Molybdenum etching using an SF6, BCl3 and Ar based recipe for high aspect ratio MEMS device fabrication

Abstract

This paper presents the development of a dry etch recipe for molybdenum (Mo), based on SF6, BCl3 and Ar gases for high-topography MEMS device fabrication. The recipe was optimized for a high Mo etch rate, a low Mo by-product generation and a low Mo undercut using photoresist (PR) masks. The presented optimized recipe is very effective in Mo etching using a PR mask. The Mo by-product generated during the Mo etch can be easily removed using the ACT NE-14 etch residue remover. This optimized recipe was also used for etching Mo electrodes using oxide, PR or composite oxide-PR masks to select the better mask and selectivity. It was observed in this study that Mo has a better selectivity when using an oxide hard mask. However, it has the serious drawback of generating by-products which are difficult to clean later on. On the other hand, Mo has a poor selectivity with PR masks compared with oxide masks but there was no issue of by-product cleaning. At the same time, no extra mask layer deposition is required for Mo etching. The optimized recipe was also used for Mo electrode etching using PR and PR-oxide composite masks for the demonstration of working film bulk acoustic wave resonators and actuator microelectromechanical system devices.