Precise reactive ion etching of Ta absorber on X-ray masks

We investigated the reactive ion etching (RIE) of the Ta absorber on X-ray masks using a mixture of chlorine (Cl 2 ) and chloroform (CHCl 3 ) gases. To improve the pattern profiles, we used a gas mixture of chlorine (Cl 2 ) and chloroform (CHCl 3 ) which enhances deposition and protects side wall. We consistently obtained vertical side walls (90°±3°) with a Ta-to-resist etch-rate ratio (selectivity) of 7 and pattern edge roughness below 0.02 µm. The transfer accuracy was 0.00±0.04 µm (3 sigma) using 40% CHCl 3 and Cl 2 with a gas pressure of 0.2 Torr and power density of 0.8 W/cm 2 .