Precise Reactive Ion Etching of Ta Absorber on X-Ray Masks

Abstract

We investigated the reactive ion etching (RIE) of the Ta absorber on X-ray masks using a mixture of chlorine (Cl2) and chloroform (CHCl3) gases. To improve the pattern profiles, we used a gas mixture of chlorine (Cl2) and chloroform (CHCl3) 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% CHCl3 and Cl2 with a gas pressure of 0.2 Torr and power density of 0.8 W/cm2.