Polymer as the protecting passivaton layer in fabricating suspended SCS structures in both anisotropic and isotropic etching

This paper presents a rapid bulk micromachining process named polymer passivation layer for suspended structures etching by using a polymer as a protecting passivation layer at both anisotropic and isotropic etching steps. Without using silicon-dioxide (SiO ₂) deposition or boron doping as a protection layer at the releasing step, the proposed method can fabricate suspended single-crystal silicon structures in an inductively coupled plasma reactive ion etching chamber directly, which would simplify the fabrication process and save fabrication time. The current study systematically investigates critical fabrication parameters to verify the feasibility of the proposed method, and discusses the polymer passivation time and removal time of a polymer at the base of a substrate at four different opening gaps of 5, 10, 30 and 50 νm with the 30 νm deep trench to establish suitable recipes for fabricating suspended microstructures. It is also shown that the proposed method can fabricate not only the suspended microstructures with the same thickness, but also suspended microstructures with different thicknesses, as well as in sub-micro scale.