A shoulder-forming process for heavily arsenic-doped silicon single crystals

Abstract

This invention discloses a shoulder-forming process for heavily arsenic-doped silicon single crystals. The parameters of this shoulder-forming process are set as follows: the shoulder-forming process is divided into an initial shoulder-forming stage, a middle shoulder-forming stage, and a later shoulder-forming stage based on the shoulder length. The initial shoulder-forming stage is the range of shoulder length 1-40 mm; the middle shoulder-forming stage is the range of shoulder length 40-220 mm; and the later shoulder-forming stage is the range of shoulder length greater than 220 mm. The cooling rate is defined as the shoulder temperature difference divided by the shoulder length difference; the cooling speed is defined as the shoulder temperature difference divided by the original temperature. In the initial shoulder-forming stage, the temperature decreases by 1-3 SP values ​​per 20 mm, with a cooling rate of 0.05-0.15, showing a decreasing cooling rate. In the middle shoulder-forming stage, the temperature decreases by 1-12 SP values ​​per 20 mm, with a cooling rate of 0.05-0.6, showing a trend of increasing, decreasing, and increasing cooling rates. In the later shoulder-forming stage, the temperature decreases by 3-15 SP values ​​per 20 mm, with a cooling rate of 0.15-0.75, showing a relatively small cooling rate. This shoulder-laying technique can greatly improve the survival rate of shoulder-laying.

Description

Technical Field

[0001] This invention relates to a shoulder-forming process for heavily arsenic-doped silicon single crystals, belonging to the field of Czochralski silicon single crystal growth technology. Background Technology

[0002] In recent years, with strong investment from the government and industry, my country's integrated circuit manufacturing industry has developed rapidly, with its output value exceeding one trillion yuan for the first time in 2021, reaching 1.0458 trillion yuan. Driven by strong demand in the semiconductor market, improving the crystal pulling efficiency of monocrystalline silicon is urgently needed, hence the emergence of water-cooled heatsinks. Using a water-cooled heatsink in the thermal field can effectively increase the temperature gradient of the thermal field, accelerating the cooling rate of the monocrystalline ingot and thus increasing the pulling speed. Because the internal temperature gradient of the thermal field changes, it is urgent to optimize and adjust the shoulder-forming process. This paper explores and optimizes the shoulder-forming process under water-cooled heatsink conditions to improve the success rate of shoulder forming.

[0003] The shoulder formation process for heavily arsenic-doped silicon single crystals is achieved through the combined effects of temperature (SP), pulling speed, crucible rise, crucible rotation, crystal rotation, argon flow rate, and pressure. However, among all parameters, the main factors affecting the shoulder shape are temperature and pulling speed. To achieve a perfect shoulder shape, the temperature and pulling speed must be properly matched to ensure a moderate temperature during shoulder formation, thereby producing a suitable shoulder shape. Summary of the Invention

[0004] The purpose of this invention is to provide a shoulder-forming process for heavily arsenic-doped silicon single crystals, wherein the thermal field used for crystal pulling is equipped with a water-cooled thermal screen, and this shoulder-forming process can greatly improve the shoulder survival rate.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A shoulder-forming process for heavily arsenic-doped silicon single crystals uses a thermal field equipped with a water-cooled thermal shield. The parameters of this shoulder-forming process are set as follows: the shoulder-forming process is divided into three stages according to the shoulder length: initial shoulder-forming, middle shoulder-forming, and late shoulder-forming. The initial shoulder-forming stage is the range of shoulder length from 1 to 40 mm; the middle shoulder-forming stage is the range of shoulder length from 40 to 220 mm; and the late shoulder-forming stage is the range of shoulder length greater than 220 mm.

[0007] The cooling rate is defined as the shoulder temperature difference divided by the shoulder length difference; the cooling speed is defined as the shoulder temperature difference divided by the original temperature.

[0008] In the initial stage of shoulder expansion, the temperature drops by 1-3 SP values ​​per 20mm, with a cooling rate of 0.05-0.15 (SP value / mm), and the cooling rate decreases.

[0009] During the middle stage of shoulder expansion, the temperature drops by 1-12 SP values ​​per 20 mm, with a cooling rate of 0.05-0.6 (SP value / mm). The cooling rate shows a trend of increasing, decreasing, and increasing again.

[0010] During the later stages of shoulder development, the temperature drops by 3-15 SP values ​​per 20mm, with a cooling rate of 0.15-0.75 (SP values / mm), which is relatively low.

[0011] In this invention, the shoulder length is 260mm-300mm.

[0012] Because the crystal pulling process mainly involves necking and dislocation alignment, which involves high temperatures, it is necessary to reduce the temperature and pulling speed in the early stage of shoulder formation, and the cooling rate is relatively slow. In the middle stage of shoulder formation, the cooling rate gradually increases. In the later stage of shoulder formation, it is necessary to balance the cooling caused by the water-cooled heat shield, so the cooling rate decreases.

[0013] During the middle stage of shoulder expansion, the cooling rate increases incrementally in increments of 20 mm, with an increment of less than 0.18.

[0014] During the initial and later stages of shoulder expansion, the cooling rate is set at 20mm increments, with a constant cooling rate between each increment.

[0015] During the initial and middle stages of shoulder formation, the pulling speed remains constant. In the later stages of shoulder formation, the pulling speed is fine-tuned according to the shoulder shape to balance the temperature drop caused by poor water cooling or inadequate temperature finding, thereby producing a suitable conical shoulder shape. This fine-tuning of the pulling speed depends on the actual growth of the single crystal, specifically whether the shoulder shape in the later stages of shoulder formation is a thick ridge or a wide facet, and the pulling speed is increased by 2-6 mm / hr accordingly.

[0016] In the early and middle stages of shoulder formation, the single crystal cone tip is controlled to grow at an angle of ≤45°; in the later stage of shoulder formation, the single crystal cone tip is controlled to grow at an angle of ≥45°.

[0017] The beneficial effects of this invention are as follows:

[0018] According to the shoulder-growing process of heavily arsenic-doped silicon single crystals provided by the present invention, in the shoulder-growing SOP parameters, the cooling rate is set in the early and middle stages, and an optimized temperature SP value is given so that the single crystal cone tip grows in a shape with an angle of ≤45° and the growth rate is relatively slow. It should not be too fast, as premature edge fullness and opening of the surface will cause the single crystal to be stuck. In the later stage of shoulder-growing, a suitable cooling rate and pulling speed are given so that the single crystal cone grows in a shape of ≥45°. This can greatly shorten the shoulder-growing time, and at the same time, it can leave room for remediation if the temperature is not found properly by artificial crystal pulling, thereby improving the shoulder survival rate. Attached Figure Description

[0019] Figure 1 A real-life image showing the ideal shape for finding the right shoulder support.

[0020] Figure 2 A real-world image showing the shape of the shoulder after overheating. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0022] In the following examples and comparative examples, the single crystal growth experiment used a 110B Czochralski silicon single crystal furnace manufactured by Zhejiang Jingsheng Electromechanical Co., Ltd. This furnace is equipped with a 24-inch hot zone, a large-diameter water-cooled heat shield, and a maximum feed rate of 140 kg. The silicon single crystals grown in the experiment were N-type with a crystal orientation of... <100> The dopant is As, the target resistivity is less than 4 mΩ·cm, the target diameter is 8 inches, and the shoulder length is 260 mm. The shoulder-forming process is divided into three stages based on the shoulder length: initial shoulder-forming (1-40 mm), middle shoulder-forming (40-220 mm), and late shoulder-forming (220-260 mm).

[0023] The cooling rate is defined as the shoulder temperature difference divided by the shoulder length difference; the cooling speed is defined as the shoulder temperature difference divided by the original temperature. Table 1 presents the same process parameters for the shoulder formation process in the examples and comparative examples, while Table 2 shows the different process parameters for the shoulder formation process in the examples and comparative examples, respectively. Here, length refers to the shoulder length; crucible lift refers to the crucible lifting speed; crucible rotation refers to the crucible rotation speed; crystal rotation refers to the single crystal rotation speed; flow rate refers to the argon flow rate; and pressure refers to the gas pressure inside the single crystal furnace.

[0024] Table 1

[0025]

[0026] Table 2

[0027]

[0028] In this embodiment, after the die pulling process is complete and the shoulder formation begins, the shoulder shape is achieved by controlling the cooling of the thermal field SP value. Figure 1 and Figure 2 There are two shapes. In the early stages of shoulder formation, shoulder growth is relatively slow and should not be too rapid, maintaining a growth angle of <45°. In the middle stages, shoulder growth accelerates slightly, but still needs to maintain a growth angle of <45°, with a maximum growth angle of 45°. This part should not allow for excessively rapid shoulder formation, as this can lead to premature facet development and, consequently, edge jamming in single-crystal shoulder formation. The later stages of shoulder formation are the most crucial. If the temperature is suitable during the crystallization stage, an ideal shoulder shape is achieved, and the shoulder will exhibit a [specific shape]. Figure 1The shape shown has the disadvantage of slow shoulder formation, but a high success rate. Secondly, it's not an ideal condition; if the temperature is too high during the crystallization stage, the shoulder shape will become... Figure 2 As shown, the severe conical shape in the early and middle stages of shoulder formation leads to a gradual and cumulative delay in shoulder cooling, resulting in excessive cooling in the later stages. This causes the shoulder to grow at an angle greater than 45°, requiring intervention to increase the pulling speed and prevent further expansion, thus ensuring the single crystal smoothly enters the constant diameter stage. Simultaneously, excessive cooling during single crystal shoulder formation shortens the time to reach the desired diameter, and also increases the risk of shoulder jamming. In contrast, maintaining the shoulder shape... Figure 1 The shape shown is relatively safe, but this also requires the operator to have a good enough skill in finding the right temperature.

[0029] In contrast, the cooling rate decreases regularly throughout the shoulder-growing process, gradually increasing until it becomes constant. The cooling rate is higher in the early part of the middle stage of shoulder growth and gradually decreases in the later part. The seemingly regular SP value cooling actually causes the shoulder to expand too early, and the shoulder shape to grow into a shape with an angle greater than 45° too early, increasing the chance of the edge getting stuck.

[0030] Extending the parameters from the example to three furnaces equipped with water-cooled heat shields, and summarizing the number of shoulder removal attempts over three months, it was found that the shoulder removal success rate increased from 40% (based on the parameters of the comparative example) to 80%. Specific comparative data are shown in Table 3.

[0031] Table 3

[0032]

Claims

1. A shoulder-forming process for heavily arsenic-doped silicon single crystals, wherein the thermal field used for crystal pulling is a thermal field equipped with a water-cooled thermal shield, characterized in that, The parameters for this shoulder-expanding process are set as follows: the shoulder-expanding process is divided into three stages according to the shoulder-expanding length: the initial stage, the middle stage, and the final stage. The initial stage is the range of shoulder-expanding length from 1 to 40 mm; the middle stage is the range of shoulder-expanding length from 40 to 220 mm; and the final stage is the range of shoulder-expanding length from 220 mm to more. The cooling rate is defined as the shoulder temperature difference divided by the shoulder length difference; the cooling speed is defined as the shoulder temperature difference divided by the original temperature. In the initial stage of shoulder expansion, the temperature drops by 1-3 SP values ​​for every 20mm, with a cooling rate of 0.05-0.15, and the cooling rate decreases. During the middle stage of shoulder expansion, the temperature drops by 1-12 SP values ​​per 20mm, with a cooling rate of 0.05-0.

6. The cooling rate shows a trend of increasing, decreasing, and increasing again. During the later stages of shoulder expansion, the temperature drops by 3-15 SP values ​​per 20mm, with a cooling rate of 0.15-0.75, which is relatively low. In the early and middle stages of shoulder formation, the single crystal cone tip is controlled to grow at an angle of ≤45°; in the later stage of shoulder formation, the single crystal cone is controlled to grow at an angle of ≥45°.

2. The shoulder-forming process for heavily arsenic-doped silicon single crystals according to claim 1, characterized in that, The shoulder length is 260mm-300mm.

3. The shoulder-forming process for heavily arsenic-doped silicon single crystals according to claim 1, characterized in that, During the middle stage of shoulder expansion, the cooling rate increases incrementally in increments of 20 mm, with an increment of less than 0.

18.

4. The shoulder-forming process for heavily arsenic-doped silicon single crystals according to claim 1, characterized in that, During the initial and later stages of shoulder expansion, the cooling rate is set at 20mm increments, with a constant cooling rate between each increment.

5. The shoulder-forming process for heavily arsenic-doped silicon single crystals according to claim 1, characterized in that, During the initial and middle stages of shoulder development, the pulling speed remains constant. In the later stages of shoulder development, the pulling speed is finely adjusted according to the shape of the shoulder.

6. The shoulder-forming process for heavily arsenic-doped silicon single crystals according to any one of claims 1 to 5, characterized in that, The target diameter of the silicon single crystal is 8 inches.

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