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

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. Please click Additional Files below to see the full abstract

Invited; Atomic-order surface reaction of reactant gas on group IV semiconductor (100) surface

Atomic-order surface reactions of reactant gases on group IV semiconductor (100) surface in ultra-clean hotwall low-pressure CVD are described as a function of reactant gas partial pressure with the fitting parameters. Now, assuming that one reactant molecule occupies one free surface site according to Langmuir-type model, total adsorption site density n0 on the (100) substrate surface is given by the sum of free site density Qs and the site density QMs where reactant molecule M is adsorbed. Surface adsorption velocity on the surface is given by dQMs/dt = kMsPMQs - k-MsQMs = kMsPMn0 - (kMsPM + k-M)QMs, where kMs and k-Ms is adsorption and desorption rate constants of M, respectively, and PM is partial pressure of M. Please click Download on the upper right corner to see the full abstract

Atomically controlled CVD processing of group IV semiconductors for ultra-large-scale integrations

One of the main requirements for ultra-large-scale integrations (ULSIs) is atomic-order control of process technology. Our concept of atomically controlled processing is based on atomic-order surface reaction control by CVD. By ultraclean low-pressure CVD using SiH4 and GeH4 gases, high-quality low-temperature epitaxial growth of Si1−xGex (100) (x=0–1) with atomically flat surfaces and interfaces on Si(100) is achieved. Self-limiting formation of 1–3 atomic layers of group IV or related atoms in the thermal adsorption and reaction of hydride gases on Si1-xGex (100) are generalized based on the Langmuir-type model. By the Si epitaxial growth on top of the material already-formed on Si(100), N, B and C atoms are confined within about a 1 nm thick layer. In Si cap layer growth on the P atomic layer formed on Si1−xGex (100), segregation of P atoms is suppressed by using Si2H6 instead of SiH4 at a low temperature of 450 °C. Heavy C atomic-layer doping suppresses strain relaxation as well as intermixing between Si and Ge at the Si1−xGex/Si heterointerface. It is confirmed that higher carrier concentration and higher carrier mobility are achieved by atomic-layer doping. These results open the way to atomically controlled technology for ULSIs

Atomically controlled processing for dopant segregation in CVD silicon and germanium epitaxial growth

Atomically controlled processing has become indispensable for the fabrication of Si-based ultra-small devices and heterodevices for ultra-large scale integration. This is because high performance devices require atomicorder abrupt heterostructures and doping profiles as well as strain engineering which is obtained by the introduction of Ge into Si. Our concept of atomically controlled processing is based on atomic-order surface reaction control in Si and Ge-based CVD growth [1-4]. The fabrication of atomic-level steep doping profiles requires the suppression of dopant segregation during epitaxial growth [5,6]. In this work, P and B impurity segregation during in-situ doping in Si and Ge CVD epitaxial growth is reviewed. Please click Additional Files below to see the full abstract