Growth of molybdenum on silicon: Structure and interface formation

Investigations of interface formation in the Mo-Si system were carried out by depositing Mo onto Si(100)-(2×1) and Si(111)-(7×7) surfaces in ultrahigh vacuum, followed by characterization with in situ reflection high-energy electron diffraction, low-energy electron diffraction, Auger-electron spectroscopy, and x-ray photoelectron spectroscopy (XPS). Continuous growth of multiple Mo coverages on a single Si wafer was accomplished with a technique involving a movable sample shutter. The formation of an amorphous interfacial silicide was observed at all substrate temperatures studied: ∼50 °C, 100 °C, and 200 °C. However, the composition quickly becomes Mo rich as the deposition continues. The data are consistent with a composition profile that has an atomically abrupt transition between Si and amorphous ${\mathrm{MoSi}}_{\mathit{x}}$, where x=2 for the first 4 Å and then decays with an error-function form with increasing overlayer thickness. The error-function interface-width parameter was found to be 10.0 Å at ∼50 °C and 12.1 Å at 200 °C. Significant differences were seen between Auger intensities calculated by two standard methods: the derivative-amplitude method and the linear-background integrated-intensity method. We attribute these differences to peak-shape changes (due to the varying chemical environment in the interfacial region) that invalidate the use of the derivative method. The XPS measurements revealed shifts in the energies of the Mo 3${\mathit{d}}_{3/2}$ and Mo 3${\mathit{d}}_{5/2}$ lines due to the reaction with the Si substrate. The maximum peak shift was -0.4 eV and originated from the Mo nearest the Si substrate.