Impurity effects in molybdenum silicide formation

The reaction between molybdenum thin films and single-crystal Si〈111〉 substrates was studied as a function of the concentrations of impurities (mainly oxygen) in the metal film. At a low oxygen concent (1–2 at.%), only the silicide phase MoSi 2 was observed, and a thickness proportional to the square root of time corresponding to an average activation energy of 3 eV in the temperature range 545–600 °C was found. During the formation of the silicide the oxygen originally present in the molybdenum films accumulates at the interface between the silicon and the MoSi 2 . In contrast, a higher oxygen content (4–5 at.%) prevents the formation of any silicide phases in the above temperature range and leads to the formation of MoSi 2 and Mo 5 Si 3 phases at temperatures near 800 °C. MoSi 2 was always observed at the inner interface with Mo 5 Si 3 on the surface. The oxygen segregates from the silicides and accumulates at the Si-MoSi 2 and MoSi 2 -Mo 5 Si 3 interfaces to form a non-uniform layer of SiO x ( x ⩽ 2).