Improvement in gate LWR with plasma curing of ArF photoresists

The line width roughness (LWR) in gate electrodes is one of the most critical issues in obtaining sufficient transistor performance in 45-nm half-pitch (hp 45) node devices. ArF (argon fluoride) photoresists are, however, very fragile and easily deformed during plasma exposure. We evaluated the change in the chemical nature of an ArF photoresist caused by various plasmas and found that “HBr plasma curing” induces the selective detachment of heterocyclic units in the photoresist. We found that the glass transition temperature (Tg) of the photoresist decreased due to this detachment, leading to surface smoothening of the photoresist layer. Finally, we applied this curing process to the fabrication of line patterns and it was demonstrated that the process remarkably improved LWR.