C-V profiling of ultrashallow junctions using a step-like background doping profile

Abstract

but W cannot be related to x.; Differentially, obtained with a step-like background doping profile. Using this technique it is possible to extract part of the highly-doped ultrashallow profile by C-V profiling. We have employed this technique for the characterization of ultrashallow and ultraabrupt junctions formed by pure boron CVD that have been used in the fabrication of state-of-the-art DUV and EUV photodiodes for lithography [5].(2)where N d and N a represent the donor and acceptor doping concentrations, respectively, x; and x p the edges of the depletion region in the n-or p-region, respectively, e is the elementary charge, £s is the permittivity of the semiconductor, Va is the applied voltage and W is the depletion region width. The case of a one-sided junction is obtained from (1) by assuming that one doping approaches infinity, but if that assumption does not hold Na and N; cannot be both extracted simultaneously [6].In our approach two devices with an identical background n-type profile are fabricated: one as a Schottky diode for the purpose of accurate extraction of the N d profile, and one as a p-n diode for the extraction of the N; profile using the known N d profile. This alone, however is not sufficient as the edge of the depletion region on the n-side is at a different depth in the p-n case and in the Schottky case. Namely, in (1) Wis directly related to the measured capacitance C as II. PROFILING OF ULTRASHALLOW JUNCTIONSIn conventional C-V profiling a doping profile of a onesided junction (Schottky or highly asymmetrical p-n junction) is extracted from its C(V a ) dependence. However, if the junction is not one-sided then both p and n doping profiles contribute to the C( Va) characteristic. Assuming the depletion approximation, it is easily obtained that [3]