ELECTRON DENSITY MEASUREMENT AND PLASMA PROCESS CONTROL SYSTEM USING A MICROWAVE OSCILLATOR LOCKED TO AN OPEN RESONATOR CONTAINING THE PLASMA

摘要

A system for measuring plasma electron densities (e.g., in the range of 10<10> to 10<12> cm<-3>) and for controlling a plasma generator (240). Measurement of the plasma density is essential if plasma-assisted processes, such depositions or etches, are to be adequately controlled using a feedback control. Both the plasma measurement method and system generate a control voltage that in turn controls the plasma generator (240) to maintain the plasma electron density at a pre-selected value. The system utilizes a frequency stabilization system to lock the frequency of a local oscillator (100) to the resonant frequency of an open microwave resonator (245) when the resonant frequency changes due to the introduction of a plasma within the open resonator. The amplified output voltage of a second microwave discriminator may be used to control a plasma generator (240).