Effects Of Gd₂O₃ Doping On The Oxygen Vacancy Exhibition And Electrical Properties Of HfO₂ High-k Dielectrics

The developments of microelectronic technique are mainly decided by the scaling of device size, improving the integrated level and increasing the area of silicon wafers. Among all the approaches, the scaling of device size is the principle one. With the evolution of CMOS integrated circuit (IC), the thickness of SiO2 which is the traditional CMOS device gate dielectric arrives to the limit and couldn't meet the technical needs for device scaling. Therefore, high permittivity (high K) materials as gate dielectric have attractive extensive interests. Transitional metal oxide HfO2 is one of the most promising high K candidates for complementary-metal-oxide-silicon (CMOS) gate dielectrics for its moderate permittivity (-21), wider band gap (-5.8eV), higher electron offset (～1.5eV) and better thermodynamic stability on Si wafers compared to other high K materials. However, there are also several disadvantages with HfO2, such as lower crystallization temperature (～375℃), high oxygen vacancy density and easily formed interfacial layer and so on.Recently, rare-earth oxides have become new focus for replacing SiO2 gate dielectric. This attributes to the higher permittivity, better thermodynamic stability on Si even in higher temperature and wider conduction band shifts. Therefore in our study, we choose HfO2 and rare-earth oxide Gd2O3 as high K dielectrics and study from the angle of oxygen vacancy. The specific contents are as follows:(1) Adopt magnetron sputtering and use HfO2 and Gd2O3 targets simultaneously to deposit 10nm Gd2O3-doped HfO2 binary amorphous high K gate dielectric thin films on n-Si (100). XRD results estimated that the deserved thin films are amorphous. HRTEM results indicated that the deposited thin films remained amorphous after 450℃,20min PDA conditions and there's very thin interfacial layer. C-V characterization of Pt/GHO/Si capacitor indicated that the doped thin films had better capacitance property, the permittivity arrived to 31.6. I-V results indicated that the thin film had lower leakage current dendisy 4.59×10-6 A/cm2 at 1V. Results proved that the Gd2O3-doped HfO2 binary amorphous thin films could meet the demands of high K gate dielectrics and the Gd2O3-doping could inhibits the leakage current.(2) Carry out a further study of the electrical characteristics of Gd2O3-doped HfO2 thin films. C-V and I-V characterizations were executed on Pt/GHO/Si capacitors, results indicated that the leakage current of GHO thin films are reduced as the doping power of Gd2O3 increased and the peak value appeared at 60W (9.35×10-7A/cm2 at 1V). The Nof andΔVFB also had extremes at 60W. This is mainly because of the lower permittivity of Gd2O3, bigger atomic radius and bigger electron negativity difference of Gd-O compared to Hf-O.(3) Analyze the effects of PDA (post depositon annealing) ambient on the electrical properties and leakage current mechanisms. The 60W Gd2O3 deposition parameter was chosen and different annealing ambient such as N2, O2, NH3 and Ar were applied. To analyze the possible leakage current mechanisms, I-V curves were fitted. Results indicate that when holes were injected from the substrate and gate, the different ambient annealing leakage current mechanisms were affected both by Frenkel-Poole and Schottky emission. It indicated that oxygen ambient annealing reduced the bulk defects in high k gate dielectrics which prove that the oxygen vacancy is the main bulk defects. NH3 annealing can minimize the bulk defects and has lower interfacial state compared to N2 annealing. C-V characterization demonstrates that O2 annealing promotes the growth of low K interface and N2 and NH3 annealing can passivity the interfacial state. NH3 annealing has minimum hysteresis and O2 annealing next to it. The result conforms well to I-V leakage current.(4) Analyze the Gd2O3-doping effect on the inhibition of oxygen vacancy in HfO2 bulks from the angle of defect chemistry. Ols peak of lattice oxygen showed that the peak intense of lattice oxygen was increased with the increase of Gd2O3 doping power. The ratio of O/M calculated by using sensitivity factor was increased, which means that more M-0 bonds were formed and the number of oxygen vacancy was reduced. The results corresponded well to the C-V electrical characterization. Compared to the I-V curve of pure HfO2 thin films, the doped thin films had lower leakage current and the Gd2O3 doping made the leakage current of pure HfO2 low three magnitudes. In conclusion, the rare-earth oxide Gd2O3 doping significantly minimized the leakage current of HfO2 dielectric thin films and improved its electrical properties by reducing the oxygen vacancy. When the doping power of Gd2O3 superior to 60W, the permittivity turned to opposite. These were mainly due to the lower permittivity of Gd2O3 compared to HfO2. When the doping amount was increased to a certain value, the permittivity came into play. Research of PDA effects on the leakage current mechanism of GHO indicated that O2, N2 and NH3 annealing could minimize the bulk defects in high K dielectric thin films and the N2 and NH3 annealing could improve the interfacial state of thin films.