Electrical Characterization of Etch Rate for Micro- and Nano-Scale Gap Formation

The capability to accurately characterize lateral etch rate is needed for the manufacture of micro/nano-electro-mechanical devices which incorporate air-gaps. Optical microscopy can be used to monitor the etch-front and to detect whether a structure has been completely undercut (“released”), but not if the gap thickness is too small, e.g., less than 10 nm. In this paper, an electrical method of lateral-etch end-point detection is presented. By electrically testing cantilever beams of differing widths, the lateral etch rate can be determined. The accuracy of this method is verified via correlation with optical interferometry (R = 0.998) for gap thicknesses down to 70 nm. This new electrical characterization method is shown to be applicable to gap thicknesses as small as 4 nm.