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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

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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