Silicon ICs are typically fabricate

Silicon ICs are typically fabricated (manufactured) using or silicon. In bulk micromachining, an anisotropic (unidirectional) etchant, such as ethylene-diamine-pyrocatechol (EDP), hydrazine (N2H4),tetramethylam-monium hydroxide (TMAH), or potassium hydroxide (KOH), attacks the plane of silicon. The plane is etched at a much faster rate than the plane, typically 35 times faster. N-type silicon is etched at a much faster rate (>50 times faster) than p+-type, so n-type material is often used as the start-ing material. P+-type material can be epitaxially grown on the wafer or diffused into the wafer to add a further control element in defining the dimensions. Agi-tation maintains uniform concentration during anisotropic etching. The char-acteristic shape (preferential etching) of anisotropic etching of silicon is shown in the cross-section of Figure 2.1(a), which produces a 54.7-degree angle for the silicon[4, 5]. The top view of etching into the surface of the sili-con appears as a pyramid-shaped pit.