magnetron sputtering and ion beam sputtering

8/3/2019 Magnetron Sputtering and Ion Beam Sputtering

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MAGNETRON SPUTTERING ANDION BEAM SPUTTERING

Pushpendra kumar2009ph10737



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ION BEAM SPUTTERING

its a method of depositing very smooth thin filmson a substrate.

In this technique Spatially restricted ion beamis used having a small cross section.

Source of ions---- ions are extracted from gasdischarge plasma

Target is isolated from the source of ion beams.



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Its a two step process

1) Generation of the ions

A Inert gas is filled in the Vacuumchamber having two electrodes.

A high potential is applied between themand this ionise the gas atoms.

These ions are then taken out from the



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2)

Ions are then accelerated by the electric field

emanating from a grid toward a target.

Energy and flux of ions can be controlled

independently.

These ions particles fall on the target material.

As the ion beam approaches the target, 2processes takes place, electronic excitation and

ejection of target atoms.



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The bombarding primary ion beam produces

monatomic and polyatomic particles of samplematerial and resputtered primary ions, along withelectrons and photons. The secondary particles carrynegative, positive, and neutral charges and they have

kinetic energies that range from zero to severalhundred eV.


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Ejection of target atoms

During the motion of ions they transfers in collisionsthe energy and momentum it has got from the ion toadjacent atoms. They, in turn, transfer the energy andmomentum they have got to next atoms and so on.

coupling forces between surface atoms are usuallyweaker than between bulk atoms so surface atoms havemuch greater chance to escape.

The atoms on the surface undergo series of secondary collisions they get enough energy toovercome the forces of interatomic coupling, they

leave the surface and, having residual momentum



A -zone where target atoms are displaced from theirpositions in structure, B - zone where target atoms

had been excited but then relaxed to theirequilibrium states, and C - surface zone where targetatoms may be sputtered from.



The target atoms after ejecting from the targetmoves to substrate and layer by layer atomdepostion takes place in the vaccum chamber



Magnetron sputtering

Similar to ion beam sputtering except thattarget and substrate are present in the samechamber.

Ion beam is not spatially focused, collisonstakes place in plsama which randomize ionmotion.



Design parameters

It is mainly of three type:

1) Planer megnetron:

Parallel target and anode electrode surfaces arepresent.

Vacuum of less than one ten millionth of anatmosphere must be achieved before it is filled by ainert gas and a high potential is applied to theelectrodes.



Ø Magnets are placed on back side of the cathode(target)

Ø Magnetic field lines emerging from the north pole arenormal to the electric field and as they enters thechamber they have a component parallel to the surface.

Ø At that point Electric field and Magnetic fields are normal

to each other.



Ø As the cathode is negatively charged , This attractsargon ions to the target surface at speed. When theycollide with the surface two important processes takeplace: Atoms are knocked out of the target surface andelectron are emitted.

Electrons launched slightly off the target normal willinitially spiral along the B field lines emanating normalto the target. In the region where E and B fields areperpendicular to one another, electrons are forced todrift in a cycloidal hopping motion.

So the electrons are trapped near to the cathode aroundthe magnet known as the tunnel track.



When a secondary electron of sufficient energy collides

with a neutral atom it can knock another electron out of theatom resulting in the creation of a positive ion, ionization.This ion is attracted towards the target surface and thewhole sputtering process is repeated.



So in this way the ionisation process is enhanced .

Large density of ions near cathode produces largedeposition rates.

electron trapping provides less free electrons tobombard the substrate resulting in the ability tocoat temperature sensitive substrates.



cathode

anode

Electronmotion



3)Sputter Gun

Uses a toroidal-conical (triangular ortrapezoidal cross section) target. Withmagnets bonded to the backside.

Outward spreading B field normaly intersectthe E field.

So a plasma discharge is created andconfined over the target surface.



Unbalanced Magnetron

For making the caotings hard and dense ionbombardment is required on the substratewhich can be increased only by reducing thesize of chamber or increasing power.

So to overcome this problem strongermagnets are attached on the outside

resulting in the expansion of the plasmaaway from the surface of the target towardsthe substrate to be coated considerablyincreasing the substrate ion bombardment.



Advantages of megnetron overion beam sputtering

One to two orders of magnitude more current istypically drawn in magnetron than simple DCdischarges for the same applied voltage.

So higher deposition rates are present and lowvoltage is required for same deposition rates.

Another important advantage is reducedoperating pressures, Therefore, for the sameelectrode spacing and minimum target voltage astable discharge can be maintained at lower

pressures.



Disadvantages

In planar magnetron sputtering, material istaken out mostly in the racetrack regionwhere the plasma is most intense.

Surface area decreases so efficiency is low.

Elastic distortion of the target may result inloss of contact to the water-cooled backingplate and a corresponding drop in coolingefficiency.

magnetron sputtering and ion beam sputtering

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