Formation of reliable HfO₂/HfSi_xO_y gate-dielectric for metal-oxide-semiconductor devices

The HfO₂/HfSi_xO_y thin film for gate oxides in the metal-oxide-semiconductor (MOS) device is obtained by a simple method which involves the oxidation of sputtered Hf metal films on Si followed by N₂ annealing. Based on the transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses, we found that a high-quality HfO₂/HfSi_xO_y stack layer is formed by the oxidation of the thin Hf film on Si. The hysteresis window of the Pd-HfO ₂/HfSi_xO_y-Si MOS capacitors was negligible (i.e., less than 10 mV). The equivalent oxide thickness (EOT) and leakage current density were 1.2 nm and 2 × 10^-3 A/cm² at 1.5V (after compensating the flatband voltage of 1.5 V), respectively. We suggested that the low leakage current characteristics were obtained due to the presence of the amorphous HfSi_xO_y buffer layer. The conduction mechanism of the Pd-HfO₂/HfSi_xO_y-Si MOS capacitors is identified as Poole-Frenkel emission and as Fowler-Nordheim tunneling in low and high electric field regions, respectively.