Fabrication and characterization of rare-earth silicide thin films

The continuous miniaturization of metal-oxide-semiconductor field-effect transistors (MOSFET) experiences increasing difficulties with the formation of source and drain contacts by ion implantation. Hence, a new MOSFET architecture based on metallic contacts over silicon was proposed to replace conventional highly doped source and drain extensions. To realize such a device, the so-called Schottky barrier (SB) MOSFET, requires materials presenting low Schottky barrier heights (SBH) to silicon. For n-type SBMOSFETs, the best candidates are rare-earth silicides, alloys between silicon and a rare-earth metal. However, the intrinsic SBH of rare-earth silicides is still too high for SBMOSFETs to compete in performance with conventional devices. The SBH can be decreased by dopant segregation, where a thin dopant layer is interposed between the silicide and silicon. First, the reaction between n-type silicon and a rare-earth metal, erbium, was investigated under various processing conditions. A SBH of 0.3 eV, comparable to the state of the art, was determined regardless of the fabrication method. The SBH was observed to drop with increasing growth temperature, in correlation with the progressive crystallization of erbium silicide. Next, the achievement of a very low effective SBH of about 0.1 eV together with the dopant redistribution in the silicide testify to efficient dopant segregation, therefore paving the way towards next generation silicon-based nanodevices. Finally, through quantum simulations, the low temperature deviations of the current-voltage characteristics in silicide/silicon contacts were attributed to the nanoscale modulation of the SB profile by the applied voltage.(FSA 3) -- UCL, 201