| 摘要 |
An alignment accuracy (AA) mark is described, including N (N>=3) pattern sets defined by N exposure steps respectively. The N exposure steps are performed also to a device area disposed on a wafer together with the AA mark. The i-th (i=1, 2 . . . N-1) pattern set surrounds the (i+1)-th pattern set. Each pattern set includes a 1st set of x-directional linear patterns, a 2nd set of x-directional linear patterns arranged opposite to the 1st set of x-directional linear patterns in the y-direction, a 1st set of y-directional linear patterns, and a 2nd set of y-directional linear patterns arranged opposite to the 1st set of y-directional linear patterns in the x-direction, wherein each set of x- or y-directional linear patterns include at least three separate parallel linear patterns.
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