Introduction
DualBeam Application
Training
Presentation: DB basic functions and cross-sections
Essential DualBeam Functionality &
Cross Sections
Hand on/demo/training:
DB concepts: working distance, eucentric height and co-incident point;
Making cross-sections: normal cross-section, corner-cross section;
cross-section for XEDS, cross-section before Slice and View;
Imaging the cross-section: SEM cross-section image and Ion beam
cross-section image;
Curtains: how to minimise the curtains;
SPI mode: SPI and manual SEM Snapshot during patterning;
Slice and Views.
Chengge Jiao
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Introduction
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DualBeam Concept: DualBeam point
DualBeam Concepts
• Eucentric Height
• Co-incident point
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DualBeam Concept: Co-incident point
Stage Positioning, Working Distance (WD)
Eucentric height:
The reference height of
the microscope
i
W
D
Ion
Be
am
Electron Beam
WD
on
tati
Ro
Sample
im
ec
Sp
Y
X
en
ge
Sta
Z
Tilt
STEM detector
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DualBeam Concept: Eucentric Height
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Cross-Section Overview: FIB/DB
SEM
The eucentric height is a stage Zheight, which means that the height
of the specimen at which its image
does not moved laterally (side
movement of the imaging) as a
function of stage tilting.
FIB
All aligned:
• Gas injectors
• SEM coincident
• Tilt axis
• Beams pre-focused
• Optical microscope
• Charge neutralizer
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High Beam currents for milling
Staircase pattern is used in making a
FIB cross section for bulk remove of
material
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Low beam currents for imaging. Stage
tilted 45 degree to allow view the face
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Cross-Section Overview
Well known Cross-section Procedures
The Feature
Bulk Mill
• Removes material in front of feature for viewing
3. Cleaning
Cross-section
2. Box pattern
or cleaning xs
<0.5 m
1-2 m
Intermediate Mill
• make face more perpendicular
Cleaning Mill
• Finely removes material to reveal feature
7-15 m
1. Regular
Cross-section
Low kV cleaning before Ebeam in-situ decoration
Imaging
10-20 m
Making a cross-section
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Why IBID before CS: General purposes
Planarize with FIB Deposition
Evens out the surface topography
Deposit Platinum bar
• x = 1-2 8m wider than crosssection
• y = ~2 microns
• z = height of step of 1 8m
• I = x * y * 6 pA / 8m* 8m
• application file: pt
E-beam Pt deposition for
planarization to protect surface
features, curtains, and TEM.
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The Ion beam deposited metal serves a few purposes
for DualBeam sample preparations
1. To locate the area of interested;
2. To prevent the outer surface of the sample from being
damaged during subsequent ion milling operations;
3. To minimize the cross-section surface curtaining.
Always put IBID before making a cross-section
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Bulk Mill
Intermediate Mill
Draw cross-section pattern
• Align top edge ~ 1-2 7m from front of feature
• For X: Allow 3-4 microns on each side
• For Y: 1 - 2 times the depth
• For Z: The desired depth of the deepest part
Set beam current upto 20 nA
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Select 1/4 - 1/2 the beam current
Remove previous pattern
Draw box pattern or cleaning cross section pattern
• Set X to be about 1 7m smaller than previous
mill
• Set Z to about 1/4 to 1/2 of desired depth
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Cross-section geometry: FIB and DB
Final Polish
Select 150 - 1000 pA
Draw Cleaning Cross-Section
• Adjust leading edge to go through feature
• Adjust trailing edge just beyond previous mill
• Set X to be about 1 8m smaller than previous
mill
• Set Z to about 1/4 to 1/2 of desired depth
Start milling
Grab frames periodically to check progress
Single Ion Beam
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DB
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Imaging cross-section by FIB
Corner cross-section
Corner cross-section:
2D/3D images
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•
•
•
Set aperture to 1-10 pA
Tilt stage to 0°; rotate 180°
Critical focus/stigmate
Use beam shift and, mag. to frame picture
perfectly
• Use a slow single scan ~40s to generate a nice
photo
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Corner Cross-section Procedure
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Preparing cross-sections for EDS analysis
Procedure
Want a clear x-ray signal
that is only derived from
the cross-section face
The back of a typical
cross-section will reflect
rays
These rays obscure the
real signal
• Make cross-section pattern
bigger than face to expose,
and use two cross-section
patterns in parallel mode;
• Use large beam current to
reduce the milling time;
• Using two boxes patterns in
parallel mode;
• Use ion beam in low current
to scan the cross-section
face for final cleaning.
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Preparing cross-sections for EDS analysis
Q3D EDS below the sample surface: Geometry
Extra materials need to remove by FIB to have shadow free to CEDS detector
So make a big box, also deeper than
before
X-ray signal just from cross-section
Typical size would be 20 7m by 20 7m
by 20 7m
Use largest beam current available for
bulk mill
FIB
XEDS detector
To limit the interaction volume, remove
material behind cross-section first.
Thin the back side like for TEM
samples, then fill with Pt as a beam
dump.
Pt not used in IC process and does not
have any overlap peaks.
SEM
Galvanized Steel
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Q3D EDS analysis below the sample surface
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Cross-section for EBSD in a SDB: Summary
a) a cross-section image of the Zn-coating on steel acquired by Q3D SSBSE
detector, b) a XEDS map mixed with Mg-Al-Zn elements of the cross-section
Galvanized Steel
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Curtains: Causes and Solutions
Minimizing curtaining from the beginning
Causes
• Surface topography - top-level
metal lines
• Below the surface inside the
materials: Sputter rate
differences – i.e., Tungsten.
The Feature
Solutions
• Planarize with FIB deposition
• Reduce beam current
• Change OL and Dwell
• Large tilt angle, for example: up
to 8 degrees, depending
materials.
• Angled cut.
• For large patterns, using box for
cleaning instead of CSCLs.
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7-15 m
10-20 m
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Angled Cut: To change the curtain directions
Angled Cut to change curtain direction
Reduces cumulative effects of stacked tungsten plugs. Voids and
edges transfer to lower levels
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1. Bulk mill as usual (an extra 3 7m wider)
2. Save stage location at 52° and 0°, respectively
3. Stage rotate 90° (at 52° tilted)
4. Tilt stage to 15° to 25° away from 52°
5. Scan rotate -90°
6. Save position -“angled”
7. Polish as usual
1. Regular
Cross-section
Tilt Axis
1.
4.
4.
7.
15° to 25° degree away from 52°
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Angled Cut: To change the curtain directions
Cross-section: No Gas/Gas as Preferential Etch
No Gas
• Can give nice results for SEM without changing features too
much.
• Reduces SEM charging and enhances edges.
• Enhances by
• implanting some Ga, making surface more conductive. The
modification of nitride layer is often seen within cross section.
Before modification, the nitride is insulating and appear dark
in images, while afterwards it appears bright indicating that ti
is at least slight conductive.
• some preferential milling.
Gas
• Can use to enhance for FIB or SEM.
• Increases the number of edges; major contrast mechanism, SE.
• Gas “prefers” some material and it is removed more.
SEM cross-section
images of sample V
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Iodine as Preferential Etch
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Example: Cross-section of car paint
Iodine (I2) = Enhanced Etch = EE
• Metal selective
• Enhances barriers
• Cleans redeposition, if any
• Metal selective etch ~5-10:1
• Mills Al about 15x than sputtering
• Mills Oxides about 1-3x than sputtering
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XeF2 and Delineation Etch as Preferential Etch
Electron beam in-situ etching with XeF2
XeF2 : Insulator Enhanced Etch (IEE)
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•
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Oxide, insulator selective
Spontaneously etches poly-Si and silicon
Oxide selective etch ~5:1
Mills thermal oxide, TEOS ~ 8x than sputtering
Delineation
• Oxide selective
• No Spontaneous etching of silicon
• Mills oxides at different rates
GaAs transistors with and without Ebeam XeF2 in-situ etching
Ebeam 2 kV, spot 5, selected area imaging with XeF2 gas valve open
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Preferential Etch Example
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Preferential Etch Procedure
Gas Procedure
• 1. Tilt cross-section face at eucentric height
• 2. Insert gas needle
• 3. Image at 10-50 pA, fast scan, med. resolution
• 4. Open valve
• For IEE, a few seconds ok
• For EE, 10-30 seconds may be needed using medium
scan, medium resolution
• For Delineation Etch, use milling pattern for 2-5 minutes
• 5. Close valve
No Gas procedure
• 1. Tilt cross-section face to ion beam
• 2. Set beam current to 5 - 10 pA
• 3. Take two 10 second photo scans
SEM Image of DRAM after XeF2 Preferential Etch
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Grounding a Floating Line
SPI, iSPI and Slice and View
• SPI: Simultaneous Patterning and Imaging mode:
Direct TV rate real time SEM imaging of FIB milling and
deposition. There are contribution of ISEs.
A few holes milled on the back of the cross-section used ion beam in spot mode.
A very thin layer of Pt is deposited around the hole and the cross-section before
the last step of cleaning. This can minimise the surface and cross-section
charging.
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Electron is doing raster imaging and ion beam is doing
patterning live image update, pure image quality, no UHR)
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SPI, iSPI and Slice and View
• SPI: Simultaneous Patterning and Imaging mode:
Direct TV rate real time SEM imaging of FIB milling and deposition.
There are contribution of ISEs.
• iSPI: Intermittent Switching Patterning and Imaging mode:
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SPI, iSPI and Slice and View
iSPI: Intermittent Switching Patterning and Imaging mode:
Highest resolution, unattended and automated SEM imaging of
FIB patterning. There no contribution of ISEs.
Highest resolution, unattended and automated SEM imaging of FIB
patterning. There no contribution of ISEs.
• SV: Slice and View:
Highest resolution, unattended and automated SEM imaging of FIB
slices for 2D and 3D reconstruction. No contribution of SE’s from the FIB.
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Automated snaphots=slow,
good image quality, HR & UHR
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SPI Mode operation
iSPI mode = clean image
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- A superposition of SE’s from FIB milling + SEM imaging
- To Image in SPI Mode:
• iSEM >> iFIB
• Use fast SEM acquisition scanning
• Use SEM frame averaging
- Alternatively: use BSE SEM imaging
- An inherently “low resolution” method
- OK for end-pointing – fast
High resolution: Snapshot SEM imaging while Patterning.
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Fast way to make a cross-section: Multiscan CS
Snapshots in time intervals (fastest 0.5 sec)
According actual UI imaging settings
HR and UHR
After complete pattern cycles
Or after defined CCS lines
Optionally to pause the patterning
• Compatible with the RTM
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Patterning – Multipass cleaning cross section
The Multiscan CS is about 3x faster than stair step pattern
The fast way to do the rough milling is to apply two or three cleaning
cross-section patterns over the patterning area. This is call Multiscan
cross-section.
Each line milled contains the number of passes needed to reach a
fraction of the specified depth where this fraction is equal to the
depth to the depth divided by the number of multi passes.
Ion Beam
current: 1 nA
Pattern time:
120 seconds
each
Two parameters are used in the UI:
(a) Scan passes: number of passes
(b) scan ratio: enables a dose ramp (i.e. low at start and high at
final face).
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Patterning – Multipass cleaning cross section
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Using Pre-tilted holder for side milling
Using pre-tilted Stage for 0º to 90° view
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AutoSlice and View G2: Red Blood Cells
Input parameters:
> Ion beam milling
and deposition
parameters.
> Total number and
dimension of slices.
> Electron beam
scan parameters.
>Imaging match for
milling (G2 version)
The total milling volume is
about:
24 um x 23 um x10 um
= 5520 um3
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AutoSlice and View G2: Red Blood Cells
AutoSlice and View G2: Red Blood Cells
ASV G2 Automatically run
about 16 hours
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• SEM image Horizontal field
Width (HFW): 9.95 um
• Image(
ResolutionX),(ResolutionY):
2048 Pixel x 1768 Pixel
• PixelWidth and PixelHeight:
X-Pixels = Y-Pixels:
6.07nm/Pixel (with out tilt
correction)
• Setup for 220 slices – 100
nm thick per slice
• Ebeam at 5 keV and
SSBSE detector with the Zcontrast.
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AutoSlice and View G2: Red Blood Cells
The END
Thanks
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