Radiation detector assembly, lithographic apparatus, method of determining an amount of radiation, an intensity of the amount of radiation, or an amount of contamination of an optical element, device manufacturing method, and device manufactured thereby

摘要

A radiation detector assembly includes an optical element including a substrate and a partially reflective optical layer. The optical element is configured to receive an amount of radiation when the assembly is in use and reflect a first portion of the amount of radiation and transmit a second portion of the amount of radiation through the optical layer and the substrate. A radiation detector is configured to receive the second portion of the amount of radiation and provide a measurement signal. A measurement system is configured to receive the measurement signal from the radiation detector and derive from the measurement signal the amount of radiation, an intensity of the amount of radiation, or an amount of contamination of the optical layer.