This paper reports on experiments in projection ion lithography in which multiple demagnified images have been etched directly into a substrate through an aperture lens array, without using a resist or proximity mask. The ion source is an 8-cm-beam-diam, Kaufman-type mercury ion thruster, which accelerates ions through a grid of perforated plates, and then neutralizes the resultant beamlets by injecting electrons at ground potential. The neutralized ion beam is allowed to pass through a suitable mask and thence onto an array of apertures of a few tens of microns in diameter. Ions impinging on the apertures are accelerated through a field produced by imposing a negative potential on a substrate placed just downstream of the aperture array. An image of the mask is etched in the substrate directly below each aperture. The substrate is a polished metal disk which has been sputter coated with a number of alternating layers of chromium and copper, each about 500 Å thick. Etching of these layers quickly produces an easily visible contour map which accurately depicts variations in the etch rate over the substrate surface. It is necessary to generate random motion of the substrate relative to the ion source to prevent projection of a superimposed image of the ion source grid system. To date, mask elements of the order of 2–3 mm in diameter have been used to produce multiple images demagnified by about 20–30× with resolution better than 10 μm. Suitable equipment is now being fabricated to permit exploration of the submicron region.
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