3. Hafnium-Based Gate Dielectric Materials

In this chapter, we focus on hafnium-based gate dielectrics. HfO₂ is regarded as the most promising material for the high–k gate dielectrics owing to its large dielectric constant and large band-gap energy. In the first part of this chapter, these characteristics are addressed in a comparison with SiO₂ and other high-k materials. Thermal stability is a major issue for the application of high-k materials to MOSFETs in LSIs. Although HfO₂ satisfies this requirement, severer process conditions may cause problems even with this material. Suppression of these issues is also addressed in the second part of this chapter. In order to enhance the characteristics of HfO₂, transformation of the monoclinic phase to the tetragonal and the cubic phases with larger dielectric constant has been pursued recently. We mention the issue in the last part of this chapter.