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/Ga0.2 5In0.75As two-dimensional electron gas heterostructures by wet etching were investigated. Bridges untreated after the development of PMMA sh owed very poor masking ability due to a substantial exposure by backwa rd scattered electrons from the surrounding exposed areas. However, if the resist was post-baked after development at a temperature higher t han the glass transition temperature, T-g, the masking properties were restored and wet etched nanobridges of a sufficient quality were obta ined. 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) 199 7 American Vacuum Society.