Effects of interface bonding and defects on boron diffusion at Si/SiO2 interface

Abstract

We perform first-principles density functional calculations to find the migration pathway and barrier for B diffusion at the Si/SiO2 interface. For various interface models, in which crystalline α-quartz or amorphous silica (a-SiO2) is placed on Si, we examine stable and metastable configurations of B-related defects which play a role in B diffusion. While a substitutional B alone is immobile in Si, it tends to diffuse to the interface via an interstitialcy mechanism in the presence of a self-interstitial and then changes into an interstitial B in oxide via a kick-out mechanism, leaving the self-interstitial at the interface. At the defect-free interface, where bridging O atoms are inserted to remove interface dangling bonds, an interstitial B prefers to intervene between the interface Si and bridging O atoms and subsequently diffuses through the hollow space or along the network of the Si-O-Si bonds in oxide. The overall migration barriers are calculated to be 2.02–2.12 eV at the Si/α-quartz interface, while they lie in the range of 2.04 ± 0.44 eV at the Si/a-SiO2 interface, similar to that in α-quartz. The migration pathway and barrier are not significantly affected by interface defects such as suboxide bond and O protrusion, while dangling bonds in the suboxide region can increase the migration barrier by about 1.5 eV. The result that the interface generally does not hinder the B diffusion from Si to SiO2 assists in understanding the underlying mechanism for B segregation which commonly occurs at the Si/SiO2 interface.