James Guerrero

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As CMOS technology pushes feature dimensions beyond the sub-wavelength threshold, the effect of lens aberrations in the imaging system becomes more relevant. Therefore, it becomes important that the optical engineer completely understands the effects lens aberrations have on aerial image and resist profile. It is also important to have a tool and a process that can accurately describe and measure the aberrations in the exposure system. With full characterization of the lens systems and through use of a lithographic simulator, it becomes possible to predict the imaging effects and ultimately critical dimensions and pattern placement. In any exposure system there exists a unique set of aberrations, which will have an effect on the aerial image. These aberrations can cause focus shifts dependant on pattern orientation, asymmetric imaging, degradation of image contrast, edge slope, pattern fidelity, resolution, and additional imaging artifacts. This paper looks at the use of a phase shifting ring structure of it radians phase shift and a lithographic simulator (PROLITH) for examination of lens aberrations in terms of Zernike coefficients Z5 through Z11(astigmatism — trifoil), Strehl ratio and wavefront OPD for a 365nm exposure system.

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