Etching Characteristics of α-Type Ta Film Using Cl2 Electron Cyclotron Resonance (ECR) Plasma

Ta film deposited by electron cyclotron resonance (ECR) sputtering (ECR-Ta) is a promising material for accurate X-ray masks. We investigated the characteristics of ECR-Ta etching with Cl2 ECR plasma in order to obtain vertical patterns. Etched ECR-Ta patterns show partial sloping along the pattern sidewall, which makes microfabrication difficult. By analyzing the crystal structure of the ECR-Ta film and estimating the ion bombardment effect of the etching process, the partial sloping can be attributed to a kind of orientation-dependent etching of ECR-Ta with a bcc cubic lattice. Vertical ECR-Ta patterns are obtained by using a Cl2–CF4 gas mixture in the overetching.