Physical Characteristics of HfO2 Dielectrics at the Physical Scaling Limit

Phase identification and the degree of crystallization in ultra-thin HfO₂ has been extremely challenging due to the > 5 nm range order sensitivity of X-ray diffraction which is not sufficient to detect nanocrystallization. Yet detailed knowledge of the nanostructure is critical to the development of accurate performance models. Therefore, atomic layer deposited (ALD) and annealed HfO₂ films have been studied by extended X-ray absorption fine-structure (EXAFS) and glancing angle X-ray diffraction (GIXRD). EXAFS is sensitive to local structural distortions on a length scale of a few Angstroms, making it a highly desirable probe for elucidating physical characteristics of ultra-scaled HfO₂. Analysis of the Fourier Transformed (FT) data provides information on the near-neighbor coordination, distance, and local disorder around the Hf atom. We report an increase in the fraction of higher-k tetragonal HfO₂ with decreasing film thickness, which is consistent with a surface energy effect and the critical grain size phenomenon.