Silicon single crystal manufacturing method and apparatus, and silicon wafer manufacturing method

Abstract

To provide a method and an apparatus for producing a silicon single crystal, the method and apparatus being capable of quantitatively evaluating the deformation or eccentricity of a quartz crucible or its the size.SOLUTION: The present invention provides a method for producing a silicon single crystal by pulling a silicon single crystal from a silicon melt 2 in a quartz crucible 11, wherein images including a mirror image 11M of the quartz crucible 11 reflected on a melt surface 2a of the silicon melt 2 are acquired at predetermined time intervals, and the deformation or eccentricity of the quartz crucible 11 or its size is evaluated from temporal changes of the position of the mirror image 11M of the quartz crucible 11 reflected on a plurality of images that are acquired during the time period where the quartz crucible 11 rotates at least once.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for producing silicon single crystals by the Czochralski method (CZ method), and in particular to a method for producing silicon single crystals by the Czochralski method (CZ method) using a quartz crucible. Deformation or eccentricity The present invention also relates to a method for producing a silicon wafer using such a silicon single crystal. [Background technology]

[0002] Most silicon wafers, which are used as substrate materials for semiconductor devices, are manufactured by processing silicon single crystal ingots produced by the CZ method. In the CZ method, polycrystalline silicon raw material is melted in a quartz crucible to produce silicon melt, a seed crystal is immersed in the silicon melt, and the seed crystal is gradually pulled up while rotating the quartz crucible and seed crystal, growing a large single crystal at the bottom of the seed crystal. The CZ method can increase the yield of large-diameter silicon single crystals.

[0003] A quartz crucible is a container made of silica glass that holds silicon melt. Therefore, quartz crucibles are required to be highly durable so that they do not deform at high temperatures above the melting point of silicon and can withstand long-term use. If the quartz crucible deforms during the crystal pulling process, the shape and quality of the silicon single crystal will change, and in the worst case, the crucible wall may come into contact with furnace internal structures, leading to an accident. To prevent such accidents, it is preferable to monitor the deformation of the quartz crucible. For example, Patent Document 1 describes a method for detecting crucible deformation from a sudden change in the height of the melt surface due to a change in the crucible volume. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-109826 Summary of the Invention [Problem to be solved by the invention]

[0005] In the raw material melting process, in which polycrystalline silicon raw material in a quartz crucible is heated and melted, a large thermal load is placed on the quartz crucible due to radiant heat from the heater, which can easily cause the upper end of the quartz crucible to collapse inward. If such deformation of the crucible occurs, the crucible and the heat shield come into contact during the single crystal pulling process, making it impossible to continue the crystal pulling process. Even if the crystal pulling process can be continued, the convection of the silicon melt in the quartz crucible changes, causing oxygen abnormalities in the silicon single crystal. Therefore, it is essential to check for crucible deformation during the crystal pulling process, especially during the raw material melting process, in which crucible deformation is likely to occur. However, in the past, the only way to determine this was for workers to visually observe the inside of the furnace, and the amount of crucible deformation was difficult to determine. of There was no method to quantitatively evaluate it.

[0006] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a method and apparatus for producing silicon single crystals, and a method for producing silicon wafers, which are capable of quantitatively evaluating the presence or absence, or the magnitude, of deformation or eccentricity of a quartz crucible. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a method for producing a silicon single crystal by pulling up a silicon single crystal from a silicon melt in a quartz crucible, and is characterized in that images including a mirror image of the quartz crucible reflected on the surface of the silicon melt are acquired at predetermined time intervals, and the amount of change due to deformation or eccentricity of the quartz crucible is calculated from the change over time in the position of the mirror image of the quartz crucible reflected in multiple images acquired during at least one rotation of the quartz crucible. According to the present invention, it is possible to objectively grasp changes in shape due to deformation or eccentricity of the quartz crucible and prevent accidents and deterioration in the quality of the silicon single crystal due to deformation of the quartz crucible.

[0008] In the method for producing a silicon single crystal according to the present invention, it is preferable to detect the position of the upper end of the quartz crucible from a mirror image of the quartz crucible and calculate the amount of deformation or eccentricity of the upper end from the change in the position of the upper end over time. This makes it possible to objectively evaluate the degree of deformation of the upper end of the quartz crucible or the degree of eccentricity of the crucible. It is also possible to evaluate the deformation of only the upper end of the quartz crucible, which does not affect the fluctuation in the height of the melt surface.

[0009] In the method for producing a silicon single crystal according to the present invention, it is preferable to detect the upper end of the quartz crucible from the differential value of the vertical brightness of the pixel in the image, thereby making it possible to objectively evaluate the degree of deformation and eccentricity of the upper end of the quartz crucible.

[0010] In the method for producing a silicon single crystal according to the present invention, it is preferable to set a detection line for the position of the upper end portion within a plane including the optical axis of the camera that captures the image, and to calculate the amount of change in the quartz crucible from the change over time in the position of the mirror image of the quartz crucible on the detection line. This makes it possible to easily calculate the amount of change in the quartz crucible.

[0011] In the method for producing a silicon single crystal according to the present invention, it is preferable to calculate the amount of change in the quartz crucible based on the multiple images acquired between the start of a raw material melting process in which the silicon raw material in the quartz crucible is melted and the start of a melting process in which a seed crystal is immersed in the silicon melt. During the raw material melting process, a large thermal load is applied to the quartz crucible, which makes it prone to inward tilting of the upper end portion of the quartz crucible. By calculating the amount of change in the quartz crucible during the raw material melting process, accidents and reduced single crystal yields due to deformation of the quartz crucible can be prevented.

[0012] The silicon single crystal manufacturing apparatus according to the present invention includes a quartz crucible for holding a silicon melt, a heater surrounding the quartz crucible for heating the silicon melt, and crucible driving means for rotating and elevating the quartz crucible. andThe present invention comprises a crystal pulling means for pulling a silicon single crystal from the silicon melt, a thermal shield disposed above the quartz crucible so as to surround the silicon single crystal pulled from the silicon melt, a camera for photographing the melt surface of the silicon melt as seen through an opening in the thermal shield from an obliquely upward direction, and an image processing unit for processing images photographed by the camera, wherein the camera acquires images including a mirror image of the quartz crucible reflected on the melt surface of the silicon melt at predetermined time intervals, and the image processing unit calculates the amount of change due to deformation or eccentricity of the quartz crucible from the change over time in the position of the mirror image of the quartz crucible reflected in a plurality of images acquired during at least one rotation of the quartz crucible. According to the present invention, it is possible to objectively grasp changes in shape due to deformation or eccentricity of the quartz crucible and prevent accidents and deterioration in the quality of the silicon single crystal due to deformation of the quartz crucible.

[0013] In the present invention, it is preferable that the image processing unit detects the position of the upper end of the quartz crucible from the mirror image of the quartz crucible and calculates the amount of deformation or eccentricity of the upper end from the change in the position of the upper end over time, thereby making it possible to objectively evaluate the degree of deformation of the upper end of the quartz crucible or the degree of eccentricity of the crucible.

[0014] In the present invention, the image processing unit preferably detects the upper end of the quartz crucible from a differential value of the vertical brightness of the pixel in the image, thereby making it possible to objectively evaluate the degree of deformation or eccentricity of the upper end of the quartz crucible.

[0015] In the present invention, it is preferable that the image processing unit sets a detection line for the position of the upper end portion within a plane including the optical axis of the camera that captures the image, and calculates the amount of change in the quartz crucible from the temporal change in the position of the mirror image of the quartz crucible on the detection line. This makes it possible to easily calculate the amount of change in the quartz crucible.

[0016] In the present invention, it is preferable that the image processing unit calculates the amount of change in the quartz crucible based on the plurality of images acquired during the period from the start of a raw material melting process for melting the silicon raw material in the quartz crucible to the start of a liquefaction process for immersing a seed crystal in the silicon melt. By calculating the amount of change in the quartz crucible during the raw material melting process, it is possible to prevent accidents and a decrease in the yield of single crystals due to deformation of the quartz crucible.

[0017] Furthermore, the method for producing a silicon wafer according to the present invention is characterized in that the silicon single crystal produced by the method for producing a silicon single crystal according to the present invention described above is processed to produce a silicon wafer. According to the present invention, the production yield of silicon wafers can be increased. [Effects of the Invention]

[0018] According to the present invention, the presence or absence of deformation or eccentricity of the quartz crucible, or the size thereof, of It is possible to provide a method and apparatus for producing a silicon single crystal and a method for producing a silicon wafer that enable quantitative evaluation. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is an explanatory diagram of a method for producing a silicon single crystal according to an embodiment of the present invention, and is a schematic cross-sectional view showing the configuration of a single crystal production apparatus. [Figure 2] FIG. 2 is a flowchart showing the steps of manufacturing a silicon single crystal according to this embodiment. [Figure 3] FIG. 3 is a schematic cross-sectional view showing the shape of a silicon single crystal ingot. [Figure 4] FIG. 4 is a diagram for explaining a method for monitoring deformation of a quartz crucible, and is a conceptual diagram of a CZ pulling furnace in a raw material melting step. [Figure 5]Figures 5(a) and (b) are schematic diagrams of images taken by a camera photographing the silicon melt in a quartz crucible, where (a) shows the state in which the upper end of the quartz crucible is not deformed, and (b) shows the state in which the upper end of the quartz crucible is deformed. [Figure 6] 6(a) and (b) are explanatory diagrams of how to determine the position of the upper end of the quartz crucible. [Figure 7] FIG. 7 is a graph showing an example of the measurement results of the deformation amount of a quartz crucible, where the horizontal axis indicates the crucible rotation angle (degrees) and the vertical axis indicates the position (pixels) of the crucible mirror image edge. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0021] FIG. 1 is an explanatory diagram of a method for producing a silicon single crystal according to an embodiment of the present invention, and is a schematic cross-sectional view showing the configuration of a single crystal production apparatus.

[0022] As shown in FIG. 1, the single crystal manufacturing apparatus 1 includes a water-cooled chamber 10, a quartz crucible 11 for holding a silicon melt 2 in the chamber 10, a graphite crucible 12 for holding the quartz crucible 11, a rotating shaft 13 for supporting the graphite crucible 12, and a connecting rod 14 for connecting the rotating shaft 13 and the graphite crucible 12. of The apparatus is equipped with a crucible drive mechanism 14 that rotates and raises and lowers the quartz crucible 11 via a heater 15 arranged around the graphite crucible 12, a heat insulating material 16 arranged outside the heater 15 and along the inner surface of the chamber 10, a heat shield 17 arranged above the quartz crucible 11, a pulling wire 18 arranged above the quartz crucible 11 and coaxial with the rotating shaft 13, a crystal pulling mechanism 19 arranged above the chamber 10, a camera 20 that takes pictures inside the chamber 10, an image processing unit 21 that processes images taken by the camera 20, and a control unit 22 that controls each part of the single crystal manufacturing apparatus 1.

[0023] The chamber 10 is composed of a main chamber 10a and a long, cylindrical pull chamber 10b connected to the upper opening of the main chamber 10a, and the quartz crucible 11, graphite crucible 12, heater 15, and heat shield 17 are provided inside the main chamber 10a. The pull chamber 10b is provided with a gas inlet 10c for introducing an inert gas (purge gas) such as argon gas and a dopant gas into the chamber 10, and the bottom of the main chamber 10a is provided with a gas outlet 10d for discharging the atmospheric gas inside the chamber 10. In addition, a viewing window 10e is provided at the top of the main chamber 10a, allowing the growth status of the silicon single crystal 3 to be observed.

[0024] The quartz crucible 11 is a container made of silica glass and has a cylindrical side wall and a curved bottom. The graphite crucible 12 is in close contact with the outer surface of the quartz crucible 11, encasing it, in order to maintain the shape of the quartz crucible 11 that has been softened by heating. The quartz crucible 11 and the graphite crucible 12 form a double-structure crucible that supports the silicon melt 2 within the chamber 10.

[0025] The graphite crucible 12 is fixed to the upper end of a rotating shaft 13, and the lower end of the rotating shaft 13 passes through the bottom of the chamber 10 and is connected to a crucible drive mechanism 14 provided outside the chamber 10. The graphite crucible 12, the rotating shaft 13, and the crucible drive mechanism 14 constitute a crucible drive means for rotating and elevating the quartz crucible 11. The rotation and elevating movements of the quartz crucible 11 driven by the crucible drive mechanism 14 are controlled by a control unit 22.

[0026] The heater 15 is used to melt the silicon raw material filled in the quartz crucible 11 to generate the silicon melt 2 and to maintain the silicon melt 2 in a molten state. The heater 15 is a resistance heater made of carbon, and is provided so as to surround the quartz crucible 11 inside the graphite crucible 12. Furthermore, a heat insulating material 16 is provided outside the heater 15 so as to surround the heater 15, thereby improving the heat retention inside the chamber 10. The output of the heater 15 is controlled by the control unit 22.

[0027] The thermal shield 17 is provided to suppress temperature fluctuations in the silicon melt 2 to provide an appropriate heat distribution near the crystal growth interface, and to prevent the silicon single crystal 3 from being heated by radiant heat from the heater 15 and the quartz crucible 11. The thermal shield 17 is a substantially cylindrical graphite member, and is provided so as to cover the region above the silicon melt 2 excluding the pulling path for the silicon single crystal 3.

[0028] The diameter of the opening 17a at the lower end of the thermal shield 17 is larger than the diameter of the silicon single crystal 3, thereby ensuring a path for pulling up the silicon single crystal 3. In addition, the outer diameter of the lower end of the thermal shield 17 is smaller than the diameter of the quartz crucible 11, and the lower end of the thermal shield 17 is located inside the quartz crucible 11. Therefore, even if the upper end of the quartz crucible 11 is raised above the lower end of the thermal shield 17, the thermal shield 17 will not interfere with the quartz crucible 11.

[0029] As the silicon single crystal 3 grows, the amount of melt in the quartz crucible 11 decreases, but the distance between the melt surface 2a and the heat shield 17 (gap value h G ) is kept constant, the temperature fluctuation of the silicon melt 2 is suppressed, and the flow rate of the gas flowing near the melt surface 2a is kept constant, thereby controlling the amount of dopant evaporated from the silicon melt 2. By controlling the gap in this way, it is possible to improve the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, etc. in the pulling axis direction of the silicon single crystal 3.

[0030] Above the quartz crucible 11, there are provided a wire 18, which is the axis for pulling the silicon single crystal 3, and a crystal pulling mechanism 19, which pulls up the silicon single crystal 3 by winding up the wire 18. These constitute a crystal pulling means for pulling up the silicon single crystal 3. The crystal pulling mechanism 19 has the function of rotating the silicon single crystal 3 together with the wire 18. The crystal pulling mechanism 19 is controlled by a control unit 22. The crystal pulling mechanism 19 is disposed above the pull chamber 10b, and the wire 18 extends downward from the crystal pulling mechanism 19 through the pull chamber 10b, with the tip of the wire 18 reaching the interior space of the main chamber 10a. FIG. 1 shows a state in which the silicon single crystal 3 is suspended from the wire 18 during growth. When pulling up the silicon single crystal 3, the wire 18 is gradually pulled up while the quartz crucible 11 and the silicon single crystal 3 are both rotated, thereby growing the silicon single crystal 3.

[0031] A camera 20 is installed outside the chamber 10. The camera 20 is, for example, a CCD camera, and photographs the interior of the chamber 10 through a viewing window 10e formed in the chamber 10. The installation angle of the camera 20 is a predetermined angle with respect to the vertical direction, and the camera 20 has a camera axis (optical axis) inclined with respect to the pulling axis of the silicon single crystal 3. In other words, the camera 20 photographs the upper surface region of the quartz crucible 11, including the circular opening 17a of the thermal shield 17 and the melt surface 2a of the silicon melt 2, from obliquely above.

[0032] The camera 20 is connected to an image processing unit 21, which is connected to a control unit 22. attitude During the pulling process of the silicon single crystal 3, the image processing unit 21 calculates the crystal diameter near the solid-liquid interface from the contour pattern of the single crystal captured in the image captured by the camera 20. The image processing unit 21 also calculates the distance from the thermal shield 17 to the melt surface (gap value h G ) is calculated.

[0033] The control unit 22 controls the crystal diameter by controlling the crystal pulling speed based on the crystal diameter data obtained from the image captured by the camera 20. Specifically, if the measured value of the crystal diameter is larger than the target diameter, the crystal pulling speed is increased, and if the measured value of the crystal diameter is smaller than the target diameter, the crystal pulling speed is decreased. The control unit 22 also controls the crystal length data of the silicon single crystal 3 obtained from the sensor output of the crystal pulling mechanism 19 and the gap value h obtained from the image captured by the camera 20. G Based on the liquid level, the movement amount of the quartz crucible 11 (crucible rising speed) is controlled so as to achieve a predetermined gap value.

[0034] Fig. 2 is a flowchart showing the steps of producing a silicon single crystal according to this embodiment, and Fig. 3 is a schematic cross-sectional view showing the shape of a silicon single crystal ingot.

[0035] As shown in Figure 2, the manufacturing process for silicon single crystals according to this embodiment includes a raw material melting process S11 in which silicon raw material in a quartz crucible 11 is heated with a heater 15 to produce a silicon melt 2, a crucible deformation detection process S12 in which the presence or absence and magnitude of deformation of the quartz crucible 11 due to the raw material melting process S11 is evaluated, a liquid contact process S13 in which a seed crystal attached to the tip of a wire 18 is lowered to contact the silicon melt 2, and a crystal growth process (S14 to S17) in which the seed crystal is gradually pulled up while maintaining contact with the silicon melt 2 to grow a single crystal.

[0036] As shown in Figures 2 and 3, the crystal growth process involves the following steps, performed in order: a necking step S14, which forms a neck portion 3a with a narrowed crystal diameter to eliminate dislocations; a shoulder portion growth step S15, which forms a shoulder portion 3b whose crystal diameter gradually increases as the crystal grows; a body portion growth step S16, which forms a body portion 3c whose crystal diameter is maintained at a specified value; and a tail portion growth step S17, which forms a tail portion 3d whose crystal diameter gradually decreases as the crystal grows.

[0037] Thereafter, a cooling step S18 is carried out in which the silicon single crystal 3 is separated from the melt surface 2a and cooled. As a result, a silicon single crystal ingot 3I having a neck portion 3a, a shoulder portion 3b, a body portion 3c, and a tail portion 3d as shown in Fig. 3 is completed. Silicon wafers are produced by sequentially subjecting the silicon single crystal ingot 3I to processes such as periphery grinding, slicing, lapping, etching, double-side polishing, single-side polishing, and cleaning.

[0038] In this embodiment, the melt surface 2a of the silicon melt 2 in the quartz crucible 11 is photographed by the camera 20 from the raw material melting step S11 to the melting step S13, and deformation of the quartz crucible 11 is detected from changes in the mirror image of the quartz crucible 11 captured in the image captured by the camera 20 (crucible deformation detection step S12). The reason for detecting deformation of the quartz crucible 11 from the raw material melting step S11 to the melting step S13 is that it becomes difficult to capture the mirror image of the quartz crucible 11 reflected on the melt surface 2a from the shoulder portion growing step S14 onwards due to the presence of the silicon single crystal 3. Furthermore, if signs of large deformation of the quartz crucible 11 can be detected early, it becomes easy to determine whether to continue or stop pulling the crystal.

[0039] FIG. 4 is a diagram for explaining a method for detecting deformation of the quartz crucible 11, and is a conceptual diagram of the CZ pulling furnace in the raw material melting step S11.

[0040] As shown in Fig. 4, in the raw material melting step S11, the melt surface 2a is photographed by the camera 20 to detect deformation of the quartz crucible 11. The camera 20 can photograph the melt surface 2a of the silicon melt 2 visible through the opening 17a of the thermal shield 17. Because the thermal shield 17 is present between the camera 20 and the quartz crucible 11, the camera 20 cannot directly capture a real image of the quartz crucible 11. A mirror image 11M of the quartz crucible 11 is reflected in the melt surface 2a, but when the upper end 11e of the quartz crucible 11 tilts inward, the position of the edge of the mirror image 11M of the quartz crucible 11 reflected in the melt surface 2a also changes. Therefore, deformation of the quartz crucible 11 can be detected from the change in the mirror image 11M of the quartz crucible 11.

[0041] When the raw material melting step S11 is started, the solid silicon raw material gradually melts, and the amount of silicon melt 2 increases. For a while after the raw material melting step S11 is started, the amount of silicon melt 2 is small and the solid silicon raw material remains, so the camera 20 cannot accurately capture the mirror image of the quartz crucible 11 reflected on the melt surface 2a. Furthermore, since the quartz crucible 11 is not yet subjected to a large thermal load, it does not deform significantly. Once the melting of the raw material progresses to a certain extent and the amount of silicon melt 2 in the quartz crucible 11 becomes sufficient, the mirror image edge of the upper end 11e of the quartz crucible 11 begins to be reflected on the melt surface 2a, making it possible to detect deformation of the quartz crucible 11. Then, when the amount of silicon melt 2 has increased sufficiently, deformation of the quartz crucible 11 due to the influence of the thermal load becomes visible.

[0042] The quartz crucible 11 is located at a relatively high position, and the distance from the lower end of the thermal shield 17 to the melt surface 2a (gap value h G ) is small, the mirror image of the upper end 11e of the quartz crucible 11 is blocked by the thermal shield 17, and the edge of the mirror image cannot be observed. However, if the quartz crucible 11 is lowered sufficiently, the edge of the mirror image of the upper end 11e of the quartz crucible 11 can be placed within the field of view of the camera 20. Therefore, in the crucible deformation detection step S12, it is desirable to set the melt surface 2a at a lower position than in the crystal growth step (especially the body portion growth step S16) and calculate the amount of deformation of the quartz crucible 11.

[0043] Figures 5(a) and (b) are schematic diagrams of images captured by a camera 20 photographing the melt surface 2a of the silicon melt 2 in the quartz crucible 11, where (a) shows an image when the upper end of the quartz crucible 11 is not deformed, and (b) shows an image when the upper end of the quartz crucible 11 is deformed.

[0044] 5(a) and 5(b), the melt surface 2a of the silicon melt 2 in the quartz crucible 11 can be observed through the opening 17a of the thermal shield 17 provided above the quartz crucible 11. In the image captured by the camera 20, the blackened area is the real image 17R of the thermal shield 17, and the entire area inside the opening 17a of the thermal shield 17 is the melt surface 2a.

[0045] Because the melt surface 2a is a mirror surface, the upper end of the quartz crucible 11 and the upper end of the heater 15 are reflected in the melt surface 2a. In real space, the upper end of the heater 15 is located higher than the upper end of the quartz crucible 11, but the relative positions of the quartz crucible 11 and the heater 15 reflected in the melt surface 2a are upside down, with the bottom in the captured image corresponding to the top in real space. Therefore, the edge of the mirror image of the quartz crucible 11 is located higher than the edge of the mirror image of the heater 15. The region between the arc-shaped edge line E1 of the thermal shield 17 and the arc-shaped edge line E2 of the upper end of the quartz crucible 11 is the mirror image 11M of the quartz crucible 11, and the region between the arc-shaped edge line E2 of the upper end of the quartz crucible 11 and the arc-shaped edge line E3 of the upper end of the heater 15 is the mirror image 15M of the heater 15.

[0046] As shown in FIG. 5(a), the edge line E2 of the mirror image 11M of the upper end 11e of an undeformed quartz crucible 11 has a beautiful arc shape. However, if the upper end 11e of the quartz crucible 11 is tilted inward as shown in FIG. 4, the arc shape of the mirror image 11M of the upper end 11e of the quartz crucible 11 changes, as shown in FIG. 5(b), and part of the edge line E2 of the mirror image 11M moves downward in the vertical direction (Y direction) of the image. Because the quartz crucible 11 rotates at a constant speed, the position of the upper end of the quartz crucible 11 moves downward when viewed along a preset detection line L0. Therefore, the amount of deformation of the upper end 11e of the quartz crucible 11 can be calculated by measuring the change in the position of the intersection P2 between the edge line E2 of the mirror image 11M of the quartz crucible 11 and the detection line L0 during one rotation of the quartz crucible 11.

[0047] The detection line L0 is preferably set in a plane including the optical axis of the camera 20. Yo This makes it possible to easily calculate the amount of deformation of the upper end 11e of the quartz crucible 11.

[0048] 6(a) and (b) are explanatory diagrams of how to determine the position of the mirror image edge of the quartz crucible 11. FIG.

[0049] As shown in Figures 6(a) and (b), the position of the edge of the mirror image of the quartz crucible 11 on the detection line L0 can be found from the differential value of the brightness distribution in the vertical direction (Y direction) of the photographed image. Looking at the brightness distribution in the vertical direction of the photographed image shown in Figure 6(a), it can be seen that the brightness changes significantly at the boundary position P1 (see Figures 5(a) and (b)) between the real image 17R of the thermal shield 17 and the mirror image 11M of the quartz crucible 11, and also at the boundary position P2 between the mirror image of the quartz crucible 11 and the mirror image of the heater 15.

[0050] Therefore, when the differential value of the brightness distribution in the vertical direction (Y direction) of this captured image is calculated, two brightness peaks are obtained as shown in Figure 6(b). The position where the first brightness peak occurs corresponds to position P1 of the lower end of the thermal shield 17, and the position where the second brightness peak occurs corresponds to position P2 of the mirror image edge of the quartz crucible 11. The position P2 of the mirror image edge of the upper end of the quartz crucible 11 thus obtained is measured at a predetermined shooting period (sampling period) while the quartz crucible 11 makes one rotation, and the amount of deformation of the upper end 11e of the quartz crucible 11 can be calculated from the amount of change in position P2 of the mirror image edge.

[0051] The image capture period (image capture interval) is preferably an angle interval that is not divisible by 360 degrees. For example, integer values ​​that are not divisible by 360 degrees, such as 7 degrees or 11 degrees, can be used. When measuring at an angle interval that is divisible by 360 degrees, data at the same angle is accumulated from the second rotation of the crucible onwards, and data gaps in the angle interval cannot be filled. On the other hand, when measuring at an angle interval that is not divisible by 360 degrees, such as a 7-degree interval, the angle from the second rotation onwards fills gaps that are multiples of 7, so data at 1-degree intervals can be obtained after seven rotations. Furthermore, the shorter the image capture period, the higher the measurement accuracy of the deformation amount of the upper end 11e of the quartz crucible 11, but the greater the image processing load. Therefore, the lower limit of the image capture period can be determined based on the crucible rotation speed and the capabilities of the image processing device. For example, it can be 0.5 degrees or more. The upper limit of the image capture period can be, for example, 15 degrees or less, or even 10 degrees or less.

[0052] As described above, the amount of deformation of the upper end 11e of the quartz crucible 11 is determined from the deviation in the vertical position of the mirror image edge during one rotation of the quartz crucible 11. Therefore, if the crucible is tilted inward along its entire circumference, the correct amount of deformation cannot be determined. However, as shown in FIG. 5(b), the inward tilt of the quartz crucible 11 occurs locally and rarely occurs along its entire circumference. Therefore, even with the above method, it is possible to accurately determine the amount of deformation of the crucible. Furthermore, if the pixel position when the crucible is not deformed is determined in advance as a reference value, the correct amount of deformation can be determined even if the crucible is tilted inward along its entire circumference.

[0053] It is preferable to calculate the average value of multiple measurements in order to eliminate measurement errors and accurately calculate the amount of deformation of the upper end 11e of the quartz crucible 11. Therefore, it is preferable to obtain N measurement results of the amount of deformation of the quartz crucible 11 from multiple images taken while the quartz crucible 11 makes N continuous rotations, and to calculate the average value of these N measurement results.

[0054] Figure 7 is a graph showing an example of the measurement results of the position of the mirror image edge of the upper end of a quartz crucible 11 rotating at a constant speed, where the horizontal axis shows the crucible rotation angle (degrees) and the vertical axis shows the pixel position (pixel) of the mirror image edge of the quartz crucible.

[0055] As shown in Figure 7, the Y-direction position of the mirror image edge of the quartz crucible 11 fluctuates vertically as the quartz crucible 11 rotates once, reaching maximums at approximately 30°, 150°, and 270°, and minimums at approximately 110°, 220°, and 330°. It can also be seen that the maximum vertical change in the crucible mirror image edge is approximately 60 pixels. In this way, the amount of deformation of the quartz crucible 11 can be determined from the change in the mirror image of the quartz crucible 11.

[0056] The deformation amount of the quartz crucible 11 obtained from the above captured image is expressed in pixels, and unit conversion is required to convert this to the deformation amount (millimeters) in real space. The method of unit conversion is not particularly limited, but for example, it can be obtained from the correspondence relationship between the number of pixels moved per unit time when a point on the top end of the quartz crucible 11 moves due to crucible rotation and the actual movement distance per unit time calculated from the diameter and rotation speed of the quartz crucible 11. That is, suppose that a point on the mirror-image edge of the quartz crucible 11 moves from one coordinate point A to another coordinate point B. Meanwhile, the movement distance of the point on the top end of the quartz crucible 11 in real space can be calculated from the diameter and rotation speed of the quartz crucible. Therefore, the real-space distance per pixel can be calculated by matching the number of pixels between A and B in the captured image with the movement distance in real space.

[0057] As a result of measuring the deformation amount of the quartz crucible 11 described above, if the deformation amount exceeds a threshold, the control unit 22 may output an alarm by sound or by displaying an alarm on a screen, thereby alerting the operator.

[0058] As explained above, in the method for producing a silicon single crystal according to this embodiment, the melt surface 2a of the silicon melt 2 in the quartz crucible 11, which is visible through the opening 17a of the thermal shield 17, is captured by the camera 20, and the amount of deformation of the quartz crucible 11 is calculated from the change over time in the mirror image 11M of the quartz crucible 11 reflected on the melt surface 2a, so that the probability of an accident due to deformation of the quartz crucible 11 can be predicted and prevented in advance. In addition, by feeding back the effect of the crystal pulling conditions on the deformation of the quartz crucible 11, deformation of the crucible can be prevented in advance.

[0059] The silicon single crystal manufacturing apparatus according to this embodiment also includes a camera 20 that captures images of the melt surface 2a of the silicon melt 2 in the quartz crucible 11 from diagonally above, as seen through the opening 17a of the thermal shield 17, and an image processor 21 that processes the images captured by the camera 20. The camera 20 captures multiple images at predetermined time intervals while the quartz crucible 11 makes at least one rotation, each including a mirror image of the quartz crucible 11 reflected on the melt surface 2a of the silicon melt 2. The image processor 21 calculates the amount of deformation of the quartz crucible 11 from the change over time in the mirror image 11M of the quartz crucible 11 reflected in each of the multiple images, thereby making it possible to predict the probability of an accident due to deformation of the quartz crucible 11 and prevent it from occurring. Furthermore, by providing feedback on the effect of the crystal pulling conditions on the deformation of the quartz crucible 11, it is possible to prevent deformation of the crucible.

[0060] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention.

[0061] For example, in the above embodiment, the case of calculating the amount of deformation due to inward tilting of the upper end 11e of the quartz crucible 11 has been described, but the present invention is not limited to calculating such amounts of deformation, and can also be applied to cases where the circumferential height of the upper end 11e varies due to sinking of the quartz crucible 11. Furthermore, the present invention can also be used as a method for calculating the amount of eccentricity when the central axis of the quartz crucible 11 rotates eccentrically, deviating from the central axis of rotation. In this case, the amount of eccentricity of the quartz crucible 11 can be calculated from the periodic deviation of the position of the mirror image edge synchronized with the rotation period of the crucible.

[0062] Furthermore, in the above embodiment, the mirror image of the quartz crucible 11 is photographed during the period from the raw material melting step S11 to before the start of the melting step S13 to calculate the amount of deformation of the quartz crucible 11, but the measurement time of the amount of deformation of the quartz crucible 11 according to the present invention is not limited to the period from the raw material melting step S11 to before the start of the melting step S13, and can be performed at any timing when the edge of the mirror image of the quartz crucible 11 reflected on the melt surface 2a can be photographed. Furthermore, if the mirror image of the quartz crucible 11 can be photographed during crystal pulling, it is also possible to continuously detect the amount of deformation of the quartz crucible 11.

[0063] Furthermore, the detection of the deformation amount of a quartz crucible according to the present invention can also be applied to the so-called multiple pulling method. The multiple pulling method is a method in which, after pulling a silicon single crystal, additional silicon raw material is supplied into the same quartz crucible and melted, and a silicon single crystal is pulled from the resulting silicon melt, and by repeating this raw material supply process and single crystal pulling process, multiple silicon single crystals are produced from one quartz crucible. By adopting the method for calculating the deformation amount of a crucible according to the present invention in the process of melting the additionally supplied raw material, , multi-pull It is possible to objectively determine whether the project can be continued.

[0064] Furthermore, in the above embodiment, an image for detecting the deformation amount of the quartz crucible 11 is acquired using the camera 20 used to measure the crystal diameter and gap value, but the present invention is not limited to such a configuration, and an image of the melt surface 2a may be taken using a dedicated camera separate from the camera used for diameter measurement, etc. [Explanation of symbols]

[0065] 1. Single crystal manufacturing equipment 2. Silicon melt 2a Melt surface 3. Silicon single crystal 3I silicon single crystal ingot 3a Neck 3b Shoulder part 3c Body 3D tail section 10 chambers 10a Main Chamber 10b Pull chamber 10c Gas inlet 10d Gas outlet 10e Sight glass 11 Quartz crucible 11M Mirror image of quartz crucible 12 Graphite crucible 13 Rotating shaft 14 Crucible drive mechanism 15 Heater Mirror image of 15M heater 16. Insulation 17 Heat shield 17R Real image of the heat shield 17a Opening in thermal shield 18 wires 19 Wire winding mechanism 20 Camera 21 Image processing section 22 Control Unit E1 Edge line of the real image of the heat shielding material E2 Mirror image edge line of quartz crucible E3 Mirror image edge line of heater L0 detection line S11 Raw material melting process S12 Crucible deformation detection process S13 Liquid application process S14 Necking process S15 Shoulder part development process S16 Body development process S17 Tail part development process S18 Cooling process

Claims

1. A method for producing a silicon single crystal by pulling a silicon single crystal from a silicon melt in a quartz crucible, A method for producing a silicon single crystal, characterized in that images including a mirror image of the quartz crucible reflected on the surface of the silicon melt are acquired at predetermined time intervals, and deformation or eccentricity of the quartz crucible is evaluated from the temporal change in the position of the mirror image of the quartz crucible reflected in multiple images acquired while the quartz crucible makes at least one rotation.

2. 2. The method for producing a silicon single crystal according to claim 1, wherein the position of the upper end of the quartz crucible is detected from a mirror image of the quartz crucible, and the amount of deformation or eccentricity of the upper end is calculated from a change in the position of the upper end over time.

3. The method for producing a silicon single crystal according to claim 2 , wherein the upper end of the quartz crucible is detected from a differential value of vertical brightness of pixels in the image.

4. 4. The method for producing a silicon single crystal according to claim 2, wherein a detection line for the position of the upper end portion is set within a plane including the optical axis of a camera that captures the image, and the amount of change in the quartz crucible is calculated from the change over time in the position of the mirror image of the quartz crucible on the detection line.

5. 4. The method for producing a silicon single crystal according to claim 1, wherein the change amount of the quartz crucible is calculated based on the plurality of images acquired between the start of a raw material melting process for melting the silicon raw material in the quartz crucible and the start of a liquid contact process for contacting a seed crystal with the silicon melt.

6. a quartz crucible for holding molten silicon; a heater provided to surround the quartz crucible and configured to heat the silicon melt; a crucible driving means for rotating and elevating the quartz crucible; a crystal pulling means for pulling a silicon single crystal from the silicon melt; a thermal shield disposed above the quartz crucible so as to surround the silicon single crystal pulled from the silicon melt; a camera that photographs the melt surface of the silicon melt visible through the opening of the thermal shield from obliquely above; an image processing unit that processes an image captured by the camera, the camera acquires an image including a mirror image of the quartz crucible reflected on the surface of the silicon melt at predetermined time intervals; The silicon single crystal manufacturing apparatus is characterized in that the image processing unit evaluates the deformation or eccentricity of the quartz crucible from the temporal change in the position of the mirror image of the quartz crucible reflected in multiple images acquired while the quartz crucible makes at least one rotation.

7. The silicon single crystal manufacturing apparatus of claim 6, wherein the image processing unit detects the position of the upper end of the quartz crucible from a mirror image of the quartz crucible, and calculates the amount of deformation or eccentricity of the upper end from the change in the position of the upper end over time.

8. 8. The silicon single crystal manufacturing apparatus according to claim 7, wherein the image processing unit detects the upper end of the quartz crucible from a differential value of vertical brightness of pixels in the image.

9. The silicon single crystal manufacturing apparatus of claim 7 or 8, wherein the image processing unit sets a detection line for the position of the upper end portion within a plane including the optical axis of the camera that captures the image, and calculates the amount of change in the quartz crucible from the temporal change in the position of the mirror image of the quartz crucible on the detection line.

10. 9. The silicon single crystal manufacturing apparatus according to claim 6, wherein the image processing unit calculates the amount of change in the quartz crucible based on the plurality of images acquired between the start of a raw material melting process for melting the silicon raw material in the quartz crucible and the start of a liquid contact process for contacting a seed crystal in the silicon melt.

11. A method for producing a silicon wafer, comprising processing a silicon single crystal produced by the method for producing a silicon single crystal according to any one of claims 1 to 3 to produce a silicon wafer.

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