Microfabrication of submicron nozzles in silicon nitride

A novel microfabrication process is described for obtaining nanometer apertures in highly cusped nozzle-like structures fabricated in silicon nitride, having apex angles of up to a few degrees. The process is based on a sacrificial etch technology using single-crystal silicon as the mold and silicon nitride as the material for the nozzle. The nitride coating on the apex of the pyramid shaped mold is selectively etched off using a polymer layer as the etch mask, which leaves the tip of the silicon mold protruding from the masked nitride, thus defining the aperture of the nozzles. The silicon mold is then removed in an alkaline etchant, which leaves the freestanding nozzles. The process is applicable to fabrication of similar structures in a variety of other materials such as silicon dioxide, boron-doped silicon, polysilicon, and refractory and noble metals. The main requirement is the preferential etchability of the mold with respect to material for the nozzles