Research On Growth And Total Dose Radiation Of La₂O₃ High-k Films

As the scaling down of integrated circuits, it has become an inevitable trend to replace Si O2 as the gate oxide with high-k materials. A variety of materials with higher dielectric constant than traditional Si O2 have been tried over years, such as Al2O3、hafnium-based materials and so on. And certain results have been acheved. But researches on La-based high-k materials which are more promising aren’t been done nearly enough. In this paper, we mainly carries on the elaboration from two aspects of dielectric material preparation and total dose radiation.In the preparation of dielectric materials, firstly we compare MBE、CVD and other material preparation methods, and choose ALD which has the best comprehensive property to deposit La2O3 material. Based on the process parameters obtained before, we find out that the most suitable temperature of La(i Pr Cp)3 precursor is 180℃.Specific researches have been made to explore the influence of La Al O3’s hierarchical structure. Keeping the deposition ratio of La: Al 3:1, and the total layers of La2O3 and Al2O3 unchanged, we only adjust the number of deposited layers and get 3:1、6:2 and 9:3 three kinds of circular structure of La Al O3 high-k gate dielectric films respectively. Then XPS spectrum analysis and electrical characteristic test are made for comparison. The results show that the 3:1 sample whose layers are most can obtain the maximum accumulation capacitance Cox 、 minimum equivalent oxide thickness(EOT) and excellent electrical characteristics. And its corresponding k value is about 11, just in between the optimal range of 10~30. But the number of its internal defects is relatively high, which will cause the hysteresis of the C-V curve. This can be improved by annealing and further research is needed to find out specific process parameters such as annealing atmosphere、temperature、time and so on.In the other aspect of total dose irradiation, the increase of dielectric constant makes the physical thickness of high k materials larger. Compared with the traditional Si O2 which only has a small amount of in situ defects, high-k gate dielectrics will produce more defects under stress and improve the charge trapping amount caused by bias. Along with the promotion of extreme ultraviolet(EUV) lithography technique, these defects willimpact on devices’ radiation characteristics. These three factors lead to more serious total dose radiation problems of high-k devices. Many specific radiation experiments have been made to explore high-k materials’ radiation characteristics and the internal defect is found to be an important factor leading to the degradation of radiation characteristics. In addition, high-k devices have different characteristic parameters such as the dielectric constant、band gap、electron affinity and gate electrodes etc. What kind of impact might they have? It needs us to do some software simulations and set the same defect density in the meantime.According to consult relevant literatures, the dielectric constant、 band gap、refractive index and other parameters of Hf O2 and La2O3 are determined. Then we add these two new high-k materials to the library of ISE TCAD software.We simulate 65 nm MOS and 69 nm SOI devices which have the same defect density as traditional Si O2 respectively by using ISE TCAD software and get their transfer characteristics in different irradiation conditions. The results show that all transfer characteristic curves shift to the negative direction with irradiation dose increasing. The greater the affinity is, the more curves shift to the right; but curves will move to the left as k value increases. Compared to traditional Si O2, the transfer characteristic curve of Hf O2 is obviously right offset, and La2O3 is relatively to its left.