Formation of platinum-based silicide contacts: Kinetics, stoichiometry, and current drive capabilities

A detailed analysis of the formation of Pt2Si and PtSi silicides is proposed, based on x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electrical characterizations. Published kinetics of the Pt2Si and PtSi transformations under ultrahigh vacuum condition are consolidated on the basis of XPS measurements performed during an in situ annealing at a constant heating rate. At room temperature, an incomplete PtxSi reaction is clearly identified by XPS depth profiling. Using rapid thermal annealing at 300, 400, and 500 °C, the sequential Pt–Pt2Si–PtSi reaction chain is found to be completed within 2 min. Outdiffusion of silicon to the top surface is shown to be responsible for the formation of a thin SiO2 capping layer at 500 °C. Pileup of oxygen occurring at the Pt2Si/Pt reaction front is clearly identified as an inhibiting factor of the silicidation mechanism. Another incomplete reaction scheme limited to the unique formation of Pt2Si is exemplified in the case of ultra thin silicon-on-insulator films. Finally, current drive measurements on PtSi Schottky contacts have allowed us to identify 300 °C as the optimum annealing temperature while TEM cross sections demonstrate the formation of a smooth and continuous PtSi/Si interface at 300 °C.