In this paper we present both experimental and theoretical results showing the effective use of material shaping to fabricate ultra-high-aspect-ratio (UHAR) vias with a focused ion beam (FIB). With this technique, one can create vias with aspect ratios of 20:1 and higher. This is achieved by placing a ‘lower sputter rate’ material on top of a ‘higher sputter rate’ material. We model the FIB as a Gaussian beam with an angular dependent sputter rate. With our model we predict a high sputter rate ratio (high/low) can achieve vias with aspect ratios near 20:1. Experimental results support this prediction. By placing a thin layer of pyrolyzed carbon on top of silicon, we fabricated UHAR vias with diameters of 75 nm.

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