| 摘要 |
For a 2-dimensional periodic array of contact holes or islands, a depth-of-focus-enhancement lithographic scheme based on a combination of alternating phase-shifting mask and off-axis illumination is revealed. The scheme is achieved by choosing appropriate off-axis illumination and smaller numerical aperture such that only two diffraction orders, which are of equal distance from the pupil center, are collected in the first exposure. The image of the 2-dimensional periodic array can be formed by superposing a second exposure on the first. In the second exposure, another appropriate off-axis illumination and smaller numerical aperture is chosen such that another two diffraction orders, which are also of equal distance from the pupil center, are collected.
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