Soft X-ray photoemission study of nitrogen diffusion in TiN/HfO:N gate stacks

The impact of HfO:N post nitridation anneal (PNA) and gate fabrication on the physico-chemical properties of the TiN/HfO:N/SiO2/Si stack are investigated using Soft X-ray Photoelectron Spectroscopy (S-XPS) and Vacuum UltraViolet Spectroscopic Ellipsometry (VUV-SE). Defects created in the high-k during plasma nitridation are passivated by PNA under O2. Both oxygen and nitrogen diffusion is observed towards the bottom SiO2/Si interface together with a regrowth of the SiO2. These defects play a major role regarding nitrogen diffusion during gate fabrication. Without PNA, no diffusion is observed because O and N atoms are trapped inside the high-k. With PNA and simultaneous defects passivation, nitrogen from both metal gate and high-k diffuses towards the bottom SiO2/Si interface.

► The post nitridation anneal of HfO:N induces nitrogen diffusion towards the Si substrate. ► Defects in the high-k are removed by incorporation of oxygen during this anneal. ► After gate fabrication and without anneal, nitrogen is trapped inside the HfO:N. ► After gate fabrication and anneal, nitrogen diffuses from the gate and high-k towards the Si substrate.