A micromachining process by removing a part of substrate itself.
An example of bulk micromachining is a processing method based on
etching by a chemical solution to remove unnecessary parts of a substrate. Covering the areas to be
preserved with a mask of SiO2 or Si3N4 ensures that etching cannot progress from the surface. Also,
a boron-doped layer can stop the etching of the part underneath the surface layer. Recently,
silicon fusion bonding has been used to fabricate still more complex structures.