Comparison of Al and Cu masks used for patterning boron-doped diamonds in oxygen plasma

Abstract

In this paper we investigate the influence of different metallic (or metal-based) masking materials and plasma techniques on the etching and patterning of polycrystalline boron-doped diamond (BDD) thin films. Lift-off technique was used to prepare various testing mask patterns with dimensions ranging from 1 µm. The results of plasma etching utilizing 100 nm Al and Cu masks are compared. Radio frequency (RF) and Inductively coupled (ICP) pure oxygen plasma techniques were used to obtain the fine etched structures. A simple etching scheme describing the obtained results is presented for each type of the plasma technique and mask type. Although Al mask is widely believed to have outstanding properties over another metallic materials, we have found that the Cu mask exhibits lower side edge etching for the both types of plasma techniques. A formation of thick and crystalline copper oxide layer in contrast with thin amorphous aluminum oxide is believed to be the reason for this behavior. Consequently, the etched structures possessed also a much better side walls angle which is a key parameter e.g. for micro-fabrication of boron doped diamond microelectrodes, microfluidics, sensors and microelectromechanical devices in general.