Characterization of ultrashallow dopant profiles using spreading resistance profiling

It has been noticed that for ultrashallow ion implanted dopant profiles, the metallurgical junction is not at the same location as the peak of the spreading resistance profile, i.e., the on-bevel junction. This can be attributed to the carrier redistribution effect. Furthermore, the pressure under the spreading resistance probes causes band-gap narrowing of the material under the probes. This pressure-induced band-gap narrowing effect increases the intrinsic carrier concentration of the semiconductor material. An inverse algorithm used to convert spreading resistance profiles into the electrically active dopant profiles, taking both carrier redistribution and band-gap narrowing into account, is presented in this article. Using this algorithm, the depth of the metallurgical junction of a shallow ion implanted $p+n$ profile is determined to be 0.121 μm from the surface, whereas the on-bevel junction depth is 0.089 μm. The recovered dopant concentration profile agrees very well with that obtained from secondary ion mass sepctrometry. The algorithm is shown to work very well also for an $n+p$ junction.