Crystal expansion method of large-area monocrystal diamond

Abstract

According to the crystal expansion method of the large-area single crystal diamond, iterative growth of the single crystal diamond substrate is carried out by continuously replacing the molybdenum table with a larger groove area in the middle, so that the large-area single crystal diamond substrate suitable for being used in the semiconductor field is obtained, and the single crystal diamond substrate can be continuously expanded after each time of growth is completed. According to the method, slice cutting is carried out along a transverse maximum expansion crystal face, transverse growing single crystal diamonds are reserved as much as possible, material waste is reduced, and the cutting mode is adopted in each iteration, so that large-area single crystal diamond growth can be realized more quickly, the growth efficiency is improved, the number of iterations is reduced, material waste is reduced, and the production cost is reduced. The production cost is reduced. The growth of the large-area single crystal diamond can be realized in a multi-round growth and processing mode.

Description

Technical Field

[0001] The invention relates to the technical field of single crystal diamond CVD growth, and in particular to a large-area single crystal diamond crystal expansion method. Background Art

[0002] As an ultra-wide bandgap semiconductor material, diamond has the advantages of large bandgap width, high carrier mobility, large carrier saturation drift velocity, strong critical breakdown field, high thermal conductivity, etc. It is very suitable for the preparation of high-frequency, high-power, high-temperature resistant, radiation-resistant electronic devices and optoelectronic devices in the deep ultraviolet band, and has broad application prospects in the fields of new energy, 6G communications, space science, etc. Therefore, diamond, which combines multiple excellent properties, is recognized as an ideal next-generation power device material, and has great application prospects in the fields of electric vehicles, photovoltaics, military industry, etc.

[0003] In order to achieve industrial promotion, semiconductor materials need to meet the requirements of high purity, low defect density, high carrier concentration and mobility, and inch-level wafer area. The preparation technology of high-quality large-area single crystal substrates is still a challenge facing the commercial application of diamond materials and devices.

[0004] The CVD method for growing single crystal diamond usually uses single crystal diamond as the substrate. Since the upper surface and the side surface of the substrate grow simultaneously during the growth process, the substrate will also expand in area while growing thicker. However, the area of ​​single lateral expansion in the prior art is limited. In addition, due to process control issues, the edges of the expansion are prone to grow into polycrystalline. After each growth, the surface layer and the polycrystalline diamond generated around are removed by laser cutting. In this way, the area of ​​the single crystal remains basically unchanged or even slightly increases, making it difficult to achieve large-area diamond expansion production. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and provide a method for expanding large-area single-crystal diamond.

[0006] The technical solution of the present invention is: a method for expanding a large-area single-crystal diamond, comprising the following steps; a. Preparation of single crystal diamond substrate The substrate is made of single crystal diamond prepared under high temperature and high pressure; b. Preparation of Molybdenum Table Prepare a molybdenum table, and process a groove with an area larger than the area of ​​the single crystal diamond substrate to be grown at the center position of the upper surface of the molybdenum table. After processing, remove impurities on the surface, clean it, and air-dry it for later use; c. Cleaning of the single crystal diamond substrate to remove metal impurities introduced during the processing.

[0007] d. Etching treatment The cleaned single crystal diamond substrate is etched in an MPCVD device to remove surface impurities, defects, and internal stress, allowing it to grow normally and stably.

[0008] e. Growth The etched single crystal diamond substrate is placed centrally in the groove in the middle of the molybdenum table prepared in step a, and then the molybdenum table is placed on the substrate table of the MPCVD device, and the MPCVD device is started for growth. After the production is completed, the single crystal diamond substrate is taken out after natural cooling; f. Replace the molybdenum stage for regrowth After the single crystal diamond substrate of step e is completed, a molybdenum holder with a larger groove area and depth is replaced, and steps b, c, d, and e are repeated in sequence to complete the re-growth of the single crystal diamond substrate, further expanding the thickness and area of ​​the diamond; g. Cutting process After repeated steps f, the single crystal diamond grown again has an overly large edge expansion area, resulting in uneven temperature on the upper surface, which is not suitable for continued crystal expansion growth. The maximum crystal expansion surface is determined by observation and measurement for laser cutting, and a single crystal diamond slice with a larger area is cut along a direction parallel to the single crystal diamond substrate. The cut surface of the single crystal diamond substrate is then used as the substrate for the next round of crystal expansion growth. This cutting method can retain as much of the single crystal diamond material grown laterally as possible, which is conducive to faster iterative growth to expand the area and reduce the number of iterative growths. At the same time, it can reduce material waste and production costs.

[0009] h. Next round of regrowth After the single crystal diamond substrate in step g is completed, steps b, c, d, e, f, and g are repeated in sequence to complete the regrowth of the single crystal diamond substrate; i. Repeat step h several times until the single crystal diamond substrate grows to a suitable area, determine its maximum crystal expansion surface by observation and measurement, and then perform laser cutting to cut out single crystal diamond slices of the required area in a direction parallel to the single crystal diamond substrate.

[0010] Preferably, in step a, the substrate is made of single crystal diamond prepared under high temperature and high pressure, the lateral square side length of the substrate is 5-12 mm, and the thickness of the substrate is 0.2-1.0 mm.

[0011] Preferably, the area of ​​the groove processed at the center position of the upper surface of the molybdenum table in step b is 1 / 3 larger than the area of ​​the single crystal diamond substrate to be grown, and the thickness of the substrate is slightly greater than the depth of the groove. The shape of the groove matches the shape of the substrate, which can control the heat and temperature accumulation at the corners during the growth process, avoid the generation of polycrystalline at the corners, and improve the growth quality; it can also prevent the polycrystalline diamond on the substrate after growth from growing together with the polycrystalline diamond at other positions of the molybdenum table and being unable to be removed.

[0012] Preferably, the step c is as follows: first, the single crystal diamond substrate is soaked in aqua regia for 24 hours; after the soaking, the diamond substrate is taken out from the aqua regia with polytetrafluoroethylene tweezers and rinsed with deionized water; the rinsed substrate is then ultrasonically cleaned in acetone, alcohol, and deionized water for 15 minutes each; the cleaned substrate is blown dry with nitrogen for later use.

[0013] Preferably, in the step e, the MPCVD equipment is first evacuated to below 10-5 Torr, then started in a hydrogen atmosphere, and then the power and pressure are increased to raise the substrate temperature to 800-900°C, and then methane and nitrogen are introduced for growth.

[0014] Preferably, the growth conditions in the MPCVD equipment in step e are: the gases introduced are hydrogen, methane and nitrogen, the hydrogen flow rate is 100-1000 sccm, the proportion of methane in the total gas is 1-6%, and the proportion of nitrogen in the total gas is 5-100 ppm.

[0015] Preferably, the maximum crystal expansion plane refers to the maximum lateral dimension of the single crystal diamond substrate after growth. When the cutting plane is determined, the loss layer burned away by the laser is determined to be within the removed portion.

[0016] Preferably, the method further comprises the following additional step: after the cutting in step g is completed, the remaining portion close to the maximum crystal expansion surface is cut again in the manner of step g to cut out a next-largest single crystal diamond slice slightly smaller than the size in step g; the next-largest slice is used as the single crystal diamond substrate selected in step a to carry out the single crystal diamond crystal expansion process of step ai.

[0017] The invention discloses a large-area single-crystal diamond crystal expansion method. The single-crystal diamond substrate is iteratively grown by continuously replacing a molybdenum table with a larger groove area in the middle, thereby obtaining a large-area single-crystal diamond substrate suitable for use in the semiconductor field. After each growth of the single-crystal diamond substrate is completed, thin slices are cut along the maximum lateral crystal expansion surface to retain as much of the single-crystal diamond grown laterally as possible, thereby reducing material waste. Such a cutting method is used in each iteration, thereby realizing large-area single-crystal diamond growth more quickly, improving growth efficiency, reducing the number of iterations, reducing material waste, and reducing production costs.

[0018] In order to change the process control of growth, a groove is set in the middle of the molybdenum table, and the single crystal substrate is placed in the groove of the molybdenum holder for growth. The shielding effect of the molybdenum holder can avoid the generation of polycrystalline at the edge of the diamond, and at the same time increase the lateral growth area of ​​the CVD single crystal diamond.

[0019] At the same time, in order to avoid the generation of polycrystals at the edge of diamond, the present invention controls other factors and parameters in the growth process on the basis of the structural control of the grooves, such as improving the gas source and substrate temperature. It is found that under suitable growth conditions, the outward expansion of single crystal growth is more obvious and polycrystals will not be generated at the edge. Figure 3 The XRD spectrum of the black part of the edge after growth detected in the figure shows that the edge part has a single component and is single crystal diamond.

[0020] When the diamond expansion area is too large, the shape changes due to multiple growth, such as Figure 1 As shown in the figure, the temperature difference between the edge and the center is obvious, making it difficult to grow uniformly. At this time, the maximum crystal expansion surface is determined through observation and measurement, and the diamond maximum crystal expansion surface is cut into thin slices to complete a round of iteration, which is used as a new round of crystal expansion growth substrate. Through multiple crystal expansion growth and processing methods, large-area single crystal diamond that meets the requirements of semiconductor use can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is one of the side views of single crystal diamond grown in the first round of this method; Figure 2 This is the second side view of the single crystal diamond grown in the first round of this method; Figure 3 yes Figure 1 A top view of the grown single crystal diamond; Figure 4 for Figure 3 XRD pattern of the black part in the middle edge; Figure 5 Large-area single-crystal diamond produced and cut through multiple rounds of crystal expansion by this growth method; Figure 6 Schematic diagram of the cutting area of ​​the second largest crystal expansion surface in Example 2; Figure 7 It is a three-dimensional schematic diagram of the shape and position relationship between the substrate and the molybdenum table groove; Figure 8 for Figure 7 A schematic diagram of the full cross-section structure of the main view; In the figure, 1. original substrate, 2. crystal growth part, 3. maximum crystal expansion surface (thinner red horizontal line in the figure), 4. cutting retained layer, 5. cutting removed part, 6. cutting retained layer of the next largest single crystal diamond slice, 41. cutting loss layer (the blue box in the figure is close to the blue horizontal line of the retained layer); 101. molybdenum table, 102. substrate, 103. groove in the middle of the molybdenum table. DETAILED DESCRIPTION

[0022] Example 1: See Figure 1-5 , a large-area single-crystal diamond crystal expansion method, comprising the following steps; a. Preparation of single crystal diamond substrate The substrate is made of single crystal diamond prepared under high temperature and high pressure; In step a, the substrate is made of single crystal diamond prepared at high temperature and high pressure, the side length of the horizontal square of the substrate is 5-12 mm, and the thickness of the substrate is 0.2-1.0 mm. Figure 1 The original substrate size shown is 7mm*7mm.

[0023] b. Preparation of Molybdenum Table Prepare a molybdenum table, and process a groove with an area larger than the area of ​​the single crystal diamond substrate to be grown at the center position of the upper surface of the molybdenum table. After processing, remove impurities on the surface, clean it, and air-dry it for later use; The area of ​​the groove is 1 / 3 larger than the area of ​​the single crystal diamond substrate to be grown, and the thickness of the substrate is slightly higher than the depth of the groove, such as Figure 7-Figure 8 The position and size relationship between the substrate and the groove are shown.

[0024] The shape of the groove matches the shape of the substrate, which can control the heat and temperature accumulation at the corners during the growth process, avoid the generation of polycrystalline at the corners, and improve the growth quality; it can also prevent the polycrystalline diamond on the substrate after growth from growing together with the polycrystalline diamond at other positions of the molybdenum table and being unable to be removed.

[0025] c. Cleaning of the single crystal diamond substrate to remove metal impurities introduced during the processing.

[0026] The single crystal diamond substrate is soaked in aqua regia for 24 hours; after the soaking, the diamond substrate is taken out from the aqua regia with polytetrafluoroethylene tweezers and rinsed with deionized water; the rinsed substrate is then ultrasonically cleaned in acetone, alcohol, and deionized water for 15 minutes each; the cleaned substrate is blown dry with nitrogen for later use; d. Etching treatment The cleaned single crystal diamond substrate is etched in the MPCVD device to remove surface impurities, defects, and internal stress, so that it can grow normally and stably. The etching conditions in the MPCVD device are: the gases introduced are hydrogen and oxygen, the hydrogen flow rate is 190 sccm, the oxygen flow rate is 10 sccm, the etching temperature is 650°C, and the etching time is 30 minutes.

[0027] e. Growth The etched single crystal diamond substrate is placed centrally in the groove in the middle of the molybdenum table prepared in step a, and then the molybdenum table is placed on the substrate table of the MPCVD device, and the MPCVD device is started for growth. After the production is completed, the single crystal diamond substrate is taken out after natural cooling; First, evacuate the MPCVD equipment to 10 -5 Torr or less, then start the ignition in a hydrogen atmosphere, then increase the power and pressure to raise the substrate temperature to 800-900°C, and then introduce gases such as methane and nitrogen for growth.

[0028] f. Replace the molybdenum stage for regrowth After the single crystal diamond substrate of step e is completed, a molybdenum holder with a larger groove area and depth is replaced, and steps b, c, d, and e are repeated in sequence to complete the re-growth of the single crystal diamond substrate, further expanding the thickness and area of ​​the diamond; g. Cutting process After repeated steps f, the edge of the regrown single crystal diamond is too large, resulting in uneven temperature on the upper surface, which is not suitable for further crystal expansion. The maximum crystal expansion surface is determined by observation and measurement, and laser cutting is performed to cut a larger single crystal diamond slice along the parallel direction of the single crystal diamond substrate. Figure 2 The green box is the cutting retaining layer, and the upper and lower blue boxes are the cutting removal parts.

[0029] The cut single crystal diamond slice is then used as the diamond substrate for the next round of crystal expansion growth; this cutting method can retain as much single crystal diamond material grown laterally as possible, which is conducive to faster iterative growth to expand the area, reduce the number of iterative growth times, and at the same time reduce material waste and production costs.

[0030] The maximum crystal expansion plane refers to the maximum lateral dimension of the single crystal diamond substrate after growth. When the cutting plane is determined, the loss layer burned by the laser is determined to be within the removed portion, such as Figure 1 The blue line shown in the figure is the burnt layer. Considering the problem of laser burnt, the waste of the material that has grown into single crystal diamond is further reduced, and the efficiency of iterative growth is improved.

[0031] h. Next round of regrowth After the single crystal diamond substrate in step g is completed, steps b, c, d, e, f, and g are repeated in sequence to complete the regrowth of the single crystal diamond substrate; i. Repeat step h3 times to complete 3 rounds of iterative growth until the single crystal diamond substrate grows to a suitable area. Determine the maximum crystal expansion surface through observation and measurement, and perform laser cutting to cut a single crystal diamond slice with a qualified area along the parallel direction of the single crystal diamond substrate, such as Figure 5 As shown, the size reaches 16mm*16mm. In this embodiment, the regrowth is iterated for 3 rounds, while the number of iterations of other growth schemes in the technology is at least 6 rounds. Due to the insufficient control of the process, the growth rate itself is slow. At the same time, more polycrystalline diamonds are produced at the edge after growth, which need to be cut off. The expanded ones are cut off again after much effort, which further affects the overall growth rate and increases the number of iterations.

[0032] Example 2: See Figure 6 The second embodiment is basically the same as the first embodiment, and the similarities are not repeated. The difference is that the second embodiment further includes the following additional steps: After the cutting in step g is completed, the remaining part close to the maximum crystal expansion surface is cut again according to the method of step g to cut out a next-largest single crystal diamond slice slightly smaller than the size in step g. The next-largest slice is used as the single crystal diamond substrate selected in step a to carry out the single crystal diamond crystal expansion process of step ai.

[0033] This allows the reuse of the remaining material after each wafer expansion. Figure 1 As described above, the width of the maximum crystal expansion surface after crystal expansion is 12.8mm*12.8mm. The size of the remaining material after cutting along the maximum crystal expansion surface, which is close to the maximum crystal expansion surface, is still much larger than the 7mm*7mm size of the original substrate. Cutting the remaining material into the next largest single crystal diamond slice and using it as a substrate is more advantageous than using the 7mm*7mm size of the original substrate. While making full use of the material and reducing the cost, it will also increase the speed of crystal expansion production. For mass production, it can further reduce the number of iterations.

[0034] Example 3: Based on Example 1 and Example 2, the step e is further optimized. The growth conditions in the MPCVD equipment in step e are: the gases introduced are hydrogen, methane and nitrogen, the hydrogen flow rate is 100-1000 sccm, the proportion of methane in the total gas is 1-6%, and the proportion of nitrogen in the total gas is 5-100 ppm. On the basis of the control of the groove on the generation of polycrystals, such control of the growth process is added, and the outward expansion of the single crystal growth is more obvious, further avoiding the generation of polycrystals at the edge.

Claims

1. A method for expanding large-area single-crystal diamond, comprising the following steps; a. Preparation of single crystal diamond substrate The substrate is made of single crystal diamond prepared under high temperature and high pressure; b. Preparation of Molybdenum Table Prepare a molybdenum table, and process a groove with an area larger than the area of ​​the single crystal diamond substrate to be grown at the center position of the upper surface of the molybdenum table. After processing, remove impurities on the surface, clean it, and air-dry it for later use; c. Single crystal diamond substrate cleaning process d. Etching treatment The cleaned single crystal diamond substrate is etched in an MPCVD device; e. Growth The etched single crystal diamond substrate is placed centrally in the groove in the middle of the molybdenum table prepared in step a, and then the molybdenum table is placed on the substrate table of the MPCVD device, and the MPCVD device is started for growth. After the production is completed, the single crystal diamond substrate is taken out after natural cooling; f. Replace the molybdenum stage for regrowth After the single crystal diamond substrate of step e is completed, a molybdenum holder with a larger groove area and depth is replaced, and steps b, c, d, and e are repeated in sequence to complete the re-growth of the single crystal diamond substrate, further expanding the thickness and area of ​​the diamond; g. Cutting process After repeated steps f, the edge expansion area of ​​the regrown single crystal diamond is too large, resulting in uneven temperature on the upper surface, which is not suitable for further crystal expansion growth; the maximum crystal expansion surface is determined by observation and measurement, and laser cutting is performed to cut a single crystal diamond slice with a larger area along the parallel direction of the single crystal diamond substrate; and the cut surface of the single crystal diamond substrate after cutting is used as the substrate for the next round of crystal expansion growth; h. Next round of regrowth After the single crystal diamond substrate in step g is completed, steps b, c, d, e, f, and g are repeated in sequence to complete the regrowth of the single crystal diamond substrate; i. Repeat step h several times until the single crystal diamond substrate grows to a suitable area, determine its maximum crystal expansion surface by observation and measurement, and then perform laser cutting to cut out single crystal diamond slices of the required area in a direction parallel to the single crystal diamond substrate.

2. The method for expanding large-area single-crystal diamond according to claim 1, characterized in that: In the step a, the substrate is made of single crystal diamond prepared at high temperature and high pressure, the lateral square side length of the substrate is 5-12 mm, and the thickness of the substrate is 0.2-1.0 mm.

3. The method for expanding large-area single-crystal diamond according to claim 1, characterized in that: In the step b, the area of ​​the groove machined at the center position of the upper surface of the molybdenum table is 1 / 3 larger than the area of ​​the single crystal diamond substrate to be grown, and the thickness of the substrate is slightly higher than the depth of the groove.

4. The method for expanding large-area single-crystal diamond according to claim 1, characterized in that: The step c is as follows: firstly, the single crystal diamond substrate is soaked in aqua regia for 24 hours; after the soaking, the diamond substrate is taken out from the aqua regia with polytetrafluoroethylene tweezers and rinsed with deionized water; the rinsed substrate is then ultrasonically cleaned in acetone, alcohol and deionized water for 15 minutes each; the cleaned substrate is blown dry with nitrogen for later use.

5. The method for expanding large-area single-crystal diamond according to claim 1, characterized in that: In the step e, the MPCVD equipment is first evacuated to 10 -5 Torr or less, then start the luminescence in a hydrogen atmosphere, then increase the power and pressure to raise the substrate temperature to 800-900°C, and then introduce methane and nitrogen for growth.

6. The process for large-area single-crystal diamond expansion growth according to claim 5, characterized in that: The growth conditions in the MPCVD equipment in step e are: the gases introduced are hydrogen, methane and nitrogen, the hydrogen flow rate is 100-1000sccm, the proportion of methane in the total gas is 1-6%, and the proportion of nitrogen in the total gas is 5-100 ppm.

7. The method for expanding large-area single-crystal diamond according to claim 1, characterized in that: The maximum crystal expansion plane refers to the maximum lateral dimension of the single crystal diamond substrate after growth. When the cutting plane is determined, the loss layer burned away by the laser is determined to be within the removed portion.

8. The method for expanding large-area single-crystal diamond according to claim 1, characterized in that: The method also includes the following additional steps: after the cutting in step g is completed, the remaining part close to the maximum crystal expansion surface is cut again according to the method of step g to cut out a next-largest single crystal diamond slice slightly smaller than the size in step g. The next-largest slice is used as the single crystal diamond substrate selected in step a to carry out the single crystal diamond crystal expansion process of step ai.

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