Molecular Glass Resists for High-Resolution Patterning

Abstract

This paper describes a series of photoresists constructed from glass-forming, low-molecular-weight organic compounds, also known as molecular glasses. Compared with traditional polymeric resists, molecular glass resists are composed of smaller and more-uniform molecular building blocks. In this work, both positive-tone and negative-tone molecular glass photoresists with a range of core structures were designed and synthesized for study in advanced lithography. These molecular glass resists have asymmetric, rigid cores, which is important for producing glassy materials with glass transition temperatures substantially above room temperature. For positive-tone molecular glass photoresists, amorphous films could be obtained by partial protection of the core structure. Images were produced using photoacid-generator-catalyzed deprotection chemistry. Amorphous negative-tone resists were obtained by mixing molecular glass core structures with another minor resist component such as a photo cross-linker. It was shown by SEC that the molecular weight of the exposed and cross-linked negative-tone resist was less than 2000 g/mol, thus indicating that the solubility change is largely due to a molecular-weight increase. Both types of materials exhibited high sensitivity and resolution. Several resist characteristics were studied to assess their potential as high-resolution resists. These molecular glasses showed high fluorocarbon etch resistance that is comparable to that of poly(hydroxystyrene). Lower line edge roughness was obtained for the negative-tone molecular glass compared to a negative-tone polymeric e-beam resist. The resulting materials exhibited high sensitivity and resolution close to the tool limit under 248 nm exposures when using a chemical amplification process. A well-resolved pattern as small as 50 nm was obtained for the negative-tone molecular glass by e-beam exposure, indicating the excellent potential of using low molecular molar mass molecular glasses to form high-resolution structures.