Experimental study of plasma non-uniformities and the effect of phase-shift control in a very high frequency capacitive discharge

Plasma spatial non-uniformities were studied experimentally in a very high frequency (100 MHz) capacitive triode-type reactor used for etching of 300 mm wafers. It has been shown that in the traditional mode of operation there is considerable plasma non-uniformity due to the electromagnetic effects, namely at a low power, the plasma density profile is determined by the standing-wave effect, while at a high power the skin effect dominates. The influence of phase-shift control on plasma uniformity was examined. Phase-shift control means applying to the top and the bottom electrodes very high frequency voltages with a controlled phase shift between them. The experiments were carried out in process (C 4 F 8 /O 2 /Ar) plasma in a wide range of pressures and powers. It has been shown that the phase-shift control can considerably improve the plasma uniformity under a wide range of experimental conditions.