Cleaning method for reaction cavity of CVD (Chemical Vapor Deposition) equipment

Abstract

The invention provides a method for cleaning a reaction cavity of CVD (chemical vapor deposition) equipment. The method comprises the following steps: placing a thermal insulation material and high-temperature-resistant metal on a substrate table in the reaction cavity; a CVD equipment cavity is sealed and vacuumized, and microwave energy is utilized to excite hydrogen introduced into the cavity to form plasma spheres; the microwave power is increased to heat the environment in the reaction cavity of the CVD equipment, so that the temperature of metal on the substrate table reaches 1200-2000 DEG C to form a high-temperature environment, and more pollutants on the cavity wall and the observation window of the CVD equipment are subjected to high-temperature heat radiation and are more easily excited out; then oxygen-containing gas such as carbon dioxide is introduced into the cavity, and pollutants in the reaction cavity are removed through the strong etching capacity of oxygen-containing plasma. The method is easy to operate, high in cleaning efficiency and high in practicability, and new impurities cannot be introduced.

Description

Technical Field

[0001] The present invention relates to a method for cleaning a reaction chamber of a CVD device. Background Art

[0002] The microwave plasma chemical vapor deposition (MPCVD) method has the advantages of less pollution, non - electrode discharge, and can grow diamond over a large area, and is widely used in growing diamond films and preparing large - size single - crystal diamonds. The working mode of preparing diamond by the MPCVD method is to use microwave energy to excite reaction gases such as hydrogen and methane into plasma under vacuum, and then form a stable plasma sphere in the reaction chamber. The reactive groups in the plasma are continuously deposited on the substrate and gradually transformed into diamond. During the reaction process, the reactive groups in the plasma will also adhere to the chamber wall and the observation window, and then form pollutants that affect subsequent reactions. These pollutants will inevitably remain in the chamber of the chemical vapor deposition (CVD) device. If these pollutants cannot be removed in a timely and effective manner, they will gradually accumulate over time. In subsequent reaction experiments, these pollutants will uncontrollably return to the plasma reaction area, affecting the reaction components of the plasma and thus affecting the deposition growth of diamond. In actual production, the CVD reaction chamber requires good vacuum tightness and cannot be disassembled casually. Limited by the shape and size design of the equipment chamber, it is difficult for manual cleaning to easily clean the pollutants attached to the chamber wall and the observation window. Using the traditional reaction chamber cleaning method, without disassembling the equipment, only simple wiping and cleaning can be carried out on the chamber of the CVD device, and there will be a large number of blind spots that cannot be cleaned. Repeated disassembly of the equipment will affect the vacuum tightness and service life of the equipment.

[0003] In the prior art, hydrogen plasma or oxygen plasma is usually used to clean the CVD reaction chamber. Patent CN105177533B discloses a method for in - situ cleaning of a CVD chamber using plasma, which sequentially uses hydrogen plasma and oxygen plasma to remove pollutants in the reaction chamber. This method can remove the amorphous carbon phase, diamond, and diamond - like carbon film layers in the reaction chamber to a certain extent, but the cleaning effect is still limited. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for efficiently cleaning the reaction chamber of a CVD device, which can not only efficiently remove pollutants in the chamber, but also not introduce other impurities and cause damage to the CVD device. To achieve the above - mentioned invention purpose, the present invention provides the following technical solutions:

[0005] A method for cleaning a reaction chamber of a CVD device, comprising the following steps:

[0006] Step (1): Place a heat-insulating material on the substrate table, and place a high-temperature-resistant metal above the heat-insulating material.

[0007] Step (2): After evacuating the air, introduce hydrogen gas, and start the microwave source to excite hydrogen gas to generate plasma.

[0008] Step (3): Increase the microwave power and the pressure inside the reaction chamber, heat the high-temperature-resistant metal to form a high-temperature environment, and make the temperature of the high-temperature-resistant metal 1200 - 2000 °C.

[0009] Step (4): Introduce an oxygen-containing gas to form an oxygen-containing plasma.

[0010] Step (5): Turn off the microwave source.

[0011] Preferably, in step (1), the heat-insulating material is selected from one or more of zirconia, alumina, and silicon carbide, and the shape of the heat-insulating material is selected from one of long plate shape, fragment shape, and spherical shape; the high-temperature-resistant metal is selected from one or more of molybdenum, tungsten, and their alloys; the contact mode between the heat-insulating material and the substrate table and the high-temperature-resistant metal is selected from one of surface contact and point contact.

[0012] Preferably, the contact mode between the heat-insulating material and the substrate table and the high-temperature-resistant metal in step (1) is point contact.

[0013] Preferably, in step (2), the hydrogen gas inlet flow rate is 80 - 100 sccm.

[0014] Preferably, in step (3), adjust the hydrogen gas inlet flow rate to 300 - 900 sccm, increase the microwave power to 0.6 - 6 kW, and increase the pressure inside the reaction chamber to 5 - 180 Torr.

[0015] Preferably, in step (3), heat the high-temperature-resistant metal to a temperature of 1400 - 2000 °C.

[0016] Preferably, in step (3), heat the high-temperature-resistant metal to a temperature of 1600 - 1800 °C.

[0017] Preferably, in step (4), the oxygen-containing gas is carbon dioxide, and the oxygen-containing gas inlet flow rate is 9 - 27 sccm.

[0018] Preferably, after step (5), it further includes: stop introducing oxygen, increase the hydrogen gas flow rate, and flush the chamber to remove the reaction residues.

[0019] Advantages of the present invention:

[0020] (1) By utilizing the high-temperature thermal radiation and the etching effect of oxygen plasma, in-situ cleaning can be achieved, without the need to disassemble the equipment for cleaning, achieving efficient and simple cleaning.

[0021] (2) Heat the high-temperature resistant metal to 1200 - 2000 °C. While ensuring the safe operation of the CVD equipment and avoiding introducing new impurities, use high-temperature thermal radiation to more effectively excite the contaminants attached to the chamber wall and observation window.

[0022] (3) Compared with oxygen, using carbon dioxide as the source of oxygen plasma can improve the equipment safety, reduce the oxidation of the equipment in the high-temperature environment, extend the service life of the equipment, avoid over-etching, and prevent the introduction of new impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Structural schematic diagram (left) and process schematic diagram (right) of the present invention

[0024] Figure 2 Relationship curve between wavelength and thermal radiation energy at different temperatures (Zhang Chao, Suo Tao, Tan Weili, etc. Chinese Journal of High Pressure Physics, 2018, 32(01): 100 - 106.)

[0025] Figure 3 Optical Emission Spectrum (OES) of the plasma of Examples 1 - 9 and Comparative Example 1

[0026] Figure 4 Curve graph showing the change of the relative intensity of the characteristic peaks of C2 and CH groups in the OES spectra of Examples 1 - 9 and Comparative Example 1 with temperature DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] To make the objectives, contents, and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings.

[0028] Figure 1 The left figure is a structural schematic diagram of an embodiment of the present invention. The device includes a vacuum chamber, in which a substrate table is provided, and heat insulation materials and high-temperature resistant metals are placed on the substrate table. A microwave source is arranged outside the vacuum chamber. After the microwave source generates microwaves, they enter the vacuum chamber through a waveguide. Figure 1 The right figure shows the cleaning flow chart of the present invention. Next, in combination with Figure 1 the method of the present invention will be described.

[0029] Step 1: First, wipe the reaction chamber of the CVD equipment. Place a heat-insulating material on the substrate table, and place a high-temperature-resistant metal above the heat-insulating material. The heat-insulating material is selected from one or more of zirconia, alumina, and silicon carbide, preferably silicon carbide. The shape of the heat-insulating material is selected from one of long plate shape, fragment shape, and spherical shape, preferably fragment shape. The high-temperature-resistant metal is selected from one or more of molybdenum, tungsten, and their alloys, preferably molybdenum. The total volume of the heat-insulating material is less than the volume of the high-temperature-resistant metal. The contact mode between the heat-insulating material and the substrate table and the high-temperature-resistant metal is selected from one of surface contact and point contact, preferably point contact.

[0030] Step 2: Seal the CVD equipment chamber. After evacuating, introduce hydrogen. The hydrogen inlet flow rate is 80 - 100 sccm (sccm: standard cubic centimeters per minute), and the pressure is increased to 5 - 8 Torr. Turn on the microwave source and use microwave energy to excite hydrogen to form a plasma sphere.

[0031] Step 3: Adjust the hydrogen inlet flow rate to 300 - 900 sccm, increase the pressure in the reaction chamber to 5 - 180 Torr. Within the microwave power range of 3 - 6 kW, try to increase the microwave power of the equipment as much as possible and control the water cooling system. On the premise of ensuring a suitable chamber temperature and safety, heat up the environment in the CVD equipment reaction chamber so that the temperature of the metal on the substrate table reaches 1200°C - 2000°C. This is the first process parameter, and the holding time is 20 min - 180 min.

[0032] Step 4: Change the gas composition. On the basis of introducing hydrogen, introduce an oxygen-containing gas such as carbon dioxide into the reaction gas. The oxygen-containing gas inlet flow rate is 9 - 27 sccm. This is the second process parameter, and the holding time is 5 min - 30 min.

[0033] Step 5: After cleaning, turn off the microwave source, stop introducing oxygen, increase the gas flow rate of hydrogen to 500 - 1000 sccm, flush the reaction chamber to remove the reaction residues, and finally turn off the CVD equipment, take out the heat-insulating material and the metal, so that the CVD equipment chamber can be used normally again.

[0034] In the present invention, by increasing the microwave power, the high-temperature resistant metal is heated by microwave plasma, and a heat-insulating material is arranged between the substrate table and the high-temperature resistant metal to retain a large amount of heat in the CVD cavity, forming a high-temperature environment. At high temperatures, more photons can be excited from the metal, generating stronger thermal radiation energy. The heat-insulating material in the present invention has high-temperature resistance and thermal stability and will not easily introduce new impurities. The contact mode between the heat-insulating material and the substrate table and the high-temperature resistant metal is preferably point contact, which can achieve a better heat-insulating effect. The pollutants attached to the cavity wall and the observation window are more excited by high-temperature thermal radiation, and then an oxygen-containing gas is introduced into the reaction cavity, and the strong etching ability of the oxygen-containing plasma is used to remove the excited pollutants, so as to achieve the purpose of cleaning the cavity. Thermal radiation is the radiation energy generated due to the temperature of the substance. As Figure 2 shown, as the temperature increases, the thermal radiation will shift to shorter wavelengths. The shorter the wavelength, the higher the energy of the radiated photons, which can more effectively excite the pollutants attached to the cavity wall and the observation window, improving the cleaning effect. On the other hand, when the temperature is too high, metal evaporation will introduce new impurities. Tungsten, molybdenum, etc. are high-temperature resistant metals and are stable in high-temperature environments. However, when the heating temperature of the metal exceeds 2000 °C, the metal is likely to be etched and evaporated in a hydrogen-oxygen plasma environment (Tao Zhou. Huazhong University of Science and Technology, Master's Thesis, 2017; Jinlong Liu, Chengming Li, Xiaohua Zhu, etc. Journal of Synthetic Crystals, 2019, 48(11): 1990-1991.). The present invention uses high-temperature resistant metals and heat-insulating materials with high-temperature resistance and thermal stability to control the metal temperature at 1200-2000 °C, improving the cleaning effect while ensuring that no new impurities are introduced during the cleaning process, and enabling the CVD equipment to operate safely and stably.

[0035] In the prior art, oxygen is usually used as the source of oxygen plasma. Compared with oxygen, carbon dioxide gas has the following advantages: (1) Oxygen is a flammable and explosive gas with high storage requirements, while carbon dioxide has low storage requirements; (2) Oxygen and hydrogen mixed have an explosion limit at normal temperature and pressure. In comparison, carbon dioxide has high safety (Chemical Industry Safety Technology [M]. Beijing: Chemical Industry Press, 1984; Huajie Wu, Yunhou Sun, Lei Zheng, etc. Shanxi Architecture, 2022, 48(13): 73-75); (3) Oxygen is more oxidizing and has stronger etching ability. At high temperatures, oxygen can not only remove the pollutant impurities in the CVD cavity but also has a high probability of corroding the metal, which will have a certain impact on the CVD equipment, and excessive etching of the metal will introduce other impurities. For example, the vacuum pump oil in the CVD equipment is a device prone to oxidation, and introducing O2 into the high-temperature environment of the CVD reaction cavity will exacerbate the oxidation of this equipment. In the cleaning method of the present invention, the cleaning effect is improved through high-temperature thermal radiation. Therefore, using carbon dioxide as the source of oxygen plasma in the present invention can improve the safety of the equipment while ensuring that no new impurities are introduced during the cleaning process.

[0036] In the present invention, by increasing the microwave power, using microwave plasma to heat a high-temperature resistant metal, and arranging a heat insulation material between the substrate table and the high-temperature resistant metal to retain a large amount of heat in the CVD cavity, a high-temperature environment is formed, so that the temperature of the high-temperature resistant metal is heated to 1200-2000 °C. More pollutants attached to the cavity wall and the observation window are excited by high-temperature thermal radiation. Then, an oxygen-containing gas is introduced into the reaction cavity, and the strong etching ability of the oxygen-containing plasma is used to remove the excited pollutants, so as to achieve the purpose of cleaning the cavity.

[0037] The present invention will be further described below in conjunction with embodiments.

[0038] In all embodiments of the present invention, the equipment used is:

[0039] CVD equipment: W-150A-6K of Boshi Optoelectronics (Shanghai) Technology Co., Ltd.

[0040] Embodiment 1

[0041] Step 1: First, wipe the reaction cavity of the CVD equipment. Place a heat insulation material and a high-temperature resistant metal on the substrate table. The high-temperature resistant metal is placed above the heat insulation material. The contact mode between the heat insulation material and the substrate table and the high-temperature resistant metal is point contact. The heat insulation material is made of silicon carbide fragments, and the high-temperature resistant metal is made of molybdenum metal sheets. The total volume of the heat insulation material is smaller than the volume of the high-temperature resistant metal, and the contact between the heat insulation material and the high-temperature resistant metal is point contact.

[0042] Step 2: Seal the cavity of the CVD equipment, use the vacuum system to evacuate the CVD equipment to 0 Torr (1 Torr = 133.322 Pa), introduce 100 sccm (sccm: standard cubic centimeter per minute) of hydrogen, the pressure rises to about 5 Torr, turn on the microwave source, and use microwave energy to excite hydrogen to form a plasma sphere.

[0043] Step 3: Continuously adjust the hydrogen inlet flow rate to 300 sccm, increase the microwave power to about 1.2 kW, increase the pressure in the reaction cavity to 40 Torr, heat the metal to increase the temperature, and measure the temperature of the metal on the substrate table to be 1200 °C through a two-color infrared thermometer, and maintain it for 30 min.

[0044] Step 4: Change the gas composition, introduce 9 sccm of carbon dioxide gas into the reaction gas on the basis of introducing hydrogen, and maintain it for 10 min.

[0045] Step 5: After turning off the microwave source, stop introducing oxygen, increase the gas flow rate of hydrogen to 800 sccm, flush the reaction cavity to remove the reaction residues, finally turn off the CVD equipment, take out the heat insulation material and molybdenum metal sheets, and the cavity of the CVD equipment can continue to be used normally.

[0046] During the process of step (3), an Ocean Optics inductively coupled plasma optical emission spectrometer with an optical resolution of 0.035 nm was used to monitor the plasma composition in the CVD reaction chamber. The detection wavelength range was 200 - 1100 nm. At normal temperature and pressure, a fiber optic probe was used to monitor the plasma in the reaction chamber of the CVD equipment through the observation window. The obtained optical emission spectrum (OES) of the plasma is as Figure 3 shown.

[0047] Example 2: The method is basically the same as that of Example 1, except that in step 3, the microwave power was increased to about 1.5 kW, the pressure in the reaction chamber was increased to 50 Torr, the metal was heated, and the temperature of the metal on the substrate table was measured to be 1306 °C. During the process of step (3), the plasma composition in the CVD reaction chamber was monitored, and the OES is as Figure 3 shown.

[0048] Example 3: The method is basically the same as that of Example 1, except that in step 3, the microwave power was increased to about 1.8 kW, the pressure in the reaction chamber was increased to 60 Torr, the metal was heated, and the temperature of the metal on the substrate table was measured to be 1399 °C. During the process of step (3), the plasma composition in the CVD reaction chamber was monitored, and the OES is as Figure 3 shown.

[0049] Example 4: The method is basically the same as that of Example 1, except that in step 3, the microwave power was increased to about 2.1 kW, the pressure in the reaction chamber was increased to 70 Torr, the metal was heated, and the temperature of the metal on the substrate table was estimated to be 1484 °C. During the process of step (3), the plasma composition in the CVD reaction chamber was monitored, and the OES is as Figure 3 shown.

[0050] Example 5: The method is basically the same as that of Example 1, except that in step 3, the microwave power was increased to about 2.4 kW, the pressure in the reaction chamber was increased to 80 Torr, the metal was heated, and the temperature of the metal on the substrate table was estimated to be 1562 °C. During the process of step (3), the plasma composition in the CVD reaction chamber was monitored, and the OES is as Figure 3 shown.

[0051] Example 6: The method is basically the same as that of Example 1, except that in step 3, the microwave power was increased to about 2.7 kW, the pressure in the reaction chamber was increased to 90 Torr, the metal was heated, and the temperature of the metal on the substrate table was estimated to be 1633 °C. During the process of step (3), the plasma composition in the CVD reaction chamber was monitored, and the OES is as Figure 3 shown.

[0052] Example 7: The method is basically the same as that of Example 1, except that in step 3, the microwave power is increased to about 3.0 kW, the pressure in the reaction chamber is increased to 100 Torr, the metal is heated, and the temperature of the metal on the substrate table is estimated to be 1695 °C. During the process of step (3), the plasma composition in the CVD reaction chamber is monitored, and the OES is as Figure 3 shown.

[0053] Example 8: The method is basically the same as that of Example 1, except that in step 3, the microwave power is increased to about 3.3 kW, the pressure in the reaction chamber is increased to 110 Torr, the metal is heated, and the temperature of the metal on the substrate table is estimated to be 1750 °C. During the process of step (3), the plasma composition in the CVD reaction chamber is monitored, and the OES is as Figure 3 shown.

[0054] Example 9: The method is basically the same as that of Example 1, except that in step 3, the microwave power is increased to about 3.6 kW, the pressure in the reaction chamber is increased to 120 Torr, the metal is heated, and the temperature of the metal on the substrate table is estimated to be 1800 °C. During the process of step (3), the plasma composition in the CVD reaction chamber is monitored, and the OES is as Figure 3 shown.

[0055] Comparative Example 1: The method is basically the same as that of Example 1, except that in step 3, the microwave power is increased to about 0.9 kW, the pressure in the reaction chamber is increased to 30 Torr, the metal is heated, and the temperature of the metal on the substrate table is measured to be 1091 °C. During the process of step (3), the plasma composition in the CVD reaction chamber is monitored, and the OES is as Figure 3 shown.

[0056] In the CVD equipment for growing diamond, since the main contaminants in the equipment are graphite, etc., during the experiment, the C2 characteristic peak at about 670 nm and the CH characteristic peak at about 766 nm can be obtained through real-time monitoring by optical emission spectrum (OES). These two peaks are not typical OES characteristic peaks in the study of microwave plasma CVD diamond, which may be related to the CHx substances provided by the graphite source rich in the plasma region (Yao K, Dai B, Ralchenko V, et al, Diamond and Related Materials, 2018, 82, 33 - 40). Therefore, under these experimental conditions, the possibility that the C2 and CH peaks come from graphite contaminants is the greatest.

[0057] Figure 3 The optical emission spectra of the plasma in the reaction chamber of the CVD equipment during the process of step (3) for Examples 1 - 9 and Comparative Example 1 are given.

[0058] Figure 4 The characteristic peak intensities of C2 and CH groups in the OES obtained from Comparative Example 1 are taken as 10, and the characteristic peak intensities I of C2 and CH groups in the OES obtained from Examples 1-9 x and the ratio I of 10 x / I0 (relative intensity) versus temperature variation curve graph.

[0059] As Figure 3 and Figure 4 shown, in the early stage of cleaning under the first process parameters (only hydrogen), it can be seen that when the metal temperature is less than 1200 °C, there are almost no characteristic peaks of C2 and CH in the OES, indicating that the pollutants are hardly excited, that is, when the metal temperature is lower than 1200 °C, the cleaning effect is poor. As the metal temperature increases, the characteristic peak intensities of the pollutant ions (C2, CH) increase, indicating that some pollutants such as graphite are more excited, forming carbon-containing plasmas and being monitored by OES. These particles can then be discharged with the gas flow, thereby achieving the purpose of cleaning the CVD chamber. When the temperature rises above 1400 °C, the characteristic peaks of the pollutant ions (C2, CH) become more prominent, so it is preferred to heat the metal temperature above 1400 °C.

Claims

1. A cleaning method for a reaction chamber of a CVD device, characterized in that, It includes the following steps: Step (1): Place a heat-insulating material on the substrate table, and place a high-temperature resistant metal above the heat-insulating material; Step (2): After evacuating the air, introduce hydrogen, start the microwave source, and excite the hydrogen to generate plasma; Step (3): Increase the microwave power and the pressure in the reaction chamber, heat the high-temperature resistant metal to form a high-temperature environment, and make the temperature of the high-temperature resistant metal be 1200 - 2000 °C; Step (4): Introduce an oxygen-containing gas to form an oxygen-containing plasma; Step (5): Turn off the microwave source.

2. The cleaning method according to claim 1, wherein In the step (1), the heat-insulating material is selected from one or more of zirconia, alumina, and silicon carbide, and the shape of the heat-insulating material is selected from one of long plate shape, fragment shape, and spherical shape; the high-temperature resistant metal is selected from one or more of molybdenum, tungsten, and their alloys; the contact mode between the heat-insulating material and the substrate table and the high-temperature resistant metal is selected from one of surface contact and point contact.

3. The cleaning method according to claim 2, characterized in that, In the step (1), the contact mode between the heat-insulating material and the substrate table and the high-temperature resistant metal is point contact.

4. The cleaning method according to claim 1, wherein In the step (2), the hydrogen inlet flow rate is 80 - 100 sccm.

5. The cleaning method according to claim 1, characterized in that, In the step (3), adjust the hydrogen inlet flow rate to 300 - 900 sccm, increase the microwave power to 0.6 - 6 kW, and increase the pressure in the reaction chamber to 5 - 180 Torr.

6. The cleaning method according to claim 1, wherein In the step (3), heat the high-temperature resistant metal to a temperature of 1400 - 2000 °C.

7. The cleaning method according to claim 1, wherein In the step (3), heat the high-temperature resistant metal to a temperature of 1600 - 1800 °C.

8. The cleaning method according to claim 1, characterized in that In the step (4), the oxygen-containing gas is carbon dioxide, and the oxygen-containing gas inlet flow rate is 9 - 27 sccm.

9. The cleaning method according to claim 1, wherein After the step (5), it further includes: stop introducing oxygen, increase the hydrogen flow rate, and flush the chamber to take away the reaction residues.

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