Methodologies and an apparatus for enabling three-dimensional scatterometry to be used to measure a thickness of dielectric layers in semiconductor devices are provided. Embodiments include initiating optical critical dimension (OCD) scatterometry on a three-dimensional test structure formed on a wafer, the three-dimensional test structure comprising patterned copper (Cu) trenches with an ultra-low k (ULK) dielectric film formed over the patterned Cu trenches; and obtaining, by a processor, a thickness of the ULK dielectric film based on results of the OCD scatterometry.