Phosphorus diffusion and deactivation during SiGe oxidation.

Dopant profiles near the semiconductor–oxide interface are critical for microelectronic device performance. As the incorporation of Si_1−xGe_x into transistors continues to increase, it is necessary to understand the behavior of dopants in Si_1−xGe_x. In this paper, the diffusion and electrical activation of phosphorus within a strained, single-crystal Si_0.7Ge_0.3 layer on Si during oxidation are reported. Both layers were uniformly doped, in situ, with an average phosphorus concentration of 4 × 10¹⁹ atoms/cm³. After high-temperature oxidation, secondary ion mass spectrometry measurements revealed that the bulk of the phosphorus diffuses out of only the SiGe layer and segregates at the oxidizing SiGe–SiO₂ interface. Hall effect measurements corroborate the observed phosphorus loss and show that the phosphorus diffusing to the oxidizing interface is electrically inactive. Through density functional theory (DFT) calculations, it is shown that phosphorus interstitials prefer sites near the SiGe–SiO₂ interface. Finally, based on a combination of experimental data and DFT calculations, we propose that the phosphorus atoms are displaced from their lattice sites by Ge interstitials that are generated during SiGe oxidation. The phosphorus atoms then migrate toward the SiGe–SiO₂ interface through a novel mechanism of hopping between Ge sites as P–Ge split interstitials. Once they reach the interface, they are electrically inactive, potentially in the form of interstitial clusters or as part of the reconstructed interface or oxide. [ABSTRACT FROM AUTHOR]