Experimental study of the effect of junction curvature on breakdown voltage in Si

Abstract

Experimental data have been obtained which substantiate predictions of Sze and Gibbons regarding the effect of junction curvature on avalanche breakdown for abrupt junctions. They predict that for abrupt junctions the breakdown voltage, V B , decreases with decreasing radius of curvature, r j , with this effect being larger for a spherical junction than for a cylindrical junction. In each case the overall average of the experimental results is slightly lower than the theoretical prediction. For cylindrical junctions, the overall average is 12 percent lower, and for spherical junctions, the overall average is only 5 percent lower than theory. The diodes were fabricated utilizing planar technology. Circular mask patterns were used in forming cylindrical junctions. Equilateral triangle patterns, with sharp corners approximated spherical junctions. Patterns of both shapes and of various sizes were incorporated in the same fabrication mask. Breakdown voltage was found to be measurably lower for triangular diodes than for the circular diodes; diodes of both shapes exhibited breakdown voltages lower than those of equivalent plane-junction diodes formed in the same samples by mesa etching. Breakdown voltage data obtained with abrupt-junction diodes of various depths using several different values of starting material resistivity were found to be in good quantitative agreement with theoretical dependence of breakdown voltage on junction curvature. Further evidence that the onset of junction breakdown occurred in regions of highest junction curvature was provided by observations of light emission during breakdown.