Stable tungsten silicide contacts for surface sensitive conductivity measurements
High-temperature stable electric contacts of tungsten disilicide (WSi2) on Si(001) are fabricated by a simple two-step process: vacuum deposition of W on the native Si dioxide and subsequent annealing under ultrahigh-vacuum conditions. Silicidation starts at 1000 K, as, it is believed to occur, the Si diffuses to the surface through the defects in the oxide. Flash annealing to 1500 K removes the oxide, resulting in stable WSi2 contacts on the surface. Contamination due to migrating W is confined to within a micrometer of the edge of the WSi2 contacts. Beyond this micrometer-sized zone, the surface is free of contamination as confirmed by low-energy electron microscopy and high-resolution low-energy electron diffraction. Reproducible resistance curves during annealing and cooling of the Si(001) sample confirm the reliability of the contacts, which can withstand many flash-annealing cycles without degradation.
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