Degradation of Nitride/W/WN_x/Poly-Si Gate Stack by Post-Thermal Processes

Abstract

We investigated the effect of post-thermal processing on the gate oxide reliability in nitride/W/WNx/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 SiO2/Si interface, resulting in the degradation of the gate oxide.

Gate Oxide Reliability Characterization of Tungsten Polymetal Gate with Low-Contact-Resistive WSix/WN Diffusion Barrier in Memory Devices

“…This phenomenon has been reported to be mainly caused by the stress mismatching between the hardmask nitride layer and the polymetal gate stack. 4) This hardmask nitride layer is crucial for self-aligned contact (SAC) processes, which are widely used in DRAM technology. Therefore, the right choice for a new diffusion barrier metal in a tungsten poly gate that ensures good characteristics both in terms of gate oxide integrity and gate R c is important for a future DRAM gate stack, which requires both good reliability and highspeed characteristics.…”