The use of insulating materials bearing higher dielectric constant than that of silicon oxide in CMOS devices is compulsory for all technology nodes requiring gate dielectric with EOT smaller than 1 nm. Two of potential candidates are LaAlO₃ and HfAlO. Investigation of film and high-k/Si interlayer composition by several non-destructive optical methods is a possible way to control the integrity of the performed structure during the fabrication process. We discuss here the morphology and composition of LaAlO₃ and HfAlO thin films accessed by X-ray reflectometry (XRR), spectroscopic ellipsometry (SE), and X-ray photoelectron spectroscopy (XPS). LaAlO₃ and HfAlO gate dielectrics were sputtered from ceramic target and deposited on HF last clean or thermally nitrided Si. Experimental XRR profile and its associated Fast Fourier Transform were used to extract absolute thicknesses, densities and interfacial roughnesses of thin films. Absolute thicknesses given by XRR were used in SE measurements to determine optical constants and composition of the films. XPS complemental analysis was performed to analyze the chemical bondings in thin films, in particular at the high-k/substrate interface.

A three-layer model was found both in XRR and SE analysis to be the best optical model for as-deposited and annealed films. It was composed of an interfacial layer, covered by a layer of pure LaAlO₃ or HfAlO, and a surface-roughness layer. XRR analysis showed that the dielectric/Si interface of the HfAlO/SiON/Si structure had a significantly smaller roughness than those of HfAlO/Si. SE studies revealed that in the case of LaAlO₃ and HfAlO deposited on Si, the interfacial layer is a mixture of high-k material and amorphous-Si inclusions. The SiON-like interface did not change significantly after thermal annealing in O₂. XPS also pointed out the superior diffusion barrier properties brought by SiON/Si substrates before LaAlO₃, and to a greater extent, HfAlO deposition.

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