A method for reducing shoulder breakage rate and improving yield rate of near-perfect single crystal with equal diameter

Abstract

The present invention relates to the technical field of semiconductor material production, and in particular to a method for reducing a shouldering breakage rate and improving a yield rate of near-perfect single crystals of equal diameter, comprising: a seeding stage: judging a seeding temperature range by the brightness of a seeding aperture, and fine-tuning the liquid surface temperature so that the seeding temperature is within a range of ±2°C of an average value of the past 10 seeding temperatures, and then starting seeding; a shouldering stage: setting a fixed target pulling speed, refining a crucible following value in a shouldering interval, matching the crucible following value with a shoulder type through data simulation, and intervening through a PID program so that a liquid mouth distance deviation is ≤0.2mm; a shoulder rotation stage: setting a fixed shoulder rotation pulling speed and a non-fixed crucible following value, intervening through a PID program, increasing an interference ratio of the crucible following, and making a liquid mouth distance deviation ≤0.3mm; and an initial stage of equal diameter: setting a corresponding crucible following value according to a temperature gradient, adjusting the crucible following value through PID, quickly stabilizing the crystal rod diameter, and making an actual value deviation of the liquid mouth distance ≤0.1mm.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor material production, and in particular to a method for reducing the shoulder breakage rate and improving the yield rate of equal-diameter near-perfect single crystals. Background Art

[0002] During the pulling process of semiconductor silicon ingots, polysilicon liquid must ultimately be converted into single crystal silicon ingots, which requires a series of steps, including seeding, shouldering, shoulder rotation, diameter equalization, and finishing. The seeding step removes dislocations from the seed crystal, followed by shouldering to gradually increase the diameter, and then the shoulder rotation to achieve the desired diameter. During the shouldering and shoulder rotation processes, the seed crystal pulling speed, the rotation speed of the seed crystal and crucible, and the thermal field distribution must be balanced. Throughout this process, excessively high temperatures can easily lead to polycrystalline formation, while excessively low temperatures can cause defects or interrupt growth.

[0003] In existing processes, a fixed crucible follower (the ratio of crucible rise to crystal rise) is used for shoulder rotation, which can result in significant deviations between the actual and set values ​​for the liquid nozzle distance during the initial stage of equalizing the diameter. Interference with the PID system during the equalizing process can lead to significant fluctuations in diameter and casting speed, and stable casting speed and diameter may not be achieved during the first 200 mm of equalizing the diameter.

[0004] The current seeding process primarily determines the seeding temperature based on aperture brightness, which fails to achieve minimal temperature fluctuations and precise control of the seeding time during the seeding process. During the shouldering process, temperature and pulling speed are jointly controlled, but the shoulder shape is not comprehensively controlled along with the crucible, temperature, and pulling speed. This results in a high rate of wire breakage during the shouldering process and increases the overall pulling time. During the shouldering process, fixed crucible control is used. Due to the rapid diameter growth in the later stages of shouldering, the difference between the actual and set liquid nozzle distances gradually increases. In the initial stage of equal diameter, in order to quickly reach the target liquid nozzle distance, additional large fluctuations in diameter and pulling speed will occur, ultimately increasing the time required to generate a perfect single crystal and reducing the yield rate of near-perfect single crystals in the crystal ingot. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the background technology and provide a method to reduce the shoulder breakage rate and improve the yield rate of equal-diameter near-perfect single crystals, reduce the proportion of shoulder breakage and shoulder rotation breakage and the difference between the set value and the actual value of the liquid mouth distance, quickly achieve stability of diameter and pulling speed in the early stage of equal diameter, and improve the output ratio of near-perfect single crystals of crystal rods.

[0006] The technical solution of the present invention is:

[0007] A method for reducing the shoulder breakage rate and improving the yield rate of uniform diameter near-perfect single crystals, comprising:

[0008] (1) Seeding stage: After adjusting the current seeding temperature to within the range of ±2°C of the average seeding temperature of several previous times, seeding begins;

[0009] (2) Shoulder release stage: set a fixed target pulling speed, calculate the matching crucible value according to the shoulder shape of the shoulder release, and intervene through the PID program to make the deviation between the liquid mouth distance during the shoulder release and the target liquid mouth distance ≤ 0.2 mm;

[0010] (3) Shoulder rotation stage: set a fixed shoulder rotation speed, preset a crucible value close to the target crucible value, intervene through the PID program, increase the interference ratio of the crucible, and make the deviation between the liquid mouth distance and the target liquid mouth distance during the shoulder rotation ≤ 0.3 mm;

[0011] (4) Initial stage of equal diameter: In the initial stage of equal diameter, the corresponding crucible value is set according to the temperature gradient, and then the crucible value is adjusted by PID to quickly stabilize the diameter of the crystal rod while making the deviation between the actual value of the liquid mouth distance and the target value ≤0.1mm.

[0012] Preferably, in the seeding stage, the method for adjusting the current seeding temperature includes: judging the current seeding temperature range by the brightness and size of the seeding aperture, and then fine-tuning the seeding temperature by the liquid surface temperature. After the aperture brightness and the liquid surface temperature reach the expected range, the seeding temperature is adjusted into place.

[0013] Preferably, during the shoulder placement stage, the weight of the shoulder at the corresponding position is calculated based on the shoulder shape of the shoulder, and then the corresponding crucible value is calculated in combination with the silicon liquid density and the inner diameter of the crucible, so that the crucible value matches the shoulder shape of the shoulder.

[0014] Preferably, the fixed target pulling speed set in the shoulder release stage is 0.8-1 mm / min.

[0015] Preferably, the fixed shoulder turning pulling speed set in the shoulder turning stage is 1 to 3 mm / min.

[0016] The present invention has the following beneficial effects:

[0017] The present invention increases the temperature control range at the beginning of seeding and controls the seeding process time; refines the temperature gradient and crucible tracking during the shouldering process, fixes the overall shape of the shouldering, and reduces the wire breakage rate during the shouldering process; improves the interference ratio of the crucible tracking and PID during the shouldering process, and reduces the deviation between the actual liquid port distance and the set liquid port distance after the shouldering is completed;

[0018] In summary, this solution strengthens the seeding time and temperature, shoulder shape, shoulder crucible rotation and PID interference ratio, reduces the liquid mouth distance deviation entering the equal diameter, thereby reducing the pulling speed and diameter stabilization time, and ultimately reduces the length consumed before the equal diameter stage enters the near-perfect single crystal, that is, the length of the near-perfect single crystal is increased, achieving a double improvement in production quality and yield.

[0019] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the relationship between the brightness and size of the aperture and the temperature in Example 1 of the present invention.

[0021] Figure 2 This is a schematic diagram of a time-temperature curve in Example 2 of the present invention, wherein the horizontal axis represents time and the vertical axis represents the temperature drop amplitude.

[0022] Figure 3 This is a shoulder release shape diagram during the shoulder release process in Example 2 of the present invention and Comparative Example 2. Curve S1 in the figure is the shoulder release shape of Example 2, and curve S2 is the shoulder release shape of Comparative Example 2. The horizontal axis in the figure represents the diameter, and the vertical axis represents the height.

[0023] Figure 4 Schematic diagram of the deviation between the actual casting speed and the target casting speed at the initial stage of equal diameter in Example 3 of the present invention, where the horizontal axis represents the equal diameter length and the vertical axis represents the casting speed.

[0024] Figure 5 Schematic diagram of the deviation between the actual casting speed and the target casting speed at the initial stage of equal diameter in comparative example 3 of the present invention, wherein the horizontal axis represents the equal diameter length and the vertical axis represents the casting speed.

[0025] Reference numerals: seed crystal 1 , aperture 2 , black indicator point 3 . DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0027] In the prior art, the control methods for each process of the crystal pulling process are as follows:

[0028] (1) Seeding stage: The seeding temperature point is determined by the brightness of the seeding aperture. When the brightness reaches the required range, seeding begins;

[0029] (2) Shoulder release stage: shoulder release is performed by setting a fixed target pulling speed (0.8-1 mm / min), the temperature gradient of the shoulder release process, and the crucible following value;

[0030] (3) Shoulder turning stage: by setting a fixed shoulder turning speed (1-3 mm / min) and a constant crucible value, the diameter of the entry into the equal diameter is determined according to the shoulder shape;

[0031] (4) Initial stage of equal diameter: by adjusting the temperature and crucible value, the actual value of the liquid-to-mouth distance is close to the target value (deviation ≤ 0.1 mm).

[0032] This embodiment provides a method for reducing the shoulder breakage rate and improving the yield rate of uniform diameter near-perfect single crystals, including:

[0033] Confirm that the appropriate seeding temperature range is 1450-1490℃, and the seeding temperature of this furnace is the average of the past 10 furnaces (±2℃);

[0034] The shoulder shape and the crucible are matched, and the deviation between the actual value and the set value of the liquid port is controlled to be ≤0.2mm during the shoulder release process;

[0035] Matching of the crucible with the shoulder turning speed and the shoulder turning shape (when the shoulder turning speed has been determined and remains unchanged, the crucible value is adjusted to match the shoulder turning shape). During the shoulder turning process, the deviation between the actual value and the set value of the liquid port distance is ≤0.3mm;

[0036] In the early stage of equal diameter, the pulling speed, diameter, temperature and crucible are matched (that is, by adjusting the four parameters of pulling speed, diameter, temperature and crucible, the test results of the pulled crystal rod meet the requirements of perfect single crystal). Before the equal diameter reaches 150mm, the actual pulling speed matches the target pulling speed, the deviation between the actual value of the liquid nozzle distance and the set value is ≤0.1mm, and the deviation between the actual value of the diameter and the set value is ≤0.1mm.

[0037] In this embodiment, the control methods for each step of the crystal pulling process are as follows:

[0038] (1) Seeding stage

[0039] The seeding temperature range is determined by the brightness and size of the seeding aperture, and then fine-tuned by the liquid surface temperature to ensure that the seeding temperature is within the range of ±2°C of the average temperature of the past 10 seeding temperatures. When both the aperture brightness and the liquid surface temperature reach the required range, seeding can begin.

[0040] (2) Shoulder release phase

[0041] By setting a fixed target pulling speed (0.8-1mm / min), refining the crucible following value in the shoulder release interval (i.e. matching the corresponding crucible following value according to the shoulder shape of the shoulder release), and through data simulation (i.e. calculating the shoulder weight at the corresponding position according to the shoulder shape of the shoulder release, and then calculating the silicon liquid volume through the shoulder weight and silicon liquid density, and then calculating the corresponding crucible elevation value through the silicon liquid volume and the inner diameter of the crucible, and further obtaining the crucible following value through the crucible elevation value), the crucible following value is matched with the shoulder shape of the shoulder release. At the same time, intervention is carried out through the PID program of the shoulder release process. The goal is to ensure that the deviation between the liquid port distance and the target liquid port distance during the shoulder release period is ≤0.2mm.

[0042] (3) Shoulder rotation phase

[0043] By setting a fixed shoulder rotation speed (1-3 mm / min) and a non-fixed crucible following value (i.e., presetting a crucible following value that is relatively close to the target crucible following value), and intervening through PID in the shoulder rotation process, the crucible following interference ratio is appropriately increased (the purpose is to make the actual crucible following value consistent with the target crucible following value), so that the deviation between the liquid port distance and the target liquid port distance during the shoulder rotation period is ≤0.3 mm;

[0044] (4) Initial stage of equal diameter

[0045] In the initial stage of equal diameter, the corresponding crucible value is set according to the temperature gradient, and then the PID is adjusted (PID has a preset interference range) to quickly stabilize the crystal rod diameter while making the actual value of the liquid nozzle distance close to the target value (deviation ≤ 0.1mm).

[0046] Example 1:

[0047] During the single crystal silicon seeding process, the seeding furnace's seeding diameter measurement camera measures the size of the seed crystal aperture. The camera also observes the aperture's brightness. A liquid level temperature sensor measures the liquid level temperature. Through dual control of both the aperture and liquid level temperatures, the seeding temperature is maintained within ±2°C of the average of the past 10 seeding temperatures before seeding begins. Based on an average seeded grain length of 300mm, the average seeding speed is 2.5mm / min, and the seeding time is 120 minutes.

[0048] like Figure 1 As shown, during the seeding process, by manually observing the real-time image of the camera, if Figure 1 If the aperture shown in (a) and (b) is too small, it means that the seeding temperature is too high and needs to be cooled appropriately; if Figure 1 If the aperture shown in (d) and (e) is too large, unclear, irregular, or has low brightness, it means that the seeding temperature is too low and needs to be properly raised. Figure 1 If the size and brightness of the aperture shown in (c) remain within the appropriate range and remain stable for a certain period of time, it means that the temperature has reached the expected range. Figure 1 Black indicator dots are used to indicate the brightness of the aperture. The more black indicator dots there are and the larger the diameter is, the lower the brightness is, and vice versa.

[0049] In actual operation, due to the different thermal fields of single crystal furnaces, the thermal insulation performance of each single crystal furnace is different. However, no matter how the thermal insulation performance is, the average value of 10 seeding temperatures must be within the range of 1460-1480℃.

[0050] Comparative Example 1:

[0051] The aperture brightness is the standard for single crystal silicon seeding. Due to differences in personal observation, the actual average seeding temperature is (1455~1485)±6℃. Taking the average seeding length of 300mm as the standard, the seeding time is (108~180)min. Under the premise of consistent seeding length, the higher the seeding temperature, the slower the seeding speed and the longer the time consumed, resulting in large differences in seeding quality.

[0052] Example 2:

[0053] On the basis of setting a fixed target pulling speed of 0.8-1 mm / min, the shoulder is placed using the time-temperature axis (such as Figure 2 As shown, the shoulder needs to continuously lower the temperature, and the time-temperature axis is how much the temperature is lowered every how much time) and the shoulder height-crushing (as the shoulder height increases, the liquid level will gradually decrease, and the crushing needs to be adjusted according to the shoulder height to maintain the liquid port distance) two parameters are comprehensively controlled, such as Figure 3 As shown in the figure, due to the precise temperature control adopted in the seeding process, the temperature difference entering the shoulder release process is small. Combined with the crucible value corresponding to the simulated shoulder shape and the intervention of the PID program, the shoulder shape change difference is small, and the wire break rate during the shoulder release process is less than 20%.

[0054] Comparative Example 2:

[0055] The shouldering process is to gradually increase the diameter of the fine grains by rapidly cooling. Figure 3 As shown, due to the lack of precise seeding temperature control in the past, the liquid surface temperature entering the shoulder release process varied significantly, resulting in large variations in shoulder shape. This large variation in shoulder shape can lead to uneven cooling of the liquid silicon as it transforms into solid silicon, forming stress that causes the single crystal to transform into polycrystalline silicon, which is known as shoulder release breakage. The shoulder release breakage rate in this case exceeds 35%.

[0056] Example 3:

[0057] After the shouldering of the single crystal silicon rod is completed, the rapidly increasing diameter needs to be gradually controlled to the target diameter through the shouldering process. Since this process requires a rapid increase of about 20mm in diameter, it is necessary to set a fixed shouldering pulling speed of 1-3mm / min and reduce the change in the liquid nozzle distance by adjusting the crucible and PID. Ultimately, the temperature and liquid nozzle distance differences entering the equal diameter process are small, making the diameter and liquid nozzle distance control more accurate in the early stage of equal diameter. Figure 4 As shown in the figure, due to the accurate control of parameters such as temperature and crucible value in the seeding, shoulder release and shoulder rotation stages, the actual pulling speed and the target pulling speed are basically consistent in the initial stage of equal diameter, which can quickly stabilize the diameter of the crystal rod.

[0058] Comparative Example 3:

[0059] In the later stage of shoulder release, the temperature drops rapidly, so the diameter grows rapidly. The single crystal silicon rod grows from 285-295mm to 305-310mm. At this time, the silicon liquid taken away by the increase in diameter is more than normal, so the liquid level will drop rapidly, which will lead to an increase in the liquid mouth distance, increasing the difficulty of diameter control during shoulder rotation. In the past, a fixed crucible was used without PID adjustment. When the shoulder rotation was completed, the actual value of the liquid mouth distance would be 3-7mm larger than the fixed value. Because the larger the liquid mouth distance, the lower the surface temperature of the liquid. When the liquid mouth distance is gradually adjusted to the target value, the liquid surface temperature will gradually increase, which may easily lead to a smaller diameter in the early stage of equal diameter, increasing the difficulty of temperature and diameter control. For example Figure 5 As shown in the figure, due to the lack of accurate control of parameters such as temperature and crucible value during the seeding, shoulder release and shoulder rotation stages, the actual pulling speed deviates significantly from the target pulling speed in the early stage of equal diameter, which ultimately requires a longer equal diameter length to enable the crystal rod to enter the near-perfect single crystal range.

[0060] The above description is merely a preferred embodiment of the present invention. For those skilled in the art, the present invention may be modified and varied in various ways. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for reducing the shoulder breakage rate and improving the yield rate of uniform diameter near-perfect single crystals, characterized in that: include: (1) Seeding stage: The current seeding temperature range is determined by the brightness and size of the seeding aperture, and the seeding temperature is fine-tuned by the liquid surface temperature. When both the aperture brightness and the liquid surface temperature reach the expected range and the current seeding temperature is adjusted to be within the range of ±2°C of the average of the past seeding temperatures, seeding begins. Regardless of the insulation performance of the single crystal furnace, the average of the 10 seeding temperatures must be within the range of 1460-1480°C. (2) Shoulder release stage: set a fixed target pulling speed, calculate the shoulder weight at the corresponding position according to the shoulder shape of the shoulder, then calculate the silicon liquid volume by the shoulder weight and the silicon liquid density, and then calculate the corresponding crucible rise value by the silicon liquid volume and the inner diameter of the crucible, and further obtain the crucible follow value through the crucible rise value, so that the crucible follow value matches the shoulder shape of the shoulder release, and intervene through the PID program of the shoulder release process to make the deviation between the liquid mouth distance and the target liquid mouth distance during the shoulder release period ≤0.2mm; Shouldering is controlled by two parameters: time-temperature axis and shouldering height-crushing. The shouldering process requires continuous temperature reduction. The time-temperature axis means the temperature is reduced by a certain amount every certain time. The shouldering height-crushing axis means the liquid level will gradually decrease as the shouldering height increases. The crushing axis needs to be adjusted according to the shouldering height to maintain the liquid port distance. (3) Shoulder rotation stage: set a fixed shoulder rotation speed, preset a crucible value close to the target crucible value, intervene through the PID program, increase the interference ratio of the crucible, and make the deviation between the liquid mouth distance and the target liquid mouth distance during the shoulder rotation ≤ 0.3 mm; (4) Initial stage of equal diameter: In the initial stage of equal diameter, the corresponding crucible value is set according to the temperature gradient, and then the crucible value is adjusted by PID to quickly stabilize the diameter of the crystal rod while making the deviation between the actual value of the liquid mouth distance and the target value ≤0.1mm.

2. The method of reducing the shoulder breakage rate and improving the yield rate of equal diameter near-perfect single crystals according to claim 1, characterized in that: The fixed target pulling speed set in the shoulder release phase is 0.8 to 1 mm / min.

3. The method of reducing the shoulder breakage rate and improving the yield rate of equal diameter near-perfect single crystals according to claim 1, characterized in that: The fixed shoulder turning pulling speed set in the shoulder turning stage is 1 to 3 mm / min.

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