Growth and Properties of Epitaxial Silicides on Si(III)

Abstract

The Schottky-barrier heights ϕB of epitaxial NiSi2 and CoSi2 layers on Si(111) have been measured as a function of growth conditions. For type B NiSi2 interfaces both I-V and photoelectric methods yield a high ϕB = 0.75 ± 0.03 eV for layers grown below 400°C, dropping below 0.7 eV for layers annealed above 550°C or grown by MBE above 550°C. ϕB of type A interfaces is always found to be low, i.e., ϕB = 0.62 ± 0.03 eV. Pinhole-free ultrathin (14-70 Å) CoSi2 layers could be grown for the first time by using a novel solid phase epitaxy (SPE) technique, in which Co and Si are coevaporated in their stoichiometric ratio near room temperature (R.T.). These layers become perfectly epitaxial with type B orientation upon annealing to only 250°C and remain continuous up to Ts ≈ 600°C. From photoelectric measurements CoSi2 layers grown at Ts < 350°C are found to exhibit a high ϕB = 0.75 ± 0.04 similar to B-type NiSi2.Thin epitaxial and continuous Si layers can be grown on CoSi2 at Ts = 350°C. The prevalence of 2-dim. growth is established from the observation of the XPS Co 2p3/2 core level peak intensity as a function of Si coverage. Kikuchi patterns observed by RHEED as well as high resolution TEM images from cross-sections show, that the orientation is the same as that of CoSi2. CoSi2/Si superstructures have been grown with individual layer thicknesses as small as 20 Å. Overgrowth of CoSi2 by thick Si layers (> 1000 Å) requires ramping up of Ts to the usual growth temperatures for Si MBE. Without any optimisation preliminary experiments indicate, that single type growth of Si can be achieved. This is determined by ion channeling of an 1150 Å thick Si layer on 30 Å of CoSi2 yielding minimum yields of 17% for the [111] and [110] directions and 40% for the [114] direction.