Etching (Stripping/Ashing) is a process used to chemically remove layers from the surface of a wafer during its production. In some cases, part of the wafer is protected from the etchant by a masking material, preventing the etching from taking place. These situations can vary from photoresist, patterned using photolithography, to more durable masks like silicon nitride.
In the manufacturing of semiconductors, an etch process is used to remove oxide in the absence of the photoresist pattern. This way, when the photoresist is stripped, the oxide is left completely on the wafer.
The process of etching begins when residual stresses are removed from the part being
etched in order to prevent warping. The masking and part undergo a degreasing and cleaning process in order to be sure that the bond between them is strong. The masking material, such as tape or paint, is then applied to the surfaces of the part, making it so the etching can only be applied to the desired places.
The reagent then etches the surfaces that are not masked. Once this is complete, the masking is removed once more the parts are washed in order to prevent the remaining reagent from carrying out further undesired etching on the part.
Many different types of elements and compounds can be used as etchants. They include but are not limited to:
Etching is used widely in the manufacturing of integrated circuits. The semiconductor industry also uses plasma etching quite commonly in lieu of the standard techniques.