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

Abstract

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 (C4F8/O2/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.

Phase-shift effect in capacitively coupled plasmas with two radio frequency or very high frequency sources

“…18, the observed profile with the phase shift is somewhat counterintuitive. 18, the observed profile with the phase shift is somewhat counterintuitive.…”

“…13 By applying graded conductivity electrodes, it also can improve the plasma uniformity significantly in VHF discharges. In the simulations 15 and experiments, [16][17][18] it was found that by controlling the phase difference between two sources, the radial uniformity of plasma can be improved greatly. [15][16][17][18] In this way, two electrical sources are applied to the top and bottom electrodes with the same frequency.…”

“…12 Recently, it was found that by mixing of 180 and 60 MHz powers, the uniform plasma density can be obtained. [15][16][17][18] In this way, two electrical sources are applied to the top and bottom electrodes with the same frequency. 14 Another method for improving the radial uniformity of plasma density in VHF discharges is using the phase-shift control in a triode CCP reactor.…”

Comparison of electrostatic and electromagnetic simulations for very high frequency plasmas

“…Recently, Ahn and Chang 27 revealed, by means of a Langmuir probe and a B-dot probe, that the strong plasma inhomogeneity, detected in a cylindrical high frequency capacitive discharge at high pressures, was created by the significant inductive electric field near the radial edge. Moreover, Sung et al [28][29][30] verified experimentally that the plasma nonuniformity could be suppressed by controlling the phase shift between the VHF voltages.…”

“…In recent years, several theoretical studies [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and experimental research [22][23][24][25][26][27][28][29][30] have been published on the plasma characteristics in a CCP sustained by VHF sources. Lieberman et al 6 first employed a uniform slab model to investigate the standing-wave and skin effects in VHF discharges.…”