Recent insights into the physical modeling of the spreading resistance point contact

The generation of accurate electrically active dopant profiles from raw spreading resistance probe (SRP) data requires a realistic physical description of the high-pressure point contact used. Comparisons between SRP and secondary ion mass spectrometry for junction isolated structures have previously indicated a need to introduce, into the one-dimensional Poisson calculations, rather high permittivity and band gap narrowing values close to the contact. To clarify the situation, a systematic survey of the literature has been made regarding the mechanical and electrical aspects of pressure contacts, including finite element calculations of the internal stress distributions and the characteristics of the high-pressure phases of silicon. Furthermore correlation has been sought with current-voltage curves of the SRP point contact, nano-SRP low weight measurements, and atomic force microscopy and transmission electron microscopy analysis of SRP probe imprints. The emerging physical contact model is one dominated under the high-pressure contact by a series of 20-50-nm-deep plastically deformed metallic beta-tin Ohmic microcontacts embedded in an elastically deformed narrow band gap and high permittivity region several micrometers deep. On junction isolated structures the higher permittivity results in an enhanced reverse carrier spilling effect causing an apparent on-bevel junction shift larger than predicted by zero-field simulations. (C) 1996 American Vacuum Society.