Abstract: Optical lithography, when extended by phase shift mask technology and modified illumination techniques, is a promising technology for sub-half-micron devices. Modified illumination can improve the resolution limit and depth of focus, but the imaging profile is changed, with pattern type, direction, and density having an effect on the result. The uniformity of the illumination system also differs according to aperture type. Because lens distortion may be affected by the aerial image and structure of illumination optics, we can expect that a modified illumination system may affect lens distortion and overlay accuracy in a real process. A comparison of changes in overlay and lens distortion was done for different illumination conditions. Focus was varied for each combination. As a result, we can observe the variation of overlay error in a modified illumination system relative to the conventional system. To use modified illumination in sub-half-micron processes distortion error must be reduced. !0
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