Effects of fluorine and chlorine on the gate oxide integrity of W/TiN/SiO2/Si metal-oxide-semiconductor structure

We investigate the effects of fluorine (F) and chorine (Cl) on the gate oxide integrity of W/TiN/SiO2 (3 nm)/Si metal-oxide-semiconductor (MOS) structure as a function of W deposition method and post-metal anneal (PMA) process. TiN films were prepared by chemical vapor deposition (CVD) using TiCl4 and NH3, while tungsten (W) electrodes were prepared by CVD using a WF6 precursor and by physical vapor deposition (PVD) using a W target. The amount of fluorine ([F]) prepared by CVD-W was two orders of magnitude higher than that prepared by PVD-W. The interface trap density (Dit) of MOS capacitor was lower with CVD-W than the one with PVD-W by a factor of two after PMA of 950 °C, resulting in the Dit in the mid-1010/eV cm−2 range. The higher Dit, fixed charges, and oxide trap charges were observed with PVD-W deposition on top of 30 nm-thick CVD-TiN, strongly suggesting damages at the SiO2/Si interface and SiO2 even after the rapid thermal anneal at 950 °C and following forming gas anneal. However, a noticeable degradation of gate oxide quality was observed with CVD-W by means of smaller breakdown field, charge to breakdown, and shorter lifetime. The reliability degradation was partially attributed to the Cl from the TiCl4 source, while more severe deterioration was assigned to the F from WF6 source after the PMA at 650 °C and above.