科研之友
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摘要
The extreme ultraviolet (EUV) mask using reflective optics has a structure totally different from that of the conventional mask. This study investigated the dry etching characteristics of the EUV mask layer in which TaN and Ru were used as the absorber and buffer layer, respectively. The TaN absorber etching requires high etch selectivity of TaN over Ru to achieve the high EUV reflectivity. In this work, the TaN etching rate was investigated with various halogen gases in the capacitively coupled plasma type etching system. The etching rates with the fluorinated gases were higher than that with the chlorinated gas. Ru could not be etched without oxygen in all of the considered etch gases. The etching rate of TaN and its etch selectivity to Ru were increased with the increase of RF power, pressure and SF6 gas flow ratio. When the real EUV mask specimens were 100% over etched under the highest selectivity etching condition, the Ru buffer layer still remained, which was confirmed by x-ray photoelectron spectroscopy analysis. The surface roughness of etched reflective mirror was very small, and the EUV reflectivity was equivalent to that of the reference mirror (EUV reflectivity is over 60%) which was confirmed by measuring the intensity and the diffracted pattern of 13.5 nm EUV obtained using x-ray charge coupled device camera. The Ru buffer layer could be removed by the O-2 plasma used in the posterior photo resist ashing process without affecting the EUV reflectivity.
- 出版日期2012-7
