Planar Laser-Induced Fluorescence of Fluorocarbon Radicals in Oxide Etch Process Plasma

Abstract

Planar laser-induced fluorescence (PLIF) has been employed to clarify the two-dimensional distribution of CF2 radicals in an inductively coupled plasma (ICP). Axial profiles and contour plots for CF2 radical density were monitored for CF4 (100%), CF4/Ar (=10%/90%) and C4F8/Ar (=10%/90%) plasmas in order to examine the roles of electron impact, fluorocarbon film deposition and ion bombardment in the production and loss mechanisms of CF2 radicals. Concave distributions which were minimal around the bulk plasma were observed for the CF4/Ar and C4F8/Ar plasmas with high electron density, demonstrating that the dominant mechanism is destruction in the bulk plasma by electron impact, rather than production on the surfaces of the substrate and chamber wall exposed to ion bombardment. Substrate biasing resulted not in the enhancement of the surface production but rather in the decrease of the CF2 density, associated with the fluorocarbon film thickness reduction due to the sputtering effect of ion bombardment.