VUV spectroscopic ellipsometry applied to the characterization of high-k dielectrics

In this study, we use vacuum UV spectroscopic ellipsometry (VUVSE) to characterize new high dielectric materials. All the candidates for high-k dielectrics become strongly absorbent when the wavelength is reduced down to 140 nm. Due to the high dispersion of the refractive index in the VUV range, it is easier to determine the thickness and the refractive index independently than in the visible range and much more precise structural information can be deduced. HfO2, Al2O3 and mixed HfAlOx layers have been studied with and without thin SiO2 oxide at the interface. X-ray reflectometry (XRR) has been used to measure precisely the layer thickness and roughness. The two techniques are included in the same automated metrology system dedicated to 300 mm technology which is also presented. We show in particular that VUVSE can detect the crystalline character of the layers and their composition can be measured in addition to the layer thickness. Results are compared to those obtained by transmission electron microscopy (TEM), X-ray fluorescence analysis (XRF) and X-ray photoemission (XPS).