Liquid phase etch chemistry
Solid materials can be dissolved in liquids or solutions of varying composition depending on the properties of the solid. Developers used in lithography simply dissolve uncrosslinked resist. Silicon can be anisotropically dissolved at very high pH, in concentrated pottasium hydroxide (KOH) at elevated temperatures, where the etch rate is strongly dependent on crystal orientation. Silicon dioxide can be removed from silicon using buffered hydrogen fluoride (BHF) Many of the chemicals and equipment needed for standard wet etch processes are provided by the Nanolab, with the exception of hydrogen fluoride.
Wet etching has the advantage of low capital cost, rapid etch rates and high selectivity. The main disadvantage is the generation of chemical waste, and the risk of exposure to toxic and potentially harmful chemicals.
Wikipedia provides a concise summary of etching methods, including wet etching here .