Machining at the Nanoscale: Applications of the Focused (FIB)/Scanning (SEM) System Paul Blanchard, Kris Bertness, Ann Chiaramonti Debay, Alexana Roshko, Aric Sanders, Norman Sanford, and Joel Weber National Institute of Standards and Technology (NIST), Boulder, CO

Introduction Sample Preparation I: the Transmission Electron Microscopy (TEM) Lamella Goal: from an arbitrary specimen of interest, create an ultra-thin (< 100 nm thick) cross-sectional slice (a lamella) suitable for TEM imaging Transmission electron microscopy (TEM) and tomography

Specimen: GaN/InGaN Lamella cut out from (APT) are powerful imaging techniques that allow quantitative material FEBID Pt coating on NW NW encased in FIBID Pt Trench milled from side 1 Trench milled from side 2 Manipulator brought in Manipulator Pt-welded Lamella cut free (NW) LED Device on Si Substrate surrounding Si analysis on the scale of individual atoms. NW to lamella encased Micromanipulator tip in FIBID Lamella However, each of these techniques places stringent constraints on the 2 μm 10 μm 10 μm 10 μm Pt cap 2 μm 1 μm 1 μm 2 μm geometry of specimens that can be analyzed. Sample cross sections for Step 1 – Protect sample by capping with Pt, then Step 2 – Cut out the cross section and use the Si Substrate TEM must be thinned to electron transparency (< 100 nm thickness); APT create a cross sectional slice (lamella) by FIB milling micromanipulator to extract it from the substrate requires a needle-shaped tip with a diameter on the order of 50 nm or less 10 μm FEBID Pt bond at its apex. 2 μm 5 μm TEM image of GaN/InGaN NW Pt cap TEM mount prepared The dual-beam focused ion beam (FIB)/scanning electron microscope Lamella thinned by FIB Lamella thinned by FIB Lamella thinned by FIB Lamella Pt-welded to post Lamella brought in Lamella TEM sample (SEM) system enables the machining and manipulation of samples with mount Possible stacking nanometer-scale control. As a result, high-quality samples for TEM and faults GaN/InGaN NW cross section Manipulator cut free 2 μm APT can be fabricated from a wide variety of material systems. In addition, 2 μm 2 μm 2 μm 5 μm 2 μm Si Substrate dual-beam techniques can be adapted to the fabrication of novel test High In-fraction Step 4 – Progressively thin lamella to Step 3 – Attach the lamella to a inclusion structures and prototype devices. Finished GaN/InGaN NW Lamella electron transparency (< 100 nm thickness) TEM sample mount

2 μm 10 μm Overview of the Dual-Beam FIB/SEM System The dual-beam system combines the high-resolution, low-damage Sample Preparation II: the Atom Probe Tomography (APT) Tip Prototype Device Example: the Nanowire (NW) Scanning Probe Tip imaging of SEM with the precise milling capabilities of FIB. With the Goal: from an arbitrary specimen of interest, remove a sample of material and shape it into an In addition to the preparation of samples for TEM and APT, the dual-beam system can be addition of a gas injector (for beam-induced deposition) and a ultra-sharp (< 50 nm diameter at tip apex) needle suitable for APT used to fabricate prototype nanoscale device structures, such as the GaN nanowire (NW) micromanipulator, the system allows samples to be imaged, milled, cut, near-field scanning microwave microscopy (NSMM) probe. moved, and welded to new substrates. Specimen: HSLA80 Steel FIBID Pt cap deposited Angled mill from side 1 Angled mill from side 2 Si cantilever GaN NW FEBID Pt FIB-milled weld 5 μm 5 μm 5 μm hole Step 1 – Cap with Pt, then FIB mill a Pt cap cantilever with a triangular cross section AFM tip Pluck NW from growth substrate and Polished surface of steel specimen 5 μm mount it to FIB-prepared AFM tip

Bottom Cantilever cut free Manipulator Pt-welded Manipulator brought in to cantilever edge of cantilever Performance of GaN NW NSMM Probe Tip Fabricated in the Dual-Beam FIB/SEM System 5 μm NW tip coated by ~3 nm Al O /25 nm W via Schematic of Test Measurement Setup Commercial Pt probe tip (not a nanowire) 2 3 Micromanipulator tip atomic layer deposition (ALD)

5 μm 2 μm 2 μm Step 2 – Cut cantilever free and extract from substrate via micromanipulator FEBID Pt weld Cantilever

5 μm Pt cap Cantilever brought in End section of cantilever Remaining cantilever cut Pt-welded to Si post free

Si mounting post Steel Color shows change in amplitude of |S11| microwave reflection parameter (relative to calibrated 10 μm prepared 2 μm 2 μm 2 μm Pt welds Weber et al., Appl. Phys. Lett. 104, 023113 (2014) minimum |S11| ≡ −45 dBm) Step 3– Attach a ~2 μm section of the cantilever to a Si post and cut free. Repeat to create a set of 10 APT tips. Si post 1 μm Other applications 3D Atom Probe Reconstruction of Steel Tip Finished Steel APT Tip The dual-beam FIB/SEM is a versatile system that continues to be adapted to new applications , such as Possible Carbide solute • 3D tomography. By taking a series of successive SEM images while FIB milling through a inclusions segregation 1 μm FIB annular mill at carbide 20 nm tip region of interest, a 3D reconstruction of the material volume can be obtained. interfaces diameter 1 μm FIB annular mill 1 μm FIB annular mill • In situ electrical and mechanical testing. With the probe micromanipulator Step 4 – Use annular milling (milling operating as an electrical or mechanical probe, materials and devices can be in ring shapes of decreasing size) to characterized in situ with high spatial resolution and simultaneous SEM observation. create final needle shape for APT. • Custom nano-milling. Because the FIB position and dwell time can be precisely 100 nm controlled, arbitrary nanoscale shapes can milled into substrates, and existing nanostructures can be reshaped.