• PDF / 2,558,089 Bytes
• 6 Pages / 417.6 x 639 pts Page_size
• 77 Downloads / 245 Views

DOWNLOAD

REPORT

---

CHARACTERIZATION OF ULTRATHIN CoSi 2 ON Si(111) LAYERS. J.L.BATSTONE, JULIA M.PHILLIPS AND J.M.GIBSON AT&T Bell Laboratories, Murray Hill NJ 07974

ABSTRACT Ultrathin epitaxial CoSi 2 films on Si(111) have been grown in ultrahigh vacuum by room temperature deposition of Co on Si(111) followed by a high temperature anneal at -600°C. Characterization of the thin films with transmission electron microscopy has revealed pseudomorphic growth up to thicknesses -30A. Pinholes present in the pseudomorphic thin films are thought to prevent the trapping of dislocations within the film. A clear transition to films containing a regular network of misfit dislocations occurs at -40A. Evidence for the growth of CoSi 2 via intermediate metal-rich silicide phases is observed. INTRODUCTION High quality molecular beam epitaxial (MBE) growth of CoSi 2 on Si(111) has led to the development of new structures such as the Si/CoSi 2 /Si [1,2,3] transistor and the CaF 2 /CoSi 2 /Si heterostructure [4,5]. Control of the electrical properties in these stuctures requires a clear understanding of the mechanisms of nucleation and growth of the silicide layer. CoSi 2 has the cubic fluorite structure with a lattice mismatch of 1.2% with silicon. Two orientations can exist on Si(011), type A silicide which has exactly the same orientation as the substrate and type B silicide which is rotated 180' about the surface normal axis. Typical microstructural characteristrics of epitaxial CoSi 2 films on Si(111) include a strain-relieving network of misfit dislocations and pinholes. The size and density of pinholes is sensitive to a number of parameters [6] and is usually controlled by deposition of Co and Si prior to reaction [6,7]. Evidence for a pseudomorphic CoSi 2 layer in a Si/CoSi 2 /Si(111) heterostructure has recently been reported, with an observed critical thickness occuring at 70A [8]. In this paper we present results of pseudomorphic growth of CoSi% on Si(111) where films are found to be dislocation-free for thicknesses up to -30A. Effects such as the reaction temperature and the degree of wafer misorientation on the uniformity of thin pseudomorphic layers have been investigated using Transmission Electron Microscopy (TEM).

EXPERIMENTAL DETAILS Epitaxial thin CoSi 2 films were grown in an ultrahigh vacuum molecular beam epitaxy system with a base pressure in the deposition chamber of