Electrical characteristics and thermal stability of W, WNx, and TiN barriers in metal/Ta2O5/Si gate devices

Tantalum pentoxide was adopted as gate dielectric for obtaining gate oxide with less than 3.0 nm of SiO2 equivalent thickness and low leakage current. Physical vapor deposited (PVD) W, PVD WNx, PVD TiN, or TiCl4-based chemical vapor deposited (CVD) TIN was used as gate/barrier material ion Ta2O5. Thermal stability and electrical property of each barrier were evaluated at elevated temperature of 900 degreesC. W and WN(x)barriers show much lower leakage current than TiN barriers at both low and high fields. Leakage current is lower with WN(x)barrier than with W barrier at high field. The breakdown characteristics of W and WN(x)barriers are noticeably improved after annealing at 900 degreesC because of the recovery from sputtering damage. The breakdown characteristic of WN, is superior to W and this is thought to come from the incorporation of nitrogen into the Ta2O5 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 Ta2O5 layer along the TiN/Ta2O5 interface in PVD TiN sample after annealing at 900 degreesC. Ta diffuses into the TiN layer leaving voids behind. Ta2O5 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 Ta2O5 in the metal/Ta2O5/Si devices containing CVD TiN as a barrier material. (C) 2001 The Electrochemical Society. All rights reserved.