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Confidential
Quanta 3D FEG
Beam Deceleration mode
Module 14
2
•New applications
•BSE at low kV (<2 kV)
•Imaging with low landing energy (down to 50 eV)
•High angle BSE
• Improved specification
•Better low kV resolution
•Improved robustness
Optional Beam Deceleration (BD-)mode
3
Beam Deceleration mode
Using BD mode a focusing lens is
created between negatively
biased specimen and polepiece
or detector above.
• Primary electrons are
decelerated EL = EP - EB
• Basic parameter of the BD
mode:
immersion ratio k = EP / EL
• Rough approximation:
chromatic and spherical
aberration coefficients of
final lens reduced by factor k
• Less chromatic aberrations at
low kV
CCdecel
CC dkV
dV
k
C
V
dVCd
/
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Beam Deceleration - mode
Primary electrons are
decelerated:
EL = EP - EB
SE and BSE are accelerated
and detected as high energy
electrons
ESE ~ EB
EBSE ~ EP
Basic parameter of the
cathode lens: immersion ratio
k = EP / EL
E = Landing energy
5 5
BD-Specifications
• Optional
• Detector needed above sample (BSED)
• Only possible in High Vacuum mode
• Landing energy: 50 eV – 30 keV
• Maximum stage bias: – 4 kV
• Touch alarm disabled and probe current
measurement disabled
• Additional UI control page
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Beam Deceleration control
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Detector – overview for BD mode
Quanta 3D FEG
Detectors for BD
mode + -BSED (4-quad) No limiting field of view, good
efficiency
Optional, Slow, large hole
diameter
Retractable vCD Faster, low kV sensitive, small hole
diameter
Optional, Limiting field of view
In Column Detector
(ICD)
Best efficiency for SE, combinable
with others, not limiting field of
view
Slow
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In-column - ICD detector
SE imaging in combination with
Beam Deceleration mode
Primary beam energy: 4keV
3keV
Landing energy: 1keV
Energy on detector: 3keV (SE) and 4keV (BS)
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Detection in BD mode
BSE collection efficiency, Stage bias 4000, landing energy 1000V
0
0.2
0.4
0.6
0.8
1
1.2
4 8 12 16 20 24 28 32
WD/mm
Co
llecte
d B
SE
's/%
of
tota
l em
issio
n
QFEG (18mm diode)
Q3DFEG (10mm diode)
Autrata detector
Optimal Q3DFEG WD=5-6mm
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• Recommendations for BD mode:
• Sample would be best flat if possible because of parallel plane to detector.
• Sample should be semi-conductive or conductive.
• Sample has compositional contrast either: atomic contrast, crystalline orientation phase contrast or chemical compositional phase contrast, or combined.
• Sample has fine physical structure that usually is lost due to edge brightness or transparency in SE mode.
• Sample that is problematic in high vacuum or low voltage mode should be tried in cathode mode.
• The Electron column should be a performer to cope with high resolution with a BSD and low voltage.
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Detection in BD mode
Calculations by Marek UncovskyClose to PB (high angle) z-contrast
Small angles: topo
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Low kV BSE
•Enabled detection of BSE at low kV
SE @ 1 kV BSE @ 1 kV
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Low landing energy
•Imaging with electrons below 200 eV
50 eV 100 eV
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Low landing energy
•Imaging with electrons below 200 eV
200 eV 100 eV
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High angle BSED
• Improved detection of high angle BSE
K = 1 K = 1.6
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•Plusses
Lower aberration
coefficients
Better low kV resolution
Easy landing energy
control
System robustness
Aperture quality
Alignments
Coulomb interactions
•Minus
Specimen part of the lens
Effected by Flatness,
Roughness,Tilt
Detector above sample
(BSED) is needed,
ETD does not work (very low signal)
Only can be used in high
vacuum mode
Beam Deceleration - mode
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Detection in BD mode
•Signal electrons are accelerated and deflected in field of cathode lens
Secondary electrons are detected with energy approximately corresponding to beam deceleration voltage
Backscattered electrons are detected with approximately primary beam energy
All signal electrons trajectories are bent to axis – SE and low angle BSE usually disappear in final lens
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Improved Resolution with Conventional Final Lens
3 nm @ 1 kV 2 nm @ 4kV - 3kV = 1 kV
2 nm (35-65%)
Quanta FEG with beam deceleration and in-column solid state detector
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ICD + solid state BSED
LE 1kV stage bias 4000V
1.55 nm (35-65%) 2.45 nm (35-65%)
LE 1kV stage bias 4000V
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Improved Resolution with Conventional Final Lens
2.5 nm @ 200 V 3 nm @ 100 V
2.94 nm (35-65%)
Quanta 3D FEG with beam deceleration and in-column solid state detector
2.4 nm (35-65%)
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BD mode – Quanta 3D FEG –detector comparison
• ICD –– almost pure SE signal - local charging visible (signal similar like on TLD-SE det e.g. Helios)
• SSBSED – BE – optimal for imaging in this case, no charging
• ETD – mixture of various BSEs – less local charging, little signal
Sample - 0 deg – cross section, HT 5kV, landing energy 2kV (stage bias 3kV)
Customer sample - CONFIDENTIAL!
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BD mode – Quanta 3D FEG – detector comparison
• ICD –– almost pure SE signal
• SSBSED – BE – optimal for imaging in this case,
• ETD – mixture of various BSEs –, little signal
Sample – steel surface , HT 5kV, landing energy 1kV (stage bias 4kV)
Customer sample - CONFIDENTIAL!
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BD on FIB cut
Quanta FEG + BD mode + Autrata detector
Standard FIB cut tilted 40deg
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BD on FIB cutThe same area but with beam deceleration (stage voltage 3.5kV)Conventional mode observation of a cross section
at low kV
Field inhomogeneity is too high - not possible to focus
It is not possible to efficiently use standard
geometry (i.e. tilted sample) for FIB cut
observation -
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•Used approach:
• FIB cut prepared at 0deg
• BD used on an inclined surface
BD on FIB cut
FIB
cut direction
SEM in BD mode
Observed surface
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BD mode – Quanta 3D FEG –BD on 0 deg FIB cut
• ICD –– almost pure SE signal - local charging visible (signal similar like on TLD-SE det e.g. Helios)
• SSBSED – BE – optimal for imaging in this case, no charging
• ETD – mixture of various BSEs – less local charging, little signal
Sample - 0 deg – cross section, HT 5kV, landing energy 2kV (stage bias 3kV)
Customer sample - CONFIDENTIAL!
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Borelia Block - BD on 0 deg FIB cut
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Borelia BlockWhy BD? – for mat with low Z - we may need small interaction volume + BEs