Degradation of Ta2O5 Gate Dielectric by TiCl4-Based Chemically Vapor Deposited TiN Film in W/TiN/Ta2O5/Si System

Tantalum pentoxide was adopted as a gate dielectric for obtaining gate oxide with less than 3.0 nm SiO2 equivalent thickness and low leakage current. Physical vapor deposited (PVD) TiN or TiCl4-based chemical-vapor-deposited (CVD) TiN was used as the barrier material between the W electrode and Ta2O5 layer. The thermal stability and electrical property of each barrier were evaluated at an elevated temperature of 900?C. In the as-deposited condition and after annealing at 800?C, PVD and CVD TiN show similar electrical properties. However, after annealing at 900?C, CVD TiN barriers show much lower breakdown fields and higher leakage current compared with PVD TiN, indicating that CVD TiN has worse barrier performance than PVD TiN. Microvoids are formed in the Ta2O5 layer along the PVD TiN/Ta2O5 interface after annealing at 900?C. It is found that Ta diffuses into the TiN layer leaving microvoids behind. Ta2O5 is more severely damaged in the CVD TiN system after annealing. The high content of residual Cl in CVD TiN was found to reduce Ta2O5 and generate free Ta and O. Free Ta and O atoms that are generated from the reduction of Ta2O5 diffuse into the TiN layer and hence produce macrovoids and disconnected areas in the Ta2O5 layer. The transmission electron microscopy (TEM) images and secondary ion mass spectrometry (SIMS) depth profiles are in good agreement with the electrical properties of W/TiN/Ta2O5/Si gate devices.