Fabrication of amorphous carbon cantilever structures by isotropic and anisotropic wet etching methods

Free-standing amorphous carbon (a-C) cantilever structures were successfully fabricated by a single photolithography step. The relatively thick (∼1 μm), smooth ( Rrms∼0.75 nm), low stress (<300 MPa) a-C films that exhibit low friction (<∼0.08) and wear rate (order of 10-9 mm3/Nm) were deposited by filtered cathodic vacuum arc (FCVA) deposition system, in conjunction with high substrate pulse biasing (5 kV, 600 Hz and 25 μs). The undercutting of the cantilever was carried out, both by isotropic (in a solution mixture of 40% HF (1 part) and 70% HNO3 (3 parts)) as well as anisotropic (in 40 wt.% KOH) Si wet etching methods. The study reveals that it is not viable to fabricate perfect free-standing a-C cantilever structure by isotropic wet etching. However, by controlling the etching duration/rate, it is possible to fabricate the as-designed free-standing cantilever structures by anisotropic wet etching method. The SEM images of the free-standing a-C cantilever structures do not show any bulging, and which clearly shows that the intrinsic stress in the film is low enough to be used for the fabrication of micro-electro-mechanical system (MEMS) devices, such as micro-motors and gears.