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

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, v_2′, 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.