Method for measuring amount of change in height of silicon raw material, and silicon single crystal production method and silicon single crystal production device using same

Abstract

[Problem] To provide: a method for stably measuring the amount of a change in the height of a silicon raw material during a raw material melting step; and a production method and a production device for a silicon single crystal using the same. [Solution] A method for measuring the height of a silicon raw material according to the present invention involves: capturing, during a raw material melting step in which a silicon raw material containing a large number of polycrystalline silicon lumps and filling the inside of a quartz crucible is heated by a heater to generate a silicon melt, an image of the silicon raw material by using a camera from above, and obtaining a first height reference point Pra of the silicon raw material from a first in-furnace image Ma captured by using the camera (S21-S23); obtaining a second height reference point Prb of the silicon raw material from a second in-furnace image Mb captured after capturing the first in-furnace image Ma (S24-S26); and obtaining the amount ∆h of a change in the height of the silicon raw material from the difference between the first height reference point Pra and the second height reference point Prb (S27).

Description

Method for measuring change in height of silicon raw material, method for manufacturing silicon single crystals using the method, and silicon single crystal manufacturing apparatus

[0001] The present invention relates to a method for measuring the amount of change in height of a silicon raw material, and a method and apparatus for producing a silicon single crystal using the same.

[0002] The Czochralski method (CZ method) is known as a method for producing silicon single crystals for semiconductor devices. The CZ method involves heating polycrystalline silicon raw material in a quartz crucible to generate a silicon melt, and then gradually pulling a seed crystal immersed in the silicon melt to grow a large single crystal at the bottom of the seed crystal. The CZ method can increase the production yield of large-diameter silicon single crystals.

[0003] In the CZ method, polycrystalline silicon raw material in a quartz crucible is heated by radiant heat from a heater to produce molten silicon. The height of the quartz crucible must be adjusted according to the progress of melting of the polycrystalline silicon raw material. If the quartz crucible is maintained at a relatively low position relative to the heater, the heat load from the heater is large, which may cause the quartz crucible to deform. If the quartz crucible deforms, the convection of the melt changes, causing abnormalities in the oxygen characteristics of the silicon single crystal. Furthermore, the quartz crucible may come into contact with a thermal shield placed above it, making it difficult to continue the crystal pulling process.

[0004] Conventionally, the vertical position of the quartz crucible has been adjusted by an operator as needed according to the progress of melting of the silicon raw material, but this has imposed a heavy burden on the operator. In addition, since the height of the silicon raw material is determined by visual inspection, there is variation in judgment depending on the operator, which can lead to human error.

[0005] Regarding the automation of adjusting the vertical position of a quartz crucible during raw material melting, Patent Document 1 describes that after the silicon raw material filling process, the position of the upper end of the raw material is measured with two cameras, and the position of the crucible is adjusted so that a predetermined distance is maintained between the lower end of the purge tube and the upper end of the raw material as the raw material filled in the crucible progresses in melting.

[0006] JP 2017-7077981 A

[0007] However, the conventional crucible position adjustment method described in Patent Document 1 uses two cameras (stereo cameras) to measure the distance to the raw material based on the principle of triangulation. This requires precise position adjustment (calibration) of the two cameras, which is subject to limitations due to the furnace interior structure. Furthermore, since it is impossible to distinguish between a change in the height of the raw material and a change in the position of the raw material in the image, this method has the problem of being unable to be applied while the crucible is rotating.

[0008] Therefore, an object of the present invention is to provide a method for stably measuring the amount of change in height of silicon raw material during a raw material melting process, and a silicon single crystal manufacturing method and silicon single crystal manufacturing apparatus using the same.

[0009] In order to solve the above problem, the method for measuring the change in height of a silicon raw material according to the present invention is characterized in that an image of the inside of a furnace including the silicon raw material is taken from above with a camera during a raw material melting process in which the silicon raw material, which includes a number of polycrystalline silicon chunks filled in a quartz crucible, is heated to produce a silicon melt, the first height reference point of the silicon raw material is determined from a first image of the furnace taken using the camera, the second height reference point of the silicon raw material is determined from a second image of the furnace taken using the camera after the first image of the furnace is taken, and the change in height of the silicon raw material is determined from the difference between the first height reference point and the second height reference point.

[0010] According to the present invention, the change in height of the silicon raw material in the quartz crucible during the raw material melting process can be stably determined from the image captured by the camera, and the vertical position of the quartz crucible can be automatically adjusted based on the image captured by the camera.

[0011] In the present invention, it is preferable that the first height reference point is the center of gravity of a plurality of feature points extracted from the first furnace image, and the second height reference point is the center of gravity of a plurality of feature points extracted from the second furnace image. In many cases, the upper surface of the aggregate of many polycrystalline silicon chunks filled in a quartz crucible is uneven, so by calculating the amount of change in the height of the silicon raw material using a value obtained by averaging the height positions of the upper surface, the accuracy of measuring the amount of change in the height of the silicon raw material can be improved.

[0012] The number of the plurality of characteristic points is preferably equal to or greater than 50 and equal to or less than 1000. If the number of characteristic points extracted from the captured image is within this range, the height of the silicon raw material can be determined with high accuracy from the plurality of characteristic points.

[0013] The plurality of feature points are preferably extracted by the Shi-Tomasi method, which makes it possible to easily obtain a predetermined number of feature points from an image with high accuracy.

[0014] In the present invention, it is preferable that the first height reference point is a reference coordinate of a template image sampled from a predetermined template region in the first furnace image, and the second height reference point is a reference coordinate of a reference image that has a maximum correlation with the template image when a predetermined search range in the second furnace image is scanned and pattern matching with the template image is performed. This makes it possible to stably measure the amount of change in height of the silicon raw material from the start to just before the end of the raw material melting process.

[0015] In the present invention, the degree of correlation is preferably calculated by comparing the average luminance value of each pixel of the template image with the average luminance value of each pixel of the reference image, thereby enabling the movement position of the template image to be calculated with high accuracy and with as little calculation effort as possible.

[0016] In the present invention, it is preferable that the search range is a region that is larger than the template region and has a center that coincides with the template region and covers the template region, thereby making it possible to accurately determine the movement position of the template image with as little calculation effort as possible.

[0017] In the method for measuring the amount of change in height of the silicon feedstock according to the present invention, it is preferable that the first amount of change and the second amount of change in height of the silicon feedstock are sequentially calculated, and the position at which the template image is collected when calculating the second amount of change in height of the silicon feedstock is the same as the position at which the template image is collected when calculating the first amount of change. This makes it possible to prevent a situation in which the template region continues to move and the template image is collected at a location that is not suitable for collecting a template image.

[0018] The method for measuring the change in height of the silicon feedstock according to the present invention preferably determines the first change in height of the silicon feedstock using the first furnace image taken at a first timing and the second furnace image taken at a second timing after the first timing, and determines the second change in height of the silicon feedstock using the first furnace image taken at a third timing after the first timing and the second furnace image taken at a fourth timing after the second and third timings. This makes it possible to continuously determine the change in height of the silicon feedstock.

[0019] The method for measuring the amount of change in height of the silicon feedstock according to the present invention preferably includes setting a plurality of template regions in the first furnace image, determining a plurality of first height reference points from a plurality of template images taken from each of the plurality of template regions, determining a plurality of second height reference points from the second furnace image corresponding to each of the plurality of first height reference points, and calculating an average value of the amount of change in height of the silicon feedstock from the plurality of first height reference points and the plurality of second height reference points. This makes it possible to more accurately determine the amount of change in height of the silicon feedstock.

[0020] In the method for measuring the change in height of the silicon raw material according to the present invention, it is preferable that the silicon raw material is heated and melted while the quartz crucible is rotated, and the first and second height reference points are respectively determined from the first and second furnace images taken in synchronization with the rotation period of the quartz crucible. This makes it possible to eliminate the influence of the rotation of the quartz crucible and accurately determine the amount of sinking of the silicon raw material due to melting.

[0021] In the method for measuring the change in height of the silicon raw material according to the present invention, it is preferable to heat and melt the silicon raw material while rotating the quartz crucible, and to calculate the change in height of the silicon raw material from the difference between the moving average values ​​of a plurality of first height reference points and a plurality of second height reference points obtained from furnace images corresponding to a rotation period of the quartz crucible. This makes it possible to accurately calculate the amount of sinking of the silicon raw material due to melting while eliminating the influence of the rotation of the quartz crucible.

[0022] In the present invention, it is preferable that the polycrystalline silicon chunks have multiple corners, and when initially filled into the quartz crucible, they are filled to a position higher than the upper end of the quartz crucible, and the opening of the quartz crucible is covered by the polycrystalline silicon chunks. Furthermore, it is preferable that the maximum diameter of each polycrystalline silicon chunk is 2 to 10 cm. By having the silicon raw material filled into the quartz crucible have these characteristics, it is possible to improve the accuracy of measuring the change in the height of the silicon raw material by image processing.

[0023] In addition, in order to solve the above-mentioned problems, the method for producing a silicon single crystal according to the present invention comprises a preparation step of placing a quartz crucible filled with a silicon raw material containing a large number of polycrystalline silicon chunks in a chamber, a raw material melting step of heating the silicon raw material with a heater to produce a silicon melt, and a crystal pulling step of pulling a silicon single crystal from the silicon melt, wherein the raw material melting step includes a height change measurement step of photographing the silicon raw material from above with a camera to measure the amount of change in height of the silicon raw material, and a crucible height adjustment step of adjusting the height of the quartz crucible in accordance with the change in height of the silicon raw material, and the height change measurement step is characterized in that the amount of change in height of the silicon raw material is measured using the above-mentioned method for measuring the amount of change in height of the silicon raw material according to the present invention.

[0024] According to the present invention, the change in height of the silicon raw material in the quartz crucible during the raw material melting process can be stably determined from the image captured by the camera, and the vertical position of the quartz crucible can be automatically adjusted based on the image captured by the camera.

[0025] Furthermore, a silicon single crystal manufacturing apparatus according to the present invention comprises a chamber, a quartz crucible that holds silicon raw material within the chamber, a heater that heats the silicon raw material, a crucible drive mechanism that rotates and raises and lowers the quartz crucible, a crystal pulling mechanism that pulls up a single crystal from the silicon melt in the quartz crucible, a camera that photographs the silicon raw material from above, an image processing unit that processes images taken by the camera, and a control unit that controls the operation of the heater, the crucible drive mechanism, and the crystal pulling mechanism, wherein the camera photographs the silicon raw material from above during a raw material melting process in which the silicon raw material, which includes a large number of polycrystalline silicon chunks, is heated by the heater to produce silicon melt, and the image processing unit measures the amount of change in height of the silicon raw material using the method for measuring the amount of change in height of the silicon raw material according to the present invention described above.

[0026] According to the present invention, the amount of change in the height of the silicon raw material in the quartz crucible during the raw material melting process can be stably determined from the image captured by the camera, and the height of the quartz crucible can be automatically adjusted based on the image captured by the camera.

[0027] According to the present invention, it is possible to provide a method for measuring the change in height of a silicon raw material, which is capable of stably measuring the change in height of the silicon raw material during the raw material melting process, and a method for manufacturing a silicon single crystal and a silicon single crystal manufacturing apparatus using the same.

[0028] FIG. 1 is a schematic cross-sectional view showing the configuration of a single crystal manufacturing apparatus used to manufacture silicon single crystals using the CZ method. FIG. 2 is a flowchart showing the steps of manufacturing silicon single crystals using the CZ method. FIG. 3 is a schematic side view showing the shape of a silicon single crystal ingot. FIG. 4 is an explanatory diagram of a raw material melting process. FIG. 5 is a schematic diagram showing a method for measuring the amount of change in the height of a silicon raw material according to a first embodiment of the present invention. FIG. 6 is a flowchart showing a method for measuring the amount of change in the height of a silicon raw material. FIG. 7 is a diagram for explaining feature points in an in-furnace image, and is a schematic diagram of a captured image of a silicon raw material in a quartz crucible. FIGS. 8(a) and 8(b) are sequence diagrams showing the timing of acquiring first and second in-furnace images in each measurement step. FIG. 9 is a graph showing a schematic change in the position of the center of gravity of a feature point when the height of a quartz crucible is adjusted. FIG. 10 is a schematic diagram showing a change in the position of a feature point when the quartz crucible is rotated. FIG. 11 is a sequence diagram showing an example of the timing of acquiring first and second in-furnace images in each measurement step. Fig. 12 is a sequence diagram showing an example of the timing of acquiring the first and second furnace images in each measurement step. Fig. 13 is a graph showing the relationship between the change in height of the silicon raw material and the height of the quartz crucible during the raw material melting process. Fig. 14 is a schematic diagram explaining a method for measuring the change in height of the silicon raw material according to a second embodiment of the present invention. Fig. 15 is a flowchart showing a method for measuring the change in height of the silicon raw material. Fig. 16 is a diagram explaining pattern matching processing of a template image of M × N pixels. Fig. 17 is a schematic diagram explaining another example of a method for measuring the change in height of the silicon raw material.

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

[0030] FIG. 1 is a schematic cross-sectional view showing the configuration of a single crystal manufacturing apparatus used for manufacturing silicon single crystals by the CZ method.

[0031] As shown in FIG. 1, the single crystal manufacturing apparatus 1 includes a chamber 10 constituting a crystal pulling furnace, a quartz crucible 11 for holding a silicon melt 2 within the chamber 10, a graphite crucible 12 for holding the quartz crucible 11, a rotating shaft 13 supporting the graphite crucible 12, a shaft drive mechanism 14 for driving the rotating shaft 13 to rotate and raise and lower, a heater 15 arranged around the graphite crucible 12, a heat insulating material 16 arranged outside the heater 15 and along the inner surface of the chamber 10, a heat shield 17 arranged above the quartz crucible 11, a pulling wire 18 arranged above the quartz crucible 11 and coaxial with the rotating shaft 13, and a wire winding mechanism 19 arranged above the chamber 10.

[0032] The chamber 10 is composed of a main chamber 10a and a long, cylindrical pull chamber 10b connected to the upper opening of the main chamber 10a, and the quartz crucible 11, graphite crucible 12, heater 15, and heat shield 17 are provided inside the main chamber 10a. The pull chamber 10b is provided with a gas inlet 10c for introducing an inert gas (purge gas) such as Ar gas or a dopant gas into the chamber 10, and a gas outlet 10d for discharging the atmospheric gas inside the chamber 10 is provided at the bottom of the main chamber 10a.

[0033] The quartz crucible 11 is a container made of quartz glass and has a cylindrical side wall and a curved bottom. The graphite crucible 12 is in close contact with the outer surface of the quartz crucible 11, encasing it, in order to maintain the shape of the quartz crucible 11 that has been softened by heating. The quartz crucible 11 and the graphite crucible 12 form a double-structure crucible that holds the silicon melt 2 within the chamber 10.

[0034] The graphite crucible 12 is fixed to the upper end of a rotating shaft 13, and the lower end of the rotating shaft 13 passes through the bottom of the chamber 10 and is connected to a shaft driving mechanism 14 provided outside the chamber 10. The rotating shaft 13 and the shaft driving mechanism 14 constitute a crucible driving mechanism that drives the quartz crucible 11 and the graphite crucible 12 to rotate and move up and down.

[0035] The heater 15 is used to melt the silicon raw material filled in the quartz crucible 11 to generate the silicon melt 2 and to maintain the molten state of the silicon melt 2. The heater 15 is a resistance heater made of carbon, and is provided so as to surround the quartz crucible 11 inside the graphite crucible 12. Furthermore, a heat insulating material 16 is provided outside the heater 15 so as to surround the heater 15, thereby improving the heat retention inside the chamber 10.

[0036] The thermal shield 17 is provided to suppress temperature fluctuations in the silicon melt 2 to form an appropriate hot zone 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 thermal shield 17 is a graphite member that covers the area above the silicon melt 2 excluding the pulling path for the silicon single crystal 3, and has, for example, an inverted truncated cone shape with an opening that increases in size from the bottom to the top.

[0037] The diameter of the opening 17a at the lower end of the thermal shield 17 is larger than the diameter of the silicon single crystal 3, thereby ensuring a pulling path for the silicon single crystal 3. The diameter of the opening 17a of the thermal shield 17 is smaller than the diameter of the quartz crucible 11, and the lower end of the thermal shield 17 is located inside the quartz crucible 11. Therefore, even if the upper end of the rim of the quartz crucible 11 is raised above the lower end of the thermal shield 17, the thermal shield 17 will not interfere with the quartz crucible 11.

[0038] Although the amount of melt in the quartz crucible 11 decreases as the silicon single crystal 3 grows, by raising the quartz crucible 11 so that the gap between the lower end of the thermal shield 17 and the melt surface 2s remains constant, it is possible to suppress temperature fluctuations in the silicon melt 2 and to keep constant the flow rate of the gas flowing near the melt surface 2s, thereby controlling the amount of dopant evaporated from the silicon melt 2. Therefore, it is possible to improve the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, etc. in the pulling axis direction of the silicon single crystal 3.

[0039] Above the quartz crucible 11, there is provided a pulling wire 18, which is the axis for pulling the silicon single crystal 3, and a wire winding mechanism 19 for winding up the pulling wire 18. The wire winding mechanism 19 functions to rotate the silicon single crystal 3 together with the pulling wire 18. The wire winding mechanism 19 is disposed above the pull chamber 10b, and the pulling wire 18 extends downward from the wire winding mechanism 19 through the pull chamber 10b, with the tip of the pulling wire 18 reaching the internal space of the main chamber 10a. FIG. 1 shows a state in which a silicon single crystal 3 is being grown, suspended from the pulling wire 18. During pulling of the silicon single crystal 3, the pulling wire 18 is gradually pulled up while the quartz crucible 11 and the silicon single crystal 3 are each rotated, thereby growing the silicon single crystal 3. In this way, the pulling wire 18 and the wire winding mechanism 19 constitute a crystal pulling mechanism that pulls the silicon single crystal 3 from the silicon melt 2.

[0040] A sight window 10e for observing the interior of the main chamber 10a is provided at the top, and the growth status of the silicon single crystal 3 can be observed through the sight window 10e. A camera 20 is installed outside the sight window 10e. During the crystal pulling process, the camera 20 photographs the boundary between the silicon single crystal 3 and the silicon melt 2, which is visible through the sight window 10e and the opening 17a of the thermal shield 17, from diagonally above. The images photographed by the camera 20 are processed in an image processing unit 21, and the processed results are used in a control unit 22 to control the crystal growth conditions.

[0041] Fig. 2 is a flowchart showing the steps of producing a silicon single crystal by the CZ method, and Fig. 3 is a schematic side view showing the shape of a silicon single crystal ingot.

[0042] As shown in FIG. 2 , the production of silicon single crystals according to this embodiment includes a preparation step S11 in which a quartz crucible 11 filled with polycrystalline silicon raw material is placed in a chamber 10, a raw material melting step S12 in which the polycrystalline silicon raw material in the quartz crucible 11 is heated with a heater 15 to produce a silicon melt 2, and a crystal pulling step S13 in which a seed crystal is gradually pulled up while being kept in contact with the silicon melt 2 to grow a single crystal.

[0043] The crystal pulling step S13 includes a dipping step S14 in which a seed crystal attached to the tip of a pulling wire 18 is lowered to dipped into the silicon melt 2, a necking step S15 in which a neck portion 3a having a narrowed crystal diameter to eliminate dislocations is formed, a shoulder portion growing step S16 in which a shoulder portion 3b having a gradually increasing crystal diameter is formed, a body portion growing step S17 in which a body portion 3c having a specified crystal diameter (e.g., 320 mm) is formed, and a tail portion growing step S18 in which a tail portion 3d having a gradually decreasing crystal diameter is formed, and at the end of the tail portion growing step S18, the silicon single crystal 3 is separated from the silicon melt 2. In this way, a silicon single crystal ingot 3i having a neck portion 3a, a shoulder portion 3b, a body portion 3c, and a tail portion 3d is completed, as shown in FIG.

[0044] In the preparation step S11, polycrystalline silicon raw material is filled into the quartz crucible 11, and then the quartz crucible 11 is placed in the chamber 10. In order to increase the yield of silicon single crystals pulled in a single crystal pulling process, it is desirable to fill the quartz crucible with as much polycrystalline silicon raw material as possible, and to achieve this, it is desirable to fill the quartz crucible with a large amount of polycrystalline silicon chunks so that the height of the upper end of the polycrystalline silicon raw material is higher than the upper end of the quartz crucible. When the polycrystalline silicon raw material is melted, the silicon raw material becomes liquid, and its volume becomes sufficiently smaller than the volume of the aggregate of polycrystalline silicon chunks, and the height of the melt surface becomes lower than the upper end of the quartz crucible.

[0045] FIG. 4 is an explanatory diagram of the raw material melting step S12.

[0046] As shown in FIG. 4 , in the raw material melting step S12, a large amount of silicon raw material 4 loaded into a quartz crucible 11 is heated and melted by a heater 15 ( FIG. 4 (I) ). Typically, the silicon raw material 4 loaded into the quartz crucible 11 is a polycrystalline silicon chunk 4a (silicon chunk) with a maximum diameter of approximately 2 to 10 cm. However, as shown in the figure, a relatively large silicon block 4b (cut rod) can also be used. Generally, high-purity silicon for semiconductor devices is produced by the Siemens process, and the resulting polycrystalline silicon rod is finely crushed and processed into chunks. Such chunk silicon raw material is easy to handle and load into the quartz crucible 11, making it suitable as a silicon raw material for the CZ process.

[0047] When a silicon block 4b is used in combination, the silicon block 4b is first loaded into the bottom of the quartz crucible 11, and then a large amount of polycrystalline silicon chunks 4a is tightly packed between the quartz crucible 11 and the silicon block 4b. Therefore, when the quartz crucible 11 is viewed from above, the opening of the quartz crucible 11 is completely covered with the polycrystalline silicon chunks 4a. Even when the polycrystalline silicon chunks 4a are piled higher than the upper end of the quartz crucible 11, it is desirable that the shape of the peaks be as flat as possible. This is because if the peaks of the piled polycrystalline silicon chunks 4a are made steep, the peaks will collapse as the silicon raw material 4 melts, preventing a sudden change in the height of the silicon raw material 4 and the positional relationship of the individual polycrystalline silicon chunks 4a.

[0048] At the start of the raw material melting step S12, the polycrystalline silicon raw material 4 is piled up in the quartz crucible 11, so the quartz crucible 11 needs to be placed at a sufficiently low position so that the polycrystalline silicon raw material 4 does not come into contact with the thermal shield 17. The initial height of the quartz crucible 11 is set so that the distance (gap) from the upper end of the polycrystalline silicon raw material 4 to the lower end of the thermal shield 17 is a predetermined distance of about several tens of mm (for example, 50 mm).

[0049] As the melting of the polycrystalline silicon source material 4 progresses, the volume of the polycrystalline silicon source material 4 in the quartz crucible 11 decreases instead of increasing the amount of silicon melt 2, causing the polycrystalline silicon source material 4 to sink (FIG. 4(II)). If the polycrystalline silicon source material 4 sinks and is heated continuously without changing its height, the radiant heat from the heater 15 is not easily transmitted to the polycrystalline silicon source material 4, which reduces the efficiency of melting the source material and increases the thermal load on the quartz crucible 11, potentially causing deformation of the quartz crucible 11.

[0050] Therefore, the quartz crucible 11 is raised by the amount by which the polycrystalline silicon source material 4 has sunk (FIG. 4(III)). Specifically, the height position of the quartz crucible 11 is adjusted so that the distance (Gap) from the upper end of the polycrystalline silicon source material 4 to the lower end of the thermal shield 17 is maintained at a predetermined distance. The height position of the quartz crucible 11 may be changed, for example, when a sinking amount of 10 mm or more from the reference position (initial height) is detected.

[0051] At the start of the raw material melting step S12, the polycrystalline silicon raw material 4 is melted without rotating the quartz crucible 11, but halfway through the raw material melting step S12, the quartz crucible 11 starts to rotate, which allows the silicon raw material 4 in the quartz crucible 11 to be uniformly heated and reduces the thermal load on the quartz crucible 11.

[0052] In this way, the height adjustment of the quartz crucible 11 is repeatedly performed at a predetermined timing in accordance with the progress of melting of the silicon source material 4, thereby maintaining the height of the upper end of the polycrystalline silicon source material 4 at a substantially constant level. The height adjustment of the quartz crucible 11 is terminated when most of the silicon source material 4 in the quartz crucible 11 has melted ( FIG. 4 (IV) ). That is, the adjustment is terminated before all of the polycrystalline silicon source material in the quartz crucible 11 is completely melted. The reason for terminating the height adjustment of the quartz crucible 11 before the polycrystalline silicon source material 4 is completely melted is that after a large amount of silicon melt 2 is produced, the remaining polycrystalline silicon chunks 4a float on the melt surface, making it difficult to detect the height position of the polycrystalline silicon source material 4 by image processing, which will be described later. Furthermore, even if the remaining polycrystalline silicon chunks 4a are completely melted, the height of the silicon melt 2 does not change significantly, and therefore there is little need to adjust the height of the quartz crucible 11.

[0053] 5 is a schematic diagram illustrating a method for measuring the amount of change in height of the silicon source material according to the first embodiment of the present invention, and FIG. 6 is a flowchart illustrating the method for measuring the amount of change in height of the silicon source material.

[0054] As shown in FIGS. 5 and 6, the method for measuring the amount of change in height of the silicon source material 4 according to this embodiment is as follows: first, a furnace image (first furnace image M ａ ) (Step S21). The camera 20 photographs the silicon raw material 4 in the quartz crucible 11 from diagonally above. The camera 20 is preferably the same as the camera used to measure the diameter of the silicon single crystal 3 and the height of the melt surface 2s during the crystal pulling process, but a different camera may also be used.

[0055] Next, the first furnace image M ａ (Step S22), and then extract a plurality of feature points P from the center of gravity P Ａｖｅ is calculated, and this is used as the first height reference point P ｒａ(Step S23). A "feature point" is a point that is easily distinguishable from its surroundings. Therefore, the feature point P is detected from the viewpoint of whether it is unique compared to its surroundings, and the pixel at the corner that is significantly different from its surroundings in all directions is detected as the feature point. In FIG. 5, the multiple feature points P extracted from the image of the furnace interior are small dot marks, and the center of gravity P of the multiple feature points P is Ａｖｅ are indicated by large dots.

[0056] Next, a new image of the inside of the furnace (second image of the inside of the furnace M) is taken using the camera 20. ｂ ) (Step S24). As will be described in detail later, the camera 20 periodically captures images of the inside of the furnace at short intervals of, for example, 0.1 to 10 seconds, and the second image M ｂ is the first furnace image M when furnace images are periodically captured. ａ The image is taken in the next frame or several frames after the previous frame.

[0057] Next, the second furnace image M ｂ (Step S25), and then extract a plurality of feature points P from the center of gravity P Ａｖｅ is calculated, and this is used as the second height reference point P ｒｂ (Step S26). The method for extracting the plurality of feature points P is to ａ The number of feature points P to be acquired is also the same.

[0058] Next, the first furnace image M ａ The first height reference point P ｒａ y coordinate of P ｒａ (y) and the second furnace image M ｂ The second height reference point P ｒｂ y coordinate of P ｒｂ The difference between (y) and ΔY = P ｒａ (y)-P ｒｂ The amount of change in height Δh of the silicon raw material 4 is calculated from (y) (step S27). Ａｖｅ The change in the height (number of pixels) of the silicon raw material 4 is proportional to the change in the height Δh of the silicon raw material 4. ｒBy multiplying the change in the y coordinate ΔY (number of pixels) by a predetermined coefficient α, the change in height of the silicon source material 4 Δh=ΔY×α (mm) can be calculated.

[0059] After the height change measurement process (steps S21 to S27), the quartz crucible 11 is raised in accordance with the change in height Δh of the silicon raw material 4 (step S28). That is, a crucible height adjustment process is performed in which the quartz crucible 11 is raised by the amount by which the silicon raw material 4 has sunk. The timing for raising the quartz crucible 11 can be determined based on a preset threshold. For example, the threshold is set to 20 mm, and when the total amount of sunk from a certain point reaches 20 mm, the quartz crucible 11 is raised by the same amount (20 mm) as the amount of sunk. Here, if the threshold is set small, the height of the quartz crucible 11 can be finely adjusted at shorter intervals (high frequency), while if the threshold is set large, the height of the quartz crucible 11 can be adjusted greatly at longer intervals (low frequency).

[0060] FIG. 7 is a diagram for explaining characteristic points in an image of the inside of a furnace, and is a schematic diagram of a photographed image of silicon raw material in a quartz crucible.

[0061] As shown in Figure 7, feature points are detected from the perspective of whether a certain point of interest is unique compared to its surroundings. For example, silicon melt 2 is present in area A1 indicated by a rectangular frame, and no abrupt change in color tone (pixel value) is observed. Therefore, a feature point cannot be extracted. Area A2 indicated by a rectangular frame contains a corner of polycrystalline silicon chunk 4a, and therefore abrupt changes in color tone (pixel value) are observed in both the X-axis and Y-axis directions. Therefore, this area is easily distinguishable from surrounding pixels and is suitable as a feature point.

[0062] Although the method for detecting the feature points P is not particularly limited, the Shi-Tomasi method is preferably used. Feature point detection using the Shi-Tomasi method is performed by searching for differences in pixel values ​​relative to the amount of movement of the pixel position (u, v) in all directions. The score value E(u, v) of a feature point at an arbitrary pixel position (u, v) can be calculated using equation (1).

[0063]

[0064] where w(x, y) is the window function, I(x + u, y + v) is the pixel value (intensity) at the shift position, and I(x, y) is the pixel value (intensity) at the measurement position. The larger the score value E(u, v), the easier it is to distinguish as a feature point.

[0065] The feature points P in the image are extracted in descending order of score value, and for example, the top 100 score values ​​are used to determine the "height reference point" of the silicon raw material. If the number of feature points (number of samples n) is too small, it will lead to a decrease in measurement accuracy, and if it is too large, it will not only increase the amount of calculation but also cause a decrease in measurement accuracy. Therefore, an appropriate number is required, and it is preferable to have 50 to 1000.

[0066] Multiple feature points P １ , P ２ , ... P ｎ Center of gravity P Ａｖｅ (x, y) are the central coordinates of the plurality of feature points, １ ~P ｎ The average value of the x-coordinate of Ａｖｅ (x) = (x １ +x ２ +...+x ｎ ) / n and a plurality of feature points P １ ~P ｎ The average value of the y coordinate of P Ａｖｅ (y) = (y １ +y ２ +...+y ｎ ) / n, where the x coordinate is the horizontal coordinate and the y coordinate is the vertical coordinate.

[0067] Multiple feature points P １ ~P ｎ Center of gravity P Ａｖｅ indicates the average height position of the upper surface of the silicon raw material 4, which has height variations. As shown in FIG. 5, the positions of the plurality of characteristic points P in the height direction vary, so that the plurality of characteristic points P １ ~P ｎ Center of gravity P Ａｖｅindicates the average value of the height position of the upper surface of an aggregate of many uneven polycrystalline silicon chunks, and does not indicate the height of the upper end of silicon source material 4. However, if the height position (Gap) of silicon source material 4 is controlled taking into account the difference between the maximum and average heights of silicon source material 4, accidents in which silicon source material 4 comes into contact with thermal shield 17 do not occur, and it is not necessary to strictly determine the absolute height of silicon source material 4.

[0068] The center of gravity P of the multiple feature points P obtained from each furnace image Ａｖｅ indicates the average height (instantaneous value) of the silicon raw material 4 at the time of photographing. As the raw material melting process progresses, multiple feature points P １ , P ２ , ... P ｎ gradually moves downward, and the center of gravity P of the multiple feature points P Ａｖｅ Therefore, the center of gravity P of the plurality of characteristic points P obtained from the plurality of images of the inside of the furnace taken at different times is Ａｖｅ By comparing these values, the amount of change (decrease) in the height of the silicon source material 4 can be determined.

[0069] 8A and 8B are sequence diagrams showing the timing of acquiring the first and second in-furnace images in each measurement step.

[0070] As shown in FIGS. 8(a) and 8(b), the camera 20 captures images of the inside of the furnace at intervals T Ｐ The photographing period for the furnace interior images is T ｐ is the crucible rotation period T when the quartz crucible 11 is rotated. ｃ In this embodiment, it is preferable that the value is an integer multiple of T Ｐ = 1 second.

[0071] The measurement method shown in FIG. 8(a) is a first furnace image M ａ After taking the second furnace image M ｂ For example, in the first measurement step, the first furnace image M ａ is time t １ The second furnace image M ｂ is time t ２ = t １+T Ｐ The first furnace image M ａ The first height reference point P ｒａ and the second furnace image M ｂ The second height reference point P ｒｂ The difference ΔP = P ｒａ -P ｒｂ From T Ｐ The amount of change Δh in the height of the silicon source material 4 per second is calculated.

[0072] In the second measurement step, the first furnace image M ａ is time t ２ The second furnace image M ｂ is time t ３ = t ２ +T Ｐ The first furnace image M ａ The first height reference point P ｒａ and the second furnace image M ｂ The second height reference point P ｒｂ The difference ΔP = P ｒａ -P ｒｂ From T Ｐ The amount of change Δh in the height of the silicon raw material 4 per second is calculated. In this case, the first furnace image M ａ is the second furnace image M in the first measurement step. ｂ The third and subsequent measurement steps are performed in the same manner as the second. In this way, the first furnace image M ａ The second furnace image M ｂ By sampling at the shortest possible interval, changes in the height of the silicon raw material can be detected early.

[0073] The measurement method shown in FIG. 8(b) is a first furnace image M ａ After a suitable time has passed, the second furnace image M ｂ For example, in the first measurement step, the first furnace image M ａ is time t １ The second furnace image M ｂ is time t ４ = t １ +3T Ｐ The first furnace image M ａThe first height reference point P ｒａ and the second furnace image M ｂ The second height reference point P ｒｂ The difference ΔP = P ｒａ -P ｒｂ From 3T Ｐ The amount of change Δh in the height of the silicon source material 4 per second is calculated.

[0074] In the second measurement step, the first furnace image M ａ is time t ２ The second furnace image M ｂ is time t ５ = t ２ +3T Ｐ The first furnace image M ａ The first height reference point P ｒａ and the second furnace image M ｂ The second height reference point P ｒｂ The difference ΔP = P ｒａ -P ｒｂ From 3T Ｐ The amount of change Δh in the height of the silicon raw material 4 per second is calculated. ａ After taking the second furnace image M ｂ The time interval between the acquisition of the images inside the furnace is set as the shooting period T Ｐ By making it longer than the above, it is possible to reliably detect changes in the height of the silicon raw material.

[0075] FIG. 9 is a graph showing a schematic diagram of the change in the position of the center of gravity of the characteristic points when the height of the quartz crucible 11 is adjusted.

[0076] As shown in FIG. 9, the center of gravity P Ａｖｅ However, the center of gravity P Ａｖｅ is the threshold P Ｔｈ When the center of gravity P of the characteristic point is reached, the quartz crucible 11 is raised by a certain amount. Ａｖｅ is the threshold P Ｔｈ That is, the silicon source material 4 can be maintained at a predetermined height, and an excessive decrease in height due to melting of the silicon source material 4 can be prevented.

[0077] As described above, the quartz crucible 11 does not need to be rotated in the first half of the raw material melting step S12, but it is better to rotate the quartz crucible 11 in the second half to reduce the thermal load on the quartz crucible 11. When the quartz crucible 11 is rotated, the positional relationship of the silicon raw material 4 with respect to the camera 20 changes, and the position of the characteristic point also changes. As a result, the center of gravity P Ａｖｅ The height of the silicon source material 4 calculated from the above also changes.

[0078] FIG. 10 is a schematic diagram showing the change in the position of the characteristic point when the quartz crucible 11 is rotated, where (a) shows the state before rotation and (b) shows the state after rotation.

[0079] 10( a) and 10(b), when the quartz crucible 11 is rotated, the feature points also rotate, and the coordinate positions of the feature points in the captured image change. Therefore, simply evaluating the time change in the center of gravity of the plurality of feature points makes it difficult to determine whether the time change in the center of gravity of the plurality of feature points is caused by the rotation of the quartz crucible 11 or by the melting of the silicon raw material 4.

[0080] On the other hand, if there is no change in the height position of the silicon raw material 4, the coordinates of a certain feature point will return to the original position before one rotation when the quartz crucible 11 rotates once. Therefore, by comparing feature points obtained from images captured in synchronization with the rotation period of the quartz crucible 11, it is possible to obtain the amount of change in height of the silicon raw material 4 without the influence of the rotation of the quartz crucible 11.

[0081] 11 and 12 are sequence diagrams showing an example of the timing of acquiring the first and second in-furnace images in each measurement step.

[0082] As shown in FIGS. 11 and 12, when measuring the amount of change in the height of the silicon raw material while rotating the quartz crucible 11, first, the crucible rotation period T ｃ and the crucible rotation period T ｃImages of the interior of the furnace are taken at a period Tp that is an integer multiple of , and the height reference point of the silicon raw material is determined in each image of the interior of the furnace. For example, if the rotation speed of the quartz crucible is 1 rpm and the photographing period of the camera is 1 second, 60 images of the interior of the furnace are taken while the quartz crucible 11 makes one rotation, and instantaneous values ​​of 60 height reference points are determined.

[0083] The measurement method shown in FIG. 11 is a first furnace image M ａ After the crucible rotation period, the second furnace image M ｂ For example, in the first measurement step, the first furnace image M ａ is time t １ The second furnace image M ｂ is time t ６１ = t １ +T ｃ The first furnace image M ａ The first height reference point P ｒａ and the second furnace image M ｂ The second height reference point P ｒｂ The difference ΔP = P ｒａ -P ｒｂ From T ｃ The amount of change Δh in the height of the silicon source material 4 per second is calculated.

[0084] In the second measurement step, the first furnace image M ａ is time t ２ The second furnace image M ｂ For example, at time t ６２ = t ２ +T ｃ The first furnace image M ａ The first height reference point P ｒａ and the second furnace image M ｂ The second height reference point P ｒｂ The difference ΔP = P ｒａ -P ｒｂ From T ｃ The amount of change Δh in the height of the silicon raw material 4 per second is calculated. ａ After taking the second furnace image M ｂ The time interval until the sample is collected is the crucible rotation period T ｃBy setting the height of the silicon raw material to an integer multiple of , the influence of the rotation of the crucible can be eliminated and the change in the height of the silicon raw material can be reliably detected.

[0085] The measurement method shown in FIG. 12 is to determine a height reference point of the silicon raw material from each of a plurality of images of the inside of the furnace, and calculate the crucible rotation period T ｃ For example, in the first measurement step, the amount of change in the height of the silicon source material is measured using a moving average value of t １ ~t ６０ 60 images of the inside of the furnace taken during １ ~M ６０ 60 first height reference points P obtained from (a plurality of first furnace interior images) ｒ１ ~P ｒ６０ Moving average value MA ａ is calculated, and then at time t ２ ~t ６１ 60 images of the inside of the furnace taken during ２ ~M ６１ 60 second height reference points P obtained from (multiple second furnace interior images) ｒ２ ~P ｒ６１ Moving average value MA ｂ is calculated, and the first height reference point P ｒ１ ~P ｒ６０ Moving average value MA ａ and the second height reference point P ｒ２ ~P ｒ６１ Moving average value MA ｂ Difference ΔMA = MA ａ -MA ｂ From T ｐ The amount of change Δh in the height of the silicon raw material 4 per second is calculated.

[0086] In the second measurement step, at time t ２ ~t ６１ 60 images of the inside of the furnace taken during ２ ~M ６１ 60 first height reference points P obtained from (a plurality of first furnace interior images) ｒ２ ~P ｒ６１ Moving average value MA ａ is calculated, and then at time t ３ ~t ６２ 60 images of the inside of the furnace taken during ３ ~M ６２60 second height reference points P obtained from (multiple second furnace interior images) ｒ３ ~P ｒ６２ Moving average value MA ｂ is calculated, and the first height reference point P ｒ１ ~P ｒ６０ Moving average value MA ａ and the second height reference point P ｒ２ ~P ｒ６１ Moving average value MA ｂ Difference ΔMA = MA ａ -MA ｂ From T ｐ The amount of change Δh in the height of the silicon source material 4 per second is calculated. ３ Thereafter, by determining the moving average value MA of the crucible rotation period of the height reference point as described above, the amount of change Δh in the height of the silicon raw material 4 can be continuously measured.

[0087] FIG. 13 is a graph showing the measurement results of the amount of change in height of the silicon source material 4 and the control results of the quartz crucible during the source material melting step S12.

[0088] As shown in FIG. 13, in the first half of the raw material melting step S12 in which the quartz crucible 11 is not rotated, the center of gravity P of the plurality of feature points P extracted from each furnace image is Ａｖｅ Since the instantaneous value of (the feature point average height) is stable, the amount of change Δh in the height of the silicon raw material 4 can be calculated from the time change in the center of gravity. Then, by gradually raising the quartz crucible 11 in accordance with the amount of change Δh in the height of the silicon raw material 4, the height position of the silicon raw material 4 can be maintained within an appropriate range, thereby improving the efficiency of melting the raw material and reducing the thermal load on the quartz crucible.

[0089] In the latter half of the raw material melting step S12 in which the quartz crucible 11 is rotated, the center of gravity P of the plurality of feature points P extracted from each furnace image is calculated. Ａｖｅ However, the center of gravity P of the plurality of characteristic points P synchronized with the rotation period of the quartz crucible 11 becomes large. ＡｖｅThe moving average value (time average value) of the rotation period of the quartz crucible 11 is a stable value that is free from the influence of the rotation of the quartz crucible 11. Therefore, by gradually raising the quartz crucible 11 in accordance with the change in the height of the silicon raw material 4 over time that is calculated from the moving average value of the rotation period of the quartz crucible 11, the height position of the silicon raw material 4 can be maintained within a certain range, thereby improving the melting efficiency of the silicon raw material and reducing the thermal load on the quartz crucible.

[0090] As described above, in the first half of the raw material melting step S12, in which the quartz crucible 11 is not rotated, the time change of the instantaneous values ​​of the centroids of the plurality of feature points is stable, and therefore, unlike the second half of the raw material melting step S12, there is no need to employ a moving average value of the centroids synchronized with the rotation period of the quartz crucible 11. However, in order to improve the reliability of the measurement accuracy of the height of the silicon raw material 4, it is preferable to use the moving average value of the centroids of the plurality of feature points also in the first half of the raw material melting step S12, and it is particularly preferable to use the moving average value of the rotation period of the quartz crucible 11.

[0091] As described above, the height measurement method for silicon source material 4 according to this embodiment involves photographing the silicon source material 4 in a quartz crucible from diagonally above with a camera during the source material melting step in the CZ method manufacturing process for silicon single crystals, extracting multiple feature points from the photographed image, and determining the height of the silicon source material 4 from the center of gravity of the multiple feature points, thereby making it possible to stably determine the height of the silicon source material 4 in the quartz crucible during the source material melting step. Therefore, the height position of the quartz crucible can be automatically adjusted based on the photographed image.

[0092] In addition, the height measurement method of the silicon raw material 4 according to this embodiment determines the amount of change in the height position of the silicon raw material 4 by comparing multiple feature points obtained from the captured image in synchronization with the rotation period of the quartz crucible, so that the amount of change in the height position of the silicon raw material 4 can be determined without being affected by the rotation of the quartz crucible.

[0093] Furthermore, the method for producing a silicon single crystal according to this embodiment includes a preparation step of placing a quartz crucible filled with silicon source material 4 in a chamber, a source material melting step of melting the silicon source material 4 to produce a silicon melt, and a crystal pulling step of pulling a silicon single crystal from the silicon melt. In the source material melting step, the silicon source material 4 in the quartz crucible is photographed obliquely from above with a camera, multiple feature points are extracted from the photographed image, and a height reference point for the silicon source material 4 is determined from the center of gravity of the multiple feature points. Therefore, the amount of change in the height of the silicon source material 4 in the quartz crucible during the source material melting step can be stably determined from the photographed image. Therefore, the height position of the quartz crucible can be automatically adjusted based on the photographed image.

[0094] Next, a second embodiment of the present invention will be described. In the first embodiment described above, the center of gravity P of a plurality of feature points P extracted from the furnace interior image is calculated. Ａｖｅ is determined as a height reference point of the silicon source material, and the amount of change in height of the silicon source material is determined from the time change of the height reference point, but in the second embodiment, the amount of change in height of the silicon source material 4 is determined from the time change of the reference coordinate of a template image taken from an image inside the furnace. This will be described in detail below.

[0095] Fig. 14 is a schematic diagram illustrating a method for measuring the amount of change in height of the silicon source material 4 according to the second embodiment of the present invention, and Fig. 15 is a flowchart showing the method for measuring the amount of change in height of the silicon source material 4.

[0096] As shown in FIGS. 14 and 15, in the measurement of the change in height of the silicon raw material 4 according to this embodiment, first, a first furnace image M ａ is photographed (FIG. 14(I), step S41).

[0097] Next, the first furnace image M ａA template region is set at an appropriate position within the source material melting step S12, and a template image TM is collected from the template region (FIG. 14(I), step S42). Here, the "appropriate position" refers to a position where the polycrystalline silicon chunks remain present as long as possible from the start to just before the end of the source material melting step S12. If the polycrystalline silicon chunks are set at a position where they cannot be observed during the source material melting step S12, continuous measurement of the amount of change in height of the silicon source material 4 becomes impossible.

[0098] Reference coordinates P of the template image TM ａ (x, y) is the coordinate of the upper left corner of the image, for example. The position of the reference coordinate of the rectangular image is not particularly limited, and may be a corner other than the upper left, a position slightly shifted from the corner, or the center of the image. In this embodiment, the upper left of the image is used as the reference coordinate P ａ (x, y), which is the first height reference point P ｒａ (FIG. 14(I), step S43) The size of the template region (template image) is not particularly limited, but can be set to, for example, 100px x 100px.

[0099] Next, the first furnace image M ａ After a predetermined time has elapsed since the image was taken, the second furnace image M ｂ (FIG. 14 (II), step S44). ｂ The timing of acquisition of the first furnace image M ａ This may be immediately after shooting (next frame) or several frames later.

[0100] Next, the second furnace image M ｂA search range SR is set within the template area, covering a range slightly wider than the template area, and pattern matching is performed between the template image TM and the reference image RM within the search range SR (FIG. 14 (II), step S45). The search range SR is a range wider than the template area including the template area, and is set so that the template area is located in the center of the search range SR. If the search range SR is too wide, unnecessary matching processing increases, and if the search range SR is too narrow, significant changes in the height of the silicon raw material 4 cannot be detected. Therefore, the size of the search range SR is determined taking into account the image processing capability and the amount of change in the template image. For example, if the size of the template image is 100px x 100px, the search range SR can be set to 200px x 200px.

[0101] First, template matching starts from the upper left of the search range SR, for example, and continues until the lower right of the search range SR is reached. After that, the reference coordinate P of the reference image RM having the same size as the template image TM, which has the highest correlation with the template image TM, is calculated. ｂ (x, y) is calculated and used as the second height reference point P ｒｂ (FIG. 14(III), step S46).

[0102] Next, the first height reference point P ｒａ y coordinate of P ｒａ (y) and the second reference point P, which is the reference coordinate of the reference image RM. ｒｂ y coordinate of P ｒｂ The difference between (y) and ΔY = P ｒａ (y)-P ｒｂ (y) = P ａ (y)-P ｂ Then, the change in height of the silicon raw material 4, Δh=ΔY×α (mm), is calculated from the difference ΔY (FIG. 14 (IV), step S47). Thereafter, the quartz crucible 11 is raised in accordance with the change in height Δh of the silicon raw material 4, thereby adjusting the height of the silicon raw material 4 (step S48).

[0103] FIG. 16 is a diagram for explaining the pattern matching process of a template image TM of M×N pixels.

[0104] 16 , the vertical size of the template image TM is M pixels and the horizontal size is N pixels, the luminance at relative coordinates (i, j) in the template image TM is T(i, j), and the luminance at relative coordinates (i, j) in the reference image RM is I(i, j). Note that the relative coordinates of the template image TM are relative coordinates when the reference coordinates of the template image TM are used as the reference, and the relative coordinates of the reference image RM are relative coordinates when the reference coordinates of the reference image RM are used as the reference.

[0105] Here, the average brightness value μ of the template image TM Ｔ and the average brightness value μ of the reference image RM Ｉ are calculated as follows, respectively:

[0106]

[0107]

[0108] Furthermore, the correlation C between the template image TM and the reference image RM is μ Ｔ and μ Ｉ It can be calculated using the following:

[0109] The correlation degree C takes a value between -1 and +1, and in the case of a perfect match, C = 1. The acquisition position of the reference image RM is shifted by one pixel at a time from the top left to the bottom right of the search range SR to perform the matching process, and the point with the highest correlation degree C becomes the current position of the template image TM.

[0110] In this way, the correlation C between the template image TM and the reference image RM is calculated by normalizing the image by the average pixel value, and the reference coordinate of the reference image RM where the correlation C is maximum is set as the current position of the template image TM, thereby determining the amount of movement of the template image TM.

[0111] In the above embodiment, one template region is set in the first furnace image and one template image TM is acquired, but multiple template regions may be set and multiple template images may be acquired. For example, as shown in Fig. 17, nine template regions may be set in the first furnace image and nine template images TM may be acquired. In this case, nine measurement values ​​(changes in the height of the silicon source material 4, Δh) are obtained in one matching process, and the average value of these measurement values ​​can be calculated to more accurately determine the change in the height of the silicon source material 4.

[0112] The acquisition position of the template image TM used to measure the amount of change in the height of the silicon raw material is fixed, and the acquisition position of the next template image TM does not change even if the previous template image TM has moved. In other words, the acquisition of the template image TM is always performed in the template area, and the set position of the template area does not change. For example, as shown in FIG. 14(IV), ａ From P ｂ Even if the movement to the original position P ａ In this way, it is possible to prevent the template area from continuing to move and the template image from being collected in a place that is not suitable for collecting a template image.

[0113] As described above, the crucible is not rotated in the first half of the raw material melting step S12, but in the second half, the crucible is rotated while the silicon raw material is heated and melted, so the position of the silicon raw material changes in the direction of rotation. Therefore, even if the position of the silicon raw material changes due to melting, it is not possible to distinguish whether the change in the position of the silicon raw material is due to rotation or due to melting. Therefore, in this embodiment as well, in the second half of the raw material melting step S12 in which the crucible is rotated, the first and second height reference points P ｒａ , P ｒｂ The timing of taking the images inside the furnace to obtain the crucible rotation period T ｃWhen the quartz crucible rotates once, the raw material returns to its original position, so by comparing images taken at the same rotational position, it is possible to detect changes in the position of the raw material due to melting, and the influence of the rotation of the crucible can be eliminated.

[0114] As described above, the method for measuring the height of the silicon raw material according to this embodiment involves photographing the polycrystalline silicon raw material in the quartz crucible 11 from obliquely above with the camera 20 during the raw material melting step S12 in the manufacturing process of silicon single crystal by the CZ method, and obtaining the first furnace image M ａ from the template image TM and the first height reference point P ｒａ is taken, and the first furnace image M ａ The second furnace image M taken after ｂ The second height reference point P ｒｂ is calculated, and the first height reference point P ｒａ and the second height reference point P ｒｂ Since the amount of change in height Δh of the silicon raw material 4 in the quartz crucible 11 during the raw material melting step S12 is calculated from the difference between the measured values ​​and the actual values, the amount of change in height Δh of the silicon raw material 4 in the quartz crucible 11 during the raw material melting step S12 can be stably calculated. Therefore, the height position of the quartz crucible can be automatically adjusted based on the image inside the furnace.

[0115] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included in the scope of the present invention.

[0116] For example, in the first embodiment, the Shi-Tomasi method is used as a method for detecting feature points in an image, but other methods may also be used.

[0117] REFERENCE SIGNS LIST 1 Single crystal manufacturing apparatus 2 Silicon melt 2s Melt surface 3 Silicon single crystal 3a Neck portion 3b Shoulder portion 3c Body portion 3d Tail portion 3i Silicon single crystal ingot 4 Polycrystalline silicon raw material 4a Polycrystalline silicon lump 4b Silicon block 10 Chamber 10a Main chamber 10b Pull chamber 10c Gas inlet 10d Gas outlet 10e Sight window 11 Quartz crucible 12 Graphite crucible 13 Rotating shaft 14 Shaft drive mechanism 15 Heater 16 Heat insulating material 17 Heat shield 17a Opening 18 Pulling wire 19 Wire winding mechanism 20 Camera 21 Image processing unit 22 Control unit 23 Straightening member (purge tube) A1 Area in photographed image A2 Area in photographed image M ａ First furnace image M ｂ Second furnace image P ｒａ First height reference point P ｒｂ Second height reference point RM Reference image SR Search range S11 Preparation process S12 Raw material melting process S13 Crystal pulling process S14 Liquid contact process S15 Necking process S16 Shoulder portion growing process S17 Body portion growing process S18 Tail portion growing process TM Template image T ｃ Crucible rotation period T ｐ Shooting period of the furnace image Δh Change in height of silicon raw material

Claims

1. A method for measuring an amount of change in height of a silicon raw material by taking an image of the inside of a furnace containing a large number of polycrystalline silicon chunks filled in a quartz crucible from above with a camera during a raw material melting process in which the silicon raw material is heated to produce molten silicon, the method comprising the steps of: determining a first height reference point of the silicon raw material from a first image of the furnace taken with the camera; determining a second height reference point of the silicon raw material from a second image of the furnace taken with the camera after the first image of the furnace is taken; and determining the amount of change in height of the silicon raw material from the difference between the first height reference point and the second height reference point.

2. A method for measuring the change in height of a silicon raw material as described in claim 1, wherein the first height reference point is the center of gravity of a plurality of feature points extracted from the first furnace image, and the second height reference point is the center of gravity of a plurality of feature points extracted from the second furnace image.

3. The method for measuring the change in height of a silicon raw material according to claim 2, wherein the number of the plurality of characteristic points is 50 or more and 1,000 or less.

4. The method for measuring the change in height of a silicon raw material according to claim 2, wherein the plurality of feature points are extracted by the Shi-Tomasi method.

5. A method for measuring the change in height of a silicon raw material as described in claim 2, which comprises heating and melting the silicon raw material while rotating the quartz crucible, and determining the first and second height reference points, respectively, from the first and second furnace images taken in synchronization with the rotation period of the quartz crucible.

6. A method for measuring the change in height of a silicon raw material as described in claim 2, comprising: heating and melting the silicon raw material while rotating the quartz crucible; and determining the change in height of the silicon raw material from the difference between a moving average value of a plurality of first height reference points and a moving average value of a plurality of second height reference points obtained from images of the inside of the furnace for the rotation period of the quartz crucible.

7. A method for measuring the change in height of silicon raw material as described in claim 1, wherein the first height reference point is the reference coordinate of a template image taken from a specified template area in the first furnace image, and the second height reference point is the reference coordinate of a reference image which has the maximum correlation with the template image when a specified search range of the second furnace image is scanned and pattern matching with the template image is performed.

8. A method for measuring the amount of change in height of a silicon raw material as described in claim 7, wherein the degree of correlation is determined by comparing the average brightness value of each pixel of the template image with the average brightness value of each pixel of the reference image.

9. The method for measuring the change in height of a silicon raw material according to claim 8, wherein the search range is an area wider than the template area and has a center coincident with that of the template area and covers the template area.

10. A method for measuring the amount of change in height of a silicon feedstock as described in claim 7, wherein a first amount of change and a second amount of change in height of the silicon feedstock are sequentially calculated, and the position at which the template image used to calculate the second amount of change in height of the silicon feedstock is sampled is the same as the position at which the template image used to calculate the first amount of change.

11. A method for measuring the amount of change in the height of a silicon raw material as described in claim 10, wherein the first amount of change in the height of the silicon raw material is determined using the first furnace image taken at a first timing and the second furnace image taken at a second timing after the first timing, and the second amount of change in the height of the silicon raw material is determined using the first furnace image taken at a third timing after the first timing and the second furnace image taken at a fourth timing after the second and third timings.

12. A method for measuring the amount of change in height of silicon raw material as described in claim 7, comprising the steps of: setting a plurality of template areas within the first furnace image; determining a plurality of first height reference points from a plurality of template images taken from each of the plurality of template areas; determining a plurality of second height reference points corresponding to each of the plurality of first height reference points from the second furnace image; and determining an average value of the amount of change in height of a plurality of silicon raw material from the plurality of first height reference points and the plurality of second height reference points.

13. A method for measuring the change in height of a silicon raw material as described in claim 7, comprising heating and melting the silicon raw material while rotating the quartz crucible, and determining the first and second height reference points, respectively, from the first and second furnace images taken in synchronization with the rotation period of the quartz crucible.

14. A method for measuring the change in height of a silicon raw material as described in claim 7, comprising heating and melting the silicon raw material while rotating the quartz crucible, and calculating the change in height of the silicon raw material from the difference between a moving average value of a plurality of first height reference points and a moving average value of a plurality of second height reference points obtained from images of the inside of the furnace for the rotation period of the quartz crucible.

15. A method for measuring the change in height of a silicon raw material as described in claim 1, wherein the polycrystalline silicon chunk has multiple corner portions, and when initially filled into the quartz crucible, the polycrystalline silicon chunk is filled to a position higher than the upper end of the quartz crucible, and the opening of the quartz crucible is covered by the polycrystalline silicon chunk.

16. A method for producing a silicon single crystal, comprising: a preparation step of placing a quartz crucible filled with a silicon raw material containing numerous polycrystalline silicon lumps in a chamber; a raw material melting step of heating the silicon raw material with a heater to produce a silicon melt; and a crystal pulling step of pulling a silicon single crystal from the silicon melt, wherein the raw material melting step includes a height change measurement step of photographing the silicon raw material from above with a camera to measure the amount of change in height of the silicon raw material; and a crucible height adjustment step of adjusting the height of the quartz crucible in accordance with the change in height of the silicon raw material, wherein the height change measurement step measures the amount of change in height of the silicon raw material using a method for measuring the amount of change in height of a silicon raw material described in any one of claims 1 to 15.

17. A silicon single crystal manufacturing apparatus comprising: a chamber; a quartz crucible for holding a silicon raw material within the chamber; a heater for heating the silicon raw material; a crucible drive mechanism for rotating and raising and lowering the quartz crucible; a crystal pulling mechanism for pulling up a single crystal from the silicon molten liquid in the quartz crucible; a camera for photographing the silicon raw material from above; an image processing unit for processing images captured by the camera; and a control unit for controlling the operation of the heater, the crucible drive mechanism and the crystal pulling mechanism, wherein the camera photographs the silicon raw material from above during a raw material melting process in which the silicon raw material, which includes a number of polycrystalline silicon chunks, is heated by the heater to produce a silicon molten liquid, and the image processing unit measures an amount of change in height of the silicon raw material using a method for measuring an amount of change in height of a silicon raw material described in any one of claims 1 to 15.

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