WO2025046999A1 - 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 - Google Patents

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 P_ra of the silicon raw material from a first in-furnace image M_a captured by using the camera (S21-S23); obtaining a second height reference point P_rb of the silicon raw material from a second in-furnace image M_b captured after capturing the first in-furnace image M_a (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 P_ra and the second height reference point P_rb (S27).

Description

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

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

The Czochralski method (CZ method) is known as a method for producing silicon single crystals for semiconductor devices. In the CZ method, polycrystalline silicon raw material is heated in a quartz crucible to produce silicon melt, and a seed crystal is immersed in the silicon melt and gradually pulled up, growing a large single crystal at the bottom end of the seed crystal. The CZ method can increase the production yield of large-diameter silicon single crystals.

In the CZ method, polycrystalline silicon raw material in a quartz crucible is heated by radiant heat from a heater to produce molten silicon. At this time, it is necessary to adjust the height position of the quartz crucible according to the progress of melting the polycrystalline silicon raw material. This is because if the quartz crucible is kept at a relatively low position compared to the heater, the thermal load from the radiant heat from the heater will be large, and there is a risk of the quartz crucible deforming. If the quartz crucible deforms, the convection of the melt will change, causing abnormalities in the oxygen characteristics of the silicon single crystal. There may also be cases where the quartz crucible comes into contact with a heat shield placed above it, making it difficult to continue the crystal pulling process.

　Conventionally, workers adjusted the height of the quartz crucible as needed according to the progress of melting the silicon raw material, but this imposed a heavy burden on the workers. In addition, because the height of the silicon raw material was judged by the worker's eyes, there was variation in judgment depending on the worker, and there was a risk of human error.

Regarding the automation of the vertical position adjustment of a quartz crucible when melting raw material, Patent Document 1 describes how, 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 specified 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.

JP 2017-7077981 A

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 using the principle of triangulation. This requires precise position adjustment (calibration) of the two cameras, and is subject to restrictions due to the structure inside the furnace. In addition, there is a problem in that it cannot be applied while the crucible is rotating, because it is not possible to distinguish between changes in the height of the raw material and changes in the position of the raw material in the image.

The object of the present invention is therefore to provide a method for stably measuring the amount of change in height of silicon raw material during the raw material melting process, and a method and apparatus for producing silicon single crystals using the same.

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

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 reliably determined from images captured by the camera. Therefore, the vertical position of the quartz crucible can be automatically adjusted based on the images captured by the camera.

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 collection of numerous polycrystalline silicon chunks filled in a quartz crucible is uneven, so the measurement accuracy of the amount of change in height of the silicon raw material can be improved by finding the amount of change in height of the silicon raw material using the average value of the height direction position of the upper surface.

The number of the multiple feature points is preferably 50 or more and 1000 or less. If the number of feature 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 multiple feature points.

The plurality of feature points are preferably extracted using the Shi-Tomasi method. The Shi-Tomasi method makes it possible to easily determine a given number of feature points from an image with high accuracy.

In the present invention, it is preferable that 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 that has the highest correlation with the template image when a specified search range in the second furnace image is scanned and pattern matching is performed with the template image. This makes it possible to stably measure the amount of change in the height of the silicon raw material from the start of the raw material melting process until just before its end.

In the present invention, it is preferable that the correlation degree is calculated 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. This makes it possible to accurately calculate the movement position of the template image with as little calculation as possible.

In the present invention, it is preferable that the search range is a region that is centered on the template region and is larger than the template region, covering the template region. This makes it possible to accurately determine the movement position of the template image with as little calculation as possible.

The method for measuring the amount of change in the height of a silicon raw material according to the present invention sequentially determines a first amount of change and a second amount of change in the height of the silicon raw material, and it is preferable that the position at which the template image is collected when determining the second amount of change in the height of the silicon raw material is the same as the position at which the template image is collected when determining the first amount of change. This makes it possible to prevent a situation in which the template area continues to move and the template image is collected in a location that is not suitable for collecting the template image.

The method for measuring the amount of change in the height of the silicon raw material according to the present invention preferably determines the first amount of change in the height of the silicon raw material 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 amount of change in the height of the silicon raw material 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 the height of the silicon raw material.

The method for measuring the amount of change in height of the silicon raw material according to the present invention preferably includes 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 the plurality of silicon raw material 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 raw material.

The method for measuring the change in height of the silicon raw material according to the present invention preferably involves 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. This makes it possible to accurately determine the amount of sinking of the silicon raw material due to melting by eliminating the effect of the rotation of the quartz crucible.

The method for measuring the amount of change in height of the silicon raw material according to the present invention preferably involves heating and melting the silicon raw material while rotating the quartz crucible, and determining the amount of change in height of the silicon raw material from the difference between the moving average value of a plurality of first height reference points and the moving average value of a plurality of second height reference points, which are obtained from images of the inside of the furnace for the rotation period of the quartz crucible. This makes it possible to accurately determine the amount of sinking of the silicon raw material due to melting by eliminating the influence of the rotation of the quartz crucible.

In the present invention, it is preferable that the polycrystalline silicon chunk has multiple corners, is filled to a position higher than the upper end of the quartz crucible when initially filled into the quartz crucible, and the opening of the quartz crucible is covered by the polycrystalline silicon chunk. It is also 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 such characteristics, it is possible to improve the measurement accuracy of the amount of change in the height of the silicon raw material by image processing.

　In order to solve the above problem, the method for producing silicon single crystals according to the present invention includes a preparation step of placing a quartz crucible filled with silicon raw material containing numerous 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, the raw material melting step including a height change measurement step of photographing the silicon raw material from above with a camera to measure the amount of change in the 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 the height of the silicon raw material, the height change measurement step being characterized in that the amount of change in the height of the silicon raw material is measured using the method for measuring the amount of change in the height of the silicon raw material according to the present invention described above.

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 reliably determined from images captured by the camera. Therefore, the vertical position of the quartz crucible can be automatically adjusted based on the images captured by the camera.

Furthermore, the silicon single crystal manufacturing apparatus according to the present invention comprises a chamber, a quartz crucible that holds silicon raw material in 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 the image captured by the camera, and a control unit that controls the operation of the heater, the crucible drive mechanism, and the crystal pulling mechanism, and is characterized in that the camera photographs the silicon raw material from above during a raw material melting process in which the silicon raw material containing 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.

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 images captured by the camera. Therefore, the height of the quartz crucible can be automatically adjusted based on the images captured by the camera.

The present invention provides a method for measuring the change in height of silicon raw material that can stably measure the change in height of silicon raw material during the raw material melting process, as well as a method and apparatus for manufacturing silicon single crystals using the same.

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. FIG. 2 is a flow chart showing the steps of manufacturing a silicon single crystal by 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 the raw material melting process. FIG. 5 is a schematic diagram for explaining a method for measuring the amount of change in height of the silicon source material according to the first embodiment of the present invention. FIG. 6 is a flow chart showing a method for measuring the amount of change in the height of the silicon raw material. 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. 8(a) and (b) are sequence diagrams showing the timing of acquiring the first and second in-furnace images in each measurement step. FIG. 9 is a graph showing a schematic diagram of a change in the position of the center of gravity of the characteristic points when the height of the quartz crucible is adjusted. FIG. 10 is a schematic diagram showing the change in the position of the characteristic point when the quartz crucible is rotated. FIG. 11 is a sequence diagram showing an example of the timing of acquiring the first and second inside-furnace images in each measurement step. FIG. 12 is a sequence diagram showing an example of the timing of acquiring the first and second inside-furnace images in each measurement step. FIG. 13 is a graph showing the relationship between the amount of change in height of the silicon raw material during the raw material melting process and the height of the quartz crucible. FIG. 14 is a schematic diagram illustrating a method for measuring the amount of change in height of the silicon source material according to the second embodiment of the present invention. FIG. 15 is a flowchart showing a method for measuring the amount of change in the height of the silicon source material. FIG. 16 is a diagram for explaining the pattern matching process of a template image of M×N pixels. FIG. 17 is a schematic diagram for explaining another example of the method for measuring the amount of change in height of the silicon raw material.

Below, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

Figure 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.

As shown in FIG. 1, the single crystal manufacturing apparatus 1 includes a chamber 10 constituting a crystal pulling furnace, a quartz crucible 11 that holds silicon melt 2 within the chamber 10, a graphite crucible 12 that holds the quartz crucible 11, a rotating shaft 13 that supports the graphite crucible 12, a shaft drive mechanism 14 that drives 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 coaxially with the rotating shaft 13 above the quartz crucible 11, and a wire winding mechanism 19 arranged above the chamber 10.

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 in the main chamber 10a. The pull chamber 10b is provided with a gas inlet 10c for introducing an inert gas (purge gas) such as Ar gas or a dopant gas into the chamber 10, and a gas outlet 10d for discharging the atmospheric gas in the chamber 10 is provided at the bottom of the main chamber 10a.

The quartz crucible 11 is a container made of quartz glass with a cylindrical side wall and a curved bottom. The graphite crucible 12 adheres closely to the outer surface of the quartz crucible 11 and encases it to maintain the shape of the quartz crucible 11 that has been softened by heating. The quartz crucible 11 and the graphite crucible 12 form a double-structure crucible that holds the silicon melt 2 within the chamber 10.

The graphite crucible 12 is fixed to the upper end of the 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 drive mechanism 14 provided outside the chamber 10. The rotating shaft 13 and the shaft drive mechanism 14 constitute a crucible drive mechanism that rotates and raises and lowers the quartz crucible 11 and the graphite crucible 12.

The heater 15 is used to melt the silicon raw material filled in the quartz crucible 11 to generate silicon melt 2, and to maintain the molten state of the silicon melt 2. The heater 15 is a resistance heating 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 on the outside of the heater 15 so as to surround the heater 15, thereby improving the heat retention inside the chamber 10.

The heat 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 quartz crucible 11. The heat shield 17 is a graphite member that covers the area above the silicon melt 2 excluding the pulling path of the silicon single crystal 3, and has, for example, an inverted truncated cone shape with an opening size that increases from the bottom end to the top end.

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

The amount of melt in the quartz crucible 11 decreases as the silicon single crystal 3 grows, but by raising the quartz crucible 11 so that the gap between the bottom end of the heat shield 17 and the melt surface 2s remains constant, it is possible to suppress temperature fluctuations in the silicon melt 2 and control the amount of dopant evaporation from the silicon melt 2 by keeping the flow rate of the gas flowing near the melt surface 2s constant. This makes it possible to improve the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, etc. in the pulling axial direction of the silicon single crystal 3.

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

A sight window 10e is provided at the top of the main chamber 10a for observing the inside, 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 image captured by the camera 20 is processed by an image processing unit 21, and the processed results are used by a control unit 22 to control the crystal growth conditions.

Figure 2 is a flow chart showing the steps for manufacturing silicon single crystals using the CZ method. Figure 3 is a schematic side view showing the shape of a silicon single crystal ingot.

As shown in FIG. 2, the manufacturing 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 by a heater 15 to produce silicon melt 2, and a crystal pulling step S13 in which a seed crystal is gradually pulled up while maintaining contact with the silicon melt 2 to grow a single crystal.

The crystal pulling process S13 includes a landing process S14 in which a seed crystal attached to the tip of the pulling wire 18 is lowered to land in the silicon melt 2, a necking process S15 in which a neck 3a is formed with a narrower crystal diameter to eliminate dislocations, a shoulder growing process S16 in which a shoulder 3b is formed with a gradually larger crystal diameter, a body growing process S17 in which a body 3c is formed with a crystal diameter maintained at a specified diameter (e.g., 320 mm), and a tail growing process S18 in which a tail 3d is formed with a gradually smaller crystal diameter. At the end of the tail growing process S18, the silicon single crystal 3 is separated from the silicon melt 2. In this way, as shown in FIG. 3, a silicon single crystal ingot 3i having a neck 3a, a shoulder 3b, a body 3c, and a tail 3d is completed.

In the preparation step S11, the quartz crucible 11 is filled with polycrystalline silicon raw material, and the quartz crucible 11 is then placed in the chamber 10. In order to increase the yield of silicon single crystals pulled in one crystal pulling step, it is desirable to fill the quartz crucible with as much polycrystalline silicon raw material as possible, and therefore 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.

Figure 4 is an explanatory diagram of the raw material melting process S12.

As shown in FIG. 4, in the raw material melting step S12, a large amount of silicon raw material 4 filled in a quartz crucible 11 is heated and melted by a heater 15 (FIG. 4(I)). Usually, the silicon raw material 4 loaded into the quartz crucible 11 is a polycrystalline silicon lump 4a (silicon chunk) with a maximum diameter of about 2 to 10 cm, but it is also possible to use a relatively large silicon block 4b (cut rod) in combination as shown in the figure. Generally, high-purity silicon for semiconductor devices is manufactured by the Siemens process, and the generated polycrystalline silicon rod is finely crushed and processed into a lump. Such a lump-shaped silicon raw material is easy to handle and easy to fill the quartz crucible 11, and is suitable as a silicon raw material for the CZ method.

When using a silicon block 4b, the silicon block 4b is first placed at the bottom of the quartz crucible 11, and then a large amount of polycrystalline silicon chunks 4a are filled between the quartz crucible 11 and the silicon block 4b without leaving any gaps. Therefore, when the quartz crucible 11 is viewed from above, the opening of the quartz crucible 11 is completely covered and filled with a large number of 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 for the shape of the peaks to be as flat as possible. This is to prevent a sudden change in the height of the silicon raw material 4 and the positional relationship of the individual polycrystalline silicon chunks 4a if the peaks of the piled polycrystalline silicon chunks 4a are made steep, as the melting of the silicon raw material 4 progresses.

At the start of the raw material melting process S12, the polycrystalline silicon raw material 4 is piled up in the quartz crucible 11, so the quartz crucible 11 must 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 several tens of mm (e.g., 50 mm).

As the melting of the polycrystalline silicon raw material 4 progresses, the volume of the polycrystalline silicon raw material 4 in the quartz crucible 11 decreases instead of increasing the amount of silicon melt 2, causing the polycrystalline silicon raw material 4 to sink (Figure 4 (II)). If heating of the sunken polycrystalline silicon raw material 4 continues without changing its height, the radiant heat from the heater 15 is less likely to be transmitted to the polycrystalline silicon raw material 4, reducing the efficiency of melting the raw material and increasing the thermal load on the quartz crucible 11, which may cause deformation of the quartz crucible 11.

Then, the quartz crucible 11 is raised by the amount that the polycrystalline silicon raw 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 top end of the polycrystalline silicon raw material 4 to the bottom end of the heat shield 17 is maintained at a predetermined distance that has been set in advance. 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.

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

In this way, the height adjustment of the quartz crucible 11 is repeated at a predetermined timing in accordance with the progress of melting of the silicon raw material 4, thereby maintaining the height of the upper end of the polycrystalline silicon raw material 4 approximately constant. The height adjustment of the quartz crucible 11 is completed when most of the silicon raw material 4 in the quartz crucible 11 is melted (FIG. 4 (IV)). In other words, it is completed before all of the polycrystalline silicon raw material in the quartz crucible 11 is completely melted. The reason why the height adjustment of the quartz crucible 11 is completed before the polycrystalline silicon raw material 4 is completely melted is that the remaining polycrystalline silicon chunks 4a after a large amount of silicon melt 2 is generated float on the melt surface, making it difficult to detect the height position of the polycrystalline silicon raw material 4 by image processing described later. In addition, even if the remaining polycrystalline silicon chunks 4a are completely melted, the height of the silicon melt 2 does not change significantly, and there is little need to adjust the height of the quartz crucible 11.

FIG. 5 is a schematic diagram illustrating a method for measuring the amount of change in height of 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 height of silicon raw material.

5 and 6, in the method for measuring the change in height of the silicon raw material 4 according to the present embodiment, first, an image of the inside of the furnace (first image of the inside of the furnace M _a ) is taken using the camera 20 (step S21). The camera 20 takes an image of the silicon raw material 4 in the quartz crucible 11 from obliquely 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 be used.

Next, a plurality of feature points P are extracted from the first in-furnace image _Ma (step S22), and the center of gravity P _Ave of the plurality of feature points P is obtained and set as the first height reference point P _ra of the silicon raw material 4 (step S23). A "feature point" is a point that is easily distinguished from its surroundings. Therefore, the feature point P is detected from the viewpoint of whether it is unique compared to its surroundings, and a pixel of a corner part that is significantly different from its surroundings in all directions is detected as a feature point. In FIG. 5, the plurality of feature points P extracted from the in-furnace image are indicated by small dot marks, and the center of gravity P _Ave of the plurality of feature points P is indicated by a large dot mark.

Next, a new in-furnace image (second in-furnace image M _b ) is captured by the camera 20 (step S24). Although details will be described later, the in-furnace images are captured by the camera 20 periodically at short intervals of, for example, about 0.1 to 10 seconds, and the second in-furnace image M _b is an image captured in the next frame or several frames after the first in-furnace image M _a when the in-furnace images are captured periodically.

Next, a plurality of characteristic points P are extracted from the second in-furnace image _Mb (step S25), and the center of gravity P _Ave of the plurality of characteristic points P is obtained and set as the second height reference point P _rb of the silicon raw material 4 (step S26). The method of extracting the plurality of characteristic points P is the same as that of the first in-furnace image M _a , and the number of characteristic points P to be obtained is also the same.

Next, the amount of change _Δh in the height of the silicon raw material 4 is calculated from the difference ΔY=P _ra (y)-P _rb (y) between the y coordinate P _ra (y) of the first height reference point P _ra calculated from the first furnace image M _a and the y coordinate P _rb (y) of the second height reference point P _rb calculated from the second furnace image M b (step S27). Since the amount of change (number of pixels) of the center of gravity P _Ave of the multiple feature points P is proportional to the amount of change Δh in the height of the silicon raw material 4, the amount of change Δh=ΔY×α (mm) in the height of the silicon raw material 4 can be calculated by multiplying the amount of change ΔY (number of pixels) in the y coordinate of the height reference point _P r in the furnace image by a predetermined coefficient α.

After the above height change amount measurement process (steps S21 to S27), the quartz crucible 11 is raised according to the amount of change Δh in the height 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 sinking from a certain point reaches 20 mm, the quartz crucible 11 is raised by the same amount (20 mm) as the amount of sinking. Here, if the threshold is made smaller, the height of the quartz crucible 11 can be finely adjusted at shorter intervals (high frequency), and if the threshold is made larger, the height of the quartz crucible 11 can be greatly adjusted at longer intervals (low frequency).

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

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, within area A1 indicated by a rectangular frame, silicon melt 2 is present, and no abrupt change in color tone (pixel value) is observed. As a result, a feature point cannot be extracted. Within area A2 indicated by a rectangular frame, a corner of polycrystalline silicon lump 4a is present, and abrupt changes in color tone (pixel value) are observed in both the X-axis and Y-axis directions. As a result, it is easy to distinguish from the surrounding pixels, making it suitable as a feature point.

There are no particular limitations on the method for detecting feature points P, but the Shi-Tomasi method is preferably used. Feature points are detected using the Shi-Tomasi method by searching for differences in pixel values relative to the amount of movement of pixel positions (u, v) in all directions. The score value E(u, v) of a feature point at any pixel position (u, v) can be calculated using equation (1).

Here, 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 it as a feature point.

Feature points P in the image are extracted in descending order of score value, and for example, the top 100 score points are used to determine the "height reference point" of the silicon raw material. Too few feature points (number of samples n) leads to a decrease in measurement accuracy, while too many can increase the amount of calculations and also cause a decrease in measurement accuracy, so an appropriate number is necessary, and a number between 50 and 1000 is preferable.

The center of gravity P _Ave (x, y) of the multiple feature points P ₁ , P ₂ , ..., P _n is the central coordinate of the multiple feature points and is composed of the average value of the x coordinates of the multiple feature points P ₁ to P _n , P _Ave (x) = (x ₁ + x ₂ + ... + x _n )/n, and the average value of the y coordinates of the multiple feature points P ₁ to P _n , P _Ave (y) = (y ₁ + y ₂ + ... + _yn )/n, where the x coordinate is the horizontal coordinate and the y coordinate is the vertical coordinate.

The center of gravity P _Ave of the characteristic points P ₁ to P _n indicates the average height position of the upper surface of the silicon source material 4, which has a variation in height. As shown in Fig. 5, the positions of the characteristic points P in the height direction vary, so that the center of gravity P _Ave of the characteristic points P ₁ to P _n indicates the average value of the positions in the height direction of the upper surface of the aggregate of many polycrystalline silicon chunks having irregularities, and does not indicate the height of the upper end of the silicon source material 4. However, if the height position (Gap) of the silicon source material 4 is controlled in consideration of the difference between the maximum value and the average value of the height of the silicon source material 4, an accident in which the silicon source material 4 comes into contact with the thermal shield 17 does not occur, and it is not necessary to strictly determine the absolute height of the silicon source material 4.

The center of gravity P _Ave of the multiple characteristic points P obtained from each furnace image indicates the average height (instantaneous value) of the silicon raw material 4 at the time of photographing. As the raw material melting process progresses, the multiple characteristic points P ₁ , P ₂ , ..., P _n in the furnace image gradually move downward, and the center of gravity P _Ave of the multiple characteristic points P also moves downward accordingly. Therefore, by comparing the centers of gravity P _Ave of the multiple characteristic points P obtained from multiple furnace images photographed at different times, the amount of change (amount of reduction) in the height of the silicon raw material 4 can be obtained.

Figures 8(a) and (b) are sequence diagrams showing the timing of acquiring the first and second furnace images in each measurement step.

8(a) and 8(b), the camera 20 continuously captures images of the inside of the furnace at a period _Tp of, for example, about 0.1 to 10 seconds. The period _Tp for capturing images of the inside of the furnace is preferably an integer multiple of the crucible rotation period _Tc when the quartz crucible 11 is rotated. In this embodiment, the case of _Tp = 1 second is shown.

8A shows a case where a first furnace image M _a is collected and then a second furnace image M _b is collected in the shortest time. For example, in the first measurement step, a first furnace image M _a is collected at time t 1, a second furnace image M _b is collected at time t ₂ = _{t 1 +} T _P , and a change amount Δh in height of the silicon raw material 4 during T _P seconds is calculated from a difference ΔP = _{P ra -} P _rb between a first height reference point P _ra calculated from the first furnace image M _a and a second height reference point P _rb calculated from the second furnace image M b.

In the second measurement step, the first furnace image M _a is collected at time t ₂ , and the second furnace image M _b is collected at time t ₃ = t ₂ + T _P , and the change amount Δh of the height of the silicon raw material 4 during T P seconds is calculated from the difference ΔP = P _ra - _{P rb} between the first height reference point P _ra obtained from the first furnace image M _a and the second height reference point _P rb obtained from the second furnace image M _b . In this case, the first furnace image M _a in the second measurement step is the same as the second furnace image M _b in the first measurement step. The third and subsequent measurement steps are also performed in the same manner as the second measurement. In this way, by collecting the second furnace image M _b following the first furnace image M _a at the shortest period, the change in the height of the silicon raw material can be detected early.

8B shows a case where a first furnace image M _a is collected and then a second furnace image M _b is collected after an appropriate time has elapsed. For example, in the first measurement step, the first furnace image M _a is collected at time t 1 and the second furnace image M _b is collected at time t ₄ = t ₁ + 3T _P , and the change amount Δh of the height _of the silicon raw material 4 during 3T P seconds is calculated from the difference ΔP = P _ra - _P rb between the first height reference point P _ra calculated from the first furnace image M _a and the second height reference point _{P rb} calculated from the second furnace image M _b .

In the second measurement step, the first furnace image M _a is collected at time t ₂ , the second furnace image M _b is collected at time t ₅ = t ₂ + 3T _P , and the change amount Δh in the height of the silicon raw material 4 during 3T P seconds is calculated from the difference ΔP = P _ra - P _rb between the first height reference point P _ra calculated from the first furnace image M _a and the second height reference point _{P rb} calculated from the second furnace image M _b . In this way, by making the time interval from when the first furnace image M _a is collected to when the second furnace image M _b is collected longer than the photographing period T _P of the furnace images, the change in the height of the silicon raw material can be reliably detected.

Figure 9 is a graph that shows 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.

9, the center of gravity P _Ave of the characteristic point P gradually decreases as the melting of the silicon raw material 4 progresses. However, by raising the quartz crucible 11 by a certain amount when the center of gravity P _Ave of the characteristic point reaches the threshold value P _Th and periodically repeating this, the center of gravity P _Ave of the characteristic point can be maintained at or above the threshold value P _Th . In other words, the silicon raw material 4 can be maintained at a predetermined height position, and an excessive decrease in the height position due to the melting of the silicon raw material 4 can be prevented.

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 in order 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 therefore the position of the characteristic point also changes, and therefore the height of the silicon raw material 4 calculated from the center of gravity P _Ave of the characteristic point in the Y-axis direction also changes.

Figure 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.

As shown in Figures 10(a) and (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 change over time in the center of gravity of multiple feature points makes it difficult to determine whether the change over time in the center of gravity of multiple feature points is caused by the rotation of the quartz crucible 11 or by the melting of the silicon raw material 4.

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 determine the amount of change in the height of the silicon raw material 4 without the influence of the rotation of the quartz crucible 11.

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

11 and 12, when measuring the amount of change in the height of the silicon raw material while rotating the quartz crucible 11, first, images of the inside of the furnace are taken at a period Tp shorter than the crucible rotation period _Tc and an integral multiple of the crucible rotation period _Tc using the camera 20, and a height reference point of the silicon raw material is obtained in each image of the inside of the furnace. For example, when the rotation speed of the quartz crucible is 1 rpm and the photographing period of the camera is 1 second, 60 images of the inside of the furnace are taken while the quartz crucible 11 makes one rotation, and instantaneous values of 60 height reference points are obtained.

11 shows a case where a first furnace image M _a is collected and then a second furnace image M _b is collected after a crucible rotation period. For example, in a first measurement step, a first furnace image M _a is collected at time t 1, a second furnace image M _b is collected at time t ₆₁ = _{t 1 +} T _c , and a change amount Δh in height of the silicon raw material 4 during T _c seconds is obtained from a difference ΔP = P _ra - _{P rb} between a first height reference point P _ra obtained from the first furnace image M _a and a second height reference point P _rb obtained from the second furnace image M b.

In the second measurement step, the first furnace image M _a is collected at time t ₂ , the second furnace image M _b is collected at time t ₆₂ = t ₂ + T _c , and the change amount Δh of the height of the silicon raw material 4 during T c seconds is calculated from the difference ΔP = P _ra - P _rb between the first height reference point P _ra obtained from the first furnace image M _a and the second height reference point P _rb obtained from the _second furnace image M _b . In this way, by setting the time interval from when the first furnace image M _a is collected to when the second furnace image M _b is collected to an integer multiple of the crucible rotation period T _c , 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.

The measurement method shown in Figure 12 illustrates a case in which a height reference point of the silicon raw material is obtained from each of multiple furnace images, and the amount of change in the height of the silicon raw material is measured using a moving average value of the crucible rotation period _Tc of the height reference point. For example, in the first measurement step, a moving average value MAa of 60 first height reference points P r1 to P _r60 is calculated from 60 furnace images M ₁ to M ₆₀ (plural first furnace images) taken between times t ₁ to t 60, and then a moving average value _MAb of 60 second height reference points P _r2 to P _r61 is calculated from 60 furnace images M ₂ to M ₆₁ (plural second furnace images) taken between times _{t 2} to _{t 61.Then} , the change in height _Δh of the silicon source material 4 over Tp seconds is calculated from the difference ΔMA = _{MAa - MAb} between the moving average value _MAa of the first height reference points P _r1 to P _r60 and the moving average value MAb of the second height reference points _{P r2} to P _r61 .

In the second measurement step, a moving average value MAa of 60 first height reference points P r2 to P r61 is calculated from 60 interior images M ₂ to M ₆₁ (multiple first interior images) taken between times t _{2 to} t ₆₁ , and then a moving average value _MAb of 60 second height reference points P _r3 to P _r62 is calculated from 60 interior images M ₃ to M ₆₂ (multiple second interior images) taken between times _{t 3} to t _62.Then , a change in height _Δh of the silicon raw material 4 over Tp seconds is calculated from the difference ΔMA = _MAa - _MAb between the moving average value _MAa of the first height reference points P _r1 to _{P r60} and the moving average value MAb of _the second height reference points P _r2 to P _r61 . After time _t3 , the amount of change Δh in the height of the silicon raw material 4 can be continuously measured by determining the moving average value MA of the crucible rotation period of the height reference point as described above.

Figure 13 is a graph showing the measurement results of the change in height of the silicon source material 4 during the source material melting process S12 and the control results of the quartz crucible.

13, in the first half of the raw material melting step S12 in which the quartz crucible 11 is not rotated, the instantaneous value of the center of gravity P _Ave (average height of feature points) of the multiple feature points P extracted from each furnace image is stable, so that the amount of change Δh in the height of the silicon raw material 4 can be obtained from the time change of 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, and the efficiency of melting the raw material can be improved and the thermal load on the quartz crucible can be reduced.

In the latter half of the raw material melting step S12 in which the quartz crucible 11 is rotated, the instantaneous value of the center of gravity P _Ave of the multiple feature points P extracted from each furnace image fluctuates greatly with time. However, the moving average value (time average value) of the center of gravity P _Ave of the multiple feature points P synchronized with the rotation period of the quartz crucible 11 becomes a stable value from which the influence of the rotation of the quartz crucible 11 is removed. Therefore, by gradually raising the quartz crucible 11 in accordance with the time change in the height of the silicon raw material 4 obtained 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, and the melting efficiency of the silicon raw material can be improved and the thermal load on the quartz crucible can be reduced.

As described above, in the first half of the raw material melting process S12, where the quartz crucible 11 is not rotated, the time change of the instantaneous values of the center of gravity of the multiple feature points is stable, so there is no need to use a moving average value of the center of gravity synchronized with the rotation period of the quartz crucible 11 as in the second half of the raw material melting process S12. However, in order to increase the reliability of the measurement accuracy of the height of the silicon raw material 4, it is preferable to use a moving average value of the center of gravity of the multiple feature points also in the first half of the raw material melting process S12, and it is particularly preferable to use a moving average value of the rotation period of the quartz crucible 11.

As described above, the height measurement method for silicon raw material 4 according to this embodiment involves photographing the silicon raw material 4 in a quartz crucible from diagonally above with a camera during the raw material melting process in the manufacturing process for silicon single crystals by the CZ method, extracting multiple characteristic points from the captured image, and determining the height of the silicon raw material 4 from the center of gravity of the multiple characteristic points, so that the height of the silicon raw material 4 in the quartz crucible during the raw material melting process can be stably determined. Therefore, the height position of the quartz crucible can be automatically adjusted based on the captured image.

In addition, the method for measuring the height 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 images 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.

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

Next, a second embodiment of the present invention will be described. In the above-mentioned first embodiment, the center of gravity P _Ave of the multiple feature points P extracted from the furnace image is determined as the height reference point of the silicon raw material, and the amount of change in height of the silicon raw 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 raw material 4 is determined from the time change of the reference coordinates of a template image taken from the furnace image. This will be described in detail below.

FIG. 14 is a schematic diagram illustrating a method for measuring the amount of change in height of silicon raw material 4 according to a second embodiment of the present invention. Also, FIG. 15 is a flowchart showing a method for measuring the amount of change in height of silicon raw material 4.

As shown in FIGS. 14 and 15, in measuring the amount of change in height of the silicon source material 4 according to this embodiment, first, a first furnace image _Ma is taken using the camera 20 (FIG. 14(I), step S41).

Next, a template region is set at an appropriate position in the first furnace image _Ma , and a template image TM is taken 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 raw material melting step S12. If the template region is set at a position where the polycrystalline silicon chunks cannot be observed during the raw material melting step S12, the amount of change in height of the silicon raw material 4 cannot be continuously measured.

The reference coordinates P _a (x, y) of the template image TM are, for example, the coordinates of the upper left corner of the image. The position of the reference coordinates of the rectangular image is not particularly limited, and may be a corner other than the upper left corner, a position slightly shifted from the corner, or the center of the image. In this embodiment, the upper left corner of the image is set as the reference coordinates P _a (x, y), which is set as the first height reference point P _ra of the silicon raw material 4 ( FIG. 14 (I), step S43). The size of the template region (template image) is not particularly limited, and may be, for example, 100px×100px.

Next, a second interior image _Mb is captured using the camera 20 after a predetermined time has elapsed since the first interior image _Ma was captured (FIG. 14(II), step S44). The timing of capturing the second interior image _Mb may be immediately after the first interior image _Ma is captured (next frame), or may be several frames later.

Next, a search range SR covering a range slightly wider than the template region is set in the second furnace image _Mb , and pattern matching is performed between the template image TM and the reference image RM in the search range SR (FIG. 14 (II), step S45). The search range SR is a range wider than the template region including the template region, and is set so that the template region 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, it cannot be detected when the height of the silicon raw material 4 changes significantly. Therefore, the size of the search range SR is determined taking into consideration the image processing ability 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.

First, for example, template matching is started from the upper left of the search range SR and is continued until the lower right of the search range SR is reached. Then, the reference coordinate _Pb (x,y) of the reference image RM having the same size as the template image TM and having the maximum correlation with the template image TM is obtained, and this is _set as the second height reference point Prb of the silicon raw material 4 (FIG. 14(III), step S46).

Next, the difference ΔY= _Pra (y)-Prb(y)= _Pa (y) _-Pb (y) between the y coordinate Pra(y) of the first height reference point _Pra, which is the reference coordinate of the template image TM, and the y coordinate _Prb (y) of the second reference _point Prb, which is the reference _coordinate of the reference image RM, is calculated, and the amount of change in height of the silicon raw material 4, Δh=ΔY×α(mm), is calculated from this difference _ΔY (FIG. 14(IV), step S47). Thereafter, the height of the silicon raw material 4 is adjusted by raising the quartz crucible 11 in accordance with the amount of change in height Δh of the silicon raw material 4 (step S48).

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

As shown in FIG. 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 base, 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 base.

Here, the average luminance value μ _T of the template image TM and the average luminance value μ _I of the reference image RM are calculated as follows.

Furthermore, the correlation C between the template image TM and the reference image RM is obtained using μ _T and μ _I as follows:

The correlation degree C takes values ranging from -1 to +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 matching processing, and the point with the highest correlation degree C becomes the current position of the template image TM.

In this way, the degree of 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 coordinates of the reference image RM where the degree of correlation C is maximum are set as the current position of the template image TM, thereby making it possible to obtain the amount of movement of the template image TM.

In the above embodiment, one template area is set in the first furnace image and one template image TM is collected, but multiple template areas may be set and multiple template images may be collected. For example, as shown in FIG. 17, nine template areas may be set in the first furnace image and nine template images TM may be collected. In this case, nine measurement values (change in height of silicon raw material Δh) are obtained in one matching process, and the change in height of silicon raw material 4 can be more accurately determined by averaging the measured values.

The collection position of the template image TM used to measure the change in the height of the silicon raw material is fixed, and the collection position of the next template image TM does not change due to the movement of the previous template image TM. That is, the collection 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, even if the movement of the template image TM from _Pa to _Pb as shown in FIG. 14 (IV) is confirmed, in the next measurement, the template image TM is collected by returning to the original position _Pa . In this way, it is possible to prevent a situation in which the template area continues to move and the template image is collected in a place that is not suitable for collecting the template image.

As described above, the crucible is not rotated in the first half of the raw material melting step S12, but the silicon raw material is heated and melted while rotating the crucible in the second half, so the position of the silicon raw material changes in the rotation direction. Therefore, even if the position of the silicon raw material changes due to melting, it is not possible to distinguish whether the position of the silicon raw material has changed due to rotation or due to melting. Therefore, in the second half of the raw material melting step S12 in which the crucible is rotated, even in this embodiment, it is preferable to synchronize the timing of taking the furnace image for determining the first and second height reference points P _ra and P _rb with the crucible rotation period T _c . Since the raw material returns to its original position when the quartz crucible rotates once, a change in position due to melting of the raw material can be detected by comparing images at the same rotation position, and the influence of the rotation of the crucible can be eliminated.

As described above, the silicon raw material height measurement method according to the present embodiment photographs the polycrystalline silicon raw material in the quartz crucible 11 from diagonally above with the camera 20 during the raw material melting step S12 in the manufacturing process of silicon single crystal by the CZ method, collects the template image TM and the first height reference point P _ra from the first furnace image M _a , obtains the second height reference point P _rb by template matching of the second furnace image M _b taken after the first furnace image M _a is taken, and obtains the change amount Δh of the height of the silicon raw material from the difference between the first height reference point P _ra and the second height reference point P _rb , so that the change amount of the height of the silicon raw material 4 in the quartz crucible 11 during the raw material melting step S12 can be stably obtained. Therefore, the height position of the quartz crucible can be automatically adjusted based on the furnace image.

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 without departing from the spirit of the present invention, and it goes without saying that these are also included in the scope of the present invention.

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.

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 Viewing window 11 Quartz crucible 12 Graphite crucible 13 Rotating shaft 14 Shaft drive mechanism 15 Heater 16 Insulating material 17 Heat shield 17a Opening 18 Pulling wire 19 Wire winding mechanism 20 Camera 21 Image processing unit 22 Control unit 23 Flow straightening member (purge tube)
A1 Area in the captured image A2 Area in the captured 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 attachment process S15 Necking process S16 Shoulder portion growth process S17 Body portion growth process S18 Tail portion growth process TM Template image T _c Crucible rotation period T _p Capture period of furnace image Δh Amount of change in height of silicon raw material

Claims (17)

A method for measuring a change in height of a silicon raw material by taking an image of an inside of a furnace including a number of polycrystalline silicon chunks filled in a quartz crucible from above during a raw material melting process for generating a silicon melt by heating the silicon raw material, the method comprising:
determining a first height reference point of the silicon raw material from a first furnace image taken by the camera;
determining a second height reference point of the silicon raw material from a second furnace image taken by the camera after the first furnace image is taken;
A method for measuring an amount of change in height of a silicon raw material, comprising: determining an amount of change in height of the silicon raw material from a difference between the first height reference point and the second height reference point. The first height reference point is a center of gravity of a plurality of feature points extracted from the first interior image,
2. The method for measuring the amount of change in height of the silicon raw material according to claim 1, wherein the second height reference point is a center of gravity of a plurality of feature points extracted from the second furnace image. 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 1000 or less. 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. The silicon raw material is heated and melted while rotating the quartz crucible.
3. The method for measuring the change in height of the silicon raw material according to claim 2, wherein 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. The silicon raw material is heated and melted while rotating the quartz crucible.
The method for measuring the change in height of a silicon raw material according to claim 2, further comprising 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 a furnace for a rotation period of the quartz crucible. the first height reference point is a reference coordinate of a template image taken from a predetermined template region in the first interior image,
2. The method for measuring the amount of change in height of a silicon raw material according to claim 1, wherein 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 of the second furnace image is scanned and pattern matching with the template image is performed. The method for measuring the change in height of a silicon raw material according to 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. The method for measuring the change in height of a silicon raw material according to claim 8, wherein the search range is a region that is wider than the template region and has a center that coincides with the template region and covers the template region. determining a first change amount and a second change amount of the height of the silicon source material in sequence;
8. The method for measuring the amount of change in height of a silicon feedstock according to claim 7, wherein a sampling position of the template image used when calculating a second amount of change in the height of the silicon feedstock is the same as a sampling position of the template image used when calculating the first amount of change. determining the first change amount of the height of the silicon raw material by using the first furnace image taken at a first timing and the second furnace image taken at a second timing after the first timing;
11. The method for measuring the amount of change in the height of the silicon raw material according to claim 10, further comprising determining the second amount of change in the height of the silicon raw material 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. A plurality of template regions are set within the first interior 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 corresponding to each of the plurality of first height reference points from the second interior image;
8. The method for measuring the amount of change in height of a silicon feedstock according to claim 7, further comprising the step of calculating an average value of the amount of change in height of a plurality of silicon feedstocks from the plurality of first height reference points and the plurality of second height reference points. The silicon raw material is heated and melted while rotating the quartz crucible.
8. The method for measuring the change in height of the silicon raw material according to claim 7, wherein 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. The silicon raw material is heated and melted while rotating the quartz crucible.
The method for measuring the change in height of a silicon raw material according to claim 7, further comprising 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 a furnace for a rotation period of the quartz crucible. The method for measuring the change in height of silicon raw material described in claim 1, wherein the polycrystalline silicon chunk has multiple corners, is filled to a position higher than the upper end of the quartz crucible when initially filled into the quartz crucible, and the opening of the quartz crucible is covered by the polycrystalline silicon chunk. 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 generate a silicon melt;
and a crystal pulling step of pulling a silicon single crystal from the silicon melt.
The raw material melting step includes:
a height change measuring step of photographing the silicon raw material from above with a camera to measure a 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 a change in the height of the silicon raw material,
16. A method for producing a silicon single crystal, comprising: measuring the amount of change in height of the silicon source material using a method for measuring the amount of change in height of the silicon source material according to claim 1 ; A chamber;
a quartz crucible for holding a silicon source within the chamber;
A heater for heating the silicon raw material;
A crucible driving mechanism that rotates and raises and lowers the quartz crucible;
a crystal pulling mechanism for pulling a single crystal from the silicon melt in the quartz crucible;
A camera for photographing the silicon raw material from above;
an image processing unit that processes an image captured by the camera;
a control unit for controlling the operation of the heater, the crucible driving mechanism, and the crystal pulling mechanism;
The camera photographs the silicon raw material from above during a raw material melting process in which the silicon raw material including a large number of polycrystalline silicon chunks is heated by the heater to generate a silicon melt,
16. A silicon single crystal manufacturing apparatus, comprising: a silicon source material height measuring unit for measuring the amount of change in height of the silicon source material using the method for measuring the amount of change in height of the silicon source material according to claim 1 ;