| CPC H01J 37/3177 (2013.01) [G03F 9/7003 (2013.01); H01J 37/09 (2013.01); H01J 37/153 (2013.01); H01J 37/20 (2013.01); H01J 37/28 (2013.01); H01J 2237/24592 (2013.01); H01J 2237/2817 (2013.01)] | 20 Claims |

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1. A substrate stack comprising a plurality of substrates, wherein:
each substrate in the substrate stack comprises at least one alignment opening set;
the at least one alignment opening set in each substrate is aligned for a light beam to pass through corresponding alignment openings in each substrate; and
each substrate comprises at least one alignment opening that has a smaller diameter than the corresponding alignment openings in the other substrates.
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