Recently, 64MDRAM and 256MDRAM whose feature sizes are smaller than 0.4μm and required patterning area is wider, require finer geometry and larger patterning area especially considering 4x exposure tools.
In order to lighten both lithography and mask process burdens, new design techniques are considered for new DRAM generations such as COB (capacitor on bit line), IDB(inter-digit bit line) and SWD(split word line driver).
Especially with the improvement of lithography technology using techniques such as phase shift mask and off axis illumination, optical proximity effect is unavoidable by nature. In order to correct this proximity effect, square cornered fine patterns well below the resolution limit of exposure tool are desirable.
In this review, detailed discussion of new technology will not be discussed but related mask making requirement will be discussed instead.