Bulk micromachining is a process used to produce micromachinery or MEMS.
Unlike surface micromachining, which uses a succession of thin film deposition and selective etching, bulk micromachining defines structures by selectively etching inside a substrate. Whereas surface micromachining creates structures on top of a substrate, bulk micromachining produces structures inside a substrate.
Most of the time, silicon wafers are used as substrates for bulk micromachining, for its anisotropic properties are used to wet etch structures.
Bulk micromachining starts with a silicon wafer or other substrate and selectively etches into it, using photolithography to transfer a pattern from a mask to the surface. Like surface micromachining, bulk micromachining can be performed with wet or dry etches, although the most common etch in silicon is the anisotropic wet etch. This etch takes advantage of the fact that silicon has a crystal structure, which means its atoms are all arranged in lines and planes. Certain planes have weaker bonds and are more susceptible to etching. The etch results in pits that have angled walls instead of vertical walls. This type of etching is inexpensive and is generally used in early and low-budget research.