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 μm 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 (δf), magnification (δM), and rotation (δθ) of a 250 μm X 250 μm field were δf ∼ ±1 μm, δM ∼ ±15 ppm and δθ ∼ ± 0.1 mrad. A straightforward path to improving these results is described.