Preparation Of Hf-based High-k Gate Dielectric Thin Films And Investigation Of Its Devices' Performance

With the increasing integration of the large scale integrated circuit,the feature size of microelectronics devices decreased constantly and traditional SiO2 gate dielectric reached its physical limits.Large tunneling current and high power consumption seriously affected the stability and service life of electronic devices.High dielectric constant(k)materials were selected to replace the traditional SiO2 gate dielectric in order to solve the problem.As an appropriate candidate for high-k gate dielectric material,HfO2 has moderate dielectric constant,wide band gap and superior thermodynamic stability.However,HfO2 has also some fatal defects,such as low crystallization temperature and high oxygen and impurities penetration,which seriously restricts its application in complementary metal oxide semiconductor field effect transistors(CMOSFETs).Thin film transistor(TFT)is the core device in flat-panel displays.Replacing the traditional SiO2 gate dielectric with high-k material can effectively improve the performance and reduce the power consumption of TFT devices.Therefore,it's extremely important to prepare high quality gate dielectric films.The preparation of Hf-based high-k dielectric films and its devices'performance were investigated in this thesis.Doping gadolinium or aluminum in HfO2 and annealing treatment were carried out so as to improve the performance of HfO2 films applied in CMOS and TFT devices.The main contents and conclusions include three parts and are as follows:1.The MoS2/HfO2 heterojunction was prepared by sputtering.The effect of Gd incorporation on the energy band alignment of heterojunction interface has been systematically investigated.Experimental results indicate that the band gap of HfO2 increases after Gd incorporation.A valence band offset(?Ev)of 2.31 eV and a conduction band offset(?Ec)of 2.43 eV were obtained for the MoS2/HfO2 interface.After Gd incorporation,a ?Ev and a ?Ec across the MoS2/HfO2 interface were found to be 2.12 eV and 2.91 eV,respectively.The increased ?Ec will benefit the n-type MoS2 based field effect transistors(FETs)in terms of suppressing the gate leakage current.2.The Gd-doped HfO2(HfGdO)films were prep(?)red by sol-gel method.The effects of different annealing temperatures on the micrc(?)tructure,band gap,interface and electrical properties were investigated.The experi(?)ental results show that the HfGdO films annealed at 600 ? begins to crystallize,indicating that Gd incorporation effectively increases the crystallization temperature of HfO2.The band gap of HfGdO films increased with the increas(?)g annealing temperature.Furthermore,it can be noted that increase in ?Ev and reduction in ?Ec have been detected.Meanwhile,annealing treatment results in the increased effective permittivity(k)of HfGdO films.The decreased flat band voltage shift(?Vfb)and the boarder trap density indicated that annealing treatmer ' effectively suppresses the appearance of boarder trap.However,the crystallization Induced by high temperature annealing and the decreased ?Ec lead to the increase of leakage current density for high-temperature-processed samples.3.Fully solution-processed InZnO thin film transistors using HfAlO dielectric were fabricated successfully and studied systematically.HfAlO films annealed at 600 ? is still in amorphous structure.In addition,the 600?-annealed HfAlO shows high transparency,low leakage current density and smooth surface.The XPS measurement indicates that annealing treatment reduc(?)s the oxygen vacancy and boned oxygen.The 450 ?-InZnO TFT with HfAlO anne(?)ed at 600 ? shows a small Vth of 1.14 V,high Ion/Ioff of?106,high carrier mobility of 5.17 cm2/Vs,small SS of 87 mV/decade and small NT of 8.93×1011cm-2.The resistor-loaded inverter with 450 ?-InZnO/HfAlO TFT shows a good swing char cteristic and well dynamic behavior.