High speed roughness measurement on blank silicon wafers using wave front phase imaging

摘要

In this paper we introduce a new metrology technique for measuring wafer geometry on silicon wafers. Wave Front Phase Imaging (WFPI) has high lateral resolution and is sensitive enough to measure roughness on a silicon wafer by simply acquiring a single image snapshot 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 24μm though it can be pushed to less than 5μm by simply adding more pixels to the image sensor. Also, we show that the amplitude resolution limit is 0.3nm. A 2-inch wafer was measured while laying on a flat sample holder and the roughness was revealed by applying a double Gaussian high pass filter to the global topography data. The same 2-inch wafer was also placed on a simulated robotic handler arm, and we show that even if gravity was causing extra bow on the wafer, the same roughness was still being revealed at the same resolution after a high pass filter was applied to the global wafer geometry data.