What Is Physical Vapor Deposition (PVD) Coating?
Physical Vapor Deposition (PVD) Coating is the coating of a thin film of a hard alloy on the surface of an object by a physical method. This makes the surface of the object very hard and tough.
It also has the effect of increasing surface smoothness and reducing friction and wear on the surface of the deposited object.
Uses of Physical Vapor Deposition (PVD) Coating
A typical application of PVD Coating is in the semiconductor manufacturing process. It has been used for a long time, specifically for the formation of multilayer electrodes, wiring, protective films, insulating films, and metal films.
It is also suitable for aluminum coating on storage media such as CDs and DVDs due to its good adhesion and cost performance, and titanium alloy coating to improve the durability of cutting tools.
Furthermore, it is also used as an alternative to plating on metal and non-metal products, for example, in decorative applications for jewelry such as bracelets and wristwatches, and architectural parts such as doorknobs.
PVD Coating is used in a variety of fields to achieve high durability, low wear, and long life of the coated object.
Principle of Physical Vapor Deposition (PVD) Coating
PVD Coating is a coating process in which a hard metal is adhered to the surface of the object to be coated by a physical method to form a film. There are three methods of metal adhesion: vacuum deposition, sputtering, and ion plating.
In each of these methods, a high vacuum (10-¹ to 10-⁵ high vacuum) is created in the deposition container, in which the material to be deposited is vaporized or evaporated by heat, electron beam, ions, or other external energy and physically deposited on the object to be deposited. The target is then physically deposited on the object to be deposited.
Types of Physical Vapor Deposition (PVD) Coating
There are three types of metal deposition methods in PVD Coating: Vacuum Evaporation, Sputtering, and Ion Plating.
1. Vacuum Deposition
Vacuum evaporation is the most basic PVD deposition method. The deposition material is vaporized and evaporated in a deposition container that has reached a high vacuum range, and is physically deposited on the surface of the object to be deposited. The electron beam heating method and resistance heating method are the most common methods for heating the deposition material.
Electron Beam Method
The electron beam method is the most versatile and widely used method. In this method, the evaporation material that forms the film is placed in a water-cooled crucible and irradiated with an electron beam to evaporate it.
Resistance Heating Method
In the resistance heating method, the evaporation material that forms the film is placed on a boat made of high-melting-point metal, and the boat is directly heated by a heater. Other methods include high-frequency induction heating, laser beam heating, high-frequency heating, and arc heating.
Vacuum Evaporation
The vacuum evaporation method does not require heating of the object to be deposited, making it possible to deposit films on resins and metal products that do not require any thermal history. In addition, the vacuum evaporation method does not require the application of negative voltage to the object to be deposited, making it possible to deposit films on materials that are not conductive.
2. Sputtering
In sputtering, active gases such as argon are ionized and bombard the deposition material in the deposition vessel, which has reached a high vacuum range, and the molecules and atoms are scattered with great force. The scattered molecules and atoms are physically deposited on the surface of the material to be deposited, forming a film.
The basic method of ionizing argon gas is to place parallel plate electrodes in a deposition container with the deposition material at the cathode and the film to be deposited at the anode, apply DC voltage to generate a glow discharge on the cathode side, and ionize argon gas in the discharge region.
The ionized argon collides with the cathode side at high energy and high speed. The material atoms released from the collision reach the material to be deposited on the anode side, where they are physically deposited.
This method is called two-pole sputtering, and magnetron sputtering, which combines the magnetic field effect (a magnet is installed on the negative electrode) to increase the ionization rate of argon, is currently the mainstream method.
3. Ion Plating
Ion plating is a method of depositing a film by ionizing a metal or compound gas that is heated and evaporated in a vacuum and striking the object to be deposited. In other words, it is a processing method that adds plasma to vacuum deposition.
Specifically, the target is evaporated by DC voltage, high-frequency voltage, electron beams, etc. in the deposition vessel, which has reached a high vacuum region. At the same time, a reaction gas (nitrogen, hydrocarbon, etc.) is introduced into the deposition vessel to react with the evaporated film material.
Since a negative voltage is applied to the target, the deposition material is accelerated and impacts the target in a high-energy state, depositing on the surface of the target to form a film. This method can deposit nitride and carbonitride films with good adhesion, and is used for cutting tools and decorations that require durability.