Practical Considerations in Atom Probe Tip Making Using FIB-SEM - PowerPoint PPT Presentation

Practical Considerations in Atom Probe Tip Making Using FIB-SEM Nicholas Antoniou & Andrew Magyar Center for Nanoscale Systems Harvard University

Outline • The 3D Atom Probe Microscope • Operation of the 3D Atom Probe • Sample requirements • Prep Process • Tricks and treats in making tips • Examples • Conclusion 2

The 3D Atom Probe • 3D location of the atoms in a sample plus chemical identification; datasets of 10 6 – 10 8 atoms • Lateral resolution ~ 0.5 nm, depth resolution ~0.2 nm • Works with metals (HV mode) and sub-3 eV bandgap semiconductors (Laser mode) • In principle, complete chemical identification from entire periodic table • Prerequisites for sample analysis: rough estimate of composition, conductivity, mechanical stability, and region of interest; sample must be free of cracks and vacuum stable • Prerequisite instruments for sample prep: SEM, FIB with lift- out capability, possibly electro-polishing (for metals)

The Tip is the Sample • Ideal Tip • 100-80 nm diameter • Taper is material dependent. Thermal conductivity is an issue. A cylinder of 1-2 um tall 100-80 nm diameter 4

The 3D Atom Probe 5

Multi-component Samples 6

The 3D Atom Probe Technique Dataset Si uncorrected Ga 10000 Counts 1000 100 0 100 200 Mass-to-Charge Ratio (Daltons) Milled at 30keV throughout, Ga implantation not useful 7

Bar Shape, Attach and Cap Material • Right Angle Wedge vs Equilateral Wedge – Prefer Right angle because of fewer interfaces in the sharpening reducing risk of fracture TOP • W stronger attach bond but less desirable for cap • Pt weaker attach but more desirable for cap • Carbon is not used for either • Low acceleration clean up but at 10keV 8

Sample Preparation Volume of interest 9

Right Angle Wedge Prep 10

Sample Preparation 11

Making a Pyramid 12

Sample Preparation Final Annular Milling at ~ 45pA 10 keV FIB 13

Tip Made Out of Nanowire • Nanowire mounted on flat top SiO2 cladded Si, with deposited Ni protective layer 14

Silicon hyperdoped with Au SiAu 6e15 implant Pulsed-Laser Melted with YAG 355 15

Conclusion • The 3D Atom Probe is a very powerful analysis tool that provides 3D location of the atoms in a sample plus chemical identification • The sample prep requirements are demanding • FIB-SEM is very well suited to prepare samples especially site specific ones • Correlating TEM to 3D Atom Probe improves results • Acknoledgements: Dr. A. Akey, Dr. M. Baram, and Peter Felfer • http://www.youtube.com/watch?v=NcG9H3v3xW4 16