The shrinking depth of focus (100-150 nm) of high numerical aperture immersion microlithography optics dictates a tight wafer flatness budget. Wafer flatness nanotopography (NT), and edge roll off (ERO) are critical parts of the equation in immersion microlithographic technology at the 45 nm node and beyond. Wafer features at the nanometer level could result not only in focus variation of the litho process, or thin film thickness variation in CMP process, but
also in structural defects of the devices. Therefore, the metrology to measure nanometer level features and to control the quality of wafer geometry is a key to the success of IC production at the 45 nm node and beyond.