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The controlled addition of La to HfxSi1−xO2/SiO2/Si dielectric stacks has been shown to enable the engineering of the work function to appropriate levels when TaN or TiN is employed as the capping metal gate. Work function tuning has been suggested to be controlled by La diffusion into the Hf-based dielectric as a result of further thermal treatments. In this paper, we performed high resolution angle resolved x-ray photoelectron spectroscopy (ARXPS) studies to investigate the chemical depth profile distribution of TaN/La2O3/HfO2/SiO2/Si dielectric stacks exposed to a nitridation treatment by NH3 at 700 °C. The stoichiometry and distribution of the HfO2 and SiO2 layers was examined using a self-consistent ARXPS analysis. This study shows that La diffuses to the SiO2/HfO2 interface, and that subsequent rapid thermal annealing at 1000 °C for 5 s does not significantly change the La distribution.