High speed and low roughness micromachining of silicon carbide by plasma etching aided femtosecond laser processing

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Silicon carbide has a high hardness and corrosion resistance. Accordingly, high rate machining of this material is a big challenge to obtain good surface quality. In this work, plasma etching aided femtosecond laser micromachining was proposed to address this issue. A series of square and circular blind holes for forming SiC pressure sensor diaphragms were obtained by using a 50fs, 800 nm, 1000Hz Ti:Sapphire laser. Using the control variable method, the effects of laser machining power, scan line spacing and scanning rate on surface topography of the structure were investigated. As demonstrated by experimental results, surface roughness of the structure increases with the laser machining power within a certain range. While the scanning rate has negligible effects on surface quality of the structure. The maximum surface roughness after femtosecond laser micromachining is 2.867 μm measured by laser scanning confocal microscope, and this value is reduced to 2.143 μm after inductively coupled plasma etching. In addition, a Raman spectroscopy shows that this composite micromachining method can eliminate accumulation of amorphous carbon on SiC surface caused by the femtosecond laser processing. The reduction of surface roughness and removal of amorphous carbon can effectively decrease probability of crack failure of the sensor diaphragm and increase its deformation capability, thereby ensuring sensitivity of the sensor. The composite micromachining method fully combines the advantages of high efficiency of femtosecond laser machining and high surface quality of plasma etching, making it has high potential to be applied in precision machining of silicon carbide and fabrication of SiC sensors.