Laser-Based Fabrication of Micromechanical Diaphragms for Pressure Sensing using Bragg Gratings

Micromechanical devices are typically fabricated in expensive cleanrooms using techniques that are not conducive towards rapid and varied prototyping. This is typically because photolithography remains the main method for patterning of layers and should a small change be desired in the design, a new mask would have to be made, which is both a costly and slow process. This work reports a laser based approach for micromechanical diaphragm fabrication. The technique uses rapid thermal heating and subsequent quenching to a pattern a hard thermal oxide layer on a silicon substrate. This method used a computer controlled 9.3 micrometre wavelength CO2 laser beam to spot mark areas that were subsequently wet etched. This approach was found to be extremely repeatable and gave good consistency. It does not require cleanroom processing and is significantly more cost and time effective. Diaphragm feature size was observed to have a variability of <1% for diaphragms of several millimetres in size.