Material removal or etching may be classified according to physical or chemical methods. Additionally, the methods may be classified as whether vacuum is needed or not. Also, masked and maskless processes provide another way of classification.
13.5.1 Wet Etching
Wet chemical etching is commonly needed to pattern thin metal or dielectric films on the substrate, either to fabricate specific features like electrodes or to open windows in surface mask layers for subsequent local processing. These materials usually etch isotropically; the undercut of the etch mask is the usual disturbing factor. In some cases, the etch may follow a particular direction. Anisotropic etching can be performed in crystals with diamond and zincblende lattices (Si, GaAs, and InP) because the 111 crystal plane is more closely packed than the 100 plane, and so is etched more slowly. For example, using the Water: EDP (ethylene diamine and pyrocatechol etch system, the etch rates for the 100, 110, and 111 ...