Deep Etching of Silicon Based on Metal-Assisted Chemical Etching

A deep etching method for silicon "micro"structures was successfully developed.This wet etching process is based on metal-assisted chemical etching (MACE), which waspreviously mainly utilized to etch the features that have lateral dimensions of"nanometers."In thisnovel MACE, the critical improvement was to promote the"out-of-plane"mass transfer at themetal/Si interface with an ultrathin metalfilm. This enabled us to etch micrometer-wide holes,which was previously challenging due to the mass transport limitation. In addition, it was foundthat when ethanol was used as a solvent instead of water, the formation of porous defects wassuppressed. Under the optimized etch conditions, deep (>200 mu m) and vertical (>88 degrees) holescould be carved out at a fast etch rate (>0.4 mu m/min). This novel deep MACE willfind utility inapplications such as microelectromechanical systems (MEMS) devices or biosensors