Fabrication And Characteristics Study Of Hf-based High-k Gate Dielectrics Thin Films

With the continuous development of semiconductor technology, the feature size of MOSFET devices is scaling down rapidly. Especially when the thickness of equivalent oxide of MOSFET is down to nanometer magnitude, the electron tunneling is becoming serious enough to endanger the stability and reliability of devices. It is an urgent task now to seek novel high k dielectrics to substitute the traditional SiO2 gate dielectric in microelectronic industry. Based on the analysis of physical properties, we select Hf-based high k gate dielectric thin films as the candidate materials due to its medium dielectric constant and good chemical stability. Some important issues, such as structural stability, assessment of defects, interfacial structure and increasing the crystallization temperature of the new gate dielectrics, have been investigated in this dissertation. The main research results and originalities of the thesis are as follows.1. We designed and set up a multifunctional deposition system of direct current (DC) and radio-frequency (RF) magnetron sputtering, and developed an incorporating N technology. A series of Hf based high k gate dielectrics and Al₂O₃-HfO₂ laminate thin films were prepared successfully through these technologies which establish the materials foundation for study the important issues mentioned above.2. We found that incorporating N into HfO₂ thin films in favor of increasing the crystallization temperature of HfO₂ thin films, suppressing the interfacial layer growth, and reducing defects of the films. Using N incorporated technology, the band gap of HfO₂ thin films can also been modulated.3. HfO₂-Al₂O₃ nanolaminate films have been obtained by magnetron sputtering. It has been found that adding Al₂O₃ to HfO₂ thin films increase the crystallization temperature of HfO₂ thin films effectively. FTIR analysis shows that relatively strong Si-O bond vibration pecks have been observed between the pure HfO₂ thin films and the Si substrate after the HfO₂ thin films were annealed at 1000 oC, while adding Al₂O₃ to HfO₂ thin films at the same annealing condition, the intensity of the Si-O peaks decreased obviously. The results indicate that HfO₂-Al₂O₃ thin films suppress Si-O bond growth at the interfacial layers effectively, and increase the thermal stability of interfacial layer.4. Through the analysis of the characteristics of HfOxNy thin films deposited at different substrate temperatures, we obtained the optimal temperature range to suppress interfacial layer growth, and to decrease defects of interfacial layer between the high k gate dielectric thin films and Si substrate.These studies are valuable for selection and optimization of HfOxNy and HfO₂-Al₂O₃ thin films as gate dielectrics in the future.