Studies On Preparation And Breakdown Characteristics Of Gd₂O₃ Doped HfO₂ High-k Gate Dielectrics

With the rapid development of Complementary Metal-Oxide-Semiconductor (CMOS) integrated circuit according to Moore's law, the device feature size will be reduced into the nanometer scale, decreasing of thickness of SiO2 gate causes dielectric high leakage current. It is necessary to find new gate materials with high dielectric constant to replace SiO2. The high-k gate dielectric material (HfSiON) has been used for 45 nm and 32 nm technology nodes, but still cannot meet the requirements of next-generation integrated circuits, it needs to find a new high-k gate dielectric material. HfO2, as a good promising high k material, can not be directly used for integrated circuits due to its low crystallization temperature and poor ability of preventing the oxygen diffusion. We selected Gd2O3 to dope in HfO2 for improving the properties of pure HfO2 gate dielectric due to its good thermalstability, larger band gap and effective prevention of oxygen diffusion.1. We prepared Gd2O3 doped HfO2 (GDH) high-k gate dielectric films under a variety of doping power by magnetron co-sputtering. The relationship between different doping power of Gd2O3 and the electrical properties of the GDH films was studied. The best electrical properties appeared when the doping power was 20 W. The relationship between the rapid thermal process (RTP) in N2 and the electrical properties of GDH-20 (doping power of 20W) gate dielectric films has been studied. The best RTP temperature was 700℃for GDH-20 films. With the RTP temperature increasing, the width of hysteresis windows of C-V curves was gradually decreased and the depletion region from the accumulation to the transition became smooth. GDH-20/Si interface has been further passivated under high RTP temperature, and the interface state density and the accumulation of negative charges were reduced. In addition, oxygen vacancies can be combined by N easily in high RTP temperatures, leading to a reduction of the oxygen vacancy density.2. We have analyzed the composition and structure of GDH-20 film. The doping content of Gd2O3 in GDH-20 film was 10mol%, there was silicate generated at the GDH-20/Si interface. The amorphous GDH-20 film was revealed by HRTEM, and the interface layer thickness was significantly reduced compared with pure HfO2, indicating the effective prevention of oxygen diffusion in the GDH gate dielectric by doping Gd2O33. Breakdown properties of GDH-20 high k dielectrics have been studied. GDH-20 gate dielectric maintained good dielectric properties after SBD (soft breakdown). QBD (the charges when breakdown) reduced with the gate voltage increasing. The tBD (time of breakdown) and QBD of breakdown under square wave pulse voltage for GDH-20 dielectric were larger than the case of DC voltage breakdown, due to the self-reparation of GDH-20 film and the dispersion of the pulse stress. The leakage current density increased significantly, while the capacitance density decreased sharply after hard breakdown (HBD). The dielectric properties of GDH-20 gate dielectric deteriorated because of the accumulation of positive charges. In addition, we have studied the effects of the working temperature on GDH-20 film breakdown charactors. GDH-20 thin films maintained good dielectric properties when the work temperature was 100℃In summary, the amorphous GDH high-k gate dielectrics grown on Si (001) substrates can be used as candidate for high-k gate dielectric applications.