Study On Thermal Stability And Tunneling Current Of Ultrathin Gate Oxidation

Since metal-oxide-semiconductor (MOS) device appeared, integration of integrated circuit (IC) expands as Moore law. Meanwhile the dimension of device scales down, the thickness of SiO2 gate dielectric shrinks as the same law. But as the thickness of SiO2 gate dielectric reaches at ISA, the gate current rises very quickly and reaches at 1×10A/cm2. The large gate current brings out a lot of questions such as thermal stability, thermal dissipation, lifetime etc, so, it affects the device's function and the device can't work normally. In order to resolve the questions, a new high K material is developed instead of the traditional SiO2 gate dielectric material to reduce the tunneling current. The La2O3 material was paid attention because of its good gate dielectric properties, but there are a lot of properties are under research, the most important property is thermal stability.To improve the situation the author has made the following research and achieved beneficial results.1. In order to measure the thickness of gate dielectric, a new algorithm is introduced to calculate the mono-layer and multi-layer thickness on the basic of theory of the angle-dependent X-ray Photoelectron Spectroscopy (XPS), and a software is developed on the basic of the algorithm. The calculational result agrees with the result which is calculated by ARCtick software which was developed by National Physical Laboratory (NPL) of UK. The multi-layer model algorithm not only calculates the thickness of gate dielectric but also validates whether the model is proper. It has high practical merit to analyze the structure of gate dielectric. The realization of the algorithm drives the research of micro-electron structure.2. The La2O3 thin film is prepared by RF technology, the film is analyzed by ARXPS, the thickness is calculated by Quantitative Analysis software, the thickness of SiO2 thin film between La2O3 and Si is 0.6nm. After annealing at temperature 700癈 for 10 minutes in O2 the thickness of SiO2 becomes thick very much and reaches at 2.1nm. After annealing at temperature 700℃ for 10-30 minutes in N2, the thickness of Si02 is 1.2nm. After annealing in N2, annealing process at temperature 700 ℃ for 10 minutes in O2 secondly, the thickness of SiO2 does not change, it shows that the SiO2 layer is stable after annealing in N2, the thickness of SiO2 is less than that annealing in O2. So a conclusion can be got that the annealing in N2 raises the La2O2, stability.3. The exact solution and WKB approximation are compared, The exact solution agrees with the WKB approximation in calculating the mono-layer SiO2 tunneling current,but the WKB approximation is inappropriate for the dual layer oxide-lanthanum structure, while the exact algorithm can give a exact result. The calculational result by exact solution shows that the substrate inject current is larger than gate inject current in the same condition. The influence of the thickness of SiO2 and La2O3 on the tunneling current is given to compare much different thickness of SiO2 and La2O3 tunneling current on the same equivalent oxide thickness (EOT) condition.