A liquid-metal gallium-ion source was imaged by unity-magnification single-gap accelerating lens with a postlens deflector to form a focused scanning probe. We report the dependence of the probe diameter and probe current on the lens acceptance half-angle. The results range between probe diameters of 1000 and 5000 Å at currents of 0.12–3.0 nA for half-angles of 1.2–6 mrad. The current density and brightness at the target for the 1000-Å-diam 57-kV probe were 1.5 A/cm2 and 3.3×106 A/cm2 sr, respectively. Astigmatic probes were also produced with dimensions smaller than 1000 Å.

A 50 keV Ga+ beam has been focused to a spot diameter of 8 nm (full width at half-maximum) in our two-lens microprobe system by reducing the contributions of both chromatic aberration and the virtual ion source size to the final image size. Features as small as 6 to 8 nm were distinctly visible in scanning ion images. To our knowledge, this is the smallest focused beam of ions produced to date. The limiting resolution in 30-nm thick films of poly(methylmethacrylate) exposed with this beam was approximately 8 to 10 nm. Effects such as ion scattering, atomic recoil, and statistical dose fluctuations during exposure are believed to set inherent limits to the lithographic resolution.

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Ion beams have increased usefulness for high-resolution microstructure fabrication if they are patterned to small dimensions before they strike a target. First, results are presented of maskless micromachining, doping, and resist exposure with a scanning focused gallium ion beam of sub-1000-Å diameter. Secondly, an ion-beam-transmission mask is described, and results are presented showing 1X replicated mask patterns with 0.6-μm features that were exposed in PMMA resist by irradiating the mask with a conventional size 150-kV proton beam. The potentials of ion-beam lithography using masks and focused ion beams are discussed.

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