Langmuir-type mechanism for in-situ doping in CVD Silicon and Germanium Epitaxial Growth

Conference Dates

May 19-23, 2019


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 into Si. The fabrication of atomic-level steep doping profiles needs the suppression of dopant segregation during epitaxial growth [1]. In this work, in-site doping of P and B in CVD Si, Ge and Si1-xGex epitaxial growth using SiH4-GeH4-dopant (PH3 and B2H6)-H2-He gas mixtures [1, – 7] is reviewed based on the Langmuir-type surface adsorption and reaction scheme.

Anomalous heavy doping of P is explained, assuming that GeH4 adsorbs/reacts partially at the sites where PH3 molecules have been adsorbed on (100) surface, although the sites become inactive for both the SiH4 and GeH4 adsorption/reactions on the surface [2]. Based on the experimental results that P atoms of 3, 2, 1 atomic layer is formed self-limitedly on the Si-Si, Si-Ge, Ge-Ge sites by PH3 at the epitaxial growth temperature [2 – 4], the adsorption/reaction site density for PH3 at each site is assumed. The adsorption and desorption rate constants of PH3 and the incorporation rate constant of P atoms into the epitaxial layer from the adsorbed PH3 molecules at each site are obtained numerically by fitting the experimental data for low PH3 partial pressure region to the modified Langmuir-type mechanism. The segregation coefficient between surface coverage of PH3 molecules and the concentration of P incorporated into the grown film at each site and growth rate constant of GeH4 on adsorbed PH3 molecules are also obtained numerically from the data for high PH3 partial pressure region. The adsorption rate constant of SiH4 and GeH4 and reaction rate constant of SiH4 at each site in refs. 2 are used.

Anomalous heavy doping of B is explained, assuming that SiH4, GeH4 and B2H6 adsorb/react partially at the sites where B2H6 molecules have been adsorbed on (100) surface [5]. It was confirmed that B atoms deposit continuously without self-limitation at the Si1-xGex epitaxial growth temperature [6] and B atoms enhances the SiH4 adsorption/reaction [7]. Therefore, it is also assumed that there is no segregation of B on the grown surface.

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