theory of scanning electron microscope
DESCRIPTION
Hitachi High-Technologies CorporationTRANSCRIPT
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Lettuce Field(16M DRAM)
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
Hitachi HighHitachi High--Technologies CorporationTechnologies Corporation
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Image
SampleObjective
Lens
(Illumination Source)Lump
O M
CondenserLens
ProjectionLens
Screen
ImageImage
Sample
Sample
ObjectiveLens
Electron Source
CondenserLens
DeflectionCoils
SE Detector
C R T
T E M S E M
Fluorescentscreen
Scanning
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
Difference among OM, TEM and SEMDifference among OM, TEM and SEM
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The Example of Observation of Alga (The Example of Observation of Alga (MesostigmaMesostigma) ) by Optical Microscope and SEMby Optical Microscope and SEM
Accelerating Voltage: 5kVAccelerating Voltage: 5kV
Optical MicroscopeOptical Microscope SEMSEM
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((αα22==1010--22~~1010--33radrad))
SpecimenSpecimen
((αα11≒≒1rad1rad))Optical MicroscopeOptical Microscope SEMSEM
Depth of FocusDepth of Focus(Shallow)(Shallow)
Depth of FocusDepth of Focus((DeepDeep))
αα11
αα22
The Difference in the Depth of Focus The Difference in the Depth of Focus of Optical Microscope and SEMof Optical Microscope and SEM
Fine Electron BeamFine Electron Beamwith Small Incident Angle with Small Incident Angle
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SE Detector
Specimen
CRT
Camera
Amplifier
Image Signal
High Voltage
DeflectionCoils
Deflection Amplifier
Vacuum Pump
FilamentWehnelt
Electron Gun
AnodeCondenser
LensDeflection
Coils
Objective Lens
SpecimenChamber
Scanning Electron Beam
Mag. Control
Configuration of a scanning electron microscopeConfiguration of a scanning electron microscope
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
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Scanning(Y)
Scanning (X)
l
Scanning Electron Probe
S E MS E M
Specimen
Scanning Electron Beam of CRT
L
Pixel
C R TMagnification :( M)=L / l
Magnifying mechanism in the SEMMagnifying mechanism in the SEM
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
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What is Magnification on Hitachi’s SEM
4 x 5 inchPolaroid unit
(120 x 90mm)
DD
Scan coil
DS
Sample
Magnification=DD/DS
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Photomultiplier
Primary Electron Beam
Specimen
PhotonsLight Guide Signal
CRT
+10kV
SecondaryElectron
ScintillatorScintillatorPhosphors
Al Coating Layer
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
Secondary electron detection systemSecondary electron detection system
Photo Multiplier Tube
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What is resolution on SEM?
Example : Digital Camera
MagnifiedMagnified
MagnifiedMagnified
Could not identify the gap between point and point
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What is resolution on SEM?
On SEM : Identify finest gap between 2 particles
Can not identify Can identify
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Specimen
Vacc
Mag.
Resolution
: Pt particle
: 30kV
: 800kX
: 0.4nm
S-5500Specimen
Vacc
Mag.
Resolution
: Au particle
: 15kV
: 220kX
: 1.0nm
S-4800
100nm
What is resolution on SEM?
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↓
↓
↓
Primary Electron Beam
SecondaryElectron
BackscatteredElectron
Cathodeluminescence
Specimen Current
TransmittedElectron
Electron BeamInduced Current
Secondary Electron Detector
~10nm (Excitation Volume forSecondary Electron Emission)
Transmitted Electron
(Scattered)
Characteristic X-Ray
The primary electron beamThe primary electron beam--specimen specimen interaction ininteraction in the SEM the SEM
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
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Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
-
-
-
-
BackscatteredElectron Secondary Electron
Sample(Metal)Sample(Metal)
Vaccum
Simons,et.al
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100 10,0001Energy of Electron (eV)
Qua
ntity
of
E
lect
rons
(Incident beam energy : 10,000eV)Energy spectrum of the electrons emitted from a specimen Energy spectrum of the electrons emitted from a specimen
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
Secondary Electrons
BackscatteredElectrons
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Electron Beam generated from SampleElectron Beam generated from Sample
Sample
Primary beamPrimary beam
High resolutionSurface feature
Composition information Crystal Orientation
less than 10nm Sample depth of SE generating~ more than 10nmsample depth of BSE
generating
SE information
BSE information
BSE Detector
SE Detector
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Comparison of electron sourcesComparison of electron sources
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
FE TipTungsten Filament
750μm
Electron SourceType of EmissionOperating Vacum (Pa)Brightness (A/cm2・str)Source Size (μm)Energy Spred (eV)Life Time (h)
Tungsten FilamentThermonic
Field EmissionCold FE
10-5 ~10-8
5x105 108
30 0.012.0 0.250 2000
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Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
Energy SpreadEnergy SpreadEffect of chromatic aberration Effect of chromatic aberration
ΔV=~2eV
Tungsten Filament
Crossover ofCrossover ofLow EnergyLow EnergyElectronsElectronsCrossover of Crossover of
High EnergyHigh EnergyElectronsElectrons
ΔV=~0.2eV
FE Tip
Crossover ofCrossover ofLow EnergyLow EnergyElectronsElectrons
Crossover ofCrossover ofHigh EnergyHigh EnergyElectronsElectrons
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ColdCold--CathodeCathode
FEFE
Tungsten(W)
LanthanumHexaboride
(LaB6)
SchottkyFE
Comparison Of Electron SourcesComparison Of Electron Sources
2300deg. Operation 1800deg. Operation 1800deg Operation Ambient TempAmbient Temp
less than 2.0eV less than 1.5eV Less than 0.8eV Less than 0.2eVLess than 0.2eV
5x105 A/cm2sr 5x106 A/cm2sr 5x108 A/cm2sr 2x102x109 9 A/cmA/cm22sr sr
less than 100hr 500 – 1000 hr 1 year More than 2 yearsMore than 2 years
Gun exchange No Gun exchangeNo Gun exchange
Need continuously Need at time of useNeed at time of use
Op. Temp
Energy spread
Brightness
Life time
Tip change
Tip activation
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Primary beam
LensSE Detector
Specimen
3)In-lens type
Primary beam
SE Detector Lens
Specimen1)Conventional type(Out-Lens)
SE Detector(Upper)
SpecimenLens
Primary beam
2)Snokel type
SE Detector(Lower)
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
S-4300
S-4500 S-5500
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Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
W filament SEM
Out lens FE-SEM
Snorkel lens FE-SEM
In-Lens FE-SEM
0.5 1.0 10 30
0.5
1.0
10
20
Acc.(kV)
Res
olut
ion
(nm
)
Comparison of resolutionComparison of resolution
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OUTERbaking
INNERINNERbakingbaking
1st anode
2nd anode
FE tip
- Hitachi is manufacturing both FE Gun and FE Tip.
- Baking is almost unnecessaryafter the installation.
- Even if required, it is very easyincluding inner baking.
- Heated Obj. aperture can eliminatecontamination for long life-time.
Reliable FE-Gan
- Hitachi’s FE tip long life has beenwell known as 3-7 years.
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High Vacc(10kV~30kV)
1)When thick metal layer is coated on the sample2)When high resolution observation3)When internal information of sample is required
Middle range Vacc(3kV~10kV)
1)When high resolution and surface information is required2)When need good contrast on uncurved surface sample
Low Vacc(0.5kV~3kV)
1)When surface feature observation2)When need to avoid Charge-up effect and sample-damage
Adjustment of Accelerating voltageAdjustment of Accelerating voltage
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Vacc 1kV Vacc 15kV
1μm
Magnified
20 nm
1μm20 nm
a) Sample :Carbon
Beam spreading in the sample Beam spreading in the sample
Monte Carlo Simulation
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0.2μm
0.2μm5 nm
5 nm
Beam spreading in the sample Beam spreading in the sample
Vacc 1kV Vacc 15kV
Magnified
b) Sample :Gold Monte Carlo Simulation
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Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
Chage-up Phenomena Eliminate Chage-up Phenomena
Vacc:1.5kVVacc:1.5kV Vacc:0.7kVVacc:0.7kV
Specimen : SiO2 on Photo Resist Line Pattern
Observation at lower accelerating voltagesObservation at lower accelerating voltages
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Comparison of high and low Comparison of high and low accleratingacclerating voltagevoltage
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
High Acclerating Voltage Low Accelerating Voltage
Vacc : 15kV Vacc : 1.0kV
Specimen : Solar Battery
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Primary electron
Sample
Primary electron
Sample
SE Detector
+1 0kV
eFE
Prim ary e lectron
Sample
SE Detector
+1 0kV
eFE
Prim ary e lectron
Sample
Electrical field effect to primary electron(E)Electrical field effect to primary electron(E)
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History of Upper SE DetectorHistory of Upper SE Detector
TEM >75kV
S-900 0.5 -30kV
S-5000
S-5200
S-4500
S-4700
S-4800
ExB equipped
Keep the detector away from axis
Insert shielding cylinder
No problem due to high HV
0.5 -30kV
0.5 -30kV
0.5 -30kV
0.5 -30kV
0.5 -30kV
Instrument H V Countermeasure
(+10kV has been applied to detector surface)Se
mi-i
nlen
sSEM
Inle
nsS
EM
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Primary electrons
SE DetectorB
Sample
eFE
OBJ Lens
FB
|FE|=|FB|
E
+V
+10kV
What is ExB ?
Current(I) direction is opposite to electrons
I
B
FB
Field
Current
Force
Fleming’s left-hand rule
<Primary electron case>
Magnetic
Patent No. : P3081393
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B
eFE
FB
E
+V
+10kV
Secondary ElectronseFE
FB
B
ICurrent
FB
Force
<Secondary electron case>
Primary electrons
SE Detector
Sample
OBJ Lens
What is ExB ?
Current(I) direction is opposite to electrons
Fleming’s left-hand rule
FieldMagnetic
Patent No. : P3081393
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Sample
Cond. Lens
Obj. Lens
a1
a2
b2
b1
d0
d1
Gund1(Beam spot size)= ・ a2
b2d0 ・ a1b1
Obj. lens aperture
b1:Adjusted by Cond. lens
b2:Adjusted by WD
Adjustment of Optics conditionsAdjustment of Optics conditions
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Relation between Cond. Lens and imageRelation between Cond. Lens and image
Beam spot size can be adjusted by changing electric current of Condenser Lens.
Lens current Small excitation Large excitation
Resolution
Beam current
S/N of image
Low High
Large Small
Large Small
b1 Long Short
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WD (Working Distance) :length between Obj. lens and sample surface
WD Long Short
Resolution
Lens excitation
Focus depth
Low High
small large
Deep Shallow
Relation between WD and imageRelation between WD and image
b2 Long Short
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WD:5mm WD:20mm
Relation between WD and imageRelation between WD and image
Focus depth: ShallowResolution : High
Focus depth : DeepResolution : Low
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1) Adjusting beam spreading angle2) Adjusting beam current eradiating to sample
Obj. Lens aperture
Obj. Lens
Gun
Shielded beam by Obj. lens aperture
W.D Beam angle(α)
Sample
B2
Relation between Obj. lens aperture and imageRelation between Obj. lens aperture and image
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Aperture Hole size Large Small
Resolution
Beam current
S/N of image
Low High
Large Small
Large Small
Focus depth Shallow Deep
Relation between Obj. lens aperture and imageRelation between Obj. lens aperture and image
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Theory of Theory of ScanningScanning Electron MicroscopeElectron Microscope
Comparison of objective movable aperture hole sizeComparison of objective movable aperture hole size
Focus Depth → Deep Focus Depth → Shallow
Aperture Size : SmallAperture Size : Small Aperture Size : LargeAperture Size : Large
Specimen : Si on Photo Resist Pattern
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*Metal coating*Observe at ultra Low Vacc.*Cooling Observation
*Change of sample shapeBeam damage
*Heating / Cooling*UV eradiation*Plasma cleaning
*Less contrastContamination
*Metal coating*Observe at Low Vacc* Observe with BSE
*Extraordinary contrast*Drift of sample
Charge-up effect
CountermeasuresPhenomenonAffection
Image detecting affection and countermeasures
Detecting Affection under SEM imagingDetecting Affection under SEM imaging
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Charge-up effectCharge-up effect
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If the sample is conductiveIin = Iout となり
Electric charge of sample is balanced
Iin :electron flow entering sample = IP
Iout:electron flow radiating from sample = ISE + IBSE + Iab
Probe current (IP)
Sample
SE flow(ISE)
SE flowSE flow((IISESE))
BSE flow (IBSE)
Absorbed electron flow(Iab)
What is Charge-up effect?What is Charge-up effect?
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If the sample is non-conductiveIin ≠ Iout となり
Charge-up effect
Sample
SE Flow(ISE)
SE Flow(ISE)
Probe current (IP)
BSE flow (IBSE)
e-e-e- e-
Electric chargeElectric charge e- e-
Absorbed electron flow(Iab)
What is Charge-up effect?What is Charge-up effect?
Iin :electron flow entering sample = IP
Iout:electron flow radiating from sample = ISE + IBSE + Iab
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Countermeasures against charge-upCountermeasures against charge-up
Metal coating
Metal coating by vacuum elaboration system or Ion sputtering system
Coating Material
Need to select optimum material for SEM observation1. Can coat at homogeneous distribution and fine particle2. Good efficiency of SE generating3. Stable against oxidization
Observation:Au、Au-Pd、Pt-Pd、Pt ....Analysis:C、Al....
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Need to avoid affecting sample shape
ArtifactChanging sample sizeContamination / Damage
Need to minimize
Coating layer
Sample
Focus point in coating work
Homogeneous distribution Not Homogeneous distribution
Coating methodCoating method
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200nm
Non coating
Vacc :2kV
Pt coating
Vacc:3kV
Artifact by coating treatment
Coating methodCoating method
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100nm
Less than 3nmLess than 3nm
Less than 3nm coating layer is ideal to avoid artifact
How about odd-shaped sample?
Coating methodCoating method
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b) Coating from several directiona) Coating from only overhead
Coating direction
Sample
Coating layer
*Coating layer become thick when you want to avoid charge-up*Surface feature is not accurate
* Surface feature is accurate
Coating methodCoating method
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What is What is ““ Just focusJust focus””??
Condensed electron beam to finest beam spotCondensed electron beam to finest beam spotis eradiated at sample surfaceis eradiated at sample surface
Spot shape should be Spot shape should be ““perfect circleperfect circle””
Imaging techniqueImaging technique
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Astigmatism correction methodAstigmatism correction method
Beam DiameterBefore correction
Objective Lens
Electron Source Electron Beam
X
Y
Electron BeamElectron Source
Objective LensStigmator
After correctionY
X
StigmatorBeam Diameter
Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
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Theory of Scanning Electron MicroscopeTheory of Scanning Electron Microscope
After correction
Before correction
Under focusUnder focus Just focusJust focus Over focusOver focus
Just focusJust focus
Astigmatism correction methodAstigmatism correction method
Specimen:Trachea of rat
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stigma focus
coarse fineX Y
Beam spot shapeBeam spot shape
Ideal adjustment of focus and stigmaIdeal adjustment of focus and stigma
Present beam spot shape
Ideal beam spot shape
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stigma focus
fineX Y
Beam spot shapeBeam spot shape
coarse
Ideal adjustment of focus and stigmaIdeal adjustment of focus and stigma
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stigma focus
fineX Y
Beam spot shapeBeam spot shape
coarse
Ideal adjustment of focus and stigmaIdeal adjustment of focus and stigma
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stigma focus
fineX Y
Adjust knob to center where image is not drifting
Beam spot shapeBeam spot shape
coarse
Ideal adjustment of focus and stigmaIdeal adjustment of focus and stigma
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stigma focus
fineX Y
Beam spot shapeBeam spot shape
coarse
Ideal adjustment of focus and stigmaIdeal adjustment of focus and stigma
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stigma focus
fineX Y
Beam spot shapeBeam spot shape
coarse
Ideal adjustment of focus and stigmaIdeal adjustment of focus and stigma
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Shorten b1:Increasing excitation of Cond. lens
Sample
1st Cond. lens
2nd Cond. lens
Obj. Lens(Focus knob)
a1
a2
b2
a3
b3
b1
d0
d1
Gun
d1= ・ a2b2 ・ a3
b3d0 ・ a1b1
Summary: Imaging technique for high resolutionSummary: Imaging technique for high resolution
How to minimize d1?
Shorten b3:Shorten WD
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Cond. Lens:1notchWD:12mm
Cond. Lens :8 notchW D:2.5mm
Sample:ITO layerVacc:3.0kVMag. : x 100,000
Summary: Imaging technique for high resolutionSummary: Imaging technique for high resolution