In a thin film process system, an anti-contamination device, anti-flake shield or collimator plate, is fit to a process chamber. By maintaining a temperature differential between the chamber body and the device, or between the device and any adapter used to conform the device to the chamber apparatus, the device expands to maintain a substantially sealing press fit to the chamber body. The temperature differential can be maintained even when the process is finished until it is time to remove the device for cleaning or disposal and replacement.