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 usually 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 into a vacuum chamber, which reduces the pressure and increases the rate of evaporation. The material is then heated to boiling, and the gaseous particles of the target material condense on the surfaces of the chamber, including on the substrate.
The two main heating methods for physical vapor deposition by evaporation are electron beam heating and resistive heating. During electron beam heating, a beam of electrons is directed at a specific area on the target material, causing that area to heat and evaporate. This method is good for controlling the specific areas of the target that are to be evaporated. During resistive heating, the target material is placed in a container, usually made of tungsten, and the container is heated with a high electric current. The method of heating used during evaporation physical vapor deposition varies depending on the nature of the target material.
Sputtering processes also start out with the target material in a vacuum chamber, but the target is broken up by gas plasma ions rather than by evaporation or boiling. During the process, a current is run through a gas plasma, causing positive cations to form. These cations bombard the target material and knock away small particles that travel through the chamber and deposit on the substrate.
Like evaporation, sputtering techniques vary according to 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 the ions, while others will have a mechanism to rotate the target material.
Casting is another main method of physical vapor deposition, and it is most commonly used for
target materials and for photolithography. During this process, the target material is dissolved in a
to form a liquid that is either sprayed or spun onto the substrate. Spinning involves spreading the liquid onto the flat substrate, which is then spun until an even layer is formed. Once the solvent evaporates, the thin film is complete.