|
GENERAL PROCESS - REF. #GP014 | View PDF
THE CHALLENGE
Precise control of vacuum pressure is critical in certain applications, particularly those involving thin film coating, to ensure even deposition and eliminate waste and rework. The coating process starts by pumping down the process chamber through a throttle valve. After the initial pump down is complete, operators will often use the same throttle valve to adjust and manage incremental variations in chamber pressure. In some cases these throttle valves are manually adjusted, making it a labor-intensive and relatively inaccurate method. In other cases, the valves are automatically controlled, but they tend to be very slow reacting. Even slight pressure fluctuations can affect process quality and product yield.
Most vacuum coating systems employ a mass flow controller to control the flow of gas into the process chamber. This gas is used to form a plasma, or to promote a surface reaction with the coating material.
THE BROOKS SOLUTION
Most systems already have a capacitance manometer pressure sensor on the process chamber. A Brooks Model RT downstream pressure controller can replace the thermal mass flow controller normally installed on the inlet side of the chamber. The pressure sensor signal would feed back to the RT to form a closed loop PID pressure control loop, without the need for external PID control. The necessary PID adjustments are accessible on the RT.
When a set point is provided, the RT will regulate the gas flow into the chamber to maintain the desired pressure.
After initial pump down, the throttle valve on the output side is adjusted to achieve the desired flow of gas into the chamber, at the desired pressure. The RT then self-corrects minute variations in chamber pressure automatically.
The Model RT not only functions as a precise pressure control device, it reports the actual mass flow while regulating the pressure. It can be easily configured as a mass flow controller, for calibration or test purposes. This arrangement can significantly reduce setup time, improve process quality and yield, and eliminate waste and rework.
BROOKS PRODUCTS
When liquid precursors are used, the QUANTIM Vaporizer liquid delivery system, shown in the above illustration, delivers pure vapor to achieve perfect, repeatable films. The Brooks model 5866RT downstream pressure controller is one of several products suitable for this application. The table below highlights a variety of model configurations and performance options. Please see Brooks specification sheets for more detailed information.
 |
|
|
