Influence of electron-beam induced microporosity on masking properties of polymethylmethacrylate in wet etching of nanometer structures

The masking properties of nanometer scale polymethylmethacrylate (PMMA) features used for definition of sub-100-nm-wide bridges in InP/Ga0.25In0.75As two-dimensional electron gas heterostructures by wet etching were investigated. Bridges untreated after the development of PMMA showed very poor masking ability due to a substantial exposure by backward scattered electrons from the surrounding exposed areas. However, if the resist was post-baked after development at a temperature higher than the glass transition temperature, T-g, the masking properties were restored and wet etched nanobridges of a sufficient quality were obtained. The post-development bake temperature and time were optimized to provide enough resist "packing" and yet not to cause resist flowing resulting in unacceptable alteration of the pattern geometry. (C) 1997 American Vacuum Society.