Ultrathin HfO2 films grown on silicon by atomic layer deposition for advanced gate dielectrics applications

We report on growth behavior, structure, thermal stability and electrical properties of ultrathin (<10 nm) hafnium oxide films deposited by atomic layer deposition using sequential exposures of HfCl4 and H2O at 300°C on a bare silicon surface or a thin thermally grown SiO2-based interlayer. Compared to good quality continuous films deposited on SiO2 surfaces, HfO2 deposited on HF-last treated Si surfaces show a non-uniform, island-like morphology and poor electrical properties due to poor nucleation on H-terminated Si. As-deposited films have a significant amorphous component and undergo crystallization to a monoclinic phase above ∼500°C. Crystallization behavior is found to be dependent on film thickness with higher crystallization temperatures for thinner films. HfO2 on an ultrathin SiO2 interlayer shows good electrical properties with gate leakage current reduced by a factor of 103 -104 with respect to conventional SiO2 gate dielectrics which justifies its consideration as a candidate for high-K dielectric for future CMOS devices.