Threshold voltage adjustment on spherical, single-crystal silicon substrates by focused ion beam implantation

摘要

The development of spherical, rather than planar, imaging arrays would enable compact wide field-of-view cameras by reducing the size and complexity of the optical components. One approach is to fabricate the sensors and readout integrated circuits directly on a spherical shell machined from a single-crystal silicon substrate. Several significant advances in processing these substrates have already been reported. This article addresses one of the fundamental electronic issues: a threshold voltage correction procedure that accounts for the dependence of oxide thickness, fixed oxide charge, and interface trapped charge on crystallographic orientation and the variation of implant depth and projected dose on substrate geometry. Substrates with 15 mm radius of curvature and 25 mm diameter were machined from a B-doped (3 0 cm) (100) silicon ingot. The threshold voltage of as-formed capacitors varied from -0.4 V in the center to -2.0 V at a radius of 10 rum. A 110 keV B+ focused ion implantation system was used to adjust threshold voltage point by point with I turn resolution. The authors demonstrate, for the first time, the ability to correct threshold voltage to within 0.12 V over an 83 degrees field of view. (c) 2006 American Vacuum Society.