Surface control of interstitial behavior for improved ultrashallow junction formation

There is increasing evidence that surface proximity effects must be incorporated into models for transient enhanced diffusion (TED). The present work examines the previously unrecognized influence that near-surface band bending can have on dopant profiles. Experiments employ the optical technique of photoreflectance to show that band bending exists at the Si-SiO₂ interface just after implantation. The effects of such band bending are investigated numerically using a simulator whose rate parameters have been developed from literature data using Maximum Likelihood (ML) estimation together with multivariate statistics to quantify accuracy. The resulting simulator yields excellent fits of SIMS profiles with no freely adjustable parameters, and shows that band bending transforms interfaces into reflectors of charged interstitials (i.e., no flux), even if the interface would otherwise serve as a good sink for these defects. This transformation deepens the junction significantly and also induces the pileup of dopant very close to the interface.