Atomic force microscopy ͑AFM͒ and high-resolution transmission electron microscope ͑HRTEM͒ cross section imaging of individual gas cluster ion impact craters on Si͑100͒ and Si͑111͒ substrate surfaces is examined. The comparison between 3 and 24 kV cluster impacts from Ar and O 2 gas sources is shown. Results for low fluence (10 10 ions/cm 2 ) 24 kV Ar individual cluster impacts onto a Si͑100͒ and Si͑111͒ substrate surfaces are compared with hybrid molecular dynamics ͑HMD͒ simulations. A HMD method is used for modeling impacts of Ar n (nϭ135, 225͒ clusters, with energies of 24 -50 eV/atom, on Si͑100͒ and Si͑111͒ surfaces. On a Si͑100͒, craters are nearly triangular in cross section, with the facets directed along the close-packed ͑111͒ planes. The Si͑100͒ craters exhibit four-fold symmetry as imaged by cross-sectional HRTEM, and AFM top view, in agreement with modeling. In contrast, the shape of craters on a Si͑111͒ shows a complicated six-pointed shape in the modeling, while AFM indicates three-fold symmetry of the impact. The lower energy 3 kV individual cluster impacts reveal the same crater shape in HRTEM cross section for both Ar and O 2 gas clusters, but with shallower crater depth than for the higher-energy impacts. The kinetics of the Ar and O 2 crater impacts may explain the successful use of higher-energy cluster impacts for etching material of higher initial surface roughness followed by the lower-energy impacts as an effective finishing step to achieve smoother surfaces.

Device quality (110)GaAs has been reproducibly grown by molecular beam epitaxy (MBE) for the first time. Angling of the substrate to expose stable, Ga-rich ledges on the (110) surface has been shown to be the necessary condition for two-dimensional growth. The layers exhibit a room-temperature electron mobility of ∼5700 cm2/V s for NSi∼4×1015 and a strong exciton photoluminescence emission at 4 K. This breakthrough in MBE growth of III-V compounds allows for fabrication of (110) GaAs devices which will take advantage of the unique properties of this orientation.

Surface processing of microelectronic materials by bombardment with nanoparticles of condensed gases (i.e., clusters) in the form of an ion beam, makes possible etching and smoothing of those surfaces to very high figures of merit. As this is not possible with any conventional ion method, gas-cluster ion-beam systems have great potential in manufacturing. The formation of gas clusters and their collision with surfaces provides an interesting arena for novel physics and surface science. This paper outlines a physical model for the clusters and surface interactions, and provides examples of surface processing. In particular, the reduction of surface roughness while etching by cluster-ion bombardment is illustrated for various materials utilized in microelectronics.

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