Description:
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Optimization for various phase-shifting masks to fabricate 0.25-µm isolated resist patterns was carried out, and their performances were compared among themselves by simulation. They were evaluated under the assumptions that isolated patterns were located on the same layer with 0.25-µm lines and spaces with the Levenson-type phase-shifters and that the exposure dose was adjusted to the dense patterns. It was found that isolated patterns need to be designed with regard to unavoidable errors in the feature size. None of the isolated line masks studied is effective in improving resolution, except in the case where the Levenson-type phase shifter (shifter edge) can be located. All isolated space masks with optimized dimensions, in contrast, are effective in improving depth of focus for the 0.25-µm isolated pattern.
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