Abnormal conditions within an RF-powered plasma process chamber are detected by detecting whether the frequency of a variable-frequency RF power supply moves outside established lower and upper limits. In a first aspect, a first pair of lower and upper limits are established as a function of the frequency...http://www.google.com.tw/patents/US8174400?utm_source=gb-gplus-share專利 US8174400 - Frequency monitoring to detect plasma process abnormality
