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".
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