Structure and properties of rapidly thermal annealed Ta/Si multilayers

The microstructure, chemistry, and phases in thin Ta/Si multilayers of various stoichiometry reacted by rapid thermal annealing (RTA) were investigated with cross-sectional transmission electron microscopy (X-TEM), Auger electron spectroscopy (AES), and glancing angle x-ray diffraction (XRD). The nucleation and growth processes of TaSi2, the only silicide formed, are illustrated and discussed. The growth kinetics are affected by contamination. In contrast to reactions between Ta films and crystalline Si substrates where Si is diffusing and Ta is stationary, both species appear to be diffusing in thin amorphous multilayers. A thin Ta oxide forms on the surface when the material in contact with the annealing atmosphere (0.999 99 Ar) is Ta, but not when it is Si or TaSi2. The resistivity is stoichiometry and temperature dependent, and is always higher in silicide-on-SiO2 than in polycide structures, indicating that polysilicon substrates shunt some of the current during measurement.