Method for manufacturing single crystal and single crystal manufacturing apparatus

Abstract

To provide a single crystal manufacturing method and apparatus capable of stably measuring a liquid level regardless of a furnace structure.SOLUTION: This invention provides a single crystal manufacturing method by the Chokralski method of lifting a single crystal from a melt in a crucible, in which a thermal shield covering over a crucible except a route of lifting a single crystal is arranged, a real image 17R of the thermal shield and a mirror image 17M of the thermal shield reflected on a melt surface 2a are taken by a first camera, a detection line L1 that extends in a direction orthogonal to a single crystal lifting axis and crosses both of a real image edge ER and a mirror image edge EM of the thermal shield is set, and a gap value that is a distance in the detection line L1 between a real image-mirror image distance D and a lower edge of the thermal shield and a melt surface 2a, which is equivalent to a distance from a first crossing point P1 between the detection line L1 and the real image edge ER to a second crossing point P2 between the detection line L1 and the mirror image edge EM is calculated.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a single crystal and a single crystal manufacturing apparatus, and particularly to a method for measuring the liquid level of a melt during the pulling process of a single crystal by the Czochralski method (CZ method).

Background Art

[0002] The CZ method is known as a method for manufacturing a silicon single crystal for semiconductor devices. In the CZ method, a polycrystalline silicon raw material in a quartz crucible is heated and melted, and a seed crystal immersed in the obtained silicon melt is gradually pulled up while being relatively rotated, thereby growing a large single crystal at the lower end of the seed crystal. According to the CZ method, it is possible to manufacture a high-quality silicon single crystal with a high yield.

[0003] In the CZ method, precise measurement and control of the crystal diameter and the liquid level are performed to improve the yield and crystal quality of the single crystal. Regarding the method for measuring the crystal diameter and the liquid level, for example, Patent Document 1 describes a method of calculating the crystal diameter and the crystal center position from a high-luminance portion called a fusion ring generated at the solid-liquid interface, and calculating the liquid level from the crystal center position. Patent Document 2 describes a method of calculating the liquid level position of the silicon melt with respect to the heat shield from the distance between the real image including the circular opening of the heat shield and the mirror image of the heat shield reflected on the melt surface. Patent Document 3 describes a method of attaching a quartz rod above the melt surface and determining that the melt surface is at a reference position when the tip of the quartz rod contacts the melt surface. Patent Document 4 describes a method of measuring the crystal diameter and calculating the height position of the silicon melt surface using a plurality of cameras.

[0004] In addition, Patent Document 5 describes a method of suppressing the evaporation of dopants in a silicon melt by setting the inside of a chamber to a high-pressure state, installing a cylindrical furnace internal member called a purge tube above a heat shield, and rectifying the purge gas introduced into the pull-up furnace using the purge tube. Further, Patent Document 6 describes a method of expanding the PvPi margin and increasing the yield of defect-free crystals by installing a cylindrical cooling body above the heat shield and controlling the residence time of a silicon single crystal in a predetermined temperature range pulled up from the silicon melt.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0006] Normally, there is one camera for photographing inside the furnace, and the center of the width direction of the photographing range is set to the center of the single crystal so that the entire diameter direction of the single crystal is captured. That is, the camera axis is set in a plane including the crystal pulling axis. However, when furnace internal structures such as a purge tube or a water-cooled body are installed above the heat shield and the camera's field of view is blocked by the furnace internal structures, there is a problem that the real image and the mirror image of the heat shield cannot be photographed and the liquid level with respect to the heat shield cannot be measured.

[0007] Accordingly, an object of the present invention is to provide a method for manufacturing a single crystal and a single crystal manufacturing apparatus capable of stably measuring the liquid level regardless of the furnace internal structure.

Means for Solving the Problems

[0008] In order to solve the above problems, a method for manufacturing a single crystal according to the present invention is a method for manufacturing a single crystal by the Czochralski method of pulling a single crystal from a melt in a crucible, wherein a heat shield covering the upper part of the crucible excluding the pulling path of the single crystal is installed, the real image of the heat shield and the mirror image of the heat shield reflected on the liquid surface of the melt are photographed by a first camera, a detection line extending in an oblique direction that is neither parallel nor perpendicular to the pulling axis of the single crystal and intersecting both the real image edge and the mirror image edge of the heat shield is set, and a gap value, which is the distance between the lower end of the heat shield and the melt surface, is obtained from the distance (distance between the real image and the mirror image on the detection line) from the first intersection point of the detection line and the real image edge to the second intersection point of the detection line and the mirror image edge.

[0009] According to the present invention, it becomes possible to photograph the real image and the mirror image of the heat shield that could not be photographed hidden by the shielding object from the photographing direction of the diameter measuring camera heretofore. Therefore, the liquid level can be stably measured regardless of the structure inside or outside the furnace.

[0010] In the present invention, it is preferable that the camera axis of the first camera is not in the same plane as the pulling axis of the single crystal and has a torsional positional relationship. In this way, by shifting the center in the width direction of the photographing range of the first camera from the center of the single crystal, the real image and the mirror image of the heat shield can be photographed, and the setting of the detection line becomes easy. Further, the distance from the first intersection point of the detection line and the real image edge to the second intersection point of the detection line and the mirror image edge can be lengthened, and the gap value, which is the distance between the lower end of the heat shield and the melt surface, can be calculated more accurately.

[0011] The present invention preferably measures the diameter of the single crystal using a second camera prepared separately from the first camera. The camera axis of the second camera is preferably in the same plane as the pulling axis and in an intersecting positional relationship. In this way, by providing the first camera for gap measurement separately from the second camera for diameter measurement, the gap value, which is the distance between the lower end of the heat shield and the melt surface, can be stably measured.

[0012] The present invention preferably installs a substantially cylindrical shield that surrounds the pulling path above the lower end of the heat shield, and the field of view of the second camera is preferably blocked by the shield. When an in-furnace structure such as a purge tube is installed above the crucible separately from the heat shield, the real image and mirror image of the heat shield cannot be observed from the main camera for diameter measurement. However, by installing a camera at a position where the real image and mirror image of the heat shield can be observed without the field of view being blocked by the shield and taking pictures of the real image and mirror image of the heat shield, the gap value can be reliably measured. In this case, since the center in the width direction of the shooting range of the camera is shifted from the center of the single crystal, it is possible to observe the real image and mirror image of the heat shield through a slight gap between the lower end of the shield and the heat shield.

[0013] The present invention preferably creates in advance a conversion table or conversion formula showing the relationship between the gap value and the distance between the real image and the mirror image on the detection line when the crucible is lifted to arbitrarily change the liquid level of the melt before the start of crystal pulling, and during the crystal pulling process, calculates the gap value using the actually measured distance between the real image and the mirror image and the conversion table or the conversion formula. Thereby, the gap value can be accurately calculated.

[0014] The present invention preferably obtains a reference liquid level by observing the contact between the measurement pin installed above the melt and the melt surface, and creates the conversion table or the conversion formula based on the reference liquid level. Thereby, the gap value can be accurately calculated.

[0015] Further, the single crystal manufacturing apparatus according to the present invention includes a crucible that supports a melt, a crucible drive mechanism that drives the crucible to rotate and move up and down, a heater that heats the melt in the crucible, a cylindrical heat shield disposed above the crucible excluding the pulling-up path of the single crystal, a first camera that captures a real image of the heat shield and a mirror image of the heat shield reflected on the liquid surface of the melt, an image processing unit that processes the captured image of the first camera to obtain a gap value between the lower end of the heat shield and the melt surface, and a control unit that controls the liquid level of the melt based on the processing result of the captured image by the image processing unit. The image processing unit sets a detection line that extends in an oblique direction that is neither parallel nor perpendicular to the pulling axis of the single crystal and intersects both the real image edge and the mirror image edge of the heat shield in the captured image, and determines the gap value, which is the distance between the lower end of the heat shield and the melt surface, from the real image-mirror image distance on the detection line, which is the distance from the first intersection of the detection line and the real image edge to the second intersection of the detection line and the mirror image edge.

[0016] In the present invention, it is preferable that the camera axis of the first camera and the pulling axis of the single crystal are not in the same plane and are in a twisted positional relationship. In this way, by shifting the center in the width direction of the imaging range of the first camera from the center of the single crystal, the real image and the mirror image of the heat shield can be captured, and the setting of the detection line becomes easy. Further, the distance from the first intersection of the detection line and the real image edge to the second intersection of the detection line and the mirror image edge can be increased, and the gap value, which is the distance between the lower end of the heat shield and the melt surface, can be calculated more accurately.

[0017] The present invention further includes a second camera that captures a real image of the heat shield and a mirror image of the heat shield reflected on the liquid surface of the melt. The image processing unit preferably measures the diameter of the single crystal using the second camera.

[0018] In the present invention, the image processing unit preferably creates in advance a conversion table or conversion formula showing the relationship between the gap value when the crucible is lifted up and down before the start of crystal pulling to arbitrarily change the liquid level of the melt and the distance between the real image and the mirror image on the detection line, and during the crystal pulling process, calculates the gap value using the actually measured distance between the real image and the mirror image and the conversion table or the conversion formula.

[0019] It further includes a measurement pin installed above the melt, and the image processing unit preferably obtains a reference liquid level by observing the contact between the tip of the measurement pin and the melt surface, and creates the conversion table or the conversion formula based on the reference liquid level.

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a single crystal manufacturing method and a single crystal manufacturing apparatus capable of stably measuring the liquid level regardless of the furnace internal structure.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] 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.

[0024] As shown in FIG. 1, the single crystal manufacturing apparatus 1 includes a water-cooled chamber 10, a quartz crucible 11 that holds a silicon melt 2 in the chamber 10, a graphite crucible 12 that holds the quartz crucible 11, a rotating shaft 13 that supports the graphite crucible 12, a crucible drive mechanism 14 that rotates and vertically drives the quartz crucible 11 via the rotating shaft 13 and the graphite crucible 12, a heater 15 disposed around the graphite crucible 12, a heat insulating material 16 disposed outside the heater 15 and along the inner surface of the chamber 10, a heat shield 17 disposed above the quartz crucible 11, a pulling wire 18 disposed above the quartz crucible 11 and coaxial with the rotating shaft 13, a crystal pulling mechanism 19 disposed above the chamber 10, two cameras 20A and 20B for photographing the inside of the chamber 10, an image processing unit 21 for processing the photographed images of the cameras 20A and 20B, and a control unit 22 for controlling each part of the single crystal manufacturing apparatus 1.

[0025] The chamber 10 is composed of a main chamber 10a and an elongated cylindrical pull chamber 10b connected to the upper opening of the main chamber 10a. The quartz crucible 11, the graphite crucible 12, the heater 15, and the heat shield 17 are provided in 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 or a dopant gas into the chamber 10, and a gas outlet 10d for discharging the atmospheric gas in the chamber 10 is provided at the lower part of the main chamber 10a. Further, a first viewing window 10e 1 and a second viewing window 10e 2 are provided, and the growth state of the silicon single crystal 3 can be observed.

[0026] The quartz crucible 11 is a container made of quartz glass having a cylindrical side wall portion and a curved bottom portion. The graphite crucible 12 is held so as to be in close contact with the outer surface of the quartz crucible 11 and wrap the quartz crucible 11 in order to maintain the shape of the quartz crucible 11 softened by heating. The quartz crucible 11 and the graphite crucible 12 constitute a double-structured crucible that supports the silicon melt 2 in the chamber 10.

[0027] The graphite crucible 12 is fixed to the upper end portion of the rotary shaft 13, and the lower end portion of the rotary shaft 13 penetrates the bottom portion of the chamber 10 and is connected to a crucible drive mechanism 14 provided outside the chamber 10. The graphite crucible 12, the rotary shaft 13, and the crucible drive mechanism 14 constitute a rotation mechanism and a lifting mechanism for the quartz crucible 11. The rotation and lifting operations of the quartz crucible 11 driven by the crucible drive mechanism 14 are controlled by the control unit 22.

[0028] 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 molten state of the silicon melt 2. The heater 15 is a carbon resistance heater and is provided so as to surround the quartz crucible 11 inside the graphite crucible 12. Further, a heat insulating material 16 is provided outside the heater 15 so as to surround the heater 15, thereby enhancing the heat retention property inside the chamber 10. The output of the heater 15 is controlled by the control unit 22.

[0029] The heat shield 17 is provided to suppress temperature fluctuations of the silicon melt 2 and give an appropriate heat distribution near the crystal growth interface, and to prevent heating of the silicon single crystal 3 by radiant heat from the heater 15 and the quartz crucible 11. The heat shield 17 is a substantially cylindrical member made of graphite and is provided so as to cover the region above the silicon melt 2 excluding the pulling-up path of the silicon single crystal 3.

[0030] The diameter of the opening at the lower end of the heat shield 17 is larger than the diameter of the silicon single crystal 3, thereby ensuring a pulling-up path for the silicon single crystal 3. Further, the outer diameter of the lower end portion of the heat shield 17 is smaller than the inner diameter of the quartz crucible 11, and the lower end portion of the heat 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 heat shield 17, the heat shield 17 does not interfere with the quartz crucible 11.

[0031] As the silicon single crystal 3 grows, the amount of melt in the quartz crucible 11 decreases. However, by raising the quartz crucible 11 so that the distance (gap value h G ) between the melt surface and the heat shield 17 becomes constant, temperature fluctuations of the silicon melt 2 are suppressed, and the flow rate of the gas flowing near the melt surface is made constant to control the evaporation amount of the dopant from the silicon melt 2. By such gap control, the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, etc. in the pulling-up axial direction of the silicon single crystal 3 can be improved.

[0032] Above the quartz crucible 11, a wire 18 which is the pulling-up axis of the silicon single crystal 3 and a crystal pulling-up mechanism 19 for pulling up the silicon single crystal 3 by winding up the wire 18 are provided. The crystal pulling-up mechanism 19 has a function of rotating the silicon single crystal 3 together with the wire 18. The crystal pulling-up mechanism 19 is controlled by a control unit 22. The crystal pulling-up mechanism 19 is disposed above the pull chamber 10b, the wire 18 extends downward through the pull chamber 10b from the crystal pulling-up mechanism 19, and the tip of the wire 18 reaches the internal space of the main chamber 10a. FIG. 1 shows a state in which the silicon single crystal 3 during growth is suspended from the wire 18. When pulling up the silicon single crystal 3, the silicon single crystal 3 is grown by gradually pulling up the wire 18 while rotating the quartz crucible 11 and the silicon single crystal 3 respectively.

[0033] Outside the chamber 10, two cameras 20A and 20B are installed. The cameras 20A and 20B are, for example, CCD cameras, and they image the inside of the chamber 10 through the first and second viewing windows 10e 1 , 10e 2 formed in the chamber 10. The installation angles of the cameras 20A and 20B form a predetermined angle with respect to the vertical direction, and the cameras 20A and 20B have camera axes (optical axes) inclined with respect to the pulling axis of the silicon single crystal 3. That is, the cameras 20A and 20B image the upper surface region of the quartz crucible 11 including the circular opening of the heat shield 17 and the liquid surface of the silicon melt 2 from an obliquely upward direction.

[0034] The cameras 20A and 20B are connected to an image processing unit 21, and the image processing unit 21 is connected to a control unit 22. The image processing unit 21 calculates the crystal diameter in the vicinity of the solid-liquid interface from the contour pattern of the single crystal shown in the captured image of the camera 20A. Further, the image processing unit 21 calculates the distance (gap value h G ) from the position of the mirror image of the heat shield 17 reflected in the liquid surface in the captured images of the cameras 20A and 20B to the liquid surface position from the heat shield 17. In order to remove the influence of noise, it is preferable to use the moving average value of a plurality of measured values as the gap measurement value used for actual gap control.

[0035] The method for calculating the gap value h G from the position of the mirror image of the heat shield 17 is not particularly limited. For example, a conversion table or conversion formula showing the relationship between the position of the mirror image of the heat shield 17 and the gap is prepared in advance, and during the crystal pulling process, the gap can be obtained by substituting the position of the mirror image of the heat shield 17 into this conversion table or conversion formula. It is also possible to geometrically calculate the gap from the positional relationship between the real image and the mirror image of the heat shield 17 shown in the captured image.

[0036] The control unit 22 controls the crystal diameter by controlling the crystal pulling speed based on the crystal diameter data obtained from the captured image of the camera 20A. Specifically, when the measured value of the crystal diameter is larger than the target diameter, the crystal pulling speed is increased, and when it is smaller than the target diameter, the pulling speed is decreased. Further, the control unit 22 controls the moving amount (crucible lifting speed) of the quartz crucible 11 so as to obtain a predetermined gap value based on the crystal length data of the silicon single crystal 3 obtained from the sensor of the crystal pulling mechanism 19 and the gap value (liquid level) obtained from the captured image of at least one of the cameras 20A and 20B. At this time, in addition to the case of controlling to maintain the gap value at a constant value, there are cases of controlling so that the gap value gradually decreases as the pulling of the single crystal progresses, and conversely, cases of controlling so that it increases.

[0037] Above the heat shield 17, a cylindrical shield 23 surrounding the crystal pulling axis is provided. This shield 23 may be a structure called a purge tube or a cooling body that promotes the cooling of the pulled silicon single crystal 3.

[0038] The purge tube is provided to control the flow of the purge gas. In order to adjust the resistivity of the silicon single crystal according to the characteristics of the semiconductor device, impurities (dopants) such as arsenic (As) and antimony (Sb) may be doped into the silicon melt. These dopants have a low boiling point and are easily evaporated. In general crystal pulling by the CZ method, since a purge gas such as Ar is flowing in the pulling furnace under reduced pressure, the dopant evaporated from the silicon melt 2 rides on the purge gas and volatilizes, contaminating the inside of the furnace. Further, the heat shield 17 provided in the furnace accelerates the flow rate of the purge gas flowing near the surface of the silicon melt 2, further promoting the evaporation of the dopant from the silicon melt 2. However, when a purge tube is provided, by making the inside of the chamber in a high-pressure state, installing the purge tube above the heat shield 17, and rectifying the purge gas introduced into the pulling furnace, the evaporation of the dopant in the silicon melt can be suppressed.

[0039] The cooling body is provided to control the time for the silicon single crystal pulled up from the silicon melt 2 to pass through a predetermined temperature range. It is known that the types and distributions of crystal defects contained in the silicon single crystal produced by the CZ method depend on the ratio V / G of the growth rate (pulling-up rate) V of the silicon single crystal and the temperature gradient G in the crystal in the pulling-up axis direction near the crystal growth interface from the melting point to 1300°C. By precisely controlling V / G, it is possible to produce a single crystal that does not contain COP (Crystal Originated Particle) or dislocation clusters. Here, when the crystal diameter increases, the crystal center part is less likely to cool compared to the outer peripheral part of the crystal, and the temperature gradient G in the cross-section of the silicon single crystal orthogonal to the pulling-up axis direction tends to become non-uniform. As a result, the allowable width of V / G that can make the entire cross-section of the silicon single crystal orthogonal to the pulling-up axis direction a defect-free region becomes very narrow, and the control of the crystal pulling-up rate V becomes extremely difficult. However, when a cylindrical cooling body is installed above the heat shield 17, the allowable width (PvPi margin) of the crystal pulling-up rate V that can make the entire cross-section of the silicon single crystal orthogonal to the pulling-up axis direction a defect-free region can be expanded, and the production yield of a large-diameter silicon single crystal that does not contain COP and dislocation clusters can be increased.

[0040] FIG. 2 is a schematic diagram for explaining the installation positions of two cameras 20A and 20B.

[0041] As shown in FIG. 2, the single crystal manufacturing apparatus 1 according to the present embodiment includes a sub-camera 20B (first camera) for gap measurement separately from the main camera 20A (second camera) for diameter measurement. The main camera 20A for diameter measurement is provided so as to face the silicon single crystal, and the camera axis of the main camera 20A is in the same plane as the crystal pulling axis and has a positional relationship intersecting the crystal pulling axis. On the other hand, the sub-camera 20B photographs the silicon single crystal from an oblique direction, and the camera axis of the sub-camera 20B is set in an oblique direction that is neither parallel nor perpendicular to the crystal pulling axis, and has a torsional positional relationship with the crystal pulling axis. Therefore, even if the field of view of the main camera 20A is blocked by the shielding object 23, the mirror image edge of the heat shield 17 reflected on the melt surface can be observed through a slight gap between the lower end of the shielding object 23 and the heat shield 17.

[0042] FIG. 3 is a schematic diagram of a photographed image 30A of the main camera 20A (diameter measurement camera), where (a) is a view not showing the contour of the single crystal, and (b) is a view showing the contour of the single crystal with auxiliary lines.

[0043] As shown in FIGS. 3(a) and 3(b), the main camera 20A photographs the silicon single crystal 3 from an obliquely upper direction. In particular, the camera axis of the main camera 20A is set in a plane including the crystal pulling axis (crystal center axis 3z), and the center of the width direction of the photographing range is aligned with the center of the silicon single crystal so that the entire diameter direction is captured. The dotted lines and dashed-dotted lines in the figure are auxiliary lines for explanation and do not exist in the actual photographed image.

[0044] When there is no shielding object 23 such as a purge tube or a water-cooled body above the heat shield 17, the main camera 20A can capture the real image 17R and the mirror image 17M of the heat shield 17. In the captured image 30A, the heat shield 17 and the shielding object 23 appear dark, but the melting surface 2a appears bright due to the radiant light or its reflected light. However, as shown in the figure, when the shielding object 23 is installed above the heat shield 17, the field of view of the main camera 20A is blocked by the shielding object 23, so the real image 17R and the mirror image 17M of the heat shield 17 cannot be captured. As shown in the figure, the shielding object 23 in the captured image 30A appears as dark as the heat shield 17 and the like, so most of the captured image is completely dark, and the bright visible area is only a small part of the melting surface 2a peeking through a small gap between the shielding object 23 and the real image 17R of the heat shield 17 and a very small part of the single crystal near the solid-liquid interface. For the sake of convenience of explanation, the real image edge E R and the mirror image edge E M of a part of the heat shield 17 are shown by broken lines, but actually nothing can be seen.

[0045] Figure 4 is a schematic diagram of the captured image 30B of the sub-camera 20B (gap measurement camera).

[0046] As shown in Figure 4, the sub-camera 20B also captures the silicon single crystal from an oblique upper direction, but the center in the width direction of its shooting range does not coincide with the center of the silicon single crystal, and the camera axis of the sub-camera 20B is oriented in a direction intersecting the plane including the silicon crystal pulling axis. As shown in the figure, the sub-camera 20B locally captures the vicinity of the solid-liquid interface on the right side (or left side) of the crystal pulling axis (crystal center axis 3z). Therefore, it is possible to observe the mirror image of the heat shield 17 reflected on the melting surface 2a through a small gap between the lower end of the shielding object 23 and the heat shield 17.

[0047] When obtaining the gap value h G from the captured image 30B of the sub-camera 20B thus obtained, first, the detection lines L R intersecting the real image edge E M and the mirror image edge E 1 of the heat shield 17 are set in the captured image 30B. So far, the detection line L 1Although it was set in the horizontal direction orthogonal to the crystal pulling axis (crystal central axis 3z), in this embodiment, it is set in the diagonal direction. In particular, the detection line L is drawn so that the distance (number of pixels) between two intersections becomes maximum. 1 It is preferable to draw the detection line L substantially parallel to the extending direction of the edge of the shielding object 23. 1 By doing so, it is possible to sufficiently secure the distance between two intersections and improve the measurement accuracy of the gap value.

[0048] Next, the coordinates of the intersection point P 1 (the first intersection point) between the detection line L and the real image edge E R and the intersection point P 1 (the second intersection point) between the detection line L and the mirror image edge E 1 are obtained respectively, and the distance from the first intersection point P M to the second intersection point P 2 (the real image-mirror image distance D on the detection line L) is obtained, and the gap value h 1 between the lower end of the heat shield 17 and the melt surface 2a is obtained from this real image-mirror image distance D. The broken line in the figure is an auxiliary line for explanation and does not exist in the actual photographed image 30B.

[0049] G When obtaining the gap value h G from the real image-mirror image distance D, it can be obtained using a conversion table or a conversion formula created in advance before starting the crystal pulling process. The conversion table or the conversion formula can be obtained from the relative change of the gap value h G when the quartz crucible 11 is moved up and down to arbitrarily change the liquid level of the silicon melt 2 and the relationship with the real image-mirror image distance D on the detection line L 1 . Furthermore, the reference value (absolute value) of the gap value h G can be obtained, for example, by a measurement method of the reference liquid level using a quartz measuring pin (quartz rod).

[0050]

[0051]

[0052] FIG. 5 is a schematic diagram showing a measurement method of the reference liquid level using a measuring pin.

[0051] As shown in Fig. 5, in the measurement of the reference liquid level using a measurement pin, a measurement pin 24 with a predetermined length Lp is attached to the lower end of a heat shield 17 that covers the upper part of the molten surface 2a. While gradually raising the molten surface 2a together with the quartz crucible 11, the contact state between the tip of the measurement pin 24 and the molten surface 2a is observed. Then, when the tip of the measurement pin 24 contacts the molten surface 2a, it is determined that the molten surface has reached the reference liquid level. That is, when the measurement pin 24 contacts the molten surface 2a, the gap value h G is consistent with the length Lp of the measurement pin 24 (Lp = h G ), and it is determined. Since this method has high measurement accuracy for the liquid level, the true value of the gap value h G can be used as a reference.

[0052] Fig. 6 is a flowchart showing the manufacturing process of a silicon single crystal.

[0053] As shown in Fig. 6, in the production of the silicon single crystal 3, the polycrystalline silicon raw material pre-filled in the quartz crucible 11 is heated by a heater 15 to generate a silicon melt 2 (step S11). Next, the liquid level position of the silicon melt 2 (gap value h G ) as seen from the heat shield 17 is measured (step S12). Then, a seed crystal attached to the tip of the wire 18 is lowered and made to land on the silicon melt 2 (step S13). The amount of descent of the seed crystal at this time is determined based on the previously measured gap value h G .

[0054] Next, a crystal pulling-up process for growing the silicon single crystal 3 is started while maintaining the contact state with the silicon melt 2. In the crystal pulling-up process, first, a seed necking (step S14) by the dash neck method is performed to make the single crystal dislocation-free. Next, a shoulder part with a gradually increasing diameter is grown to obtain a single crystal with the required diameter (step S15), and when the single crystal reaches the desired diameter, a body part with a constant diameter is grown (step S16). After growing the body part to a predetermined length, a tail necking (growth of the tail part, step S17) is performed to cut off the single crystal from the silicon melt 2 in a dislocation-free state.

[0055] During the process of pulling up the single crystal, the diameter of the silicon single crystal 3 and the liquid level position of the silicon melt 2 are controlled. The control unit 22 controls the pulling conditions such as the pulling speed of the wire 18 and the power of the heater 15 so that the diameter of the silicon single crystal 3 becomes the target diameter. Further, the control unit 22 controls the vertical position of the quartz crucible 11 so that the gap value h G corresponding to the liquid level position becomes a predetermined value.

[0056] As described above, in the method for manufacturing a silicon single crystal according to the present embodiment, a sub-camera 20B for gap measurement is provided separately from the main camera 20A for diameter measurement, and the real image and mirror image of the heat shield 17 are photographed using the sub-camera 20B. Therefore, even when the field of view of the main camera 20A is blocked by a shielding object 23 such as a purge tube, the real image and mirror image of the heat shield 17 can be photographed, and the gap value h G can be stably measured. Further, when obtaining the gap value h G from the photographed image of the sub-camera 20B, the detection line L 1 is drawn in an oblique direction instead of the horizontal direction, and the gap value h 1 is calculated from the intersections P R and P M of this detection line L 1 with the real image edge E 2 and the mirror image edge E G respectively. Therefore, the measurement accuracy of the gap value h G can be improved.

[0057] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention, and it goes without saying that those are also included in the scope of the present invention.

[0058] For example, in the above embodiment, the case where the field of view of the diameter measurement camera is blocked by an obstacle is taken as an example. However, the present invention is not limited to such a case. Even when there is no obstacle blocking the field of view of the diameter measurement camera, it is also possible to measure the gap using a gap measurement camera separately from the diameter measurement camera. Thereby, the gap measurement accuracy and reliability can be improved. Further, it is also possible to provide only the gap measurement camera without providing the diameter measurement camera. Furthermore, the present invention is not limited to the case where the gap measurement camera is used in combination with the diameter measurement camera, and it is also possible to use the gap measurement camera alone.

[0059] Also, in the above embodiment, the method for manufacturing a silicon single crystal has been described. However, it is possible to apply the CZ method to various methods for manufacturing single crystals to which the CZ method is applicable.

Explanation of Reference Numerals

[0060] 1 Single crystal manufacturing apparatus 2 Silicon melt 2a Melt surface 3 Silicon single crystal 3z Crystal central axis (crystal pulling axis) 10 Chamber 10a Main chamber 10b Pull chamber 10c Gas inlet 10d Gas outlet 10e 1 First viewing window 10e 2 Second viewing window 11 Quartz crucible 12 Graphite crucible 13 Rotating shaft 14 Crucible drive mechanism 15 Heater 16 Heat insulating material 17 Heat shield 17M Mirror image of heat shield 17R Real image of heat shield 18 Wire 19 Crystal pulling mechanism 20A Main Camera (Diameter Measurement Camera) 20B Sub Camera (Gap Measurement Camera) 21 Image Processing Unit 22 Control Unit 23 Shield (In-furnace Structure) 24 Measurement Pin 30A Captured Image of Main Camera 30B Captured Image of Sub Camera E M Mirror Edge of Thermal Shield E R Real Image Edge of Thermal Shield L 1 Detection Line P 1 Intersection of Detection Line and Real Image Edge (First Intersection) P 2 Intersection of Detection Line and Mirror Edge (Second Intersection)

Claims

1. A method for manufacturing a single crystal by the Czochralski method of pulling a single crystal from a melt in a crucible, comprising: installing a heat shield that covers the upper part of the crucible except for the pulling path of the single crystal; photographing a real image of the heat shield and a mirror image of the heat shield reflected on the liquid surface of the melt with a first camera; setting a detection line that extends in an oblique direction that is neither parallel nor perpendicular to the pulling axis of the single crystal and intersects both the real image edge and the mirror image edge of the heat shield; obtaining a gap value, which is the distance between the lower end of the heat shield and the melt surface, from the real image-mirror image distance on the detection line, which is the distance from a first intersection of the detection line and the real image edge to a second intersection of the detection line and the mirror image edge. A method for manufacturing a single crystal, characterized by this.

2. The method for manufacturing a single crystal according to claim 1, wherein the camera axis of the first camera is not in the same plane as the pulling axis of the single crystal and has a twisted positional relationship.

3. The method for manufacturing a single crystal according to claim 1 or 2, wherein the diameter of the single crystal is measured using a photographed image of a second camera prepared separately from the first camera.

4. Prepare in advance a conversion table or conversion formula showing the relationship between the gap value and the real image-mirror image distance on the detection line when the crucible is raised and lowered before the start of crystal pulling to arbitrarily change the liquid surface level of the melt, and during the crystal pulling process, use the actually measured real image-mirror image distance and the conversion table or the conversion formula to calculate the gap value. The method for manufacturing a single crystal according to any one of claims 1 to 3.

5. The method for manufacturing a single crystal according to claim 4, wherein a reference liquid surface level is obtained by observing the contact between a measurement pin installed above the melt and the melt surface, and the conversion table or the conversion formula is created based on the reference liquid surface level.

6. A crucible for supporting a melt, a crucible drive mechanism for rotating and lifting the crucible, a heater for heating the melt in the crucible, a cylindrical heat shield disposed above the crucible except for the pulling path of the single crystal, a first camera for photographing a real image of the heat shield and a mirror image of the heat shield reflected on the liquid surface of the melt, an image processing unit that processes the photographed image of the first camera to obtain a gap value between the lower end of the heat shield and the melt surface, and a control unit that controls the liquid surface level of the melt based on the processing result of the photographed image by the image processing unit. The image processing unit, ​ A detection line that extends in an oblique direction that is neither parallel nor perpendicular to the pulling axis of the single crystal and intersects both the real image edge and the mirror image edge of the heat shield is set in the captured image. A single crystal manufacturing apparatus, characterized by obtaining a gap value, which is the distance between the lower end of the heat shield and the melt surface, from the real image-mirror image distance on the detection line, which is the distance from the first intersection of the detection line and the real image edge to the second intersection of the detection line and the mirror image edge.

7. The single crystal manufacturing apparatus according to claim 6, wherein the camera axis of the first camera is not in the same plane as the pulling axis of the single crystal and is in a twisted positional relationship.

8. The apparatus further includes a second camera that captures the real image of the heat shield and the mirror image of the heat shield reflected on the liquid surface of the melt. The single crystal manufacturing apparatus according to claim 6 or 7, wherein the image processing unit measures the diameter of the single crystal using the captured image of the second camera.

9. The image processing unit creates in advance a conversion table or a conversion formula showing the relationship between the gap value and the real image-mirror image distance on the detection line when the crucible is raised and lowered to arbitrarily change the liquid surface level of the melt before the start of crystal pulling, and during the crystal pulling process, calculates the gap value using the actually measured real image-mirror image distance and the conversion table or the conversion formula. The single crystal manufacturing apparatus according to any one of claims 6 to 8.

10. The apparatus further includes a measurement pin installed above the melt. The single crystal manufacturing apparatus according to claim 9, wherein the image processing unit obtains a reference liquid surface level by observing the contact between the tip of the measurement pin and the melt surface, and creates the conversion table or the conversion formula based on the reference liquid surface level.

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