Abstract
As the semiconductor technology development continues, device and interconnect line spacing are scaling down for achieving density and speed improvements. As the spacing is shrinking, it is accompanied by larger parasitic resistance and capacitance and hence larger interconnect delay. This interconnect delay has become one of the bottleneck for circuit design. In order to reduce interconnect delay, the use of Cu metallization and low-k dielectrics are required. Although Cu/low-k interconnect technology can effectively reduce RC delay, time dependent dielectric breakdown (TDDB) phenomenon of low-k material has become an important reliability issue. In this thesis, several low-k TDDB models are reviewed and it is observed that the conduction mechanism of leakage current plays an important role in low-k TDDB phenomenon. Therefore, several leakage current models for low-k material are investigated. These include Schottky emission current model, Poole-Frenkel emission current model and Fowler-Nordheim tunneling current model. These leakage current models have been implemented in an interconnect simulation program, kappa, and can be compared to real silicon measurements. Some Cu/ELK interconnect test structures have been fabricated by TSMC. I-V measurements are carried out to assess the leakage current, including at three different temperatures. By comparing the slopes of the I-V curves, obtained from measurement and simulations, it shows that the Schottky emission current model has the best match with the measurement results. The barrier height between copper and ELK is found to be 0.87eV. Using one set of model parameters, we can get excellent matches between simulation and measurement data. Using this set of model coefficients, we also find that the most sensitive parameters of the leakage current are the line-to-line spacing and the ELK dielectric constant. Smaller spacing increases leakage current; while smaller dielectric constant also increases leakage current. Since this is the direction of technology scaling, it can be predicted that interconnect leakage current is getting more severe with scaling, so is the TDDB issue.