2022.03.21
Application of digital control valve in Precision Control of Vacuum Pressure in MOCVD Process
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Application of digital control valve in Precision Control of Vacuum Pressure in MOCVD Process
Abstract: Focusing on problems existing in vacuum pressure control in the current MOCVD equipment and process, such as most equipment can only use the downstream control mode, the response speed of throttling valve is not enough; the corrosion resistance of throttling valve and the acquisition accuracy of pressure controller are not high. This article proposes corresponding solutions to improve MOCVD equipment and improve process and product quality.
1. Question
In semiconductor industry, MOCVD has many remarkable features. It can be used for large area growth, can precisely control composition and thickness, has high repeatability and growth rate, can cover complex substrate shapes, can quickly switch gas paths to prepare steep multi-layer interfaces, suitable for original annealing, etc. However, in the development and process commissioning of MOCVD equipment, it is necessary to research and select production-related growth parameters, including reaction chamber shape, working pressure, growth temperature, base rotational speed, gas flow rate, and inlet temperature.
The working pressure of MOCVD is generally in the range of 10 mtorr-500 torr. The precise control of working pressure determines the flow stability of reaction chamber, but there are still the following problems in the current vacuum pressure control:
(1) As shown in Figure 1, the current MOCVD equipment basically uses the downstream mode to control working pressure, that is, install throttling valve at exhaust end to adjust the exhaust flow to reach pressure control in the reaction chamber, but this is only applicable to processes with higher pressure, such as working pressure range of 100~500torr. However, for the low pressure requirements of some processes, adopting downstream control mode will cause large fluctuations in working pressure, which cannot be accurately controlled, thereby affecting product quality. For the precise control of low working pressure, it is best to use upstream control mode, that is, to control flow at inlet end to stabilize pressure of the reaction chamber.
(2) The MOCVD process is always with temperature changes, and temperature changes will seriously affect the stability and controllability of working pressure. Thus, it is required to reach accurate control of working pressure during temperature changing process, which requires air intake and exhaust. This requires that response speed of air intake and exhaust control valves is as fast as possible, and control valve should be controlled within 5 seconds from fully open to fully closed, preferably within 1 second.
(3) Some MOCVD working gases are corrosive, and corresponding valves may have strong corrosion resistance to improve continuous and normal operation of the equipment.
(4) At present, most of the controls use PLC modules, but very few PIC controllers can reach 24-bit analog-to-digital conversion accuracy. For the precise control of working pressure, it is recommended to use a 24-bit precision PID controller to apply completely to the high-precision measurement advantages of capacitive pressure sensors. Using KaoLu’s pneumatic proportional valve is also the best choice for customers.
This article will focus on corresponding solutions for the above problems existing in the current MOCVD equipment and processes.
For further information, please visit https://www.genndih.com/proportional-flow-control-valve/mid-flow-proportional-valve-0-130L-min.html
2. Pressure Precision Control Scheme
Within the working pressure range of MOCVD, it is generally required that the working pressure in the reaction chamber can be accurately controlled and can stay constant at any set point within a certain range. In order to meet the precise control of different pressure ranges of low and high pressure, the proposed pressure control scheme is to add an upstream control mode to the original downstream control mode. The structure of vacuum pressure control system is shown in Figure 2, and the details are as follows:
(1) Install KaoLu’s FC series pneumatic proportional valve driven by a stepper motor at air inlet and exhaust port of reaction chamber, respectively. The pneumatic proportional valve is directly installed at air inlet, and pneumatic proportional valve is installed between the exhaust port and the vacuum pump. For MOCVD equipment, an air cell can be added to mix the incoming working gas in proportion and then enter the reaction chamber through pneumatic proportional valve. When the control is performed under high pressure, the opening of pneumatic proportional valve can be fixed, and only the downstream pneumatic proportional valve can be adjusted; when the control is performed under low pressure, the opening of pneumatic proportional valve can be fixed, and only the upstream pneumatic proportional valve can be adjusted. This can meet the needs of different pressure control. (2) Both pneumatic proportional valve and electronic needle valve have high-speed throttling valves. The response time of pneumatic proportional valve is 0.8 seconds. The electronic needle valve has two response speed models, 5 seconds and 1 second. The valve body of pneumatic proportional valve and electronic needle valve is made of stainless steel, and the seal is made of FFKM perfluoroether rubber, which has super corrosion resistance and can be used for various corrosive gases and liquids.
(3) In MOCVD, a capacitance pressure gauge with a range of 1000torr or 10torr is generally used for pressure measurement, and its accuracy can reach ±0.2%. A vacuum pressure sensor with a higher accuracy of ±0.05% can also be used for measurement. Therefore, a dedicated 24-bit A/D acquisition high-precision PID vacuum pressure controller is used in scheme to match the measurement accuracy of high-precision capacitive pressure sensor and ensure the control accuracy.
In summary, through the implementation of above scheme, pressure fluctuation can be controlled within ±1% in the entire vacuum pressure range, and pressure can be quickly and constant in response to temperature change of reaction chamber, while the corrosion-resistant seal will greatly increase the life of valve. Therefore, KaoLu’s pneumatic proportional valve is the great choice for you!
Abstract: Focusing on problems existing in vacuum pressure control in the current MOCVD equipment and process, such as most equipment can only use the downstream control mode, the response speed of throttling valve is not enough; the corrosion resistance of throttling valve and the acquisition accuracy of pressure controller are not high. This article proposes corresponding solutions to improve MOCVD equipment and improve process and product quality.
1. Question
In semiconductor industry, MOCVD has many remarkable features. It can be used for large area growth, can precisely control composition and thickness, has high repeatability and growth rate, can cover complex substrate shapes, can quickly switch gas paths to prepare steep multi-layer interfaces, suitable for original annealing, etc. However, in the development and process commissioning of MOCVD equipment, it is necessary to research and select production-related growth parameters, including reaction chamber shape, working pressure, growth temperature, base rotational speed, gas flow rate, and inlet temperature.
The working pressure of MOCVD is generally in the range of 10 mtorr-500 torr. The precise control of working pressure determines the flow stability of reaction chamber, but there are still the following problems in the current vacuum pressure control:
(1) As shown in Figure 1, the current MOCVD equipment basically uses the downstream mode to control working pressure, that is, install throttling valve at exhaust end to adjust the exhaust flow to reach pressure control in the reaction chamber, but this is only applicable to processes with higher pressure, such as working pressure range of 100~500torr. However, for the low pressure requirements of some processes, adopting downstream control mode will cause large fluctuations in working pressure, which cannot be accurately controlled, thereby affecting product quality. For the precise control of low working pressure, it is best to use upstream control mode, that is, to control flow at inlet end to stabilize pressure of the reaction chamber.
(2) The MOCVD process is always with temperature changes, and temperature changes will seriously affect the stability and controllability of working pressure. Thus, it is required to reach accurate control of working pressure during temperature changing process, which requires air intake and exhaust. This requires that response speed of air intake and exhaust control valves is as fast as possible, and control valve should be controlled within 5 seconds from fully open to fully closed, preferably within 1 second.
(3) Some MOCVD working gases are corrosive, and corresponding valves may have strong corrosion resistance to improve continuous and normal operation of the equipment.
(4) At present, most of the controls use PLC modules, but very few PIC controllers can reach 24-bit analog-to-digital conversion accuracy. For the precise control of working pressure, it is recommended to use a 24-bit precision PID controller to apply completely to the high-precision measurement advantages of capacitive pressure sensors. Using KaoLu’s pneumatic proportional valve is also the best choice for customers.
This article will focus on corresponding solutions for the above problems existing in the current MOCVD equipment and processes.
For further information, please visit https://www.genndih.com/proportional-flow-control-valve/mid-flow-proportional-valve-0-130L-min.html
2. Pressure Precision Control Scheme
Within the working pressure range of MOCVD, it is generally required that the working pressure in the reaction chamber can be accurately controlled and can stay constant at any set point within a certain range. In order to meet the precise control of different pressure ranges of low and high pressure, the proposed pressure control scheme is to add an upstream control mode to the original downstream control mode. The structure of vacuum pressure control system is shown in Figure 2, and the details are as follows:
(1) Install KaoLu’s FC series pneumatic proportional valve driven by a stepper motor at air inlet and exhaust port of reaction chamber, respectively. The pneumatic proportional valve is directly installed at air inlet, and pneumatic proportional valve is installed between the exhaust port and the vacuum pump. For MOCVD equipment, an air cell can be added to mix the incoming working gas in proportion and then enter the reaction chamber through pneumatic proportional valve. When the control is performed under high pressure, the opening of pneumatic proportional valve can be fixed, and only the downstream pneumatic proportional valve can be adjusted; when the control is performed under low pressure, the opening of pneumatic proportional valve can be fixed, and only the upstream pneumatic proportional valve can be adjusted. This can meet the needs of different pressure control. (2) Both pneumatic proportional valve and electronic needle valve have high-speed throttling valves. The response time of pneumatic proportional valve is 0.8 seconds. The electronic needle valve has two response speed models, 5 seconds and 1 second. The valve body of pneumatic proportional valve and electronic needle valve is made of stainless steel, and the seal is made of FFKM perfluoroether rubber, which has super corrosion resistance and can be used for various corrosive gases and liquids.
(3) In MOCVD, a capacitance pressure gauge with a range of 1000torr or 10torr is generally used for pressure measurement, and its accuracy can reach ±0.2%. A vacuum pressure sensor with a higher accuracy of ±0.05% can also be used for measurement. Therefore, a dedicated 24-bit A/D acquisition high-precision PID vacuum pressure controller is used in scheme to match the measurement accuracy of high-precision capacitive pressure sensor and ensure the control accuracy.
In summary, through the implementation of above scheme, pressure fluctuation can be controlled within ±1% in the entire vacuum pressure range, and pressure can be quickly and constant in response to temperature change of reaction chamber, while the corrosion-resistant seal will greatly increase the life of valve. Therefore, KaoLu’s pneumatic proportional valve is the great choice for you!