Preparation of lamellae for TEM viewing

Patent metadata

Field	Value
Publication number	US-10068749-B2
Application number	US-201313899278-A
Country	US
Kind code	B2
Filing date	May 21, 2013
Priority date	May 21, 2012
Publication date	Sep 4, 2018
Grant date	Sep 4, 2018

Abstract

A method and apparatus for producing thin lamella for TEM observation. The steps of the method are robust and can be used to produce lamella in an automated process. In some embodiments, a protective coating have a sputtering rate matched to the sputtering rate of the work piece is deposited before forming the lamella. In some embodiments, the bottom of the lamella slopes away from the feature of interest, which keeps the lamella stable and reduces movement during thinning. In some embodiments, a fiducial is used to position the beam for the final thinning, instead of using an edge of the lamella. In some embodiments, the tabs are completed after high ion energy final thinning to keep the lamella more stable. In some embodiments, a defocused low ion energy and pattern refresh delay is used for the final cut to reduce deformation of the lamella.

First claim

We claim as follows:

1. A method of forming a lamella having an observation face for transmission electron microscope observation of a feature of interest in the observation face, comprising:
directing a charged particle beam toward a work piece in the vacuum chamber of a charged particle beam system to induce deposition from a precursor gas of a protective layer above the feature of interest, the ratio of the sputtering rate of the work piece and the sputtering rate of the protective layer being within a ratio of 1.5 to 1 and a ratio of 1:1, the work piece comprising silicon;
directing a focused ion beam toward the sample to mill one or more fiducials near the feature of interest;
directing the focused ion beam to mill cavities on both sides of the region of interest to form a lamella;
from each side of the lamella, directing the focused ion beam to mill progressively closer to the observation face from the cavity, successively milling to remove less material from the lamella as the beam approaches the region of interest to provide a bottom surface of the lamella that slopes away from the observation face, the ions in the focused ion beam having a first landing energy;
after milling progressively closer to the observation face from the cavity, milling to remove material separating the cavities to leave tabs supporting the cavity;
after milling to remove material separating the cavities, directing an ion beam toward the observation face, the ion beam having a second landing energy, lower than the first landing energy.

2. The method of claim 1 in which the first landing energy is greater than 20,000 eV and the second landing energy is less than 15,000 eV.

3. The method of claim 2 in which the first landing energy is greater than 25,000 eV and the second landing energy is less than 10,000 eV.

4. The method of claim 2 in which the first landing energy is greater than 28,000 eV and the second landing energy is less than 6,000 eV.

5. The method of claim 1 further comprising separating the lamella milling from the sample inside the vacuum chamber.

6. The method of claim 1 further comprising separating the lamella milling from the sample outside the vacuum chamber.

7. The method of claim 1 in which directing a focused ion beam to mill progressively closer to the observation face from the cavity, successively milling to remove less material from the lamella as the beam approaches the region of interest to provide a bottom surface of the lamella that slopes away from the observation face includes thinning the lamella to less than 100 nm thickness.

8. The method of claim 7 in which the steps are performed automatically without human intervention.

9. The method of claim 7 in which the lamella is thinned to less than 70 nm.

10. The method of claim 7 in which the lamella is thinned to less than 50 nm.

11. The method of claim 1 in which directing a focused ion beam to mill progressively closer to the observation face from the cavity includes determining a beam position using the fiducial prior to the final milling.

12. The method of claim 1 further comprising after milling progressively closer to the observation face from the cavity directing a defocused ion beam to toward the observation face, the energy of the ions in the defocused ion beam less than the energy of the ions used to form the cavities.

13. The method of claim 12 in which directing a defocused ion beam to toward the observation face includes successively directing the defocused ion beam toward the observation face, with a delay between successive applications of the beam.

14. The method of claim 1 further comprising viewing the lamella with a scanning electron microscope to determine its thickness.

15. The method of claim 14 further comprising milling a cross section in the lamella and viewing the cross section with the scanning electron microscope before the lamella is separated from the work piece.

16. The method of claim 1 in which directing a focused ion beam toward the sample to mill one or more fiducials near the feature of interest includes milling two fiducials, one on either side of the lamella to be formed, the fiducials aligned with the center of the lamella to be formed.

17. The method of claim 1 in which directing a focused ion beam toward the sample to mill one or more fiducials near the feature of interest includes milling two fiducials, one on either side of the lamella to be formed, the fiducials offset from the center of the lamella to be formed.

18. The method of claim 1 in which directing a focused ion beam to mill progressively closer to the observation face from the cavity includes determining a beam drift at least once during milling and correcting the position of the beam to compensated for the drift.

19. The method of claim 1 in which the protective layer comprises: tungsten or carbon.

20. The method of claim 1 in which directing the focused ion beam to mill progressively closer to the observation face from the cavity further comprises directed the focused ion beam at a grazing angle with respect to the observation face, the grazing angle being no greater than 40 degrees with respect to the observation face.

Assignees

• Fuller Scott Edward
• Routh Jr Brian Roberts
• Moriarty Michael
• Fei Co

Inventors

• Fuller Scott Edward
• Routh Jr Brian Roberts
• Moriarty Michael

Classifications

• G01N1/32 Primary

  Polishing; Etching · CPC title

• H01J2237/31745

  for preparing specimen to be viewed in microscopes or analyzed in microanalysers · CPC title

• H01J37/3026 Primary

  Patterning strategy · CPC title