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A new line of optical wafer steppers is discussed. These tools, which have been developed in conjunction with Sematech and its member companies, feature new high-numerical aperture, widefield reduction lenses for operation at either i-line (365nm) or deep-UV (248nm) wavelengths. The i-line tool achieves practical resolution at the 0.5Oitm level with usable working focal depth, while the deep-UV tool is capable ofpractical resolution at the 0.35im level with usable working focal depth. The design of these tools incorporates and expands upon optical wafer stepper technologies which have been fieldproven, particularly in the areas of alignment, focusing, INSITtJ" metrology, automatic calibration, and diagnostic utilities. New features added to these tools, to support their application at or below 0.50j.tm, include a new system structure designed for inherent stability to maintain tight coupling among the imaging and alignment subsystems, and wafer stage advancements to achieve increased positioning accuracy, which supports obtaining overall tool overlay accuracy commensurate with sub-half-micron resolution. Of particular significance is the incorporation of a field-by-field leveling system, which optimizes the usable depth of focus over large image fields on product wafers. The tools also include an entirely new control system, which has been designed based on a new hierarchical control architecture, and incorporates digital servo controls and automated diagnostics. The control interface is designed as an intuitive graphical touch screen display, providing simplicity to the operator and significant job process flexibility, compatible with advanced memory and Application Specific Integrated Circuits (ASIC) fab operations. Design considerations for these tools are described together with performance results obtained in the field.
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