OPTIMIZED MICROWAVE COUPLING IN AN ELECTRON-CYCLOTRON RESONANCE ETCH TOOL

We have improved the operational characteristics of an electron cyclotron resonance (ECR) plasma etch tool by optimizing the coupling of the 2.45-GHz microwaves to the plasma. Improved coupling is achieved by using a right-hand circularly polarized (r.h.c.p.) mode which is matched to the plasma impedance through a quarter-wave transformer. This design reduces microwave reflected power typically to < 5% of the incident power without external tuning and simplifies control of the plasma etch tool operation. The r.h.c.p. mode is azimuthally symmetric when averaged over one microwave cycle and adapts easily to ECR source chambers of larger radii. We present an analytic model, the results of which are in good agreement with our experiments for microwave coupling in ECR etch tools.