Preventing sidelobe printing in applying attenuated phase-shift reticles

One major limitation of applying attenuated phase shift mask (PSM) is sidelobe printing. The sidelobe is caused by constructive interference of the first order of diffraction maximum from nearby features, plus the electrical fields from semi-transparent materials in the surrounding area. The impact of defocus, lens aberration, and layout design on sidelobe printing are discussed. A detailed comparison between printed wafers and aerial image simulations shows how these factors affect sidelobe printing. Data show tight control on both the third and the fifth order aberrations is critical in PSM application. Since the degree of coherence and the stepper's response to coherence transfer function will significantly affect the performance of PSM, tests on phase shift mask are necessary to qualify a stepper. An alternative approach that uses attenuated rim shifter PSM to prevent sidelobe printing is presented and discussed.