Abstract
Zone plate alignment is routinely used in x‐ray exposure tools and in optical step and repeat cameras. As with any alignment technique, the time taken to acquire and analyze the alignment data must be added to the wafer exposure time. This paper describes a technique in which the data may be acquired very rapidly by scanning the focused zone plate spot over a system of slits. For step and repeat systems this may be done during the time the table is moving to the next site. We have obtained alignments of 0.1 μ (3σ) by scanning across slits. In addition, we have developed analog circuitry which extracts the centroid of the focused spot in a few microseconds. With this circuit, the precision of spot location is <1% of the spot width. The combination of these two techniques should minimize the overhead in wafer exposure arising from the alignment process.
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