Multi-variable adaptive control of CF/sub 4//O/sub 2/ plasma etching of silicon nitride thin films

A two input real time feedback adaptive controller for the electron cyclotron resonance (ECR) CF/sub 4//O/sub 2/ plasma etching of plasma enhanced chemical vapor deposited (PECVD) silicon nitride thin films is designed and simulation tested. Variations in etch rate resulting from factors such as etch chamber wall seasoning which are inherent to plasma etching necessitate the use of feedback and adaptive control to achieve precise and reliable etching of ultra-thin films. In this paper, an adaptive controller is designed which maintains a constant desired etch rate by adjusting the microwave power which drives the plasma and a throttle valve which determines the pressure in the etching chamber. The controller is tested using a simulation based upon laboratory empirical data.