The theory and application of a simple etch contour for near ideal breakdown voltage in plane and planar p-n junctions

Abstract
It is shown that high avalanche breakdown voltage in both plane and planar p-n junctions can be achieved by extending the heavily doped side of the junction beyond the contact and partially etching into it. This forces the depletion region to spread back some distance in the heavily doped side. The technique, when properly applied, is capable of giving virtually ideal breakdown voltages for both plane and planar type p-n junctions and uses only a fraction of the area required for a typical negative bevel. The actual breakdown voltage depends on how carefully the etch is controlled. For planar junctions, the breakdown voltages that can now be achieved are better than any previously reported. Moreover, since the technique is based on etching, mechanical contouring is avoided. This, in itself, is beneficial. Both the new method, termed the depletion etch method (DEM), and the negative bevel technique are discussed using a simple theory of charge balancing which appears to simplify qualitative comparison of different geometries used to increase avalanche breakdown voltage. From this theory, it is easy to see why the new method is potentially superior in terms of peak surface to peak bulk field trade-off. Exact numerical three-dimensional (with radial symmetry) electric field calculations as well as a number of experimental results using both plane and planar junctions bear out the predictions of the simple theory. Moreover, both the calculations and the experiments performed to date show that close to the ideal p-n junction, breakdown voltage can be reached for both plane and planar type p-n junctions if the etch depth can be controlled with sufficient precision.

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