24.8. Popular Wet Etchants
Basic data are provided for the most popular isotropic and anisotropic wet etchants.
24.8.1. EDP
EDP is also referred to as EDA (Ethylene DiAmine) [4]. It can be masked by SiO2, Si3N4, Au, Cr, Ag, Cu, and Ta. The etch rate anisotropy ratio is about 35:1 for {100}:{111}. Although EDP was used actively in the 1970s, 1980s, and early 1990s [1, 4], it is toxic, is very corrosive, ages very fast, and is not allowed in areas designated for the fabrication of microelectronics. Hence, alternative etchants such as KOH and TMAH are preferred nowadays.
24.8.2. KOH
KOH admits the use of Si3N4, SiO2, Cr, and Au as masks. Although the selectivity is poor between Si and SiO2 (≈100), it is very good for Si3N4 (≈1000). KOH is comparatively ...
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