4. Etching Technologies

Solid surfaces can be etched by wet processes (wet-chemical or electrochemical), dry processes (physical, chemical, or a combination of both), or mechanical processes (without or with a chemical contribution). The wet etch attack may be chemical by a liquid etchant or electrochemical (a reversal of electrochemical deposition) by an electrolyte under the influence of a current. In physical dry etching, the substrate is bombarded by ions (ion beam etching). Chemical etching may either use a plasma, enhancing the chemical attack by dissociating the etchant’s volatile chemical species (plasma etching), or a vapor (vapor phase etching). Physical-chemical processes combine ion bombardment with chemical attack through dissociated chemical species. Mechanical processes are powder blasting and (on the border between mechanical and physical, with and without a chemical component) cluster beam technologies. Subject to etching may be either the substrate material itself (bulk etching/micromachining) or thin-films at the surface (surface etching/micromachining). Particularly bulk micromachining of single crystal silicon takes advantage of etch-limiting crystal planes for constructing three-dimensional patterns in the substrate material.