clickin pt

FEI DB235 ex-situ lift out TEM sample preparation procedure
Nicholas G. Rudawski
[email protected]
(805) 252-4916
Last updated: 06/19/15
DISCLAIMER: this procedure describes one specific method for preparing ex-situ lift-out
TEM samples via FIB. It is not by any means universal, for there is no one correct way
to make a sample. Depending on the material, type of analysis needed, and amount of
area needed for imaging, significant deviations from this guide may be necessary. You
should always check the literature to see what, if anything, has been published
regarding FIB-based TEM sample preparation of your materials and/or analysis needs.
That being said, this method has been successfully applied to a wide range of materials
where high-resolution TEM imaging over a relatively small analysis area is needed.
1.
Preliminary sample preparation
1.1.
2.
Prior to FIB processing, samples may need to be coated with a conductive
layer of sufficient thickness to prevent surface damage during the initial
stages of I-beam imaging and protective Pt layer deposition. If surface
preservation is not needed and the specimen is conductive, this is not
needed. However, this is needed if the specimen is insulating, even if
surface preservation is not required because it will be impossible to get a
stable I-beam image of an insulating specimen otherwise. A layer >200
nm-thick of conductive C (three coatings from the MAIC evaporator) or Cr
are known to work well for this application. Other materials may also work
well, but Au-Pd is not recommended for a protective conductive layer
since it is known to become porous upon exposure to the I-beam.
Sample loading
2.1.
Log on to the TUMI system (you cannot proceed further until this is done).
2.2.
The FIB software (xP) should already be open and running. Login with
your username and password (you will receive this at the start of training).
2.3.
On the far upper right corner of the software, enter the “key” panel by
clicking on the
icon.
2.4.
Under the “Vacuum” control click “Vent” to start venting.
2.5.
It will take 2 – 3 min for the chamber to vent You will know the chamber is
vented when the door can be pulled open with little resistance.
1 3.
2.6.
Insert the pin end of the stub into the stage and firmly tighten the
setscrew. Use the metal “dog-ear” and adjust the Z control knob on the
outside of the door until the top of the sample is just under the bottom
edge of the dog-ear.
2.7.
Remove the dog-ear from the stage, close the chamber door and click
“Pump”; be sure to apply light pressure to the door during the initial pump
down.
During evacuation
3.1.
In the “Confirm holder…” dialogue box that pops up after starting pumping,
under “Select Holder” select “Stub Holder” if using a single stub or “MultiStub Holder” if using a multi-stub holder and select “OK”.
3.2.
While the chamber is pumping down, if Pt deposition will be needed during
your session, enter the
menu, go to “GIS Heating” and click “On” next
to “PT GIS 1” to start heating the Pt. The “Status” light will change from
blue to red when the Pt is ready to be used.
3.3.
Along the top menu bar, select “E-Mag” and make sure “Mags Coupled” is
checked from the dropdown menu.
2 3.4.
Along the row of icons below the menu bar, select
the I-beam.
3.5.
Along the top menu bar, select “Stage” and select “Zero Beam Shift” from
the dropdown menu to reset the beam shift for the I-beam.
3.6.
Along the row of icons below the menu bar, select
the E-beam.
3.7.
Along the top menu bar, select “Stage” and select “Zero Beam Shift” from
the dropdown menu to reset the beam shift for the E-beam.
3 and
and
to active
to activate
3.8.
4.
5.
In the
menu, go down to the “Status” and check that “Vacuum Status”
reads “Vac OK” AND “Chamber Pressure” is < 1.0E-4 mbar and stable.
Turning on the beams and finding an area of interest
4.1.
In the
4.2.
Under “Status”, check that the “Ion Column HV” is reading 30 kV, “Ion
Emission Current” is ~2.5 µA, and “E – Column HV” and “E – Spotsize”
are reading 5.0 kV and 3, respectively (appropriate settings for general Ebeam imaging). This will usually take ~30 sec.
4.3.
Make sure
4.4.
Select
4.5.
Use the joystick and move around until you find a general area of interest
where you wish to make a sample (alternatively, you can double click on a
point in the image and the stage will move to center that point in the
image).
and
are selected to active the E-beam.
to start live imaging with the E-beam.
Setting eucentric height
5.1.
Enter the “Swiss army knife” panel by selecting the
of the
5.2.
menu under “System,” select “Beams On” to turn on the beams.
icon to the right
icon.
Use the magnification selector knob on the desktop control panel to
increase the magnification to ~1 k×.
4 6.
5.3.
Find and center in the image a flat recognizable feature on the sample
surface near the area of interest.
5.4.
Select
5.5.
In the bottom of the panel, find the stage tilt “T” and input a value of 5°.
The image will shift either up or down (probably down) as stage is tilted.
5.6.
Use the “Z” control knob on the chamber door and adjust until the feature
is once again centered.
5.7.
Repeat the previous 3 steps inputting T = 10, 20, 35, and 52°.
5.8.
Return the stage tilt to T = 0°.
5.9.
Find and center the feature in the image.
5.10.
Increase the magnification to ~10k× (this will be the magnification used for
much of rest of the sample prep procedure) and focus the image using the
desktop control panel.
5.11.
Tilt to T = 52° and adjust “Z” to return the feature to the center of the
image.
5.12.
Return the stage tilt to T = 0°.
5.13.
Find and center the feature in the image (it shouldn’t have moved much),
and focus the image using the desktop control panel.
5.14.
Tilt to T = 52° and adjust “Z” to return the feature to center of the image
(this should need little, if any, adjustment at this point).
5.15.
Leave the stage tilt set to T = 52°.
(stage cannot be tilted unless this is done).
Linking the beams
6.1.
Make sure the stage tilt is set to T = 52°.
6.2.
In the menu bar under “I-beam,” select “30 pA” and then select
to active the I-beam for imaging.
5 and
7.
6.3.
On the right panel, select “Scan Rotation” and input 180°; this rotates the
I-beam image 180° relative to E-beam image and preserves the top-down
orientation when the stage is tilted (NOTE: some users may opt to leave
the I-beam scan rotation at 0°; this is a matter of stylistic preference, but I
recommend leaving it at 180° to start with).
6.4.
Select the auto contrast/brightness icon
image for optimal viewing.
6.5.
Use the shift knobs (DO NOT translate the stage!) on the desktop control
panel to move the I-beam image so the center of the image is coincident
with the same point in the E-beam image (where you want to make your
TEM sample); this “links the beams” so that the E-beam and I-beam
image the same area on the sample. If you properly set eucentric height,
the need to shift the I-beam image should be minimal.
6.6.
If needed, you can translate the stage left or right by a small amount to
move to a different area (perhaps a cleaner one); however, do not
translate the stage up or down or you will no longer be at eucentric height.
6.7.
Select
(or press F9) to adjust the
to stop live I-beam imaging.
Protective Pt strip deposition
7.1.
Make sure the stage tilt is set to T = 52°; if you start this procedure at T =
0°, your sample won’t turn out right!
7.2.
In the menu bar under “I-beam,” select a “300 pA” setting
6 .
7.3.
Under “Gas Injection” click “In” next to “PT GIS 1”.
7.4.
Along the row of milling patterns icons, select the filled box pattern icon
and give it X, Y, and Z dimensions of 10, 1.0, and 1.0 µm (NOTE:
these are only suggestions; you can adjust the dimensions to whatever is
required for your samples).
8.
7.5.
Under “Material File” select “pt_tem.mtr”
of the box should be green).
(the outline
7.6.
Perform auto contrast/brightness by selecting
every time the I-beam current is changed).
7.7.
Select
7.8.
Select the arrow icon
to position the box in the desired location for Pt
deposition (try to stay near the center of the image).
7.9.
Select the patterning icon
(this should be done
to take a single I-beam image.
to start deposition.
Milling deep trenches
7 8.1.
Select “Out” next to “PT GIS 1” to retract the Pt needle.
8.2.
Change the I-beam current to “5000 pA” and perform auto
contrast/brightness
.
8.3.
Take a single I-beam image
.
8.4.
Change “Material File” to “si.mtr”
should change to yellow).
8.5.
Erase the pattern by selecting the eraser icon
8.6.
Select the regular cross-section pattern icon
and click/drag/release on
the image to draw the pattern. Set the X, Y, and Z dimensions to 12, 4,
and 2.0 µm (NOTE: for Si, milling trenches with Z = 2.0 µm will actually
produce trenches ~6.0 µm deep, just FYI).
8.7.
Position this pattern centered and below the Pt strip.
8.8.
Take a single I-beam image
to see if any drift occurred and adjust the
pattern position if necessary and then start the pattern
.
8.9.
Select “Edit” under “Patterning”
“Advanced Features” dialogue box
8 (the pattern outline
.
and input 180° for rotation in the
.
8.10.
Take a single I-beam image
and then position the pattern centered
and above the Pt strip. NOTE: whenever a regular cross-section pattern
is executed below (above) the Pt strip, the pattern rotation should be
set to 0° (180°).
8.11.
9.
Take another single I-beam image
to make sure the image is stable
(adjust the pattern position, if necessary) and then start the pattern
.
Rough thinning cuts
9.1.
Change the I-beam current to “1000 pA”, perform auto contrast/brightness
, and take a single I-beam image
.
9.2.
Select the arrow icon
, click in the middle of pattern, and change the Y
and Z dimensions to 0.5 and 1.0 µm.
9.3.
Change the pattern rotation to 0°.
9.4.
Take another single I-beam image
to make sure the image is stable,
position the pattern centered and below the Pt strip, and start patterning
.
9.5.
Change the pattern rotation to 180°, then take a single I-beam image
9 .
10.
9.6.
Position the pattern centered and above the Pt strip and start the pattern
.
9.7.
Perform the previous two milling steps (alternating) until the Pt layer is
~0.75 µm-wide (Y dimension).
Undercutting
10.1.
Change the stage tilt to T = 7°.
10.2.
When the stage is done tilting, take a single I-beam image
auto contrast/brightness
; perform
if necessary.
10.3.
Erase the pattern
and then select the filled box pattern icon
.
Draw one pattern with X, Y, and Z dimensions 12, 0.7, and 1.0 and two
other patterns with X, Y, and Z dimensions of 0.7, 3.0, and 1.0 µm.
10.4.
Position the first pattern centered and ~2/3 of the distance from the
sample surface to the bottom of the trench; position the other two patterns
along the outer edges of the sample making sure the outer patterns are
slightly below the surface of the sample.
10 11.
10.5.
Take a single I-beam image
and adjust the patterns if any drift
occurred (NOTE: it may take a few seconds for the drift to settle after
stage tilting), and then start the patterns
.
10.6.
You can check the progress of the undercut by intermittently taking single
E-beam images
during the milling. The sample will look similar to the
following when the undercut has gone completely through. Basically, you
need to verify the U-shaped undercut has gone completely through the
specimen (otherwise, you won’t be able to lift it out!).
Fine thinning cuts
11.1.
The next series of steps alternates executing patterns from the top and
bottom of the sample with stage tilts of 54 and 50° and pattern rotations of
180 and 0°, respectively; this helps to preserve the protective Pt strip while
creating a more uniformly-thick sample.
11.2.
Increase magnification to 15k× for the rest of the procedure (optional, but
helpful).
11.3.
Tilt the stage to T = 54.0°.
11.4.
Erase the solid box patterns used for the undercut
, draw a regular
cross-section pattern
, and set the X, Y, and Z pattern dimensions to
12, 0.25, and 0.5 µm (make sure the pattern rotation is set to 180°).
11.5.
Reduce the I-beam current to “300 pA”, perform auto contrast/brightness
, and take a single I-beam image
11.6.
.
Position the pattern along the top edge of the sample and start the pattern
. Occasionally take E-beam images
during milling to make sure
the Pt strip is still intact.
11 11.7.
Tilt the stage to T = 50° and change the pattern rotation back to 0°.
11.8.
Take single I-beam images
to verify the sample isn’t drifting, then
position the pattern below the bottom edge of the sample and start the
pattern
. Occasionally take E-beam images
during milling to make
sure the Pt strip is still intact. The sample should be ~0.3 µm thick after
this step.
11.9.
Tilt the stage to T = 54°, reduce the I-beam current to “100 pA”, perform
auto contrast/brightness
, and take a single I-beam image
.
11.10. Reduce the X dimension of the pattern to 6.0 µm and change the pattern
rotation to 180°.
11.11. Take a single I-beam image
to make sure the sample isn’t drifting,
position the pattern centered and over the top edge of the sample and
start the pattern
. During milling, frequently take E-beam images
to make sure the Pt strip is still intact.
12 11.12. Tilt the stage to T = 50° and change the pattern rotation to 0°.
11.13. Take single I-beam
images to ensure the sample isn’t drifting, position
the pattern centered and over the bottom edge of the sample, and start
milling
. During milling, frequently take E-beam images
to make
sure the Pt strip is still intact.
11.14. Repeat the previous 2 milling steps (alternatively) until the sample is thin
enough for TEM; the sample is usually thin enough for TEM when the Pt
layer decreases in height and becomes very bright. The sample may now
be freed for lift-out or given additional low kV cleaning to further thin it and
reduce the damage layer.
12.
Low kV cleaning (a good idea for HR-TEM imaging)
13 12.1.
To perform low kV cleaning, change the I-beam to “Low kV: 300 pA 5.00
kV”. This will ramp the I-beam voltage down to 5 kV over a few seconds.
12.2.
Select
and
to activate the E-beam and select
to start live
imaging; the magnification will now be ~100× as a result of switching to
the low kV I-beam setting (the magnifications will still be coupled).
12.3.
Increase the magnification back to ~15k× and select
beam imaging.
12.4.
Select
and
to stop live E-
to activate the I-beam, perform auto
contrast/brightness
, and take a single I-beam image
; due to the
reduced I-beam voltage, the I-beam image resolution will not be as good
as when the voltage was set to 30 kV.
12.5.
Tilt the stage to 57° and take a single I-beam image
12.6.
Draw a filled box
with X, Y, and Z dimensions of 6.0, 0.4, and 0.5 µm
(the pattern rotation does not need to be adjusted here).
12.7.
Take single I-beam images
to make sure the sample is not drifting,
and position the pattern so the bottom edge of the pattern is over the top
edge of the sample; this will result in most of the sample being covered by
the milling pattern (don’t freak out, this is what you want to do).
12.8.
Start the pattern
and take frequent E-beam images
during milling
to make sure the sample thins a little further but the Pt strip remains intact.
12.9.
Tilt the stage to 47° and take single I-beam images
sample is not drifting.
14 .
to make sure the
12.10. Position the pattern so the top edge of the box is over the bottom edge of
the sample; again this will result in most of the sample being covered by
the milling pattern.
12.11. Start the pattern
and take frequent E-beam images
during milling
to make sure the sample thins a little further but the Pt strip remains intact.
12.12. If the sample was thin enough after thinning with the I-beam at 30 kV, one
cleaning step per side should be sufficient, but the previous two steps can
be repeated, if needed.
13.
Release cuts (shown here with the low kV I-beam used for final thinning)
13.1.
Leave the I-beam at the last setting used for milling the sample; for
example, if the low kV setting was used as the last step, the low kV Ibeam setting should be used for doing the release cuts.
13.2.
Tilt the stage to T = 52°; take single I-beam images
sample is not drifting.
13.3.
Draw a filled box pattern
0.7, 1.0, and 2.0 µm.
13.4.
Position the pattern over one attached end of the sample and start milling
; take frequent E-beam images
during milling to check if the end
to make sure the
with X, Y, and Z dimensions of the pattern to
has been freed; stop the milling pattern
immediately when the end has
been released. If the end wasn’t freed after this step, repeat this step
again.
15 13.5.
Repeat the previous step for the remaining attached end of the sample;
make sure to take frequent E-beam images
during milling to check if
the sample has been freed; the sample should appear to have moved in
the E-beam image after being freed. Stop the milling pattern
immediately when the sample has been freed.
14.
13.6.
Change the I-beam back to the 30 pA 30 kV setting. DO NOT do any
more imaging of the specimen with the I-beam or the specimen will
unnecessarily acquire further damage.
13.7.
The sample is now ready for ex-situ lifting out using the micro-manipulator
system. To make another sample in another location, first tilt the stage
back to T = 0°, select the E-beam and enter live imaging, and find your
new area of interest. You will have to reset eucentric height and re-link
the beams as described earlier before making another sample.
Finishing the session
14.1.
Make sure the I-beam is set to the 30 pA 30 kV setting (DO NOT leave the
I-beam at the “Low kV” setting when finishing your session).
14.2.
Tilt the stage back to T = 0°.
14.3.
Enter the key menu
should turn gray).
and turn off the Pt heating (the “On” button
16 14.4.
Turn off the beams; the I-Beam HV and E-beam HV will be 1 and 0 kV
when the beams have been turned off, respectively (takes a few seconds
to complete).
14.5.
Select
to freeze the live image; (DO NOT continue live imaging with
the beams off).
14.6.
When the beams are off, select “Vent” under the “Vacuum” control and
agree to the dialogue box that pops up asking if you want to proceed with
venting.
14.7.
After venting has started, select “Stage” from the main menu bar and
select “Initialize Stage” from the dropdown menu. Select “Ok” from the
dialogue box that comes up.
14.8.
Once the chamber is vented, remove your sample, close the chamber
door, and click “Pump” under the “Vacuum” control.
17 14.9.
Log off the TUMI system.
Appendix A: shorthand description of above procedure (steps 4 – 13 only)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Find and align area of interest using E-beam
Set eucentric height
Tilt stage to 52° and link beams with I-beam scan rotation set to180°.
Deposit Pt layer with 300 pA I-beam
Cut trenches on top and bottom side of Pt layer with 5000 pA I-beam
Performing rough thinning cuts on top and bottom side of Pt layer with 1000 pA Ibeam until Pt layer is ~0.75 µm wide
Tilt to 7° and perform undercut with 1000 pA I-beam
Reduce I-beam current to 300 pA and perform alternating thinning cuts on top and
bottom sides of the Pt layer with stage tilts 54 and 50° until sample is ~0.3 µm
wide
Reduce I-beam current to 100 pA and perform alternating thinning cuts on top and
bottom sides of the Pt layer with stage tilts 54 and 50° until sample is (or is nearly)
electron transparent; take frequent E-beam images during milling to make sure Pt
layer is intact if surface preservation is needed
If desired, I-beam voltage can be reduced to low kV setting and alternating
cleaning steps performed from top and bottom sides of sample at stage tilts of 57
and 47° to further thin the sample and reduce the damage layer
When the specimen is finished, perform release cuts using the last used I-beam
setting; take frequent E-beam images and stop milling as soon as specimen is free
Return I-beam to 30 pA 30 kV setting; DO NOT perform anymore I-beam imaging
of the specimen
18