New mechanisms governing diffusion in silicon for transistor manufacture

There is increasing evidence that nature of chemical bonding at surfaces or Si-SiO₂ interfaces can affect dopant activation and transient enhanced diffusion (TED) in the underlying silicon bulk during ultrashallow junction formation. There are two separate mechanisms for this influence: surface-bulk coupling by electrostatic repulsion and by intrinsic interstitial annihilation. For both mechanisms, the type of bonding at the surface or interface influences the rate at which interstitial atoms are annihilated there. Changing the effective annihilation probability changes the average concentration of interstitials in the underlying bulk, which in turn influences the degree of dopant activation and TED. The present work employs experiments with the optical technique of photoreflectance to quantify electrostatic coupling, and isotopic labeling experiments to quantify intrinsic interstitial annihilation. The resulting effects 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 activation energies.