On the absence of post-plasma etch surface and line edge roughness in vinylpyridine resists

The authors show that poly(4-vinylpyridine) (P4VP) resist eliminates plasma-induced surface roughening for dry etch process conditions (100% Ar, 90% Ar/C4F8) that produce significant roughness in a wide variety of other polymers. In hot-embossed patterned structures, P4VP also shows no sidewall striations and line edge roughness after plasma etching, in contrast to other polymers investigated in this work. The mechanism underlying the retention of smooth surfaces for P4VP was investigated based on the observation that plasma-induced surface roughness in polystyrene (PS) has been linked to wrinkling caused by the formation of a thin, dense, ion-damaged layer. By x-ray photoelectron spectroscopy and in situ ellipsometry analysis, the authors studied two possible mechanisms that would suppress wrinkling in plasma-exposed P4VP: softening of the ion-damaged layer by nitrogen addition and stiffening of the polymer underlayer by VUV modification. While the authors report that the elastic modulus of the ion-damaged layer is reduced in Ar plasma-exposed PS when nitrogen is added to the gas discharge, the ion-damaged layer of P4VP showed no significant change relative to PS. However, by examining only the VUV radiation effect of the Ar discharge on P4VP, evidence of VUV cross-linking was observed. Mechanical stiffening of the VUV cross-linked layer is likely to suppress wrinkling in P4VP when an ion-damaged layer is formed during normal plasma exposure and explain the lack of surface and line edge roughness in the vinylpyridine material. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3607604]