Effect of microwave annealing on electrical characteristics of TiN/Al/TiN/HfO₂/Si MOS capacitors

In this letter, microwave annealing over a wide range of power (300-2700 W) in nitrogen ambient was performed on TiN/Al/TiN/HfO₂/Si metal-oxide-semiconductor capacitors. Capacitors with rapid thermal annealing at 500 °C were also fabricated for comparison at the same wafer temperature measured during microwave annealing at 2700 W. For microwave annealed capacitors, key parameters such as equivalent oxide thickness, interface state density, oxide trapped charge, leakage current density, and breakdown voltage were all improved with increasing microwave annealing power. For the capacitor with rapid thermal annealing at 500 °C, diffusion of Al into TiN and growth of the interfacial oxide layer are detected, leading to the shift in flat-band voltage and increase in equivalent oxide thickness, respectively. The results further indicate that it is more effective to remove the charged traps by microwave annealing than by rapid thermal annealing, and the reduction in leakage current density after microwave annealing corresponds to the reduction in charge traps based on a trap-assisted tunneling model. With no trade-off relationship between the electrical characteristics and no undesired effect such as diffusion of species, microwave annealing demonstrates great potential for the post-metallization annealing process for the high-k/metal gate structure.