PVD vs CVD | CVD Coating vs PVD Coating
PVD and CVD are coating techniques, which can be used 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 external harmful forces, etc. so these are important techniques. Both processes share similar methodologies except few differences; therefore, they are used in different instances.
What is PVD?
PVD or physical vapor deposition is mainly a vaporization coating technique. This process involves several steps. The whole process is done under vacuum conditions. First, the solid precursor material is bombarded with a beam of electrons, so that it will give atoms of that material. These atoms are then transported into the reacting chamber where the coating substrate is. While transporting, atoms can react with other gases to produce a coating material or the atoms themselves can be the coating material. Then they deposit on the substrate making a thin coat. PVD coating is used to reduce friction, or to improve oxidation resistance of a substance or to improve the hardness, etc.
What is CVD?
CVD or chemical vapor deposition is a method to deposit solid and form a thin film from gaseous phase material. This method is somewhat similar to physical vapor deposition. There are different types of CVD such as, laser CVD, photochemical CVD, low pressure CVD, metal organic CVD, etc. In CVD, a material is coated on a substrate material. To do this coating, the coating material is sent to the reaction chamber in the form of a vapor having a certain temperature. Then at the reaction chamber, the gas reacts with the substrate, or it is decomposed and deposited on the substrate. So in a CVD apparatus there should be a gas delivery system, reacting chamber, substrate loading mechanism and an energy supplier. Other than this, the reaction is carried out in a vacuum to ensure that there are no gases other than the reacting gas. The substrate temperature is critical for determining the deposition; thus, there should be a way to control the temperature and pressure inside the apparatus. Finally, the apparatus should have a way to remove the excess gaseous waste out. The coating material should be volatile, and the same time stable in order to be converted to 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 used in producing coatings, semiconductors, composites, nanomachines, optical fibers, catalysts, etc.
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What is the difference between PVD and CVD? • In PVD, the material that is introduced onto the substrate is introduced in solid form whereas, in CVD, it is introduced in a gaseous form. • In PVD, atoms are moving and depositing on the substrate, but in CVD, the gaseous molecules will react with the substrate. • The deposition temperatures of PVD and CVD are different. PVD coating is deposited at a relatively low temperature (around 250°C~450°C) than CVD (CVD uses high temperatures in the range of 450 oC to 1050 oC). • PVD is suitable for coating tools that are used in applications that demand a tough cutting edge. CVD is mainly used for depositing compound protective coatings.
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