The Effect of Si ON TiAl3 Formation EV Ti/Al Alloy Bilayers

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 TiAl 3 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 TiAl 3 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 TiAl 3 layer.