Impact of Microstructure and Defects on Surface Reactivity during Wide Bandgap Semiconductor Epitaxy

A great amount of research on wide bandgap semiconductors is currently focused on point and 1D defects, due to its key role in device performance. It is therefore surprising that the interplay between defects and surface kinetics is relatively unexplored. There is a strong interaction between these two aspects that goes both ways: surface kinetics can promote the formation of surface defects that get subsequently incorporated into the bulk. If we were able to predict the role that surface kinetics has on defect formation, this would allow us to greatly assist process development to achieve a further reduction in the density of defects. Conversely, surface defects and surface morphology affects the reactivity of the surface, and this can lead to intra-wafer variability based on the morphology and defect density at different points of a wafer substate. However, despite this strong correlation, the atomistic aspects of precursor-surface interaction are not well understood.

In this talk we will focus on the impact of surface morphology and defects on the surface reactivity during epitaxy. In a step flow growth mode, the density of step sites will play an important role in the overall reaction probability of the different surface species. We have therefore developed models that explore the interaction between the effective reactor probability (the probability that a precursor molecule reacts with the surface) and both surface morphology and defect concentration. One of our key results is that, under the reaction-limited conditions in which the growth rate is linear with precursor concentration, it is possible to greatly accelerate the determination of the statistical outcome of precursor-surface interaction. We can use this  information to understand where particles are more likely to react locally on the surface and the relative stability of certain surface configuration.  We have used this result to investigate the impact that surface residence time has on the reaction probability as a function of miscut and in the presence of thread screw dislocations, and the role that step roughening can have in promoting surface vacancies that can lead to point defects in the solid.