| 摘要 |
Benchmark detector (46) has two light pipe fingers (48, 50) which lie adjacent to each other at an acute angle to the orthogonal axes of movement of the stage on which the benchmark is positioned. The light pipe fingers have notches which define a rectangular opening therebetween through which a benchmark (52) can be excited to produce secondary electrons. Scintillator material adjacent the notches produces photons in the light pipes so that the position of the benchmark with respect to the detector can be established.
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