Fundamental understanding of exposure and process chemistry of Sn-based metal oxide resists: effects of ambient environment during post-exposure delay and bake

Abstract

Metal oxide resists (MORs) have shown great promise for high-resolution patterning in extreme ultraviolet (EUV) lithography, with potential for integration into high-volume manufacturing. However, MORs have recently been shown to exhibit sensitivity to process conditions and environment, leading to critical dimension (CD) variation. Although this variation can be reduced with proper process control, there is a current lack of fundamental knowledge on how these aspects affect the pattern formation mechanism. Moreover, the diverse composition of atmospheric environments makes it difficult to disentangle the role of individual atmospheric components on the lithographic performance of this promising class of EUV photoresists. To bridge these knowledge gaps, we deploy a coordinated, fundamentals-focused approach to yield deep insights into MOR exposure and process chemistry. Our results on a model MOR, an n-butyl Sn-Ox system, reveal how parameters such as exposure dose, post-exposure bake (PEB) temperature, and atmospheric environment influence the EUV exposure and post-exposure delay (PED) and PEB mechanisms. Using an advanced toolset, we show that EUV-induced ligand cleavage likely occurs via homolytic Sn–C bond breaking, resulting in a Sn-based radical “active site,” which serves as a reactive center that endows MOR materials with their sensitivity to atmospheric components (e.g., H2O and O2) during PED and PEB. We resolve the roles of H2O during PED and PEB, and in particular, we show that PEB environments containing O2 exhibit increased litho performance (reduced dose and improved development contrast), suggesting that O2 plays a critical role in the exposure and thermal mechanisms of MOR materials. Our results, and the coordinated approach using correlative spectroscopies, provide a strong foundation for understanding the critical EUV exposure and PED and PEB mechanisms in MOR materials, provide insights into potential optimization routes via environmental control during the process, and finally offer the potential to link mechanistic aspects and MOR lithographic performance and stability.