Enhanced Diffusion in Silicon Processing

Dopant diffusion in silicon is unexpectedly rich in complexities. In the early days of silicon technology, dopant motion appeared to obey a simple concentration-dependent Fick's Law diffusion process. As technology advanced, a series of anomalous diffusion phenomena became evident, known under process-related names such as "emitter-push effect," oxidation-enhanced diffusion (OED), or ion implant-induced "transient enhanced diffusion" (TED). These effects, arising from perturbations in the point defect population, must be understood and predicted in order to avoid costly design trials. 

This article illustrates how all the anomalies arise from a single driving force - the reduction in total energy of the crystal, by transport and agglomeration of point defects in the bulk and recombination of point defects at the surface. Equilibrium dopant-defect coupled diffusion is discussed first, followed by more complex nonequilibrium effects like surface processing and damage evolution.