Fabrication of nanoelectromechanical resonators using a cryogenic etching technique

The details of the fabrication of nanomechanical resonators through cryogenic etching methodology is described. The cryogenic etching is conducted in an Oxford Plasmalab 100 DRIE system. The instrument is equipped with a liquid nitrogen cooled chuck and a temperature controller to maintain the temperature of the silicon wafer at a set value. The etching process consists of four steps. The wafer is loaded into the plasma reactor and rested on the cooled chuck for five minute to achieve the desired temperature. An O2 plasma is run for 10 seconds to clean the silicon substrate and prepare it for etching. The SF6/O2 etching plasma is lit to etch the substrate. A helium release step is used to ensure that the process wafer is not stuck to the cooled chuck. Control over the relative strength of passivation and the etch steps has enabled the machining of high-aspect-ratio NEMS with lateral dimensions as small as 150 nm.