TEM specimen preparation in FIB

by Aleksander Mosberg ([email protected]), reproduced with permission from notes by Ruben Bjørge

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Getting started

Warm up the Pt and C needles. Imaging parameters:

• e-beam:
  • 15 kV
  • 0.17 nA
• Ga-beam
  • 30 kV
  • 9.7pA

Deposit Pt with electron beam (gentler than ion beam)...

1. Tilt stage to 0°
2. Deposit Pt with electron beam:
   1. Draw a rectangle approximately 12 µm x 3 µm x 1 µm on top of your lamella site
      • Application: Pt e-dep structure
      • e-beam settings: 3 kV (!), 2.7 nA
        
   2. Insert Pt needle.
   3. ~4 minutes (dwell time 1µs).
   4. Retract needle when finished.

...or deposit Pt with ion beam

1. Tilt to 52°
2. Align beam coincidence away from TEM specimen area (so as not to contaminate it with the Ga beam)
3. Ga-beam settings: 30 kV, 9.7 pA for imaging, 93 pA for Pt deposition
4. Retract needle when finished

Deposit C with ion beam

1. Tilt to 52°
2. Align beam coincidence away from TEM specimen area
3. Ga-beam settings: 30 kV, 9.7 pA for imaging, 0.46 nA for C deposition
4. Create a 12 µm x 3 µm x 1.5 µm rectangle
   • Application: C dep
5. Insert C needle
6. ~4 minutes (dwell times 200 ns)
7. Retract C needle

General comments:

• Pt needle: Can be inserted and used at any tilt angle, both for e-beam and ion-beam assisted deposition
• C needle: Need at least a tilt angle of ca. 35° before it can be inserted in order not to crash the needle into the sample.
• These comments apply as long as the sample is at eucentric height. But all needles should (preferably) be used only at eucentric height.

Three wedge cuts

1. Regular cross section 22 µm (12 + 5 + 5) x 12 µm x 9 µm
2. Below coated area (pad): From Bottom to Top (i.e., thick line close to pad).
3. Leave a small gap between wedge cut and pad.
4. Application: Si, Scan method: Multiscan, Multipasses = 4
5. Ion beam current 21 nA (maximum).
6. ~2 minutes (dwell time 1 µs).
7. Depth depends on sputtering rate. Measure depth using Line tool (tilt correction).
8. Cut first below (in y) the coated area, then above, then on the left side.

Cut underneath (in z)

1. Change ion beam current to 9.7pA.
2. Tilt to 7° (ion beam at a 45° angle).
3. Realign beam coincidence.
4. Sputter Rectangle 18.15 µm x 1.5 µm x 3 µm. Application: Si.
5. Ion beam current 6.5 nA.
6. Cut away underneath pad. Avoid redeposition, forming bridges.
7. Check by tilting to 52°.
8. Switch to Cleaning cross section once sample is almost free below.

Inserting Omniprobe needle

1. Go to 0° tilt.
2. Start AutoProbe. Username and password: service.
3. Go to Park.
4. Insert Omniprobe.
5. Go to Eucentric high.
6. Position needle in XY above sample using electron beam to view.
7. Lower needle with Z using ion beam to view (9 pA).
8. Make needle surface flat with Cleaning cross section.
9. Position needle on side of pad using both electron and ion beam views (sequentially).

Attaching omiprobe needle to TEM specimen

1. Insert Pt needle. Might get a touch alarm (before click sound).
2. Rectangle 2 µm x 2µm x 2 µm (depending on needle sharpness).
3. Application: Pt dep. Ion beam 93pA.
4. From Top (pad) to Bottom (needle).
5. Cracks visible in the Pt if gluing did not work.
6. Use 0.28 nA ion beam to get a mix of deposition and sputtering.
7. Careful if the needle or pad blocks the Pt needle. Use a lower current in this case (46 pA).
8. Remove Pt needle.
9. Do not move the stage!

Remove bridge on right side

1. Rectangle. Right to left. Ion beam 6.5 nA.
2. Use Cleaning cross section if needed.

Remove Omniprobe

1. Lift up Omniprobe. Speed 1 µm/s in positive Z direction.
2. Go to Park.
3. Retract Omniprobe needle.

Find TEM grid

1. Find TEM grid.
2. Set eucentric height.
3. Rotate 180°if needed (compucentric rotation). Flat surface of post should be up.

Carve out space for the specimen

1. Tilt to 52°.
2. Cut out space for specimen: Cleaning cross section 12 µm (same width as pad) x ~22 µm x 3 µm. From Top to Bottom. Ion beam, 21 nA.
3. Clean sides of cut with Cleaning cross section, 21 nA.

Reinsert Omniprobe

1. Tilt to 0°.
2. Make sure height is eucentric.
3. Insert Omniprobe needle.
4. Go to Eucentric high.
5. Lower needle while monitoring with ion beam, 1 µm/s.

Attach specimen to TEM grid

1. Trim TEM specimen so that it fits with Cleaning cross section, towards the centre, 0.90nA.
2. Lower TEM specimen into place (also move in x/y if needed).
3. Insert Pt needle.
4. Rectangle z = 1.5 µm. Application: Pt dep.
5. 0.28 nA for first attachment (or 90 pA). From TEM specimen to TEM grid.
6. Remove Pt needle.

Detach Omniprobe needle

1. Application: Si. Sputter towards TEM specimen. 0.46 nA(?).
2. Lift up Omniprobe needle with Z.
3. Go to Park.
4. Remove needle.
5. Tilt to 52°.

Final thinning

1. Tilt to 54°.
2. Cleaning cross section. Start with 0.92nA. Monitor with electron beam!
3. Repeat at 50° tilt.
4. Try to get even thickness by adjusting Z of sputtering (1 → 0.7 µm). Monitor thickness with electron beam (lighter = thicker).
5. Check at 52° tilt. Use Digital zoom in Measurement tab.
6. Reduce current to 0.46nA. Reduce Z of cleaning cross section if necessary.
7. Continue cutting from both sides.
8. Reduce current to 0.26nA and repeat.
9. Reduce current to (0.17 nA) 93pAand repeat. Monitor with iSPI. (93pA is the last current uses at 30 kV). After 93pA at 30 kV the TEM sample should more or less have reached the final thickness (ca. 100 nm, depending on the sample and the purpose of the TEM characterization)
10. Reduce ion beam voltage to 5 kV (Contrast / SNR is quite poor at low kV so it can help to position the milling window on the specimen before reducing the HT, then make small adjustments as needed at 5 kV).
11. Tilt to 56°.
12. Cleaning cross section, 44 pA, Z = 0.07 µm.
13. Repeat at 48° tilt. 41: 39.5 and 42.5

Finishing

Measure thickness at 0° tilt with electron beam. Final thickness should be less than 100 nm.

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