26 July 1999 Off-axis illumination for improving depth of focus for isolated features
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Off-axis illumination is an optical enhancement method that has been widely used and discussed. The basic idea has been that for dense features, two diffracted orders 0th and 1st, symmetrically located about the optical axis of the projection optics, interfere so that the phase difference between them is minimized producing enhanced depth of focus (DOF). As discrete orders to not exist for isolated features, little if any improvement is seen in DOF. However it will be shown that for isolated features that are print biased, off-axis illumination can provide significant improvement in DOF over conventional illumination techniques and consequently improved CD control. The results from both aerial image and resist simulations will be compared for a 157 nm, .7 NA system. It will be shown that the nonlinear properties of the resist, reduces the DOF.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
James G. Tsacoyeanes, James G. Tsacoyeanes, } "Off-axis illumination for improving depth of focus for isolated features", Proc. SPIE 3679, Optical Microlithography XII, (26 July 1999); doi: 10.1117/12.354392; https://doi.org/10.1117/12.354392


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