Langmuir-Type Mechanism for In-Situ Doping in CVD Si and Si _1−x Ge _x Epitaxial Growth

In-situ doping process of B and P in CVD Si and Si _1−x Ge _x (100) epitaxial growth is investigated using SiH ₄ –GeH ₄ –dopant gas (B ₂ H ₆ or PH ₃ )–H ₂ gas mixture. For lower dopant gas partial pressure, the in situ doping is explained quantitatively by the Langmuir-type adsorption and reaction at Si–Si, Si–Ge or Ge–Ge pair sites on the (100) surface. For higher B ₂ H ₆ gas partial pressure ( P _B2H6 ), it is proposed that SiH ₄ , GeH ₄ and B ₂ H ₆ molecules are adsorbed and react partially at the B-occupied sites where B ₂ H ₆ molecules have been adsorbed on the (100) surface. For higher PH ₃ gas partial pressure ( P _PH3 ), it is proposed that the in situ doping and Ge incorporation are enhanced by the self-limited adsorption of PH ₃ molecules and the decomposition of GeH ₄ at the P-occupied sites where PH ₃ molecules have been adsorbed on the (100) surface, respectively, and that the decrease of P concentration with increasing P _PH3 in high P _PH3 region is caused by lower segregation coefficients of P at Si–Ge and Ge–Ge pair sites than that at Si–Si pair sites according to the Henry’s law. Fairly good agreement is obtained between all the experimental data and the modified Langmuir-type mechanism for in situ doping.