Repetition: Evaporation

Schematic:

Repetition: Distribution of Vapor Streams

21 coscos),,(

rmrR Θ⋅= απ

θα

Hertz-Knudsen-Equation:

Special geometries: Point source – plane substrateHemisphereKnudsen-Sphere

Prerequisites: Point source Line - of - Sight process

αααα ... Angle normal/sourceΘΘΘΘ ... Angle substrate normal/

impingement point

Repetition: Evaporation of alloys

Evaporation of an alloy corresponds to a fractional destillation. The reason for this is the unhindered material transport within the source.

100

10

1

0.1

0 n/n0

log(R /R )A B

Alloy Composition: A:B=1:1

Repetition: Sources

Resistivity heated sources:

Repetition: Evaporation Materials

PowdersGranulatesWiresPelletsShape parts

It is important, that the source material and the evaporation material do not chemically react with each other!

Sputtering I

Solid source, i. e. arbitrary source geometry

Low deposition temperature

Wide parameter field

High deposition rates can be reached

Good coating adhesion

Coating composition =source composition

Interesting film propertiesSource (water cooled)

+

+

+

+ +

Substrate

-600V

Ground

+Deposition materialWorking gas, neutral or reactive

Elementary Processes: Characteristics:

Sputtering II

Nature of ejected particles:AtomsIonsClusterMolecules

Projectiles:Gas dischargeIon gun

Gas DischargeExperiment:

Criteria for a self sustained discharge:It is possible to sustain a gas discharge if:

-

-

+

+

U≈1kV

p Pa≈10

the mean free path of electrons is long enough to ionize neutral gas particles

diluted gas necessary

there are enough gas molecules to trigger a ionization cascade

no high vacuum possible or necessary

The Sputtering Yield I

Yn

n= +

<n> = mean number of particles emitted per impingementn+ = number of impinging ions

Y is dependent on several parameters of the ions and of the target material.

The Sputtering Yield II

Dependence on :

Target materialIon energy

The Sputtering Yield III

Dependence on:

Ion impingement angleIon mass

Linear Collission Cascade: Characteristcs

Y = 0,5 - 4

+

Ejection-Volume:approx. 1 nm3

Energy Distribution of Ejected Particles

The energy distribution of sputtered particles is significantly different from that of thermally evaporated ones.

Linear Collision Cascade: Energy Distribution

E-2

E

n(E)dE

U /20 EmaxE

( ) dEUEEdEEn 3

0

)(+

∝ Emax = Maximum energy,E Emax ∝ +

E = Average emission energy

Linear Collision Cascade: Angular Distribution

n<1n=1

n>1α

n n( ) cosα α∝n ≤ 1 E < 1 keVn > 1 E > 1 keV

Sputtering of Alloys: Different Y

In the case of the homogenous distribution of the constituents the vapor composition is (after a transient regime) identical to the target composition.

Sputtering of Alloys : Cone Formation I

If a low yield material is present in the form of macroscopic preciptates, cones can be formed on the target surface.

Sputtering of Alloys : Cone Formation II

The terminating surfaces of the cones are often low index crystal planes or have an inclination corresponding to surfaces with maximum sputter yield.

Sputtering of Single Crystals: Sputter YieldThe sputtering yield depends on the crystallographic orientation of the surface plane, i. e. in it's Miller indices.Example: cone formation

Y = Y(h,k,l)

Sputtering of Single Crystals: Channelling

Ions may penetrate a single crystal more or less deep in dependence on their impingement direction.

Sputtering of Single Crystals: Wehner-Spots

Focusing of the impulse along densly packed crystallographic directions:

Y = maximum along these directions! If a hemispherical collector is placed above the target, one can detect the so-called "Wehner Spots".