Thermal stability of amorphous-like WNx/W bilayered diffusion barrier for chemical vapor deposited-tungsten/p(+)-Si contact system

Abstract

The barrier characteristics of tungsten nitride/tungsten (WNx/W) bilayer formed by an in situ nitridation on a thin chemical vapor deposited amorphous-like tungsten (CVD a-W) film in CVD-W/Si contact system have been investigated. The thickness of WNx layer after a 5 min of N-2 plasma exposure at 300 degrees C approximated 50 nm and the atomic ratio of W to N in WNx layer was 2 : 1. In the CVD-W/a-WNx/a-W/Si multilayered sample, no discernible tungsten silicide was detected by X-ray diffractometer (XRD) at W/Si interface after annealing at 750 degrees C. Meanwhile, with the Rutherford backscattering spectroscopy (RBS) analysis and the measurement of p(+)n junction leakage current, the CVD-W/a-WNx/a-W/Si multilayer maintained the integrity of interface and the CVD-W/a-WNx/a-W/p(+)n diode kept the reverse leakage current density less than 9 x 10(-9) A/cm(2) while the post annealing was carried out at 700 degrees C for 30 min. As the experimental results, the effectiveness of amorphous-like WNx/W bilayered diffusion barrier is attributed to stuff grain boundary with N atoms as well as to eliminate the rapid diffusion paths by using CVD a-W material.