Etching is the technique of using an acid to cut into a metal surface and create a pattern from an already established guideline. In the semiconductor industry, it is used to chemically remove surface layers of a wafer. It is a major step in manufacturing and all wafers must undergo this chemical etching before completion. The wafer is usually encased in a masking material that causes resist. This allows the etchant to only remove the necessary parts of the wafer and not etch into anything that need be kept whole.

There are two main types of etching systems: liquid and plasma etching (otherwise known as wet and dry). In wet etching, the wafer is immersed in a bath of etchant. The etchant needs to be agitated before it can achieve a good control. There are several different specialized etchants which can be used for this process. This results in a high amount of toxic waste and requires the disposal of it, making it somewhat obsolete for state-of-the-art processes. There is also the possibility of using wafer machines to employ gas for etching rather than immersing the wafer in chemicals.

Dry etching is a process that is used for very-large-scale integration (VLSI). Instead of immersing the wafer in liquid chemicals, a plasma is used instead. There are multiple parameters that can be set for dry etching, making many different operations possible. Plasma produces free radicals that have a neutral charge. These react at the surface of the wafer, energetically moving all about the wafer. Dry etching uses a source gas containing fluorine or chlorine.

Either wet or dry etching can be used to etch a great deal of elements. Some substrates, however, can only be etched through one type of process.  For instance, while aluminum can be etched by many different methods using wet or dry etching, gold can only be done through the process of wet etching, just as tantalum can only be etched using dry etchants. There are also cases of etching that model photolithography when a design is etched using a photoresist. The photographic developer used in this process very closely resembles wet etching.

In etching, the idea is to fully remove a top layer from the wafer, so etching systems must be well controlled. Though rarely would one want to damage the masking layers, sometimes a cavity is necessary to be formed. In this case, the depth of the etch must be controlled by two factors: the time and rate. This allows a cavity to be etched into the material. Etchants that create a large amount of undercutting these cavities are known as isotropic etchants, versus the more commonly and easier controlled anisotropic etchants. 

Etching at the wafer level allows chemicals to be removed from the wafer. It etches a pattern into the wafer in areas where a mask is not protecting it in order to allow fine microcuts to be made. Etching can be established in two different processes, either wet or dry. Each of these processes can be used for a number of different elements, but some elements can only be etched using one of the methods, as well as only using a certain chemical compound to do this. Etching must be applied to all wafers before going onto the finishing stages of semiconductor manufacturing and is critical to the process.