Pulsed helium ion beam induced deposition: A means to high growth rates

Abstract

The sub-nanometer beam of a helium ion microscope was used to study and optimize helium-ion beam induced deposition of PtC nanopillars with the (CH 3 ) 3 Pt(C P CH 3 ) precursor. The beam current, beam dwell time, precursor refresh time, and beam focus have been independently varied. Continuous beam exposure resulted in narrow but short pillars, while pulsed exposure resulted in thinner and higher ones. Furthermore, at short dwell times the deposition efficiency was very high, especially for a defocused beam. Efficiencies were measured up to 20 times the value for continuous exposure conditions. The interpretation of the experimental data was aided by a Monte Carlo simulation of the deposition. The results indicate that two regimes are operational in ion beam induced deposition (IBID). In the first one, the adsorbed precursor molecules originally present in the beam interaction region decompose. After the original precursor layer is consumed, further depletion is averted and growth continues by the supply of molecules via adsorption and surface diffusion. Depletion around the beam impact site can be distinguished from depletion on the flanges of the growing pillars. The Monte Carlo simulations for low precursor surface coverage reproduce measured growth rates, but predict considerably narrower pillars, especially at short dwell times. Both the experiments and the simulations show that the pillar width rapidly increases with increasing beam diameter. Optimal writing strategy, good beam focusing, and rapid beam positioning are needed for efficient and precise fabrication of extended and complex nanostructures by He-IBID.

Tungsten-based pillar deposition by helium ion microscope and beam-induced substrate damage

“…3(a) the vertical growth rate decreases with increasing the defocus voltage. Similar trends are observed by Alkemade et al 16 and indicate that the dominant growth mode gradually changes from vertical to lateral growth as the beam size increases. 3(b) reveals that the pillar width increases with increasing defocus voltage except for a considerable decrease caused by insufficient pillar growth at a defocus voltage of 6 V for the 10-keV sample [bottom-right circle in Fig.…”

Branched High Aspect Ratio Nanostructures Fabricated by Focused Helium Ion Beam Induced Deposition of an Insulator

“…The widths of the tungsten-based nanopillars were measured at ∼30-40 nm, irrespective of the substrate and in agreement with the widths of metallic (platinum and tungsten) helium FIBID nanopillars reported in the literature [18,19,21,23,24]. Beam focus is known to have an effect on nanopillar diameters, with tighter focus resulting in the narrowest pillars [20,21] and beam current can also be used to tune the nanopillar diameter [18,19,23,24]. However, the larger diameters of the PMCPS nanopillars seen in the present study (Figure 2) are primarily attributed to the precursor, as opposed to changes in beam focus or current.…”

“…Compared with the nanopillars, the deposition efficiencies and yields are about a factor of 2 greater for the nanocylinder geometry. This can be attributed to the fact that as opposed to the continuous illumination used to deposit the nanopillars, the nanocylinders were deposited using a beam refresh time (i.e., pause) between the the circular scan paths, which enables replenishment of precursor molecules at the reaction site, thus mitigating precursor depletion effects [7,20].…”

“…Early helium FIBID work also included exploratory studies of the deposition of insulator nanowires (grown along the surface of the substrate) [9] and nanopillars (grown vertically) [10]. In contrast, helium FIBID using metallic precursors is more advanced, incorporating both broad-based deposits [11][12][13], and a range of other structures including various nanowires [12,[14][15][16][17], nanopillars [18][19][20][21][22][23][24], nanohelices [25], and nanoscale mesh-based polyhedra [26]. Moving forward, further work investigating helium FIBID of more complex insulator nanostructures is required.…”

Structural characterization of He ion microscope platinum deposition and sub-surface silicon damage

“…The relatively high measured resistivity results (70-750 lXcm [35][36][37] were reported for Pt FIB planar deposition) are generally attributed to the low purity of the FIB metal deposition, due to insufficient activation of the metal precursor molecules on the surface, which result in trapped organic residues (from the metal precursor) in the deposited material. We compare our findings with the recently published studies on HIM metal deposition, [40][41][42] and assess the suitability of HIM as a future CE tool. 38 In the present study we explore a scanning ion beam HIM/HIBID Pt deposition process, using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) for deposit analysis.…”