Difference Between PVD and CVD

The key difference between PVD and CVD is that the coating material in PVD is in solid form whereas in CVD it is in gaseous form.

PVD and CVD are coating techniques, which we can use to deposit thin films on various substrates. Coating of substrates is important on many occasions. Coating can improve the functionality of the substrate; introduce new functionality onto the substrate, protect it from harmful external forces, etc. so these are important techniques. Although both processes share similar methodologies, there are few differences between PVD and CVD; therefore, they are useful in different instances.

1. Overview and Key Difference
2. What is PVD
3. What is CVD
4. Side by Side Comparison – PVD vs CVD in Tabular Form
5. Summary

What is PVD?

PVD is physical vapour deposition. It is mainly a vaporisation coating technique. This process involves several steps. However, we do the whole process under vacuum conditions. Firstly, the solid precursor material is bombarded with a beam of electrons, so that it will give atoms of that material.

Figure 01: PVD Apparatus

Secondly, these atoms then enter the reacting chamber where the coating substrate exists. There, while transporting, the atoms can react with other gases to produce a coating material or the atoms themselves can become the coating material. Finally, they deposit on the substrate making a thin coat. PVD coating is useful in reducing friction, or to improve oxidation resistance of a substance or to improve the hardness, etc.

What is CVD?

CVD is chemical vapour deposition. It is a method to deposit solid and form a thin film from gaseous phase material. Even though this method is somewhat similar to PVD, there is some difference between PVD and CVD. Moreover, there are different types of CVD such as laser CVD, photochemical CVD, low-pressure CVD, metal organic CVD, etc.

In CVD, we are coating material on a substrate material. To do this coating, we need to send the coating material into a reaction chamber in the form of vapour at a certain temperature. There, the gas reacts with the substrate, or it decomposes and deposits on the substrate. Therefore, in a CVD apparatus, we need to have a gas delivery system, reacting chamber, substrate loading mechanism and an energy supplier.

Furthermore, the reaction occurs in a vacuum to ensure that there are no gases other than the reacting gas. More importantly, the substrate temperature is critical for determining the deposition; thus, we need a way to control the temperature and pressure inside the apparatus.

Figure 02: A Plasma Assisted CVD Apparatus

Finally, the apparatus should have a way to remove the excess gaseous waste out. We need to choose a volatile coating material. Similarly, it has to be stable; then we can convert it into the gaseous phase and then coat onto the substrate. Hydrides like SiH4, GeH4, NH3, halides, metal carbonyls, metal alkyls, and metal alkoxides are some of the precursors. CVD technique is useful in producing coatings, semiconductors, composites, nanomachines, optical fibres, catalysts, etc.

What is the Difference Between PVD and CVD?

PVD and CVD are coating techniques. PVD stands for physical vapour deposition while CVD stands for chemical vapour deposition. The key difference between PVD and CVD is that the coating material in PVD is in solid form whereas in CVD it is in gaseous form. As another important difference between PVD and CVD, we can say that in PVD technique atoms are moving and depositing on the substrate while in CVD technique the gaseous molecules will react with the substrate.

Moreover, there is a difference between PVD and CVD in the deposition temperatures as well. That is; for PVD, it deposits at a relatively low temperature (around 250°C~450°C) whereas, for CVD, it deposits at relatively high temperatures in the range of 450°C to 1050°C.

Summary – PVD vs CVD

PVD stands for physical vapour deposition while CVD stands for chemical vapour deposition. Both are coating techniques. The key difference between PVD and CVD is that the coating material in PVD is in solid form whereas in CVD it is in gaseous form.

Reference:

1. R. Morent, N. De Geyter, in Functional Textiles for Improved Performance, Protection and Health, 2011
2. “Chemical Vapor Deposition.” Wikipedia, Wikimedia Foundation, 5 Oct. 2018. Available here

Image Courtesy:

1.”Physical Vapor Deposition (PVD)”By sigmaaldrich (CC BY-SA 4.0) via Commons Wikimedia
2.”PlasmaCVD”By S-kei – Own work, (Public Domain) via Commons Wikimedia