Patent ID: 9086638
Filing Date: 2015-07-21
Classification: G03F,Y10T

Abstract:
1. A sensor for sensing contamination in an application system, the sensor comprising: a substrate with a reflective multi-layer coating; and a capping layer, wherein one or more of the thickness, material, composition or refractive index of the capping layer is adapted to cause a first reflectivity change upon initial formation of a first contamination layer of a first thickness on the capping layer when the sensor is provided in the application system, the first reflectivity change being larger than an average reflectivity change upon further formation of a contamination layer having a thickness greater than the first thickness on the capping layer, and wherein a reflectivity of the sensor as a function of a thickness of a contamination layer on the capping layer is a superposition of a decreasing reflectivity function and an oscillating reflectivity function, the capping layer being adapted so that the reflectivity change of the sensor upon initial formation of the first contamination layer on the capping layer when the sensor is provided in the application system corresponds to a falling edge of the oscillating reflectivity function.