The dielectric characteristics and thermal stability of Hf-silicate films with different Si contents

We investigated the dielectric characteristics of Hf-silicate films which were grown on Si(100) substrates by atomic layer deposition. The X-ray photoelectron spectroscopy results indicated that the atomic concentrations of Hf O2 and Si O2 in the Hf-silicate films were similar to the cycle ratio between the number of Hf O2 deposition cycles and that of Si O2 deposition cycles. The flatband voltage of Hf-silicate films increased as the compositional deviation from the stoichiometric compound HfSi O4 increased. For Hf-rich silicate films, the flatband voltages were lowered due to the increase of the positive fixed charge in Si O2 with the increase of Si O2 content. In addition, the crystallization temperatures were below 900°C after postannealing for 1 min in N2 ambient and accompanied the phase-separation process as the Si content increased. However, in the case of Si-rich Hf-silicate films, the increase of the effective metal work function dominated and increased the flatband voltages as the Si composition increased. The crystallization and phase separation of Hf-silicate films were not observed even after annealing at 900°C.