Thin film sputtering is a process in which a thin film is applied to a surface by knocking particles off a separate target source. The process generally takes place in a low-pressure chamber into which gaseous plasma is pumped. Positively charged ions in this plasma knock particles free from the target source in a process known as sputtering. These particles then travel to the recipient surface, known as a substrate, where they are deposited on it in the form of a thin film.
The two main thin film sputtering methods are direct current (DC) sputtering and radio frequency (RF) sputtering. In DC sputtering, a direct current positively charges the plasma whereas RF sputtering uses radio waves to charge it. The positively charged plasma accelerates into a negatively charged target, freeing particles of the target material which deposit onto the substrate. DC sputtering is restricted to use for conductive materials that can hold an electric current, whereas RF sputtering is appropriate for insulating materials as well.
As they are ejected from the target material, the particles travel in a straight line until they come into contact with something. Some of these particles are deposited on the surface that needs to be coated. Particles traveling in other directions may instead be deposited on the chamber walls or other surfaces inside the chamber.
Argon gas is typically the plasma material used to knock particles free from the target material, but other inert gases such as neon or krypton are sometimes used. Accelerated plasma may knock particles free from this target material in the form of individual atoms, groups of atoms, or as molecules. Numerous types of sputtering materials are available for use in a variety of applications. Thin film sputtering may be used to deposit either metallic or non-metallic films on substrates made of metal, glass, or other materials.
Common applications using thin film sputtering include the coating of optical instruments such as telescope mirrors and the coating of consumer products such as compact discs and digital video discs. Electronic semiconductor devices and photovoltaic panels are also manufactured with this technology. Use of thin film sputtering has even expanded into the manufacture of drugs that are administered to the patient in the form of a thin film.
There are a number of advantages to using this method. Thin film sputtering is relatively rapid compared to other similar processes. It also allows for good control of the thickness of the deposited film. In addition, target materials do not need to be heated as in evaporation processes, so they can be kept at a low temperature if needed.