High Speed Wafer Geometry on Silicon Wafers Using Wave Front Phase Imaging for Inline Metrology

In this paper we introduce a new metrology technique for measuring wafer geometry on silicon wafers. Wafer geometry will be critical for the next generation integrated circuits (IC) for improvements in lithography overlay and to measure Nanotopography (NT) and roughness in conjunction with Chemical Mechanical Polishing (CMP). Wave Front Phase Imaging (WFPI) has high lateral resolution and is sensitive enough to measure NT and 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. First, 3 mirrors simulating a 50mm blank wafer with a known geometry was used to compare WFPI to the industry standard chromatic confocal microscopy. Then, a 2-inch wafer was measured while laying it on a flat sample holder without chucking it and NT and roughness was revealed by applying a double Gaussian high pass filter to the global topography data. The exposure time was 0.1 seconds and the time to analyze the data was just under 2 seconds while processing 4.34 million topography data points.