Degradation of nitride/W/WN_x/poly-Si gate stack by post-thermal processes

We investigated the effect of post-thermal processing on the gate oxide reliability in nitride/W/WN_x/polycrystalline-Si (poly-Si) gated metal-oxide-semiconductor (MOS) capacitors. As the thermal processing became severer, grater development of mechanical stress and degradation of the gate oxide were observed. Microvoids were also found at the triple point between the gate oxide and two poly-Si grains. The wide variation in mechanical stress during post-thermal processing is believed to create the microvoids and generate additional dangling and strained bonds in the oxide and at the SiO ₂/Si interface, resulting in the degradation of the gate oxide.