Study of 193 nm photoresist degradation during short time fluorocarbon plasma exposure III. Effect of fluorocarbon film and initial surface condition on photoresist degradation

The effect of fluorocarbon film and surface pretreatments on roughness formation of 193 nm photoresist (PR) during short time fluorocarbon plasma exposure was investigated. The present work complements two earlier reports by this group on surface modifications of 193 nm PR during plasma etching. The authors employed a shutter approach to minimize initial plasma transient effects on processing of PR surfaces. Surface chemical conditions after plasma etching were observed by x-ray photoelectron spectroscopy. The authors investigated the effect of deposited fluorocarbon film and pretreatments using several gas chemistries on PR roughening. Pretreated samples exhibited smaller roughness after plasma etching as compared to specimens processed without pretreatment. Three main mechanisms were identified for surface roughness reduction after pretreatment: (a) the formation of a fluorinated surface layer-having a large amount of fluorine on the PR surface at the beginning of the etch reduces PR surface roughening, (b) the improvement of durability of the PR under plasma exposure by removal of the ester group, and (c) a rapid fluorination and a reduction in the PR etch rate during the initial etch period due to the formation of a protective film on the top of the PR. The authors conclude from this work that the initial surface chemical state is an important factor that determines the degree of surface roughness formation for 193 nm PR during the initial etch period.