Electrical characteristics of postdeposition annealed HfO2 on silicon

Electrical characteristics of ultrathin HfO2 films on p-type silicon (100) substrates were determined by capacitance-voltage and current density-voltage measurements. The as-deposited HfO2 films showed a dielectric constant of ∼22, a leakage current density of 5A∕cm2 and an interface state density of 6.5×1012cm2eV−1 at an equivalent oxide thickness (EOT) of 7.6Å due to the poor quality of HfO2∕Si interface. However, annealing in O2 and NH3 significantly reduced the interface state densities to 8.4×1011cm2eV−1 and 7.38×1011cm2eV−1, respectively, although the annealing increased the EOTs to 12.3Å and 11.3Å respectively, due to the growth of an additional interfacial layer. The forming gas anneal with either H2 or D2, however, significantly improved the quality of the HfO2∕Si interface without affecting the EOT. Postdeposition annealing in all chemistries decreased the leakage current densities by orders of magnitude at the same EOT compared to that of SiO2. The current transport mechanism in the as-deposed HfO2 sample is determined to be direct tunneling, and an Al∕HfO2 barrier height of 1.3eV and a HfO2∕Si barrier height of 1.4eV were obtained. The latter is in good agreement with the band offset determined by x-ray photoelectron spectroscopy analysis and ab initio calculations.