Method of and apparatus for detecting and controlling in situ cleaning time of vacuum processing chambers

摘要

The end of a cleaning process of a vacuum workpiece processing chamber evacuated to a constant pressure vacuum condition is controlled. The chamber is cleaned by exciting a cleaning gas to a plasma state by a field including an electric component. The process is terminated in response to detection of a substantial decrease in the time rate of change of pressure in a foreline of a vacuum pump evacuating the chamber after the plasma electrical impedance has been stabilized. The substantial decrease signals that the chamber is clean. A horn in the chamber that excites the gas to a plasma is indicated as being clean when the plasma electrical impedance is stable. The indication of plasma impedance stabilization is derived by monitoring horn DC bias voltage, or one or both variable reactances of a matching network connected between the horn and an r.f. excitation source for the horn.