Formation and structure of epitaxial nickel silicide on Si{111}

Abstract

A LEED (low-energy electron diffraction) study of the reaction of very thin Ni films on Si{111} suggests the existence of a threshold coverage of Ni for the formation of Ni${\mathrm{Si}}_{2}$. If the initial Ni coverage is 6 monolayers or less, high-temperature anneals at 900-1200\ifmmode^\circ\else\textdegree\fi{}C for times of a few seconds up to a few minutes produce a 1\ifmmode\times\else\texttimes\fi{}1 structure. The LEED spectra from this structure are practically identical to those of the quenched "1\ifmmode\times\else\texttimes\fi{}1" phase that can be obtained by quenching from high to room temperature the 1\ifmmode\times\else\texttimes\fi{}1 phase of clean Si{111}. If the initial Ni coverage is higher than 6 monolayers then the above high-temperature anneals produce epitaxial Ni${\mathrm{Si}}_{2}$. The top layer of the Ni${\mathrm{Si}}_{2}${111} film contains only Si atoms; the second layer contains only Ni atoms. The first interlayer spacing is contracted approximately 25% with respect to the bulk value.