A fundamental study on dissolution behavior of high-resolution molecular glass photoresists

Abstract

Understanding the dissolution behavior of photoresist materials is an important step in being able to control their lithographic performance. In this paper, we present a fundamental study of dissolution behavior of a new type of photoresist based on molecular glasses (MGs). This study focuses on MG resists derived from a phenolic functionality similar to poly(4-hydroxystyrene), but designed with different types of branched and ring architecture that grant amorphous character. The work describes the unique dissolution behavior of MGs in aqueous base developer and evaluates the effect of molecular structure on their dissolution properties. In this study, we compare the dissolution behavior of two types of positive tone MG resists, ring and branched architectures. We have monitored their dissolution as deprotection takes place converting the resist materials from base insoluble to base soluble. The protection level of each MG system is probed in detail to identify where the solubility switch occurs and to understand the structural effects that govern swelling and dissolution behavior. We have found that the hydrophobic nature of the resist film surface causes severe swelling before dissolution in branched MGs. But the increase in hydrophilicity of the ring MG system is identified as the main reason for its smooth transition from insoluble to soluble in aqueous developer without swelling and with improved resist contrast. The effect of processing conditions such as post exposure bake (PEB) temperature and developer concentration have been evaluated as a means of controlling the swelling behavior in branched MG resists. © 2008 American Chemical Society.