ABSTRACT A high resolution trilayer resist system based on the copolymer e-beam resist P[MMA/MAA], an SiC>2 interlayer, and a polyimide base layer will be described. High resolution reactive ion etch processes have been developed that minimize base layer undercut and provide for cleanly patterned windows for 150 nm thick aluminum lift-off. Residue formation on the base layer sidewalls after reactive ion etching has been found to depend on the substrate film composition. Linewidth variations as a function of exposure dose, development time, and reactive ion etch conditions will be discussed. The extent to which trilayer stencils can be used for high resolution reversal processes has been found to be limited by the polyimide thickness required for planarization and proximity effect reduction, aluminum film thickness required, and the minimum line space desired. 1. INTRODUCTION Trilayer resist systems have beenbeen employed for the last decade for the advantages theseapproaches lend to photolithography 1~5/ electron beam lithography6, and X-ray lithography1. The trilayer structure moves the imaging layer away from the substrate by placing this layer on top of a thin interlayer and thick base layer. Base layers of PMMA and photoresists have been the most popular choices, but both have low glass transition temperatures. A low glass transition temperature may be a problem if excessive radiative substrate heating occurs during film deposition. Polyimides typically have high glass transition temperatures (approximately 320°C) and are not affected by most deposition processes. Unfortunately, polyimides do not planarize as well as PMMA or photoresist7. Polyimide was chosen as a base layer in this work for its high temperature stability. The interlayer of the trilayer system must be readily etched by dry processes and easy to deposit. The interlayer's primary purpose is to eliminate the interactions between the image layer and the polyimide base layer and to provide a sharp discontinuity or lip for reliable lift-off**. Many materials have been used; these include Cr9, Ge6, Si10, and SiO23. Silicon dioxide was chosen as an interlayer for its high temperature stability and ease of deposition and etching.One of the major drawbacks to employing electron beam lithography in VLSI is the technique's low throughput. The low throughput stems from many factors; apart from the serial nature of the exposure, one primary contributor is the low sensitivity of the resists available. Polymethylmethacrylate (PMMA) has typically been the choice for high resolution patterning. However, its sensitivity at 100 uC/cm2 is far too low. Copolymers of methylmethacrylate and methacrylic acid P[MMA/MAA] with sensitivities approaching 20 jiC/cm2 have been used in various bilayer and trilayer schemes11. The copolymer P[MMA/MAA] was chosen for this application as an imaging layer to increase the electron beam system throughput.