While it was known that F modifies dopant diffusion in crystalline Si, the physical mechanisms behind this process were still unclear. Experimental studies were made here of F control of the point defect density in pre-amorphized Si layers. These studies established a basis for the understanding of the F behavior and for the realization of ultra-shallow junctions. An investigation was first made of the F incorporation process during the solid phase epitaxy (SPE) of amorphous Si layers. The effect of the SPE temperature upon F incorporation was elucidated and a new route to F profile engineering was suggested. Moreover, the role of F in modifying the point defect population (self-interstitials, Is, and vacancies, Vs) was explained by using B and Sb spike layers as markers for was and Vs, respectively. It was clearly shown that F decreases the B diffusion while enhancing the Sb one, pointing out the capacity to induce an was undersaturation or a Vs supersaturation. These data rule out the hypothesis of a chemical bonding between F and the dopants. Such F ability in modifying the Is/Vs density resulted to be a transient effect, because strictly correlated with the presence of F in the Si samples, which decreases with the annealing time. In addition, It was shown that, even if F was spatially separated from B, i.e., localized between shallow-implanted B and the end-of-range region, it still suppresses the enhancement of B diffusivity, due to the end of range defect dissolution. These studies, besides improving the current understanding of the physical mechanisms by which F influences the dopant diffusion in Si, could be helpful for the realization of ultra-shallow junctions for the future metal-oxide-semiconductor devices.

Fluorine in Pre-Amorphized Si - Point Defect Engineering and Control of Dopant Diffusion. G.Impellizzeri, S.Mirabella, F.Priolo, E.Napolitani, A.Carnera: Journal of Applied Physics, 2006, 99[10], 103510 (8pp)