10 Targets UHV Magnetron Sputtering Machine

This equipment in our laboratory uses the principle of Magnetron Sputtering for thin film deposition. It is a state of the art facility allowing possibility of 10 different targets to be deposited one over the other. A Turbo molecular Pump is used to drive the chamber down to the UHV regime (order of 10-7~10-8 Pa.). This prevents the surface from contamination. In addition to the sputtering chamber(i.e: the setup on the right) where we perform deposition ,there is also an oxidation chamber (seen on the left) and a transport chamber enabling heat treatment and sample loading/unloading respectively.

UHV multichamber sputtering system. Currently, 10 targets sputtering chamber and oxidation chamber are installed.

Plasma is a collection of highly ionized gas atoms. Every atom (in this case gas) has a positive core and a negative e- around it. Plasma is a state when the gases are separated to +ve and -ve ions leading to the ionization of the gas. This is achieved by application of power (DC or RF). However they occasionally tend to recombine that gives the color of plasma. The color is usually a characteristic of the gas we use. To name a few, Argon: Purple, Nitrogen: Red, Fluorocarbon: Blue. So when air is ionized we observe Red color characteristic of N2.We generally use Ar gas for our experiments.

Magnetron sputtering is a Physical Vapor Deposition technique for deposition of thin films and works on the principle of thermal/ballistic energy transfer assisted by magnetic field. The principle is shown in the figure.

Schematic of Magnetron sputtering

Plasma generated during magnetron sputtering

Thin films are deposited on a substrate usually oxides. (MgO, SiO2) and the substrate is placed on the top surface and acts as the anode. The target atom to be deposited is at the bottom. It can either be an alloy or a pure metal. In our group we use a wide range of systems from Huesler alloys to single metals like Ag, Ta, Ru. The target is connected as cathode and the gas is filled in between these two electrodes. Upon the application of power, the gas (usually Ar) is ionized. This leads to the formation of PLASMA. Gas ions are having a high energy and are attracted by the target cathode due to coulomb attraction. This causes bombardment of the gas onto the target leading to ejection of target atoms from the surface. This is the principle of sputtering.

The variations in the technique arise from the different modes of application of power so it is either DC (direct current) or RF (radio frequency). DC mode is most commonly used for deposition of metals and conductors. But the problem in DC is the charge buildup at the target. Hence we prefer RF to alternate the current to prevent charge buildup. Mostly RF mode is used for insulators and can be operated at a lower Ar pressure. It is also improves plasma handling and line of sight deposition. The magnets in this setup has a different purpose, the field it produces will hold the electrons for a longer time in the plasma due to the effect of the Lorentz force. The typical magnetic field created due to these magnets is 200 Guass. The electrons are thus held far from the substrate reducing chances of substrate heating. There is also an increase in the ionization of the Ar gas. This will greatly reduce the pressure of the gas to 0.5 mTorr as compared to only DC/RF modes which is usually 100mTorr.
It has to be remembered that the magnets are only an additional attachment and not the real power source. So in a typical magnetron sputtering machine like ours we will use DC/RF coupled with magnetron. The advantages of this setup being higher sputter rate at lower pressure, higher film purity, less diffuse scattering of sputtered atoms and localization of plasma.

Such equipment comes in very handy for Spintronics Applications where there is a need for deposition of multi-layers and a precise thickness control. Hence we have been putting it to maximum use to get a successful device for Spintronics applications.