Development of a probe-type optical absorption spectroscopic system for spatially resolved CF2 density measurement in inductively coupled C4F8/Ar plasmas

Abstract

A spatially resolvable optical probe is developed for the measurement of absolute CF2 radical density in inductively coupled plasmas using the broadband ultraviolet absorption spectroscopic method. The probe-type system is implemented inside a low-pressure inductively coupled plasma chamber and is built using a series of optical fibers, feedthroughs, collimators, and an ultraviolet light emitting diode. Using the CF2 A(0, v2′, 0) ← X(0, 0, 0) absorption spectra, the spatial profile of CF2 density in the remote region of an inductively coupled C4F8/Ar plasma is investigated. The CF2 density is found to decrease from 4.06 × 1013 cm-3, around the chamber center, to 2.66 × 1013 cm-3, near the chamber wall. The spatial profile of the measured CF2 density, layer thickness, and composition of deposited films are compared. Plasma properties such as electron temperature and ion density are also discussed.