Interface Control And MOS Device's Performance Optimization Of Hf-based High-k Gate Dielectrics

MOSFET as the basic unit of integrated circuits,the size of the device scaling down with the continuous development of integrated circuits.Prior to the 45 nm semiconductor processes,gate dielectric materials in MOSFETs use conventional SiO2 thin films and maintain the scaling down the gate capacitance with decreasing SiO2 thicknesses.When the thickness of SiO2 is reduced to the limit thickness of 0.7 nm,scaling down can not be continued.In 45nm and later processes,high-k gate dielectric materials with a dielectric constant k of more than 3.9(SiO2 dielectric constant)are used to satisfy the scaling down of gate capacitance.Compared with SiO2,the high-k gate dielectric has a physical thickness several times higher than that of SiO2 while maintaining the same gate capacitance,which helps to reduce the leakage current of the device.With the advent of semiconductor technology nodes,especially after the 10nm process,integrated circuits need to use high mobility channel materials to improve the scattering of channel carriers after introducing high-k gate dielectrics and to meet the semiconductor industry's demand for high drive capability.In addition,new device structures are also being actively developed to enhance the control of channel conductance at small gate voltages.In this paper,Gd-doped HfO2(HGO)thin film has been selected to acts as the gate dielectric material and,Si and GaAs are selected as the substrate material.The effects of different Gd doping concentrations on the microstructure,composition,optical and electrical properties of HGO/Si gate stacks and the influence of GaAs pretreatment process,annealing temperature,Al2O3 passivation layer thickness and annealing temperature on the structure of HGO/GaAs gate stacks interface and electrical performance effects.The specific research results are as follows:(1)Effect of Gd sputtering power on the structure,optical and electrical properties of HGO thin films has been studied.It was found that the incorporation of Gd element into HfO2 can change the crystal structure of the films.The Gd sputtering power of 30 W(EDS spectrum calculated the doping concentration of Gd element is 23%)makes the HGO films present cubic phase.The sputtering power of more than 30 W distorts the lattice of the HGO film,causing a sudden increase in the hysteresis voltage of the corresponding C-V curve in electrical properties.Optical results show that the optical bandgap of HGO films increases with the Gd sputtering power.The increase of the bandgap is due to the decrease of the oxygen vacancies in the HGO film,which leads to the decrease of density of localizatized states in the bandgap of the HGO film,thereby increasing the band gap value.The value of the flat band voltage extracted from the C-V curve is decreasing,which shows that the oxygen vacancies in the HGO film decrease with the increase of the Gd doping concentration.In addition,Al/HGO/Si/Al MOS capacitors constructed at 30 W Gd sputtering power have the lowest frequency dispersion.In conclusion,the Gd sputtering power of 30W,ie,namely the doping concentration of Gd is 23%,HGO thin film processes the best performance.(2)The influence of sulfur passivation and annealing temperature on the interfacial and electrical properties of HGO/GaAs gate stacks has been investigated.GaAs has a very high surface activity and requires efficient passivation of the film before the deposition of thin films.Sulfur passivation experiments show that the HGO films deposited on GaAs substrates cleaned by organic cleaning,acid cleaning and ammonia sulfide passivation have the least AsOx,GaOx and Aso content in the gate stack structure The results show that sulfur passivation is beneficial to the optimization of the interface of HGO/GaAs and the performance of MOS devices.However,only GaAs pretreatment can not effectively remove the interfacial material.Appropriate-annealing of the thin films can help to optimize the interface and electrical properties.The annealing experiments show that the Ga-O bonds and Aso at the HGO/GaAs gate stack interface annealed at 600? are completely eliminated and the electrical properties are the best.(3)The modulation of Al2O3 passivation layer thickness on the HGO/GaAs gate stack structure interface and electrical performance,and the optimozation of Forming gas annealing on the MOS capacitor electrical performance have been analyzed.The experimental results show that Al2O3 passivation layer obviously inhibits AsOx and GaOx.The 20 cycles Al2O3 passivation layer has the largest suppression on low-k interface layer and the introduction of Al2O3 passivation layer can improve the conduction band offset value,reduce leakage current.However,the improvement of the electrical properties after introducing the passivation layer of Al2O3 is not obvious.The overall electrical C-V curve has the larger "stretch-out" when transitions from the depletion region to accumulation region,the smaller slope and obvious cross-over in the inversion region,and the capacitance of the accumulation region is not saturated enough,all indicating that these samples have higher interface trap density and slower interface state density.Forming gas annealing is used to neutralize the trap charge in the thin film and to optimize the contact between the metal electrode and the thin film.The results of forming gas annealing show that the MOS capacitors annealed at 300? exhibit the best C-V behavior with the smallest "stretch-out",Vfb and ?Vfb values,and the steep depletion region and the saturated accumulation region.In addition,the leakage mechanism analysis shows that there are mainly three kinds of leakage mechanisms,direct tunneling,Schottky emission and P-F emission at room temperature.Low temperature can suppress Schottky emission and P-F emission,and only direct tunneling works.