Characterization of Highly Doped Si:P, Si:As and Si:P:As Epi Layers for Source/Drain Epitaxy

Abstract

This work reports on the activation behavior of highly doped epitaxial Si:P, Si:As and Si:P:As layers grown on Si with a non-selective process at 450°C and with a selective process at higher temperatures below 700°C. Using identical process conditions, it is found that As is more efficiently incorporated into the epi layer as compared to P. For the same dopant concentration, a much lower strain is observed in the case of As-doping. At a high dopant concentration (e.g. at ~ 3.3%), the activation of the as-grown Si:As and Si:P:As layers is lower as compared to Si:P. At a low concentration, however, (e.g. at ~ 1.2%) we observe an enhanced activation for the 450°C process due to the co-doping of P and As which is possibly related to a more efficient vacancy trapping by As. The activation enhancement after post epitaxy anneals like laser or spike anneal is lower as compared to P. A reduced diffusion is confirmed for Si:As after spike anneal, making the layer an interesting candidate for an extension liner. We find that Si:As can be combined with Si:P in a bi-layer without appreciable quality-or activation loss.