid-stage equal-diameter process, and the second mid-stage equal-diameter process is a period from 30%-35% of the overall crystal rod length of the mid-stage equal-diameter process to 100% of the overall crystal rod length of the mid-stage equal-diameter process.

[0007] Preferably, the length of the crystal rod in the early equal-diameter process accounts for 20%-30% of the length of the equal-diameter grown crystal rod, the length of the entire crystal rod in the middle equal-diameter process accounts for 50%-60% of the length of the equal-diameter grown crystal rod, and the length of the crystal rod in the late equal-diameter process accounts for 10%-30% of the length of the equal-diameter grown crystal rod.

[0008] Preferably, in the preliminary equal-diameter process and the first intermediate equal-diameter process, the crucible rotation speed is 5-8 rpm, the crystal rotation speed is 6-12 rpm, the furnace pressure is 3.5-6 Torr, and the argon gas flow rate is 40-65 slmp.

[0009] Preferably, in the second equal-diameter medium stage, the crucible rotation is 5-8 rpm, the crystal rotation is 6-12 rpm, the furnace pressure is 2.5-3.5 Torr, and the argon gas flow rate is 40-65 slmp.

[0010] Preferably, in the later equal diameter process, the crucible rotation speed is 5-8 rpm, the crystal rotation speed is 6-12 rpm, the furnace pressure is 1.5-2.5 Torr, and the argon gas flow rate is 65-100 slmp.

[0011] Preferably, the equal-diameter early stage process, the equal-diameter mid-stage process and the equal-diameter late stage process which are carried out in sequence also include a material chemical process, a crystal seeding process, a necking process, a shoulder releasing process and a shoulder turning process which are carried out in sequence. In the material chemical process, the crystal seeding process, the necking process, the shoulder releasing process and the shoulder turning process, the crucible rotation is 5-8rpm, the crystal rotation is 6-12rpm, the furnace pressure is 2-6Torr, and the argon gas flow rate is 40-100slmp.

[0012] Preferably, in the material chemical step, crystal seeding step, necking step, shoulder release step, shoulder rotation step, and equal diameter preliminary step, the crucible rotation, crystal rotation, furnace pressure, and argon gas flow rate remain unchanged.

[0013] It can be seen from the above technical scheme that the crystal pulling method for reducing the longitudinal oxygen content of a single crystal silicon rod provided by the present invention comprises an equal-diameter pre-process, an equal-diameter mid-process, and an equal-diameter late-process performed in sequence, and the equal-diameter mid-process is divided into a first equal-diameter mid-process and a second equal-diameter mid-process; in the equal-diameter pre-process and the first equal-diameter mid-process, the crucible rotation, crystal rotation, furnace pressure, and argon flow rate of crystal rods of different lengths remain unchanged; in the second equal-diameter mid-process, the furnace pressure of the second equal-diameter mid-process is less than the furnace pressure of the first equal-diameter mid-process, and the crucible rotation, crystal rotation, and argon flow rate remain unchanged; in the equal-diameter late-process, the furnace pressure of the equal-diameter late-process is less than the furnace pressure of the second equal-diameter mid-process, the argon flow rate of the equal-diameter late-process gradually increases, and the crucible rotation and crystal rotation remain unchanged; The present application adopts a process of gradually reducing furnace pressure and gradually increasing argon flow rate in the equal-diameter early stage process, the equal-diameter mid-stage process, and the equal-diameter late stage process. Specifically, the equal-diameter mid-stage process is divided into a first equal-diameter mid-stage process and a second equal-diameter mid-stage process. First, in the equal-diameter early stage process and the first equal-diameter mid-stage process, stable crucible rotation, crystal rotation, furnace pressure and argon flow rate ensure the stability of the silicon solution liquid level during the crystal rod drawing process, so that the longitudinal oxygen content distribution of the crystal rod is more uniform. Subsequently, by reducing the furnace pressure in the second equal-diameter mid-stage process, on the one hand, the silicon monoxide in the silicon solution is fully volatilized, and most of the silicon monoxide gas is carried by the argon gas flow to avoid silicon monoxide from entering the silicon crystal from the solid-liquid interface, thereby achieving the purpose of reducing the longitudinal oxygen content of the crystal rod. On the other hand, a smooth transition is made to further reduce the furnace pressure in the equal-diameter late stage process, so that the furnace pressure tends to gradually decrease during the entire equal-diameter growth process, thereby ensuring the stability of crystal growth. Finally, in the equal-diameter late stage process, by further reducing the furnace pressure and gradually increasing the argon flow rate, the oxygen content at the tail of the crystal rod is greatly reduced, thereby improving the quality of the tail crystal rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The figure is a schematic diagram of the structure of pulling a complete crystal rod by the method of the present invention.

[0015] Figure 2 It is a scatter diagram of the longitudinal oxygen content detection results of the embodiment of the method of the present invention and the comparative example of the traditional method.

[0016] Figure 3 It is a box plot of the overall longitudinal oxygen content detection results of the experimental group of the method of the present invention and the control group of the traditional method. DETAILED DESCRIPTION

[0017] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0018] Please see Figure 1, a method for pulling a single crystal silicon rod to reduce the longitudinal oxygen content, comprising an equal diameter early stage process, an equal diameter middle stage process, and an equal diameter late stage process performed in sequence, wherein the equal diameter middle stage process is divided into a first equal diameter middle stage and a second equal diameter middle stage; In the above-mentioned pre-diameter equalization process and the first mid-diameter equalization process, the crucible rotation, crystal rotation, furnace pressure and argon gas flow rate of the crystal rods of different lengths remain unchanged; In the second equal-diameter mid-stage, the furnace pressure in the second equal-diameter mid-stage is less than the furnace pressure in the first equal-diameter mid-stage, and the crucible rotation, crystal rotation, and argon gas flow rate remain unchanged; In the equal-diameter late stage process, the furnace pressure of the equal-diameter late stage process is lower than the furnace pressure of the second equal-diameter mid stage process, the argon gas flow rate of the equal-diameter late stage process increases gradually, and the crucible rotation and the crystal rotation remain unchanged.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The present application adopts a process of gradually reducing furnace pressure and gradually increasing argon flow rate in the equal-diameter early stage process, the equal-diameter mid-stage process, and the equal-diameter late stage process. Specifically, the equal-diameter mid-stage process is divided into a first equal-diameter mid-stage process and a second equal-diameter mid-stage process. First, in the equal-diameter early stage process and the first equal-diameter mid-stage process, stable crucible rotation, crystal rotation, furnace pressure, and argon flow rate ensure the stability of the silicon solution level during the crystal rod drawing process, so that the longitudinal oxygen content distribution of the crystal rod is more uniform. Subsequently, by reducing the furnace pressure in the second equal-diameter mid-stage process, on the one hand, the silicon monoxide in the silicon solution is fully volatilized, wherein Most of the silicon monoxide gas is carried by the argon flow to prevent silicon monoxide from entering the silicon crystal from the solid-liquid interface, thereby achieving the purpose of reducing the longitudinal oxygen content of the crystal rod. On the other hand, it is used to further reduce the furnace pressure in the later equal-diameter process to make a smooth transition, so that the furnace pressure tends to gradually decrease during the entire equal-diameter growth process. The slow change of furnace pressure has little effect on crystallization, ensuring the stability of crystal growth. Finally, in the later equal-diameter process, by further reducing the furnace pressure and gradually increasing the argon flow rate, the oxygen content at the tail of the crystal rod is greatly reduced, thereby improving the quality of the tail crystal rod.

[0020] In one embodiment, the first mid-stage equal-diameter process is a period from the beginning of pulling the crystal rod of the mid-stage equal-diameter process to 30%-35% of the overall crystal rod length of the mid-stage equal-diameter process, and the second mid-stage equal-diameter process is a period from 30%-35% of the overall crystal rod length of the mid-stage equal-diameter process to 100% of the overall crystal rod length of the mid-stage equal-diameter process.

[0021] In one embodiment, the length of the crystal rod in the early equal-diameter process accounts for 20%-30% of the length of the equal-diameter grown crystal rod, the length of the entire crystal rod in the middle equal-diameter process accounts for 50%-60% of the length of the equal-diameter grown crystal rod, and the length of the crystal rod in the late equal-diameter process accounts for 10%-30% of the length of the equal-diameter grown crystal rod.

[0022] Specifically, in the process of pulling a complete crystal rod, the length of the equal-diameter grown crystal rod is L, the equal-diameter early stage process is the period from the start of pulling to the length of the equal-diameter grown crystal rod L×(20%-30%), the equal-diameter middle stage process is the period from the length of the equal-diameter grown crystal rod L×(20%-30%) to the length of the equal-diameter grown crystal rod L×(70%-90%), wherein the overall crystal rod length of the equal-diameter middle stage process is S=L×(50%-60%), and the equal-diameter late stage process is the period from the length of the equal-diameter grown crystal rod L×(70%-90%) to the length of the equal-diameter grown crystal rod L×100%; The length of the crystal rod in the first equal-diameter mid-stage is 30%-35% of the overall length of the crystal rod in the equal-diameter mid-stage process, and the length of the crystal rod in the second equal-diameter mid-stage is 65%-70% of the overall length of the crystal rod in the equal-diameter mid-stage process; The first mid-stage equal-diameter process is a period from the beginning of pulling the entire crystal rod of the mid-stage equal-diameter process to the length S×(30%-35%) of the crystal rod of the mid-stage equal-diameter process, and the second mid-stage equal-diameter process is a period greater than the length S×(30%-35%) of the entire crystal rod of the mid-stage equal-diameter process to the length S×100% of the entire crystal rod of the mid-stage equal-diameter process.

[0023] In one embodiment, in order to ensure the stability of the silicon solution level during the crystal rod pulling process and to make the longitudinal oxygen content distribution of the crystal rod more uniform, in the preliminary equal-diameter process and the first intermediate equal-diameter process, the crucible speed is 5-8rpm, the crystal speed is 6-12rpm, the furnace pressure is 3.5-6Torr, and the argon gas flow rate is 40-65slmp.

[0024] In one embodiment, on the one hand, in order to fully volatilize the silicon monoxide in the silicon solution, most of the silicon monoxide gas is carried by the argon gas flow to prevent silicon monoxide from entering the silicon crystal from the solid-liquid interface, thereby achieving the purpose of reducing the longitudinal oxygen content of the crystal rod; on the other hand, in order to further reduce the furnace pressure in the later equal-diameter process and make a smooth transition, so that the furnace pressure tends to gradually decrease during the entire equal-diameter growth process, the slow furnace pressure change has little effect on crystallization and ensures the stability of crystal growth. In the second middle equal-diameter process, the crucible speed is 5-8rpm, the crystal speed is 6-12rpm, the furnace pressure is 2.5-3.5Torr, and the argon flow rate is 40-65slmp.

[0025] In one embodiment, in order to greatly reduce the oxygen content at the tail of the crystal rod and improve the quality of the tail crystal rod, in the equal diameter later process, the crucible rotation is 5-8rpm, the crystal rotation is 6-12rpm, the furnace pressure is 1.5-2.5Torr, and the argon gas flow rate is 65-100slmp.

[0026] In one embodiment, the equal-diameter early stage process, the equal-diameter mid-stage process, and the equal-diameter late stage process, which are performed in sequence, also include a material chemical process, a crystal seeding process, a necking process, a shoulder releasing process, and a shoulder turning process. In the material chemical process, the crystal seeding process, the necking process, the shoulder releasing process, and the shoulder turning process, the crucible speed is 5-8rpm, the crystal speed is 6-12rpm, the furnace pressure is 2-6Torr, and the argon flow rate is 40-100slmp. Under the above-mentioned high temperature and low pressure environment, the volatilization rate of silicon monoxide in the silicon melt is adapted to the argon flow rate, and most of the silicon monoxide gas is carried away by the argon gas flow to prevent silicon monoxide from entering the silicon crystal from the solid-liquid interface, forming a good dynamic balance, thereby achieving the purpose of reducing the longitudinal oxygen content of the crystal rod.

[0027] In one embodiment, in the material chemical process, crystal induction process, necking process, shoulder release process, shoulder rotation process, and equal diameter preliminary process, the crucible rotation, crystal rotation, furnace pressure and argon gas flow rate remain unchanged to make the liquid level of the silicon melt more stable, reduce the liquid level fluctuation of the silicon melt, improve the crystallization rate, and make the longitudinal oxygen content distribution of the crystal rod more uniform.

[0028] In one embodiment, in the seeding process, necking process, shoulder release process, shoulder rotation process, equal diameter early process, equal diameter middle process, and equal diameter late process, the crystal rod pulling speed is constant at 1.3-1.9 mm / min.

[0029] In order to further understand the present invention, the following illustrates the ingot pulling process and the detection results of the longitudinal oxygen content of the ingot through the embodiments of the method of the present invention and the comparative examples of the conventional method.

[0030] The embodiment and the comparative example pulled a crystal rod with the same length of 3300 mm, and the process parameters of the embodiment and the comparative example in the material chemical step, the crystal seeding step, the necking step, the shoulder release step, and the shoulder rotation step were the same, the crucible rotation was 6 rpm, the crystal rotation was 9 rpm, the furnace pressure was 4 Torr, and the argon gas flow rate was 60 slmp. At the same time, in the crystal seeding step, the crystal rod pulling speed at the beginning of pulling the crystal rod was 1.6 mm / min and was constant. Except for the process parameter relationships specifically pointed out in the above application, all others were carried out in a manner familiar to those skilled in the art. Example

[0031] The pulling was carried out according to the process parameters in the above-mentioned material chemical step, crystal seeding step, necking step, shoulder release step and shoulder rotation step, and in the equal-diameter early step, the first equal-diameter middle step, the second equal-diameter middle step and the equal-diameter late step, the furnace pressure and the argon flow rate were set in stages as shown in Table 1, and two crystal rods were pulled, respectively, which were experimental group ① and experimental group ②.

[0032] Table 1: Data table of furnace pressure and argon flow rate segmented settings during equal diameter growth

[0033] Comparative Example: The pulling is carried out according to the process parameters in the above-mentioned material chemical step, crystal seeding step, necking step, shoulder release step and shoulder rotation step, while in the equal-diameter early step, the first equal-diameter middle step, the second equal-diameter middle step and the equal-diameter late step, the furnace pressure and the argon flow rate are kept constant as shown in Table 2, and two crystal rods are pulled respectively, which are control group ① and control group ②.

[0034] Table 2: Data table showing constant pressure and argon during the entire isodiameter growth process

[0035] The longitudinal oxygen content of the experimental group ① crystal rod, the experimental group ② crystal rod obtained by the method embodiment of the present invention and the control group ① crystal rod, the control group ② crystal rod obtained by the conventional method comparison were respectively tested. The test results are as follows: Figure 2 As shown by Figure 2 It can be observed that the growth trend of the longitudinal oxygen content of the experimental group ① crystal rod and the experimental group ② crystal rod is significantly slower than that of the control group ① crystal rod and the control group ② crystal rod, and the longitudinal oxygen content distribution is relatively uniform. The longitudinal oxygen content of the experimental group is obtained by testing the overall longitudinal oxygen content of the experimental group ① crystal rod and the experimental group ② crystal rod, and the longitudinal oxygen content of the control group is obtained by testing the overall longitudinal oxygen content of the control group ① crystal rod and the control group ② crystal rod. The test results are as follows: Figure 3 As shown, through Figure 3 It can be observed that the longitudinal oxygen content of the experimental group was 9.42% lower than that of the control group, which greatly reduced the breakage rate of the crystal rod due to excessive longitudinal oxygen content.

[0036] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for reducing the longitudinal oxygen content of a single crystal silicon rod, characterized in that: It includes an equal diameter early stage process, an equal diameter mid-stage process, and an equal diameter late stage process, which are performed in sequence. The equal diameter mid-stage process is divided into a first equal diameter mid-stage process and a second equal diameter mid-stage process; In the above-mentioned pre-diameter equalization process and the first mid-diameter equalization process, the crucible rotation, crystal rotation, furnace pressure and argon gas flow rate of the crystal rods of different lengths remain unchanged; In the second equal-diameter mid-stage, the furnace pressure in the second equal-diameter mid-stage is less than the furnace pressure in the first equal-diameter mid-stage, and the crucible rotation, crystal rotation, and argon gas flow rate remain unchanged; In the equal-diameter late stage process, the furnace pressure of the equal-diameter late stage process is lower than the furnace pressure of the second equal-diameter mid stage process, the argon gas flow rate of the equal-diameter late stage process increases gradually, and the crucible rotation and the crystal rotation remain unchanged.

2. The method for pulling a single crystal silicon rod to reduce the longitudinal oxygen content according to claim 1, characterized in that: The first mid-stage equal-diameter process is the period from the beginning of pulling the crystal rod of the mid-stage equal-diameter process to 30%-35% of the overall crystal rod length of the mid-stage equal-diameter process, and the second mid-stage equal-diameter process is the period from 30%-35% of the overall crystal rod length of the mid-stage equal-diameter process to 100% of the overall crystal rod length of the mid-stage equal-diameter process.

3. The method for pulling a single crystal silicon rod to reduce the longitudinal oxygen content according to claim 2, characterized in that: The length of the crystal rod in the early equal-diameter process accounts for 20%-30% of the length of the equal-diameter grown crystal rod, the length of the overall crystal rod in the middle equal-diameter process accounts for 50%-60% of the length of the equal-diameter grown crystal rod, and the length of the crystal rod in the late equal-diameter process accounts for 10%-30% of the length of the equal-diameter grown crystal rod.

4. The method for pulling a single crystal silicon rod to reduce the longitudinal oxygen content according to claim 1 or 2, characterized in that: In the preliminary equal-diameter process and the first intermediate equal-diameter process, the crucible rotation speed is 5-8 rpm, the crystal rotation speed is 6-12 rpm, the furnace pressure is 3.5-6 Torr, and the argon gas flow rate is 40-65 slmp.

5. The method for pulling a single crystal silicon rod to reduce the longitudinal oxygen content according to claim 1 or 2, characterized in that: In the second middle stage of equal diameter, the crucible is rotated at 5-8 rpm, the crystal is rotated at 6-12 rpm, the furnace pressure is 2.5-3.5 Torr, and the argon flow rate is 40-65 slmp.

6. The method for pulling a single crystal silicon rod to reduce the longitudinal oxygen content according to claim 1 or 2, characterized in that: In the later equal diameter process, the crucible rotation speed is 5-8 rpm, the crystal rotation speed is 6-12 rpm, the furnace pressure is 1.5-2.5 Torr, and the argon gas flow rate is 65-100 slmp.

7. The method for pulling a single crystal silicon rod to reduce the longitudinal oxygen content according to claim 1, characterized in that: The equal-diameter early stage process, the equal-diameter mid-stage process and the equal-diameter late stage process which are carried out in sequence also include a material chemical process, a crystal seeding process, a necking process, a shoulder releasing process and a shoulder turning process which are carried out in sequence. In the material chemical process, the crystal seeding process, the necking process, the shoulder releasing process and the shoulder turning process, the crucible rotation is 5-8rpm, the crystal rotation is 6-12rpm, the furnace pressure is 2-6Torr and the argon gas flow rate is 40-100slmp.

8. The method for pulling a single crystal silicon rod to reduce the longitudinal oxygen content according to claim 7, characterized in that: In the material chemical process, crystal seeding process, necking process, shoulder release process, shoulder rotation process and equal diameter preliminary process, the crucible rotation, crystal rotation, furnace pressure and argon gas flow rate remain unchanged.

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