CVD (Chemical Vapor Deposition) system and method for low-pressure pulse type gas supply deposition of silicon carbide coating

Abstract

The invention discloses a CVD (Chemical Vapor Deposition) system and method for depositing a silicon carbide coating through low-pressure pulse type gas supply. The system comprises a furnace body, a gas distribution disc, a gas supply loop, an atmosphere switching module, a vacuum buffer cavity and a control unit, the vacuum buffer cavity is used for controlling the furnace cavity pressure of the furnace body to be maintained in a low-pressure environment of 50-200 Pa, and the control system is used for controlling precursor gas supply and inert gas purging to be periodically switched. And thus, periodic stable refreshing of the boundary layer reaction atmosphere is realized. According to the method, through alternate operation of pulse gas supply and purging, dynamic refreshing of the reaction atmosphere is achieved, a boundary layer is effectively thinned, gas retention is eliminated, the effective flux of the reaction gas reaching the surface of a matrix is improved, and then the compactness, uniformity and surface quality of the silicon carbide coating are remarkably improved. Therefore, the problems of boundary layer enrichment, raw material waste, uneven coating and the like in the traditional continuous gas inlet CVD process are solved.

Description

Technical Field

[0001] This invention relates to the field of chemical vapor deposition technology, specifically to a CVD system and method for low-pressure pulsed gas supply deposition of silicon carbide coatings. Background Technology

[0002] Silicon carbide (SiC) is widely used in high-performance ceramics and wide-bandgap semiconductor materials due to its high hardness, high thermal conductivity, and excellent high-temperature resistance and corrosion resistance. The mainstream industrial technique for preparing SiC coatings is chemical vapor deposition (CVD), which involves fusing precursors (such as trichloromethylsilane MTS or...) at high temperatures. The reaction decomposes in a hydrogen atmosphere, forming a dense SiC film on the substrate surface. However, the traditional continuous gas inlet + constant pressure operation mode suffers from problems such as boundary layer enrichment, low precursor utilization, poor coating uniformity, and poor system dynamic response. For example, an excessively thick boundary layer leads to reactant retention, causing particle defects and increased surface roughness; continuous gas supply results in a large waste of unreacted precursors, leading to insufficient raw material utilization; uneven airflow distribution leads to large differences in coating thickness, especially for workpieces with complex geometries.

[0003] In existing technologies, Huang et al. proposed the "precursor alternating pulse CVD" scheme in 2023 (Journal of Vacuum Science & Technology A), which employs... and Alternating pulses and purging with H2 within each pulse cycle are used to achieve superconducting SiC coatings. However, this approach has the following limitations: the operating pressure is relatively high (about 1 kPa), resulting in limited boundary layer thinning; the use of alternating supply of dual precursors makes the process complex and difficult to industrialize; the use of H2 as the purging gas may trigger side reactions; and the lack of high-speed switching and buffering structures leads to significant airflow disturbances. Summary of the Invention

[0004] The purpose of this invention is to provide a CVD system and method for depositing silicon carbide coatings using low-pressure pulsed gas supply, in order to solve problems such as boundary layer enrichment, numerous particle defects, low precursor utilization, and poor coating uniformity in existing technologies. By alternating low-pressure pulsed gas supply with inert gas purging, dynamic atmosphere refresh and stable reaction control are achieved, thereby improving the quality and economy of silicon carbide coatings.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings, comprising: The furnace body has a rotatable support inside its furnace cavity to support the workpiece; The gas distribution plate is located at the top of the furnace body and is used to evenly distribute the airflow. The gas supply circuit includes an independent precursor gas supply circuit and an inert gas supply circuit; An atmosphere switching module is installed between the gas distribution plate and the gas supply circuit to achieve alternating supply of precursor gas and inert gas. The vacuum buffer chamber is connected to the furnace cavity of the furnace body and is used to absorb pressure difference fluctuations during the gas supply switching process and maintain the reaction chamber pressure at 50-200Pa. The control unit, which is connected to the gas supply circuit, atmosphere switching module and vacuum buffer chamber, is used to perform closed-loop regulation of gas switching, pressure and flow to realize periodic pulse gas supply and purging. Furthermore, the precursor gas supply circuit is connected to a first flow control valve connected to the control unit to control the precursor gas supply flow rate, and the inert gas supply circuit is connected to a second flow control valve connected to the control unit to control the inert gas supply flow rate.

[0006] Furthermore, the precursor gas supply circuit and the inert gas supply circuit are respectively connected to a first solenoid valve and a second solenoid valve, which are connected to the control unit, to realize the switching between precursor gas supply and inert gas supply.

[0007] Furthermore, the precursor gas supply circuit and the inert gas supply circuit are also connected to a one-way valve connected to the control unit to prevent gas mixing.

[0008] Furthermore, the precursor gas supply circuit and the inert gas supply circuit are also connected to a bypass exhaust channel connected to the control unit to prevent pressure difference shocks during the gas switching process.

[0009] Furthermore, a pressure sensor is connected inside the vacuum buffer chamber to monitor the pressure inside the furnace chamber in real time, thereby adjusting the exhaust rate to maintain a stable flow field and constant pressure inside the furnace chamber.

[0010] Secondly, the present invention also provides a CVD method for depositing a silicon carbide coating using a low-pressure pulsed gas supply, the method being used to achieve the aforementioned low-pressure pulsed gas supply deposition of a silicon carbide coating, specifically including the following steps: S100, the control unit controls the vacuum buffer chamber to evacuate the furnace body to 50-200Pa and heat it to the set temperature; S200, the control unit controls the start of the precursor gas supply circuit, and the precursor gas enters the furnace cavity of the furnace body through the atmosphere switching module and the gas distribution plate, thereby depositing silicon carbide coating on the substrate pre-placed on the support. S300, the control unit controls the precursor gas supply circuit to close and the inert gas supply circuit to open to achieve gas supply switching. The inert gas enters the furnace cavity of the furnace body through the atmosphere switching module and the gas distribution plate, thereby replacing the residual gas and by-products of the precursor in the furnace cavity. S400, the control unit controls the inert gas supply to shut off and the precursor gas supply circuit to open to achieve gas supply switching; S500, repeat steps S200-S400, forming a silicon carbide coating on the substrate surface by alternating pulse gas supply and purging, while using a vacuum buffer chamber to control and maintain a constant pressure in the furnace cavity during the deposition process.

[0011] Furthermore, the response time for the gas supply switching is no more than 0.1s.

[0012] Furthermore, the pulse gas supply cycle time is 1-10s, wherein the control unit controls the precursor gas supply circuit to open - the precursor gas supply circuit to close - the inert gas supply circuit to open - the inert gas supply circuit to close - the precursor gas supply circuit to open, which constitutes one pulse gas supply cycle.

[0013] Compared with the prior art, the present invention has the following beneficial technical effects: (1) The present invention uses pulse gas supply and purging to alternately refresh the boundary layer gas formed on the surface of the workpiece to be deposited, avoids local retention of reactants and gas phase polymerization, fundamentally inhibits the generation of particle defects, the precursor gas only enters the reaction zone during the deposition stage, and the gas supply is completely shut off during the purging stage, which significantly improves the reaction ratio of reactants, increases the utilization rate of precursor gas by 20-30%, and significantly reduces raw material consumption.

[0014] (2) The present invention achieves millisecond-level atmosphere switching through the atmosphere switching module, that is, the gas in the reaction zone of the furnace body and furnace cavity is periodically and dynamically controlled, thereby achieving precise adjustment of deposition rate and film formation characteristics.

[0015] (3) The present invention adjusts the reaction pressure in the furnace cavity in real time through the vacuum buffer chamber, so that the reaction pressure is always maintained in a low pressure environment of 50-200Pa. The thickness of the boundary layer formed on the surface of the workpiece to be deposited is significantly reduced, and the gas diffusion efficiency is effectively improved. At the same time, with the help of the gas distribution plate, the uniformity of the silicon carbide coating thickness can be controlled within ±3%.

[0016] (4) The present invention uses pulsed gas supply and purging alternately to make the instantaneous concentration of the reaction gas high, the reaction rate fast, and the deposition rate per unit time increased by 30-40%, thereby obtaining a high-thickness coating in a short time and reducing energy consumption and running time.

[0017] (5) The present invention adopts a combined process of vacuum buffer chamber and control system, so that the atmosphere switching of precursor gas and inert gas is undisturbed, the parameters are highly repeatable, and the quality of silicon carbide coating is stable between batches. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of a CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings according to the present invention. Figure 2 This is a flowchart of a CVD method for depositing silicon carbide coatings using low-pressure pulsed gas supply, as described in this invention.

[0020] In the diagram: 1. Furnace body, 2. Support frame, 3. Gas distribution plate, 41. Precursor gas supply circuit, 42. Inert gas supply circuit, 5. Atmosphere switching module, 6. Vacuum buffer chamber, 71. First flow control valve, 72. Second flow control valve, 81. First solenoid valve, 82. Second solenoid valve. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0022] like Figure 1 As shown, the present invention provides a CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings, comprising: Furnace body 1, with a rotatable support 2 for carrying workpieces inside its furnace cavity; The gas distribution plate 3 is located at the top of the furnace body 1 and is used to evenly distribute the airflow. The gas supply circuit includes an independent precursor gas supply circuit 41 and an inert gas supply circuit 42. Atmosphere switching module 5 is located between gas distribution plate 3 and gas supply circuit to realize the alternating supply of precursor gas and inert gas. The vacuum buffer chamber 6 is connected to the furnace chamber of the furnace body 1 and is used to absorb pressure difference fluctuations during the gas supply switching process and maintain the reaction chamber pressure at 50-200 Pa. The control unit (not shown in the figure) is connected to the gas supply circuit, atmosphere switching module 5 and vacuum buffer chamber 6. It is used to perform closed-loop regulation of gas switching, pressure and flow rate to realize periodic pulse gas supply and purging. In the above embodiments, the furnace body 1 can be a vertical structure or a European-style structure. The furnace cavity of the furnace body 1 is made of high-purity graphite or silicon carbide ceramic. The inner wall of the furnace cavity is polished to reduce particle adsorption. The outer wall of the furnace body 1 is equipped with resistance heating elements and multi-layer heat insulation materials, which can stably control the temperature within the range of 1100-1300℃. The rotatable bracket 2 is installed in the furnace cavity of the furnace body 1 to support the workpiece and improve the airflow distribution. The gas distribution plate 3 is set at the furnace cavity inlet end of the furnace body 1 and connected to the atmosphere switching module 5 to form a radially uniform gas distribution. The system eliminates dead zones in the airflow within the furnace cavity. An atmosphere switching module 5, located between the gas distribution plate 3 and the gas supply circuit, switches the gases supplied by the precursor gas supply circuit 41 and the inert gas supply circuit 42, thereby achieving alternating supply of precursor gas and inert gas. A vacuum buffer chamber 6, connected to the furnace cavity of the furnace body 1, absorbs pressure fluctuations during gas supply switching and maintains a stable reaction chamber pressure of 50-200 Pa. A control unit performs closed-loop regulation of gas switching, pressure, and flow rate, enabling periodic pulse gas supply and purging. This system utilizes the vacuum buffer chamber 6 to maintain the furnace cavity pressure of the furnace body 1 at a low pressure of 50-200 Pa. Simultaneously, the control system controls the atmosphere switching module 5 to periodically switch between precursor and inert gas, thereby periodically refreshing the reaction atmosphere on the workpiece surface boundary layer. This effectively thins the boundary layer, eliminates gas stagnation, and increases the effective throughput of the reaction gas reaching the substrate surface, significantly improving the density, uniformity, and surface quality of the silicon carbide coating. Therefore, this invention solves the problems of boundary layer enrichment, raw material waste and uneven coating in traditional continuous air intake CVD processes.

[0023] In some embodiments, the precursor gas supply circuit 41 is connected to a first flow control valve 71 connected to a control unit for controlling the precursor gas supply flow rate, and the inert gas supply circuit 42 is connected to a second flow control valve 72 connected to a control unit for controlling the inert gas supply flow rate.

[0024] In the above embodiments, the control system can adjust the gas flow rate of the precursor gas supply circuit 41 and the inert gas supply circuit 42 through the first flow control valve 71 and the second flow control valve 72.

[0025] In some embodiments, the precursor gas supply circuit 41 and the inert gas supply circuit 42 are respectively connected to a first solenoid valve 81 and a second solenoid valve 82 connected to the control unit, for switching between precursor gas supply and inert gas supply.

[0026] In the above embodiments, the control system can achieve high-speed gas supply switching between the precursor gas supply circuit 41 and the inert gas supply circuit 42 through the first solenoid valve 81 and the second solenoid valve 82. The switching response time is less than 0.1s, that is, the switching between gas supply and purging is achieved at the millisecond level, which provides the prerequisite for maintaining a low-pressure environment and improving reaction efficiency.

[0027] In some embodiments, the precursor gas supply circuit 41 and the inert gas supply circuit 42 are also connected to a one-way valve connected to the control unit to prevent gas mixing.

[0028] In the above embodiments, by setting a one-way valve, it is possible to effectively prevent the precursor from entering the inert gas supply circuit 42 and causing mixed flow, and to prevent the inert gas from entering the precursor supply circuit 41 and causing mixed flow, thus ensuring the purity of the precursor and the inert gas and providing a guarantee for the quality of the deposited silicon carbide coating.

[0029] In some embodiments, the precursor gas supply circuit 41 and the inert gas supply circuit 42 are also connected to a bypass exhaust channel connected to the control unit to prevent pressure difference shocks during the gas switching process.

[0030] In the above embodiments, by connecting a bypass exhaust channel to the precursor gas supply circuit 41 and the inert gas supply circuit 42, the pressure difference impact during the gas supply switching between the precursor gas supply circuit 41 and the inert gas supply circuit 42 can be effectively prevented, thereby providing the prerequisite for maintaining a low-pressure environment in the reaction chamber.

[0031] In some embodiments, a pressure sensor is connected inside the vacuum buffer chamber 6 to monitor the pressure inside the furnace chamber of the furnace body 1 in real time, thereby adjusting the exhaust rate to maintain a stable flow field and constant pressure inside the furnace chamber of the furnace body 1.

[0032] In the above embodiments, by setting a pressure sensor to monitor the pressure inside the furnace cavity of the furnace body 1 in real time, the control system can adjust the exhaust rate in a timely manner, thereby ensuring that the furnace cavity of the furnace body 1 always maintains a stable flow field and constant pressure.

[0033] Secondly, the present invention also provides a CVD method for depositing a silicon carbide coating using a low-pressure pulsed gas supply, the method being used to achieve the aforementioned low-pressure pulsed gas supply deposition of a silicon carbide coating, specifically including the following steps: S100, the control unit controls the vacuum buffer chamber 6 to evacuate the furnace body 1 to 50-200Pa and heat it to the set temperature; S200, the control unit controls the start of the precursor gas supply circuit 41, and the precursor gas enters the furnace cavity of the furnace body 1 through the atmosphere switching module 5 and the gas distribution plate 3, and then deposits silicon carbide coating on the substrate pre-placed on the support 2. S300, the control unit controls the precursor gas supply circuit 41 to close and the inert gas supply circuit 42 to switch the gas supply. The inert gas enters the furnace cavity of the furnace body 1 through the atmosphere switching module 5 and the gas distribution plate 3, thereby replacing the residual gas and by-products of the precursor in the furnace cavity. S400, the control unit controls the inert gas supply to close and the precursor gas supply circuit 41 to open to achieve gas supply switching; S500, repeat steps S200-S400, and form a silicon carbide coating on the substrate surface by alternating pulse gas supply and purging. At the same time, the vacuum buffer chamber 6 is used to control the constant pressure in the furnace cavity during the deposition process.

[0034] In the above embodiments, the response time of the gas supply switching is no more than 0.1s; the pulse gas supply cycle time is 1-10s, wherein the control unit controls the precursor gas supply circuit 41 to open - the precursor gas supply circuit 41 to close - the inert gas supply circuit 42 to open - the inert gas supply circuit 42 to close - the precursor gas supply circuit 41 to open as one pulse gas supply cycle.

[0035] Based on the description of the beneficial technical effects of the CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings, it can be seen that the CVD method used to achieve the same technical effects has the same technical effects, and will not be repeated here.

[0036] To further illustrate the working principle and technical effects of the present invention, the following examples illustrate the deposition of a 100μm thick silicon carbide coating on a workpiece using the low-pressure pulsed gas supply CVD method provided by the present invention and the traditional continuous gas supply CVD method.

[0037] Example 1 The CVD method for depositing silicon carbide coatings using low-pressure pulsed gas supply provided by this invention is used to deposit silicon carbide coatings on workpieces. The reaction pressure inside the furnace 1 is 100 Pa, the reaction temperature is 1200 °C, the pulsed gas supply cycle time is 5 s (2 s for precursor gas supply and 3 s for inert gas purging), and the pulsed gas supply cycle is repeated 5 times to obtain a workpiece with a silicon carbide coating thickness of 100 μm.

[0038] Example 2 The CVD method for depositing silicon carbide coatings using low-pressure pulsed gas supply provided by this invention is used to deposit silicon carbide coatings on workpieces. The reaction pressure inside the furnace 1 is 50 Pa, the reaction temperature is 1000 °C, the pulsed gas supply cycle time is 1 s (precursor gas supply 0.4 s, inert gas purging 0.6 s), and the pulsed gas supply cycle is repeated 10 times to obtain a workpiece with a silicon carbide coating thickness of 100 μm.

[0039] Example 3 The CVD method for depositing silicon carbide coatings using low-pressure pulsed gas supply provided by this invention is used to deposit silicon carbide coatings on workpieces. The reaction pressure inside the furnace 1 is 200 Pa, the reaction temperature is 1600 °C, the pulsed gas supply cycle time is 10 s (4 s for precursor gas supply and 6 s for inert gas purging), and the pulsed gas supply cycle is repeated 3 times to obtain a workpiece with a silicon carbide coating thickness of 100 μm.

[0040] Comparative Example 1 A silicon carbide coating with a thickness of 100 μm was deposited on the workpiece using the traditional continuous air intake CVD method.

[0041] The precursor gas utilization rate and the coating thickness uniformity and coating roughness of the corresponding workpieces in Examples 1-3 and Comparative Example 1 were tested, and the test results are shown in Table 1.

[0042] Table 1. Detection results of Examples 1-3 and Comparative Example 1 Precursor gas utilization rate (%) Silicon carbide coating thickness uniformity (%) Roughness (μm) Example 1 85 ±2.5 ≤0.2 Example 2 88 ±2.7 ≤0.2 Example 3 83 ±2.3 ≤0.2 Comparative Example 1 57 ±4.5 ≤0.6 As can be seen from Table 1, the precursor gas utilization rate of Examples 1-3 all reached over 80%, while the precursor gas utilization rate of Comparative Example 1 was only 57%. This shows that the CVD system and method for low-pressure pulse gas supply deposition of silicon carbide coatings provided by the present invention can effectively improve the utilization rate of precursor gas by alternating pulse gas supply and purging.

[0043] As can be seen from Table 1, the workpiece coating thickness uniformity obtained in Examples 1-3 is all below ±2.7%, and the roughness is ≤0.2μm; while the workpiece coating thickness uniformity obtained in Comparative Example 1 reaches ±4.5%, and the roughness is ≤0.6μm. This shows that the CVD system and method for low-pressure pulse gas supply deposition of silicon carbide coating provided by the present invention can effectively improve the uniformity of the deposited coating thickness, and at the same time greatly reduce the particle defects on the coating surface.

[0044] Therefore, compared with the prior art, the CVD system and method for low-pressure pulsed gas supply deposition of silicon carbide coatings provided by the present invention can effectively improve the utilization rate of precursor gas, reduce particle defects in the deposited coating, and improve the thickness uniformity of the deposited coating.

[0045] The CVD system and method for low-pressure pulsed gas supply deposition of silicon carbide coatings provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings, characterized in that, include: The furnace body has a rotatable support inside its furnace cavity to support the workpiece; The gas distribution plate is located at the top of the furnace body and is used to evenly distribute the airflow. The gas supply circuit includes an independent precursor gas supply circuit and an inert gas supply circuit; An atmosphere switching module is installed between the gas distribution plate and the gas supply circuit to achieve alternating supply of precursor gas and inert gas. The vacuum buffer chamber is connected to the furnace cavity of the furnace body and is used to absorb pressure difference fluctuations during the gas supply switching process and maintain the reaction chamber pressure at 50-200Pa. The control unit, which is connected to the gas supply circuit, atmosphere switching module and vacuum buffer chamber, is used to perform closed-loop regulation of gas switching, pressure and flow to realize periodic pulse gas supply and purging.

2. The CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings according to claim 1, characterized in that, The precursor gas supply circuit is connected to a first flow control valve connected to the control unit to control the precursor gas supply flow rate, and the inert gas supply circuit is connected to a second flow control valve connected to the control unit to control the inert gas supply flow rate.

3. The CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings according to claim 2, characterized in that, The precursor gas supply circuit and the inert gas supply circuit are respectively connected to a first solenoid valve and a second solenoid valve, which are connected to the control unit, to switch between precursor gas supply and inert gas supply.

4. The CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings according to claim 3, characterized in that, The precursor gas supply circuit and the inert gas supply circuit are also equipped with one-way valves connected to the control unit to prevent gas mixing.

5. The CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings according to claim 4, characterized in that, The precursor gas supply circuit and the inert gas supply circuit are also connected to a bypass exhaust channel connected to the control unit to prevent pressure difference shocks during the gas switching process.

6. The CVD system for low-pressure pulsed gas supply deposition of silicon carbide coatings according to claim 5, characterized in that, The vacuum buffer chamber is connected to a pressure sensor to monitor the pressure inside the furnace chamber in real time, thereby adjusting the exhaust rate to maintain a stable flow field and constant pressure in the furnace chamber.

7. A CVD method for depositing silicon carbide coatings using low-pressure pulsed gas supply, characterized in that, The method is used to achieve the low-pressure pulsed gas supply deposition of silicon carbide coating as described in any one of claims 1-6, and specifically includes the following steps: S100, the control unit controls the vacuum buffer chamber to evacuate the furnace body to 50-200Pa and heat it to the set temperature; S200, the control unit controls the start of the precursor gas supply circuit, and the precursor gas enters the furnace cavity of the furnace body through the atmosphere switching module and the gas distribution plate, thereby depositing silicon carbide coating on the substrate pre-placed on the support. S300, the control unit controls the precursor gas supply circuit to close and the inert gas supply circuit to open to achieve gas supply switching. The inert gas enters the furnace cavity of the furnace body through the atmosphere switching module and the gas distribution plate, thereby replacing the residual gas and by-products of the precursor in the furnace cavity. S400, the control unit controls the inert gas supply to shut off and the precursor gas supply circuit to open to achieve gas supply switching; S500, repeat steps S200-S400, forming a silicon carbide coating on the substrate surface by alternating pulse gas supply and purging, while using a vacuum buffer chamber to control and maintain a constant pressure in the furnace cavity during the deposition process.

8. The CVD method for depositing silicon carbide coatings using low-pressure pulsed gas supply according to claim 7, characterized in that, The response time for the gas supply switching is no more than 0.1s.

9. The CVD method for depositing silicon carbide coatings using low-pressure pulsed gas supply according to claim 8, characterized in that, The pulse gas supply cycle time is 1-10s, wherein the control unit controls the precursor gas supply circuit to open - the precursor gas supply circuit to close - the inert gas supply circuit to open - the inert gas supply circuit to close - the precursor gas supply circuit to open, which constitutes one pulse gas supply cycle.

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