We present a mathematical model to describe the spatial phase of gratings produced by interferometric lithography, as well as a set of experiments to verify the model’s validity and to measure any distortions introduced when the lithography is performed. The implementation of two methods to measure the phase progression of these gratings is described. We find the results obtained from an initial set of experiments to be in good agreement with the theoretical model, i.e., the absence of significant distortions, such as coherent phase noise, is confirmed. These results arealso applicable to the metrology of grids.