Application and advantage of RAFT polymerization in high-resolution lithography formulation

Since the invention of chemical amplified resist (CAR), the polymers in resist have been predominantly produced by free radical polymerization (FRP) with complicatedly elaborate process control, for the non-living character of reaction. Reversible addition fragmentation chain transfer (RAFT) technology provides highly controlled and living character for radical polymerization but has been overlooked in manufacture of CAR. As sizes of pattern become smaller, local variations in resist film are increasingly influential factors and need to be urgently addressed to meet further requirements of critical dimension uniformity (CDU) and line edge roughness (LER) in ArF and extreme ultraviolet (EUV) lithography. The advantages of RAFT polymerization match these demands perfectly as it can produce polymers in higher uniformity of both size and composition. On the other hand, although RAFT technique can provide polymers with high uniformity, it introduces an undesired dithio or trithio terminal group. The terminal group needs to be removed cautiously before applied in resist formulation for its weak but nontrivial instability. In this study, the heterogeneity sourced from polymerization is analyzed, resins meeting requirements of photoresist are prepared through RAFT polymerization, and the improvements of applying RAFT technique rather than FRP is discussed and evaluated.