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PVD - Physical Vapour Deposition

Sputtering and Cathodic Arc technology

The PVD family includes several vacuum deposition methods, used to produce thin film coatings. During a PVD deposition, the material is driven from solid state material to its vapour phase and, after a certain flight time, it condenses into a surface forming a thin film. The transition from solid state to the vapour phase can be achieved delivering energy with different methods. Main methods are Sputtering, Cathodic Arc and Evaporation; in this section the focus is on the first two because their similarities.

Sputtering:

Sputtering is a complex phenomenon in which the main actors are:

  •         Evacuated chamber (a robust chamber able to withstand high vacuum, equipped with a pumping system)
  •         Rarefied atmosphere (composed of a noble gas, i.e. Argon)
  •         Plasma (the forth state of matter)
  •         Cathode (Diode or Magnetron, if it is equipped with magnets array)
  •         Target (source material mounted on the cathode)
  •         High Voltage (via DC, DC PULSED, RF or HIPIMS technology)

In an evacuated chamber, equipped with a magnetron insulated towards ground, it is introduced a gas  flow (most likely Argon) that generates a rarefied atmosphere (in a pressure range of 10-3mbar).  A H.V. is applied between the chamber and the magnetron in order to ignite a plasma. The plasma particles are then attracted by the magnetron polarity and they hit the target acting like bullets. These "bullets" erode the material and extract the atoms that will then settle on the substrate in a uniform manner, giving birth to a thin film (in a range of nanometers).

Sputtering is called reactive if the rarefied atmosphere is composed of noble and reactive gas (i.e. Oxygen or Nitrogen). In this case the eroded material reacts during its flight time with the reactive gas and bonds chemically creating a compound.

The possibilities offered by Sputtering are unlimited, since it is practically possible to deposit any kind of material: from pure metals to alloys, from nitrides, carbides to oxides, such as glass and ceramics. The thin film is very smooth, uniform and pure. In the other hand, the deposition rates are low and the technology itself is more expensive than Cathodic Arc.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cathodic Arc:

The arc evaporation process begins with the striking of a high current, low voltage arc on the surface of a cathode (also called target) that gives rise to a highly energetic emitting area a few micrometers wide. Locally the temperature is extremely high (around 15000 °C), so that the material is sprayed out at high velocity (10 km/s) as a jet of vaporized material, leaving a crater behind on the cathode surface. The cathode spot is only active for a short time, after which it self-extinguishes and re-ignites in a new area close to the previous crater. This behavior causes the apparent motion of the arc.

Cathodic arc plasma deposition is a coating technology with great potential because its plasma is fully ionized with very energetic ions, promoting adhesion and the formation of dense films. There are disadvantages and problems too; films may be under high compressive stress, and so-called “macroparticles” may be incorporated into it.

Cathodic Arc is highly recommended for getting high deposition rates, high adhesion, high wear resistance of the film so that it became the favourite choice for decorative and functional applications. There is another flip side of the coin: macroparticles problem has prevented cathodic arc to be used in high-tech applications like Semiconductor Industry, in which high purity and high film homogeneity is fundamental.