Determination of flatness on patterned wafer surfaces using wavefront sensing methods

New lithography technologies, as for example Extreme Ultra Violet (EUV), require high flatness on the exposure surfaces as the depth of focus is impacted. It is essential for semiconductor manufacturing to measure and control flatness of wafer surfaces at nanometer scale. In-plane geometrical defects on wafer surfaces following Chemical Mechanical Planarization (CMP) processing in the lateral millimeter range and in vertical dimensions in the nanometer range are of increasing importance. They will become a severe yield limiting factor in the 32 nm generations and below. This paper shows the result from improvement and optimization of metrology using wavefront sensing methods according to Makyoh and Shack Hartmann. Magnification and increased density of measurement points were identified to improve the existing performance with respect to vertical resolution significantly below 100 nm. The achieved lateral resolution on the wafer surface was 750 μm. The accuracy of the measurement on patterned wafer surfaces was determined to be less than 15 nm. The accuracy was determined by repeating the topography measurement and filtering of the according data of the sensors using cross section analysis and spatial processing with double Gaussian filters. The samples were taken from different manufacturing steps, such as Shallow Trench Isolation (STI) and interconnect metallization. Wavefront sensing based on methods according to Makyoh and Shack Hartmann enabled instantaneous and non-destructive flatness measurement of surfaces.