Positive-tone processing of plasma-polymerized methylsilane (PPMS)

Abstract

Plasma polymerized methylsilane (PPMS) films exposed to UV light in the presence of air undergo photo-oxidation to produce a glass-like material, PPMSO, which can be selectively removed using aqueous HF based chemistries. We find that PPMS, used in such positive tone imaging processes, suffers from several drawbacks which make it an unattractive candidate for use as an imaging layer in positive tone resist schemes. We have used infrared and X- ray photoelectron spectroscopy to characterize the PPMS films. We have found evidence for the presence of bridging methylene groups in the Si-Si backbone of the PPMS polymer at the PPMS/Substrate interface. This thin underlayer of a polycarbosilane material is initially deposited in the PPMS CVD process and is insoluble in aqueous or vapor HF contributing to residue after the development. The limitation as to how rapidly PPMS films can be photo- oxidized in the presence of air using high-fluence laser steppers is determined by the rate of oxygen diffusion into the PPMS films during exposure. This reciprocity failure exhibited by PPMS films may limit positive tone PPMS processing from consideration in high-throughput UV based lithography.