Plasma-surface interactions of model polymers for advanced photoresists using C4F8/Ar discharges and energetic ion beams

Plasma based transfer of photoresist (PR) patterns into underlying films and substrates is basic to micro- and nanofabrication but can suffer from excessive surface and line edge roughness in the photoresist and resulting features. The authors have studied the interaction of a set of adamantyl methacrylate-based model polymers with fluorocarbon/Ar discharges and energetic Ar+ ion beams. Through systematic variation of the polymer structure, the authors were able to clarify the contributions of several critical polymer components on the chemical and morphological modifications in the plasma environment. Etching rates and surface chemical and morphological changes for the model polymers and fully formulated 193 and 248 nm photoresists were determined by ellipsometry, atomic force microscopy, time of flight static secondary ion mass spectrometry, and x-ray photoelectron spectroscopy. The polymer structure in the near surface region (similar to 10 nm) of all materials is destroyed within the first seconds of exposure to a fluorocarbon/Ar plasma. The plasma-induced changes include destruction of polymeric structure in the near surface region and oxygen and hydrogen loss along with fluorination. For the 193 nm PR material, the initial densification of the near surface region was followed by the introduction of pronounced surface roughness. This change was not seen for 248 nm PR processed under identical conditions. When comparing the responses of different polymer materials, the authors observed a strong dependence of plasma-induced surface chemical and morphological changes on polymer structure. In particular, the adamantane group of 193 nm PR showed poor stability under plasma exposure. On the other hand, the plasma-induced changes for polymer resins with or without the low molecular weight chemicals required to make the photoresist system photoactive did not differ significantly. The behavior of the same materials during energetic argon ion beam bombardment was also investigated. No significant differences in etch yield and surface roughness evolution for the different materials were seen in that case. (c) 2007 American Vacuum Society.