UV nanosecond laser machining and characterization for SiC MEMS sensor application

In this paper, we design a symmetric quad-beam accelerometer structure for z-axis sensing. Considering the extremely high chemical stability of SiC, traditional dry etching is not suitable for machining SiC MEMS sensor. Thus, we put forward a method using ultraviolet laser cutting to release cantilever beam of SiC accelerometer and using laser ablating to process mass. Pulse Repetition Frequency (PRF) and processing laps are optimized to obtain high-quality surface morphology and much less thermal effect. Finally, we use the optimal parameters with 35 kHz pulse frequency, 4 processing laps, 200 mm/s scanning speed to process through-hole. Combing with Raman spectrum and EDS spectrum, the feasibility of laser machining SiC sensor is studied. The result shows that in machining cantilever beam the carbonization and generation of silicon accelerates the trepanning depth of SiC. However, in machining the hole, the thermal effect of photon energy barely adds influence on region from boundary of hole to 30 μm. Thus, it is feasible to use laser cutting to release cantilever beam while it is difficult to use laser ablating processing back cavity of accelerometer. The time of laser micromachining 4 H-SiC cantilever beam is less than 2 s. Compared with the traditional ICP etching (0.2-1.3 μm/min), etching rate with laser ablating in releasing cantilever beam significantly increases nowadays. Finally, the sensitivity of SiC accelerometer is measured to 0.644 μV/g.