In-line thickness monitoring of CoSi2 films is usually carried out by four-point probe resistivity measurements on blanket samples. This method, however, reveals no information about the thickness variation and stoichiometry of the CoSi2 films. Transmission Electron Microscopy (TEM) can provide this information but the technique is destructive, whereas Raman spectroscopy is non-invasive and offers a technique for patterned wafers compatible with current VLSI technology.
The CoSi and Co2Si phases exhibit very characteristic Raman signatures which, with glancing angle X-ray diffraction (GA-XRD), can be used to investigate the silicidation sequence. Although CoSi2 does not produce a Raman spectrum, the silicon local mode can be easily detected through the film and is very sensitive to variations in thickness. The intensity of the silicon local mode was measured on a series of ten samples of CoSi, on silicon and the precise CoSi, film thickness subsequently determined by cross sectional TEM. From these measurements, the absorption coefficient of CoSi2 at 500nm was determined.