Mechanism of dopant segregation to SiO₂/Si(001) interfaces

Dopant atoms can segregate to SiO₂/Si(001) interfaces and be deactivated there. Using phosphorus as a typical example of a donor and guided by results of ab initio calculations, we present a model of donor segregation. We find that P is trapped at the interface in the form of threefold-coordinated atoms. The atomic detailed configuration and the process of P incorporation depend on P concentration C_P in the vicinity of the interface. At low C_P, phosphorus atoms prefer to substitute Si atoms with dangling bonds. At high C_P, phosphorus pairs are formed. At intermediate C_P, (around 10¹⁷–10¹⁹ cm^-3) segregation occurs to sites associated with interface roughness and to interface Si-Si bridges, and is mediated by diffusion and annihilation of Si dangling bonds and by reoxidation during oxide annealing. Making diffusion of dangling bonds more difficult (for example, by nitridation) should, therefore, reduce the trapping efficiency of SiO₂/Si(001) in the technologically important regime of intermediate C_P.