TANTALUM DRY-ETCHING CHARACTERISTICS FOR X-RAY MASK FABRICATION

Directional dry etching of Tantalum is described X-ray lithography mas k absorber patterns. Experiments are carried out using both reactive i on etching in CBrFs-based plasma and electron-cyclotron-resonance ion- stream etching in Cl2-based plasma. Ta absorber patterns with perpendi cular sidewalls cannot be obtained by RIE when only CBrF3 gas is used as the etchant. While adding CH4 to CBrF3 effectively improves the und ercutting of Ta patterns, it deteriorates etching stability because of the intensive deposition effect of CH4 fractions. By adding an Ar/CH4 mixture gas to CBrF3, it is possible to use RIE to fabricate 0.2-mum Ta absorber patterns with perpendicular sidewalls. ECR ion-stream etch ing is investigated to obtain high etching selectivity between Ta and SiO2 (etching mask) / SiN (membrane). Adding O2 to the Cl2 etchant imp roves undercutting without remarkably decreasing etching selectivity. Furthermore, an ECR ion-stream etching method is developed to stably e tch Ta absorber patterns finer than 0.2 mum. This is successfully appl ied to X-ray lithography mask fabrication for LSI test devices.