Dry etch behavior of different TaN absorber layers for EUVL mask making

Abstract

Extreme Ultraviolet Lithography (EUVL) is the favourite next generation lithography candidate for IC device manufacturing with feature sizes beyond 32nm. Different absorber layers and manufacturing concepts have been published for the fabrication of reflective EUVL masks. A mandatory step in the EUVL mask making is the patterning of sub 100nm features. The layer composition of such a TaN absorber consists of an anti reflective coating (ARC) on top of a base layer. We investigated the dry etch behaviour of TaN based absorbers with four different top ARC layers. Our focus was to determine a dependency of patterning criteria e.g. etch selectivity, minimum resolution, CD uniformity and linearity on the different ARC layers. Before, the deposition parameters of the top ARC layers have been optimized by SCHOTT Lithotec towards minimum stress and the appropriate reflectance property at the 257nm inspection wavelength. The mask blank exposure was done on a 50kV Vistec SB350 MW variable shaped e-beam writer using a 300nm thick Fuji FEP171 resist film. Our test pattern covered a quality area of 132mm x 132mm and comprised dense/iso line structures and contacts from 60nm-1200nm. Testmasks with the four different TaN based absorbers have been dry etched on an Oerlikon mask etcher III. The dry etch recipe and parameters have been kept constant for the different absorber testmasks. Line and contact hole patterns with a minimum feature size of ~70nm and perpendicular profiles have been realized. CD uniformity on 180nm L&S and linearity measurements on dense and iso features from 100nm-1200nm havbe been carried out. Overall, a TaN based absorber including dry etch process has been developed, able to fulfill the requirements for IC device manufacturing with feature sizes down to 22nm - suitable for EUV-Lithography.