SiO 2 buffer-etch processes with a TaN absorber for EUV mask fabrication

Abstract

Extreme Ultraviolet Lithography (EUVL) is the favourite next generation lithography candidate for IC device manufacturing with feature sizes beyond 32nm. The SiO₂ buffer dry etching is a crucial step in the manufacture of the EUV mask due to stringent CD and reflectance requirements. In contrast to conventional chromium absorber layers new absorber materials e.g. TaN require an adjustment of the SiO₂ buffer etch chemistry and process parameters to avoid a strong influence on the initial absorber profile and thickness. We have developed a SiO₂ buffer dry etch process that uses the structured TaN absorber as masking layer. A laser reflectometer was used during the SiO₂ dry etch process for process control and endpoint detection. Different dry etch processes with SF₆/He, CF₄ and CHF₃/O₂ etch chemistry have been evaluated and compared with regard to TaN- and SiO_2- etch rate, TaN- and SiO₂ etch profile and Si capping layer selectivity. We focused our work on minimum feature sizes and simultaneous etching of different line (e.g. dense- and isolated lines) and hole patterns. Line and contact hole structures with feature sizes down to 100nm have been realized and characterized in a SEM LEO 1560. The whole mask patterning process was executed on an advanced tool set comprising of a Leica SB 350 variable shaped e-beam writer, a blank coater Steag HamaTech ASR5000, a developer Steag HamaTech ASP5000 and a two chamber UNAXIS mask etcher III.