Roughness and nanotopography measurement of a Silicon Wafer using Wave Front Phase Imaging : High speed single image snapshot of entire wafer producing sub nm topography data

Abstract

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 optical 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, or Z-height resolution limit, is 0. 3nm. A 2-inch wafer was measured while resting flat on a sample holder and the nanotopography and roughness was revealed by applying a Butterworth high pass filter to the global topography data using a spatial cutoff frequency of 440μm. The same 2-inch wafer was also placed on a simulated robotic wafer handler arm, and we show that even if gravity was causing extra bow on the wafer, the same roughness and nanotopography was still being revealed at the same resolution after the same high pass filter was applied to the global wafer geometry data.