| Popis: |
Since island patterns are subject to optical proximity effect, it is not easy to maintain island patterns as good image as same sized periodic lines with a conventional lithographic method such as a chrome transmission mask and on-axis illumination. Five different approaches, including a conventional mask with a conventional illumination, an alternating PSM, a half-tone PSM, a quadruple illumination, and a quadruple illumination with a half-tone PSM, were evaluated to compare pattern fidelity, meaning overlay tolerance, as well as process latitude. Conventional critical dimension (CD) measurement proved not to be a proper method as the criteria of the pattern fidelity. It is found that measurement of the shortest length of the island pattern, regardless of measurement orientation, is more meaningful. Under the condition that the dot size should be as small as possible without generating of any bridging between dots, the alternating PSM showed the widest process latitude. None of the methods except for the alternating PSM showed better result than the conventional method. From this study it is found that only the alternating PSM can substitute the conventional technique. |
