The migration of Sn was studied by using molecular beam epitaxially grown layers, into which Sn and Sb distributions (table 24) were introduced during growth. The Sn and Sb profiles were measured by using secondary-ion mass spectrometry. By comparing the diffusion of Sb, in an inert N ambient, to that in a nitriding NH3 ambient (where vacancies were injected), the fractional vacancy contribution to the diffusion of Sn was found to be equal to that of Sb; which, in turn, was known to be close to unity. It was therefore concluded that Sn (figure 14) diffused predominantly via a vacancy-mediated mechanism in Si. On the other hand, the activation energy for diffusion was found to be higher than expected for a vacancy-mediated diffusion mechanism. This was explained by assuming the existence of Sn-vacancy configurations which were different from the configuration in which a vacancy was trapped next to a Sn atom.

Anomalous Diffusion of Tin in Silicon. P.Kringhøj, A.N.Larsen: Physical Review B, 1997, 56[11], 6396-9

Figure 14

Diffusivity of Sn in Si