Effect of poly-Si on electromigration behaviors and microstructure characteristics of Au metallization

摘要

For BJT and MOSFET, poly-Si is the most critical layer used as an emitter to improve the current gain in BJT and as a gate to improve the gate oxide reliability in MOSFET. In both cases, the poly-Si is then connected to the conductor. It is very imporatant to understand how poly-Si affects the microstructure and the electromigration behavior of conductor. NIST test structures (length=800 #mu#, thickness=0.7#mu#, widths= 1, 5, 10#mu#) with Au conductor and TiW/TiWN/TiW barrier were used to study the impact of poly-Si. Two groups of samples were used: one with poly-Si under the barrier were used to study the impact of poly-Si. Two groups of samples were used: one with poly-Si under the barrier and the other without poly-Si. Thermal oxide was used to isolate the substrate from the conductor and Si_3N_4, was used as passivations. DC stress was performed at 175, 200, and 225 deg. Microbeam X-ray Diffraction (#mu# XRD) was used to characterize the microstructure of the TiW barrier and Au metallization layers as a function of line length and width. The data indicates that samples with poly-Si have lower electromigration resistance for Au conductors for all widths and temperatures, with higher initial deformation fault densities on poly-Si.