Xe+ FIB Milling and Measurement of Amorphous Silicon Damage

Abstract

Minimizing surface damage during FIB specimen preparation is an important factor for high quality analytical results, especially in the case of TEM membrane and EBSD sample preparation. For conventional Ga + FIB milling, techniques using reduced accelerating voltages for final polishing to minimize sample damage are commonly used [1]. With newer ion species available for FIB milling, namely Xe + , the ion-solid interaction will be slightly different from Ga+, but the same low ion energy strategies can be applied for minimizing ion milling damage.Previous studies on single crystal silicon with a conventional Ga + FIB show ~22 nm amorphous sidewall damage when milled with an energy of 30 keV and less sidewall damage with lower energies . On the same substrate, modeling indicates that milling with heavier ions will produce less sidewall damage than with a lighter ion of the same energy [2]. Hence, less sidewall damage should be achievable when FIB milling with Xe + (54) in comparison to Ga + (31). In this study, the sidewall amorphization damage on single crystal silicon after Xe + FIB milling and also Ga+ FIB milling has been measured for comparison.Cross-sections of a blanket silicon wafer were prepared using both a Vion Plasma FIB (Xe + ) and a Helios DualBeam at 30 keV. Specimens were polished with energies of 5, and 2 keV using incident angles of 88°, 86°, 84° respectively. After sputter coating the surface with iridium as an initial protection layer, conventional in-situ liftout TEM samples of the milled cross-sections were prepared using a Helios NanoLab 450HP DualBeam equipped with an EasyLift nanomanipulator. Amorphous silicon damage was analyzed by HRTEM on a Tecnai Osiris TEM operating at 200 keV.Figs. 1a, 1b and 1c show HRTEM images of the amorphous sidewall damage from Ga+ FIB milling with 30 keV, 5 keV and 2 keV, respectively. Figs. 2a, 2b and 2c show HRTEM images of the amorphous sidewall damage from Xe+ FIB milling with 30 keV, 5 keV and 2 keV, respectively. As expected, the experimental results follow SRIM calculations and predictions from fundamental ion-solid interactions [3]. The Xe+ sidewall amorphous damage decreases dramatically as a function of energy and is smaller than 30 keV Ga+ FIB results by as much as ~ 40%.

Ellipsoidal mesoscale mineralization pattern in human cortical bone revealed in 3D by plasma focused ion beam serial sectioning

“…The PFIB is capable of much higher ion beam currents (few pA to >1 μA) compared to Ga-FIB (1pA to 20nA), and retains a focused spot size unlike Ga+ at high ion beam currents to enable thin slicing (Smith et al, 2006). The PFIB also maintains a quality surface for imaging, with the amount of surface amorphization decreased by 20-40% on silicon compared to Ga + -FIB (Kelley et al, 2013), and the surface roughness reduced by an order of magnitude (from 400 to 50 nm RMS on interconnects) when using a rocking polish (Altmann and Young, 2014). These potential benefits translate for biological imaging in 3D, ultimately offering possibility for larger, smoother, and less damaged volumes to be acquired by the PFIB in shorter times with the same nanoscale resolution as images afforded by the Ga + FIB-SEM (Bassim et al, 2014;Burnett et al, 2016).…”

On the Application of Xe+ Plasma FIB for Micro-fabrication of Small-scale Tensile Specimens

“…Furthermore, it has been clearly demonstrated that the use of Xe + ions results in a reduced depth of amorphisation when compared to Ga + FIB [26,27]. The efficient sputtering rate and relatively high operating currents make the Xe + PFIB an ideal candidate for the fabrication of mesoscale tensile specimens.…”

Novel Methods for Recording Stress-Strain Curves in Proton Irradiated Material

“…This difference corresponds to a variation of nearly 40 MPa, with the specimens prepared using PFIB having the largest yield shift. Although the samples prepared using PFIB accumulate some surface damage due to ion beam milling, previous observations have shown that the damage layer is approximately 40% shallower compared to that induced using Ga + FIB, being in the order of 10 s of nano meters 43,44 . This represents approximately 5 × 10 −3 % of the sample volume which is not thought to contribute significantly to the measured shift.…”