Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) are two processes used to produce a very thin layer of material, known as a thin film, onto a substrate.
Vapor deposition techniques are the preferred processes for thin films because the techniques produce products with superior hardness, wear resistance, smoothness and oxidation resistance. Thin films made through vapor deposition are typically able to function in unique, high-stress environments.
Whether it is produced through CVD or PVD, the outcome very similar as both processes generate a very thin layer of material of desired thickness. CVD and PVD are very broad categories of techniques. Various CVD and PVD processes may be quite different; however, the objective is the same. Some solutions may be preferred over others for a range of various reasons, such as cost and ease.
PVD and CVD are mostly used in the generation of semiconductors where very thin layers of n-type and p-type materials are used to create the required structural junctions. The fundamental difference between the two processes is their approach to addressing the same task.
Physical Vapor Deposition
As the name suggests, PVD is a technique that uses primarily physical means to deposit a thin layer of material. PVD involves a number of steps performed under high-temperature vacuum conditions. First, a solid precursor material is gasified, typically through the use of high-power electricity or laser. The gasified atoms are then moved into a reacting chamber where the coating substrate is located. Source material atoms then stick to the substrate, forming a thin coat.
PVD is used as the deposition method to produce an extremely hard, corrosion-resistant coating. Thin films made with PVD have a high-temperature tolerance and superior ablation resistance. PVD is also considered an environmentally-friendly process.
The process does have a few drawbacks. One of the main drawbacks is its high cost, due in part to the intense heating and cooling that is required. PVD is also a ‘line of sight’ technique, which means it is not ideal for coating non-visible surfaces. The process is also considered to be relatively slow.
Chemical Vapor Deposition
Similar to PVD in that it is used to produce high-purity, specialized thin coatings, CVD involves mixing the source material with one or more volatile precursors that functions as a carrier device.
These precursors, which are typically halides or hydrides, chemically interact and break down the source material. The entire CVD process is known to generate volatile by-products that must be safely removed via gas flow through the reaction chamber.
Once created, the source material is transported into the reaction chamber, which contains a substrate, by forced convection. Through the process of diffusion, reactants are deposited into the substrate. After the mixture adheres to the substrate, the precursor eventually breaks down, is removed by diffusion and leaves behind the desired layer of source material on the substrate. The decomposition process can be facilitated or accelerated using heat, plasma or various techniques.
One of the biggest advantages of using CVD is that it can be used to evenly coat irregular surfaces, including screw threads and recesses. The process is also extremely versatile; it has been used with an extremely wide range of elements and compounds. CVD also produces a thin film with very high purity and density. Because numerous parts can be coated simultaneously, CVD is a relatively economical deposition process.
CVD has been used across a wide range of industries. Some organizations use it to apply coatings for wear resistance and temperature protection. Others use it to produce semiconductors for electronic devices. CVD has also been used to fabricate dense structural parts that are difficult or cost-prohibitive to make with conventional techniques.