A novel etch method for TaBO/TaBN EUVL masks

摘要

Etching of TaBO/TaBN absorbers on EUVL masks was studied. The self-mask strategy and etch selectivity optimization were used for obtaining the best etch CD performance. Gibbs Energy Minimization was used for determining etch gas selection and product volatility. Calculated results suggest the use of a two-step etch process, i.e. using fluorinecontaining gas to etch the antireflective (AR) layer and using chlorine-containing gas to etch the bulk absorber beneath AR. High selectivity of TaBN-to-TaBO was obtained and the AR hard mask function was proven. By using this method, one EUVL mask can be used many times by selectively exposing portions of a mask during etch. A profilometer was used for etch product characterization and etch CD results were verified by using CD SEM measurement. Optimal conditions developed on the Applied Materials Tetra Mask Etch System by using just one mask gave etch CD bias of 3 nm, etch CD uniformity of <3 nm, excellent sidewall profile, and high selectivity of absorber layer to resist and absorber to buffer layer. Etch effects on the backside chrome coating were also examined. No arcing on the backside during EUVL absorber and buffer etching was identified.