Metallization lines in advanced integrated circuits are often fabricated from sputter-deposited Ti/Al layers. It is well known that the Ti/Al react above ∼350°C to form T1AI3 with a rate that is dependent on anneal temperature and the alloying content of Cu and Si in the Al. In the present work, the thickness of TiAl3 formed during annealing at 430°C has been determined from the measurement of the sheet resistance of Ti/Al-.5%Cu and Ti/Al-.5%Cu-l%Si bilayers. Analyses of the reacted structures were performed by cross-section transmission electron microscopy and Auger depth profiling. We find that the Si exhibits a greater retardation effect on the Ti/Al reaction than does Cu, as shown previously. Kinetic analysis for the Ti/AlCuSi reaction shows that the TiAl3 formation rate is a function of the Ti/AlCuSi thickness ratio. We propose that this effect is due to several mechanisms which involve diffusion and incorporation of Si into the growing TiAl3layer.