JP6885301B2 - Single crystal manufacturing method and equipment - Google Patents

Description

The present invention relates to a method and an apparatus for producing a single crystal, and more particularly to a method for measuring a crystal diameter performed during a single crystal pulling step by the Czochralski method (CZ method).

Most of the silicon single crystals used as substrate materials for semiconductor devices are manufactured by the CZ method. In the CZ method, a seed crystal is immersed in a silicon melt contained in a quartz crucible, and the seed crystal and the crucible are gradually raised while rotating to grow a single crystal having a large diameter at the lower end of the seed crystal. Let me.

Regarding the CZ method, for example, Patent Document 1 describes a method of pulling up a single crystal while controlling the position of a crucible so that the liquid level position of the silicon melt with respect to a structure in a furnace such as a heater is always held at a constant position. Are listed. In this method, the measured value of the liquid level position and the correction value of the ascending speed of the crucible are calculated, and the correction value is added to the quantitative value of the ascending speed of the crucible required to keep the liquid level constant, and after the correction. The liquid level position is controlled using the ascending speed of. In this method, the crystal diameter is measured from the output of the one-dimensional CCD camera, and the liquid level position is calculated from the mirror image of the reference reflector reflected on the melt surface.

Further, in Patent Document 2, the first crystal diameter measured from the fusion ring at the boundary between the silicon melt and the silicon single crystal taken with a CCD camera is parallel to both ends of the crystal diameter of the silicon single crystal. The second crystal diameter measured using two CCD cameras installed in the above was obtained, and from the difference between the first crystal diameter and the second crystal diameter, the silicon melt surface in the rutsubo during the pulling of the silicon single crystal. It is described that the height position of is calculated.

Further, in Patent Document 3, a fusion ring appearing at a boundary between a single crystal and a melt surface is photographed with a camera, and a row in the horizontal direction in the photographed image orthogonal to the pulling axis direction of the single crystal is set as a diameter measurement line. However, a method of obtaining the diameter of a single crystal from the diameter measurement line intersecting the fusion ring and the position of the two intersections is described.

In the conventional method described in Patent Document 1 in which the liquid level position is always kept constant during pulling up of a single crystal, the in-plane distribution of crystal defects is constant from the upper end (top) to the lower end (bottom) of the single crystal. It is difficult to achieve, and there is a limit to increasing the production yield of high-quality silicon single crystals. Therefore, a control method for changing the liquid level position while pulling up a single crystal is being studied. According to this control method, it is possible to realize the stabilization even in a portion where it has been difficult to stabilize the crystal thermal history, and to make the in-plane distribution of crystal defects constant from the top to the bottom of the single crystal. ..

When the liquid level position is changed during the single crystal pulling process, the position of the fusion ring in the image captured by the camera also changes. Therefore, when the diameter measurement line is fixed to a specific pixel array in the captured image, the position of the intersection with the fusion ring changes, and a single crystal diameter measurement error is likely to occur. Therefore, a method of changing the vertical position of the diameter measurement line according to the change of the liquid level position is adopted. By changing the position of the diameter measurement line in the captured image according to the change in the liquid level position, the diameter measurement line can be made to follow the fusion ring, and the diameter measurement error of the single crystal can be reduced. ..

Japanese Unexamined Patent Publication No. 2001-342095 Japanese Unexamined Patent Publication No. 2013-17007 JP-A-2017-154901

However, when the position of the diameter measurement line in the captured image is changed according to the change in the liquid level position, there is a problem that the fluctuation of the diameter measurement value becomes large due to the change in the position of the diameter measurement line. During the single crystal pulling process, the crystal pulling speed is controlled based on the measurement result of the crystal diameter, and if the crystal pulling speed is not strictly controlled to stabilize the crystal thermal history, a high quality single crystal can be produced. Since the yield cannot be increased, it is strongly required to accurately measure and control the crystal diameter.

Therefore, an object of the present invention is a method and apparatus for producing a single crystal capable of reducing fluctuations in the diameter measurement value even if the position of the diameter measurement line in the captured image is changed according to the change in the liquid level position. Is to provide.

The inventor of the present application has diligently studied the cause of the large fluctuation of the diameter measurement value when the position of the diameter measurement line in the captured image is changed according to the change of the liquid level position, and as a result, the diameter measurement value fluctuates. It was found that the timing coincides with the timing when the position of the diameter measurement line changes, and that the fluctuation of the diameter measurement value can be reduced by correcting the diameter measurement value obtained at this timing.

The present invention is based on such technical knowledge, and the method for producing a single crystal according to the present invention is a method for producing a single crystal by the Czochralski method in which the single crystal is pulled up from the melt in the rutsubo. The position of the two intersections of the step of photographing the boundary between the single crystal and the melt, the at least one diameter measurement line set in the horizontal direction in the photographed image, and the fusion ring appearing at the boundary, and the above. A step of obtaining the diameter of the single crystal from the center position of the fusion ring, a step of changing the vertical position of the diameter measurement line in the photographed image according to a change in the liquid level position of the melt, and the diameter. A step of correcting the second diameter measurement value of the single crystal based on the first and second diameter measurement values of the single crystal obtained at positions before and after the position of the measurement line changes is provided. It is characterized by.

According to the present invention, it is possible to suppress fluctuations in the diameter measurement value that occur when the vertical position of the diameter measurement line in the captured image is changed according to the change in the liquid level position. Therefore, the stability of the acquired crystal diameter can be improved, and the production yield of a high-quality single crystal can be increased.

In the present invention, the step of correcting the second diameter measurement value includes a step of calculating the ratio of the second diameter measurement value to the first diameter measurement value as a correction coefficient and the second diameter measurement value. It is preferable to include a step of multiplying the correction coefficient. According to this, the measured value of the crystal diameter can be corrected by a simple calculation.

In the present invention, in the step of obtaining the diameter of the single crystal, a plurality of diameter measurement values of the single crystal are simultaneously calculated using a plurality of diameter measurement lines set in the captured image, and the vertical direction of the diameter measurement line is calculated. In the step of moving the position of, it is preferable to move the plurality of diameter measurement lines in parallel in the vertical direction. According to this, the reliability of the diameter measurement value can be improved.

In the present invention, the first diameter measurement value is a value obtained from the diameter measurement line before the position of the diameter measurement line changes, and the second diameter measurement value is the position of the diameter measurement line. Is preferably a value obtained from the diameter measurement line after the change. According to this, the crystal diameter can be calculated and corrected using one diameter measurement line.

In the present invention, the captured image includes first to third pixel sequences that are continuous in the vertical direction, and the plurality of diameter measurement lines are the first diameter measurement line set in the first pixel sequence and the said. In the step of changing the vertical position of the diameter measurement line including the second diameter measurement line set in the second pixel row adjacent to the first pixel row, the first and second diameters are included. The measurement line was moved to the second pixel row and the third pixel row adjacent to the second pixel row, respectively, and the position of the plurality of diameter measurement lines was changed in the first diameter measurement value. It is a value later obtained from the first diameter measurement line, and the second diameter measurement value is a value obtained from the second diameter measurement line after the positions of the plurality of diameter measurement lines have changed. Is preferable. According to this, the correction amount of the crystal diameter can be accurately obtained by using the two diameter measurement values obtained at the same time.

The method for producing a single crystal according to the present invention includes a gap variable control step for gradually expanding or contracting a gap between a heat shield arranged above the melt and the melt, and the diameter measurement line. In the step of changing the vertical position of the above, it is preferable to change the vertical position of the diameter measurement line in the captured image in accordance with the change of the liquid level position by the gap variable control step. In this case, the method for producing a single crystal according to the present invention may have a gap constant control step for controlling the gap to be constant. According to this, the single crystal can be stably pulled up from the top to the bottom, and the production yield of the high quality single crystal can be increased.

Further, the single crystal manufacturing apparatus according to the present invention includes a crucible that supports the melt, a heater that heats the melt, a pull-up shaft that pulls the single crystal from the melt, and a crucible elevating mechanism that drives the crucible up and down. A crystal pulling mechanism for pulling a single crystal from the melt in the crucible, a camera for photographing the boundary between the single crystal and the melt, an image processing unit for processing an image taken by the camera, and the above. The image processing unit includes a heater, a pull-up shaft, and a control unit for controlling the crucible elevating mechanism, and the image processing unit includes at least one diameter measurement line set in the horizontal direction in the captured image and a fusion ring appearing at the boundary portion. The diameter of the single crystal is obtained from the positions of the two intersections and the center position of the fusion ring, and the vertical position of the diameter measurement line in the captured image is changed according to the change in the liquid level position of the melt. Then, the second diameter measurement value of the single crystal is corrected based on the first and second diameter measurement values of the single crystal obtained at the positions before and after the position of the diameter measurement line changes. It is characterized by.

According to the present invention, it is possible to suppress fluctuations in the diameter measurement value that occur when the vertical position of the diameter measurement line in the captured image is changed according to the change in the liquid level position. Therefore, the stability of the acquired crystal diameter can be improved, and the production yield of a high-quality single crystal can be increased.

According to the present invention, there is provided a method and an apparatus for manufacturing a single crystal capable of reducing the fluctuation of the diameter measurement value even if the position of the diameter measurement line in the captured image is changed according to the change of the liquid level position. To do.

FIG. 1 is a side sectional view schematically showing a configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart showing a manufacturing process of the silicon single crystal 3. FIG. 3 is a schematic cross-sectional view showing the shape of a silicon single crystal ingot. FIG. 4 is a diagram showing a general relationship between V / G and the type and distribution of crystal defects. FIG. 5 is a schematic diagram for explaining the relationship between the gap profile and the crystal defect distribution during the crystal pulling process, and shows the case of the conventional constant gap control. FIG. 6 is a schematic diagram for explaining the relationship between the gap profile and the crystal defect distribution during the crystal pulling step, and shows the case of the gap variable control of the present invention. FIG. 7 is a perspective view schematically showing an image of the boundary between the single crystal 3 and the melt 2 taken by the camera 20. FIG. 8 is a schematic diagram for explaining a method of calculating the diameter R of the fusion ring 4. FIG. 9 is a graph showing the relationship between the change in the position of the diameter measurement line and the measured value of the crystal diameter. FIG. 10 is a schematic diagram for explaining a method of correcting the measured value of the crystal diameter obtained immediately after the position of the diameter measuring line is changed. FIG. 11 is a schematic diagram for explaining a method of correcting the measured value of the crystal diameter according to the second embodiment of the present invention. 12A and 12B are graphs showing the diameter measurement results of a silicon single crystal according to Comparative Examples and Examples, in which FIG. 12A shows Comparative Examples and FIG. 12B shows Examples.

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

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

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 a quartz crucible 11, and a graphite crucible. A rotating shaft 13 that supports 12, a crucible drive mechanism 14 that rotates and moves the quartz crucible 11 up and down via the rotating shaft 13 and the graphite crucible 12, a heater 15 arranged around the graphite crucible 12, and the outside of the heater 15. The heat insulating material 16 arranged along the inner surface of the chamber 10, the heat shield 17 arranged above the quartz crucible 11, and the heat shield 17 arranged above the quartz crucible 11 and coaxially with the rotating shaft 13. A wire 18 which is a crucible pulling shaft, a crystal pulling mechanism 19 arranged above the chamber 10, a camera 20 for photographing the inside of the chamber 10, an image processing unit 21 for processing the captured image of the camera 20, and a single crystal. It includes a control unit 22 that controls each unit in the manufacturing apparatus 1.

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, and the quartz crucible 11, the graphite crucible 12, the heater 15 and the heat shield 17 are the main chambers 10. It is provided in the chamber 10a. The pull chamber 10b is provided with a gas introduction port 10c for introducing an inert gas (purge gas) such as argon gas or a dopant gas into the chamber 10, and an atmospheric gas in the chamber 10 is provided below the main chamber 10a. A gas discharge port 10d for discharging the gas is provided. Further, a viewing window 10e is provided in the upper part of the main chamber 10a, and the growing state of the silicon single crystal 3 can be observed from the viewing window 10e.

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

The graphite crucible 12 is fixed to the upper end of the rotary shaft 13, and the lower end of the rotary shaft 13 penetrates the bottom of the chamber 10 and is connected to the crucible drive mechanism 14 provided on the outside of the chamber 10. The graphite crucible 12, the rotating shaft 13, and the crucible driving mechanism 14 constitute a rotating mechanism and an elevating mechanism of the quartz crucible 11. The rotation and elevating operation of the quartz crucible 11 driven by the crucible drive mechanism 14 is controlled by the control unit 22.

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 heating type heater, and is provided so as to surround the quartz crucible 11 in the graphite crucible 12. Further, a heat insulating material 16 is provided on the outside of the heater 15 so as to surround the heater 15, thereby enhancing the heat retention in the chamber 10. The output of the heater 15 is controlled by the control unit 22.

The heat shield 17 suppresses the temperature fluctuation of the silicon melt 2 to give an appropriate heat distribution in the vicinity of the crystal growth interface, and prevents the silicon single crystal 3 from being heated by the radiant heat from the heater 15 and the quartz crucible 11. It is provided in. The heat shield 17 is a member made of graphite having a substantially cylindrical shape, and is provided so as to cover the region above the silicon melt 2 excluding the pulling path of the silicon single crystal 3.

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, whereby the pulling path of the silicon single crystal 3 is secured. Further, since the outer diameter of the lower end of the heat shield 17 is smaller than the diameter of the quartz crucible 11 and the lower end of the heat shield 17 is located inside the quartz crucible 11, the upper end of the rim of the quartz crucible 11 is the heat shield 17. The heat shield 17 does not interfere with the quartz crucible 11 even if it is raised above the lower end of the quartz crucible.

Although the amount of melt in the quartz rut 11 decreases as the silicon single crystal 3 grows, silicon is raised by raising the quartz rut 11 so that the distance (gap) between the melt surface and the heat shield 17 becomes constant. While suppressing the temperature fluctuation of the melt 2, the evaporation amount of the dopant from the silicon melt 2 is controlled by keeping the flow velocity of the gas flowing near the melt surface constant. By such gap control, it is possible to improve the stability of the crystal defect distribution, the oxygen concentration distribution, the resistivity distribution, etc. in the pull-up axial direction of the silicon single crystal 3.

Above the quartz crucible 11, a wire 18 which is a pulling shaft of the silicon single crystal 3 and a crystal pulling mechanism 19 which pulls up the silicon single crystal 3 by winding the wire 18 are provided. The crystal pulling mechanism 19 has a function of rotating the silicon single crystal 3 together with the wire 18. The crystal pulling mechanism 19 is controlled by the control unit 22. The crystal pulling mechanism 19 is arranged above the pull chamber 10b, the wire 18 extends downward from the crystal pulling mechanism 19 through the inside of the pull chamber 10b, and the tip of the wire 18 extends to the internal space of the main chamber 10a. Has reached. FIG. 1 shows a state in which the silicon single crystal 3 being grown 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. The crystal pulling speed is controlled by the control unit 22.

A camera 20 is installed outside the chamber 10. The camera 20 is, for example, a CCD camera, and photographs the inside of the chamber 10 through the viewing window 10e formed in the chamber 10. The installation angle of the camera 20 is a predetermined angle with respect to the vertical direction, and the camera 20 has an optical axis inclined with respect to the pulling axis of the silicon single crystal 3. That is, the camera 20 photographs the upper surface region of the quartz crucible 11 including the circular opening of the heat shield 17 and the liquid level of the silicon melt 2 from diagonally above.

The camera 20 is connected to the image processing unit 21, and the image processing unit 21 is connected to the 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 captured in the captured image of the camera 20, and the position of the mirror image of the heat shield 17 reflected on the melt surface in the captured image. The gap (Gap), which is the distance from the heat shield 17 to the liquid level position, is calculated from. In order to eliminate the influence of noise, it is preferable to use a moving average value of a plurality of measured values as the gap measured value used for the actual gap control.

The method of calculating the gap from the position of the mirror image of the heat shield 17 is not particularly limited, but for example, a conversion formula obtained by linearly approximating the relationship between the position of the mirror image of the heat shield 17 and the gap is prepared in advance. During the crystal pulling process, the gap can be obtained by substituting the position of the mirror image of the heat shield into this 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 reflected in the photographed image.

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, 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 moves the quartz crucible 11 (crucible) 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 taken by the camera 20. Ascending speed) is controlled.

FIG. 2 is a flowchart showing a manufacturing process of the silicon single crystal 3. Further, FIG. 3 is a schematic cross-sectional view showing the shape of the silicon single crystal ingot.

As shown in FIG. 2, the manufacturing process of the silicon single crystal 3 according to the present embodiment includes the raw material melting step S11 in which the silicon raw material in the quartz rut 11 is heated by the heater 15 to generate the silicon melt 2, and the wire 18 A single crystal is grown by gradually pulling up the seed crystal while maintaining the contact state between the liquid landing step S12 in which the seed crystal attached to the tip is lowered and landed on the silicon melt 2 and the silicon melt 2. It has a crystal pulling step (S13 to S16).

In the crystal pulling step, a necking step S13 for forming a neck portion 3a whose crystal diameter is narrowed to eliminate dislocations and a shoulder portion growing step S14 for forming a shoulder portion 3b whose crystal diameter gradually increases as the crystal grows. The body portion growing step S15 for forming the body portion 3c maintained at a constant crystal diameter and the tail portion growing step S16 for forming the tail portion 3d whose crystal diameter gradually decreases with crystal growth are sequentially carried out. ..

After that, a cooling step S17 is performed in which the silicon single crystal 3 is separated from the melt surface to promote cooling. As described above, the silicon single crystal ingot 3I having the neck portion 3a, the shoulder portion 3b, the body portion 3c, and the tail portion 3d as shown in FIG. 3 is completed.

Since the type and distribution of crystal defects contained in the silicon single crystal 3 depend on the ratio V / G of the crystal pulling rate V and the intra-crystal temperature gradient G, it is necessary to control the crystal quality in the silicon single crystal 3. It is necessary to control V / G.

FIG. 4 is a diagram showing a general relationship between V / G and the type and distribution of crystal defects.

As shown in FIG. 4, when the V / G is large, the voids become excessive, and void defects (COP), which are aggregates of the voids, occur. On the other hand, when the V / G is small, the interstitial silicon atoms become excessive, and dislocation clusters, which are aggregates of interstitial silicon, are generated. Further, between the region where COP is generated and the region where dislocation clusters are generated, there are three regions, an OSF region, a Pv region, and a Pi region, in descending order of V / G. In order to say that the silicon single crystal is a defect-free crystal, it is necessary that the entire cross section of the silicon single crystal orthogonal to the pull-up axial direction is a defect-free region. Here, the “defect-free region” refers to a region that does not contain Green-in defects such as COP and dislocation clusters and that does not generate OSF ring after the evaluation heat treatment, and is a Pv region or a Pi region. ..

In order to grow a defect-free crystal composed of a Pv region or a Pi region with a high yield by controlling the crystal pulling speed V, it is preferable that the PvPi margin is as wide as possible. Here, the PvPi margin means a permissible width of a crystal pulling speed V in which an arbitrary region in the silicon single crystal 3 can be a Pv region or a Pi region in a broad sense, and in a narrow sense, a pulling axial direction. It refers to the minimum value (PvPi in-plane margin) of the PvPi margin in the cross section of the silicon single crystal orthogonal to. Since the intra-crystal temperature gradient G is usually constant, the PvPi margin is the width of V / G from the Pv-OSF boundary to the Pi-dislocation cluster boundary in FIG.

The diameter of the silicon single crystal 3 is mainly controlled by adjusting the crystal pulling speed V, and since the crystal pulling speed V is appropriately changed in order to suppress the diameter fluctuation, the fluctuation of the pulling speed V should be completely eliminated. Can't. Therefore, a PvPi margin that allows speed fluctuation to some extent is required.

On the other hand, the types and distribution of V / G and crystal defects are strongly influenced by the thermal environment in the furnace surrounding the crystal, that is, the hot zone. Therefore, when the hot zone changes as the crystal pulling process progresses, the hot zone changes. Even if the gap is maintained at a constant distance, it may not be possible to secure the desired in-plane margin of PvPi. For example, in the middle part of the body portion growing step S15 shown in FIG. 1, a single crystal ingot of a sufficient length exists in the space above the silicon melt, whereas at the start of the body portion growing step S15, such a single crystal ingot exists. Since there is no single crystal ingot, the heat distribution in the space will be slightly different even if the heat shield 17 is provided. Further, at the final stage of the body portion growing step S15, the output of the heater 15 is increased in order to prevent the silicon melt from solidifying due to the decrease of the silicon melt 2 in the crucible, so that the heat distribution around the crystal also changes. .. When the hot zone changes in this way, even if the gap is maintained at a constant distance, the thermal history in the crystal changes, so that the in-plane distribution of crystal defects cannot be maintained constant.

Therefore, in the present embodiment, the gap is not always maintained at a constant distance from the top to the bottom of the silicon single crystal ingot, but the gap is changed according to the crystal growth stage. By changing the gap in this way, the in-plane distribution of crystal defects can be controlled as intended from the top to the bottom of the ingot, suppressing the decrease in the PvPi in-plane margin and improving the production yield of defect-free crystals. Can be made to. How the gap can be changed to suppress the decrease in the PvPi in-plane margin depends on the hot zone. Therefore, in order to make the in-plane distribution of crystal defects constant from the top to the bottom of the crystal, it was adjusted to the crystal growth stage while considering how the hot zone changes as the crystal pulling process progresses. It is necessary to set the gap profile appropriately.

5 and 6 are schematic views for explaining the relationship between the gap profile and the crystal defect distribution during the crystal pulling process, and FIG. 5 shows the gap of the present invention in the case of conventional gap constant control. The case of variable control is shown respectively.

As shown in FIG. 5, in the constant gap control in which the gap is always maintained at a constant distance during the crystal pulling process, the thermal history in the crystal changes due to the change in the hot zone, so that the in-plane distribution of crystal defects is constant. Cannot be maintained. That is, since the in-plane distribution of crystal defects is different at the top (Top), center (Mid), and bottom (Bot) of the silicon single crystal ingot 3I, a desired PvPi in-plane margin is secured at the center of the ingot 3I. However, the desired in-plane margin of PvPi cannot be secured at the top and bottom of the ingot 3I.

On the other hand, in the present invention, as shown in FIG. 6, the gap profile is set so that the gap is gradually narrowed as the crystal pulling step progresses. In particular, the gap profile according to the present embodiment is a first gap constant control section S1 that keeps the gap constant from the start of the crystal pulling process, and a first gap that is provided in the first half of the body portion growing process and gradually reduces the gap. Variable control section S2, second gap constant control section S3 that keeps the gap constant, second gap variable control section S4 that is provided in the latter half of the body part growing process and gradually reduces the gap, until the end of the crystal pulling process A third gap constant control section S5 that keeps the gap constant is provided in this order. Such a gap profile is set according to changes in the hot zone, thereby maintaining a constant in-plane distribution of crystal defects from the top to the bottom of the Ingot 3I and increasing the production yield of defect-free crystals as shown in the figure. Is possible.

The above gap profile is an example, and is not limited to a profile in which the gap gradually narrows as the crystal pulling process progresses. Therefore, for example, it is possible to gradually reduce the gap in the first gap variable control section S2 and gradually increase the gap in the second gap variable control section S4.

Next, a method for measuring the diameter of the silicon single crystal 3 will be described. In order to control the diameter of the silicon single crystal 3 during the pulling process, the boundary portion between the single crystal 3 and the melt surface is photographed by the CCD camera 20, and the center position of the fusion ring generated at the boundary portion and the fusion ring 2 The diameter of the single crystal 3 is obtained from the distance between the two luminance peaks. Further, in order to control the liquid level position of the melt 2, the liquid level position is obtained from the center position of the fusion ring. The control unit 22 controls the pulling conditions such as the pulling speed of the wire 18, the power of the heater 15, and the rotation speed of the quartz crucible 11 so that the diameter of the single crystal 3 becomes the target diameter. Further, the control unit 22 controls the vertical position of the quartz crucible 11 so that the liquid level position becomes a desired position.

FIG. 7 is a perspective view schematically showing an image of the boundary between the single crystal 3 and the melt 2 taken by the camera 20.

_{As shown in FIG. 7, the image processing unit 21 starts from the coordinate position of the center C 0} of the fusion ring 4 generated at the boundary between the single crystal 3 and the melt 2 and the coordinate position of an arbitrary point on the fusion ring 4. The radius r and the diameter R = 2r of the fusion ring 4 are calculated. That is, the image processing unit 21 calculates the diameter R of the single crystal 3 at the solid-liquid interface. The position of the center C ₀ of the fusion ring 4 is the intersection of the extension line 5 of the pulling shaft of the single crystal 3 and the melt surface.

Since the CCD camera 20 photographs the boundary between the single crystal 3 and the melt surface from diagonally above, the fusion ring 4 cannot be regarded as a perfect circle. However, if the CCD camera 20 is accurately installed at a predetermined position in the design and at a predetermined angle, the substantially elliptical fusion ring 4 is corrected to a perfect circle based on the viewing angle with respect to the melt surface. It is possible to geometrically calculate the diameter of the corrected fusion ring 4.

The fusion ring 4 is a ring-shaped high-intensity region formed by the light reflected by the meniscus and occurs on the entire circumference of the single crystal 3, but it is not possible to see from the viewing window 10e to the fusion ring 4 on the back side of the single crystal 3. Can not. When the fusion ring 4 is viewed from the gap between the opening 17a of the heat shield 17 and the single crystal 3, if the diameter of the single crystal 3 is large, it is on the front side (lower side in FIG. 7) in the viewing direction. A part of the fusion ring 4 located is also hidden behind the heat shield 17, so that it cannot be seen. Therefore, the visible portion of the fusion ring 4 is only a part 4L on the front left side and a part 4R on the front right side when viewed from the viewing direction. According to the present invention, even when only a part of the fusion ring 4 can be observed in this way, the diameter thereof can be calculated from the part.

FIG. 8 is a schematic diagram for explaining a method of calculating the diameter R of the fusion ring 4.

As shown in FIG. 8, in the calculation of the diameter R of the fusion ring 4, to set the diameter measurement line L ₁ in the two-dimensional images taken by the CCD camera 20. The diameter measurement line L ₁ is a straight line that intersects the fusion ring 4 twice and is orthogonal to the extension line 5 of the pull-up shaft. The diameter measurement line L ₁ is set below _{the center C 0} of the fusion ring 4. The Y-axis of the captured image is parallel to the extension line 5 of the pull-up axis, and the X-axis is set in a direction orthogonal to the extension line 5 of the pull-up axis. The fusion ring 4 shown in FIG. 5 has an ideal shape that matches the outer circumference of the single crystal.

_{When the coordinates of the center C 0} of the fusion ring 4 with respect to the origin O (0, 0) of the XY coordinates of the captured image are (x ₀ , y ₀ ), the distance Y = (from the center C ₀ to the diameter measurement line L _1). y _{1 −} y ₀ ). The position of the center C ₀ of the fusion ring 4 can be, for example, the position of the intersection of the horizontal scanning line and the pull-up axis that maximizes the distance between the two luminance peaks of the fusion ring.

Next, to detect the two intersection points _P 1, _{P 1} 'of the diameter measurement line _{L 1} and the fusion ring 4. One of the coordinate intersection _{P 1} of the fusion ring 4 and the diameter measurement line _{L 1} and _{(x 1, y 1),} ' the coordinates _{(x 1'} the other intersection _{P 1, y 1)} and. Approximate position of the intersection point P _1, P 1 _'of the fusion ring 4 and the diameter measurement line L ₁ is the position of the brightness peak on the diameter measurement line L _1. It will be described in detail later position of intersection P _1, P _{1 'of} the fusion ring 4 and the diameter measurement line L _1.

Then, a '= the distance between X _{(x 1'} 2 two intersections _P 1, _{P 1} on the diameter measurement line _{L 1} -x _1), the diameter of the fusion ring 4 R, the radius r = R / 2 Then, equation (1) is obtained.

r ² = (R / 2) ² = (X / 2) ² + Y ² ... (1)

Therefore, from the equation (1), the diameter R of the fusion ring 4 becomes as in the equation (2).

R = {X ² + 4Y ² } ^1/2 ... (2)

Because fusion ring is a high-luminance region of the strip having a constant width, in order to accurately calculate the coordinates of an intersection between the diameter measurement line L ₁ has to be a fusion ring 4 with the line pattern. Therefore, in the intersection of the detection of the fusion ring 4 and the diameter measurement line L _1, detects an edge pattern of fusion ring 4 from the captured image by using the reference value of the luminance, fusion the intersection of the edge pattern and diameter measurement line It is the intersection of rings 4. The edge pattern of the fusion ring 4 is a pattern composed of pixels having a brightness that matches the reference value of the brightness. The brightness reference value used to define the edge pattern can be a value obtained by multiplying the maximum brightness in the captured image by a predetermined coefficient (for example, 0.8).

In the variable gap control that changes the liquid level position, the position of the fusion ring generated at the solid-liquid interface in the captured image also changes in the vertical direction. Therefore, if the vertical position of the diameter measurement line is fixed, The position of the fusion ring relative to the diameter measurement line changes, and the position of the intersection of the two also changes. However, as described above, if the position of the intersection of the diameter measurement line and the fusion ring changes according to the change in the liquid level position, a diameter measurement error is likely to occur. Therefore, in the present embodiment, the diameter measurement line is made to follow the change in the liquid level position, and the change in the distance from the camera to the measurement target is reflected in the diameter measurement result to minimize the diameter measurement error. ..

FIG. 9 is a graph showing the relationship between the change in the position of the diameter measurement line and the measured value of the crystal diameter, and the horizontal axis and the vertical axis display the crystal length and the crystal diameter as relative values from the reference values, respectively. Is.

As shown in FIG. 9, when the crystal pulling condition is controlled so that the crystal diameter becomes constant, the crystal diameter fluctuates slightly up and down but remains almost constant, but at the moment when the diameter measurement line changes. There is a tendency to move significantly to the minus side. That is, it can be seen that the fluctuation of the diameter measurement value becomes large immediately after the position of the diameter measurement line changes according to the change of the liquid level position, and is affected by the change of the position of the diameter measurement line. The vertical position of the diameter measurement line becomes smaller as the crystal length increases, but since the origin of the captured image is set at the upper end, this is because the diameter measurement line of the captured image is set as the liquid level rises. It means that it is moving upward.

It is considered that the reason why the diameter measurement value fluctuates as described above is that the control of the diameter measurement line is a non-linear control (step control) that selects a specific row in the captured image. While the change in the liquid level position is continuous (linear), the change in the diameter measurement line is a discontinuous (non-linear) change in pixel units, so the position of the diameter measurement line was changed by one pixel. Immediately after, the measurement result of the crystal diameter fluctuates. Therefore, in the present embodiment, the fluctuation of the diameter measurement value is suppressed by correcting the crystal diameter measurement value at the timing when the diameter measurement line changes.

FIG. 10 is a schematic diagram for explaining a method of correcting the diameter measurement value according to the change in the position of the diameter measurement line.

As shown in FIG. 10 (a), the diameter measurement line L ₁ intersects the two points of fusion ring 4 extends in the horizontal direction. This diameter measurement line L ₁ is a pixel array for one pixel, and its vertical position shifts upward (or downward) by one pixel only when the liquid level position rises (or falls) by one pixel. .. Here, while the liquid level position changes continuously, the change in the diameter measurement line is discontinuous (discrete) and can move only in pixel units.

As shown in FIG. 10 (b), when the liquid level position is moved by one pixel from the fusion ring 4 also dashed position to the solid line position moves upward, from even the position indicated by the broken line position of the diameter measurement line L ₁ It is changed to the position of the solid line. _{The broken line diameter measurement line L 1a} on the lower side is the diameter measurement line before the position change, and the solid diameter measurement line L _{1b on} the upper side is the diameter measurement line after the position change. _{The measured value of the crystal diameter based on the lower diameter measurement line L1a} , which is the diameter measurement line immediately before changing the vertical position, and the upper side, which is the diameter measurement line immediately after changing the vertical position by 1 pixel. The measured value of the crystal diameter based on the diameter measurement line _L1b of the above should be the same value because the crystal diameter of the fusion ring 4 at almost the same position is originally measured.

In practice, however, it has occurred out to the diameter measured values of both, the deviation of the measured value is affecting the diameter variations immediately after changing the position of the diameter measurement line L _1. For example, when the liquid level position rises, even if the actual crystal diameter is the same before and after the liquid level position rises, the crystal diameter after the liquid level position rises is measured shorter than before the rise. On the contrary, the crystal diameter after the liquid level position is lowered is measured longer than that before the liquid level is lowered. Therefore, in the present embodiment, the correction coefficient for correcting the deviation of the diameter measurement value is calculated to correct the crystal diameter measurement value.

When the crystal diameter measurement value D _{Sb immediately before the vertical position is changed and the crystal diameter measurement value D Sa} immediately after the diameter measurement line position is changed by 1 pixel, the crystal diameter correction coefficient D _Pi is as follows. become that way.
D _Pi = D _Sb ÷ D _Sa ... (3)

The crystal diameter D _Sc after correction is a value obtained by multiplying the correction coefficient D _Pi on the current crystal diameter D _S, as follows.
_{D Sc = D S × D Pi} ··· (4)

As described above, in the method for producing a silicon single crystal according to the present embodiment, the fusion ring appearing at the solid-liquid interface during the single crystal pulling process is photographed, and the diameter measurement line and the fusion ring set in the photographed image are two. When determining the crystal diameter from the position of the intersection, the position of the diameter measurement line in the vertical direction is changed according to the change in the liquid level position of the melt, and the crystal diameter obtained immediately after the position of the diameter measurement line is changed. Since the measured value is corrected, it is possible to suppress the fluctuation of the diameter measured value that occurs immediately after the position of the diameter measuring line changes. In particular, in the correction of the diameter measurement value, the ratio of the measurement value of the crystal diameter obtained immediately after the position of the diameter measurement line is changed to the measurement value of the crystal diameter obtained immediately before changing the position of the diameter measurement line is used as the correction coefficient. Since the measured value of the crystal diameter after the position change is corrected by using this correction coefficient, the measured value of the crystal diameter can be corrected by a simple calculation. Therefore, the stability of the crystal diameter acquired by the variable gap control can be improved, and the crystal pulling speed can be stably controlled to increase the production yield of a high-quality single crystal.

FIG. 11 is a schematic diagram for explaining a method of correcting the measured value of the crystal diameter according to the second embodiment of the present invention.

As shown in FIG. 11, the method for correcting the measured value of the crystal diameter according to the present embodiment is to obtain a plurality of diameter measurement values at the same time by using a plurality of (here, three) diameter measurement lines instead of one. is there. Further, the average value of a plurality of diameter measurement values is adopted as the final crystal diameter measurement value.

In the present embodiment, the three diameter measurement lines L ₁ , L ₂ , and L ₃ are continuous in the vertical direction and are adjacent to each other without any gap. Here, it is assumed that the three diameter measurement lines L ₁ , L ₂ , and L ₃ are set on the vertically continuous pixel trains PL ₁ , PL ₂ , and PL _{3 in} the captured image, respectively. If in accordance with the change in the liquid level position is moved by one pixel diameter measurement line _{L 1,} L 2, _{L 3} above, three diameter measurement line _{L 1,} L 2, _{L 3} keeps the mutual positional relationship However, they change together, so that the diameter measurement lines L ₁ , L ₂ , and L ₃ move on the pixel trains PL ₂ , PL ₃ , and PL _{4, respectively.} That is, the diameter measurement line L ₁ moves from the pixel row PL _{1 to PL 2} , the diameter measurement line L ₂ moves from the pixel row PL _{2 to PL 3} , and the diameter measurement line L ₂ moves from the pixel row PL ₃ to PL ₄ . Moving.

When calculating the correction coefficient of the crystal diameter using only one diameter measurement line (see FIG. 10), it is necessary to calculate the correction coefficient using the diameter measurement values obtained before and after the position of the diameter measurement line changes. there were. However, when using a plurality of adjacent diameter measurement lines, another diameter measurement line has moved to the position before moving one diameter measurement line, and two adjacent diameter measurement lines have been measured after the position change. It is possible to calculate the correction coefficient using the two diameter measurement values obtained from the line. That is, the correction coefficient for correcting the measured value of the crystal diameter is the diameter measured value obtained from the diameter measuring line immediately after the vertical position is changed by one pixel and the position before the diameter measuring line moves. It is obtained based on the diameter measurement value obtained from the newly moved adjacent diameter measurement line.

For example, since the pixel rows PL ₂ which had a diameter measuring line L ₂ before repositioning diameter measurement line L ₁ comes newly moved, corrected based on the diameter measurement line L ₂ and L ₁ immediately after the position change The coefficient is calculated. Since the pixel rows PL ₃ in which there is a diameter measurement line L ₃ before repositioning diameter measurement line L ₂ come to move new, corrected based on the diameter measurement line L ₃ and L ₂ immediately after the position change coefficient Is required. If the diameter measurement line L _{2 is} in the center, the correction coefficient can be calculated together with the diameter measurement line L ₁ below when the diameter measurement lines L _{1 to} L _{3 move upward, and the diameter measurement lines L 1} to L 1 to When L ₃ moves downward, the correction coefficient can be calculated together with the upper diameter measurement line L _3.

In this way, when measuring the crystal diameter using three adjacent diameter measurement lines L ₁ , L ₂ , and L ₃ , the measured values of the crystal diameter simultaneously measured from the fusion ring 4 at the same position are used. Since the correction coefficient can be calculated, there is no diameter measurement error due to the time lag, and the correction accuracy of the crystal diameter can be improved. The number of diameter measurement lines is not limited to three, and may be three or more. Further, during the pulling process of the single crystal, if the vertical position of the diameter measurement line moves in only one direction, either the upward direction or the downward direction, two lines may be used.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention, and these are also the present invention. Needless to say, it is included in the range.

For example, in the above embodiment, the production of a silicon single crystal has been mentioned as an example, but the present invention is not limited to this, and can be applied to the production of various single crystals grown by the CZ method.

Further, in the above embodiment, the case where the diameter measurement value is corrected when the liquid level position changes in the variable gap control is given as an example, but since the liquid level position changes even in the constant gap control, the diameter according to the present invention. Measurement value correction can be applied.

A silicon single crystal having a diameter of about 300 mm was pulled up using the single crystal manufacturing apparatus 1 shown in FIG. In the crystal pulling step, the constant gap control was switched to the variable gap control to gradually raise the liquid level position. In the diameter measurement of the single crystal, as shown in FIG. 8, the crystal diameter was appropriately measured using one diameter measurement line, and the position of the diameter measurement line was changed according to the change in the liquid level position.

Here, in the comparative example, the measurement value of the crystal diameter was not corrected immediately after the position of the diameter measurement line changed, but in the example, the above calculation formula (3), immediately after the position of the diameter measurement line changed, The measured value of the crystal diameter was corrected based on (4). The results of the final measured crystal diameters in Comparative Examples and Examples are shown in FIGS. 12 (a) and 12 (b). The vertical axis of FIGS. 12A and 12B displays the measured value of the crystal diameter as a relative value from the reference value.

As shown in FIG. 12A, in the comparative example in which the measurement value of the crystal diameter was not corrected immediately after the position of the diameter measurement line was changed, a steep dip occurred periodically in the graph of the diameter variation. This steep drop moves to the minus side at the moment when the diameter measurement line moves according to the liquid level position, and changes the position of the diameter measurement line according to the gradual rise of the liquid level position (reduction of the gap). It turned out to be affected. The standard deviation σ of the diameter measurement value was 0.1033, the maximum value on the plus side of the diameter fluctuation was 0.248, the maximum value on the minus side was -0.410, and the fluctuation range was 0.658.

As shown in FIG. 12 (b), in the embodiment in which the measured value of the crystal diameter is corrected immediately after the position of the diameter measurement line is changed, a steep and periodic dip may occur in the graph of the diameter fluctuation. There wasn't. That is, it was possible to eliminate the diameter fluctuation that occurs when the position of the diameter measurement line changes. The standard deviation σ of the diameter measurement value was 0.0780, the maximum value on the plus side of the diameter fluctuation was 0.208, the maximum value on the minus side was -0.197, and the fluctuation range was 0.405.

1 Single crystal manufacturing equipment 2 Silicon melt 3 Silicon single crystal 3a Neck part 3b Shoulder part 3c Body part 3d Tail part 3I Silicon single crystal ingot 4 Fusion ring 4L Part on the left side of the fusion ring 4R Part on the right side of the fusion ring 5 Extension line of pull-up shaft 10 Chamber 10a Main chamber 10b Pull chamber 10c Gas inlet 10d Gas outlet 10e Peep window 11 Quartz crucible 12 Graphite crucible 13 Rotating shaft 14 Crucible drive mechanism 15 Heater 16 Insulation 17 Heat shield 17a Opening 18 Wire 19 Mechanism 20 Camera 21 Image processing unit 22 Control unit L ₁ , L ₂ , L ₃ Diameter measurement line L _1a Diameter measurement line _{before position change L 1b} Diameter measurement line before position change PL ₁ pixel row PL ₂ pixel row PL ₃ Pixel train R Diameter S1, S3, S5 Gap constant control section S2, S4 Gap variable control section S11 Raw material melting process S12 Liquidation process S13 Necking process S14 Shoulder part growing process S15 Body part growing process S16 Tail part growing process S17 Cooling step

Claims (7)

A method for producing a single crystal by the Czochralski method, in which the single crystal is pulled up from the melt in the crucible.
The step of photographing the boundary between the single crystal and the melt,
A step of obtaining the diameter of the single crystal from the positions of two intersections of at least one diameter measurement line set in the horizontal direction in the captured image and the fusion ring appearing at the boundary and the center position of the fusion ring.
A step of changing the vertical position of the diameter measurement line in the captured image according to a change in the liquid level position of the melt, and a step of changing the position in the vertical direction.
A step of correcting the second diameter measurement value of the single crystal based on the first and second diameter measurement values of the single crystal obtained at positions before and after the position of the diameter measurement line changes, respectively. A method for producing a single crystal, which comprises the present invention. The step of correcting the second diameter measurement value is
A step of calculating the ratio of the second diameter measurement value to the first diameter measurement value as a correction coefficient, and
The method for producing a single crystal according to claim 1, further comprising a step of multiplying the second diameter measurement value by the correction coefficient. The first diameter measurement value is a value obtained from the diameter measurement line before the position of the diameter measurement line changes.
The method for producing a single crystal according to claim 1 or 2 , wherein the second diameter measurement value is a value obtained from the diameter measurement line after the position of the diameter measurement line has changed. In the step of obtaining the diameter of the single crystal, a plurality of diameter measurement values of the single crystal are simultaneously calculated using a plurality of diameter measurement lines set in the captured image.
Step of moving the vertical position of the diameter measurement line moves in parallel the plurality of diameter measurement line in the vertical direction,
The first diameter measurement value is an average value of a plurality of diameter measurement values obtained from the plurality of diameter measurement lines before the positions of the plurality of diameter measurement lines change.
The single according to claim 1 or 2, wherein the second diameter measurement value is an average value of a plurality of diameter measurement values obtained from the plurality of diameter measurement lines after the positions of the plurality of diameter measurement lines have changed. Crystal manufacturing method. The captured image includes first to third pixel sequences that are continuous in the vertical direction.
The plurality of diameter measurement lines include a first diameter measurement line set in the first pixel row and a second diameter measurement line set in the second pixel row adjacent to the first pixel row. Including
In the step of changing the vertical position of the diameter measurement line, the first and second diameter measurement lines are arranged in the second pixel row and the third pixel row adjacent to the second pixel row, respectively. Move,
The first diameter measurement value is a value obtained from the first diameter measurement line after the positions of the plurality of diameter measurement lines have changed.
The method for producing a single crystal according to claim 1 or 2 , wherein the second diameter measurement value is a value obtained from the second diameter measurement line after the positions of the plurality of diameter measurement lines have changed. It has a gap variable control step that gradually expands or contracts the gap between the heat shield arranged above the melt and the melt.
The step of changing the vertical position of the diameter measurement line is claimed to change the vertical position of the diameter measurement line in the captured image in accordance with the change of the liquid level position by the gap variable control step. Item 2. The method for producing a single crystal according to any one of Items 1 to 5. A crucible that supports the melt and
A heater that heats the melt and
A heat shield placed above the melt and
A pull-up shaft that pulls up a single crystal from the melt,
A crucible elevating mechanism that elevates and drives the crucible,
A crystal pulling mechanism that pulls a single crystal from the melt in the crucible,
A camera that photographs the boundary between the single crystal and the melt,
An image processing unit that processes images taken by the camera, and
The heater, the pulling shaft, and a control unit for controlling the crucible raising / lowering mechanism are provided.
The control unit performs gap variable control for expanding or contracting the gap between the heat shield and the melt in accordance with the progress of the crystal pulling step.
The image processing unit
The diameter of the single crystal was obtained from the positions of the two intersections of at least one diameter measurement line set in the horizontal direction in the captured image and the fusion ring appearing at the boundary and the center position of the fusion ring.
The vertical position of the diameter measurement line in the captured image is changed according to the change in the liquid level position of the melt.
It is characterized in that the second diameter measurement value of the single crystal is corrected based on the first and second diameter measurement values of the single crystal obtained at positions before and after the position of the diameter measurement line changes. Single crystal manufacturing equipment.

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