Method for improving stability of growth temperature field of CVD (chemical vapor deposition) single crystal diamond and stabilizing device thereof

Abstract

The invention relates to a CVD monocrystalline diamond growth temperature field stability improving method and a stabilizing device thereof.A through hole is formed in a sunken groove of a molybdenum table, after a monocrystalline diamond substrate in the sunken groove is tightly attached to the molybdenum table, nickel-based paste brazing filler metal is injected into the through hole, vacuum heating and welding are conducted, and the stability of a CVD monocrystalline diamond growth temperature field is improved. The substrate is pulled to be in close contact with the bottom face of the concave groove of the molybdenum table through the brazing filler metal which is welded and solidified, no gap is reserved, the heat conduction uniformity between the substrate and the concave groove is improved, the problem of local concentration of heat and temperature is avoided, the temperature field distribution consistency of the substrate and the upper surface of the molybdenum table is better, growth of all parts of the substrate is more uniform, and the service life of the substrate is prolonged. And the grown monocrystal diamond has fewer edge polycrystals, the morphology of the monocrystal diamond is regular, the internal stress is greatly reduced, and the application of the product in various industries and fields is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of single crystal diamond CVD growth, and in particular to a method for improving the stability of a temperature field of CVD single crystal diamond growth and a stabilizing device thereof. Background Art

[0002] As a leader among the third-generation semiconductor materials, diamond materials have excellent properties such as high thermal conductivity, high breakdown electric field, high carrier mobility, high carrier saturation rate and low dielectric constant. They meet the requirements of modern electronic technology for harsh conditions such as high temperature, high pressure, high power, high frequency and radiation resistance, and are recognized by the industry as the "ultimate semiconductor material".

[0003] The preparation technology of high-quality single-crystal diamond is now mature, and the most widely used microwave chemical vapor deposition technology can achieve quality comparable to or even better than natural diamond. Due to the high cost of manufacturing equipment, small size of diamond substrate, long growth cycle, and unstable production yield, the price of high-quality single-crystal diamond remains high. How to prepare large-area, high-quality single-crystal diamond in large quantities at low cost is an urgent problem that currently limits the large-scale industrial application of diamond. The process parameter that most affects the yield of single-crystal diamond preparation is the uneven and unstable temperature field distribution of the single-crystal diamond itself during the long growth cycle.

[0004] The temperature is difficult to control mainly due to the following two reasons: First, single crystal diamond can be deposited at the place where the middle position of the front side of the single crystal diamond substrate contacts the plasma ball. However, the position where the back side of the diamond substrate contacts the front side of the molybdenum table and the position where the back side of the molybdenum table contacts the water-cooled substrate table have a certain temperature due to heat conduction. Some carbon-containing groups in the plasma that have not fully participated in the reaction will deposit a layer of black or gray carbon film at these two positions, affecting heat dissipation, resulting in inconsistent heat dissipation in various parts of the substrate, uneven temperature field distribution on the substrate, and even the deposited carbon film will push up the substrate or the molybdenum table, further causing the temperature to rise rapidly or even exceed the temperature range required for growth.

[0005] Second, the tip effect of the microwave electromagnetic field will form a strong electromagnetic field at the edge of the single crystal diamond substrate, causing the edge temperature of the single crystal diamond substrate to be higher than the middle position, and polycrystalline diamond will be deposited at the edge. As the growth time increases, more and more polycrystalline diamond is deposited at the edge under higher temperature conditions, which further aggravates the concentration of microwave electromagnetic fields at the edge, leading to further temperature rise, which indirectly causes the actual growth temperature in the middle of the single crystal diamond substrate to drop in the opposite direction.

[0006] In addition, the high-temperature polycrystalline diamond at the edge of the single-crystal diamond substrate will extend to the middle, resulting in a decrease in the quality of the grown single-crystal diamond. Figure 6 shown. Summary of the invention

[0007] The purpose of the present invention is to solve the above problems and to provide a method for improving the stability of the temperature field of CVD single crystal diamond growth and a stabilizing device thereof.

[0008] The technical solution of the present invention is: a method for improving the stability of the temperature field of CVD single crystal diamond growth, comprising the following steps; a. Prepare the molybdenum table with depression and the single crystal diamond substrate to be grown Prepare a circular molybdenum table, and machine a concave groove in the center of the table to match the shape of the single crystal diamond substrate to be grown. The concave groove is used to suppress the corner effect during the plasma action during the growth in the CVD equipment, so that the growing material can go to the middle of the substrate as much as possible. Open a through hole in the center of the concave groove to the lower surface of the molybdenum table; the through hole is used for the subsequent pouring of brazing material.

[0009] b. Prepare a molybdenum pad that matches the diameter of the molybdenum table. The thickness of the two are similar. After the two are stacked and the centers are aligned, open upper and lower connecting holes in the area near the edge of the circumference. The upper connecting hole is on the molybdenum table, and the lower connecting hole is on the molybdenum pad. The molybdenum table and the molybdenum pad can be stacked and fixed together through the connecting holes to transfer heat.

[0010] c. Pressing of single crystal diamond substrate The single crystal diamond substrate to be grown and the molybdenum table are cleaned, and then the single crystal diamond substrate is placed in the center of the concave groove, and the middle part of a pressing plate is pressed onto the single crystal diamond substrate, and the outer part of the pressing plate is installed in the upper connecting hole by bolts; the single crystal diamond substrate is pressed to fit with the molybdenum table by the pressing plate, and the purpose of pressing is to achieve a tight fit between the bottom surface of the single crystal diamond substrate and the bottom surface of the concave groove without leaving a gap, so as to avoid the problem of carbon film between the two and affecting heat conduction when growing in the CVD equipment.

[0011] d. Brazing Flip the molybdenum table with the single crystal diamond substrate pressed on it so that the through hole below faces upwards, and inject nickel-based paste solder into the through hole; then place the molybdenum table in a vacuum furnace and heat it to solidify the solder, and take it out after natural cooling; the heating temperature in the vacuum furnace is 900℃-1200℃, and the heating time is 30 minutes. During the heating, melting and solidification of the solder, the solder welds the bottom surface of the single crystal diamond substrate to the side of the inner wall of the through hole, and the solder generates a pulling force between the inner wall of the through hole and the bottom surface of the single crystal diamond substrate, so that the other bottom surface areas of the single crystal diamond substrate are tightly fitted with the bottom surface of the groove, so that after removing the pressing plate, the two are still tightly fitted without any gaps.

[0012] e. Assembly After step d is completed, the pressing plate and its bolts are removed, the surface of the molybdenum table and the substrate are cleaned, and then the molybdenum table and the molybdenum pad are connected together by upper and lower connecting holes and bolts; f. After assembling the molybdenum table, the molybdenum pad and the single crystal diamond substrate, the lower surface of the molybdenum pad is tightly fitted to the substrate table of the CVD equipment, and then locked by bolts, and then grown in the CVD equipment. The growth process is the same as in the prior art. It should be noted that the flow rate of cooling water on the substrate table of the CVD needs to be adjusted to match the growth temperature requirements of the single crystal diamond substrate.

[0013] Preferably, after the single crystal diamond substrate is pressed, the area of ​​the concave groove is greater than 1 / 3 of the area of ​​the single crystal diamond substrate, and the thickness of the single crystal diamond substrate is slightly greater than the depth of the concave groove. Through the size relationship between the two, the heat and temperature concentration generated at the corners during the plasma action in the CVD equipment can be suppressed as much as possible, so that the heat distribution is uniform, the temperature of each area of ​​the substrate is as consistent as possible, and the single crystal diamond growth in each area of ​​the substrate is also uniform, and the grown single crystal diamond product has a regular and neat shape, low internal stress, and high toughness.

[0014] Preferably, the nickel-based paste solder is BNi-5 model produced by Changsha Tianjiu Metal Materials Co., Ltd.

[0015] Preferably, the molybdenum platform and the molybdenum pad are made by machining, and the bonding surfaces of the molybdenum platform and the molybdenum pad and the concave surface of the molybdenum platform are made smooth and clean by fine machining; they are cleaned by ultrasonic cleaning in alcohol before use, and then blown dry with high-pressure gas. In this way, the bonding surface after smoothing is more tightly bonded, and the heat conduction capacity of each part is basically the same, and the problem of uneven temperature field caused by uneven heat conduction will not occur.

[0016] Preferably, the single crystal diamond substrate and the molybdenum table bonding surface are finely processed to make them smooth and clean, and are placed in alcohol and ultrasonically cleaned before use, and then blown dry with high-pressure gas. The diamond substrate and the molybdenum table groove are more closely fitted, and the heat conduction capacity of each part is basically the same, and there will be no problem of uneven temperature field caused by uneven heat conduction.

[0017] Preferably, there is a cleaning and washing step between steps d and e. After step d is completed, use a file or micro-grinding head to clean the brazing material overflowing from the front and back of the molybdenum table. After cleaning, put the welded molybdenum table and substrate into alcohol and add ultrasonic cleaning, and then blow dry with high-pressure gas. The cleaning and cleaning mesh is to remove impurities on the surface of the molybdenum table to prevent them from entering the product during growth, while ensuring the thermal conductivity after tight fitting, without affecting the uniformity and stability of heat dissipation.

[0018] Preferably, the cross-sectional area of ​​the through hole is not greater than half of the area of ​​the single crystal diamond substrate. This prevents the contact surface between the brazing material and the single crystal diamond substrate from being too large, which would cause a large difference between the thermal conductivity of the brazing material and the thermal conductivity of the molybdenum stage, resulting in large stress on the substrate and causing the substrate to crack. On the premise of ensuring the fit between the single crystal diamond substrate and the groove of the molybdenum stage, the smaller the through hole, the less likely it is to crack.

[0019] A temperature field stabilization device for CVD single crystal diamond growth according to the method described above, the device comprises a molybdenum table, a molybdenum pad and a pressure plate, and is characterized in that: a recessed groove is provided in the middle of the molybdenum table, a through hole is provided in the center of the recessed groove, the shape of the molybdenum pad matches the shape of the molybdenum table, upper and lower corresponding connecting holes are provided at the edges of the molybdenum table and the molybdenum pad, an extension plate extends outward from the outer side of the pressure plate, and a mounting hole corresponding to the upper connecting hole is provided on the extension plate.

[0020] Preferably, the device also includes connecting bolts made of molybdenum, and the connecting bolts are inserted into the upper and lower connecting holes to fit and fix the molybdenum table and the molybdenum pad together.

[0021] The present invention provides a method for improving the stability of the temperature field of CVD single crystal diamond growth and a stabilizing device thereof. A through hole is opened in the concave groove of a molybdenum platform. After the single crystal diamond substrate in the concave groove is closely attached to the molybdenum platform, a nickel-based paste solder is injected into the through hole, and vacuum heating and welding are performed. The solder after welding and solidification is used to pull the substrate into close contact with the bottom surface of the concave groove of the molybdenum platform without leaving a gap, thereby improving the uniformity of thermal conductivity between the two, avoiding the problem of local concentration of heat and temperature, making the temperature field distribution consistency of the substrate and the upper surface of the molybdenum platform better, and each part of the substrate grows more evenly. The edge of the grown single crystal diamond has less polycrystalline, and the morphology of the single crystal diamond is regular. See Figure 6 , the internal stress is greatly reduced, which is conducive to the application of the product in various industries and fields.

[0022] Furthermore, the molybdenum table and the molybdenum pad are pressed and fitted together by bolts, and the molybdenum pad and the substrate table of the CVD equipment are also pressed and fitted together by bolts, so that a good and evenly distributed thermal conductive heat dissipation structure is established at the bottom, which lays a foundation for the heat dissipation between the molybdenum table and the substrate above. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of the molybdenum stage of the CVD single crystal diamond growth temperature field stabilization device; Figure 2 This is one of the state diagrams of step c in Example 1; Figure 3 This is the second state diagram of step c in embodiment 1; Figure 4 This is a state diagram of step d in Example 1; Figure 5 This is a state diagram of step e in Example 1; Figure 6 It is the product image that grows when no improvement is made; Figure 7 This is a product picture of a single crystal diamond grown by the CVD single crystal diamond growth temperature field stability improvement method; In the figure, 1. molybdenum table, 11 upper connecting hole, 12. recessed groove, 13. through hole, 2. single crystal diamond substrate, 3. pressing plate, 4. nickel-based paste solder, 5 bolts, 6. molybdenum pad, 61. lower connecting hole. DETAILED DESCRIPTION

[0024] Example 1: See Figure 1-5 , 7, A method for improving the stability of the temperature field of CVD single crystal diamond growth in the figure includes the following steps; a. Prepare the molybdenum table with depression and the single crystal diamond substrate to be grown Prepare a circular molybdenum table, and machine a concave groove in the center of the table that matches the shape of the single crystal diamond substrate to be grown. The concave groove is used to suppress the effect of heat accumulation at the corners during the plasma action during growth in the CVD equipment, so that the growing material can go to the middle of the substrate as much as possible. Open a through hole in the center of the concave groove, which penetrates to the lower surface of the molybdenum table, and the through hole is used to pour the brazing material. ; b. Prepare a molybdenum pad that matches the diameter of the molybdenum table. The thickness of the two is equivalent. After the two are stacked and the centers are aligned, upper and lower connecting holes are opened in the area near the edge of the circumference. The upper connecting hole is on the molybdenum table, and the lower connecting hole is on the molybdenum pad. Through the connecting hole, the molybdenum table and the molybdenum pad can be stacked and fixed together, and further fixed to the substrate stage of the CVD equipment for heat transfer; c. Pressing of single crystal diamond substrate The single crystal diamond substrate to be grown and the molybdenum table are cleaned, and then the single crystal diamond substrate is placed in the center of the concave groove, and the middle part of a pressing plate is pressed onto the single crystal diamond substrate, and the outer part of the pressing plate is installed in the upper connecting hole by bolts; the single crystal diamond substrate is pressed to fit with the molybdenum table by the pressing plate, and the purpose of pressing is to achieve a tight fit between the bottom surface of the single crystal diamond substrate and the bottom surface of the concave groove without leaving a gap, so as to avoid the problem of carbon film between the two and affecting heat conduction when growing in the CVD equipment.

[0025] d. Brazing The molybdenum table on which the single crystal diamond substrate is pressed is turned over so that the through hole below faces upward, and a nickel-based paste solder is injected into the through hole; the molybdenum table is then placed in a vacuum furnace for heating to solidify the solder, and is taken out after natural cooling; during the heating, melting and solidification of the solder, the solder welds the bottom surface of the single crystal diamond substrate to the side surface of the inner wall of the through hole, and a pulling force is generated between the inner wall of the through hole and the bottom surface of the single crystal diamond substrate through the solder, so that the other bottom surface area of ​​the single crystal diamond substrate is tightly fitted to the bottom surface of the groove, so that after the pressure plate is removed, the two are still in a tightly fitted state without any gap.

[0026] e. Assembly After step d is completed, the pressing plate and its bolts are removed, the surface of the molybdenum table and the substrate are cleaned, and then the molybdenum table and the molybdenum pad are connected together by upper and lower connecting holes and bolts; f. Assemble the completed molybdenum table, molybdenum pad and single crystal diamond substrate together, fit the lower surface of the molybdenum pad tightly with the substrate table of the CVD equipment, lock it with bolts, and then grow it in the CVD equipment; the growth process is the same as in the prior art, it should be noted that the flow rate of cooling water on the CVD substrate table is adjusted to match the growth temperature requirement of the single crystal diamond substrate.

[0027] After the single crystal diamond substrate is pressed, the area of ​​the concave groove is larger than 1 / 3 of the area of ​​the single crystal diamond substrate, and the thickness of the single crystal diamond substrate is slightly larger than the depth of the concave groove. Through the size relationship between the two, the heat and temperature concentration generated in the corners during the plasma action in the CVD equipment can be suppressed as much as possible, so that the heat distribution is uniform, the temperature of each area of ​​the substrate is as consistent as possible, and the single crystal diamond growth in each area of ​​the substrate is also uniform. The grown single crystal diamond product has a regular and neat shape, low internal stress, and high toughness.

[0028] The nickel-based paste solder is the BNi-5 model produced by Changsha Tianjiu Metal Materials Co., Ltd.

[0029] The molybdenum platform and the molybdenum pad are made by machining, and the fitting surfaces of the molybdenum platform and the molybdenum pad and the concave surface of the molybdenum platform are made smooth and clean by fine machining; they are cleaned by ultrasonic cleaning in alcohol before use, and then blown dry with high-pressure gas. In this way, the fitting surfaces after lamination are more closely fitted, and the heat conduction capacity of each part is basically the same, and the problem of uneven temperature field caused by uneven heat conduction will not occur.

[0030] The single crystal diamond substrate and the molybdenum table bonding surface are finely processed to make them smooth and clean, and are placed in alcohol and ultrasonically cleaned before use, and then blown dry with high-pressure gas. The diamond substrate and the molybdenum table groove fit more closely, and the heat conduction capacity of each part is basically the same, and there will be no problem of uneven temperature field caused by uneven heat conduction.

[0031] In the step d, the heating temperature in the vacuum furnace is 900° C.-1200° C., and the heating time is 30 minutes.

[0032] There is a cleaning and washing step between steps d and e. After step d is completed, use a file or micro-grinding head to clean the brazing material overflowing from the front and back of the molybdenum table. After cleaning, put the welded molybdenum table and substrate into alcohol and add ultrasonic cleaning, and then blow dry with high-pressure gas. The cleaning and cleaning mesh is to remove impurities on the surface of the molybdenum table to prevent them from entering the product during growth, while ensuring the thermal conductivity after tight fitting, without affecting the uniformity and stability of heat dissipation.

[0033] The cross-sectional area of ​​the through hole is not greater than half of the area of ​​the single crystal diamond substrate. This prevents the contact surface between the brazing material and the single crystal diamond substrate from being too large, which would cause a large difference between the thermal conductivity of the brazing material and the thermal conductivity of the molybdenum stage, resulting in large stress on the substrate and causing the substrate to crack. On the premise of ensuring the fit between the single crystal diamond substrate and the groove of the molybdenum stage, the smaller the through hole, the smaller the possibility of cracking.

[0034] See the product photos produced in this embodiment for details. Figure 7 , Figure 7 The single crystal diamond grown in the process has a regular overall shape, a smooth and flat surface, and uniform thickness. The black carbon deposits formed around the edges are obviously Figure 6 It is shown that the control method of the temperature field uniformity and stability is improved by the embodiment scheme, which produces positive and beneficial technical effects.

[0035] Example 2: See Figure 1-5, the figure shows a CVD single crystal diamond growth temperature field stabilization device of the aforementioned lifting method, the device includes a molybdenum platform, a molybdenum pad and a pressure plate, and is characterized in that: a concave groove is provided in the middle of the molybdenum platform, a through hole is provided in the center of the concave groove, the shape of the molybdenum pad matches the shape of the molybdenum platform, the edges of the molybdenum platform and the molybdenum pad are provided with upper and lower corresponding connecting holes, an extension plate extends outward from the pressure plate, and a mounting hole corresponding to the upper connecting hole is provided on the extension plate. The device also includes a connecting bolt made of molybdenum, and the connecting bolt is inserted into the upper and lower connecting holes to fit and fix the molybdenum platform and the molybdenum pad together.

[0036] The device, when used in combination with brazing materials, can improve the contact effect between the single crystal diamond substrate and the bottom surface of the molybdenum table groove, improve the uniformity of thermal conductivity, and improve the stability control of the temperature field during the growth of single crystal diamond, which is conducive to the growth of higher quality single crystal diamond.

[0037] The specific method of using the device refers to the specific steps of Example 1, which will not be described in detail here.

Claims

1. A method for improving the stability of the temperature field of CVD single crystal diamond growth, comprising the following steps: a. preparing a molybdenum table with a depression and a single crystal diamond substrate to be grown A circular molybdenum table is prepared, a concave groove matching the shape of the single crystal diamond substrate to be grown is machined in the center of the top, and a through hole is opened in the center of the concave groove to penetrate to the lower surface of the molybdenum table; b. Prepare a molybdenum pad that matches the diameter of the molybdenum table. The thickness of the two is equivalent. After the two are stacked and the centers are aligned, open the upper and lower connecting holes in the area near the edge of the circumference. The upper connecting hole is on the molybdenum table, and the lower connecting hole is on the molybdenum pad; c. Pressing of single crystal diamond substrate Clean the single crystal diamond substrate to be grown and the molybdenum stage, then place the single crystal diamond substrate in the center of the concave groove, press the middle of a pressing plate onto the single crystal diamond substrate, and install the outer part of the pressing plate into the upper connection hole through bolts; press the single crystal diamond substrate and the molybdenum stage together through the pressing plate, d. Brazing The molybdenum table with the single crystal diamond substrate pressed on it is turned over so that the through hole below faces upward, and a nickel-based paste solder is injected into the through hole; the molybdenum table is then placed in a vacuum furnace for heating to solidify the solder, and taken out after natural cooling; e. Assembly After step d is completed, the pressing plate and its bolts are removed, the surface of the molybdenum table and the substrate are cleaned, and then the molybdenum table and the molybdenum pad are connected together by upper and lower connecting holes and bolts; f. After assembling, the single crystal diamond substrate of the molybdenum table and the molybdenum pad is put together, and the lower surface of the molybdenum pad is tightly fitted to the substrate table of the CVD equipment, locked by bolts, and then grown in the CVD equipment.

2. The method for improving the stability of the temperature field of CVD single crystal diamond growth according to claim 1, characterized in that: After the single crystal diamond substrate is pressed, the area of ​​the concave groove is larger than 1 / 3 of the area of ​​the single crystal diamond substrate, and the thickness of the single crystal diamond substrate is slightly larger than the depth of the concave groove.

3. The method for improving the stability of the temperature field of CVD single crystal diamond growth according to claim 1, characterized in that: The nickel-based paste solder is the BNi-5 model produced by Changsha Tianjiu Metal Materials Co., Ltd.

4. The method for improving the stability of the temperature field of CVD single crystal diamond growth according to claim 1, characterized in that: The molybdenum platform and the molybdenum pad are manufactured by machining, and the fitting surfaces of the molybdenum platform and the molybdenum pad and the concave surface of the molybdenum platform are made smooth and clean by fine machining; they are placed in alcohol and ultrasonically cleaned before use, and then blown dry with high-pressure gas.

5. The method for improving the stability of the temperature field of CVD single crystal diamond growth according to claim 1, characterized in that: The single crystal diamond substrate and the molybdenum table bonding surface are finely processed to make them flat and smooth, and are placed in alcohol and ultrasonically cleaned before use, and then blown dry with high-pressure gas.

6. The method for improving the stability of the temperature field of CVD single crystal diamond growth according to claim 1, characterized in that: In the step d, the heating temperature in the vacuum furnace is 900° C.-1200° C., and the heating time is 30 minutes.

7. The method for improving the stability of the temperature field of CVD single crystal diamond growth according to claim 1, characterized in that: There is a cleaning and washing step between steps d and e. After step d is completed, use a file or a micro-grinding head to clean the brazing material overflowing from the front and back of the molybdenum table. After cleaning, place the welded molybdenum table and the substrate in alcohol and add ultrasonic cleaning to clean them, and then blow dry with high-pressure gas.

8. The method for improving the stability of the temperature field of CVD single crystal diamond growth according to claim 1, characterized in that: The cross-sectional area of ​​the through hole is no greater than half the area of ​​the single crystal diamond substrate.

9. A CVD single crystal diamond growth temperature field stabilization device for use in any of the methods described in claims 1 to 8, the device comprising a molybdenum table, a molybdenum pad and a pressure plate, characterized in that: A recessed groove is provided in the middle of the molybdenum table, and a through hole is provided in the center of the recessed groove. The shape of the molybdenum pad matches the shape of the molybdenum table. Upper and lower corresponding connecting holes are provided on the edges of the molybdenum table and the molybdenum pad. An extension plate extends outward from the outer side of the pressure plate, and a mounting hole corresponding to the upper connecting hole is provided on the extension plate.

10. The CVD single crystal diamond growth temperature field stabilization device according to claim 9, characterized in that: The device also includes connecting bolts made of molybdenum. The connecting bolts are inserted into the upper and lower connecting holes to fit and fix the molybdenum platform and the molybdenum pad together.

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