Single crystal furnace and single crystal preparation method

Abstract

The invention provides a single crystal furnace and a single crystal preparation method. The single crystal furnace comprises: a crucible for placing a molten material; the imaging device faces the solid-liquid interface position of the pulling growth single crystal material in the crucible and is used for imaging the interface position; the calibration plate is arranged at the position of a solid-liquid interface in advance before the single crystal material is lifted and grown, and is used for calibrating the view field coordinates of the imaging device, so that the imaging device can convert the imaging coordinates of the view field image into real size coordinates; and the lifting process adjusting module is used for receiving the image of the solid-liquid interface position formed by the imaging device, calculating the real size of the solid-liquid interface by adopting the relation between the imaging coordinate and the real size coordinate, calculating the growth diameter of the crystal bar, and feeding back to the single crystal furnace for controlling the lifting process and realizing the accurate control of the diameter of the crystal bar. The imaging view field is calibrated based on visual detection, the shape data of the imaging graph is accurately converted into an actual graph, and the crystal bar diameter measurement precision is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a single crystal furnace and a single crystal preparation method. Background Art

[0002] Semiconductor silicon wafers refer to silicon wafers cut from single crystal silicon ingots. They are the chip base material used in many industries such as consumer electronics (smartphones, laptops), new energy fields (automobiles, photovoltaics), and artificial intelligence fields (AGI, smart robots).

[0003] During the growth of silicon crystals, the diameter fluctuation of silicon crystals will directly affect the morphology and quality of the growing crystal rods. A diameter change of 1 mm may cause an exponential change in crystal defects. Due to the high temperature in the single crystal furnace (the melting point of silicon is as high as 1450 degrees Celsius) and the extremely high requirements for environmental cleanliness, existing technologies make it difficult to achieve high-precision measurement of the diameter of the crystal rod during growth. Therefore, new diameter measurement technology is urgently needed to obtain high-quality single crystal silicon to meet the high-performance requirements of emerging fields such as current electronics, new energy, and AI. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a single crystal furnace and a single crystal preparation method, and to achieve high-precision diameter measurement by designing a crystal rod diameter measurement method, thereby controlling the quality of the single crystal silicon rod.

[0005] In order to solve the above problems, the present invention provides a single crystal furnace, comprising: a crucible for placing molten material; an imaging device, which faces the solid-liquid interface position of the single crystal material being pulled and grown in the crucible and images the interface position; a calibration plate, which is pre-placed at the solid-liquid interface position before pulling the single crystal material to calibrate the field of view coordinates of the imaging device so that the imaging device can convert the imaging coordinates of the field of view image into real size coordinates; and a pulling process adjustment module, which receives the image of the solid-liquid interface position formed by the imaging device, and uses the relationship between the imaging coordinates and the real size coordinates to calculate the real size of the solid-liquid interface, calculates the growth diameter of the crystal rod, and feeds back to the single crystal furnace for controlling the pulling process to achieve precise control of the crystal rod diameter.

[0006] Optionally, the calibration plate is a black and white grid calibration plate.

[0007] Optionally, the calibration plate is placed above the support plate of the single crystal furnace with a horizontal accuracy of less than 0.05°, and the position of the calibration plate is adjusted to correspond to the solid-liquid interface position of the pulled single crystal material through the movement of the graphite spindle.

[0008] Optionally, the ordinate values ​​of the imaging coordinates of the field of view image of each pixel point along the lower edge of the calibration plate are the same.

[0009] Optionally, the imaging device selects two fan-shaped regions of interest at the solid-liquid interface to detect the outer edge of the meniscus region after grayscale binarization, and then fits the diameter of the crystal rod based on the real size calculated based on the relationship between the imaging coordinates and the real size coordinates.

[0010] In order to solve the above problems, the present invention provides a single crystal preparation method, comprising: setting an imaging device, pulling the growing single crystal material toward the solid-liquid interface position in the crucible of the single crystal furnace, and imaging the interface position; placing a calibration plate in advance at the solid-liquid interface position of the growing single crystal material, calibrating the field of view coordinates of the imaging device, so that the imaging device can convert the imaging coordinates of the field of view image into real size coordinates; removing the calibration plate, and placing the crucible in the single crystal furnace; placing the raw material in the crucible to melt, and pulling to form a crystal rod, receiving the image of the solid-liquid interface position formed by the imaging device during the pulling process, and using the relationship between the imaging coordinates and the real size coordinates to calculate the real size of the solid-liquid interface, calculating the growth diameter of the crystal rod, and feeding it back to the single crystal furnace for controlling the pulling process, thereby achieving precise control of the crystal rod diameter.

[0011] Optionally, the calibration plate is a black and white grid calibration plate.

[0012] Optionally, the method of pre-placing a calibration plate at the solid-liquid interface position of the pulled single crystal material includes placing the calibration plate above the support plate of the single crystal furnace with a horizontal accuracy of less than 0.05°, and adjusting the position of the calibration plate to correspond to the solid-liquid interface position of the pulled single crystal material through the movement of the graphite spindle.

[0013] Optionally, the step of placing a calibration plate at the solid-liquid interface position in advance during the Czochralski growth of the single crystal material includes rotating the calibration plate so that the ordinate values ​​of the imaging coordinates of the field of view image of each pixel point at the lower edge are the same.

[0014] Optionally, the image of the solid-liquid interface position formed by the imaging device is received during the pulling process, including the imaging device selecting two fan-shaped regions of interest at the solid-liquid interface position to detect the outer edge of the meniscus area after grayscale binarization, and then fitting the diameter of the crystal rod based on the real size obtained by calculating the relationship between the imaging coordinates and the real size coordinates.

[0015] The present invention calibrates the imaging field of view based on visual detection, accurately converts the shape data of the imaging figure into the actual figure, and improves the measurement accuracy of the crystal rod diameter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attached Figure 1 Shown is a schematic structural diagram of a single crystal furnace according to a specific embodiment of the present invention.

[0017] Attached Figure 2Shown is a schematic structural diagram of a single crystal furnace according to a specific embodiment of the present invention.

[0018] Attached Figure 3 Shown is a schematic diagram of a calibration plate in a single crystal furnace according to a specific embodiment of the present invention.

[0019] Attached Figure 4 Shown is a schematic diagram of the implementation steps of the single crystal preparation method described in a specific embodiment of the present invention.

[0020] Attached Figure 5 Shown is a curve showing the relationship between the actual crystal rod size and the corresponding measurement data according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0021] The specific implementation modes of the single crystal furnace and the single crystal preparation method provided by the present invention are described in detail below with reference to the accompanying drawings.

[0022] Attached Figure 1 The figure is a schematic diagram of the structure of a single crystal furnace according to a specific embodiment of the present invention, including: a crucible, an imaging device, a calibration plate, and a pulling process adjustment module.

[0023] The crucible 10 includes a graphite crucible 102 and a quartz crucible 101, which are used to place the molten material 11. In this specific embodiment, the single crystal furnace is used to prepare single crystal silicon ingots, so the molten material 11 is polycrystalline silicon. Figure 1 It is a schematic diagram of a pulling state, in which a part of the molten material 11 has been pulled to form a single crystal rod 12 .

[0024] The interface between the two is a solid-liquid interface13

[0025] The imaging device 20 faces the position of the solid-liquid interface 13 of the single crystal material being pulled and grown in the crucible 10, and images the position of the interface 13. The molten material 11 is pulled to form a single crystal rod 12, and the single crystal rod 12 is in a solid state, and the interface between the two is the solid-liquid interface 13. The morphology of the interface reflects the diameter of the single crystal rod 12. In this specific embodiment, the diameter of the single crystal rod 12 can be calculated by accurately monitoring the position and size of the interface 13, and the pulling process can be adjusted in real time to obtain a single crystal rod 12 with stable dimensions.

[0026] The calibration plate 30 is placed at the position of the solid-liquid interface 13 before the single crystal material is pulled and grown, and the field coordinates of the imaging device 20 are calibrated so that the imaging device 20 can convert the imaging coordinates of the field image into real size coordinates. In a specific embodiment of the present invention, the calibration plate 30 is placed above the support plate 40 of the single crystal furnace and the horizontal accuracy is less than 0.05°. The support plate 40 is used to support the crucible 10 during the pulling process and includes a main shaft 41, and the preferred material is graphite.

[0027] The spindle 41 can be rotated and raised and lowered, and is used to control the position and rotation speed of the crucible during the process of preparing the single crystal rod. Figure 2 As shown, in this specific embodiment, before the single crystal material is pulled and grown, the calibration plate 30 is placed on the support plate 40 of the single crystal furnace, and the position of the calibration plate is adjusted to correspond to the position of the solid-liquid interface 13 of the pulled and grown single crystal material through the lifting and lowering movement of the spindle 41. In the process of pulling and growing the single crystal rod 12, as the single crystal rod 12 grows, the molten material 11 is consumed, and the crucible 11 rises accordingly, ensuring that the position of the solid-liquid interface 13 remains unchanged. Therefore, the position of the solid-liquid interface 13 can be pre-determined before growth, and the calibration plate 30 can be placed at this position through the spindle 41. Adjust the camera parameters such as the camera aperture and focal length of the imaging device 20 to ensure that the calibration plate 30 can be clearly photographed, and the image is still clear when the graphite spindle is raised / lowered within a range of 5mm.

[0028] Preferably, the ordinates, i.e., y values, of the imaging coordinates of the field of view images of each pixel point along the lower side of the calibration plate 30 can be made the same by rotating the main shaft 41. That is, the calibration plate 30 and the field of view of the imaging device 20 are horizontally parallel, so that the calculation of coordinate conversion can be mainly concentrated on the horizontal coordinate, making the calculation error smaller.

[0029] As attached Figure 3 The figure shows a schematic diagram of the calibration plate 30 in the field of view, which is a trapezoidal shape. Preferably, the calibration plate 30 is a black and white grid calibration plate with a thickness of 5.5 mm, each black and white grid is 20×20 mm, and the accuracy is 5 um. Since we know the size of each square of the calibration plate 30, we can calculate the real coordinates of the calibration plate. We can obtain the imaging coordinates from the imaging of the calibration plate 30. By comparing the two, we can calculate the mapping relationship between the imaging coordinates of the field of view image and the real size coordinates.

[0030] In other specific embodiments, the calibration plate 30 may also be a plurality of nested concentric circles, and polar coordinates are established. The center position of the concentric circles is kept unchanged by translating and rotating the calibration plate 30, that is, the rotation of the concentric circles is coaxial with the rotation of the support plate 40. In this way, the calibration plate 30 can be used to simulate the state of the crucible 10 rotation, which is closer to the real monitoring environment.

[0031] The pulling process adjustment module 50 is used to receive the image of the position of the solid-liquid interface 13 formed by the imaging device 20, and use the imaging device 20 to calculate the relationship between the imaging coordinates and the real size coordinates obtained by the calibration plate 30 to obtain the real size of the solid-liquid interface 13, calculate the growth diameter of the crystal rod, and feed it back to the single crystal furnace for controlling the pulling process, including adjusting the heating temperature, crystal rod rotation speed, crucible rotation speed, furnace pressure, etc., so as to achieve precise control of the crystal rod diameter. In a specific embodiment, as shown in the attached Figure 4As shown, the imaging device 20 selects two or more fan-shaped regions of interest at the solid-liquid interface 13 to detect the outer edge of the meniscus region after grayscale binarization, and then fits the diameter of the crystal rod based on the real size calculated according to the relationship between the imaging coordinates and the real size coordinates. Selecting two or more fan-shaped regions of interest can monitor the growth by only monitoring the specified fan-shaped region during the growth process. If the boundary morphology is not captured in the fan-shaped region, it means that the diameter has exceeded the maximum allowable threshold, and the growth should be stopped or other emergency measures should be taken to compensate.

[0032] Attached Figure 4 The figure shows a schematic diagram of the implementation steps of the single crystal preparation method described in a specific embodiment of the present invention, including: step S10, setting an imaging device, pulling the growing single crystal material toward the solid-liquid interface position in the crucible of the single crystal furnace, and imaging the interface position; step S11, placing a calibration plate in advance at the solid-liquid interface position of the growing single crystal material, calibrating the field of view coordinates of the imaging device, so that the imaging device can convert the imaging coordinates of the field of view image into real size coordinates; step S12, removing the calibration plate, and placing the crucible in the single crystal furnace; step S13, placing the raw material in the crucible for melting, and pulling to form a crystal rod, receiving the image of the solid-liquid interface position formed by the imaging device during the pulling process, and using the relationship between the imaging coordinates and the real size coordinates to calculate the real size of the solid-liquid interface, calculating the growth diameter of the crystal rod, and feeding it back to the single crystal furnace for controlling the pulling process, so as to achieve precise control of the crystal rod diameter.

[0033] Please refer to the attached Figure 1 -Attached Figure 3 The single crystal furnace structure shown is not limited to the implementation relying on the structure of the above single crystal furnace. Any single crystal furnace that can support the above method should be regarded as the equipment that can be used for the above method.

[0034] Step S10, setting an imaging device, pulling the single crystal material to grow in the crucible of the single crystal furnace toward the position of the solid-liquid interface, and imaging the position of the interface. The imaging device pulls the single crystal material to grow in the crucible toward the position of the solid-liquid interface, and images the position of the interface. The molten material is pulled to form a single crystal rod, and the single crystal rod is in a solid state. The interface between the two is a solid-liquid interface. The morphology of the interface reflects the diameter size of the single crystal rod. In this specific embodiment, the diameter size of the single crystal rod can be calculated by accurately monitoring the position and size of the interface and adjusting the pulling process in real time to obtain a single crystal rod with stable size.

[0035] Step S11, pre-place a calibration plate at the solid-liquid interface position of the pulled single crystal material, calibrate the field of view coordinates of the imaging device, so that the imaging device can convert the imaging coordinates of the field of view image into real size coordinates. Preferably, the calibration plate 30 is a black and white grid calibration plate with a thickness of 5.5mm, each black and white grid is 20×20mm, and the accuracy is 5um. Since we know the size of each square of the calibration plate 30, we can calculate the real coordinates of the calibration plate. And we can obtain the imaging coordinates from the imaging of the calibration plate 30. By comparing the two, we can calculate the mapping relationship between the imaging coordinates of the field of view image and the real size coordinates.

[0036] The calibration plate is placed in advance at the position of the solid-liquid interface before the single crystal material is pulled and grown, and the field of view coordinates of the imaging device are calibrated so that the imaging device can convert the imaging coordinates of the field of view image into real size coordinates. In a specific embodiment of the present invention, the calibration plate is placed above the support plate of the single crystal furnace and the horizontal accuracy is less than 0.05°. The support plate is used to support the crucible during the pulling process and includes a spindle, and the preferred material is graphite. The spindle can rotate and rise and fall, and is used to control the position and rotation speed of the crucible during the preparation of the single crystal rod. In this specific embodiment, before the single crystal material is pulled and grown, the calibration plate is placed on the support plate of the single crystal furnace, and the position of the calibration plate is adjusted to correspond to the solid-liquid interface position of the pulled single crystal material through the lifting and lowering movement of the spindle. Adjust the camera parameters of the imaging device such as the camera aperture and focal length to ensure that the calibration plate can be clearly photographed, and at the same time, the image is still clear when the graphite spindle is raised / lowered within a range of 5mm.

[0037] Preferably, the main axis can be rotated to make the ordinates, i.e., y values, of the imaging coordinates of the field of view image of each pixel point along the lower edge of the calibration plate the same, that is, to ensure that the calibration plate and the field of view of the imaging device are horizontally parallel, so that the calculation of coordinate conversion can be mainly concentrated on the horizontal coordinate, making the calculation error smaller.

[0038] Step S12, remove the calibration plate and place the crucible in the single crystal furnace. The crucible is used to place the molten material. In this specific embodiment, the single crystal furnace is used to prepare single crystal silicon rods, so the molten material is polycrystalline silicon. In the process of pulling and growing the single crystal rod, as the single crystal rod grows, the molten material is consumed, and the crucible rises accordingly to ensure that the position of the solid-liquid interface remains unchanged. Therefore, the position of the solid-liquid interface can be pre-determined before growth, and the calibration plate can be placed at this position through the spindle.

[0039] Step S13, placing the raw material in a crucible for melting, and pulling to form a crystal rod, receiving the image of the solid-liquid interface position formed by the imaging device during the pulling process, and using the relationship between the imaging coordinates and the real size coordinates to calculate the real size of the solid-liquid interface, calculating the crystal rod growth diameter, and feeding it back to the single crystal furnace for controlling the pulling process to achieve precise control of the crystal rod diameter. The single crystal furnace is used to control the pulling process, including adjusting the heating temperature, the crystal rod rotation speed, the crucible rotation speed, the furnace pressure, etc. In a specific embodiment, two fan-shaped regions of interest can be selected at the solid-liquid interface position to detect the outer edge of the meniscus area after grayscale binarization, and then the diameter of the crystal rod is fitted according to the real size calculated based on the relationship between the imaging coordinates and the real size coordinates. In this way, only the specified fan-shaped area can be monitored during the growth process, that is, the growth can be monitored. If the boundary morphology is not captured in the fan-shaped area, it means that the diameter has exceeded the maximum allowed threshold. At this time, the growth should be stopped or other emergency measures should be taken to compensate.

[0040] The following are examples of the above technical solution.

[0041] Based on the above technology, experiments were conducted during the actual crystal growth process to measure the diameter of the crystal rod in real time and obtain the measured value. After the crystal rod was taken out, the diameter of the crystal rod was measured and the difference between the measured value and the actual value was compared. As can be seen in the figure, the consistency between the measured diameter value and the actual measured value was achieved. At the same time, based on the fan-shaped ROI method, the diameter measurement value converges smoothly, which can effectively avoid the traditional tangent measurement method, which causes the diameter value divergence caused by the inability to detect the meniscus due to the change in diameter. The actual crystal rod size data is shown in the following table, and the corresponding data curve is shown in the attached figure. Figure 5 As shown, it can be seen that the measured data is highly consistent with the actual data and has good stability.

[0042] Table 1 Actual crystal rod size data obtained by using the technical solution described in this specific embodiment

[0043] Actual length of crystal rod Actual diameter This method measures This method measures the diameter 50 312 50 308.7 100 310 100.1 316.02 150 317 150 316.13 200 299 200.1 295.27 220 294 220.1 296.21 250 305 250 320.99 300 312 300.1 307.35 350 316 350 308.05 400 302 400 300.45 450 313 450.1 314.42 500 309 500.1 311.93 550 309 550 306.05 600 311 600.1 309.74 650 308 650 308.27 700 311 700.1 310.2 750 309 750 310.4 800 311 800 308.61 850 312 850 313.06 880 310 880.1 312.02 920 328 920 328.23 1000 308 1000 306.93 1050 306 1050 314.2 1100 319 1100.1 317.75 1200 312 1200 310.95 1250 311 1250 311.66 1300 311 1300 310.71 1350 311 1350 310.47 1400 310 1400 310.85 1450 310 1450.1 310.8 1500 310 1500 310.65

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A single crystal furnace, characterized in that: include: Crucible, used to place molten material; An imaging device is used to pull the solid-liquid interface of the growing single crystal material in the crucible and to image the interface position; A calibration plate, which is placed at the solid-liquid interface before the single crystal material is grown by pulling, and calibrates the field coordinates of the imaging device so that the imaging device can convert the imaging coordinates of the field image into real size coordinates; as well as The pulling process adjustment module receives the image of the solid-liquid interface position formed by the imaging device, and uses the relationship between the imaging coordinates and the real size coordinates to calculate the real size of the solid-liquid interface, calculates the growth diameter of the crystal rod, and feeds back to the single crystal furnace for controlling the pulling process to achieve precise control of the crystal rod diameter.

2. The single crystal furnace according to claim 1, characterized in that: The calibration plate is a black and white grid calibration plate.

3. The single crystal furnace according to claim 1, characterized in that: The calibration plate is placed above the support plate of the single crystal furnace with a horizontal accuracy of less than 0.05°, and the position of the calibration plate is adjusted to correspond to the solid-liquid interface position of the pulled single crystal material through the movement of the graphite spindle.

4. The single crystal furnace according to claim 1, characterized in that: The ordinate values ​​of the imaging coordinates of the field of view image at each pixel point along the lower side of the calibration plate are the same.

5. The single crystal furnace according to claim 1, characterized in that: The imaging device selects two fan-shaped regions of interest at the solid-liquid interface to detect the outer edge of the meniscus area after grayscale binarization, and then fits the diameter of the crystal rod based on the real size calculated based on the relationship between the imaging coordinates and the real size coordinates.

6. A method for preparing a single crystal, characterized in that: include: An imaging device is provided to pull the solid-liquid interface position of the growing single crystal material in the crucible of the single crystal furnace toward the solid-liquid interface position and to image the interface position; A calibration plate is placed at the solid-liquid interface position in advance on the Czochralski-grown single crystal material to calibrate the field coordinates of the imaging device so that the imaging device can convert the imaging coordinates of the field image into real size coordinates; removing the calibration plate and placing the crucible in the single crystal furnace; The raw materials are placed in a crucible to be melted and pulled to form a crystal rod. During the pulling process, the image of the solid-liquid interface position formed by the imaging device is received, and the relationship between the imaging coordinates and the real size coordinates is used to calculate the real size of the solid-liquid interface, calculate the growth diameter of the crystal rod, and feed it back to the single crystal furnace for controlling the pulling process to achieve precise control of the crystal rod diameter.

7. The method according to claim 6, characterized in that The calibration plate is a black and white grid calibration plate.

8. The method according to claim 6, characterized in that The method of pre-placing a calibration plate at the solid-liquid interface position of the Czochralski grown single crystal material includes placing the calibration plate above the support plate of the single crystal furnace with a horizontal accuracy of less than 0.05°, and adjusting the position of the calibration plate to correspond to the solid-liquid interface position of the Czochralski grown single crystal material through the movement of the graphite spindle.

9. The method according to claim 6, characterized in that The step of placing a calibration plate at the solid-liquid interface position in advance during the pulling and growing of the single crystal material includes rotating the calibration plate so that the ordinate values ​​of the imaging coordinates of the field of view images of each pixel point at the lower edge are the same.

10. The method according to claim 6, characterized in that The image of the solid-liquid interface position formed by the imaging device is received during the pulling process, including the imaging device selecting two fan-shaped areas of interest at the solid-liquid interface position to detect the outer edge of the meniscus area after grayscale binarization, and then fitting the diameter of the crystal rod based on the real size obtained by calculating the relationship between the imaging coordinates and the real size coordinates.

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