Etch selectivities of mask materials for micromachining of ultrananocrystalline diamond film

Ultra-nanocrystalline diamond (UNCD) is a very promising candidate for microelectromechanical system moving mechanical assemblies (MEMS MMAs) due to its excellent mechanical and tribological properties. In order to fabricate UNCD-based MEMS MMAs, it is important to find the mask material suitable for micromachining process. The etch characteristics of UNCD and selected mask materials (Ni, Al and SiO2) were examined in O-2/Ar, O-2/CF4 and O-2/SF6 inductively coupled plasmas, and the etch selectivities of the mask materials were compared. The Ni showed very high etch selectivities to UNCD (>= 50 : 1) in all three oxygen-based ICP discharges and the maximum etch selectivity of similar to 140 : 1 for UNCD over Ni was obtained in 10O(2)/5Ar ICP discharges. The Al and SiO2 mask layers presented relatively good etch selectivities in 10O(2)/5Ar ICP discharges, 6.3-28.3 : 1 for UNCD over Al and 4-20 : 1 for UNCD over SiO2, respectively. Under most of the conditions examined in 10O(2)/ 5CF4 and 10O(2)/5SF6 discharges, the Al mask showed relatively low etch selectivities of similar to 5 : 1 while the SiO2 showed etch selectivities less than unity due to the extremely high volatility of SiFx etch products.