Marks for SCALPEL® tool optics optimization

A method for optimizing the electron optics of the SCALPEL exposure tool is described. The method uses the SCALPEL mark detection method with a grating mark as an aerial image monitor. The root-mean-square deviation of the recorded backscattered electron signal from an ideal triangle waveform was used as a measure of the image fidelity, scale and orientation. The resolution of the technique is limited only by signal-to-noise and the fidelity of the marks. Experiments were performed using 2 @mm period grating marks that were fabricated in a SiO"2/WSi"2 structure using SCALPEL lithography and plasma processing. The projector lenses and magnification/rotation coils were optimized. For these experiments the measured resolutions for determining focus (@df), magnification (@dM), and rotation (@d@q) of a 250 @mm X 250 @mm field were @df ~ +/-1 @mm, @dM ~ +/-15 ppm and @d@q ~ +/- 0.1 mrad. A straightforward path to improving these results is described.