Far- and mid-infrared absorption study of HfO₂/SiO ₂/Si system

This paper discusses thermal stability and bonding characteristics of HfO₂ in comparison with those of SiO₂ through the infrared absorption study with Fourier Transform Infrared (FT-IR) measurement. X-ray diffraction study was also performed to determine the macroscopic crystal structure. HfO₂: films on (100) Si wafers were prepared by rf-sputtering in Ar or reactive de-sputtering in O₂. Since the high dielectric constant dominantly originates from the bonding characteristics of HfO₂, which are closely related to the infrared active vibration modes, the infrared absorption characteristics are fundamentally important material properties of high-k dielectrics. The far-infrared region study is especially important for investigating high-k films, since high-k dielectrics are generally heavy metal oxides, and show characteristic infrared absorption peaks in the far-infrared region. The interface layer underneath the HfO ₂ film was also studied by the transmission FT-IR. In addition, by introducing a small amount of other atoms into HfO₂, the infrared absorption spectrum is dramatically changed. This fact implies that the high-k film structure is sensitive to an external perturbation. It will be an advantage as well as a disadvantage in high-k gate stack technology for advanced CMOS, and is discussed from the viewpoints of the phase separation and the phase transformation of HfO₂.