| 摘要 |
A level sensor for a lithographic projection apparatus, the level sensor comprising a light source, a first reflector, a second reflector and a detector, the first reflector being positioned to direct light from the light source towards a wafer surface, and the second reflector being positioned to direct light reflected from the wafer surface to the detector, wherein the first and second reflectors are selected to incur a minimal process dependent apparent surface depression.
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