A combination of a common ellipsometric thickness determination from a plane surface and volume-related information gained from a Fourier transform infrared measurement enables monitoring of thin nm-scale layers in 3-D structures. This method was established to characterize dielectric layers deposited by atomic layer deposition within a capacitor structure of a 65-nm DRAM technology. The influence of precursor flow and pulse time on the overall homogeneity and step coverage of zirconium aluminum oxide was investigated. A clear correlation to the precursor amount and the geometry of the deposition tool can be shown.