Upstream pressure control increases stability and speed for vacuum deposition
Vacuum deposition setups with pressure control instruments upstream of the vacuum chamber provide faster response times and better stability, through use of a fast-acting, proportional control valve. This upstream method also eliminates the need for additional valves, which reduces the number of potential leak points in your system and minimizes the costs associated with equipment and setups.
This is in contrast to traditional vacuum deposition tools, which use downstream pressure control to maintain pressure of the gases in the vacuum chamber. This setup involves a throttle valve which can cost thousands of dollars, and requires delays when changing the gases being flowed into the chamber or while waiting for the gas in the chamber to settle. It also requires a separate control module with which to power the valve, provide PID data, and control the setpoint of the pressure controller.
Control vacuum levels upstream with Alicat PC-EXTSEN
When speccing new equipment into a setup which includes a vacuum gauge, you likely don’t want to redo your entire setup to accommodate a new piece of equipment. So what do you do if you’re looking to upgrade your legacy equipment?
Alicat’s MCE- and MCV-Series mass flow controllers are designed for drop in replacement in these instances. They meet all SEMI standards, and allow you to make the switch to differential-pressure based mass flow control of gases into your vacuum chamber.
Similarly, the PC-EXTSEN pressure controller is designed to smoothly integrate into your existing system without requiring any other design changes. This device uses an external sensor, such as the existing vacuum gauge, to control vacuum levels while mounted upstream from the vacuum chamber.
This pressure controller is most useful when the process requires high or ultra-high vacuum, necessitating the external gauge. The PC-EXTSEN takes an analog signal from the gauge and provides closed-loop control using a proportional valve. It powers the external vacuum gauge, and is compatible with all gauge technologies including ion, pirani, and cold cathode, as well as active or passive gauges and combination gauges.
Using this external pressure sensor in conjunction with the vacuum gauge allows you to most accurately maintain the vacuum chamber pressure, even while changing or adjusting the gases being flowed in. This allows for for faster application of neutral gases and overall improved system control via the steady pressure levels in the coating environment.
Eliminate the throttle valve bulk using IVC-Series integrated vacuum controllers
For setups without an existing vacuum gauge, the IVC-Series pressure controllers eliminate the need for a gauge. Similarly to the PC-EXTSEN, this device is able to cut out the bulk, complication and expense of a traditional throttle valve pressure control method.
The IVC-Series directly integrates a vacuum sensor, making it possible to control pressure in a vacuum chamber with this device immediately out of the box. The high accuracy of the sensor allows for reliable control as low as 0.01 milliTorr
An Alicat IVC-series pressure controller can also be configured with a pneumatically isolated sensor, which can be plumbed directly into your vacuum chamber. It is this sensor which provides the high accuracy of this solution, allowing for precision measurement of the vacuum chamber regardless of the composition of the flowing gas.
Conclusion: advantages of upstream pressure control
Alicat applications engineers will always recommend upstream pressure control for thin film deposition applications. Depending on the parameters of your setup and whether you are looking to design with or without an external vacuum gauge, either a PC-EXTSEN or an IVC-Series pressure controller may be advantageous. Pressure controllers with external sensors are able to integrate gauge signals directly while providing upstream control. Pressure controllers with integrated vacuum sensors are simple solutions, requiring less equipment in a setup.
In either case, placing pressure control devices upstream of the chamber in vacuum coating applications saves time and cost, and increases accuracy in vacuum deposition tools.