Submicron contact lithography for etching and lift-off applications using an i-line negative-tone photoresist with controllable slope

Abstract

We have used an i-line negative tone photoresist to define submicron masking features with contact lithography for applications in plasma etching, wet chemical processing, and liftoff. The resist used for our study is the Futurrex NR8 series. It is based on a polyhydroxystyrene resin structure rather than the polyisoprene matrix resin found in most conventional negative resists, and it uses an aqueous alkaline solution instead of an organic solvent for development. We have found this resist to be very thermally stable at relatively high temperatures, and is compatible with various plasma and wet chemical processes. Moreover, through proper selection of lithography parameters, the resist profile can be tailored to accurately obtain positive, vertical or negatively sloped sidewalls for specific applications. We have established liftoff processes of numerous kinds of evaporated and sputtered metals and oxides using the unique profile-controlling property of this resist. We present SEM images and data from a study of the effects of lithography parameters on resist profiles. Also included is the fabrication sequence of a submicron single layer selfaligned liftoff process using the NR8 resist. These results suggest potential applications in a wide variety of processes.