Langmuir-Type Mechanism for In-Situ Doping in CVD Si and Si1−xGex Epitaxial Growth

Abstract

In-situ doping process of B and P in CVD Si and Si1−xGex (100) epitaxial growth is investigated using SiH4–GeH4–dopant gas (B2H6 or PH3)–H2 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 B2H6 gas partial pressure (P B2H6), it is proposed that SiH4, GeH4 and B2H6 molecules are adsorbed and react partially at the B-occupied sites where B2H6 molecules have been adsorbed on the (100) surface. For higher PH3 gas partial pressure (P PH3), it is proposed that the in situ doping and Ge incorporation are enhanced by the self-limited adsorption of PH3 molecules and the decomposition of GeH4 at the P-occupied sites where PH3 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.