Method for reducing stress in large-size direct-current arc plasma CVD (Chemical Vapor Deposition) diamond thick film

Abstract

The invention discloses a method for reducing stress in a large-size direct-current arc plasma CVD diamond thick film, and belongs to the field of diamond material preparation. After the diamond thick film is deposited through direct-current arc plasma CVD, an alternating-current coil is adopted for carrying out heating and annealing treatment on the Mo substrate, and the growth stress is reduced; and after annealing is completed, the temperature of the Mo substrate is slowly reduced, so that the thermal stress of the diamond thick film is slowly released, and the low-stress crack-free large-size diamond thick film is obtained. The alternating current coil is used for carrying out heating annealing and slow cooling treatment on the Mo substrate, the growth stress of the diamond thick film can be reduced, thermal stress can be slowly released, the possibility that the diamond thick film cracks due to too large stress is reduced, the application process is relatively simple, and the effect is good. The prepared large-size diamond thick film can be used for a heat sink material or an optical window of an integrated semiconductor device.

Description

Technical Field

[0001] The invention belongs to the technical field of diamond semiconductor material preparation, and in particular relates to a method for reducing stress in a large-size DC arc plasma CVD diamond thick film. Technical Background

[0002] Diamond is an emerging ultra-wide bandgap semiconductor material with a large bandgap width (-5.5eV) and a high breakdown voltage (>10MV•cm -1 ), high carrier mobility (holes: 3800 cm 2 •V -1 •s -1 , electron: 4500 cm 2 •V -1 •s -1 ), extremely high thermal conductivity (22 W•K -1 •cm -1 ), radiation resistance and other advantages. It has great application potential in the fields of heat sinks, high-power, high-frequency devices, optical windows, quantum information, etc. As various electronic devices gradually develop towards miniaturization, integration and high power, the heat dissipation problem of devices is becoming more and more important and has become one of the key factors restricting the further development of the above fields. Diamond has an ultra-high thermal conductivity, making it one of the best choices for ultra-wide bandgap semiconductor heat sink materials. Chemical vapor deposition (CVD) technology is one of the main technologies for preparing high-quality diamond films. At present, the main CVD diamond film preparation methods include hot wire CVD (HFCVD), DC arc plasma CVD (DC Jet CVD), DC hot cathode CVD (DC-PACVD) and microwave plasma CVD (MPCVD). The plasma density and temperature excited by DC arc plasma CVD are relatively high, and in theory, high-efficiency preparation of high-quality diamond films can be achieved. The preparation research of large-size CVD diamond thick films is of great practical significance. Large-sized CVD diamond thick films are mainly used in heat sink materials and optical windows to solve the heat dissipation problem of high-power devices and improve device performance and life. However, in practical applications, we always hope to obtain large-sized thick films of diamond. In the preparation process of large-sized CVD diamond thick films, due to the drastic temperature changes and the continuous accumulation of growth defects, huge stress will be generated in the diamond film, causing the diamond thick film to warp or even break, which will seriously affect the acquisition of complete large-sized CVD diamond thick films and further affect the subsequent processing and application. For example, large warpage will limit the bonding of diamond thick films with semiconductor materials (such as GaN), which not only increases production costs but also greatly limits the application of diamond thick films in the semiconductor field.

[0003] In order to prepare complete, crack-free diamond films, some methods for reducing the stress of CVD diamond films have been proposed. For example, Li Qingli et al. proposed a method for separating the substrate from the water-cooled stage after growth is completed (CN113684466B) in the patent to reduce the cooling rate and reduce thermal stress. However, this method is to perform the separation operation after shutting down the equipment, and the temperature of the substrate will drop by about 200°C in a very short time, resulting in large thermal stress. Liu Duo et al. proposed a method for preparing low-stress diamond films by synthesizing a metal Ga buffer layer using ultrasonic cavitation technology (CN117026201A), but this method can only reduce thermal stress. Peng Yan et al. proposed a multi-coil adjustable resistance-assisted heating MPCVD device and a method for growing diamond films (CN117026201A), which can also only reduce thermal stress.

[0004] In summary, in order to achieve the goal of depositing a large-area diamond thick film with low stress and no cracks, it is very meaningful to propose a method that can simultaneously reduce thermal stress and growth stress and avoid temperature mutation of the diamond film. Summary of the invention

[0005] The present invention provides a method for reducing stress in a large-sized DC arc plasma CVD diamond thick film, which solves the technical problem in the prior art that the stress in the diamond thick film is too large due to too fast cooling speed and accumulation of growth defects, especially for large-sized thick films, which are prone to warping or even cracking.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for reducing stress in a large-size DC arc plasma CVD diamond thick film, characterized in that the steps include: after the growth is completed, raising the AC coil to the same height as the Mo substrate, and using the AC coil to heat the Mo substrate and keep it at the growth temperature while cooling it down until the arc is extinguished and the machine is shut down; after the vacuum pump pumps the chamber pressure to below 1 Pa, continue to use the AC coil to heat the Mo substrate to 100-400°C above the growth temperature, and perform annealing treatment; after the treatment is completed, slowly reduce the temperature of the Mo substrate to room temperature.

[0008] Further, the step of heating the Mo substrate with the AC coil includes:

[0009] 1) Grow a diamond thick film on a Mo substrate at a growth temperature of 800-950°C. After the growth is completed and before the machine is cooled down and shut down, control the AC coil to rise from its initial position to the same height as the substrate;

[0010] 2) Start to gradually reduce the current of the DC arc plasma CVD equipment and turn on the AC coil power system to generate induced eddy currents in the Mo substrate;

[0011] 3) While reducing the current, gradually increase the current of the AC coil, and keep the temperature of the Mo substrate at the growth temperature;

[0012] 4) After the arc is extinguished, the gas is quickly turned off, and the vacuum pump is used to pump the chamber pressure to below 1Pa. The AC coil current is continued to be increased to increase the output power. The Mo substrate is heated to 100-400℃ above the growth temperature and annealed for 1.5-2.5 hours;

[0013] 5) After the annealing process is completed, slowly reduce the current of the AC coil until the temperature of the Mo substrate slowly decreases to room temperature;

[0014] The Mo substrate is heated and slowly cooled by the AC coil, which can effectively reduce the stress in the diamond thick film.

[0015] Furthermore, the AC coil can be freely raised and lowered during the growth of the diamond thick film, and its diameter is 2 cm larger than the diameter of the water cooling table.

[0016] Furthermore, the diameter of the AC coil is 100-260 mm, the lifting range is 0-240 mm, and the AC coil is wound by a hollow copper tube with an outer diameter of 4-5 mm and an inner diameter of 2-3 mm, and cooling water flows inside.

[0017] Furthermore, the temperature change of the Mo substrate should be kept below 8-10° C. / h.

[0018] The annealing temperature is maintained at 100-400°C above the growth temperature.

[0019] Furthermore, the number of turns of the AC coil is 4-10. Since the size of the Mo substrate is relatively large, and the heating speed cannot be too fast and the temperature must be uniform, a low-frequency coil with a frequency of 50-500 Hz is selected.

[0020] The key to the implementation of the present invention is:

[0021] (1) To ensure that the magnetic field generated by the AC coil has the smallest possible effect on the arc shape, a coil with a low number of turns is required.

[0022] (2) To ensure that the temperature does not change suddenly when reducing the input power of the DC arc plasma CVD equipment, the infrared thermometer reading must be kept at the growth temperature ±10°C.

[0023] (3) To ensure that the AC coil is not melted by the high-temperature arc, cooling water must be passed through the coil, the temperature is maintained below 30-35°C, and the flow rate is maintained at 5-15L / M.

[0024] (4) To ensure the slow release of thermal stress, the temperature change of the Mo substrate observed by the infrared thermometer was kept at 1°C / min during the cooling process.

[0025] (5) To ensure that the diamond thick film is not oxidized during the annealing process, the temperature must be raised only when the chamber pressure is less than 1 Pa.

[0026] (6) To ensure the quality of the prepared diamond thick film, the ultimate vacuum of the vacuum chamber should be less than 0.7 Pa and the leakage rate should be less than 1·10 -3 Pa·m 3 / s, the cavity pressure is between 2.8-3.0kPa.

[0027] The beneficial effects of the present invention and the prior art are:

[0028] (1) The heating annealing process after growth is completed can effectively reduce the growth stress.

[0029] (2) It avoids rapid cooling of the Mo substrate, allowing the thermal stress to be released slowly and fully.

[0030] (3) The present invention is particularly suitable for large-sized diamond thick films, and is conducive to the preparation of large-sized, crack-free diamond thick films in the future.

[0031] (4) The present invention is an in-situ treatment, does not require additional equipment, and is relatively simple to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of a working state of a CVD device with reduced power according to an embodiment of the present invention;

[0033] Figure 2 It is a schematic diagram of the working state during growth of one embodiment of the present invention.

[0034] Figure 3 FIG. 5 is a curve showing the change of the temperature of the Mo substrate with time according to an embodiment of the present invention.

[0035] In the figure:

[0036] 1. Upper magnetic field coil 2. Lower magnetic field coil 3. AC coil 4. Mo substrate 5. Water cooling stage 6. Infrared thermometer 7. Vacuum chamber 8. Anode. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0038] Embodiment 1:

[0039] Check the ultimate vacuum and leakage rate of the vacuum chamber 7. The ultimate vacuum is 0.5 Pa, and the leakage rate is calculated to be 9.7·10 -4 Pa·m 3 / s. Place the processed Mo substrate 4 on the water cooling table 5 to ensure that the centers of the two are on the same axis and in good contact, and perform vacuum treatment until the pressure is 0.5Pa. Adjust the AC coil 3 to the initial position, such as Figure 2 As shown. First, introduce 5.0 slm argon gas and adjust the chamber pressure to 2.5 kPa. The initial current of the upper magnetic field coil 1 is 2.5A. Set the DC power supply current of the arc plasma generator to 160A, and turn on the power switch to allow the arc to break through the gas. At the same time, introduce hydrogen in proportion (H2:Ar=1.5:1) to control the chamber pressure at 2.8kPa. After the arc stabilizes, gradually increase the DC power supply current of the arc plasma generator to 230A. Adjust the upper and lower magnetic field coils 1 and 2, adjust the arc shape, the substrate surface temperature reaches 870°C, and the diamond film begins to grow stably. After 800 hours of stable growth, start to slowly reduce the power of the CVD equipment. Raise the AC coil 3 to the same height as the Mo substrate 4, as shown Figure 1 As shown. Reduce the power of the CVD equipment, and turn on the power supply of the AC coil 3 to heat the Mo substrate 4, so that it stabilizes at the growth temperature of 870°C. After the arc is extinguished, quickly turn off each gas, and the chamber pressure drops to 0.9Pa. Continue to increase the current of the AC coil 3, slowly increase the temperature of the Mo substrate 4 to 1250°C, and keep annealing for 2h. After the annealing is completed, slowly reduce the current of the AC coil 3, so that the temperature of the Mo substrate 4 slowly drops to room temperature. Open the vent valve to slowly vent.

[0040] The diamond thick film was taken out and found to be intact with uniform surface thickness distribution and no cracks.

[0041] Embodiment 2:

[0042] Check the ultimate vacuum and leakage rate of the vacuum chamber 7. The ultimate vacuum is 0.43 Pa, and the leakage rate is calculated to be 8.4·10 - 4 Pa·m 3 / s. Place the processed Mo substrate 4 on the water cooling table 5 to ensure that the centers of the two are on the same axis and in good contact, and perform vacuum treatment until the pressure is 0.57 Pa. Adjust the AC coil 3 to the initial position, such as Figure 2As shown. First, introduce 5.0 slm argon gas and adjust the chamber pressure to 2.6 kPa. The initial current of the upper magnetic field coil 1 is 2.5A. Set the DC power supply current of the arc plasma generator to 160A, and turn on the power switch to allow the arc to break through the gas. At the same time, introduce hydrogen in proportion (H2:Ar=1.5:1) to control the chamber pressure at 2.9kPa. After the arc stabilizes, gradually increase the DC power supply current of the arc plasma generator to 230A. Adjust the upper and lower magnetic field coils 1 and 2, adjust the arc shape, the substrate surface temperature reaches 870°C, and the diamond film begins to grow stably. After 800h of stable growth, start to slowly reduce the power of the CVD equipment. Raise the AC coil 3 to the same height as the Mo substrate 4, as shown Figure 1 As shown. Reduce the power of the CVD equipment, and turn on the power supply of the AC coil 3 to heat the Mo substrate 4, so that it stabilizes at the growth temperature of 860°C. After the arc is extinguished, quickly turn off the gases, and the chamber pressure drops to 0.9Pa. Continue to increase the current of the AC coil 3, slowly increase the temperature of the Mo substrate 4 to 1200°C, and keep annealing for 2h. After the annealing is completed, slowly reduce the current of the AC coil 3, so that the temperature of the Mo substrate 4 slowly drops to room temperature. Open the vent valve to slowly vent.

[0043] The diamond thick film was taken out and found to be intact with uniform surface thickness distribution and no cracks.

[0044] Implementation Case 3:

[0045] Check the ultimate vacuum and leakage rate of the vacuum chamber 7. The ultimate vacuum is 0.53 Pa, and the leakage rate is calculated to be 7.8·10 - 4 Pa·m 3 / s. Place the processed Mo substrate 4 on the water cooling table 5 to ensure that the centers of the two are on the same axis and in good contact, and perform vacuum treatment until the pressure is 0.83 Pa. Adjust the AC coil 3 to the initial position, such as Figure 2 As shown. First, introduce 5.0 slm argon gas and adjust the chamber pressure to 2.95 kPa. The initial current of the upper magnetic field coil 1 is 2.5A. Set the DC power supply current of the arc plasma generator to 160A, and turn on the power switch to allow the arc to break through the gas. At the same time, introduce hydrogen in proportion (H2:Ar=1.5:1) to control the chamber pressure at 2.95kPa. After the arc stabilizes, gradually increase the DC power supply current of the arc plasma generator to 240A. Adjust the upper and lower magnetic field coils 1 and 2, adjust the arc shape, the substrate surface temperature reaches 870°C, and the diamond film begins to grow stably. After 800h of stable growth, start to slowly reduce the power of the CVD equipment. Raise the AC coil 3 to the same height as the Mo substrate 4, as shown Figure 1As shown. Reduce the power of the CVD equipment, and turn on the power supply of the AC coil 3 to heat the Mo substrate 4, so that it stabilizes at the growth temperature of 880°C. After the arc is extinguished, quickly turn off the gases, and the chamber pressure drops to 0.9Pa. Continue to increase the current of the AC coil 3, slowly increase the temperature of the Mo substrate 4 to 1100°C, and keep annealing for 2h. After the annealing is completed, slowly reduce the current of the AC coil 3, so that the temperature of the Mo substrate 4 slowly drops to room temperature. Open the vent valve to slowly vent.

[0046] The diamond thick film was taken out and found to be intact with uniform surface thickness distribution and no cracks.

Claims

1. A method for reducing stress in a large-scale DC arc plasma CVD diamond thick film, characterized in that the steps include: A diamond thick film is grown on a Mo substrate. After the growth is completed, the AC coil is raised to the same height as the Mo substrate. While cooling down, the Mo substrate is heated by the AC coil and kept at the growth temperature until the arc is extinguished and the machine is shut down. After the vacuum pump pumps the chamber pressure to below 1 Pa, the Mo substrate is continued to be heated by the AC coil to 100-400° C. above the growth temperature for annealing. After the treatment is completed, the temperature of the Mo substrate is slowly reduced to room temperature.

2. The method for reducing stress in a large-scale DC arc plasma CVD diamond thick film according to claim 1, characterized in that: The steps of heating the Mo substrate with an AC coil include: 1) Grow a diamond thick film on a Mo substrate at a growth temperature of 800-950°C; after the growth is completed and before the machine is cooled down and shut down, control the AC coil to rise from the initial position to the same height as the substrate; 2) Start to gradually reduce the current of the DC arc plasma CVD equipment and turn on the AC coil power system to generate induced eddy currents in the Mo substrate; 3) While reducing the current, the current of the AC coil is gradually increased, and the temperature of the Mo substrate is maintained at the growth temperature; 4) After the arc is extinguished, the gas is quickly turned off, and the vacuum pump is used to pump the chamber pressure to below 1Pa. The AC coil current is continued to be increased to increase the output power. The Mo substrate is heated to 100-400℃ above the growth temperature and annealed for 1.5-2.5 hours; 5) After the annealing process is completed, slowly reduce the current of the AC coil until the temperature of the Mo substrate slowly decreases to room temperature; The Mo substrate is heated and slowly cooled by the AC coil, which can effectively reduce the stress in the diamond thick film.

3. The method for reducing stress in a large-scale DC arc plasma CVD diamond thick film according to claim 1, characterized in that: The AC coil can be freely raised and lowered during the growth of the diamond thick film and its diameter is 2 cm larger than the diameter of the water cooling stage.

4. The method for reducing stress in a large-scale DC arc plasma CVD diamond thick film according to claim 1, characterized in that: The diameter of the AC coil is 100-260 mm, the lifting range is 0-240 mm, and the AC coil is wound by a hollow copper tube with an outer diameter of 4-5 mm and an inner diameter of 2-3 mm, and cooling water flows inside.

5. The method for reducing stress in a large-scale DC arc plasma CVD diamond thick film according to claim 1, characterized in that: The temperature change of the Mo substrate should be kept below 8-10°C / h.

6. The method for reducing stress in a large-scale DC arc plasma CVD diamond thick film according to claim 1, characterized in that: The annealing temperature is maintained at 100-400°C above the growth temperature.

7. According to the method for reducing stress in large-size DC arc plasma CVD diamond thick film as described in claim 1, the number of turns of the AC coil is 4-10 turns; since the size of the Mo substrate is large, and the heating speed cannot be too fast and the temperature must be uniform, a low-frequency coil with a frequency of 50-500 Hz is selected.

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