CHARACTERISTICS OF PECVD GROWN TUNGSTEN NITRIDE FILMS AS DIFFUSION-BARRIER LAYERS FOR ULSI DRAM APPLICATIONS

We have. developed tungsten nitride (W-Nitride) films grown by plasma enhanced chemical vapor deposition (PECVD) for barrier material applic ations in ultra large scale integration DRAM devices. As-deposited W-N itride films show an amorphous structure, which transforms into crysta lline, beta-W2N and alpha-W phases upon annealing at 800 degrees C. Th e resistivity of the as-deposited films grown at the NH3/WF6 gas flow ratio of 1 is about 160 mu Ohm-cm, which decreases to 50 mu Ohm-cm cm after an rapid thermal annealing treatment at 800 degrees C. In the co ntact holes with the size of 0.35 mu m and aspect ratio of 3.5, the bo ttom step coverage of the tungsten nitride films is about 60%, which i s about three times higher than that of collimated-TiN films. We obtai ned contact resistance and leakage current with the tungsten nitride b arrier layer comparable to those with conventional collimated TiN film s. The contact resistance and leakage current are stable upon thermal stressing at 450 degrees C up to 48 h.