A comparison of neon versus helium ion beam induced deposition via Monte Carlo simulations.

The ion beam induced nanoscale synthesis of PtCx (where x âˆ¼ 5) using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPt(IV)Me3) precursor is investigated by performing Monte Carlo simulations of helium and neon ions. The helium beam leads to more lateral growth relative to the neon beam because of its larger interaction volume. The lateral growth of the nanopillars is dominated by molecules deposited via secondary electrons in both the simulations. Notably, the helium pillars are dominated by SE-I electrons whereas the neon pillars are dominated by SE-II electrons. Using a low precursor residence time of 70 µs, resulting in an equilibrium coverage of ∼4%, the neon simulation has a lower deposition efficiency (3.5%) compared to that of the helium simulation (6.5%). At larger residence time (10 ms) and consequently larger equilibrium coverage (85%) the deposition efficiencies of helium and neon increased to 49% and 21%, respectively; which is dominated by increased lateral growth rates leading to broader pillars. The nanoscale growth is further studied by varying the ion beam diameter at 10 ms precursor residence time. The study shows that total SE yield decreases with increasing beam diameters for both the ion types. However, helium has the larger SE yield as compared to that of neon in both the low and high precursor residence time, and thus pillars are wider in all the simulations studied.

Fundamental proximity effects in focused electron beam induced deposition.

Fundamental proximity effects for electron beam induced deposition processes on nonflat surfaces were studied experimentally and via simulation. Two specific effects were elucidated and exploited to considerably increase the volumetric growth rate of this nanoscale direct write method: (1) increasing the scanning electron pitch to the scale of the lateral electron straggle increased the volumetric growth rate by 250% by enhancing the effective forward scattered, backscattered, and secondary electron coefficients as well as by strong recollection effects of adjacent features; and (2) strategic patterning sequences are introduced to reduce precursor depletion effects which increase volumetric growth rates by more than 90%, demonstrating the strong influence of patterning parameters on the final performance of this powerful direct write technique.

Nanopillar growth by focused helium ion-beam-induced deposition.

A 25 keV focused helium ion beam has been used to grow PtC nanopillars on a silicon substrate by beam-induced decomposition of a (CH(3))(3)Pt(C(P)CH(3)) precursor gas. The ion beam diameter was about 1 nm. The observed relatively high growth rates suggest that electronic excitation is the dominant mechanism in helium ion-beam-induced deposition. Pillars grown at low beam currents are narrow and have sharp tips. For a constant dose, the pillar height decreases with increasing current, pointing to depletion of precursor molecules at the beam impact site. Furthermore, the diameter increases rapidly and the total pillar volume decreases slowly with increasing current. Monte Carlo simulations have been performed with realistic values for the fundamental deposition processes. The simulation results are in good agreement with experimental observations. In particular, they reproduce the current dependences of the vertical and lateral growth rates and of the volumetric deposition efficiency. Furthermore, the simulations reveal that the vertical pillar growth is due to type-1 secondary electrons and primary ions, while the lateral outgrowth is due to type-2 secondary electrons and scattered ions.

Monte Carlo simulation of focused helium ion beam induced deposition.

The details of a Monte Carlo helium ion beam induced deposition simulation are introduced and initial results for reaction rate and mass transport limited growth regimes are presented. Reaction rate limited growth leads to fast vertical growth from incident primary ions and minimal lateral broadening, whereas mass transport limited growth has lower vertical growth velocity and exhibits broadening due to scattered ions and secondary electrons. The results are compared to recent experiments and previous electron beam induced deposition simulations.

Understanding the kinetics and nanoscale morphology of electron-beam-induced deposition via a three-dimensional Monte Carlo simulation: the effects of the precursor molecule and the deposited material.

The electron-beam-induced deposition of silicon oxide from tetraethyorthosilicate and tungsten from tungsten hexafluoride is simulated via a Monte Carlo simulation. Pseudo one-dimensional nanopillars are grown using comparable electron-beam parameters and a comparison of the vertical and lateral growth rate and the pillar morphology is correlated to the precursor and deposited material parameters. The primary and secondary electrons (type I) are found to dominate the vertical growth rate and the lateral growth rate is dominated by forward and secondary electrons (type II). The resolution and morphology of the nanopillars are affected by the effective electron interaction volume and the resultant surface coverage of the precursor species in the effective electron interaction region. Finally, the simulated results are compared to previously reported experimental results.

Simulating the effects of surface diffusion on electron beam induced deposition via a three-dimensional Monte Carlo simulation.

The effects that adsorbed precursor surface diffusion has on electron beam induced deposition are explored via a three-dimensional Monte Carlo simulation. Initially the growth rate and resolution are compared for a common set of deposition conditions with a variable surface diffusion coefficient ranging from 0 to 1 × 10(-8) cm(2) s(-1). The growth rate and resolution are shown to both be enhanced as the growth changes from a mass transport limited regime to a reaction rate limited regime. The complex interplay between the vertical growth rate, the lateral growth rate, the interaction volume and the adsorbed and diffused precursor species are discussed. A second scenario is also simulated in which only gas diffused from a constant source at the perimeter of the simulation boundary is assumed (no gas phase adsorption). At low diffusion coefficients, the diffusing gas is consumed by secondary and backscattered electrons and experimentally observed ring-like structures are generated. At higher diffusion coefficients, the diffusion length is sufficient for the precursor atoms to diffuse to the center (and up the pillar sidewalls) to generate nanowires.

Pressure effect of growing with electron beam-induced deposition with tungsten hexafluoride and tetraethylorthosilicate precursor.

Electron beam-induced deposition (EBID) provides a simple way to fabricate submicron- or nanometer-scale structures from various elements in a scanning electron microscope (SEM). The growth rate and shape of the deposits are influenced by many factors. We have studied the growth rate and morphology of EBID-deposited nanostructures as a function of the tungsten hexafluoride (WF6) and tetraethylorthosilicate (TEOS) precursor gas pressure and growth time, and we have used Monte Carlo simulations to model the growth of tungsten and silicon oxide to elucidate the mechanisms involved in the EBID growth. The lateral radius of the deposit decreases with increasing pressure because of the enhanced vertical growth rate which limits competing lateral broadening produced by secondary and forward-scattered electrons. The morphology difference between the conical SiO(x) and the cylindrical W nanopillars is related to the difference in interaction volume between the two materials. A key parameter is the residence time of the precursor gas molecules. This is an exponential function of the surface temperature; it changes during nanopillar growth and is a function of the nanopillar material and the beam conditions.