Application of RF sensors for real time control of inductively coupled plasma etching equipment

A radio frequency (RF) sensor has been used to monitor and characterize processes and to support real time control of deposited power in a Lam Research Corporation TCP 9600SE metal etching system. This etcher has separate power supplies for the TCP source power that generates the plasma and for the bias power at the wafer surface. The RF sensor was installed only in the bias power circuit between the matching network and the chamber. It was found that in open loop mode, where only the generator output was controlled, the efficiency of the RF system was significantly less than unity, and it varied with changes in either process or chamber hardware. These losses can be accounted for mainly by losses in the matching network and a simple relation was found between the overall efficiency and the resistance of: the load. Closed loop control based on the sensor output was found to compensate well for these effects and to give better defined and better controlled power deposition.