Study of photoresist etching and roughness formation in electron-beam generated plasmas

Abstract

A modulated, electron-beam generated plasma processing system was used to study plasma-polymer interactions for 193 and 248nm photoresists (PRs) that differed significantly in polymer structure. Because of the low plasma potential of the electron-beam generated plasma, the authors were able to study plasma etching and surface roughening of the photoresists at very low ion energies (<5eV) without sacrificing high ion flux (>1014cm−2). Typical conditions in the experiments were 2kV∕4ms electron-beam pulses with a 20ms period. The effects of ion bombardment energy, chemically assisted etching using fluorine, and the presence of a thin fluorocarbon overlayer on surface roughness formation during PR etching were examined. Gas mixtures containing SF6 resulted in much higher etch rates and an increased surface roughness relative to values measured in pure Ar plasmas. However, the rms roughness per nanometer of photoresist removed was greater for pure Ar plasmas. Overall the 248nm PR showed less surface roughness than 193nm PR after identical treatments, which was explained by a higher etching rate of the 193nm photoresist material. Finally, it was found in a pure argon plasma that the thickness of a fluorocarbon overlayer determined the roughness of the underlying photoresist; specifically, thicker layers resulted in smoother PR surfaces after plasma exposure.