OVERLAY REPEATABILITY IN MIX-AND-MATCH EXPOSURE USING THE SR STEPPER - SS-1

Proximity X-ray lithography using synchrotron orbital radiation (SR) is potentially able to replicate patterns with a width of less than 0.2 mu m. We developed a die-by-die alignment basis SR stepper, which is equipped with air-lubricated lead screws for the XY stage and an optical heterodyne alignment system. An overlay repeatability of 23 nm (3 sigma) is obtained with only X and Y alignment when evaluated by the double exposure method. In practice, the mix-and-match scheme between the SR and optical exposures is important for reducing the cost of lithography. In the mix-and-match exposure between the SR and optical steppers, an overlay repeatability of 45 nm (3 sigma) is achieved with the X, Y, and theta alignment mode of the SR stepper. Analysis of the error factors in this overlay exposure experiment showed that the optically printed patterns have chip shape distortions causing overlay error of about 35 nm (3 sigma).