X-ray reflectometry (XRR) has been used in R and D for many years to provide thickness, density and interface roughness measurements of thin films and thin film stacks, independent of other material properties. However, because obtaining data with conventional XRR is very time consuming, it has not until recently been viewed as a practical tool for semiconductor material and process development. In this study, a new rapid x- ray reflectometry (RXRR) technique, capable of obtaining thin film structural data from blanket or patterned wafers in seconds, was used to optimize process development of various materials used for Cu Damascene processing. CU seed and Ta/Tan barrier films were measure din as-deposited film stacks, and the result used to optimize deposition rate and cross-wafer deposition uniformity for various PVD processes. Correlation with Rutherford backs-scattering (RBS) measurements demonstrated that the RXRR measurements provided accurate thickness measurements independently for both the Cu seed and underlying Ta/Tan films. Next, thickness and density measurements were obtained for reactively sputtered TaN and TiN films, and then correlated to the CMP properties of the films., Thickness measurements were used to calibrate the CMP rate for each film, while density differences were correlated to the reactive PVD process conditions, including gas flow rate and wafer temperature. Finally, the densities of various low-k dielectric materials were measured and used to estimate percentage residual porosity, which can be used to predict k value for the film.