Multilayered Ti/TiN and TaN for Cu Metallization and Al Metallization
In this research, a novel multilayered Ti/TiN diffusion barrier was proposed and successfully applied for Cu and Al metallization. Multilayered Ti/TiN could block fast diffusion path of columnar grain structure in TiN diffusion barrier, and hence alleviates the interdiffusion between metal and silicon. Metal films were deposited by physical vapor deposition, and multilayered Ti/TiN was deposited sequentially without vacuum break. TEM, SEM, XRD, RBS, SIMS, AES, and AFM were used for material characterization. Sheet resistance, contact resistance, and junction leakage current were measured and used to evaluate the barrier performance. It was found that TiN grain boundary was discontinuous while a Ti layer was inserted in TiN. Multilayered Ti/TiN has better barrier performance than single-layer TiN in Al metallization. However, more titanium layer or thickness enhanced chemical reactions between titanium and aluminum, produced more titanium-aluminum compounds, and reduced the total effective thickness of titanium nitride, and hence barrier performance would be affected. Total thickness of introduced Ti layers should be reduced to improve barrier performance. The more titanium layers were inserted in TiN, the more enhanced barriers was obtained in Cu metallization. It was found that the diffusion of copper into silicon was slowed and hence barrier performance was improved. On the other hand, tantalum nitride was reactively sputtered by various nitrogen/argon flow ratios. It was found that grain size of tantalum nitride reduced with increasing nitrogen flow ratio. Compressive stress of the tantalum nitride thin film would lower as sputtering at high nitrogen flow ratio. The barrier performance of tantalum nitride deposited at high nitrogen flw ratio was better because tantalum reacted spontaneously with silicon producing tantalum-silicon compounds.