Dry etch release processes for micromachining applications

The authors report on the comparative study of two dry etch processes for polysilicon sacrificial layer release using vapor phase xenon difluoride (XeF2) continuous etching and inductively coupled plasma (ICP) etching with sulfur hexafluoride (SF6) gas. Test structures of 0.5μm thick polysilicon have been patterned and etch channels varying in widths from 1to500μm have been fabricated successfully for the purpose of comparison. The influence of etch pressure, aperture opening size, and ICP etch power on the undercut etching rate as well as selectivity between mask and substrate have been studied. It has been possible to achieve an undercut etch rate of up to 11.6μm∕min under a pressure of 3Torr in XeF2 etch gas, while for SF6 plasma, an undercut etch rate of 2.56μm∕min at 65mTorr is obtained. Moreover, the optimized process has been employed for the fabrication of silicon carbide (SiC) resonators.