Automated Tool for Measuring Nanotopography of 300 mm Wafers at early Stages of Wafer Production

Abstract

Leading edge lithography processes require silicon wafers of nearly perfect flatness. In order to improve wafer manufacturing processes as well as the wafer quality, already early manufacturing processes like grinding and lapping have to be monitored. Assessment of nanotopography (NT) is an established approach to analyze surface features in a spatial wavelength range of 0.2 to 20 mm on silicon wafers end of line. This paper presents a fully automated measurement tool to measure NT on wafers with low reflectivity and wafer sizes up to 300 mm, based on the FRT MicroProf® MFE series. The system features a newly developed white-light interferometry sensor with a field of view of approximately 85 x 85 mm2. 16 single measurements are stitched to cover the entire surface of a 300 mm wafer. An NT analysis optimized stitching algorithm was developed in order to combine the individual images to a complete wafer map. The stitched map of the non-polished wafer is subsequently high-pass filtered and analyzed to quantify NT. Measurement system analysis studies provided repeatability values below 1 nm at a throughput of > 20 wafer/h.