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In lithographic scanner, many different physical factors could impact to image quality and CD uniformity. In optical systems, the pupil filling quality (source shape), wavefront error and stray light can decrease the intensity contrast and shrink the process window. In mechanical domain, the vibration and scanning synchronization error have the similar effect to imaging process. Imaging in scanner is a dynamic exposure process and in this process, aerial image should keep the same relative position to the wafer. It requests the lithographic tool must have a very stable mechanical frame and very good motion control performance. In addition, the wafer stage, reticle stage's coordinate and projection lens' grid should be matched exactly, include the scanning direction and velocity ratio. The tool's alignment system can calibrate the statistic coordinate for overlay, but it cannot calibrate the dynamic coordinate in scanning direction very well because projection lens' grid has a small asymmetric signiture. This systematic error should be calibrated for CDU improvement. An imaging model considering the motion blurring is represented in this paper and based on this model, the dynamic coordinate's error could be analyzed. Furthermore, exposure method can be used to calibrate the dynamic coordinate and improve the CD uniformity. Exposure latitude will be used to check and calibrate the lithographic tool's dynamic coordinate. We designed a special calibration process to obtain the best dynamic coordinate setting for scanner. In this process, some tool's coordinate parameters (scanning skew and scale) have been changed for every field to obtain the multi-dimensions' exposure information. Exposure window can be represented from this result, and in this exposure window, the best dynamic coordinate setting could be found. After the dynamic coordinate calibrated, the CDU is improved.

A new company in the lithography world, SMEE has developed and produced a prototype wafer exposure tool, with an ArF laser light source. This tool, SMEE SSA600/10, adopted step and scan technology to obtain a large exposure filed and to average optical aberrations for a scanned image to improve CD uniformity and reduce distortion. The maximum numerical aperture is 0.75 and the maximum coherence factor of illumination system is 0.88. The illuminator provides continuously variable conventional and off-axis illumination modes to improve resolution. In this paper, the configuration of the exposure tool is presented and design concepts of the scanner are introduced. We show actual test data such as synchronization accuracy, focus and leveling repeatability, dynamic imaging performance (resolution, depth of focus) and overlay.

A prototype of ArF scanning exposure tool using a projection lens has been developed by SMEE. As the first lithography tool, the maximum numerical aperture is 0.75 and the maximum coherence factor of illumination system is 0.88 for the maximum numerical aperture. The illuminator provides continuously variable conventional and off-axis illumination mode to improve the resolution. The design concepts of synchronous scanning are researched. The configurations and actual data of the system will be shown and discussed.