Single crystal manufacturing method

Abstract

[Problem] To accurately measure the space between a seed crystal and a melt surface and thereby reduce variation in the pre-heating position of the seed crystal. [Solution] The present invention comprises: a step for measuring the space LS between a melt surface 2a and the lower end of a seed crystal 5 provided above the melt; a step for lowering the seed crystal 5 on the basis of the space and bringing the same into contact with the melt; and a step for growing a single crystal by raising the seed crystal 5 while maintaining a state of contact with the melt. The step for measuring the space LS involves: using a camera 20 installed diagonally above the melt surface 2a to capture an image of the seed crystal 5 and the melt surface 2a; generating a real-image edge approximate circle by approximating a circle from the edge pattern of the lower end of a straight-trunk portion 5a of the seed crystal 5 in a real image 5R thereof in the captured image as well as generating a mirror-image edge approximate circle by approximating a circle from the edge pattern of the upper end of the straight-trunk portion 5a of the seed crystal 5 in a mirror image 5M thereof reflected on the melt surface 2a; and calculating the space LS between the melt surface 2a and the lower end of the seed crystal 5 from the distance from the center coordinates of the real-image edge approximate circle to the center coordinates of the mirror-image edge approximate circle.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a single crystal by the Czochralski method (CZ method), and in particular to a method for measuring the distance between a seed crystal and a melt surface and a method for preheating the seed crystal using the same.

[0002] Most silicon single crystals used as substrate materials for semiconductor devices are manufactured using the CZ method. In the CZ method, polycrystalline silicon raw material is heated in a quartz crucible to produce a melt, and a seed crystal is immersed in the melt. The seed crystal and the melt are then rotated while the seed crystal is slowly pulled up, growing a large-diameter single crystal at the bottom of the seed crystal. The CZ method makes it possible to increase the production yield of large-diameter single crystals.

[0003] Regarding a method for producing a single crystal by the CZ method, for example, Patent Document 1 describes a method in which a seed crystal is photographed with an optical camera before growing a single crystal, the image captured by the camera is processed to detect the position of the seed crystal, the tip of the seed crystal is stopped at a reference position set above the raw material melt, the distance from the reference position to the surface of the raw material melt is detected, and a crucible containing the raw material melt is moved up and down according to the detected distance.

[0004] Patent Document 2 describes a method in which a seed crystal is preheated above the melt surface to minimize the temperature difference between the two, and then the seed crystal is placed in the melt, in order to prevent dislocations in the seed crystal due to thermal shock during the contact. Patent Document 2 also describes a method for accurately measuring the distance between the source material melt surface and the seed crystal. The method obtains positional information for the real image lower end point, which is a specific point at the bottom of the seed crystal, and positional information for the mirror image point, which is a point on the seed crystal's mirror image reflected on the melt surface that corresponds to the real image lower end point. The distance between the source material melt surface and the bottom end of the seed crystal is determined by determining the distance between the source material melt surface and the bottom end of the seed crystal as zero at the point where the real image lower end point and the mirror image point coincide. Patent Documents 1, 3, and 4 also describe the use of a seed crystal with a tapered tip to prevent dislocations from occurring due to thermal shock during the contact.

[0005] Patent Document 5 describes a method for reducing variation in the preheating position of the seed crystal and improving the dislocation-free landing rate of the seed crystal, in which an image including a real image of the seed crystal and a mirror image of the seed crystal reflected on the melt surface is captured from obliquely above with a camera, and the position of the lower end point of the real image, which is a point at the lower end of the straight body portion of the real image of the seed crystal on the image, and the position of the mirror image point, which is a point at the upper end of the straight body portion of the mirror image of the seed crystal corresponding to the lower end point of the real image, are determined, and the distance between the melt surface and the lower end of the straight body portion of the seed crystal is determined by assuming that the distance between the melt surface and the lower end of the straight body portion of the seed crystal becomes zero at the point where the position of the lower end point of the real image and the position of the mirror image point on the image coincide. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-170773 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-155729 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-128691 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-234889 [Patent Document 5] Japanese Patent Application Laid-Open No. 2019-214486 Summary of the Invention [Problem to be solved by the invention]

[0007] When controlling the preheating position of a seed crystal based on the height position of the seed crystal determined from the image captured by the camera, it is desirable to bring the seed crystal as close as possible to the melt surface without contacting the melt. However, since the camera captures the seed crystal and the melt surface from an obliquely upward angle, when a tapered seed crystal is used, the tip of the tapered shape is hidden behind the seed crystal, making it impossible to capture the tip of the tapered shape with the camera. Furthermore, since the tip of the tapered portion cannot be captured from the mirror image of the seed crystal reflected on the melt surface, it is also difficult to detect the position of the bottom end of the seed crystal from the mirror image of the seed crystal. Furthermore, since the tapered shape of the seed crystal is subject to processing variability, it is necessary to control the position of the seed crystal taking such processing variability into consideration.

[0008] Patent Document 5 describes a method for determining the distance from the tip of a tapered seed crystal to the melt surface. However, the accuracy of the calculation of the distance from the tip of the seed crystal to the melt surface is insufficient, and there is a need for a method for calculating the distance more accurately to further improve the dislocation-free melt landing rate of the seed crystal.

[0009] Therefore, an object of the present invention is to provide a method for producing a single crystal that can accurately measure the distance between the lower end of the seed crystal and the melt surface, even when a seed crystal having a tapered lower end is used, thereby reducing variation in the preheating position when preheating above the melt surface and improving the dislocation-free melt landing rate of the seed crystal. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, a method for producing a single crystal according to the present invention is a method for producing a single crystal by the Czochralski method, comprising the steps of: measuring a distance between a lower end of a seed crystal provided above a melt and a melt surface; lowering the seed crystal based on the distance so that the seed crystal is immersed in the melt; and pulling up the seed crystal while maintaining contact with the melt to grow a single crystal on the lower end of the seed crystal, wherein the step of measuring the distance between the lower end of the seed crystal and the melt surface comprises: photographing the seed crystal and the melt surface using a camera installed diagonally above the melt surface; generating a real image edge approximation circle by performing a circular approximation on a substantially arc-shaped edge pattern of a lower end of a real image of the seed crystal captured in the image captured by the camera; and generating a mirror image edge approximation circle by performing a circular approximation on a substantially arc-shaped edge pattern of an upper end of a mirror image of the seed crystal reflected on the melt surface; and calculating the distance between the lower end of the seed crystal and the melt surface from the distance from the center coordinates of the real image edge approximation circle to the center coordinates of the mirror image edge approximation circle.

[0011] According to the present invention, even if the lower end of the seed crystal has a tapered shape, the distance between the lower end of the seed crystal and the melt surface can be accurately determined, thereby reducing the variation in the preheating position when the seed crystal is preheated above the melt and improving the dislocation-free melt landing rate of the seed crystal.

[0012] In the method for producing a single crystal according to the present invention, it is preferable to convert the distance into a distance unit in real space by multiplying half the number of pixels from the center coordinates of the real image edge approximation circle to the center coordinates of the mirror image edge approximation circle by a conversion coefficient, thereby making it possible to accurately determine the distance in real space between the lower end of the seed crystal and the melt surface.

[0013] Preferably, the method for producing a single crystal according to the present invention further comprises a step of calculating the conversion factor from a change in pixel position of the seed crystal in the captured image when the position of the seed crystal is moved a certain distance in the vertical direction before measuring the distance between the lower end of the seed crystal and the melt surface, thereby enabling accurate calculation of the distance between the lower end of the seed crystal and the melt surface in real space.

[0014] In the method for producing a single crystal according to the present invention, the coordinates of the real image edge approximation circle and the mirror image edge approximation circle in the captured image may be projected and converted into coordinates in real space based on the installation angle and focal length of the camera, and then the distance between the lower end of the seed crystal and the melt surface may be calculated, thereby making it possible to calculate the distance between the lower end of the seed crystal and the melt surface without performing calibration in advance to obtain a conversion factor.

[0015] In the method for producing a single crystal according to the present invention, it is preferable to set a reference plane at the same height as the lower end of the seed crystal, project the real image edge approximation circle and the mirror image edge approximation circle onto the reference plane, and calculate the distance between the lower end of the seed crystal and the melt surface from the coordinates of the center of the real image edge approximation circle, the coordinates of the center of the mirror image edge approximation circle, and the coordinates of the center of the camera lens. This makes it possible to easily calculate the distance between the lower end of the seed crystal and the melt surface using the coordinates after the projective transformation.

[0016] In the present invention, the step of measuring the distance between the lower end of the seed crystal and the melt surface preferably includes determining the mirror image edge approximation circle from the captured image and then determining the real image edge approximation circle located above the mirror image edge approximation circle, thereby enabling efficient identification of the positions of the real image and mirror image of the seed crystal in the captured image.

[0017] In the present invention, the step of determining the mirror image edge approximation circle preferably includes the steps of: identifying an upper end position of the mirror image of the seed crystal from a brightness distribution in a first region preset in the captured image; setting a second region including the upper end position of the mirror image of the seed crystal and binarizing the second region to detect an edge pattern of a straight body portion of the mirror image of the seed crystal; and circularly approximating the edge pattern of the straight body portion of the mirror image; and the step of determining the real image edge approximation circle preferably includes the steps of: identifying a position where a brightness differential value exceeds a predetermined threshold when the first region is scanned upward from the center coordinate of the mirror image edge approximation circle as the lower end position of the real image of the seed crystal; setting a third region including the lower end position of the real image of the seed crystal and binarizing the third region to detect an edge pattern of the straight body portion of the real image of the seed crystal; and circularly approximating the edge pattern of the straight body portion of the real image. This allows the center coordinates of the real image edge approximation circle and the mirror image edge approximation circle in the captured image to be determined efficiently.

[0018] In the present invention, the step of measuring the distance between the lower end of the seed crystal and the melt surface preferably includes successively taking a plurality of images, including real and mirror images, of the seed crystal when the seed crystal is at the same height, and calculating the distance between the lower end of the seed crystal and the melt surface from an average value of values ​​obtained from each of the plurality of images, thereby improving the accuracy of measurement of the distance between the lower end of the seed crystal and the melt surface.

[0019] In the present invention, the seed crystal further has a tapered portion provided below the straight body portion, the lower end of the seed crystal being the lower end of the tapered portion, the taper angle of the tapered portion being greater than the installation angle of the camera, and the method further comprises a step of pre-measuring the length of the tapered portion before measuring the distance between the lower end of the seed crystal and the melt surface, and the step of measuring the distance between the lower end of the seed crystal and the melt surface preferably includes a step of subtracting the length of the tapered portion from the distance between the lower end of the straight body portion of the seed crystal and the melt surface. If the taper angle of the seed crystal is greater than the installation angle of the camera, the tip of the seed crystal cannot be photographed with the camera, and the position of the tip of the seed crystal cannot be directly determined from the photographed image. However, according to the present invention, the distance between the seed crystal and the melt surface can be accurately measured without photographing the tip of the seed crystal.

[0020] The method for producing a single crystal according to the present invention preferably further comprises the steps of: adjusting the height position of at least one of the seed crystal and the crucible supporting the melt so that the distance between the lower end of the seed crystal and the melt surface becomes a target value after measuring the distance between the lower end of the seed crystal and the melt surface and before immersing the seed crystal in the melt; and preheating the seed crystal while keeping it stationary at the target value. According to the present invention, when a seed crystal having a tapered tip is preheated above the melt surface, variation in the preheating position can be reduced, thereby improving the dislocation-free immersion rate of the seed crystal.

[0021] The present invention also provides a method for measuring a distance between a lower end of a seed crystal provided above a melt and a melt surface, the method comprising: photographing the seed crystal and the melt surface using a camera installed diagonally above the melt surface; generating a real image edge approximation circle by circularly approximating a substantially arc-shaped edge pattern at a lower end of a real image of the seed crystal captured in the image captured by the camera; and generating a mirror image edge approximation circle by circularly approximating a substantially arc-shaped edge pattern at an upper end of a mirror image of the seed crystal reflected on the melt surface; and calculating the distance between the lower end of the seed crystal and the melt surface from the number of pixels from the center coordinates of the real image edge approximation circle to the center coordinates of the mirror image edge approximation circle.

[0022] According to the present invention, even if the lower end of the seed crystal has a tapered shape, the distance between the lower end of the seed crystal and the melt surface can be accurately determined, thereby reducing the variation in the preheating position when the seed crystal is preheated above the melt and improving the dislocation-free melt landing rate of the seed crystal.

[0023] Furthermore, the method for preheating a seed crystal according to the present invention is characterized by comprising the steps of: measuring the distance between the lower end of the seed crystal and the melt surface by the above-described distance measurement method; adjusting the height position of at least one of the seed crystal and the crucible supporting the melt so that the distance becomes a target value; and preheating the seed crystal while keeping it stationary at the target value position.

[0024] According to the present invention, when a seed crystal having a tapered tip is preheated above the melt surface, the variation in the preheating position can be reduced, thereby improving the dislocation-free melting rate of the seed crystal.

[0025] Furthermore, a single crystal manufacturing apparatus according to the present invention includes a crucible for supporting a melt, a heater for heating the melt, a crystal pulling mechanism for raising and lowering a seed crystal placed above the melt, a camera for photographing the seed crystal and the melt surface from an obliquely upward direction, an image processing unit for processing the image captured by the camera, and a control unit for controlling the crystal pulling mechanism based on the processing results of the image processing unit, wherein the image processing unit generates a real image edge approximation circle by performing a circular approximation on a substantially arc-shaped edge pattern of a lower end of a real image of the seed crystal captured in the image captured by the camera, and generates a mirror image edge approximation circle by performing a circular approximation on a substantially arc-shaped edge pattern of an upper end of a mirror image of the seed crystal reflected on the melt surface, and calculates the distance between the lower end of the seed crystal and the melt surface from the number of pixels from the center coordinates of the real image edge approximation circle to the center coordinates of the mirror image edge approximation circle.

[0026] According to the present invention, even if the lower end of the seed crystal has a tapered shape, the distance between the lower end of the seed crystal and the melt surface can be accurately determined, thereby reducing the variation in the preheating position when the seed crystal is preheated above the melt and improving the dislocation-free melt landing rate of the seed crystal. [Effects of the Invention]

[0027] According to the present invention, a method for producing a single crystal can be provided that makes it possible to accurately determine the distance between the lower end of a seed crystal and the melt surface, even if the lower end of the seed crystal has a tapered shape. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a side cross-sectional view schematically showing the configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a flowchart showing the steps of manufacturing a silicon single crystal. [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 side cross-sectional view that schematically shows the arrangement of seed crystals in a single crystal manufacturing apparatus during a preheating step. [Figure 5] FIG. 5 is a diagram for explaining a method for measuring the distance between the lower end of the seed crystal and the melt surface, and is a schematic diagram showing the positional relationship between the real image and the mirror image of the seed crystal. [Figure 6] Figures 6(a) to (c) are diagrams for explaining the positional relationship between the seed crystal and the melt surface, where Figure 6(a) is a schematic diagram when the distance from the seed crystal to the melt surface is long, Figure 6(b) is a schematic diagram when the distance from the seed crystal to the melt surface is short, and Figure 6(c) is a graph showing the relationship between the height position of the seed crystal and the number of pixels between the real image and the mirror image. [Figure 7] 7(a) to 7(c) are diagrams for explaining how to obtain the number of pixels ND between the real image and the mirror image. [Figure 8] FIG. 8 is a flowchart for explaining in detail a method for detecting the real image center coordinates PR and the mirror image center coordinates PM of the seed crystal 5 in the captured image. [Figure 9] FIG. 9 is a schematic diagram for explaining a method for projecting and transforming two-dimensional coordinates of a captured image into coordinates in real space. [Figure 10]FIG. 10 is a schematic diagram for explaining a method for calculating the seed crystal-melt surface distance from the central coordinates of the circular peripheral edge patterns at the lower ends of the straight body portions of the real and mirror images of the seed crystal. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] FIG. 1 is a side cross-sectional view schematically showing the configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention.

[0031] 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 crucible driving mechanism 14 for rotating and raising and lowering the quartz crucible 11 via the heater 15; 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 wire 18 serving as a crystal pulling shaft 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 installed outside the chamber 10 for photographing the inside of the chamber 10 through the viewing window 10e; an image processing unit 21 for processing the images taken by the camera 20; and a control unit 22 for controlling each unit within the single crystal manufacturing apparatus 1.

[0032] 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 sight glass 10e is provided at the top of the main chamber 10a, and the growth status of the silicon single crystal 3 can be observed through the sight glass 10e.

[0033] The quartz crucible 11 is a container made of quartz 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, enveloping it 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 within the chamber 10.

[0034] 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 rotation mechanism and an elevation mechanism for the quartz crucible 11. The rotation and elevation operations of the quartz crucible 11 driven by the crucible drive mechanism 14 are controlled by a control unit 22.

[0035] 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.

[0036] 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.

[0037] The diameter of the opening 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 rim 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.

[0038] As the silicon single crystal 3 grows, the amount of melt in the quartz crucible 11 decreases, but by raising the quartz crucible 11 so that the distance (gap) between the melt surface 2a and the thermal shield 17 remains constant, temperature fluctuations in the silicon melt 2 are 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.

[0039] Above the quartz crucible 11 are provided a wire 18, which is the shaft 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. 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 a silicon single crystal 3 is being grown, suspended from the wire 18. 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. The crystal pulling speed is controlled by the control unit 22.

[0040] A camera 20 is installed outside the chamber 10. The camera 20 is, for example, a CCD camera, and takes images of the inside of the chamber 10 through a viewing window 10e formed in the chamber 10. The camera 20 is installed at a predetermined angle (preferably 20 to 30 degrees) with respect to the vertical direction, and the camera 20 has an optical axis that is tilted with respect to the pulling axis of the silicon single crystal 3. In other words, the camera 20 takes images of the circular opening of the thermal shield 17 and the upper surface area of ​​the quartz crucible 11, including the surface of the silicon melt 2, from obliquely above.

[0041] The camera 20 is connected to an image processing unit 21, which is connected to a control unit 22. 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 gap, which is the distance from the bottom of the thermal shield 17 to the melt surface 2a, from the position of the mirror image of the thermal shield 17 reflected on the melt surface in the captured image. The method for calculating the gap is not particularly limited. For example, a conversion formula obtained by linearly approximating the relationship between the position of the mirror image of the thermal shield 17 and the gap can be prepared in advance, and the position of the mirror image of the thermal shield can be substituted into this conversion formula during the crystal pulling process to determine the gap. Alternatively, the gap can be geometrically calculated from the positional relationship between the real image and mirror image of the thermal shield 17 captured in the captured image.

[0042] 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 crystal diameter is larger than the target diameter, the crystal pulling speed is increased, and if the measured crystal diameter is smaller than the target diameter, the crystal pulling speed is decreased. The control unit 22 also controls the movement amount of the quartz crucible 11 (crucible rising speed) based on the crystal length data of the silicon single crystal 3 obtained from the sensor of the crystal pulling mechanism 19 and the crystal diameter data obtained from the image captured by the camera 20.

[0043] Fig. 2 is a flowchart showing the steps of manufacturing the silicon single crystal 3. Fig. 3 is a schematic cross-sectional view showing the shape of the silicon single crystal ingot.

[0044] As shown in Figure 2, the manufacturing process for silicon single crystal 3 according to this embodiment includes a raw material melting process S11 in which silicon raw material in quartz crucible 11 is heated by heater 15 to produce silicon melt 2, a preheating process S12 in which a seed crystal attached to the tip of wire 18 is preheated before being immersed in the silicon melt, a immersion process S13 in which the seed crystal is lowered to immerse it in the silicon melt 2, and a crystal pulling 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.

[0045] The crystal pulling process (S14 to S17) involves the following steps, carried out in order: necking process S14, which forms a neck portion 3a in which the crystal diameter is narrowed to eliminate dislocations; shoulder portion growing process S15, which forms a shoulder portion 3b in which the crystal diameter gradually increases as the crystal grows; body portion growing process S16, which forms a body portion 3c in which the crystal diameter is maintained at a constant value; and tail portion growing process S17, which forms a tail portion 3d in which the crystal diameter gradually decreases as the crystal grows.

[0046] Thereafter, a cooling step S18 is carried out in which the silicon single crystal 3 is separated from the melt surface to promote cooling. 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.

[0047] FIG. 4 is a side cross-sectional view that schematically shows the arrangement of seed crystals in the single crystal manufacturing apparatus 1 during the preheating step S12.

[0048] As shown in Figure 4, the preheating step S12 is a step in which the seed crystal 5 is heated while remaining stationary above the melt surface 2a for a certain period of time. When the seed crystal 5 is placed in the melt at a temperature significantly different from that of the silicon melt 2, slip dislocations occur due to thermal shock. However, the preheating step S12 can suppress dislocations and improve the dislocation-free placement rate of the seed crystal. If the seed crystal 5 is placed far from the melt surface 2a in the preheating step S12, it will not be heated sufficiently, and the temperature difference between the seed crystal 5 and the silicon melt 2 cannot be reduced. Therefore, it is necessary to control the distance between the bottom end of the seed crystal 5 and the melt surface 2a to 5 mm or less. To achieve this, it is necessary to accurately measure the distance between the bottom end of the seed crystal 5 and the melt surface 2a.

[0049] FIG. 5 is a diagram for explaining a method for measuring the distance between the lower end of the seed crystal 5 and the melt surface 2a, and is a schematic diagram showing the positional relationship between a real image 5R and a mirror image 5M of the seed crystal 5.

[0050] As shown in FIG. 5, the seed crystal 5 according to this embodiment has a straight body portion 5a with a constant thickness and a tapered portion 5b extending downward from the lower end of the straight body portion 5a. The diameter of the straight body portion 5a is preferably 6 to 12 mm, and the length of the straight body portion 5a is preferably 30 to 80 mm. The length of the tapered portion 5b is preferably 5 to 10 mm. Such a seed crystal 5 is produced by cutting a cylindrical silicon single crystal rod to a predetermined length, performing a grinding process to sharpen the tip, and then performing an etching process to remove processing damage. The tapered shape may be a cone shape or a truncated cone shape with a flat tip.

[0051] The taper angle θ1 of the seed crystal 5 is larger than the installation angle θ0 of the camera 20. When the tip of the seed crystal 5 has such a tapered shape, the tip P0 of the seed crystal 5 (the lower end of the tapered portion 5b) is in the blind spot of the camera 20, and therefore the tip P0 of the seed crystal 5 cannot be captured by the camera 20. Therefore, the length L of the tapered portion 5b T is accurately measured in advance, and the distance L between the lower end P1 of the straight body portion 5a of the seed crystal 5 and the melt surface 2a, which can be photographed by the camera 20, is P1 After calculating this interval L P1 from the length L of the tapered portion 5b T By subtracting the distance L between the tip P0 of the seed crystal 5 and the melt surface 2a, S =L P1 -L T of demand.

[0052] Here, the distance L between the lower end P1 of the straight body portion 5a of the seed crystal 5 and the melt surface 2a is P1 is the distance L from the bottom end P1 of the straight body portion 5a of the real image 5R of the seed crystal 5 to the mirror image P2 of the bottom end P1 (the distance between the real image and the mirror image) D Therefore, the distance between the real image and the mirror image, L D By calculating the distance L between the tip P0 of the seed crystal 5 and the melt surface 2a, S can be obtained.

[0053] Length L of tapered portion 5b TIt is desirable to measure the length of the tapered portion 5b accurately, for example, by a non-contact measurement method. When measuring the length of the tapered portion 5b in advance, it is preferable to measure the length of the tapered portion 5b at multiple points in the circumferential direction and use the average value of the multiple measurements. This is because, depending on the processing accuracy of the tapered portion 5b, the length of the tapered portion 5b may vary depending on the circumferential position of the tapered portion 5b.

[0054] Details will be described later, but the distance between the real image and the mirror image in real space, L D is the distance between the real image and the mirror image L D The number of pixels in the captured image corresponding to the number of pixels between the real image and the mirror image (N D ) by a predetermined conversion coefficient α. D are the center coordinates of the circular outer edge of the lower end of the straight body portion 5a of the real image 5R of the seed crystal 5 (the real image center coordinates P R (X R ,Y R )) to the central coordinates of the circular outer peripheral edge of the upper end of the straight body portion 5a of the mirror image 5M of the seed crystal 5 (mirror image central coordinates P M (X M ,Y M )) can be calculated as the number of pixels up to

[0055] The conversion coefficient α can be obtained by a calibration operation that determines a relational expression between the relative movement amount (millimeters) in real space when the seed crystal 5 is moved a certain distance in the vertical direction and the relative movement amount (number of pixels) on the captured image. In the calibration, first, while moving the seed crystal 5 in the vertical direction, images including the seed crystal 5 and the melt surface 2 a are captured by the camera 20 at multiple height positions of the seed crystal 5. The multiple height positions of the seed crystal 5 need only be relative height positions rather than absolute height positions. Therefore, multiple height positions of the seed crystal 5 relative to the melt surface 2 a may be set by fixing the height position of the seed crystal 5 and changing the height position of the melt surface 2 a (height position of the crucible).

[0056] Figures 6(a) to (c) are diagrams for explaining the positional relationship between the seed crystal and the melt surface, where Figure 6(a) is a schematic diagram when the distance from the seed crystal to the melt surface is long, Figure 6(b) is a schematic diagram when the distance from the seed crystal to the melt surface is short, and Figure 6(c) is a graph showing the relationship between the height position of the seed crystal and the number of pixels between the real image and the mirror image.

[0057] 6(a) and (b), the real image 5R and the mirror image 5M of the seed crystal 5 are symmetrical with respect to the melt surface 2a, and this relationship does not change even if the seed crystal 5 is moved vertically. For example, when the seed crystal 5 is lowered from the first height position h1 to the second height position h2, the amount of descent (amount of wire feed) Δh=h1-h2 (mm), and the number of pixels between the real image and the mirror image is N. D1 From N D2 (N D1 >N D2 ), the ratio of the change in the number of pixels to the wire feed amount Δh is ΔN D / Δh=(N D1 -N D2 ) / (h1-h2), and this ΔN D By using / Δh as the conversion coefficient α, the change in the height position of the seed crystal 5 in the captured image can be converted into the change in the height position of the seed crystal 5 in real space. As shown in FIG. 6(c), the conversion coefficient α is calculated by dividing the number of height positions h of the seed crystal 5 and the corresponding number of pixels N between the real image and the mirror image by D It can be calculated as the slope of the linear regression line (y=αx+β) that shows the relationship between

[0058] Distance between real and mirror images L D It is preferable to use the average value of multiple values ​​obtained from multiple images taken continuously of the seed crystal 5 at the same height. The continuous photographing period is several hundred ms. This reduces measurement errors due to fluctuations in the measurement environment and improves measurement accuracy.

[0059] 7(a) to (c) show the number of pixels between the real image and the mirror image, N D FIG. 10 is a diagram for explaining how to obtain

[0060] As shown in Figure 7(a) to (c), the distance between the real image and the mirror image, L D is the number of pixels between the real image and the mirror image, N D The number of pixels between the real image and the mirror image, N D is the coordinates P of the center of the real image of the seed crystal 5 in the photographed image. R From the mirror image center coordinate P M The coordinates of the center of the real image of the seed crystal 5, P R and the mirror image center coordinate P M The captured image is subjected to binarization processing to detect the approximately arc-shaped edge patterns of the straight body portion 5a of each of the real image 5R and the mirror image 5M of the seed crystal 5, and the center coordinates of the approximate circle when the edge patterns are approximated to a circle can be obtained.

[0061] The distance L between the real image and the mirror image from the lower end surface of the straight body portion 5a of the real image 5R of the seed crystal 5 to the upper end surface of the straight body portion 5a of the mirror image 5M of the seed crystal 5 D As a method for determining the distance between the real image and the mirror image, L is the distance from the bottom of the edge pattern of the straight body portion 5a of the real image 5R of the seed crystal 5 in the photographed image to the bottom of the edge pattern of the straight body portion 5a of the mirror image 5M of the seed crystal 5. D However, this method is prone to large measurement errors due to the influence of eccentric rotation caused by changes in the brightness distribution in the captured image and deviations in the mounting position or inclination of the seed crystal 5. On the other hand, as in this embodiment, the coordinates of the centers of the approximation circles of the edge patterns of the straight body portion 5a of the real image 5R and the mirror image 5M obtained from the captured images are calculated, and the distance between the coordinates of the centers of the two points is defined as the real image-mirror image distance L D In this case, it is less susceptible to changes in brightness distribution and eccentric rotation of the seed crystal, and the real image-mirror distance L D This can reduce measurement errors.

[0062] FIG. 8 shows the coordinates P of the center of the real image of the seed crystal 5 in the photographed image. R and the mirror image center coordinate P M 10 is a flowchart for explaining in detail a method for detecting the

[0063] As shown in FIG. 8, in this embodiment, after a first region including the real image 5R and the mirror image 5M of the seed crystal 5 is cut out from the image captured by the camera 20 (step S20), the mirror image center coordinates P M (X M ,Y M ) is calculated (steps S21 to S24), and then the real image center coordinates P R (X R ,Y R ) is calculated (steps S25 to S28). The reason for cutting out the first region from the image captured by the camera 20 is that the image captured by the camera 20 captures a wide range of the furnace interior, and the region in which the seed crystal 5 is captured is only a small part of the captured image, so that the target range for image processing is limited. In addition, the mirror image center coordinates P M The reason why is determined first is that the brightness of the mirror image 5M of the seed crystal 5 in the photographed image is higher than the brightness of the real image 5R, making it easier to identify its position.

[0064] Mirror image center coordinate P of seed crystal 5 M In the detection (steps S21 to S24), a brightness level of, for example, 99.9% of the brightness peak value in the first region is set as the threshold for mirror image detection, and this threshold is used to identify the upper end position of the mirror image 5M at the position of the uppermost white pixel obtained when the first region is binarized (step S21).

[0065] Next, using the upper end position of the pixel recognized as the mirror image 5M as a reference, an image within a certain range below that (for example, 50 vertical pixels × 100 horizontal pixels) is set as a detailed detection range (second region) of the mirror image 5M (step S22), and a brightness level of, for example, 99% of the brightness peak value within the second region is set as a threshold for edge detection. Then, using this threshold, the image within the second region is binarized, and the position of the black-white boundary of the binary image is determined as the edge of the straight body portion 5a of the mirror image 5M of the seed crystal 5 (step S23). Thereafter, the approximately arc-shaped edge pattern is circularly approximated by the least squares method, and the mirror image center coordinates P, which are the center coordinates of the mirror image edge approximation circle, are determined. M is calculated (step S24).

[0066] Next, the real image center coordinates P RIn the detection, a detailed detection range (third region) of the real image 5R is obtained from a first region, which is a rough detection range of the real image 5R and the mirror image 5M of the seed crystal 5. Since it is known that the real image 5R of the seed crystal 5 exists above the mirror image 5M, the mirror image center coordinate P M The first region is scanned upward from the reference position, and the position where the differential value of the brightness level exceeds a predetermined threshold is determined to be the lower end position of the real image 5R (step S25). The bottom end position of the real image 5R detected in this way is used as the reference position, and an image within a certain range (for example, 50 pixels vertically × 100 pixels horizontally) above it is scanned. Third area (step S26). Third A brightness level of, for example, 99% of the brightness peak value in the region is set as a threshold value for edge detection. Then, the image in the third region is binarized using this threshold value, and the position of the black-white boundary of the binary image is determined as the edge of the straight body portion 5a of the real image 5R of the seed crystal 5 (step S27). Thereafter, the approximately arc-shaped edge pattern is circularly approximated by the least squares method, and the real image center coordinates P R is calculated (step S28).

[0067] If the bottom end of the seed crystal 5 is close to the melt surface 2a and the bottom end of the real image 5R of the seed crystal 5 overlaps with the top end of the mirror image 5M, the mirror image 5M of the seed crystal 5 becomes noise in the real image 5R, making it difficult to separate the real image 5R from the mirror image 5M. In such a case, by performing an opening process (expansion / contraction process) on the binary image, it is possible to separate the mirror image 5M from the real image 5R and identify the edges of the real image 5R.

[0068] Thus, the real image center coordinates P R and the mirror image center coordinate P M After calculating each of these, the number of pixels between the two points, N D The distance between the real image and the mirror image of the seed crystal 5, L D can be obtained.

[0069] In the preheating step S12 of the seed crystal 5, the distance L between the melt surface 2a and the seed crystal 5 is increased by the above-mentioned method. SAfter measuring the actual distance L between the melt surface 2a and the seed crystal 5, the seed crystal 5 is moved in a direction that reduces the difference between the actual measurement value and the target value. That is, the control unit 22 adjusts the height of the seed crystal 5 by operating the crystal pulling mechanism 19 or adjusts the height of the quartz crucible 11 by operating the crucible driving mechanism 14 so as to eliminate the difference between the actual measurement value and the target value. As a result, the actual distance L between the melt surface 2a and the seed crystal 5 is reduced. S can be set to the target interval.

[0070] The distance (target value) between the melt surface 2a and the lower end of the seed crystal 5 in the preheating step S12 of the seed crystal 5 is preferably 5 mm or less, and particularly preferably 3 mm or less. This sufficiently reduces the temperature difference between the seed crystal and the melt, thereby improving the dislocation-free liquid contact rate of the seed crystal. On the other hand, the initial distance between the melt surface 2a and the seed crystal 5 before measuring the distance between the melt surface 2a and the lower end of the seed crystal 5 is preferably 5 mm or more. This is because there is a risk that the seed crystal 5 will contact the melt if the seed crystal 5 is brought too close to the melt surface 2a without accurately knowing the distance between the melt surface 2a and the seed crystal 5.

[0071] In the preheating step S12 of the seed crystal 5, the seed crystal 5 is maintained in proximity to the melt surface 2a for, for example, several minutes to several hours. As a result, the seed crystal 5 is heated by radiant heat from the silicon melt 2. By preheating the seed crystal 5 at a predetermined position above the melt surface 2a each time, the reproducibility of the temperature of the seed crystal 5 after preheating can be increased. Furthermore, by setting the target distance to a sufficiently small value, the temperature difference between the two can be sufficiently reduced, thereby reducing the thermal shock when the seed crystal 5 is immersed in the melt. Therefore, the introduction of dislocations into the seed crystal 5 can be suppressed.

[0072] Furthermore, in a conventional method in which an operator visually adjusts the distance between the melt surface 2 a and the lower end of the seed crystal 5 when preheating the seed crystal 5, if the target distance is set to a very small value, such as 3 mm, the seed crystal 5 may unintentionally come into contact with the silicon melt 2. However, by accurately measuring the distance between the melt surface 2 a and the lower end of the seed crystal 5 as in the present embodiment, it is possible to avoid contact between the seed crystal 5 and the melt surface 2 a.

[0073] After the seed crystal 5 is preheated in this manner, the seed crystal 5 is lowered to be immersed in the silicon melt 2, and then the seed crystal 5 is raised to grow the silicon single crystal 3.

[0074] As described above, in the method for producing a single crystal according to this embodiment, the edge patterns of the real image and mirror image of the seed crystal 5 are approximated as circles, and the center coordinates P R and the center coordinate P of the mirror image edge approximation circle M The distance between the real image and the mirror image of the seed crystal 5 is L D is obtained, the distance between the lower end of the seed crystal 5 and the melt surface 2a can be accurately obtained even when the seed crystal 5 has a tapered portion 5b.

[0075] Next, another method for measuring the distance between the lower end of the seed crystal 5 and the melt surface 2a will be described. The above-described seed crystal-to-liquid surface distance measurement method requires calibration to convert the distance between the real image and mirror image of the seed crystal in the image into the distance between the real image and mirror image of the seed crystal in real space, and for this purpose, calibration is required to determine the conversion coefficient α.

[0076] Therefore, in this embodiment, the seed crystal-melt surface interval is calculated directly without calibration by projecting coordinate points in a captured image of the furnace interior captured by a camera onto coordinates in real space. Specifically, an image of the melt surface 2 a in the furnace is captured, and the coordinates of the real image of the seed crystal 5 in the captured image and the mirror image of the seed crystal 5 reflected on the melt surface 2 a are detected. The coordinates of each of the real image and mirror image of the seed crystal 5 are projected onto coordinates in real space, and the interval ΔG between the seed crystal and the melt surface is calculated from the real space coordinates of each of the real image and mirror image of the seed crystal. A method for projecting and converting the two-dimensional coordinates of the captured image onto coordinates in real space will be described in detail below.

[0077] FIG. 9 is a schematic diagram for explaining a method for projecting and transforming two-dimensional coordinates of a captured image into coordinates in real space.

[0078] As shown in the left diagram of Figure 9, the camera 20 photographs the inside of the chamber from diagonally above, and therefore the circular outer periphery of the lower end of the straight body part of the seed crystal 5 in the photographed image is distorted. In order to accurately calculate the dimensions of the real image and the mirror image of the seed crystal 5, it is necessary to correct the distortion of the image. Therefore, the coordinates of the image photographed by the camera 20 are projected onto coordinates on a reference plane set at the same height as the lower end of the straight body part of the seed crystal 5 to correct the distortion.

[0079] The diagram on the right side of FIG. 9 shows a coordinate system for performing image correction. In this coordinate system, the reference plane is the xy plane. The origin C0 of the XY coordinates is the distance from the center position C of the imaging device 20a of the camera 20 to the center position F(0, y f ,z f ) and the reference plane. This line is the optical axis of the camera 20.

[0080] The direction of pulling up the silicon single crystal 3 is the positive direction of the z axis, and the center position C(0, y c ,z c ) and the center position F(0, y f ,z f ) is in the yz plane. The coordinates (u, v) in the image shown in the left diagram of FIG. 9 are expressed by the pixels of the imaging device 20a, and an arbitrary point P(x p ,y p ,z p ) is supported.

[0081]

number

[0082] where α u and α v are the pixel sizes of the imaging device 20a in the horizontal and vertical directions, and y c and z c are the y and z coordinates of the center position C of the imaging device 20a. Also, as shown in the right diagram of FIG. cis the angle that the optical axis of the camera 20 makes with the z-axis, and is the installation angle of the camera 20.

[0083] The coordinate origin C0 on the reference plane is used to determine the center position C(0, y c ,z c ) is the distance L c When y c ,z c are expressed as the following equation (2):

[0084]

number

[0085] When the distance from the coordinate origin C0 to the center position F of the lens 20b of the camera 20 is a and the distance from the center position F of the lens 20b to the center position C of the imaging device 20a is b, the distance L from the coordinate origin C0 to the center position C of the imaging device 20a is c is expressed as the following equation (3).

[0086]

number

[0087] Also, from the lens imaging formula, the focal length f l is expressed as the following equation (4) using the distances a and b.

[0088]

number

[0089] Eliminate the distance L2 from equations (3) and (4) and obtain L c The distance L1 and the focal length f l This can be expressed as the following equation (5): of It becomes like this.

[0090]

number

[0091] The value of the distance L1 from the coordinate origin C0 to the center position F of the lens 20b of the camera 20 is the center position F(0, y f ,z f ) can be expressed as the following equation (6).

[0092]

number

[0093] Therefore, the above formula (2) is expressed as the center position F(0, y f ,z f ) and the focal length f of lens 20b l Using this, it is expressed by the following equation (7).

[0094]

number

[0095] When the lens 20b is considered as a pinhole, an arbitrary point P on the imaging device 20a (x p ,y p ,z p ) is F(0,y f ,z f ) onto the reference plane, and this projection point P'(X, Y, 0) can be expressed by the following equation (8).

[0096]

number

[0097] Therefore, by using equations (1), (7) and (8), the coordinates of the real image and mirror image of the seed crystal projected onto the reference plane can be obtained.

[0098] Next, we will explain how to calculate the center coordinates and radius of the circular peripheral edge pattern at the bottom end of the straight body portion of the seed crystal. The least squares method can be used to calculate the coordinates (x0, y0) of the center of the seed crystal and the radius r from the coordinates of the real image and mirror image projected onto the reference plane. The shape of the peripheral edge at the bottom end of the straight body portion of the seed crystal is circular, and the image of the peripheral edge satisfies the equation of a circle shown in the following formula (9).

[0099]

number

[0100] Here, the least squares method is used to calculate (x0, y0) and r in equation (9). To simplify the calculation using the least squares method, the following transformation shown in equation (10) is performed.

[0101]

number

[0102] The variables a, b, and c in equation (10) are found using the least squares method, which involves finding the condition where the sum of squares of the difference between equation (10) and the measured points is minimized, and this can be obtained by solving the partial differential equation shown in equation (11) below.

[0103]

number

[0104] The solution of this equation (11) can be calculated using the simultaneous equations shown in the following equation (12).

[0105]

number

[0106] By using the least squares method in this manner, the center coordinates and radii of the circular outer edges at the bottom ends of the straight body portions of the real image 5R and mirror image 5M of the seed crystal projected onto the reference plane can be calculated.

[0107] FIG. 10 is a schematic diagram for explaining a method for calculating the seed crystal-melt surface distance ΔG from the central coordinates of the circular outer peripheral edge patterns at the lower ends of the straight body portions of the real image 5R and the mirror image 5M of the seed crystal 5.

[0108] As shown in FIG. 10, the center coordinate C m is originally the melt surface 2a The center coordinate C of the lower end of the straight body portion 5a of the real image 5R of the seed crystal 5 is h (X hc ,Y hc ,0) and the line connecting these two points is C h (X hc ,Y hc ,0) and is a straight line parallel to the Z axis.

[0109] On the other hand, the center coordinate C of the lower end of the straight body part of the mirror image 5M of the seed crystal 5 on the reference plane m '(X mc ,Y mc , 0) is the center coordinate C of the lower end of the straight body part of the real image 5R of the seed crystal 5 h (X hc ,Y hc , 0) are the coordinates projected onto the reference plane, so the center coordinates (X mc ,Y mc ,Z gap ) are the coordinates (X mc ,Y mc , 0) and the center position F(0, y f ,z f ) on the straight line passing through the seed crystal. Therefore, the seed crystal-liquid surface distance ΔG that we want to calculate is Z gap and can be calculated using the following formula (13).

[0110]

number

[0111] In this way, the seed crystal-liquid surface distance ΔG is determined by the center coordinate C of the real image of the seed crystal 5 on the reference plane. h (X hc ,Y hc , 0), the center coordinates C of the mirror image of the seed crystal 5 on the reference plane m '(X mc ,Y mc , 0) and the center coordinates F(0, y f ,z f ) can be obtained. In this embodiment, the reference plane for projection transformation is set at the same height as the lower end of the straight body portion 5a of the seed crystal 5, but it can also be set at another height position. Therefore, for example, the reference plane may be set at the same height as the opening edge of the lower end of the thermal shield 17.

[0112] 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.

[0113] For example, in the above embodiment, the real image edge is obtained after the mirror image edge is obtained, but it is also possible to obtain the mirror image edge after the real image edge is obtained.

[0114] In the above embodiment, the case where the tip of the seed crystal 5 has a tapered shape has been exemplified, but the present invention can also be applied to the case where the seed crystal 5 consists of only the straight body portion 5a. R From the mirror image center coordinate P M Number of pixels up to N D Based on this, the distance L between the lower end of the seed crystal 5 and the melt surface 2a S can be accurately measured.

[0115] Furthermore, in the above embodiment, a method for producing a silicon single crystal has been taken as an example, but the present invention can also be applied to methods for producing various single crystals that can be pulled by the CZ method, such as germanium and sapphire. [Explanation of symbols]

[0116] 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 5 seed crystals 5M mirror image 5R Real Image 5a Straight body part 5b Tapered section 10 chambers 10a Main Chamber 10b Pull chamber 10c Gas inlet 10d Gas outlet 10e Sight glass 11 Quartz crucible 12 Graphite crucible 13 Rotating shaft 14 Crucible drive mechanism 15 Heater 16. Insulation 17 Heat shield 18 wires 19 Crystal pulling mechanism 20 Camera 21 Image processing section 22 Control Unit L D Distance between real and mirror images L P1 Distance between the bottom end of the seed crystal's body and the melt surface L S Distance between the bottom of the seed crystal and the melt surface N D Number of pixels between real and mirror images Tip of P0 seed crystal The bottom end of the straight body of the P1 seed crystal Mirror image of the bottom end of the P2 seed crystal's straight body P M mirror image center coordinates P R Real image center coordinates S11 Raw material melting process S12 Preheating process S13 Liquid application process S14 Necking process S15 Shoulder part development process S16 Body development process S17 Tail section growing process S18 Cooling process S20 First region extraction step S21 Mirror image position detection step S22 Second region extraction step S23 Second region binarization step S24 Mirror image center coordinate calculation step S25 Real image position detection step S26 Third region extraction step S27 Third region binarization step S28 Real image center coordinate calculation step h, h1, h2 Height position of seed crystal Δh Seed crystal feed rate α Conversion factor θ,θ0 camera installation angle θ1 taper angle

Claims

1. A method for producing a single crystal by the Czochralski method, comprising the steps of: measuring the distance between the bottom end of a seed crystal provided above the melt and the melt surface; a step of lowering the seed crystal based on the interval to make it contact the melt; and pulling up the seed crystal while maintaining contact with the melt to grow a single crystal at the bottom end of the seed crystal, The step of measuring the distance between the lower end of the seed crystal and the melt surface includes: taking an image of the seed crystal and the melt surface using a camera installed obliquely above the melt surface; generating a real image edge approximation circle by performing a circular approximation on a substantially arc-shaped edge pattern at a lower end of a real image of the seed crystal captured in the image captured by the camera, and generating a mirror image edge approximation circle by performing a circular approximation on a substantially arc-shaped edge pattern at an upper end of a mirror image of the seed crystal reflected on the melt surface; converting the distance into a distance unit in real space by multiplying half the number of pixels from the center coordinates of the real image edge approximation circle to the center coordinates of the mirror image edge approximation circle by a conversion coefficient; A method for producing a single crystal, comprising: calculating the distance between the lower end of the seed crystal and the melt surface from the distance from the center coordinates of the real image edge approximation circle to the center coordinates of the mirror image edge approximation circle.

2. 2. The method for producing a single crystal according to claim 1, further comprising: a step of calculating the conversion coefficient from an amount of change in a pixel position of the seed crystal in the captured image when the position of the seed crystal is moved a certain distance in an up-down direction, before measuring the distance between the lower end of the seed crystal and the melt surface.

3. 3. The method for producing a single crystal according to claim 1, wherein the step of measuring the distance between the lower end of the seed crystal and the melt surface comprises determining the mirror image edge approximation circle from the captured image, and then determining the real image edge approximation circle located above the mirror image edge approximation circle.

4. The step of obtaining the mirror image edge approximation circle includes: identifying an upper end position of the mirror image of the seed crystal from a brightness distribution of a first region set in advance in the captured image; setting a second region including an upper end position of the mirror image of the seed crystal, and performing binarization processing on the second region to detect an edge pattern of a straight body portion of the mirror image of the seed crystal; a step of approximating the edge pattern of the straight body portion of the mirror image to a circle; The step of obtaining a real image edge approximation circle includes: a step of identifying a position where a differential value of brightness exceeds a predetermined threshold when scanning the first region upward from the center coordinate of the mirror image edge approximation circle as a lower end position of the real image of the seed crystal; setting a third region including a lower end position of the real image of the seed crystal, and performing binarization processing on the third region to detect an edge pattern of a straight body portion of the real image of the seed crystal; The method for producing a single crystal according to claim 3 , further comprising a step of circularly approximating the edge pattern of the straight body portion of the real image.

5. The step of measuring the distance between the lower end of the seed crystal and the melt surface includes:

5. The method for producing a single crystal according to claim 1, wherein a plurality of images including a real image and a mirror image of the seed crystal are continuously taken when the seed crystal is at the same height position, and the distance between the lower end of the seed crystal and the melt surface is calculated from an average value of values ​​obtained from each of the plurality of images.

6. the seed crystal further has a tapered portion provided below the straight body portion, a lower end of the seed crystal is a lower end of the tapered portion, a taper angle of the tapered portion is greater than an installation angle of the camera; the installation angle of the camera is the angle of the optical axis of the camera inclined with respect to the pulling axis of the single crystal; a step of measuring a length of the tapered portion in advance before measuring a distance between the lower end of the seed crystal and the melt surface; 5. The method for producing a single crystal according to claim 4, wherein the step of measuring the distance between the lower end of the seed crystal and the melt surface includes a step of subtracting the length of the tapered portion from the distance between the lower end of a straight body portion of the seed crystal and the melt surface.

7. a step of adjusting a height position of at least one of the seed crystal and a crucible supporting the melt so that the distance between the lower end of the seed crystal and the melt surface becomes a target value after measuring the distance between the lower end of the seed crystal and the melt surface and before immersing the seed crystal in the melt; The method for producing a single crystal according to claim 1 , further comprising the step of preheating the seed crystal while keeping it stationary at the target position.

8. A method for producing a single crystal by the Czochralski method, comprising the steps of: measuring the distance between the bottom end of a seed crystal provided above the melt and the melt surface; a step of lowering the seed crystal based on the interval to make it contact the melt; and pulling up the seed crystal while maintaining contact with the melt to grow a single crystal at the bottom end of the seed crystal, The step of measuring the distance between the lower end of the seed crystal and the melt surface includes: taking an image of the seed crystal and the melt surface using a camera installed obliquely above the melt surface; generating a real image edge approximation circle by performing a circular approximation on a substantially arc-shaped edge pattern at a lower end of a real image of the seed crystal captured in the image captured by the camera, and generating a mirror image edge approximation circle by performing a circular approximation on a substantially arc-shaped edge pattern at an upper end of a mirror image of the seed crystal reflected on the melt surface; calculating a distance between the lower end of the seed crystal and the melt surface from a distance from a center coordinate of the real image edge approximation circle to a center coordinate of the mirror image edge approximation circle; The step of measuring the distance between the lower end of the seed crystal and the melt surface further includes: a method for producing a single crystal, comprising: successively taking a plurality of images, each including a real image and a mirror image, of the seed crystal when the seed crystal is at the same height; and calculating a distance between the lower end of the seed crystal and the melt surface from an average value of values ​​obtained from each of the plurality of images.

9. the seed crystal has a straight body portion and a tapered portion provided below the straight body portion, a lower end of the seed crystal is a lower end of the tapered portion, a taper angle of the tapered portion is greater than an installation angle of the camera; the installation angle of the camera is the angle of the optical axis of the camera inclined with respect to the pulling axis of the single crystal; a step of measuring a length of the tapered portion in advance before measuring a distance between the lower end of the seed crystal and the melt surface; 9. The method for producing a single crystal according to claim 8, wherein the step of measuring the distance between the lower end of the seed crystal and the melt surface includes a step of subtracting the length of the tapered portion from the distance between the lower end of a straight body portion of the seed crystal and the melt surface.

Images