Characterization of sub-nm AlOx and LaOx capping layers on high-k gate stack film systems using VuV (λ=120 nm) reflectivity

This paper details the use of vacuum ultraviolet (120 nm <; λ <; 800 nm) spectroscopic reflectivity to simultaneously measure AlO_x and LaO_x capping layers and the underlying high-k film stack system. It is demonstrated that the sensitivity of the method originates in the VuV portion of the spectra where absorption of these materials contributes significantly to the overall optical response. As a result, the reflectivity in the VuV region accurately resolves sub-nm changes in these capping layer thicknesses, while data in the Vis-uV (190 <; λ <; 800 nm) wavelengths show negligible differences. The extracted physical thicknesses are shown to trend consistently with the EOT and V_fb data from identically prepared MOSCAP samples, thus highlighting this method as a suitable candidate for in-line metrology of sub-nm capping layers on high-k film stacks.