The Effect of Si ON TiAl 3 Formation EV Ti/Al Alloy Bilayers
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THE EFFECT OF Si ON TiAI3 FORMATION IN Ti/Al ALLOY BILAYERS Paul R. Besser, John E. Sanchez, Jr, and Roger Alvis Advanced Micro Devices, Integrated Technology Division, One AMD Place, Sunnyvale, CA ABSTRACT Metallization lines in advanced integrated circuits are often fabricated from sputter-deposited Ti/AI layers. It is well known that the Ti/Al react above -350'C to form TiAI3 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 TiA13 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. INTRODUCTION Sputtered Ti is widely used in integrated circuits as an underlayer film for Al-based multilayer metallizations. The Ti/Al bilayer has improved electromigration resistance compared to single layer Al metallization. This improvement is due to both increased Al (111) film texture' and the Ti/TiAl 3 layers which serve as a redundant conductor in the event of void formation in the Al line, thus minimizing the effect of void formation. However, the Ti + Al react above 350 0 C to form TiAl 3, producing a -5.9% volumetric contraction. In a typical interconnect processing sequence, the Ti/Al alloy metallization stack is deposited (at temperatures
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