Physical vapor deposition (PVD) transfers target materials onto substrates through physical means to create thin films. Evaporation, sputtering, and casting are the three main types of PVD. Heating methods vary depending on the target material, and casting is used for polymer target materials and photolithography.
Physical vapor deposition (PVD) is a process used to create thin films by transferring a target material onto a substrate. The transfer is achieved through purely physical means unlike chemical vapor deposition, which uses chemical reactions to create the thin films. Semiconductors, computer chips, compact discs (CDs), and digital video discs (DVDs) are typically created by this process.
There are three main types of physical vapor deposition: evaporation, sputtering and casting. Evaporation techniques begin by placing the target material in a vacuum chamber, which reduces the pressure and increases the rate of evaporation. The material is then heated to boiling, and gaseous particles of the target material condense on the surfaces of the chamber, including the substrate.
The two main heating methods for evaporative physical vapor deposition are electron beam heating and resistive heating. During electron beam heating, a beam of electrons is directed at a specific area of the target material, causing that area to heat up and evaporate. This method is useful for checking specific areas of the target that need to be evaporated. In resistive heating, the target material is placed in a container, usually tungsten, and the container is heated with a high electric current. The heating method used during the evaporation of physical vapor deposition varies depending on the nature of the target material.
Sputtering processes also begin with the target material in a vacuum chamber, but the target is shattered by plasma gas ions rather than evaporation or boiling. During the process, a current passes through a gas plasma, causing the formation of positive cations. These cations bombard the target material and drive away the small particles which travel through the chamber and settle on the substrate.
Like evaporation, sputtering techniques vary depending on the target material. Some will use direct current (DC) power sources, while others will use radio frequency (RF) power sources. Some sputtering systems also employ magnets to direct the movement of ions, while others will have a mechanism to rotate the target material.
Casting is another major method of physical vapor deposition and is most commonly used for
of polymer
target materials and for photolithography. During this process, the target material is dissolved into a
solvent
to form a liquid which is sprayed or spun onto the substrate. Spinning involves spreading the liquid onto the flat substrate, which is then spun into a uniform layer. Once the solvent evaporates, the thin film is complete.
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