The objective of this work is to determine the origin of a decohesion problem that occurs during the fabrication process of certain integrated circuits. This decohesion takes place at the Ti/dielectric interface with the dielectric being either SiO2 or borophosphosilicate glass (BPSG). The frequency of the decohesion increased when the dielectric is BPSG. In order to understand the reason for the difference in decohesion rates for the two dielectrics, a comparative study was performed before and after annealing. X-ray Diffraction was used to determine the microstructure of the different layers and Transmission Electron Microscopy coupled to Electron Energy Loss Spectroscopy and X-ray Energy Dispersive Spectroscopy was mainly used to characterize the interfaces and nanophases that had formed during annealing. A fundamental difference observed was the Ti/dielectric interface reactivity: in the case of BPSG, an amorphous layer rich in P is formed before the Ti5Si3 silicide. Two hypothesis are put forward in order to explain adhesion failures: a decrease in the rate of Ti5Si3 formation kinetics and/or a decrease of the glass transition temperature induced by P enrichment.