Repetition: Thickness Measurement

Amd

S

d = ThicknessS = DensityA = Substrate surface

Attention:The coating density, S , is in most cases different from the bulk density, D .

Optical Methods: Photometer

Operation:ReflexionTransmission

1 Modulated light source2 Detector f. reflected light3 Detector f. transmitted light4 Controller5 Substrate holder6 Beam deflection

Photometer: Transmission of Metals

T ... Transmission degreed ... Coating thickness

= 550 nm

Photometer: ReflexionPrinziple:Two beaminterference

Example:Multiple coatingOptical thickness:

alReOptical dndn

Interferometer: Multi-Beam Interference

cosd2sinF1

1II2

0t

Transmitted Intensity It

2)R1(R4F

Fineness FI , A0 0

A0r

A0t

d

A1t

A1r

R...Reflectivity

d

It

F small

F large

Tolansky-Interferometer: Interference Wedge

d(x)

x

d(x)

d(x)

x

d(x)

N

2ND

FECO: White Light InterferometryFringes of Equal Chromatic Order

t=const (no interference wedge)

= variable (white light)

Principle: Interferograms:

d = 0t = 2 µm

d = 100 nmt = 2 µm

d = 0t = 1 µm

d = 100 nmt = 2 µm

Other Optical Methods

Nomarski-Interferometry+ Uses polarization and birefringence+ Can easily be integrated into optical microscope

VAMFO (Variable Angle Monochromatic Fringe Observation)+ Variation of light impingement angle+ Simultaneous determination of n and d+ In Situ-method

Ellipsometry+ Variation of light impingement angle+ Simultaneous determination of n and d+ Determination of roughness+ In Situ-method

Friction and Wear

Friction:No removal of material

Wear:Removal of material associated with weight loss

F =mgg Fg

FgFgF=μr

Fg

nr FF No dependence on the

extension of theinteracting surfaces!

=>microscopic interaction unclear!µ = Friction coefficient

0 < µ < 4 - 5(!); µ is not confined to values smaller 1

Friction and Wear: Measurement

Wear:+ All above methods with analysis of transfer

films and abraded coatings+ Abrasion measurement by thickness control+ Slurry-abrasion+ Special test rigs

Friction:+ Linear load (scratch-test)+ Pin on disc+ Disc on disc+ Special tribometers

Micro Hardness

Defined by the residual deformation of a material due to the penetration of an (ideally) undeformable test body.

Test body material:+ Diamond

Test body geometries:+ Vickers: Pyramid with diagonal vs. height 1:7+ Knoop: three sided pyramid+ Rockwell: sphere+ Wedge

Test loads: + 10-5 – 2 N

Micro Hardness: Test GeometryUltra micro hardness-tester, Vickers geometry:

a) Strain gageb) Samplec) Double springd) Coile) Clutchf) Base plate

Test body

This type of hardness tester can easily be implemented into an optical or a scanning electron microscope.

Micro hardness impressions

NanoindenterThe Nanoindenter also allows the determination of the elastic (reversible) deformation (i. e. of the elastic modulus) of the sample.

In the case of coatings care has to be taken that the indentation depth of the test body is less than 1/3 of the film thickness.

Only under this condition the influence of the substrate can be neglected.

Penetration depthResidual deformation

load

Elasti

c m

odul

us

unload

Forc

e

Non-Destructive Hardness MeasurementHertzian contact:

w(r) corresponds to the indentation depth of the test body.G and

result from

the elastic constants of the sample:

r

z

0 w(r)

w(r)=f(F,G, )F

Point force acting ontoan ideally elastic half-plain:

G...Shear modulus...Poisson ratio

G c 44

cc c

12

44 122( )

Determination of Elastic Constants

Elastic constants can be determined by the measurement of the sound velocity of longitudinal und transversal vibrational modes wthin a solid body.

Surface Acoustic WavesExciatation of longitudinal and transversal surface modes by a defined laser pulse:

From the runtime of the wave package the sound velocity can be determined. From this the elastic constants can be deduced.The excitation of surface waves allows the application of this principle to thin films.

Laser pulseat time t0

Surface wavepackage

Piezoelectr.transducer

Hardness: Important Influences

The follwing material parameters may influence hardness:

+ Sress state+ Temperature+ Grain size+ Impurities+ Degree of deformation

Mechanical Properties: Spatial Resolution

By Scanning Force Microscopy the following mechanical (surface) properties can be determined spatially resolved on the nanometer scale:

+ Elastic modulus+ Hardness + Adhesion strength

This is possible by the so-called force spectroscopy

Force-Distance curves:

a/b: Approach

b/c: “Snap-on”

c/d: Repulsive region

d/f: Pull-back

e: Zero transient

f/g: Detatchment of tip

g/h: Force free pull-back

Pulsed Force Mode

free cantileveroscillation

Repated recording of force/distance curves during an AFM-scan with electronic analysis:

Topography

Adhesion

Stiffness

Polymer chains:Force-distance curve:

ArtifactsImportant artifact of force spectroscopy: Formation of a water meniscus between tip and surface under regular envronmental conditions.

Preventive measures:+ Work under dry nitrogen+ Work in liquids+ Work under inert gas+ Work under HV

The meniscus primarily modifies the values for the adhesion of the tip to the surface due to the high surface tension of water.

AFM-tip

Water meniscus

DuctilityBulk material: breaking strain b [%]

Thin film: 3-point-bending test

0

0ZB l

ll

lZ = Sample length at breaking pointl0 = Length of uncharged sampleB = Breaking strain [%]

dR2d100

B d = Film thickness

R = Radius of curvature for first crack formation

Cracks

StressesKinds of stress:

Mechanical Stress:

MECH T I

MECHCan be triggered by clamping the substrate and subsequent relaxation

Thermal stress:Triggered by different coefficients of thermal expansion (CTE) of substrate and coating

)TT)((E MBUSST ES ... Elastic modulus coatingS ... CTE, coatingU ... CTE. substrateTB ... Coating temperatureTM ... Temperature of stress measurement

Stresses and Film Structure

Intrinsic stress:

IIntrinsic stresses are a direct consequence of the coating structure and the deposition conditions.

Tensile stressCompressive stressVariable

Tensile stress

Compressive stress

Intrinsic Stress: Sputtering

Stress Measurement: FundamentalsCurved Substrate:

Tensile stress Compressive Stress

a) Substrateb) Coatingc) Reference plate

Total stress

of a thin film:

2s1sFs

2ss

R1

R1

d)1(6dE

ES ... Elastic Modulus substrateS ... Poisson Ratio substratedS ... Substrate thicknessdF ... Film thicknessRS1 , RS2 ... Radius of curvature before/after coating, respectively

Stress Measurement: Interference Optics

a) Substrateb) Coatingc) Reference plate

(plane glass)d) Beam dividere) Light sourcef) to acquisition optics

DM ... Diameter m-th Newton-fringeDN ... Diameter n-th Newton-fringe

... Wavelength of incident light

RD D

m nsm n

2 2

4( )

Stress Measurement: Geometric Optics

a) Coated substrateb) Glass plate with reflecting coatingc) Beam dividerd) Displaye) Image uncoated substratef) Image coated substrateg) Incident light

y ... Sample diametery+ ... Image diameter uncoated sampley' ... Image diameter coated sampleD ... Distance sample/display

RyD

y y

2'

Stress Measurement: Cantilever

Principle:

CoatingSubstrate

Geometry:

l

RS

l

H

H)2tan(

Htana

21

SRlsin

lH2

Htana

l2RS

Neglections and assumptions:a) no lateral displacement of cantileverb) no vertical displacement of cantilever()c) low /H

Compressive stress

Tensile stress

Stress Measurement: X-RaysPrinciple:

Measurement of the global deformationof the elementary cell by:+ Interstitials+ Vacancies

Advantages:+ Non-destructive+ In Situ possible

Disadvantages:Numerous error sources:+ Lattice defects+ Dislocations+ Impurities+ Impurity phases