Characterization of atomic layer deposition using X-ray reflectometry

This work addresses current limitations of X-ray reflectometry (XRR) for modeling thin films and provides a basis for their improvement. Better accuracy in the characterization of novel thin film structures requires better model selection techniques and better knowledge of the theoretical limitations of current XRR analysis techniques. We use hafnium dioxide (HfO2) nanoscale (approximate to 1 nm) thin films deposited by atomic layer deposition (ALD) to study the limitations of current techniques. These structures are of strategic importance as CMOS gate and barrier materials. We show that XRR modeling-for our measured data range and counting statistics-will fail for thicknesses less than 1 nm. We also show that a two-layer model (HfO2/SiOxHfy/Si substrate) is more plausible than a one-layer model (HfO2/Si substrate) for the measured data.