Effect of surface NH3 anneal on the physical and electrical properties of HfO2 films on Ge substrate

Metal-oxide-semiconductor capacitors were fabricated on germanium substrates by using metalorganic-chemical-vapor-deposited ${\mathrm{HfO}}_2$ as the dielectric and TaN as the metal gate electrode. It is demonstrated that a surface annealing step in ${\mathrm{NH}}_3$ ambient before the ${\mathrm{HfO}}_2$ deposition could result in significant improvement in both gate leakage current and the equivalent oxide thickness (EOT). It was possible to achieve a capacitor with an EOT of 10.5 Å and a leakage current of ${\text{5.02×10}}^{\text{−5}}\hspace{0.17em}{\mathrm{A/cm}}^2$ at 1 V gate bias. X-ray photoelectron spectroscopy analysis indicates the formation of GeON during surface ${\mathrm{NH}}_3$ anneal. The presence of Ge was also detected within the ${\mathrm{HfO}}_2$ films. This may be due to Ge diffusion at the high temperature (∼400 °C) used in the chemical-vapor deposition process.