At Nikalyte we are asked quite often, “What exactly is Physical Vapour Deposition?”. Our entire business is centred around this technology and so we thought it useful to explain it in simple detail. Physical Vapour (Vapor) Deposition or PVD for short, is a form of thin film coating. There are many other methods of thin film coating, including electroplating [1], spin coating and spray coating. PVD forms the hardest and most adherent coatings available by any technique. So much so that PVD is used to coat drill bits for the oil and gas industry to increase the lifetime of drill bits. PVD is also used in other markets such as semiconductors, photovoltaics, architectural, decorative and food packaging. Generally, in PVD a solid material is vaporized, the vapor is transported through a vacuum and then condenses onto a surface.
Magnetron Sputtering.
At Nikalyte we specialise in a specific type of PVD known as magnetron sputtering [2]. The metal to be evaporated is normally referred to as the ‘target’, and the product to be coated as the ‘substrate’. We choose magnetron sputtering as it allows us to add significant energy to the evaporated material resulting in dense adherent coatings. The target material is sputtered by introducing a gas at low pressure into the vacuum of the deposition chamber. A voltage is applied to the target which allows a plasma to form above the target. The plasma is shaped by magnets behind the target. Electrons and ions are generated above the target. The ions are accelerated towards the target with enough energy to remove, or sputter atoms from its surface. As the atoms are sputtered in a vacuum they are free to travel through the vacuum towards the substrate, or product.
How well do they adhere to the surface? Substrate materials and their preparation are critical to the quality of the resulting coating and will be the subject of future blogs. Briefly, the substrate is chemically cleaned before it is introduced to the vacuum chamber. It can then be heated to outgas and remove unwanted surface contamination. Finally, a glow discharge process is used to atomically clean the surface, essentially a sputtering process in itself.
Reactive Sputtering
Another critical part of the PVD process is the power supply used to generate the sputter plasma. If the target material is a pure metal, or alloy then a simple DC power supply can be used. If a more complex material is to be deposited such as a metal oxide (known as reactive sputtering) then a pulsed DC power supply is used. It is even possible to evaporate insulating materials such a silica by using a radio frequency (RF) power supply. By controlling and optimising the deposition conditions extremely hard and adherent coatings can be deposited. Such coatings can improve the appearance of a product as well as increasing the durability, scratch resistance and decreasing coefficients of friction. PVD coated products can be found in everyday use, even on the inside of your packet of potato chips [3]!
Find out more about our flexible PVD chambers, NEXUS and NL-FLEX or contact us to speak to our technical team.
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