1986/01/01 by J. Melngailis, C. R. Musil, E. H. Stevens +5
paper · doi:10.1116/1.583373
One of the capabilities of focused ion beam systems is ion milling. The purpose of this work is to explore this capability as a tool for integrated circuit restructuring. Methods for cutting and joining conductors are needed. Two methods for joining conductors are demonstrated. The first consists of spinning nitrocellulose (a self-developing resist) on the circuit, ion exposing an area, say, 7×7 μm, then milling a smaller via with sloping sidewalls through the first metal layer down to the second, e-beam evaporating metal, and then dissolving the nitrocellulose to achieve liftoff. The resistance of these links between two metal levels varied from 1 to 7 Ω. The second, simpler method consists of milling a via with vertical sidewalls down to the lower metal layer, then reducing the milling scan to a smaller area in the center of this via, thereby redepositing the metal from the lower layer on the vertical sidewall. The short circuit thus achieved varied from 0.4 to 1.5 Ω for vias of dimensions 3×3 μm to 1×1 μm, respectively. The time to mill a 1×1 μm via with a 68 keV Ga+ beam, of 220 Pa current is 60 s. In a system optimized for this application, this milling time is expected to be reduced by a factor of at least 100. In addition, cuts have been made in 1-μm-thick Al films covered by 0.65 μm of SiO2. These cuts have resistances in excess of 20 MΩ. This method of circuit restructuring can work at dimensions a factor of 10 smaller than laser zapping and requires no special sites to be fabricated.