(Invited) In-Situ Co-Doping in CVD Si1-xGex Epitaxial Growth Based on the Langmuir-Type Mechanism
Authors: Murota Junichi , Ishii Hiromu 
Published: May 2020

High performance Si-based devices require atomically ordered interface of heterostructures and doping profiles as well as strain engineering due to the introduction of Ge and C into Si. Our interest is the generalization of atomic-order surface reaction processes for group IV semiconductors based on thermodynamical treatments [1-6]. In this work, in-site co-doping of dopant (P or B) and C in CVD Si, and Si1-xGex (100) epitaxial growth using SiH4-GeH4-PH3 or B2H6-SiH3CH3-H2-He gas mixtures [1- 7] is reviewed based on the Langmuir-type surface adsorption and reaction scheme.

The adsorption rate constants of SiH4 and GeH4 and reaction rate constants of SiH4 at each site of Si-Si, Si-Ge and Ge-Ge on (100) surface in ref. 2 are used.

For heavy doping of P, the adsorption and desorption rate constants of PH3, the incorporation rate constants of P, the segregation coefficient of P between the surface coverage of PH3 molecules and the concentration of P incorporated at each pair site, and growth rate constant of GeH4 at the site where PH3 molecules have been adsorbed are obtained from the experimental data, assuming that GeH4 molecules decomposes at P-occupied sites and P atoms of 3, 2, 1 atomic layer is formed self-limitedly on the Si-Si, Si-Ge, Ge-Ge sites by PH3, respectively [8].

For heavy doping of B, the adsorption and desorption rate constants of B2H6, the incorporation rate constants of B at each pair site, and growth rate constants of SiH4 and GeH4 and B precipitation rate constant of B2H6 at the site where B2H6 molecules have been adsorbed are obtained from the experimental data, assuming that SiH4, GeH4 and B2H6 adsorb/react partially at the B-occupied sites [8].

For heavy doping of C, the adsorption and desorption constants of SiH3CH3 and incorporation rate of C at each pair site are obtained from the experimental data [9], assuming that the sites where SiH3CH3 molecules have been adsorbed become inactive for both the SiH4 and GeH4 adsorption/reactions on the surface.

For in-situ co-doping of P and C, the calculated growth rate, P concentration, Ge fraction and C concentration using the above fitting parameters are in good agreement with the experimental data [10] for the C concentration below 1021 cm-3. It is proposed that the decrease of growth rate and the increase of P concentration by SiH3CH3 addition for higher GeH4 and lower PH3 partial pressure is caused mainly by the increase of inactive site density for both the SiH4 and GeH4 due to the adsorption of SiH3CH3 at Ge-Ge pair sites.

For in-situ co-doping of B and C, the calculated values of B concentration correspond to the experimental data [11] except for the samples grown at P
GeH4=1.2 Pa and P
SiH3CH3=0.09 Pa. For those samples (Ge fraction>0.44 and C concentration>8 x 1020 cm-3), it was suggested that the B and C atoms exist at interstitial site [8]. Therefore, it is considered that the incorporation rate constants for interstitial B are different from that for substitutional B. It should be noted that the calculated C concentration, which is almost independent of B concentration, results from C precipitation by reaction of SiH3CH3 gas at B-occupied sites.

These results open the way for generalization of atomically controlled surface reaction process in group IV semiconductors by CVD.

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