Dry & Wet Etching - Advantages & Disadvantages of Plasma Etching & Wet Etching
Etching is the process of material being removed from a material’s surface. The two major types of etching are wet etching and dry etching (e.g., plasma etching). The etching process that involves using liquid chemicals or etchants to take off the substrate material is called wet etching. In the plasma etching process, also known as dry etching, plasmas or etchant gases are used to remove the substrate material. Dry etching produces gaseous products, and these products should diffuse into the bulk gas and be expelled through the vacuum system. There are three types of dry etching (e.g., plasma etching): chemical reactions (by using reactive plasma or gases), physical removal (generally by momentum transfer), and a combination of chemical reactions and physical removal. On the other hand, wet etching is only a chemical process.
Advantages and Disadvantages of Dry Etching (Plasma Etching) and Wet Etching
The advantages of wet etching processes are the simple equipment, high etching rate, and high selectivity. However, there are many disadvantages. Wet etching is generally isotropic, which results in the etchant chemicals removing substrate material under the masking material. Wet etching also requires large amounts of etchant chemicals because the substrate material has to be covered with the etchant chemical. Furthermore, the etchant chemicals have to be consistently replaced in order to keep the same initial etching rate. As a result, the chemical and disposal costs associated with wet etching are extremely high. Some advantages of dry etching are its capability of automation and reduced material consumption. Dry etching (e.g., plasma etching) costs less to dispose of the products compared to wet etching. An example of purely chemical dry etching is plasma etching. A disadvantage of purely chemical etching techniques, specifically plasma etching processes, is that they do not have high anisotropy because reacting species can react in any direction and can enter from beneath the masking material. Anisotropy is when the etching exclusively occurs in one direction. This property is useful when it is necessary to remove material only in the vertical direction since the material covered by the masking material would not be removed. In cases where high anisotropy is vital, dry etching techniques that use only physical removal or a combination of both physical removal and chemical reactions are used.
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