Analysis of the reverse patterning phenomenon caused by a light source change in an attenuated phase shift mask

An attenuated phase shift mask (PSM) (half-tone PSM) is an effective and common technique for resolution enhancement and for forming specific patterns. When an ArF-attenuated PSM with hole- or space-type patterns is used under a KrF light source scanner, the original hole or space patterns are changed to island or bar patterns. In other words, reverse patterns are obtained from the original patterns. This phenomenon is explained by the transmittance change in the attenuated PSM due to the change in the light source. The wavelength of the original light source is extended when the light source is changed, and consequently, the dark field transmittance of this attenuated PSM becomes greater than the original transmittance. Thus, the final pattern becomes the inverse of the original pattern.

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► Reverse patterns are easily observed when the light source is changed for the same attenuated PSM.
► The resulting pattern becomes the inverse of the original pattern.
► The pattern reversal effect appears for the iso contact hole, the line and space dense pattern.
► The original and reverse pattern can be formed using light source changes.