Uniform low stress oxynitride films for application as hardmasks on x-ray masks

A low stress silicon oxynitride deposition process has been developed in which the average stress level can be tailored by adjusting silane flow in the plasma enhanced chemical vapor deposition reactor. Stress gradients, as might be caused by nonuniform heating or gas distribution, were not found to exist. By volume, the SiON films were found to be approximately 81% silicon dioxide and 19% silicon nitride. Because the films are easily removed in hydrofluoric acid, this composition is ideally suited for use as a hardmask patterning layer on x-ray masks. A reactive ion etch process employing CHF3, O-2, and Ar gases has demonstrated selectivity to Shipley SNR 200 resist of better than 3:1. Smooth pattern transfer into TaSi and TaSiN absorber layers of test features as small as 0.1 mu m has been achieved using SiON as the hardmask layer. Image placement distortions on the order of 15 nm (3 sigma) occur from etching the SiON films on 64 Mbit SRAM x-ray test masks. (C) 1997 American Vacuum Society.