Synthesis and lithographic performance of poly-4-hydroxyphenyl ethyl methacrylate based negative resists

Abstract

Currently, most photosensitive coating formulations for use in 248 nm semiconductor lithography use polyhydroxy styrene resin homopolymers, and a myriad of copolymers, as the base material for positive acting resists. For negative resists, many polyhydroxy styrene homopolymer derivatives, where the pendant phenolic hydroxy has been modified, are used. This is because of the current commercial availability of the polymer material in a broad range of controlled and reproducible molecular weights, the ability to form uniform films, and the compatibility with a wide range of commonly used resist formulation organic solvents, additives and aqueous base developers. Probably the most important attribute of polyhydroxy styrene resins that led to its ubiquitous use is the lack of a competitive UV serf-absorption of this resin at 248 nm wavelengths compared to the well known novolac resins. In this paper we will describe an alternative methacrylate based polymer that contains a pendant phenolic functionality, show some initial imaging results and discuss the general advantages and disadvantages of substituting polyhydroxy styrene homopolymer resins. In particular the use of polymers based on 4-hydroxyphenyl ethyl methacrylate monomer in negative resist formulations for 248 nm (KrF) applications will be discussed.