Extreme ultraviolet lithography mask patterning and printability studies with a Ta-based absorber

Abstract

Extreme ultraviolet (EUV) lithography masks were fabricated using a stack of TaSi or TaSiN (absorber), SiON (repair buffer), and Cr (conductive etch stop) on a Mo/Si multilayer mirror deposited on a Si wafer. High-resolution structures were exposed using a commercial i-line resist, and the pattern was transferred using both electron cyclotron resonance and reactive ion etching with halogen-based gases. Process temperatures to fabricate these reticles were always maintained below 150 °C. EUV properties after patterning were measured using a synchrotron source reflectometer. Completed masks exhibited a negligible shift in the peak wavelength and less than 2% loss in reflectivity due to processing. Qualified masks were exposed with a 10× EUV exposure system. The exposures were made in 80-nm-thick DUV resist and with numerical apertures (NA) of 0.08, 0.088, and 0.1. Resolution down to 70 nm equal lines and spaces was achieved at a NA of 0.1. Line edge roughness in the resist features was 5.5 nm (3σ, one side), and the depth of focus for ±10% CD control was ±1 μm for 100 nm equal lines and spaces.