Crystal pulling method for improving heavily arsenic-doped D-shaped striations

Abstract

The present invention provides a crystal pulling method for improving heavily doped arsenic D-shaped stripes, which relates to the technical field of single crystal silicon crystal pulling. By controlling the crystal growth rate, the temperature gradient of the solid-liquid interface and the cooling rate, the heat conduction is made to be uniformly transmitted along the radial direction, and the solid-liquid interface is flat during the crystal growth process, thereby eliminating the D-shaped stripes and improving the yield of the device end.

Description

Technical Field

[0001] The present invention relates to the technical field of single crystal silicon crystal pulling, and specifically relates to a crystal pulling method for improving the heavily doped arsenic D-shaped stripe. Background Art

[0002] Vortex defects include D-shaped stripes, concentric circles, impurity stripes, impurity pipe defects, etc.; according to research, when the size of impurities or defects in the active area of a single crystal silicon wafer approaches 1 / 3 of the process width, it will cause a reduction in device performance and even complete failure. During the thermal process of device production, regions with vortex defects often generate thermal oxidation defects distributed along the vortices, causing harm to device production. During the device manufacturing process, vortex defects may also be converted into dislocations, stacking faults, and form local precipitates, thereby causing microplasma breakdown or increasing the reverse current of the PN junction. Microdefects not only deteriorate the performance of high-power high-voltage devices, but also cause dark current spikes in CCDs, and also seriously affect the yield of integrated circuits.

[0003] In a heavily doped arsenic crystal bar, the solubility of arsenic is 1.7×10 21 atom / cm 3 and the diffusion coefficient of arsenic is 2.5×10 - 13 cm 2 / s. The segregation coefficient of arsenic element is less than 1. Due to the limitations of crystal growth conditions, microdefects of macroscopically dislocation-free single crystal silicon will be generated during the crystal growth process at high doping concentrations. These microdefects are closely related to the growth conditions. Some microdefects will be distributed in a shape similar to the letter "D" on the cross-section of the crystal perpendicular to the growth axis, that is, D-shaped stripe defects. Such D-shaped stripes will cause the failure of the power device end and reduce the yield of the device end. Summary of the Invention

[0004] In view of this, the present invention provides a crystal pulling method for improving the heavily doped arsenic D-shaped stripe to improve the yield of the device end.

[0005] The technical solution adopted by the present invention to solve its technical problems is:

[0006] A crystal pulling method for improving the heavily doped arsenic D-shaped stripe specifically includes the following steps:

[0007] S1. In the thermal field of the single crystal furnace, reduce the upper heat insulation material to a predetermined thickness for crystal pulling to reduce the lateral temperature gradient of the solid-liquid interface and eliminate the D-shaped stripes in the early stage of crystal pulling;

[0008] S2. During the equal diameter process, use the first predetermined pulling speed to pull the crystal bar and control the rotation speed of the crystal bar to rotate stably within the predetermined crystal rotation. Among them, the liquid port distance is kept at a predetermined value to control the crystal growth speed, make the solid-liquid interface flat during the crystal growth process, and eliminate the D-shaped stripes;

[0009] S3. During the cooling process, the ingot is pulled into the cooling chamber for cooling at a second predetermined drawing speed to accelerate the cooling speed, so that the D-shaped stripes are further aggregated and eliminated.

[0010] Preferably, in step S1, the predetermined thickness is 1 / 3 of the original thickness of the upper thermal insulation material.

[0011] Preferably, in step S2, the first predetermined drawing speed is 1.2 - 1.3 mm / min.

[0012] Preferably, during the equal-diameter process, when pulling from 0 mm of equal diameter to the predetermined equal-diameter length, the first predetermined drawing speed is 1.3 mm / min, and the upper and lower limits of the first predetermined drawing speed range from ±0.2 mm / min to ±1.0 mm / min.

[0013] Preferably, from the predetermined equal-diameter length to the end of equal diameter, the first predetermined drawing speed is 1.2 mm / min, and the upper and lower limits of the first predetermined drawing speed range from ±0.1 mm / min.

[0014] Preferably, in step S2, the predetermined crystal rotation speed is 16 - 18 rpm.

[0015] Preferably, in step S2, the predetermined value of the liquid orifice distance is 14 - 16 mm.

[0016] Preferably, in step S3, the second predetermined drawing speed is 9 - 11 mm / min.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] A crystal pulling method for improving the D-shaped stripes of heavily doped arsenic provided by the present invention eliminates the D-shaped stripes and improves the yield rate of the device end by controlling the crystal growth rate, the temperature gradient of the solid-liquid interface, and the cooling speed, so that the heat conduction is uniformly transmitted along the radial direction and the solid-liquid interface is flat during the crystal growth process. Description of the Drawings

[0019] Figure 1 It is a partial sectional view of the thermal field.

[0020] Figure 2 It is a detection diagram of the embodiment.

[0021] Figure 3 It is a detection diagram of the comparative example.

[0022] In the figure: upper thermal insulation material 10, thermal shield 20, furnace wall 30, liquid orifice distance 40. Detailed Embodiments

[0023] The technical solutions and technical effects of the embodiments of the present invention will be further elaborated in detail below in conjunction with the accompanying drawings of the present invention.

[0024] Please refer to Figure 1 , a crystal pulling method for improving the D-shaped stripes of heavily doped arsenic, specifically including the following steps:

[0025] S1. In the thermal field of the single crystal furnace, reduce the upper heat insulation material 10 to a predetermined thickness for crystal pulling to reduce the transverse temperature gradient of the solid-liquid interface and eliminate the D-shaped stripes in the early stage of crystal pulling;

[0026] S2. During the equal diameter process, use the first predetermined pulling speed to pull the crystal rod and control the rotation speed of the crystal rod to rotate stably within the predetermined crystal rotation. Among them, the liquid port distance is kept at a predetermined value to control the growth rate of the crystal, make the solid-liquid interface flat during the crystal growth process, and eliminate the D-shaped stripes;

[0027] S3. During the cooling process, use the second predetermined pulling speed to pull the crystal rod into the cooling chamber for cooling to accelerate the cooling speed and further aggregate and eliminate the D-shaped stripes.

[0028] A crystal pulling method for improving the D-shaped stripes of heavily doped arsenic provided by the present invention makes the heat conduction transmit uniformly along the radial direction by controlling the crystal growth rate, the temperature gradient of the solid-liquid interface and the cooling speed, and the solid-liquid interface is flat during the crystal growth process, thereby eliminating the D-shaped stripes and improving the yield rate of the device end.

[0029] Specifically, by reducing the thickness of the upper heat-insulating material 10, the lateral temperature gradient in the crystal near the solid-liquid interface is reduced, the in-situ heat treatment effect is enhanced, and point defects such as interstitial atoms and vacancies in the crystal have more opportunities to diffuse outward, recombine and be eliminated. The axial temperature gradient at the crystal interface should be appropriately large to form the necessary undercooling so that the single crystal has sufficient growth momentum, and at the same time, the predetermined pulling speed of the present invention is matched to make the solid-liquid interface flat. When natural convection is dominant in the thermal field, the shape of the solid-liquid interface becomes convex to the melt, but when the forced convection caused by crystal rotation is dominant, the interface shape becomes convex to the crystal, indicating that in the straight pulling process, the convex interface can be turned over by changing the crystal rotation. Therefore, the present invention makes the convex interface flatter by adjusting the crystal rotation. In the growth process of single crystal silicon, the liquid mouth distance (i.e., the distance from the crystal growth liquid surface to the lower mouth of the guide tube-Gap value) is also a very important parameter. The liquid mouth distance will affect the longitudinal growth rate of the crystal, the appearance shape of the crystal, the crystal quality, etc. In general, the smaller the liquid mouth distance, the faster the speed of the liquid phase rises and falls, resulting in an accelerated pulling speed. Therefore, the present invention adjusts the liquid inlet distance to coordinate the adjustment of the pulling speed, so that the pulling speed can reach the predetermined pulling speed, thereby controlling the growth rate of the crystal and making the solid-liquid interface flat during the crystal growth process. Finally, after the crystal rod is finished, the pulling speed is increased during the cooling process to accelerate the cooling speed to overcool the crystal rod components, thereby making it difficult for vortices to appear and impurities to be gathered and eliminated.

[0030] Further, in step S1, the predetermined thickness is 1 / 3 of the original thickness of the upper heat-insulating material. In some embodiments, the predetermined thickness is 15 mm-20 mm. The thickness of the upper heat-insulating material is thinned to 1 / 3 of the original thickness on the original thermal field, and the thinned thermal field is assembled before crystal pulling for crystal pulling.

[0031] Further, in step S2, the first predetermined pulling speed is 1.2-1.3 mm / min.

[0032] Furthermore, in the process of equalizing the diameter, when pulling from the equalizing diameter of 0 mm to the equalizing diameter of the predetermined length, the first predetermined pulling speed is 1.3 mm / min, and the upper and lower limits of the first predetermined pulling speed are in the range of ±0.2 mm / min to ±1.0 mm / min. By setting the upper and lower limits of the first predetermined pulling speed, the pulling speed fluctuation can be better controlled and the pulling speed can be stabilized, and the stable pulling speed can better control the shape of the crystal interface and reduce the generation of D-shaped stripes.

[0033] Furthermore, from the predetermined length of equal diameter to the end of equal diameter, the first predetermined pulling speed is 1.2 mm / min, and the upper and lower limits of the first predetermined pulling speed are within the range of ±0.1 mm / min.

[0034] Further, in step S2, the predetermined crystal rotation speed is 16-18 rpm.

[0035] Further, in step S2, the predetermined value of the liquid orifice distance is 14 - 16 mm. Since the smaller the liquid orifice distance, the faster the liquid phase rises and falls, resulting in an increase in the pulling speed. However, if the equal-diameter liquid orifice distance is too small, the liquid phase in the crystal growth region cannot flow in a timely manner, leading to deterioration of the crystal growth environment and even defects such as "cavities". Therefore, the predetermined value of the liquid orifice distance in the present invention is set to 14 - 16 mm.

[0036] Further, in step S3, the second predetermined pulling speed is 9 - 11 mm / min. Example

[0037] When pulling a 5-inch single crystal, the upper heat insulation material 10 is a hollow cylinder, and the upper heat insulation material 10 is located above the heat shield 20, and the bottom of the upper heat insulation material 10 is connected to the furnace wall 30. The thickness of the upper heat insulation material is 15 mm. The set value of the first predetermined pulling speed and the upper and lower limits of the pulling speed during the equal-diameter process are shown in Table 1, the predetermined crystal rotation is shown in Table 2, the liquid orifice distance 40 is 15 mm, and the second predetermined pulling speed during the cooling process is 10 mm / min. According to the above, the crystal bar is pulled by the Czochralski method to obtain a 5-inch single crystal bar, where SL is the predetermined pulling speed, SL (upper limit) is the upper limit of the predetermined pulling speed, SL (lower limit) is the lower limit of the predetermined pulling speed, and SR is the crystal bar rotation speed.

[0038] Table 1

[0039]

[0040] Table 2

[0041]

[0042] Comparative Example

[0043] When pulling a 5-inch single crystal, the upper heat insulation material 10 is a hollow cylinder, and the upper heat insulation material 10 is located above the heat shield 20, and the bottom of the upper heat insulation material 10 is connected to the furnace wall 30. The thickness of the upper heat insulation material is 45 mm. The pulling speed during the equal-diameter process is shown in Table 3, the crystal rotation is shown in Table 4, the liquid orifice distance 40 is 30 mm, and the pulling speed during the cooling process is 5 mm / min. According to the above, the crystal bar is pulled by the Czochralski method to obtain a 5-inch single crystal bar, and other conditions are the same as those in the example.

[0044] Table 3

[0045]

[0046] Table 4

[0047]

[0048] The 5-inch ingots obtained from the examples and comparative examples were cut into single-crystalline silicon wafers, heat-treated at 1100 °C for 2 h, etched with sirtl solution, and visually inspected under a halogen lamp to obtain Figure 2 with Figure 3 the detection results of Figure 2 and Figure 3 Comparing, it can be seen macroscopically that the D-shaped stripe distribution in the center of the silicon wafers prepared in the comparative examples is obvious, while there are no D-shaped stripes in the center of the silicon wafers prepared in the examples of this solution, proving that the D-shaped stripes are eliminated and the yield of the device end is improved.

[0049] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A method for improving the D-shaped stripes of heavily arsenic-doped crystals, characterized in that: The specific steps include: S1. In the single crystal furnace thermal field, lower the upper heat-insulating material to a predetermined thickness for crystal pulling to reduce the lateral temperature gradient of the solid-liquid interface and eliminate the D-shaped stripes in the early stage of crystal pulling; S2. In the process of equal diameter, the crystal rod is pulled using a first predetermined pulling speed, and the rotation speed of the crystal rod is controlled to be stable within a predetermined crystal rotation range, wherein the liquid mouth distance is maintained at a predetermined value to control the growth rate of the crystal, so that the solid-liquid interface is flat during the crystal growth process, and the D-shaped stripes are eliminated, wherein the first predetermined pulling speed is 1.2-1.3 mm / min; S3. During the cooling process, the crystal rod is pulled into a cooling chamber for cooling using a second predetermined pulling speed to accelerate the cooling speed so that the D-shaped stripes are further gathered and eliminated.

2. The crystal pulling method for improving heavily arsenic-doped D-shaped stripes according to claim 1, characterized in that: In step S1, the predetermined thickness is 1 / 3 of the original thickness of the upper thermal insulation material.

3. The crystal pulling method for improving heavily arsenic-doped D-shaped stripes according to claim 1, characterized in that: In the process of equalizing the diameter, when pulling from the equalizing diameter of 0 mm to the equalizing diameter of the predetermined length, the first predetermined pulling speed is 1.3 mm / min, and the upper and lower limits of the first predetermined pulling speed are in the range of ±0.2 mm / min to ±1.0 mm / min.

4. The crystal pulling method for improving heavily arsenic-doped D-shaped stripes according to claim 3, characterized in that: From the predetermined length of equal diameter to the end of equal diameter, the first predetermined pulling speed is 1.2 mm / min, and the upper and lower limits of the first predetermined pulling speed are within the range of ±0.1 mm / min.

5. The crystal pulling method for improving heavily arsenic-doped D-shaped stripes according to claim 1, characterized in that: In step S2, the predetermined crystal rotation speed is 16-18 rpm.

6. The crystal pulling method for improving heavily arsenic-doped D-shaped stripes according to claim 1, characterized in that: In step S2, the predetermined value of the liquid port distance is 14-16 mm.

7. The crystal pulling method for improving heavily arsenic-doped D-shaped stripes according to claim 1, characterized in that: In step S3, the second predetermined pulling speed is 9-11 mm / min.

Images