Sputtering is a type of Physical Vapor Deposition (PVD), in which its mechanisms are mostly based on non-thermal processes, which leads to the accumulation and deposition of ejected atoms from the Target onto the desired substrate. This approach entails three basic steps including; the momentum transfer from high energetic ions of ionized gas to a cathode (Target), the ejection of atoms from the Target, and then the deposition onto a substrate (anode).
This procedure needs a plasma medium as a prerequisite and the common diagnosis of plasma formation is a phenomenon called glow discharge. The glow discharge is a sign of electron transaction between energy levels inside atoms, which is caused by occurrence of electric discharge between two oppositely polarized electrodes-target and substrate. As implied by the mechanism, for inception of the glow discharge, and consequently layer deposition, a minimum electric potential, controlled reduced pressure and suitable gaseous reactants are required.
The application of sputtering is not limited to layer deposition, but covers much wider range including cleaning, etching and activation as a route for surface preparing before coating. One of the unrivaled advantages of sputtering compared with other coating techniques is that a variety of materials even those with very high melting point (Tantalum with melting point exceeding 3000°C, for example) can be employed to produce thin films on different substrates. So far, different types of sputtering coaters have emerged, some of which are; Diode/triadic sputtering, magnetron sputtering, DC/Pulsed DC/RF sputtering, planar/tubular sputtering.
The diode sputtering is the most common sputtering technique, and typically used for deposition of conductive layers onto samples for the electron microscope. In magnetron sputtering, an external magnetic field is used to modify plasma and increase sputtering rate. Under the external magnetic field that is parallel to the cathode plate, electrons are forced to move in a spiral trajectory near the cathode rather than straight path towards the anode. Thus, the electrons generate localized plasma with higher density near the cathode. As a consequence, the plasma seems to be confined in an area near the cathode which results in the higher sputtering rate. This feature also makes the layer deposition in a lower gas pressure possible. Therefore, the ejected atoms from the Target can move towards the substrate without much collision with interfering particles of gaseous medium, thereby leading to a higher deposition rate.
Regarding the type of cathodes power supply, DC and RF are two different choices which have their own pros and cons. DC power is suitable for conductive materials, while in the case of dielectric target materials, DC Sputtering is limited because non-conducting insulating materials can be electrically polarized, thereby preventing further layer deposition. One the other hand, RF power can also sputter non-conductive materials, because by alternating the polarity with RF Sputtering, the surface of the target material can be cleaned of a charge buildup with each cycle. Pulsed DC would be the other option, which has advantages for some processes such as reactive sputtering.
The Sigma series deposition systems are capable of producing different coatings using sputtering and/or resistive thermal evaporation methods. Discharge module in these series consists of rotary and turbo molecular pumps, which is suitable for experimental investigations and R&D applications. These systems have glass chamber along with a discharge channel. It should be noted that the high vacuum, direct and backing valves have removed from this systems; for this reason this device are offered at the lower price compared to the Omega series. Details of technical specifications of this device are presented in the following Table.
Sputtering is an exquisite method for producing various coatings. In fact, each material which can undergo the sputtering conditions (plasma formation, ion bombardment, etc.) can be a good choice as a coating or substrate. Therefore, by choosing the device functional parameters appropriately, a material with different structures such as microstructures, nanostructures, nanocomposites, etc. can be produced.