Bulk micromachining is a process fo

Bulk micromachining is a process for making three-dimensional microstruc-tures in which a masked silicon wafer is etched in an orientation-dependent etching solution [3]. Using micromachining technology, several wafers can be fabricated simultaneously and lot-to-lot consistency is maintained by control-ling a minimal number of parameters. Key parameters in bulk micromachining include crystallographic orientation, etchant, etchant concentration, semicon-ductor starting material, temperature, and time. Photolithography techniques common in IC technology precisely define patterns for etching both sides of silicon wafers. The crystallographic orientation, etchant, and semiconductor starting material are chosen by design, leaving etchant concentration, tempera-ture, and time as lot-to-lot control items.