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.
Magnetron sputtering is a unique method for producing a wide range of conductive coatings on different substrates. Some of its applications are as follows:
- Deposition of conductive layers for high-resolution imaging by scanning and transmission electron microscopes.
- Conductive coatings on large scale samples (wafer, compact discs, etc.).
- Metallic layers using aluminum, chromium, cobalt, copper, gold, silver, platinum, molybdenum and titanium for industrial and laboratory processes.
Omega systems are designed and produced in ten different models and base on the costumer order involve one to three different deposition methods which are DC, RF and resistive or electron beam thermal evaporation. These devices have a cylindrical chamber made up of stainless steel type 304; that is equipped with a front door which facilitates accessibility to all parts inside the chamber. The other features are direct (Roughing) and backing discharge channels along with high vacuum electro-pneumatic valves and diffusion pump with discharge rate of 700 liter per second. Details of technical specifications 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.
- Since this system is designed for a particular type of coatings, do not change the location of the assembled components.
- Entry of any kind of contaminations into the vacuum chamber leads to the increase in gas release of inner parts, and so the pressure reduction of the chamber would be problematic. Thus, touch the components and inner parts of the chamber, which are subjected to the vacuum, by using clean gloves.
- Before plasma formation, pursue the following instructions; if shutters are open, turn them over the “CLOSE” position to place upper the target.
- In case of need, enable the substrate rotating system and by moving the holder, place the substrate on top of the target.
- If the target is oxidized or contaminated, it slightly produces sparks in the beginning of the plasma formation. In such case, allow it to form a weak-plasma in a low-voltage and clean the surface within 1 to 2 minutes, then adjust the voltage on the desired level.
- Increase the filament current gradually and monitor the electron current at this interval. In an electron current of about 10 mA, a bright spot is visible on the crucible surface. Set the bright spot to the center of the crucible by adjusting the voltage.
- For more details on how to use the device, refer to the device catalog and user guide.
- By enabling the cooling valve of the diffusion pump, the corresponding sensor must be turned on the HMI screen. Otherwise, the PLC does not allow the diffusion pump to be enabled.
- For discharging the chamber, make sure that the needle and aeration valves are closed. Turn the needle valve clockwise to be completely closed. Disable the aeration valve through the HMI to be closed.
- When the diffusion pump is in operation, the direct and baking valves should not be open simultaneously because the pressure behind the diffusion pump begins to increase which may be dangerous for pump.
- In case of abrupt increase of the chamber pressure, instantly disable the butterfly valve through the HMI to close the valve, and then probe the possible problems.
- Never use the acetone to clean the O-rings because it may corrode them.
Standard Date : 2017/11/21
Expire Date : 2020/11/21
Certificate of Nanotechnology
Standard Date : 2017/11/21
Expire Date : 2020/11/21