19 sputtering and evaporation presentation-ravi chawla

8/12/2019 19 Sputtering and Evaporation Presentation-Ravi Chawla

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By Ravi Chawla


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MOTIVATION


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Film growth/deposition


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Physical Vapor Deposition (PVD)

The physical vapor deposition technique is based on the formation ofvapor of the material to be deposited as a thin film. The material insolid form is either heated until evaporation (thermal evaporation) orsputtered by ions (sputtering). In the last case, ions are generated by a

plasma discharge usually within an inert gas (argon). It is also possibleto bombard the sample with an ion beam from an external ion source.This allows to vary the energy and intensity of ions reaching the targetsurface.


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a) Physical Vapor Deposition (PVD) systems -

continued

The range of materials that may be deposited using thesemethods include:

Metals such as:

Al

Cu

Au

Ag

etc.

Compound & hard materials such as: Cr

TiN

CrN

AlCuSi

etc.


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PhysicalVapor

Deposition

ThermalEvaporation

Sputtering

Resistive

Inductive

Electron Beam

DC

RF

Magnetron(RF or DC)

ReactiveSputtering


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THERMAL EVAPORATION

Thermal evaporation, using different types of heat sources, was theearliest method used for achieving supersaturated vapor. Preparationof nanoparticles from supersaturated vapor produced by thermalevaporation was first established in 1930 to prepare nanoparticles ofelements.

Oxides were later prepared by the same method by introducingoxygen to the metal vapor.


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The material to be deposited is placed

in a crucible within a high-vacuum

chamber.

After the chamber is pumped down, the

source is heated via (typically) resistive

or e-beam heating. The material isheated to its boiling point such that it

sublimates onto all exposed surfaces in

the vacuum chamber.

The amount of material deposited is

controlled via a thickness monitor which

is placed within the deposition chamber.

The source material must be of high

purity.

Vacuum levels are on the order of 10-5

to 10-7Torr.

Thermal Evaporation

Resistive Heating

Thermal Evaporation

e-Beam

Thermal Evaporation - General


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Fig: Example of an inductively heated crucibleused to create moderately charged temperatures


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Single Source Evaporation : Method of evaporatingmulticomponent film


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Thermal Evaporation - drawbacks

Resistive heating is the simplest method of evaporating metals such as Al or Au,

but it is also the dirtiest in that contaminants which find their way onto the

filament tend to be evaporated along with the metal.

The purity issue can be addressed via e-beam evaporation since the cooled,non-molte high-purity material to be deposited acts as a crucible during the

process (as seen on one of the schematic previously ).

In the case of resistive heating, temperature uniformity across the filament is

difficult to control and therefore, evaporation uniformity onto the substrates may

be a problem. This is not an issue with e-beam evaporation

E-beam evaporation may cause surface damage due to ionizing radiation and/or

X-rays (@ voltages above 10kV, the incident electron beam will give rise to X-ray

emission).


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SPUTTERING


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Sputtering: General


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The Mechanism of Sputtering


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Sputtering Deposition


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Sputtering

The substrate is placed in a vacuum chamber with the source material, named a target,and an inert gas (such as argon) is introduced at low pressure. A gas plasma is struckusing an RF power source, causing the gas to become ionized. The ions are acceleratedtowards the surface of the target, causing atoms of the source material to break off from

the target in vapor form and condense on all surfaces including the substrate.


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Sputtering Process


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Physical vapor deposition (PVD): Sputtering

W= kV i

PTd

-V working voltage- i discharge current- d, anode-cathode distance- PT, gas pressure- k proportionality constant

Momentum transfer

The sputter yield depends on: (a) the energy of the

incident ions; (b) the masses of the ions and target

atoms; (c) the binding energy of atoms in the solid

and (d) the incident angle of ions.


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Reactive Sputtering

Sputtering metallic target in the presence of

a reactive gas mixed with inert gas (Ar)

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oxides Al2O3, SiO2, Ta2O5 (O2)nitrides TaN, TiN, Si3N4 (N2, NH3)carbides TiC, WC, SiC (CH4, C2H4, C3H8)

A mixture of inert +reactive gases used for sputtering


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Reactive Sputtering (Cont.)

chemical reaction takes place on substrate and target

can poison target if chemical reactions are faster thansputter rate

adjust reactive gas flow to get good stoichiometry

without incorporating excess gas into film


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Reactive Magnetron Sputtering

Zinc Oxide Thin films

Zinc oxide is one of the most interesting semiconductors It has been investigated

extensively because of its interesting electrical, optical and piezoelectric

properties

Reactive sputtering isthe best technique forZinc Oxidedeposition.


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Process Parameters

The physical properties of ZnO films are influenced not only by

the deposition techniques, but also by process parameters.

The film deposited on hightemperature substrate willshow finer uniform grainsand smoother surface


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Process Parameters

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Quality of the film dependents on deposition conditions, such assubstrate temperature, deposition power, deposition pressure andargonoxygen flow.


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Conclusion

Sputter deposition is a widely used technique for depositing

thin metal layers on semiconductor wafers.

The range of applications of sputtering and the variations of the

basic process, is extremely wide.

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Sputtering advantages/disadvantages


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Thank You!

19 sputtering and evaporation presentation-ravi chawla

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