Method for improving 111 single crystal forming rate and product thereof
By reducing the cooling rate and pulling speed during the shoulder release stage, controlling the temperature gradient and applying a magnetic field to suppress melt convection, the problem of frequent dislocations during the growth of <111> single crystal silicon is solved, and high crystallization rate and high-quality single crystal silicon production is achieved.
Patent Information
- Application Number
- CN202510478894.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-16
- Publication Date
- 2025-07-11
AI Technical Summary
During the process of drawing the single crystal silicon in <111>, the problem of crystal growth interface morphology and stress control causes frequent dislocations, resulting in reduced crystallization rate and high energy consumption, which is difficult to effectively solve in the existing technology.
In the shoulder release stage, reduce the cooling rate and pull speed, control the axial and radial temperature gradients, and apply a lateral magnetic field to suppress melt convection, ensure the stability of the solid-liquid interface, and avoid dislocation caused by thermal stress. The specific parameters are pull speeds of 0.3 mm/min to 0.8 mm/min, an axial temperature gradient from 10 K/cm to 30 K/cm and a radial temperature gradient from 1 K/cm to 3 K/cm, and a radial temperature gradient from 1 K/cm to 3 K/cm, and a suitable magnetic field and gas flow rate.
The crystal formation rate of <111> single crystal silicon has been significantly improved, from the traditional 33% to 50% to 100%, reducing the dislocation density, reducing the melting rate, and improving the consistency and quality of the crystal structure.
Smart Images
Figure CN120291196A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of semiconductor material processing, and particularly relates to a method for improving the crystal growth rate of <111> single crystals and its products. Background Art
[0002] In the semiconductor and photovoltaic industries, single-crystalline silicon, as a key basic material, its crystal quality directly affects the performance and reliability of devices. <111>-oriented single-crystalline silicon has irreplaceable advantages in specific application scenarios due to its special atomic arrangement structure. However, in the process of growing <111>-oriented single-crystalline silicon by the Czochralski method, the problems of crystal growth interface morphology and stress control are particularly prominent, resulting in significantly higher process difficulty than that of conventional <100>-oriented products.
[0003] During the pulling process of <111> single-crystal products, due to the particularity of the <111> product crystal orientation, when the solid-liquid interface is concave during crystal growth, since the peripheral region solidifies prior to the central region, the mechanical stress generated by lattice contraction will accumulate towards the central region. If this stress exceeds the elastic limit of the silicon crystal, it will induce rapid dislocation proliferation and even cause crystal slip or cracking. Therefore, to avoid dislocation occurrence during the pulling of similar products, crystal growth requires a relatively stable solid-liquid interface. In the process of single-crystalline silicon growth, the shoulder-forming stage refers to the process in which the crystal diameter gradually expands from the seed crystal part to form shoulders. If the temperature is stable during the shoulder-forming stage, it will balance the heat transfer at the solid-liquid interface, thereby inhibiting the occurrence of dislocations.
[0004] However, during the shoulder-forming stage, traditional processes tend to adopt a flat-shoulder design to simplify the control logic, but this shape is prone to component supercooling phenomena. Specifically, the flat-shoulder structure leads to uneven temperature gradient distribution near the solid-liquid interface, and solutes (such as dopants or oxygen) accumulate at the interface, forming local supercooled regions, which in turn induce dislocation nucleation and propagation along the slip plane. Once the dislocations extend to the crystal body, it will force the production to be interrupted and remelted, not only reducing the crystal growth rate but also increasing energy consumption and time costs. Summary of the Invention
[0005] In view of this, the present invention provides a method for improving the crystal growth rate of <111> single crystals and its products to solve the technical problem in the prior art that when pulling <111> single-crystal products, dislocations are easily induced and remelting and redrawing are required, resulting in a reduction in the crystal growth rate of <111> single crystals.
[0006] To achieve the above object, the present application adopts the following solutions: A method for improving the crystallization rate of 111 single crystals. During the shoulder formation stage, the cooling rate and the pulling rate are reduced to avoid the concentration of thermal stress inside the crystal, reduce the dislocation density, lower the axial temperature gradient and the radial temperature gradient near the solid-liquid interface, and avoid the generation of dislocations caused by uneven thermal stress. Among them, the pulling rate is 0.3 mm / min to 0.8 mm / min, the axial temperature gradient is 10 K / cm to 30 K / cm, and the radial temperature gradient is 1 K / cm to 3 K / cm.
[0007] Preferably, the reduction of the axial temperature gradient and the radial temperature gradient near the solid-liquid interface includes: increasing the transverse magnetic field with a magnetic strength of 2000 Gs to 3000 Gs to suppress melt convection, reduce interface disturbance, and avoid the generation of dislocations caused by uneven thermal stress.
[0008] Preferably, the cooling rate is 14°C / h ± 2°C.
[0009] Preferably, the rotation speed during the shoulder formation stage is 12 rpm to 16 rpm.
[0010] Preferably, the rotation speed of the crucible during the shoulder formation stage is 2 rpm to 5 rpm.
[0011] Preferably, the flow rate of the inert gas introduced during the shoulder formation stage is 100 slm to 150 slm.
[0012] Preferably, the inert gas is argon.
[0013] A single crystal product prepared by the above method for improving the crystallization rate of 111 single crystals.
[0014] In the above method for improving the crystallization rate of 111 single crystals, during the shoulder-opening stage of crystal growth (the process of gradually expanding the crystal diameter), while reducing the cooling rate, the crystal pulling speed is reduced from the conventional 1.0 mm / min to 1.5 mm / min to 0.3 mm / min to 0.8 mm / min. Reducing the pulling speed while cooling can extend the residence time of the crystal in the high-temperature zone, promote stress relaxation, avoid thermal stress concentration inside the crystal, and reduce the dislocation density; too fast pulling speed will cause the solid-liquid interface (growth front) to be concave or steep, exacerbating local stress concentration, while reducing the pulling speed can keep the solid-liquid interface flat or slightly convex, avoiding the generation of dislocation arrays caused by interface instability. At the same time, a lower pulling speed allows more heat to be conducted out through the crystal rather than relying on rapid cooling. And the axial temperature gradient near the crystal growth interface is controlled at 10 K / cm to 30 K / cm. A moderate gradient ensures the orderly transfer of heat along the axis, preventing interface instability (such as "stepped" growth), and the upper limit of the gradient (30 K / cm) can avoid cracks caused by a sudden drop in temperature near the interface; the radial temperature gradient is limited to 1 K / cm to 3 K / cm. A low gradient can eliminate the temperature difference on the melt surface and prevent stress concentration caused by inconsistent growth rates at the crystal edge and center; through this step, lattice distortion caused by uneven temperature distribution near the solid-liquid interface can be avoided, thereby reducing the dislocation density, and uniform axial and radial temperature gradients promote the orderly growth of single crystals and improve the crystal structure consistency. Therefore, by reducing the cooling rate, pulling speed, and temperature gradient during the shoulder-opening stage, the dislocations in the single-crystal product can be significantly reduced, and the remelting rate can be decreased, thereby increasing the crystallization rate of 111 single crystals from 33% to 50% in the traditional process to 50% to 100%. Description of the Drawings
[0015] Figure 1 It is a broken-line graph of the pulling speed in the embodiment.
[0016] Figure 2 It is a schematic diagram of the shoulder-opening shape in the embodiment.
[0017] Figure 3 It is a real picture of the shoulder-opening shape in the embodiment.
[0018] Figure 4 It is a broken-line graph of the pulling speed in the comparative example.
[0019] Figure 5 It is a real picture of the shoulder-opening shape in the comparative example. Detailed Description of the Invention
[0020] To facilitate the understanding of this application, the following will provide a more comprehensive description of this application in conjunction with the accompanying drawings. And preferred embodiments of this application are given. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of this application more thoroughly and comprehensively understood.
[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.
[0022] In a specific embodiment, a method for improving the crystallization rate of 111 single crystals reduces the cooling rate and the pulling rate during the shoulder growth stage to avoid the concentration of thermal stress inside the crystal, reduce the dislocation density, lower the axial temperature gradient and the radial temperature gradient near the solid-liquid interface, and avoid the generation of dislocations due to uneven thermal stress. Among them, the pulling rate is 0.3 mm / min to 0.8 mm / min, the axial temperature gradient is 10 K / cm to 30 K / cm, and the radial temperature gradient is 1 K / cm to 3 K / cm.
[0023] Compared with the traditional method for preparing single-crystalline silicon, the method provided by the present invention only differs in the shoulder formation stage. Therefore, the steps in other stages will not be elaborated herein. In this embodiment, during the shoulder formation stage of crystal growth (the process of gradually expanding the crystal diameter), by adjusting the heating power of the furnace body or adjusting the thermal field distribution, while reducing the cooling rate, the pulling rate is also reduced, that is, the crystal pulling rate is reduced from the conventional 1.0 mm / min to 1.5 mm / min to 0.3 mm / min to 0.8 mm / min. Reducing the pulling rate can extend the residence time of the crystal in the high-temperature zone, promote stress relaxation, avoid the concentration of internal thermal stress in the crystal, and reduce the dislocation density; too fast pulling rate will cause the solid-liquid interface (growth front) to be concave or steep, exacerbating local stress concentration, while reducing the pulling rate can keep the solid-liquid interface flat or slightly convex, avoiding the generation of dislocation arrays caused by interface instability. At the same time, a lower pulling rate allows more heat to be conducted out through the crystal, rather than relying on rapid cooling. The axial temperature gradient near the crystal growth interface is controlled at 10 K / cm to 30 K / cm. A moderate gradient ensures the orderly transfer of heat along the axis, preventing interface instability (such as "stepped" growth). The upper limit of the gradient (30 K / cm) can avoid cracks caused by a sudden drop in temperature near the interface; the radial temperature gradient is limited to 1 K / cm to 3 K / cm. The low gradient can eliminate the temperature difference on the melt surface, preventing stress concentration caused by inconsistent growth rates at the crystal edge and center; through this step, lattice distortion caused by uneven temperature distribution near the solid-liquid interface can be avoided, thereby reducing the dislocation density, and the uniform axial and radial temperature gradients promote the orderly growth of single crystals and improve the crystal structure consistency. Therefore, by reducing the cooling rate, pulling rate, and temperature gradient in the shoulder formation stage, the dislocations in the single-crystal product can be significantly reduced, and the crystallization rate of 111 single crystals can be increased from 33% to 50% in the traditional process to 50% to 100%.
[0024] Specifically, the reduction of the axial temperature gradient and the radial temperature gradient near the solid-liquid interface includes: increasing a transverse magnetic field with a magnetic strength of 2000 Gs to 3000 Gs to inhibit melt convection, reduce interface disturbance, and avoid dislocations caused by uneven thermal stress.
[0025] For example: Around the melt region of the crystal growth furnace, a transverse electromagnet (with the magnetic field direction perpendicular to the crystal pulling axis) can be installed. Adjust the current of the electromagnet to keep the magnetic field strength stable at 2000 Gs to 3000 Gs (Gauss). A water cooling system can be used to maintain the temperature of the electromagnet ≤ 50°C to avoid magnetic field attenuation caused by high temperature. Turn on the magnetic field at the initial stage of the shoulder forming stage (when the crystal diameter reaches 20% to 30% of the target size). Use 2000 Gs to 2500 Gs in the initial stage (crystal diameter < 50 mm) to avoid excessive inhibition of melt flow resulting in compositional segregation; increase it to 2500 Gs to 3000 Gs in the middle and later stages (diameter > 50 mm) to enhance the convective inhibition effect. When the magnetic field is turned on, the pulling speed can be synchronously reduced to 0.3 mm / min to 0.5 mm / min to extend the stable time of the melt under the action of the magnetic field. The thermal field can be appropriately adjusted to keep the axial temperature gradient at 10 K / cm to 20 K / cm and the radial gradient at 1 K / cm to 3 K / cm. The reduction of the axial temperature gradient and the radial temperature gradient weakens the melt convection, making the solute distribution at the solid-liquid interface more uniform, avoiding dendrite growth and dislocation sources caused by constitutional supercooling; and the uniform temperature gradient can reduce the thermal stress inside the crystal and inhibit dislocation slip. While improving the crystal quality, the crystallization rate is also increased.
[0026] Preferably, the cooling rate is 14°C / h ± 2°C. This cooling rate can allow heat to be fully released through conduction and radiation, avoiding the "thermal lock effect" (local heat accumulation) caused by rapid cooling; during the solidification of silicon single crystals, slow cooling allows silicon atoms to fully migrate to the lattice equilibrium positions, reducing point defects such as vacancies and interstitial atoms and inhibiting dislocation nucleation; in this method, the low pulling speed (0.3 mm / min to 0.8 mm / min) and slow cooling act synergistically, which can extend the residence time of the crystal at the solid-liquid interface, enabling the lattice strain energy to be gradually released through atomic rearrangement, avoiding stress concentration, and thus reducing dislocations; and slow cooling can promote the diffusion of impurity atoms to the grain boundaries or the surface, reducing the possibility of impurity atoms pinning dislocations in the lattice. While improving the crystal quality, the crystallization rate is also increased.
[0027] Specifically, the rotation speed of the crystal during the shoulder forming stage is 12 rpm to 16 rpm, the rotation speed of the crucible during the shoulder forming stage is 2 rpm to 5 rpm, the flow rate of the inert gas introduced during the shoulder forming stage is 100 slm to 150 slm, and the inert gas is argon. Through the regulation of the crystal rotation / crucible rotation speed ratio, the melt turbulence can be inhibited, and the uniformity of the solute distribution at the solid-liquid interface can be improved; high-flow argon can effectively carry volatile substances (such as SiO and CO), reduce the adsorption of impurities at the interface, and reduce the dislocation density.
[0028] The single crystal product prepared according to the above method for improving the crystallization rate of 111 single crystals has fewer dislocations and higher quality.
[0029] The following specific experimental examples are used to further illustrate the technical solutions and technical effects of the present invention. It should be noted that the following experimental examples are only for further explaining the present invention and do not limit the technical solutions of the present invention. Example
[0030] In the shoulder release stage, the pulling speed is controlled to 0.75 mm / min. Figure 1 As shown in the figure, the cooling rate is 14℃ / h, the transverse magnetic field is increased from 2000Gs to 3000Gs, the axial temperature gradient of the solid-liquid interface is 10 K / cm to 30 K / cm, and the radial temperature gradient is 1 K / cm to 3 K / cm. Under these conditions, the shape of the shoulder is as follows: Figure 2 As shown, the actual picture is as Figure 3 As shown, the average number of Dips and the average crystallization rate of single crystal silicon pulled for one week using the method provided in this embodiment are statistically shown in Table 1.
[0031] Comparative Example During the shoulder release phase, use the traditional pull speed, as follows Figure 4 As shown in Figure 1, the cooling rate is 20℃ / h, no magnetic field is applied, the axial temperature gradient of the solid-liquid interface is 20 K / cm to 50 K / cm, and the radial temperature gradient is 3 K / cm to 5 K / cm. Under these conditions, the actual shape of the shoulder is as follows: Figure 5 As shown, the average number of Dips and the average crystallization rate of single crystal silicon pulled for one week using the method provided in the comparative example are statistically shown in Table 1.
[0032] Table 1 Statistical table of examples and comparative examples
[0033] The data in Table 1 above show that the average number of Dips in the above embodiment is significantly reduced compared with the average number of Dips in the comparative example, indicating that Figure 5 The shoulder shape in the Figure 3 The shoulder shape in the embodiment can reduce the occurrence of dislocations. Therefore, the method of pulling single crystal silicon in the embodiment can significantly reduce dislocations and reduce the melting rate, so that the average crystallization rate of the embodiment is increased by 34% compared with the average crystallization rate of the comparative example.
[0034] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should be included in the protection scope of the present invention.
Claims
1. A method for improving the crystallization rate of 111 single crystals, characterized in that, During the shoulder growth stage, reduce the cooling rate and the drawing speed to avoid the concentration of thermal stress inside the crystal, reduce the dislocation density, lower the axial temperature gradient and the radial temperature gradient near the solid-liquid interface, and avoid the generation of dislocations caused by uneven thermal stress. Among them, the drawing speed is 0.3 mm / min to 0.8 mm / min, the axial temperature gradient is 10 K / cm to 30 K / cm, and the radial temperature gradient is 1 K / cm to 3 K / cm.
2. The method for improving the crystal formation rate of 111 single crystal according to claim 1, wherein The reduction of the axial temperature gradient and the radial temperature gradient near the solid-liquid interface includes: increasing the transverse magnetic field with a magnetic intensity of 2000 Gs to 3000 Gs to suppress the melt convection, reduce the interface disturbance, and avoid the generation of dislocations caused by uneven thermal stress.
3. The method for improving the crystallization rate of 111 single crystal according to claim 1, characterized in that, The cooling rate is 14 °C / h ± 2 °C.
4. The method for improving the crystallization rate of 111 single crystal according to claim 1, characterized in that, During the shoulder growth stage, the crystal rotation speed is 12 rpm to 16 rpm.
5. The method for improving the crystallization rate of 111 single crystal according to claim 1, characterized in that, During the shoulder growth stage, the crucible rotation speed is 2 rpm to 5 rpm.
6. The method for improving the crystallization rate of 111 single crystals according to claim 1, wherein During the shoulder growth stage, the flow rate of the inert gas introduced is 100 slm to 150 slm.
7. The method for improving the crystallization rate of 111 single crystal according to claim 1, characterized in that, The inert gas is argon.
8. A single crystal product prepared by the method for improving the crystal formation rate of 111 single crystal according to any one of claims 1 to 8.