Study On Radiation Effect And Mechanism Of Alumina Gate Dielectric

In order to further improve the performance of the device,high ? dielectric material is needed instead of SiO2 as the gate dielectric,which can reduce the direct tunneling effect of the gate dielectric layer,thereby reducing the leakage current of the gate dielectric layer and improving the reliability of the device.At present,high ?materials have been widely used in the manufacturing process of advanced devices.As these advanced devices are used in space environments,their high ? dielectric layers are susceptible in radiation environments,to degrade device performance.Therefore,in order to enable advanced nano-devices to be applied to the radiation environment,the research on the radiation effect and mechanism of the high-K materials inside has become a focus of attention.Firstly,ionization total dose experiments of metal-oxide-semiconductor(MOS)capacitors of Al2O3 gate dielectric layer using gamma rays were studied.It is found that the Al2O3 gate dielectric layer contains a large number of hole trapping centers,which will capture the holes generated by the irradiation,causing the left drift of the Capacitor-Voltage(C-V)curve of the MOS capacitor.Secondly,synergistic irradiation using 30 MeV Si heavy ions after gamma ray irradiation showed that the new defect caused by Si ions was the electron trapping center or negative fixed charge,causing the right drift of the C-V curve.Then,experimental and simulation data of the Current density-Voltage(J-V)curve confirm that the transport mechanism of leakage current in the Al2O3 layer is mainly determined by the Frenkel-Poole mechanism.The change in leakage current is mainly due to the local built-in electric field assist current leakage and the conduction path assist current leakage,and it is found to depend on the irradiation conditions and the Al2O3 thickness.Finally,the reduction in the gate oxide capacitance of the MOS capacitor is attributed to the increase in series resistance and leakage current in the MOS capacitor.The paper also theoretically analyzes the physical mechanism of the device after irradiation.The ?-Al2O3 crystal form was selected as the initial structure.Through the first-principles calculation,it was found that the heavy ion-irradiated alumina dielectric layer may indeed introduce an electron trapping center or a negative fixed charge.Irradiation causes two defects,2VO and 2Oi,which are related to the actual Fermi level position in the alumina as an electron capture center or a hole trapping center.2VAl?2Ali?Hi?HO?AlO?OAl?Hi-Oi?Hi-VAl?H2-VAl and H3-VAl defects caused by irradiation.They can only be used as negatively charged fixed charges,uncharged fixed charges or positively charged fixed charges in irradiated Al2O3 gate dielectrics.The Hi-VAl?H2-VAl and H3-VAI structures also become more negatively fixed charges after the bond cleavage is lost H,and these negative fixed charges may cause C-V right drift.The dangling bonds,such as Si+ ions generated in the structure will introduce the interface state to stretch the C-V curve or become the electron capture center to make the C-V curve drift right.In addition,the defects introduced by these irradiations not only serve as a trapping center or a fixed charge center,but also become a conductive path,which increases the leakage current of the aluminum oxide gate dielectric.