CONTRAST TRANSFER-FUNCTION MEASUREMENTS OF DEEP ULTRAVIOLET STEPPERS

The aerial image contrast is a key parameter for the evaluation of the performance of optical projection systems. State-of-the-art deep ultraviolet steppers and some i-line steppers were investigated for comparison by measuring the contrast transfer function, i.e., contrast versus linewidth. Examples are shown how specific weaknesses of an imaging system like astigmatism and sensitivity from internal reflections can be quantified with this technique. For comparison the contrast transfer functions were also calculated, assuming ideal, purely diffraction limited image transfer of the optics, and with the numerical aperture and partial coherence as parameters. Interestingly none of the steppers meet the imaging performance which can be expected from theory.