Quadriwave Lateral Shearing Phase Imaging Of Euv Masks

We present a phase imaging technique for measuring the phase of EUV masks. In this technique we use a Quadriwave Zone Plate (QZP) to superpose four laterally separated copies of the complex amplitude function in the image plane, causing them to interfere onto a detector. By changing the scanning angle, we can control the relative phase between these images, which allows us to extract two orthogonal derivative phases directly, and then subsequently reconstruct the phase of the EUV mask. If the region of interest contains a reference region such as a clear field, the phase can be extracted from the derivative phases directly. Simulations and an experiment are performed to demonstrate the method accuracy.