Electrical Characteristics and Thermal Stability of W, WN[sub x], and TiN Barriers in Metal/Ta[sub 2]O[sub 5]/Si Gate Devices

Tantalum pentoxide was adopted as gate dielectric for obtaining gate oxide with less than 3.0 nm of equivalent thickness and low leakage current. Physical vapor deposited (PVD) W, PVD PVD TiN, or chemical vapor deposited (CVD) TiN was used as gate/barrier material on Thermal stability and electrical property of each barrier were evaluated at elevated temperature of 900°C. W and barriers show much lower leakage current than TiN barriers at both low and high fields. Leakage current is lower with barrier than with W barrier at high field. The breakdown characteristics of W and barriers are noticeably improved after annealing at 900°C because of the recovery from sputtering damage. The breakdown characteristic of is superior to W and this is thought to come from the incorporation of nitrogen into the layer. Breakdown property is not degraded significantly in the samples with PVD TiN barrier. However, the samples with CVD TiN barrier show significant degradation in electrical property at the elevated temperature. Microvoids are formed in layer along the interface in PVD TiN sample after annealing at 900°C. Ta diffuses into the TiN layer leaving voids behind. is more severely damaged in the CVD TiN sample. Diffusion of Ta and O becomes significant in this sample after annealing. The Cl content is also much higher in CVD TiN samples than PVD TiN samples. Thus residual Cl is considered to be the main reason for the degradation of in the devices containing CVD TiN as a barrier material.