Wave Front Phase Imaging of Wafer Geometry Using High Pass Filtering for Improved Resolution

In this paper we show that Wave Front Phase Imaging (WFPI) has good enough lateral resolution and is sensitive enough to measure roughness on a silicon wafer by simply acquiring a simple image of the entire wafer. WFPI is achieved by measuring the reflected light intensity from monochromatic uncoherent light at two different planes along the optical path with the same field of view. We show that the lateral resolution in the current system is $24 \mu\mathrm{m}$ but can be pushed to less than $5 \mu\mathrm{m}$ by simply adding more pixels to the image sensor, and that the amplitude resolution limit is 0.3nm. Three 2-inch wafers were measured, and the roughness was revealed by applying a double Gaussian high pass filter to the global topography data.