Sell Wet Etching representation and distribution

Description

Wet Etching is an etching process that utilizes liquid chemicals or etchants to remove materials from the wafer, usually in specific patterns defined by photoresist masks on the wafer. Materials not covered by these masks are &#**9;etched away&#**9; by the chemicals while those covered by the masks are left almost intact. These masks were deposited on the wafer in an earlier wafer fab step known as &#**9;lithography.&#**9; A simple wet etching process may just consist of dissolution of the material to be removed in a liquid solvent, without changing the chemical nature of the dissolved material. In general, however, a wet etching process involves one or more chemical reactions that consume the original reactants and produce new species. A basic wet etching process may be broken down into three (3) basic steps: 1) diffusion of the etchant to the surface for removal; 2) reaction between the etchant and the material being removed; and 3) diffusion of the reaction byproducts from the reacted surface. Reduction-oxidation (redox) reactions are commonly encountered in wafer fab wet etching processes, *****, an oxide of the material to be etched is first formed, which is then dissolved, leading to the formation of new oxide, which is again dissolved, and so on until the material is consumed. Wet etching is generally isotropic, *****, it proceeds in all directions at the same rate. An etching process that is not isotropic is referred to as &#**9;anisotropic.&#**9; An etching process that proceeds in only one direction (*****, vertical only) is said to be &#**9;completely anisotropic&#**9;.