Atomic layer deposition enhanced rapid dry fabrication of micromechanical devices with cryogenic deep reactive ion etching

A fast, dry microfabrication process combining atomic layer deposition, electron beam lithography and cryogenic deep reactive ion etching is presented. The process exploits the extremely high selectivity of atomic layer deposited amorphous Al2O3 (alumina) to silicon in cryogenic etching by using an ultra-thin (t < = 5nm) Al2O3 film as a mask. The process rules and limitations are carefully analyzed and a thorough understanding of the limiting factors is reached, and the effect of the limitations on the critical output current of a dc-biased clamped-clamped beam is studied. To test the process, multiresonant tuning fork resonators are fabricated and found to exhibit Q 8000 at fr 11.4 MHz. Both values are the highest reported for resonators fabricated with the dry process and comparable with values achieved with existing silicon micromachining processes.