Preparation method of ultra-low resistance single crystal silicon based on mcz method

Abstract

The application provides a preparation method of ultralow-resistance monocrystalline silicon based on an MCZ method and relates to the technical field of monocrystalline silicon growth. During the whole constant-diameter process, the center position of the magnetic field is adjusted according to the center position of the silicon liquid height, so that the center position of the magnetic field is flush with the center position of the silicon liquid height, the convection of the silicon liquid is suppressed through the magnetic field, the volatilization of the dopant is reduced, the doping efficiency of the dopant is improved, the center position of the magnetic field is kept flush with the center position of the silicon liquid height, the stability of the convection of the silicon liquid to the magnetic field is improved, the convection of the silicon liquid is in a stable state, and then the stability of the crystal pulling process is improved. Meanwhile, the furnace pressure, the liquid port distance, the argon flow, the crucible rotation speed and the crystallization rotation speed in the constant-diameter process are adjusted, so that the bulk microdefects of the monocrystalline silicon are reduced, the crystal survival rate is improved, and the preparation of the defect-free ultralow-resistance monocrystalline silicon is realized.

Description

Technical Field

[0001] This invention relates to the field of single-crystal silicon growth technology, and specifically to a method for preparing ultra-low resistivity single-crystal silicon based on the MCZ method. Background Technology

[0002] With the miniaturization and increased portability of electronic products, stringent requirements are placed on the operating voltage and energy consumption of the corresponding devices. This necessitates silicon substrate materials with extremely low resistivity. Red phosphorus has high solid solubility, which is beneficial for achieving low substrate resistivity. Therefore, currently, low-resistivity silicon substrate materials are prepared by doping with red phosphorus. However, red phosphorus is highly volatile, making it difficult to incorporate into silicon melt at high concentrations, thus reducing doping efficiency. When the solute concentration in the melt is very high, compositional supercooling can easily occur at the solid-liquid interface, thereby disrupting the growth of dislocation-free single crystals. Furthermore, the micro-defects in the prepared silicon single crystals are difficult to detect and control, making it difficult to guarantee crystal quality.

[0003] In the prior art, such as Chinese invention application number 202111594443.4, a method for preparing heavily phosphorus-doped ultra-low resistivity silicon single crystals is disclosed. By controlling the crystal pulling speed and furnace pressure in the equal diameter process, the phenomenon of dislocations caused by excessive impurity concentration due to segregation in the later stage of equal diameter is overcome, thereby obtaining a dislocation-free complete single crystal. However, this patent can only overcome the phenomenon of dislocations caused by excessive impurity concentration due to segregation in the later stage of equal diameter, and cannot solve the problems of low red phosphorus doping efficiency and bulk micro-defects generated in silicon single crystals. On the other hand, it frequently changes the furnace pressure at different stages of equal diameter, and frequent changes in furnace pressure will affect the stability of the crystal pulling process, thereby affecting the crystal survival rate. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing ultra-low resistivity single crystal silicon based on the MCZ method.

[0005] A method for preparing ultra-low resistivity single crystal silicon based on the MCZ method involves adjusting the center position of the magnetic field according to the center position of the silicon liquid height during the entire constant diameter process, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height; and adjusting the furnace pressure, liquid outlet distance, argon flow rate, crucible rotation speed, and crystallization rotation speed during the constant diameter process.

[0006] Preferably, during the constant diameter process, the furnace pressure of the single crystal furnace is adjusted to 9 kPa to 31 kPa, the liquid outlet distance is adjusted to 19 mm to 31 mm, the argon flow rate is adjusted to 59 slpm to 101 slpm, the crucible rotation speed is adjusted to 0.9 rpm to 8.1 rpm, and the crystallization rotation speed is adjusted to 9.9 rpm to 16.1 rpm.

[0007] Preferably, adjusting the center position of the magnetic field according to the center position of the silicon liquid height, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height, includes: obtaining the pulling speed during the equal diameter process; determining the silicon liquid height according to the pulling speed to obtain the center position of the silicon liquid height; and raising the magnetic field according to the center position of the silicon liquid height, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height.

[0008] Preferably, the strength of the magnetic field is reduced throughout the constant-diameter process.

[0009] Preferably, the strength of the magnetic field is reduced from 3000 Gs to 2000 Gs.

[0010] Preferably, during the material preparation process, the heater is adjusted to a first height so that the center position of the heater is aligned with the center position of the molten silicon.

[0011] Preferably, after the melting process is completed, the heater is adjusted to a second height so that the center of the heater is flush with the surface of the molten silicon.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] This invention relates to a method for preparing ultra-low resistivity monocrystalline silicon based on the MCZ method. Throughout the constant diameter process, the center position of the magnetic field is adjusted according to the center position of the silicon melt height, ensuring that the center position of the magnetic field is aligned with the center position of the silicon melt height. This suppresses silicon melt convection through the magnetic field, thereby reducing dopant volatilization and improving doping efficiency. Maintaining the alignment of the magnetic field center position with the center position of the silicon melt height enhances the stability of the magnetic field's suppression of silicon melt convection, ensuring stable silicon melt convection and thus improving the stability of the crystal pulling process. Simultaneously, adjusting the furnace pressure, liquid outlet distance, argon flow rate, crucible rotation speed, and crystallization rotation speed during the constant diameter process reduces bulk micro-defects in the monocrystalline silicon, increases crystal survival rate, and achieves the preparation of defect-free ultra-low resistivity monocrystalline silicon. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the device used in this invention.

[0015] Figure 2 The graphs show the resistivity of the single-crystal silicon rods prepared in Examples 1, 2, 1, 2, and 3 as a function of rod length.

[0016] In the diagram: heater 10, magnetic field 20. Detailed Implementation

[0017] The technical solutions and effects of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0018] A method for preparing ultra-low resistivity single crystal silicon based on the MCZ method involves adjusting the center position of the magnetic field according to the center position of the silicon liquid height during the entire constant diameter process, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height. The furnace pressure, liquid outlet distance, argon flow rate, crucible rotation speed, and crystallization rotation speed are adjusted during the constant diameter process.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This invention relates to a method for preparing ultra-low resistivity monocrystalline silicon based on the MCZ method. Throughout the constant diameter process, the center position of the magnetic field is adjusted according to the center position of the silicon melt height, ensuring that the center position of the magnetic field is aligned with the center position of the silicon melt height. This suppresses silicon melt convection through the magnetic field, thereby reducing dopant volatilization and improving doping efficiency. Maintaining the alignment of the magnetic field center position with the center position of the silicon melt height enhances the stability of the magnetic field's suppression of silicon melt convection, ensuring stable silicon melt convection and thus improving the stability of the crystal pulling process. Simultaneously, adjusting the furnace pressure, liquid outlet distance, argon flow rate, crucible rotation speed, and crystallization rotation speed during the constant diameter process reduces bulk micro-defects in the monocrystalline silicon, increases crystal survival rate, and achieves the preparation of defect-free ultra-low resistivity monocrystalline silicon.

[0021] Furthermore, during the constant diameter process, the furnace pressure of the single crystal furnace is adjusted to 9 kPa to 31 kPa, the liquid outlet distance is adjusted to 19 mm to 31 mm, the argon flow rate is adjusted to 59 slpm to 101 slpm, the crucible rotation speed is adjusted to 0.9 rpm to 8.1 rpm, and the crystallization rotation speed is adjusted to 9.9 rpm to 16.1 rpm.

[0022] Specifically, furnace pressure has two effects on the single-crystal constant-diameter growth process. Firstly, it affects the volatilization of dopants, oxygen, and impurities. Too low a furnace pressure allows more dopants to volatilize, resulting in insufficient resistivity reduction. Too high a furnace pressure hinders the volatilization of oxygen and impurities, making single-crystal pulling impossible. Secondly, it affects the crystallization of the single crystal, as well as the magnitude of resistivity and the uniformity of oxygen content distribution. Furnace pressure affects the surface tension of the silicon melt, which in turn influences the crystallization front. Too low a surface tension results in weak suppression of forced convection, leading to larger liquid surface fluctuations that affect the crystallization temperature gradient, thus impacting lateral resistivity and oxygen content distribution. Conversely, too high a surface tension prevents uniform distribution of dopants and oxygen, resulting in uneven resistivity and oxygen distribution, affecting product usability. Therefore, this invention adjusts the furnace pressure to 9 kPa–31 kPa to reduce resistivity and improve the uniformity of oxygen content.

[0023] The liquid outlet distance, i.e., the distance between the heat shield and the liquid surface, significantly affects the resistivity and oxygen content uniformity after crystallization. This is because the heat shield emits heat within the furnace cavity, influencing the furnace temperature convection and affecting the lateral temperature gradient. Furthermore, the liquid outlet distance affects the argon gas flow rate, thus impacting impurity removal and leading to micro-defects in the crystal formation. Therefore, this invention adjusts the liquid outlet distance to 19mm–31mm to reduce resistivity, improve oxygen content uniformity, and minimize micro-defects in crystal formation.

[0024] Argon flow rate affects dopant volatilization. Reducing the argon flow rate decreases dopant volatilization, thus lowering resistivity. However, excessively low argon flow rate results in even less dopant volatilization, allowing more dopant to enter the silicon melt, which can disrupt single-crystal growth and lead to polycrystalline formation. Therefore, this invention adjusts the argon flow rate to 59 slpm to 101 slpm to reduce resistivity while preventing polycrystalline formation.

[0025] In this process, crucible rotation and crystallization rotation interact with natural convection, forming true convection for crystal growth. Appropriate true convection allows dopant atoms and oxygen atoms to dissolve more uniformly in the molten silicon, resulting in more uniform growth at the crystallization front. Simultaneously, appropriate true convection effectively controls the lateral and longitudinal temperature gradients during crystallization, controlling the unevenness of the crystallization interface and thus reducing bulk micro-defects in the single crystal. Therefore, this invention controls the lateral and longitudinal temperature gradients by adjusting the crucible rotation speed to 0.9 rpm–8.1 rpm and the crystallization rotation speed to 9.9 rpm–16.1 rpm, thereby reducing bulk micro-defects in the single crystal and improving the crystallization survival rate.

[0026] Furthermore, adjusting the center position of the magnetic field according to the center position of the silicon liquid height, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height, includes: obtaining the pulling speed during the constant diameter process; determining the silicon liquid height based on the pulling speed to obtain the center position of the silicon liquid height; and raising the magnetic field according to the center position of the silicon liquid height, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height.

[0027] Specifically, this invention controls the center position of the molten silicon height to remain aligned with the center position of the magnetic field, suppressing molten silicon convection through the magnetic field and thus reducing dopant volatilization. However, as the length of the crystal rod increases, the amount of molten silicon gradually decreases, resulting in a shorter molten silicon height. Furthermore, to maintain a constant molten silicon surface position, the quartz crucible is typically raised, causing the center position of the molten silicon height to rise. At this point, the center position of the magnetic field and the center position of the molten silicon height are no longer aligned, but offset. This renders the magnetic field's suppression of molten silicon convection ineffective, leading to turbulent convection and uneven dopant volatilization. Therefore, to maintain a consistent suppression effect of the magnetic field on molten silicon convection during the crystal pulling process, this invention can obtain the pulling speed during the constant diameter process. Based on the pulling speed, it can be determined how much the molten silicon height has decreased with changes in crystal rod length or over time, allowing for the calculation of the current molten silicon height. This height can then be used to determine the center position of the molten silicon height. As described above, as the length of the crystal rod increases, the center position of the silicon liquid height also rises. At this time, the center position of the magnetic field is lower than the center position of the silicon liquid height. Therefore, by increasing the magnetic field, the center position of the magnetic field can be moved upward to reach a position level with the center position of the silicon liquid height, thereby ensuring the consistency and stability of the magnetic field's effect on suppressing silicon liquid convection as the length of the crystal rod increases.

[0028] Furthermore, as the length of the crystal rod increases, the amount of molten silicon gradually decreases, reducing the radiation from the molten silicon to the melt surface. This, in turn, lowers the temperature at the crystallization front, leading to component supercooling caused by segregation and affecting crystal growth. Therefore, this invention can also reduce the strength of the magnetic field throughout the constant diameter process. By reducing the magnetic field strength, melt convection is improved, thereby increasing the diffusion of dopants in the silicon melt, avoiding component supercooling caused by segregation, and thus stabilizing the crystal growth interface, which is beneficial for single crystal growth. Furthermore, the magnetic field strength is reduced from 3000 Gs to 2000 Gs.

[0029] Furthermore, during the material preparation process, the heater is adjusted to reach the first height so that its center is aligned with the center of the molten silicon. Specifically, the heater's position is moved using a drive motor. For example... Figure 1 As shown, during the melting process, the heater is moved to the first height by the drive motor, so that the center position of the heater is aligned with the center position of the silicon liquid height, thereby ensuring that the silicon block is heated evenly and improving the melting efficiency.

[0030] Furthermore, after the chemical reaction is complete, the heater is adjusted to a second height, so that the center of the heater is level with the surface of the molten silicon. Specifically, after the chemical reaction is complete, the heater is moved to the second height by a drive motor, so that the center of the heater is level with the surface of the molten silicon. The center of the heater is where the heater temperature is highest. Aligning the center of the heater with the surface of the molten silicon maintains the stability of the solid-liquid interface. Simultaneously, the molten silicon below the solid-liquid interface is located below the center of the heater, where the temperature is lower. This reduces the thermal radiation of the molten silicon, weakens natural convection, and consequently reduces the volatilization of dopants in the molten silicon, thus lowering the resistivity of the single crystal.

[0031] To facilitate understanding, the present invention is further illustrated through the following embodiments and comparative examples. The following comparative analysis focuses solely on the improvements involved in the technical solution of the present invention, omitting descriptions of other operations and related parameter controls during the single-crystal pulling process. The omitted content indicates that the operations and related parameter controls performed in the embodiments and comparative examples are identical.

[0032] 1. Examples and comparative examples of magnetic field adjustment are shown below:

[0033] Comparative Example 1 (Condition 1): During the entire constant diameter process, the magnetic field strength was adjusted to 3000 Gs, and the center of the magnetic field was adjusted to be flush with the surface of the molten silicon.

[0034] Comparative Example 2 (Condition 2): During the entire constant diameter process, the magnetic field strength was adjusted to 3000 Gs, and the center position of the magnetic field was adjusted to be level with the center position of the silicon liquid height.

[0035] Comparative Example 3 (Condition 3): During the entire constant diameter process, the magnetic field strength was adjusted from 3000Gs to 2000Gs, and the position of the center of the magnetic field was adjusted to be flush with the surface of the molten silicon.

[0036] Example 1 (Invention-1): During the entire constant diameter process, the magnetic field strength was adjusted from 3000Gs to 2000Gs, and the center position of the magnetic field was adjusted to be level with the center position of the silicon liquid height.

[0037] Example 2 (Invention-2): A repeatability experiment was conducted on Example 1. The resistivity of the single crystals pulled in Examples 1, 2, and Comparative Examples 1 to 3 is as follows: Figure 2 As stated above.

[0038] The specific settings of the schemes in Embodiment 1, Embodiment 2, and Comparative Examples 1 to 3 are shown in Table 1:

[0039] Table 1:

[0040] condition magnetic field strength Location Condition 1 3000Gs flush with the surface of the molten silicon Condition 2 3000Gs Aligned with the center of the molten silicon (magnetic field rises). Condition 3 3000→2000Gs flush with the surface of the molten silicon This invention-1 3000→2000Gs Aligned with the center of the molten silicon (magnetic field rises). This invention-2 3000→2000Gs Aligned with the center of the molten silicon (magnetic field rises).

[0041] Please refer to Figure 2 In the figure, the horizontal axis represents the length of the crystal rod in mm, and the vertical axis represents the resistivity in Ω*cm. A comparison between Comparative Example 1 and Comparative Example 2 shows that, under the same magnetic field strength, aligning the center of the magnetic field with the center of the silicon molten metal height can reduce the resistivity of the crystal rod.

[0042] By comparing Comparative Example 1 and Comparative Example 3, it can be seen that, under the same magnetic field location, reducing the magnetic field strength from 3000 Gs to 2000 Gs does not reduce the resistivity.

[0043] A comparison of Comparative Example 2 and Example 1 shows that when the center position of the magnetic field is aligned with the center position of the molten silicon, and the magnetic field strength is reduced from 3000 Gs to 2000 Gs, the resistivity of the crystal rod decreases significantly, especially at the tail of the crystal rod, where the resistivity reaches less than 0.0012. This demonstrates that changing only the position or strength of the magnetic field alone does not significantly reduce the resistivity of the crystal rod, and may even increase it. However, by simultaneously changing both the position and strength of the magnetic field, a synergistic effect occurs, resulting in a significant decrease in the resistivity of the crystal rod, particularly at the tail.

[0044] 2. Examples and comparative examples of parameter adjustment for the constant diameter process are shown below:

[0045] Example 3: Throughout the constant diameter process, the center of the magnetic field was aligned with the center of the molten silicon height. During the constant diameter process, the furnace pressure of the single crystal furnace was adjusted to 10 kPa, the liquid outlet distance to 30 mm, the argon flow rate to 100 slpm, the crucible rotation speed to 8 rpm, and the crystallization rotation speed to 16 rpm. The resistivity of the crystal rods obtained under this method was measured, and the number of crystal pulling operations under this method was counted. The measurement and statistical results are shown in Table 2.

[0046] Example 4: Throughout the constant diameter process, the center of the magnetic field was aligned with the center of the molten silicon height. During the constant diameter process, the furnace pressure of the single crystal furnace was adjusted to 10 kPa, the liquid outlet distance to 20 mm, the argon flow rate to 60 slpm, the crucible rotation speed to 4 rpm, and the crystallization rotation speed to 16 rpm. The resistivity of the crystal rods obtained under this method was measured, and the number of crystal pulling operations under this method was counted. The measurement and statistical results are shown in Table 2.

[0047] Example 5: Throughout the constant diameter process, the center of the magnetic field was aligned with the center of the silicon melt height. During the constant diameter process, the furnace pressure of the single crystal furnace was adjusted to 30 kPa, the liquid outlet distance to 30 mm, the argon flow rate to 100 slpm, the crucible rotation speed to 1 rpm, and the crystallization rotation speed to 14 rpm. The resistivity of the crystal rods obtained under this method was measured, and the number of crystal pulling operations under this method was counted. The measurement and statistical results are shown in Table 2.

[0048] Example 6: Throughout the constant diameter process, the center of the magnetic field was aligned with the center of the molten silicon height. During the constant diameter process, the furnace pressure of the single crystal furnace was adjusted to 30 kPa, the liquid outlet distance to 20 mm, the argon flow rate to 60 slpm, the crucible rotation speed to 4 rpm, and the crystallization rotation speed to 14 rpm. The resistivity of the crystal rods obtained under this method was measured, and the number of crystal pulling operations under this method was counted. The measurement and statistical results are shown in Table 2.

[0049] Table 2: Statistical results of Examples 3 to 6.

[0050]

[0051] Please refer to Table 2. The various parameters in Example 3 are mainly set based on the current crystal pulling technology. When the crucible rotation speed and crystallization rotation speed are set to be high, and at the same time, with low pressure and high argon flow rate, the resistivity is 0.00126Ω*cm, which does not reach the target of less than 0.001Ω*cm.

[0052] Next, please refer to Example 4. Based on Example 3, Example 4 reduces the argon flow rate, the liquid outlet distance, and the crucible rotation speed. It can be seen that the resistivity is improved compared to Example 3. This is because reducing the argon flow rate reduces dopant volatilization, thus effectively improving resistivity. However, excessive reduction in dopant volatilization would allow more dopant to enter the silicon melt, disrupting single-crystal growth and resulting in polycrystalline formation. Therefore, Example 4 simultaneously reduces the liquid outlet distance and crucible rotation speed, resulting in a smaller lateral temperature gradient at the crystallization front, which is more conducive to single-crystal growth, thereby reducing the number of crystal initiation attempts and improving the single-crystal survival rate.

[0053] Next, please refer to Example 5. To further reduce resistivity, Example 5 increased the furnace pressure. While increasing the furnace pressure significantly reduces dopant volatilization and effectively lowers resistivity, it also reduces impurity volatilization, leading to polycrystalline formation. Therefore, Example 5 improved polycrystalline formation by increasing the argon flow rate. Simultaneously, by reducing the crucible rotation speed and crystallization rotation speed, the liquid outlet distance was increased to control the lateral and longitudinal temperature gradients, thereby improving the crystallization survival rate. However, the resistivity and number of crystal pulling attempts in Example 5 were not improved compared to Example 4, which may be related to the crucible rotation speed or liquid outlet distance settings.

[0054] Therefore, to further reduce resistivity, Example Six, based on Example Five, reduced the argon flow rate. Simultaneously, to improve the single crystal survival rate, the crucible rotation speed was increased, and the liquid outlet distance was reduced. The results show that, through the parameter settings of Example Six, the resistivity of the crystal rod was reduced to below 0.001 Ω*cm, and the number of crystal pulling attempts was correspondingly reduced, resulting in an improved crystal survival rate.

[0055] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for preparing ultra-low resistivity single-crystal silicon based on the MCZ method, characterized in that, Throughout the equal diameter process, the position of the magnetic field center is adjusted according to the center position of the silicon liquid height, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height; the furnace pressure, liquid outlet distance, argon flow rate, crucible rotation speed, and crystallization rotation speed are adjusted during the equal diameter process. The step of adjusting the position of the magnetic field center according to the center position of the silicon liquid height, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height, includes: Obtain the tension rate during the constant diameter process; The height of the molten silicon is determined based on the pulling speed to obtain the center position of the molten silicon height; The magnetic field is raised according to the center position of the silicon liquid height, so that the center position of the magnetic field is aligned with the center position of the silicon liquid height. During the entire constant-diameter process, the strength of the magnetic field decreases from 3000 Gs to 2000 Gs.

2. The method for preparing ultra-low resistivity single-crystal silicon based on the MCZ method according to claim 1, characterized in that, During the constant diameter process, the furnace pressure of the single crystal furnace is adjusted to 9 kPa~31 kPa, the liquid outlet distance is adjusted to 19 mm~31 mm, the argon flow rate is adjusted to 59 slpm~101 slpm, the crucible rotation speed is adjusted to 0.9 rpm~8.1 rpm, and the crystallization rotation speed is adjusted to 9.9 rpm~16.1 rpm.

3. The method for preparing ultra-low resistivity single-crystal silicon based on the MCZ method according to claim 1, characterized in that, During the material preparation process, the heater is adjusted to reach the first height so that the center position of the heater is aligned with the center position of the silicon liquid height.

4. The method for preparing ultra-low resistivity single-crystal silicon based on the MCZ method according to claim 3, characterized in that, After the material is melted, the heater is adjusted to a second height so that the center of the heater is level with the surface of the molten silicon.

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