We report the first measurements of the composition and molecular orientation at the surface of a room-temperature ionic liquid1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6]. Recoil spectrometry using rare gas ions on continuously refreshed liquid surfaces in vacuo shows that neither ion is significantly enriched in the surface. The average orientation of the cation is with the plane of the ring vertical. The cation ring is rotated about an axis through its center such that the nitrogen atoms and side chains are deeper in the surface with the surface normal passing between the two nitrogen atoms (with an estimated error of ±30°).

Focused ion beam ͑FIB͒ methodologies for successfully milling copper ͑U.S. Patent No. 6,322,672 B1͒ have been demonstrated. Approaches to milling copper ͑Cu͒ are required because standard FIB mill procedures produce rough, uneven cuts that are unsuitable for circuit edits, a principal FIB function. Efforts to develop gas assisted etching ͑GAE͒ processes which would smoothly mill Cu failed because Cu halides are not volatile and remain on the substrate as corrosive electrically conductive debris. Single crystal studies show that Cu grains with different crystal orientations vary in mill rate by as much as 4ϫ. Moreover, the ͑110͒ crystal orientation, which mills most slowly, forms a Cu 3 Ga phase when milled with a focused Ga ion beam. This phase is particularly resistant to milling and, in polycrystalline Cu, propagates during the milling operation, contributing to the uneven trench profiles. CoppeRx, a novel scan strategy, cleanly and uniformly removes polycrystalline Cu with minimal damage to the underlying dielectric. CoppeRx minimizes the formation and propagation of the Cu 3 Ga phase and equalizes the etch rates of the Cu crystal orientations. The CoppeRx strategy includes the milling of an ''egg crate'' topography to minimize the propagation of the Cu 3 Ga phase and the creation of a heavy atom sacrificial layer of the Cu surface ͑U.S. Patent Application No. 20010053605͒ which scatters the incident Ga ion beam, thereby reducing the channeling influence on Cu milling rates. This heavy atom layer is created by flowing W͑CO͒ 6 vapor during the FIB milling process. The CoppeRx scan strategy is especially beneficial for milling thick ͑Ͼ0.8 m͒ Cu structures with large, prominent grains. Because Cu interconnect lines are relatively thin ͑Ͻ0.4 -0.5 m͒, grain-related milling roughness is less of a problem. The CoppeRx egg crate topography and W scattering layer are not required. Instead, the successful cutting of 40 ohm Cu interconnect lines to produce Ͼ20 M ohm open circuits is achieved by flowing O 2 or H 2 O during the milling process ͑U.S. Patent No. 6,322,672B1͒. The O 2 /H 2 O flow smoothes the Cu milling by producing an amorphous surface oxide, thereby reducing channeling, and by enhancing the etch selectivity for Cu relative to the surrounding and underlying SiO 2 based dielectric. These interconnect cuts have been routinely done at the bottom of high aspect ratio holes ͑e.g., 1ϫ1ϫ9 m͒.

Purification and crystallization of tungsten wires fabricated by focused-ion-beam-induced deposition Appl. Phys. Lett. 86, 192112 (2005); 10.1063/1.1927714 Microstructural comparisons of ultrathin Cu films deposited by ion-beam and dc-magnetron sputtering J. Appl. Phys. 97, 093301 (2005); 10.1063/1.1886275 Evolution of tungsten film deposition induced by focused ion beam

We have shown that ion beams can be used to probe the surface composition and molecular orientation of liquid surfaces. Time-of-flight analysis of the kinetic energy of scattered inert gas ions and recoil atoms ejected from the surface reveals the identity of atoms in the topmost atomic surface layer of the liquid. In this report we describe the first scattering/recoil experiments on surfaces of a liquid siloxane and glycerol using helium, neon and argon ions in the 2–3 keV energy range. Analysis of peak intensities as a function of experimental parameters can be used to infer average molecular orientations in the surface. Spectra from the liquid siloxane are similar to that reported by Bertrand et al. [J. Phys. Chem. 97, 131 788 (1993)] for the long-chain hydrocarbon hexatriacontane deposited as oriented solid films on Si wafers. Our data indicates that the siloxane backbone is effectively shielded by the attached hydrocarbon groups, and for incoming ions the molecule effectively resembles a hydrocarbon. Recent sum-frequency generation spectroscopy experiments [J. Phys. Chem. B 101, 4607 (1997)] suggest that a glycerol molecule in the liquid is, on average, oriented with the carbon backbone normal to the surface. Our data is consistent with this result, but scattering/recoiling simulations are needed to definitively determine the orientation.

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