Effect of the radio-frequency voltage phase in a balanced triode plasma etching reactor

Abstract

The effect of the relative electrical phase applied to the two driven electrodes of a rf excited (13.56 MHz) triode plasma reactor has been investigated. Langmuir probe measurements, visible light emission, external voltage measurements, and CF4 and SF6/O2 etching of silicon were used to characterize the plasma formed by exciting the electrodes in phase and 180° out of phase. In-phase excitation does not result in the formation of a plasma between the plates. For 180° out-of-phase excitation, a plasma is formed and the intense glow regions observed next to their respective electrodes appear to originate from a region between the sheath and the plasma. The plasma potential, ion energy, and electron energy are strongly affected by phase. These initial results indicate the critical importance of the phase angle in determining the fundamental plasma parameters in triode plasma etchers and deposition reactors.