Epitaxial CoSi2 formation on Si(001) from an amorphous Co75W25 sputtered layer

Abstract

The formation of epitaxial CoSi2 on (001) Si using the solid state reaction between an amorphous Co75W25 sputtered layer and Si has been studied. Auger electron spectroscopy depth profiling, Rutherford backscattering spectrometry, x-ray diffraction, transmission electron microscopy, and resistivity and mobility measurements on Van der Pauw structures have been used to investigate the interaction between the amorphous alloy and Si. By employing anneals in vacuum between 500 and 600 °C for 60 or 120 min, Co diffuses out of the alloy into the substrate to form CoSi2. X-ray diffraction measurements indicate that the greater part (about 75%) of the disilicide film is epitaxial. The CoSi2 film is unstrained at the growth temperature. At room temperature a tetragonal distortion of the silicide lattice is noted, which results from cooling from the growth temperature, and is caused by the difference in the thermal expansion coefficients of Si and CoSi2. After a selective etch to remove the remaining amorphous alloy, a second anneal at a higher temperature has been performed to improve the quality of the silicide. As a result of the second anneal, the Rutherford backscattering channeling minimum yield and the residual resistivity of the film decrease to values of about 25% and 2.6 μΩ cm, respectively. Only the epitaxial (A type) orientation of CoSi2 could be detected after the second anneal by x-ray pole figure measurements. Both the vertical and the lateral distortions in the silicide lattice, measured at room temperature, appear to decrease during this anneal. The Debye temperature, obtained from electrical measurements, increases from 382 K, after Co outdiffusion, to 412 K after the second anneal.