Photoresist selectivity mechanism in SiO2 etching by inductively coupled plasma using fluorocarbon gases

The generation of large molecular species in an inductively coupled plasma using fluorocarbon gases was investigated to elucidate the selective etching mechanism of SiO2 to photoresist. In this study, the source gases C2F6, C4F8, and C5F8 were used to provide a range of fluorine-to-carbon content ratios. It was found that larger quantities and a wider variety of large-mass species are generated in C5F8 plasma than in C2F6 and C4F8 plasmas. Our results also revealed that the gas residence time was an important parameter for controlling the radical composition of the plasma. With increased residence time, the ratio of species with larger masses than the parent molecule to the sum of all product species increased in the C2F6 plasma, whereas this ratio decreased in the C4F8 and C5F8 plasmas. The ratio of larger mass species correlates apparently with the selectivity of SiO2 to photoresist etch rates. However, in any explanation of physical mechanisms, the redeposition of etching byproducts should be taken into account as well as the dependence of polymer deposition tendency on substrate materials under biased etching conditions. (C) 2002 American Vacuum Society.