Deep reactive ion etching of silicon using an aluminum etching mask

A method for fast and efficient deep etching of bulk silicon, using parallel capacitively coupled plasma is presented. The effects of the masking materials and RIE conditions are discussed. Based on the experimental results, a 1000 Å thick Al film sufficiently protects the unexposed substrate while allowing the etching of a 350 μm deep hole with an area of 3×3mm² when etching with SF₆/CHF₃/O₂ plasma. A 2000 μm long and 100 μm wide (with layers of Al/SiO₂/Si and thickness of 0.1μm/2.2μm/40μm respectively) cantilever has been achieved. A silicon etch rate up to 2.5 to 2.8μm/min has been obtained and an anisotropy of A = 0.5 (A=I-V/H, where V=horizontal undercut, H=etch depth) has been obtained. The technique was developed mainly for bulk micromachining of silicon or composite silicon cantilever structures.