Femtosecond pulsed laser processing of thin films for MEMS devices

Microfabrication of MEMS devices involving deposition and surface micromachining of thin films is becoming an increasingly complex process due to the multi-layers and difficult-to-etch materials. Laser microfabrication is an excellent alternative to the traditional wet and dry chemical etching techniques especially for chemically resistant materials. In this work, a 120-fs pulsed, 800-nm wavelength Ti: Sapphire laser was used for micromachining thin films of ultra-hard AlMgB₁₄ and polysilicon thin films on silicon substrate. Polysilicon was first deposited by low-pressure chemical vapor deposition followed by boride using femtosecond pulsed laser deposition. Channels were then machined in thin films to pattern a device that would produce a linear resistance/deflection curve. Results show that the ultrafast laser has precisely ablated the thin films. However, the high-energy fluence used in single-pass surface micromachining enabled the formation of recast layer from the melting of silicon substrate. Multi-pass surface micromachining at low energy fluences eliminated the recast layers and produced clean features. Ultrafast laser micromachining is certainly beneficial over wet and dry etching in reproducibility, material choice, and minimal number of processing steps. However, the cleanliness remains to be improved.