Abstract
A new wafer alignment mark is introduced which, when used in conjunction with a linear Fresnel zone plate on the mask, results in an alignment method with a wide range while retaining the high resolution implicit in the method. This new mark eliminates the need for several separate marks with different alignment ranges and/or accurate prealignment of the mask−wafer system. If a large mark is used, as is needed for the initial alignment in a step and repeat system, a unique point of alignment is determined even if the initial misalignment is as large as the mark, in this case initial misalignment as large as ±1 mm. When it is desirable to occupy less wafer area with alignment marks, the alignment signal can be attained by using a portion of this configuration with a range of ±50 μm. The optimum operating conditions which result from theoretical analysis of this alignment system are discussed, and the results of experiments using this technique are given.
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