Silicon micromachining by CO₂ laser

In this paper, a novel silicon micromachining using CO₂ laser has been demonstrated for the first time. The wavelength of CO₂ laser is 10.64 μ and not absorbed by silicon material. So, it cannot do any micromachining for pure silicon. However, as we put a silicon on the top of a glass material, CO₂ laser can etch the silicon, even etch through the wafer to be a hole structure. For example, a silicon hole of 525 μm deep can be obtained by CO₂ laser machining circular shape for 80 passes at power of 24 W, spot size of 76 μm and scanning speed of 6 mm/sec. In comparison with conventional laser micromachining of silicon, shorter wavelength lasers e.g. Nd:YAG laser with wavelength of 1.06 μm and excimer laser of 248 or 193 nm are used due to the good adsorption of silicon. But the cost of shorter wavelength laser is much higher than CO₂ laser. In comparison with conventional silicon micromachining by dry plasma etching, wet KOH/TMAH etching or wire electrodischarge grinding (WEDG), CO₂ laser micromachining is much easier, cheaper and has faster etching rate than plasma etching, and more flexible to make different geometry than wet etching and WEDG. This CO₂ laser micromachined silicon technology will be a promising one for the application of microfabrication and MEMS.