A simple process to fabricate self-aligned, high-performance torsional microscanners; demonstrated use in a two-dimensional scanner

CMOS-compatible process carried out on SOI wafers, we have built high-performance torsional microscanners having vertically offset interdigitated-comb actuators. Our microscanner-fabrication process requires three photolithography masks: two to form the front-side microscanner structures and a third to define the backside openings. Both moving and fixed combs are fabricated in the same device layer (30 mum in thickness), and the offset combs are created by reducing the thickness of the fixed combs, but not that of the moving combs. Our process begins by removing the 1-mum thick thermal oxide selectively to open rectangular windows at locations where the fixed combs are to be defined. In the following step, both fixed- and moving-comb sets are defined simultaneously with a single photolithography mask; this is followed by deep-reactive ion etching (DRIE). We then perform a tuned-etch in the DRIE-etcher to obtain the desired vertical thickness for the fixed combs without affecting the moving combs. The minimum gap between comb fingers can be as small as twice the alignment accuracy of the photolithography process, which is les0.4 mum for state-of-the-art photolithography steppers. We consider these microscanners as especially well adapted for applications to refractive laser surgery of ocular corneas where small spot size and high scan speeds are important assets