|
The thermal stability of multilayered TiN/AlCu/TiN interconnect metallization and its impact on electromigration reliability performance has been investigated. Upon heat treatments at 450 degree(s)C, a monotonic increase in sheet resistance of the metal structure was observed. The test results on samples with different structures, including single-layered AlCu, AlCu/TiN(cap), TiN(bottom)/AlCu, and TiN(bottom)/AlCu/TiN(cap), showed that the sheet resistance increase due to heat treatment effect occurred only for the last two structures which had a TiN barrier. This indicates that the observed sheet resistance increase resulted from occurrence of some intermetallic reactions between AlCu and the underlying TiN barrier, but similar reactions did not occur between AlCu and the TiN in the capping layer. The result was further verified by cross sectional TEM and RBS analysis on samples with heat treatments. The heat treatment effect on electromigration performance was found to be significant leading to lifetime variations over an order of magnitude. A bell-shaped relationship between electromigration lifetime and the metal sheet resistance was found on samples receiving varying cycles of heat treatments. The observed effect is believed to be due to doping effect of Ti diffusing from the underlying TiN barrier into AlCu. It is concluded that a good control over the cumulative thermal budget is essential to assure electromigration reliability for TiN/AlCu/TiN metallizations, which is especially critical for multilevel metallizations.
|
