Electrical and material characteristics of hafnium-based multi-metal high-k gate dielectrics for future scaled CMOS technology: Physics, reliability, and process development

For the last four decades, the scaling down of physical thickness of SiO2 gate dielectrics has improved the speed of output drive current by shrinking of transistor area in front-end-process of integrated circuits. The studies in this field have been focusing on adaptable high-k materials to Si substrate with conventional CMOS process, such as Hf, Zr, or La based binary metal oxide and their silicates. Among them, the hafnium oxide (HfO 2) has received a great deal of attention, and seems to be the most promising high-k dielectric so far. The HfO2 has know to have a dielectric constant (22 ∼ 25), a relatively large energy bandgap (∼ 5.7 eV) with sufficient band offsets with silicon DeltaEc ∼ 1.5 eV and DeltaEv ∼ 3.1 eV), and a good thermally stability in contact with silicon and metal gates. Although a significant amount of experimental work to understand the basic characteristics of HfO2 has been conducted, there are still much remaining challenges: e.g. low immunity to oxygen and boron, crystallization at high temperature, and channel mobility degradation.; In this research, the focus is primarily placed on the understanding of HfO2 high-k dielectric material in terms of device physics, reliability, and application for process development. The effect of charges in HfO2 to device characteristics and the role of its interfacial layer are studied. The charge trapping characteristics of HfO2 under external AC and DC stress, and the device lifetime with stress condition are examined. The Hf-based multi-metal gate dielectric is developed to overcome the drawbacks of HfO2. Improved material and electrical characteristics are reviewed. (Abstract shortened by UMI.)...