Ultra-nanocrystalline diamond (UNCD) is a very promising candidate for microelectromechanical system moving mechanicalassemblies (MEMS MMAs) due to its excellent mechanical and tribological properties. In order to fabricate UNCD-basedMEMS MMAs, it is important to find the mask material suitable for micromachining process. The etch characteristics ofUNCD and selected mask materials (Ni, Al and SiO2) were examined in O2/Ar, O2/CF4 and O2/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 ~140 : 1 for UNCD over Ni was obtained in10O2/5Ar ICP discharges. The Al and SiO2 mask layers presented relatively good etch selectivities in 10O2/5Ar 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 10O2/5CF4 and 10O2/5SF6 discharges, the Al mask showed relatively low etch selectivities of ~ 5 : 1 while the SiO2 showed etchselectivities less than unity due to the extremely high volatility of SiFx etch products.

Keywords: Ultrananocrystalline diamond, Micromachining, High density plasma etching, Mask material, Etch selectivity