Investigation Of High Dielectric Ta₂O₅ Thin Films Deposited By Reactive Sputtering

As astounding progress of ULSI being made, continual scaling of semiconductordevices to ever smaller dimensions, especially in the range of 0.10μm, it directlyresults in an increase of power consuming and a decrease in the control ability ofgate voltage, if the conventional gate dielectric materials(SiO2/SiONx) are still used.To maintain continued growth in CMOS performance beyond 100 nm, therefore, aneed for an alternative gate material with excellent dielectric properties to producelarge oxide capacitance and low leakage current has emerged. Metal-oxides areattractive candidates for gate dielectrics due to their electrical and physical propertiessuitable for high dielectric applications, such as tantalum pent-oxide (Ta2O5), whichis considered one of the promising alternative materials in the next generationDRAM devices. Thus, the fabrication and characteristic study of Ta2O5 thin filmswith high-quality has widely attracted attention in recent years. Recently, many methods have been developed for deposition of Ta2O5 dielectricthin films. In this thesis, crystalline and oriented Ta2O5 dielectric thin films werefabricated by reactive-magnetron sputtering. The influence of some processparameters deposited the thin films, such as substrate bias, relative humidity ofworking gas on the structure and dielectric properties of the films was investigated.Besides, correlative discussion on the mechanism of the crystallinity and orientationof the thin films was also done. The main research progresses of this thesis are shown as follow:1. By introducing some water into the working gas in order to change the relative humidity, crystalline Ta2O5/Si thin films were obtained at the low substrate temperature of 500oC and primarily analyzed the effect of water on the crystallinity of the thin films. This method applied to deposite the thin film has yet not reported.2. Crystalline Ta2O5 thin films have been successfully fabricated at low substrate III北京工业大学工学博士学位论文 temperature, by applying a bias to Si substrates. At 620oC, it was found that the thin films as-prepared are amorphous without the bias and of high crystallinity with the bias over –100V. Furthermore, when the bias was increased to –200V, partially crystallized films could be attained at temperatures even as low as 400oC, which is the lowest temperature of deposited Ta2O5 dielectric thin films, as we known.3. Oriented Ta2O5/Si thin films as-deposited with high <001>orientation have been obtained under the optimal process parameters. Usually, oriented Ta2O5 films with exceptionally high dielectric constant were fabricated by post-annealing at high temperature. In this thesis, as-deposited Ta2O5 thin films with orientation were sputtered at 620oC under the suitable substrate bias assistance. The orientation of the films is modified to be better with the bias being increased. The bias effect on the orientation of the films is discussed in details.4. The interfacial layer between crystalline Ta2O5 thin films and Si substrate were experimentally and theoretically investigated, based on RBS results. We find that, under the negative bias, the diffusion of tantalum is rapid, that of oxygen is restrained. So, the Ta/O ratio in the interfacial layer is higher than that in the thin films. The formation mechanism of the bias effect on the interfacial layer is also analyzed.5. The influence of process parameters deposited the thin films, such as substrate bias, on the optical and dielectric properties was characterized. We found that, as the substrate bias increasing, the dielectric constant is enhanced, especially, at the substrate bias of -200 V,the thin films with relative dielectric constant of 34 and leakage density of 10-7A/cm2 at 800kV/cm had been obtained. This is owing to the improvement of the crystallinity and preferential ori...