Oxygen ion beam etching for pattern transfer

Abstract

Oxygen ion beam etching for resist materials has been studied. Etch rates of resists depend on oxygen pressure and on acceleration ion energy. The oxygen pressure dependence of etch rates is attributed to the effect of ion assisted neutral oxygen molecules. The neutral oxygen contribution leads to high etch selectivity for resist materials over metals; a selectivity more than 50 is obtained for AZ1350J over Au at 100 eV acceleration energy condition. The oxygen ion beam etching is applied to the pattern transfer for the multilevel resist technique. Hard baked AZ1350J, titanium, and PMMA are applied for a bottom layer, a middle layer, and a top imaging resist layer material, respectively. Under low acceleration energy conditions, an undercut profile is observed in the transferred patterns due to large ion beam divergence. At 500 eV, patterns having square cross sections are obtained. However, with the increase in gap aspect ratio (etch depth over gap width), a slight widening of etched channels at their midpoint (barrel shaped channel) is observed.