We have studied the effects of the gate hard mask and the gate spacer nitride film on the reliability of W/WNx/poly-Si gated devices. When the gate hard mask nitride film is used, severe degradation of the stress-induced leakage current (SILC) and the interface trap density (D-it) characteristics are observed in the large metal-oxide-semiconductor (MOS) capacitors. On the other hand, as the devices become smaller, the effects of the hard mask nitride film are relieved. The gate spacer stack plays a more critical role in the reliability of smaller devices. The oxide/nitride (ON) spacered devices exhibit better reliability m terms of SILC, D-it, threshold voltage (V-th) shift, and transconductance (G(m)) compared to those of the nitride/oxide/nitride (NON) spacered ones. These behaviors are explained by the mechanical stress of the nitride films. (c) 2005 American Vacuum Society.