(Invited, Digital Presentation) Langmuir-Type In-Situ Doping Mechanism in Si1-xGex Epitaxial Growth by Chemical Vapor Deposition
Authors: Murota Junichi , Ishii Hiromu 
Published: July 2022

Accurate knowledge of atomically controlled processing for group IV semiconductors is very important for the fabrication of Si-based ultrasmall metal–oxide–semiconductor (MOS) devices and Si-based heterodevices in ultralarge scale integration because high-performance devices require atomically ordered interface of heterointerfaces and doping profiles as well as strain engineering due to introduction of Ge and C into Si [1-6]. In this work, in-situ doping of dopant (P or B) and C in Si1-xGex (100) epitaxial growth using SiH4-GeH4-SiH3CH3-B2H6 or PH3- H2 gas mixtures at around 550 oC [7-9] is reviewed based on the Langmuir-type surface adsorption and reaction scheme and the experimental data.
It is assumed that one SiH4 or GeH4 molecule in Si1-xGex growth is adsorbed at one free surface site in Si-Si, Si-Ge or Ge-Ge pair sites on the (100) surface and decomposes there, and that one dopant (SiH3CH3 or B2H6 or PH3) molecule occupies one free surface site, independently of SiH4 and GeH4 partial pressures.
For in-situ doping of C, it is proposed that SiH3CH3 molecules are adsorbed and react at the pair sites and react at the B-occupied sites where B2H6 molecules have been adsorbed at the pair sites.
For in-situ doping of B, it is proposed that B2H6 molecules are adsorbed and react at the pair sites and SiH4, GeH4, SiH3CH3 and B2H6 molecules react at the B-occupied sites.
For in-situ P doping, it is proposed that both the P concentration and the Ge fraction x in Si1-xGex are enhanced by the self-limited adsorption of PH3 molecules with maximum 2 and maximum 1 atomic layers at the P-occupied sites where PH3 molecules have been adsorbed at Si-Si and Si-Ge pair sites, respectively and that the decrease of P concentration in Si1-xGex with increasing PH3 partial pressure in high P concentration region is caused by lower segregation coefficient 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 calculated values using the modified Langmuir-type mechanism.
These results open the way for generalization of atomically controlled surface reaction process in group IV semiconductors by CVD.
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