Surface kinetics with low ion energy bombardment in fluorocarbon plasmas

Abstract

This paper examines the complex nature of highly polymerizing fluorocarbon plasmas. An inductively coupled modified GEC reference cell is used to look at process rates on SiO2, p-Si and Si3N4 samples using various chamber geometries and gas chemistries. In an attempt to understand the process rates, a simple model based on the sticking and etch yield coefficients of radicals and ions is employed. Development of the model requires knowledge of radical flux, ion flux, ion energy and related process rates. These values are determined using in situ spectroscopic ellipsometry, in situ optical emission spectroscopy, in situ Fourier transform infrared spectroscopy and chuck self-bias measurements. Through the use of a variable electrode gap and changing feed gas chemistry, sticking radical densities are controlled almost independently of ions and etching radical densities. This control allows a partial deconvolution of the process rate equation. Estimated values for the upper bound sticking coefficients of fluorocarbon radicals are made. Additionally, values are reported for ion sticking coefficients and the fluorine etch yield coefficient. These values are then used in a basic low ion energy model to compare with experimental process rates.