Ultrathin HfO_2 films grown on silicon by atomic layer deposition for advanced gate dielectrics applications

摘要

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 HfCl_4 and H_2O at 300 ℃ on a bare silicon surface or a thin thermally grown SiO_2-based interlayer. Compared to good quality continuous films deposited on SiO_2 surfaces, HfO_2 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 ℃. Crystallization behavior is found to be dependent on film thickness with higher crystallization temperatures for thinner films. HfO_2 on an ultrathin SiO_2 interlayer shows good electrical properties with gate leakage current reduced by a factor of 10~3-10~4 with respect to conventional SiO_2 gate dielectrics which justifies its consideration as a candidate for high-K dielectric for future CMOS devices.