TWI910772B - Methods and apparatus for manufacturing silicon single crystals - Google Patents

Abstract

The purpose of this invention is to detect leaks or deformations of the quartz crucible at an early stage and prevent secondary damage. According to the silicon single crystal manufacturing method of this invention, during the crystallization and stretching process, a camera 20 photographs the molten silicon surface 2a inside the quartz crucible 11; the gap value h _GAP between the lower end of the heat insulation body 17 positioned above the molten surface 2a and the molten surface 2a is obtained from the photographed image; and the height of the quartz crucible 11 is controlled according to the change in the gap value h _GAP . In controlling the height of the quartz crucible 11, the correction amount for the crucible's rising speed is obtained from the difference between the measured value and the target value of the gap value h _GAP , and the liquid level position is judged to have changed suddenly based on whether this correction amount exceeds the threshold.

Description

Methods and apparatus for manufacturing silicon single crystals

This invention relates to a method for manufacturing silicon single crystals and an apparatus for manufacturing silicon single crystals.

The Tchaikovsky process (CZ process) is a known method for manufacturing silicon single crystals used in semiconductor devices. The CZ process involves attaching a seed crystal to molten silicon within a quartz crucible, then slowly stretching it while rotating it relative to the substrate to grow a large single crystal at the lower end of the seed crystal. The CZ process can improve the crystallization quality and manufacturing yield of large-diameter silicon single crystals.

In the CZ process, to improve the yield and quality of single crystals, precise measurement and control of the crystal diameter and liquid level are performed. Regarding methods for measuring the crystal diameter and liquid level, for example, Patent 1 describes a method for calculating the crystal diameter and crystal center position from a high-brightness portion generated at the solid-liquid interface, called a fusion ring, and then calculating the liquid level height from the crystal center position. Furthermore, Patent 2 describes a method for calculating the liquid level position of the molten silicon relative to the insulation from the interval between the real image of the circular opening containing the insulation and the mirror image of the insulation reflected on the molten liquid surface.

In the CZ process, the quartz crucible is raised and controlled to stabilize the level of the molten silicon, which would otherwise drop due to the growth of the silicon single crystal. This allows for the stable stretching of the silicon single crystal from the molten silicon, and also achieves stabilization of crystal quality and oxygen concentration distribution along the crystal growth direction.

During the crystallization stretching process, damage or deformation of the quartz crucible can sometimes occur. If the quartz crucible is damaged, leakage of molten silicon and damage to the electrodes at the bottom of the chamber or the heater can cause malfunctions in the crucible drive mechanism. In addition, damage to the cooling water piping may also pose a risk of phreatic eruption. Furthermore, if the quartz crucible is deformed, contact between the quartz crucible and furnace components such as the heat shield or the silicon single crystals during the stretching process becomes difficult, making it impossible to continue the crystallization stretching process.

Previously, leakage from the quartz crucible was observed visually inside the furnace, or detected based on changes in furnace pressure or crucible rotation. In addition, deformation of the quartz crucible was confirmed visually during or after the crystallization stretching process.

Regarding methods for detecting leakage of molten silicon within a quartz crucible, for example, Patent 3 describes a method for accurately detecting leakage by combining a first detection method and a second detection method. The first detection method involves capturing images of a high-brightness region, termed the fusion ring, generated at the contact point between the molten silicon and the silicon single crystal during crystal stretching using a CCD camera, and processing the image to detect leakage. The second detection method involves intermittently applying an AC or DC voltage from a power supply between the crucible support axis and the seed crystal holding wire, and using a comparator to compare changes in the conductivity state to detect leakage. [Prior Art Documents] [Patent Documents]

[Patent Document 1] Japanese Patent Application Publication No. 2019-85299 [Patent Document 2] Japanese Patent Application Publication No. 2013-216505 [Patent Document 3] Japanese Patent Application Publication No. Hei 11-180794

[The problem that the invention aims to solve]

However, the aforementioned methods for detecting quartz crucibles cannot quantitatively detect abnormalities caused by damage or deformation of the quartz crucible, nor can they detect abnormalities at an early stage. Furthermore, the leakage detection method described in Patent Document 3 cannot accurately detect leakage in processes where the silicon single crystal and the molten silicon are not in contact. Additionally, it cannot detect changes in the liquid level caused by deformation of the quartz crucible. In cases of leakage or crucible deformation during the crystallization stretching process, early detection is necessary due to the significant damage it causes to the apparatus or chamber.

Therefore, the purpose of this invention is to provide a method and apparatus for manufacturing silicon single crystals capable of detecting damage or deformation of quartz crucibles at an early stage. [Means for solving the problem]

To solve the above problems, the silicon single crystal manufacturing method of the present invention is characterized in that, during the crystallization stretching process, the molten surface of the silicon melt in the quartz crucible is photographed by a camera; the gap value between the lower end of the heat insulation body disposed above the quartz crucible and the molten surface is obtained from the photographed image; the height of the quartz crucible is controlled according to the change of the gap value; and in the control of the height of the quartz crucible, the correction amount of the crucible rising speed is obtained from the difference between the measured value and the target value of the gap value, and the position of the liquid surface is determined to have changed suddenly based on whether the correction amount exceeds a threshold.

According to the silicon single crystal manufacturing method of the present invention, it is preferable to stop the crystallization stretching process when a sudden change in the liquid level is detected. This improves the safety of the crystallization stretching process.

According to the silicon single crystal manufacturing method of the present invention, it is preferable to determine whether there is an abnormality in the edge detection result of the furnace structure shown in the aforementioned photographed image when a sudden change in the aforementioned liquid level is detected. If there is no abnormality in the edge detection result, the aforementioned crystal stretching process is terminated. In this case, the aforementioned furnace structure is preferably the aforementioned heat insulation body, and the aforementioned gap value is obtained from the real image edge of the aforementioned heat insulation body and the mirror image edge of the aforementioned heat insulation body reflected on the aforementioned molten liquid surface. In this way, unnecessary termination of the crystal stretching process can be avoided, and the reliability of the crystal stretching process can be improved.

The aforementioned threshold system preferably includes an upper and lower limit threshold for the aforementioned correction amount, and is set for each crystallization stretching process based on the record of crucible rise rate changes in past silicon single crystal mass production records. This improves the accuracy of judging whether there are sudden changes in the liquid level position.

Furthermore, the silicon single crystal manufacturing apparatus of the present invention is characterized by comprising: a chamber; a quartz crucible holding molten silicon within the chamber; a heater disposed around the quartz crucible and heating the molten silicon; a crucible driving mechanism driving the rotation and lifting of the quartz crucible; a crystal stretching mechanism stretching a silicon single crystal from the molten silicon; a heat insulation body disposed above the quartz crucible to surround the stretching path of the silicon single crystal; a camera capturing images of the interior from the outside of the chamber; an image processing unit processing the images captured by the camera; and a control unit controlling the heating device based on the processing result of the image processing unit. The device includes a heater, the aforementioned crucible driving mechanism, and the aforementioned crystal stretching mechanism; the aforementioned image processing unit, during the crystal stretching process, captures the molten silicon surface of the aforementioned quartz crucible using the aforementioned camera; obtains the gap value between the lower end of the aforementioned heat insulation body and the aforementioned molten surface from the captured image; the aforementioned control unit, in response to changes in the aforementioned gap value, controls the height of the aforementioned quartz crucible; in controlling the height of the aforementioned quartz crucible, obtains a correction amount for the crucible's rising speed from the difference between the measured value and the target value of the aforementioned gap value, and determines whether there is a sudden change in the liquid surface position based on whether the aforementioned correction amount exceeds a threshold.

According to this invention, sudden changes in the liquid level caused by damage or deformation of the quartz crucible can be detected at an early stage by observing changes in the rising speed of the quartz crucible. Therefore, secondary damage such as device damage caused by damage or deformation of the quartz crucible can be prevented. [Invention Benefits]

According to the present invention, a method for manufacturing silicon single crystals and an apparatus for manufacturing silicon single crystals are provided, which can detect damage or deformation of quartz crucibles at an early stage.

[The form in which the invention is implemented]

The preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings.

Figure 1 is a schematic cross-sectional view showing the structure of a silicon single crystal manufacturing apparatus according to an embodiment of the present invention.

As shown in Figure 1, the silicon single crystal manufacturing apparatus 1 includes: a water-cooled chamber 10; a quartz crucible 11 holding molten silicon 2 within the chamber 10; a graphite crucible 12 holding the quartz crucible 11; a rotation shaft 13 supporting the graphite crucible 12; a crucible driving mechanism 14 that drives the quartz crucible 11 to rotate and move up and down via the rotation shaft 13 and the graphite crucible 12; a heater 15 disposed around the graphite crucible 12; and a structure located at the heater 15. 5. Insulating material 16 disposed on the outer side and along the inner surface of the chamber 10; heat insulation body 17 disposed above the quartz crucible 11; stretching guide 18 disposed above the quartz crucible 11 and coaxial with the rotation shaft 13; crystal stretching mechanism 19 disposed above the chamber 10; camera 20 for capturing images inside the chamber 10; image processing unit 21 for processing images captured by camera 20; and control unit 22 for each part of the control device.

The chamber 10 consists of a main chamber 10a and a slender cylindrical traction chamber 10b connected to the upper opening of the main chamber 10a. A quartz crucible 11, a graphite crucible 12, a heater 15, and a heat insulation body 17 are disposed within the main chamber 10a. A gas inlet 10c is provided at the traction chamber 10b to introduce inert gases such as argon (purge gases) or doped gases into the chamber 10. A gas outlet 10d is provided at the lower part of the main chamber 10a to discharge atmospheric gases from the chamber 10. Furthermore, an observation window 10e is provided at the upper part of the main chamber 10a to observe the growth status of the silicon single crystal 3.

The quartz crucible 11 is a quartz glass container with cylindrical side walls and a curved bottom. The graphite crucible 12 is formed by tightly fitting and covering the outer surface of the quartz crucible 11 to maintain its shape after it softens upon heating. The quartz crucible 11 and the graphite crucible 12 constitute a dual-structure crucible that supports the molten silicon 2 within the chamber 10.

The graphite crucible 12 is fixed to the upper end of the rotating shaft 13, the lower end of which passes through the bottom of the chamber 10 and is connected to the crucible drive mechanism 14 located outside the chamber 10. The graphite crucible 12, the rotating shaft 13, and the crucible drive mechanism 14 constitute the rotation mechanism and lifting mechanism of the quartz crucible 11. The rotation and lifting of the quartz crucible 11 driven by the crucible drive mechanism 14 are controlled by the control unit 22.

The heater 15 is used to maintain the molten silicon 2 in a molten state while melting the silicon raw material filled in the quartz crucible 11 to generate molten silicon 2. The heater 15 is a carbon-made resistance heater and is installed to surround the quartz crucible 11 inside the graphite crucible 12. Furthermore, an insulating material 16 is provided on the outside of the heater 15 to surround the heater 15, thereby improving the heat preservation inside the chamber 10. The output of the heater 15 is controlled by the control unit 22.

The heat insulation 17 is configured to suppress temperature fluctuations in the molten silicon 2 and provide appropriate heat distribution near the crystal growth interface, while preventing the silicon single crystal 3 from being heated by radiant heat from the heater 15 and the quartz crucible 11. The heat insulation 17 is a generally cylindrical graphite component, configured to cover the area above the molten silicon 2 except for the stretching path of the silicon single crystal 3.

The diameter of the lower opening of the heat insulation body 17 is larger than the diameter of the silicon single crystal 3, thereby ensuring the stretching path of the silicon single crystal 3. In addition, the outer diameter of the lower end of the heat insulation body 17 is smaller than the diameter of the quartz crucible 11. Because the lower end of the heat insulation body 17 is located inside the quartz crucible 11, even if the upper edge of the quartz crucible 11 is raised to a position higher than the lower end of the heat insulation body 17, the heat insulation body 17 will not interfere with the quartz crucible 11.

Although the amount of molten liquid in the quartz crucible 11 decreases as the silicon single crystal 3 grows, by raising the quartz crucible 11 to keep the gap (gap value h _GAP ) between the molten liquid surface 2a and the heat insulation body 17 constant, the temperature variation of the silicon molten liquid 2 is suppressed, the gas flow rate near the molten liquid surface 2a is kept constant, and the evaporation of dopants from the silicon molten liquid 2 is controlled. Through such gap control, the stability of the distribution of crystal defects, oxygen concentration, and resistivity along the tensile axis of the silicon single crystal 3 can be improved.

Above the quartz crucible 11, a stretching shaft (i.e., guide wire 18) for silicon single crystal 3 and a crystallization stretching mechanism 19 for stretching silicon single crystal 3 by winding the guide wire 18 are provided. The crystallization stretching mechanism 19, together with the guide wire 18, has the function of rotating silicon single crystal 3. The crystallization stretching mechanism 19 is controlled by a control unit 22. The crystallization stretching mechanism 19 is disposed above the traction chamber 10b, and the guide wire 18 extends from the crystallization stretching mechanism 19 through the traction chamber 10b and downwards, with the front end of the guide wire 18 reaching the interior space of the main chamber 10a. In Figure 1, the state in which the silicon single crystal 3 is being grown is shown suspended by the guide wire 18. During the stretching of silicon single crystal 3, the quartz crucible 11 and silicon single crystal 3 rotate on their own while the conductor 18 is slowly stretched, thereby allowing silicon single crystal 3 to grow.

A camera 20 is disposed on the outer side of the chamber 10. The camera 20 is, for example, a CCD camera, which captures images of the interior of the chamber 10 through an observation window 10e formed in the chamber 10. The camera 20 has a camera axis (optical axis) that is tilted relative to the tensile axis of the silicon single crystal 3, and the camera 20 is positioned at a predetermined angle relative to the vertical direction. In other words, the camera 20 captures images of the upper region of the quartz crucible 11 from an obliquely upward position, including the circular opening of the heat insulation body 17 and the surface of the molten silicon 2.

The camera 20 is connected to the image processing unit 21, which in turn is connected to the control unit 22. The image processing unit 21 calculates the crystal diameter near the solid-liquid interface from the single-crystal profile pattern of the image captured by the camera 20. Furthermore, the image processing unit 21 calculates the distance (gap value _hGAP ) from the heat insulation body 17 to the liquid surface position from the mirror position of the heat insulation body 17 reflected in the image captured by the camera 20. To remove the influence of noise, it is preferable to use the moving average of multiple measurements (instantaneous values) as the gap value _hGAP for actual gap control.

While there are no particular limitations on the method for calculating the gap value from the mirror position of the heat insulation 17, a conversion table or formula showing the relationship between the mirror position of the heat insulation 17 and the gap value can be prepared in advance, and the mirror position of the heat insulation 17 can be substituted into this conversion table or formula during the crystal stretching process to obtain the gap value. Alternatively, the gap value can also be calculated geometrically from the positional relationship between the real image of the heat insulation 17 and the mirror image presented in the captured image.

The control unit 22 controls the crystal stretching speed based on the crystal diameter data obtained from the image captured by the camera 20, thereby controlling the crystal diameter. Specifically, when the measured crystal diameter is larger than the target diameter, the crystal stretching speed is increased; when it is smaller than the target diameter, the crystal stretching speed is decreased. Furthermore, the control unit 22 controls the movement (crucible rising speed) of the quartz crucible 11 to a predetermined gap value based on the crystal length data of the silicon single crystal 3 obtained from the sensor of the crystal stretching mechanism 19 and the gap value _hGAP (liquid level position) obtained from the image captured by the camera 20. The displacement of the quartz crucible 11 can be controlled to maintain the gap value h _GAP at a certain value. As the single crystal is stretched, the gap value h _GAP can be gradually reduced, and conversely, the gap value h _GAP can be increased.

Above the heat insulation body 17, a cylindrical shield 23 surrounding the crystal stretching axis may also be provided. This shield 23 may also be a structure called a purge tube, or a coolant that promotes the cooling of the stretched silicon single crystal 3.

A purge tube is used to control the flow of purge gas. To match the characteristics of semiconductor devices and adjust the resistivity of silicon single crystals, impurities such as arsenic (As) and antimony (Sb) are sometimes added to the molten silicon. These dopants have low boiling points and evaporate easily. In general crystallization stretching using the CZ method, in order to flow purge gas such as Ar through the reduced-pressure stretching furnace, the dopants evaporating from the molten silicon 2 evaporate along with the purge gas, contaminating the furnace. Furthermore, the heat insulation 17 installed in the furnace accelerates the flow rate of the purge gas flowing near the surface of the molten silicon 2, further promoting the evaporation of impurities from the molten silicon 2. However, when a purge pipe is installed and the purge gas is rectified and introduced into the stretching furnace, the evaporation of impurities in the molten silicon can be suppressed while maintaining a high-pressure state in the chamber.

The cooling system is configured to control the time it takes for a silicon single crystal drawn from molten silicon 2 to pass through a predetermined temperature range. It is known that the type or distribution of crystallization defects in silicon single crystals produced by the CZ method depends on the ratio V/G of the silicon single crystal growth rate (drawing rate) V to the temperature gradient G along the drawing axis near the crystal growth interface from the melting point to 1300°C. By strictly controlling V/G, single crystals free of crystal-originating particles (COPs) or dislocation clusters can be produced.

In this paper, if the crystal diameter increases, the center of the crystal is more difficult to cool than the outer periphery, and the temperature gradient G within the cross-section of the silicon single crystal orthogonal to the stretching axis tends to become uneven. Consequently, the allowable range of V/G for designating the entire surface of the silicon single crystal cross-section orthogonal to the stretching axis as a defect-free region becomes very narrow, making it difficult to control the crystal stretching rate V rapidly. However, by providing a cylindrical coolant above the heat insulation body 17, the allowable range (PvPi margin) of the crystal stretching rate V for designating the entire surface of the silicon single crystal cross-section orthogonal to the stretching axis as a defect-free region can be expanded, thereby improving the manufacturing yield of large-diameter silicon single crystals that do not contain crystal source grains or dislocation clusters.

Figure 2 is a flowchart showing the manufacturing process of silicon single crystal. Figure 3 is a schematic side view showing the shape of a silicon single crystal ingot.

As shown in Figure 2, the manufacturing process of silicon single crystal includes: a melt generation process S11 in which polycrystalline silicon raw material in quartz crucible 11 is heated by heater 15 to generate silicon melt 2; a melt attachment process S12 in which seed crystal installed at the front end of wire 18 is lowered and attached to silicon melt 2; and a crystallization stretching process S13 in which seed crystal is slowly stretched and silicon single crystal 3 is grown while maintaining contact with silicon melt 2.

In the crystallization stretching process S13, the following processes are performed sequentially: a necking process S14 to narrow the crystal diameter and form a neck 3a to prevent misalignment; a shoulder growth process S15 to form a shoulder 3b with a gradually increasing crystal diameter during crystal growth; a body growth process S16 to form a body portion 3c with a constant crystal diameter; and a tail growth process S17 to form a tail portion 3d with a gradually decreasing crystal diameter during crystal growth. Then, a cooling process S18 is performed to separate the silicon single crystal 3 from the molten liquid surface 2a and promote cooling. Through the above, a silicon single crystal ingot 3i having a neck 3a, a shoulder 3b, a body 3c, and a tail 3d is completed.

In the crystallization stretching process S13, especially in the body growth process S16, the quartz crucible 11 is slowly raised to keep the gap (gap value) between the lower end of the heat insulation body 17 and the molten liquid surface 2a constant.

Figure 4 is a flowchart illustrating an example of a method for controlling the height of the quartz crucible 11.

As shown in Figure 4, in the height control of the quartz crucible 11, the camera 20 photographs the furnace during a predetermined sample period, and the measured value of the gap, h _GAP, is obtained from the images captured by the camera 20 (step S21). Then, the gap correction Δh _GAP is obtained from the difference between the measured gap value h _GAP and the target value h _GAPt (step S22). The target value h _GAPt is obtained from a pre-set gap data profile, taking into account the crystal length. The gap correction Δh _GAP is positive when the measured gap value h _GAP is larger than the target value h _GAPt , and negative when the measured gap value h _GAP is smaller than the target value h _GAPt .

Next, the correction amount _ΔVc for the crucible rise rate is obtained from the gap correction amount Δh _GAP (step S23). The crucible rise rate _Vc is the fixed value of the crucible rise rate _Vcs plus the correction amount _ΔVc , _Vc = _Vcs + _ΔVc . The fixed value of the crucible rise rate _Vcs is obtained from a predetermined crucible rise rate data profile, taking into account the crystal length. The correction amount _ΔVc is obtained from the gap correction amount Δh _GAP . The correction amount _ΔVc for the crucible rise rate becomes positive when the gap correction amount Δh _GAP is positive, and becomes negative when the gap correction amount Δh _GAP is negative. In other words, if the measured gap value _hGAP is larger than the target value _hGAPt , slightly increasing the crucible rising speed _Vc will decrease the gap. Conversely, if the measured gap value _hGAP is smaller than the target value _hGAPt , slightly decreasing the crucible rising speed _Vc will increase the gap.

Next, the correction for the crucible rise rate, ΔV _{_c} , is compared with the threshold, ΔV _{_cth} (step S24). In this paper, the threshold ΔV_{_cth} is set for each crystal stretching process based on past records of crucible rise rate variations in silicon single crystal mass production. This is because the allowable gap error or crucible rise rate error varies depending on the required quality or equipment environment of the silicon single crystal. Furthermore, the threshold ΔV _{_cth} is set with both an upper threshold ΔV _{_cuth} and a lower threshold ΔV_{_clth} . In other words, while determining whether the correction amount _ΔVc for the crucible's rising speed is higher than the upper limit threshold _ΔVcuth , it is also necessary to determine whether it is lower than the lower limit threshold _ΔVclth . This is because there are not only cases where the liquid level drops rapidly due to leakage caused by damage to the quartz crucible 11, but also cases where the liquid level rises rapidly due to deformation of the quartz crucible 11.

Typically, although the crucible rising speed _Vc is mostly constant, in cases where leakage or deformation due to damage to the quartz crucible 11 causes a change in volume, the sudden change in the liquid level position (interval value) causes the crucible rising speed _Vc to change in order to offset it. In this situation where corrections are always made relative to the liquid level position, it is difficult to determine whether a decrease in the liquid level position is indeed due to crystal growth or damage to the quartz crucible 11. In other words, it is difficult to detect minute changes in the liquid level position and determine whether there are any abnormalities through visual observation.

Therefore, in this embodiment, the change of the crucible rising speed _Vc is monitored, and when the correction amount _ΔVc (crucible rising correction speed) exceeds the threshold _ΔVcth , it is determined that the leakage caused by the damage of the quartz crucible 11 or the deformation of the quartz crucible has caused a sudden change in volume, and the crystallization stretching process S13 is terminated (step S24 is yes, step S25). Furthermore, when the correction amount _ΔVc for the crucible rising speed is below the threshold _ΔVcth , the possibility of continuing the crystallization stretching process S13 directly leading to accidents is lower while controlling the height of the quartz crucible 11 based on the determined crucible rising speed _Vc (step S24 is not applicable, step S26 is not applicable). This allows for early detection of damage or deformation of the quartz crucible 11 and prevents secondary damage.

The threshold _ΔVcth is determined based on past records of crucible rise rate corrections during mass production. For example, the average of these correction records, ±3σ, can be set as the threshold. In this paper, σ represents the standard deviation. Deviations exceeding ±3σ from the average may indicate an anomaly, including leakage.

Furthermore, when determining the threshold (average ± 3σ), it can be obtained using both recorded values from cases where abnormalities such as leakage or crucible deformation occurred during the crystallization stretching process and cases where no abnormalities occurred. Alternatively, it can be obtained solely from recorded values from cases where no abnormalities occurred during the crystallization stretching process. The option of obtaining the threshold solely from recorded values from cases where no abnormalities occurred represents a safer threshold setting. This is because leakage or crucible deformation rarely occurs in reality, and there are situations where it is difficult to prepare data that includes these abnormalities.

The threshold _ΔVcth is best set according to the growth length of the crystals, because the gap compensation amount can sometimes vary depending on the growth length of the crystals.

Figure 5 is a flowchart illustrating another example of a method for controlling the height of the quartz crucible 11.

As shown in Figure 5, the control method is the same as that in Figure 4, from the step of obtaining the gap value h _GAP (step S21) to the step of comparing the correction amount _ΔVc of the crucible rising speed with the threshold value _ΔVcth (step S24). The key feature of this control method is that when the correction amount _ΔVc of the crucible rising speed exceeds the threshold value _ΔVcth , the crystallization stretching process S13 is not directly stopped. Instead, the edge detection results of the furnace internal structures such as the heat insulation body 17 reflected in the captured image are evaluated (step S27). If there are no abnormalities in the edge detection results, the crystallization stretching process S13 is stopped (step S27 is not, step S25). Furthermore, if there is an abnormality in the edge detection result (yes in step S27), it is not necessary to directly stop the crystallization stretching process S13. The crystallization stretching process S13 can continue by eliminating the cause of the abnormality in the edge detection result. Sometimes, the abnormality in the edge detection result is also due to an erroneous detection, for example, by switching to a backup camera, and the process can return to edge detection processing normally.

In calculating the gap value h _GAP , edge detection processing is performed on the real image of the heat insulation body 17 and the mirror image of the heat insulation body 17 reflected on the molten liquid surface 2a, and the gap value h _GAP is obtained based on the edge detection results. Therefore, if there are abnormalities in the edge detection results, the probability that the obtained gap value h _GAP is an abnormal value that differs from the actual gap value h _GAP is relatively high. If the height control of the quartz crucible 11 is performed based on such a gap value, incorrect gap control will be performed. However, in this embodiment, it is possible to prevent erroneous operation by determining whether the increase in the correction amount _ΔVc of the crucible's rising speed is indeed caused by the change in the gap value h _GAP due to damage to the quartz crucible 11, or by errors in the image processing results.

Figure 6 is a schematic diagram of an example of edge detection results, (a) showing a normal edge detection result, and (b) showing an abnormal edge detection result.

As shown in Figures 6(a) and (b), in the image captured by the camera, molten silicon 2 is presented through the opening of the heat insulation 17, and the mirror image of the heat insulation 17 is reflected at the surface 2a of the molten liquid. By binarizing this image, the real image edge and the mirror image edge of the heat insulation 17 can be detected, and the gap value can be geometrically calculated from the real image edge and the mirror image edge of the heat insulation 17.

In this paper, for example as shown in Figure 6(a), when the edge detection result is normal, an edge line (approximate curve) is obtained from the edge of the mirror. On the other hand, as an example of an abnormal edge detection result, as shown in Figure 6(b), two edges are detected on a portion of the upper left edge of the mirror. In cases where the approximate circle diameter obtained from the two edge lines detected from the mirror edge exceeds the controllable range, the edge detection result is determined to be abnormal, and an error message is issued. In the event of such an error, as mentioned above, even if the correction amount _ΔVc for the crucible rise rate exceeds the threshold _ΔVcth , it is not necessarily necessary to stop the crystallization stretching process S13.

As explained above, the silicon single crystal manufacturing method according to this embodiment involves capturing the molten surface 2a of the silicon melt 2 inside the quartz crucible 11 using a camera 20 during the crystallization stretching process S13. The gap value h _GAP is obtained from the captured image. As the gap value h _GAP increases, the rise of the quartz crucible 11 is controlled. The correction amount _ΔVc of the rising speed of the quartz crucible 11 is obtained from the deviation between the measured gap value and the target value. Based on whether the correction amount _ΔVc exceeds the threshold _ΔVcth, it is determined whether there is a sudden change in the liquid surface position. Therefore, without relying on human visual observation, damage or deformation of the quartz crucible 11 can be detected early and automatically. Therefore, it can prevent secondary damage such as device damage caused by breakage or deformation of the quartz crucible 11.

In cases where the single crystal stretching apparatus suffers significant damage due to the breakage of the quartz crucible 11, it is necessary to replace the damaged parts or components and restore it to its original state so that the single crystal stretching apparatus can be reused. During this restoration process, waste is generated, increasing the environmental impact. However, according to this invention, waste generation can be prevented, reducing the environmental impact and contributing to achieving UN Sustainable Development Goals (SDGs) Goal 12, "Responsibility for Creation, Responsibility for Use" (preventing waste generation).

While the preferred embodiments of the invention have been described above, the invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention, and these modifications are of course included within the scope of the invention.

[Example] The stretching of multiple silicon single crystals was performed using the silicon single crystal manufacturing apparatus according to the present invention. As a result, most stretching batches were normal, but in some batches, leakage caused abnormalities in the crucible's rising speed.

Figure 7 is a chart showing the change in the crucible rise correction speed with gap control. The horizontal axis shows the crystal length (length of the body 3c), and the vertical axis shows the crucible rise correction speed.

As shown in Figure 7, it can be understood that although the crucible rise correction speed does not change significantly in normal batches, remaining within the range of the upper threshold ΔV _cuth to the lower threshold ΔV _clth used for anomaly detection, the crucible rise correction speed changes rapidly in abnormal batches. In this abnormal batch, the gap measurement records were checked when the anomaly occurred. Since no anomalies were found in the edge detection results, the possibility of leakage was high, rather than a control anomaly caused by incorrect gap measurement, and the crystallization stretching process was stopped. After turning off the heater power and cooling the chamber, the chamber was opened to the atmosphere and the leak traces from the side wall of the quartz crucible were checked. However, the leakage is minimal, thus minimizing the damage.

1: Silicon single crystal manufacturing apparatus 2: Molten silicon 2a: Molten surface 3: Silicon single crystal 3a: Neck 3b: Shoulder 3c: Body 3d: Tail 3i: Silicon single crystal ingot 10: Chamber 10a: Main chamber 10b: Traction chamber 10c: Gas inlet 10d: Gas outlet 10e: Observation window 11: Quartz crucible 12: Graphite crucible 13: Rotating shaft 14: Crucible drive mechanism 15: Heater 16: Insulation material 17: Insulator 18: Conductor 19: Crystal stretching mechanism 20: Camera 21: Image processing unit 22: Control unit 23: Shielding material h: _GAP : Measured value of gap (gap value) S11: Molten Liquid Generation Process; S12: Molten Liquid Adhesion Process; S13: Crystallization and Stretching Process; S14: Neck Reduction Process; S15: Shoulder Development Process; S16: Body Development Process; S17: Tail Development Process; S18: Cooling Process; S21, S22, S23, S24, S25, S26, S27: Steps

Figure 1 is a schematic cross-sectional view showing the structure of a silicon single crystal manufacturing apparatus according to an embodiment of the present invention. Figure 2 is a flowchart showing the silicon single crystal manufacturing process. Figure 3 is a schematic side view showing the shape of a silicon single crystal ingot. Figure 4 is a flowchart showing an example of a method for controlling the height of a quartz crucible. Figure 5 is a flowchart showing another example of a method for controlling the height of a quartz crucible. Figure 6 is a schematic diagram showing an example of edge detection results: (a) showing a normal edge detection result, and (b) showing an abnormal edge detection result. Figure 7 is a graph showing the change in the crucible rise correction speed with gap control.

without

1: Silicon Single Crystal Manufacturing Equipment

2: Molten silicon

2a: Molten liquid surface

3: Silicon Single Crystal

10: Chambers

10a: Main chamber

10b: Traction Chamber

10c: Gas inlet

10d: Gas exhaust port

10e: Observation Window

11: Quartz Crucible

12: Graphite crucible

13: Rotation axis

14: Crucible Drive Mechanism

15: Heater

16: Thermal Insulation Materials

17: Thermal Insulation

18: Wire

19: Crystallization stretching mechanism

20: Camera

21: Image Processing Department

22: Control Department

23: Coverings

h _GAP : Measured value of the gap (gap value)

Claims (10)

A method for manufacturing a silicon single crystal includes the following steps: During a crystallization stretching process, photographing the molten silicon surface within a quartz crucible; Obtaining from the photographed image the gap value between the lower end of a heat-insulating element positioned above the quartz crucible and the molten surface; Controlling the height of the quartz crucible in response to changes in the gap value; and In controlling the height of the quartz crucible, obtaining a correction amount for the crucible's rising speed from the difference between the measured and target values of the gap value, and determining whether the molten surface position has suddenly changed based on whether the correction amount exceeds a threshold. As described in claim 1, in the method for manufacturing silicon single crystals, the crystallization stretching process is stopped when a sudden change in the liquid level is detected. As described in claim 1, in the method for manufacturing silicon single crystals, when a sudden change in the liquid level is detected, it is determined whether there is an abnormality in the detection result of the edge of the furnace structure presented in the captured image, and if there is no abnormality in the edge detection result, the crystal stretching process is stopped. As described in claim 3, in the method for manufacturing a silicon single crystal, the furnace internal structure is the heat insulation body, and the gap value is obtained from the real image edge of the heat insulation body and the mirror image edge of the heat insulation body reflected on the molten liquid surface. As described in claim 1, in the method for manufacturing silicon single crystals, the threshold is a system having an upper limit threshold and a lower limit threshold for the correction amount, and is set for each crystal stretching process based on the record of changes in crucible rise rate in past silicon single crystal mass production records. A silicon single crystal manufacturing apparatus includes: a chamber; a quartz crucible holding molten silicon within the chamber; a heater disposed around the quartz crucible and heating the molten silicon; a crucible driving mechanism driving the rotation and lifting of the quartz crucible; a crystallization stretching mechanism stretching a silicon single crystal from the molten silicon; a heat insulation body disposed above the quartz crucible to surround the stretching path of the silicon single crystal; a camera capturing images of the interior from the outside of the chamber; an image processing unit processing the images captured by the camera; and a control unit controlling the heater, the crucible driving mechanism, and the crystallization stretching mechanism based on the processing results of the image processing unit; The image processing unit, during the crystallization stretching process, captures the molten silicon surface within the quartz crucible using a camera; obtains the gap value between the lower end of the heat insulation element and the molten surface from the captured image; the control unit, controls the height of the quartz crucible in response to changes in the gap value; in controlling the height of the quartz crucible, it calculates a correction amount for the crucible's rising speed from the difference between the measured and target gap values, and determines whether there has been a sudden change in the molten surface position based on whether the correction amount exceeds a threshold. As described in claim 6, in the silicon single crystal manufacturing apparatus, the control unit stops the crystallization stretching process when it detects a sudden change in the liquid level position. As described in claim 6, in the silicon single crystal manufacturing apparatus, the control unit determines whether there is an abnormality in the detection result of the edge of the furnace structure presented in the captured image when a sudden change in the liquid level is detected, and stops the crystal stretching process if there is no abnormality in the edge detection result. As described in claim 8, in a silicon single crystal manufacturing apparatus, the furnace internal structure is the heat insulation body, and the gap value is obtained from the real image edge of the heat insulation body and the mirror image edge of the heat insulation body reflected on the molten liquid surface. As described in claim 6, the silicon single crystal manufacturing apparatus has an upper limit threshold and a lower limit threshold for the correction amount, and is set for each crystal stretching process based on the record of changes in crucible rise rate in past silicon single crystal mass production records.