This work is aimed at in-line thickness and composition analysis of Co silicides by spectroscopic ellipsometry (SE). The silicides were formed by a two-step rapid thermal annealing (RTA) in nitrogen at different temperatures from initial Co layers deposited on Si (100) substrates and capped by a protective layer of TiN. The optical constants of Co, CoSi and CoSi2 films were calculated in the wavelength range of 240-800 nm, describing the optical dispersions by harmonic oscillator models. These models were applied for in-line thickness and composition control of the main steps of Co SALICIDE process. The effects of the first RTA temperature and initial Co thickness on formation of silicide phases and their thickness were evaluated. For phase identification, additional methods (sheet resistance, Auger electron spectroscopy and X-ray diffraction) were used. Finally, the suitability of SE for layer thickness uniformity evaluation was demonstrated for the main steps of Co SALICIDE process. (C) 2003 Elsevier B.V. All rights reserved.