Deep reactive ion etching of silicon using an aluminum etching mask

A method for fast and efficient deep anisotropic etching of bulk silicon, using a parallel capacitively coupled plasma is presented. The effect of the masking materials and RIE conditions are discussed. Based on the experimental results, a 1000 angstrom thick Al film sufficiently protects the unexposed substrate while allowing the etching of a 350mm deep hole with an area of 3x3mm2 when etching with SF₆ /CHF₃/O₂ plasma. A 2000mm long and 100mm wide (with layers of Al/SiO2/Si and thicknesses of 0.1mm/2.2mm/40mm respectively) cantilever is also achieved. A silicon etch rate up to 2.2 mm/min has be obtained and an anisotropy of A= 0.5 (A=1-V/H, where V=horizontal undercut, H=etch depth) has been observed. The technique was developed mainly for bulk micromachining of silicon or composite silicon cantilever structures.