CF A~2EPSILON~+ - X~2PI and B~2DELTA - X~2PI study by broadband absorption spectroscopy in a plasma etch reactor: Determination of transition probabilities, CF X~2PI concentrations, and gas temperatures

摘要

Broadband absorption spectroscopy was applied to study the CF A~2EPSILON~+ -X~2PI and B~2DELTA-X~2PI transitions in a plasma etch reactor. We report a previously unobserved band, which is assigned as CF A~2EPSILON~+ - X~2PI (3,0). This band is significantly broadened by predissociation, and we estimate the average collision-free lifetime of the CF A~2EPSILON~+ v' = 3 level to be 0.30 (+-) 0.08 ps. Experimental relative oscillator strength measurements, together with ab initio calculations, Rydberg-Klein-Rees-based wave functions and expeirmental lifetimes were used to calculate a full set of transition probabilities for the CF A~2EPSILON~+ - X ~2PI and B~2DELTA-x~2PI bands. The maximum observed number densities of CF X~2PI were approx 2 X 10~13 cm~(-3) with sensitivity to measure to 10~10 cm~(-3). The excited state and ground state temperatures were determined by comparing the spectra to simulations. The ground state rotational temperature was 450 (+-) 30 K and the vibrational temperature was 850 (+-) 80 K near the substrate surface. The CF B~2DELTA excited state rotational temperatures are higher than those of the ground state. We show that this absorption technique is practical for determining gas temperatures and absolute concentrations in plasma etch reactors.