Detection of contamination in euv systems

Abstract

A sensor for sensing contamination in an application system is disclosed. In one aspect, the sensor comprises a capping layer. The sensor is adapted to cause a first reflectivity change upon initial formation of a first contamination layer on the capping layer when the sensor is provided in the system. The first reflectivity change is larger than an average reflectivity change upon formation of a thicker contamination layer on the capping layer and larger than an average reflectivity change upon formation of an equal contamination on the actual mirrors of the optics of the system.

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 a top layer of the reflective multi-layer coating and/or the capping layer is adapted to cause a first reflectivity change upon initial formation of a first contamination layer on the top layer of the reflective multi-layer coating and/or the capping layer when the sensor is provided in the application system, the first reflectivity change being larger than an average reflectivity change upon formation of a thicker contamination layer on the capping layer.   
     
     
         2 . The sensor according to  claim 1 , wherein a reflectivity of the sensor as 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 a first contamination layer on the capping layer when the sensor is in the application system corresponds to a falling edge of the oscillating reflectivity function. 
     
     
         3 . The sensor according to  claim 1 , wherein the reflectivity change upon initial contamination of the capping layer is at least about 0.5% reflectivity reduction per nanometer contamination layer thickness, preferably at least about 1% reflectivity reduction per nanometer contamination layer thickness, and more preferably at least about 2% reflectivity reduction per nanometer contamination layer thickness. 
     
     
         4 . The sensor according to  claim 1 , wherein the capping layer comprises a substantially non-oxidizing material. 
     
     
         5 . The sensor according to  claim 1 , wherein the capping layer comprises at least one of the following: silicon, ruthenium, titanium dioxide, rhodium, palladium, iridium, platinum, gold, silicon carbide, carbon, boron nitride, silicon nitride, and titanium nitride. 
     
     
         6 . The sensor according to  claim 1 , wherein the capping layer is the top layer of the reflective multi-layer coating. 
     
     
         7 . The sensor according to  claim 1 , the sensor comprising a sub-layer between the capping layer and the reflective substrate, wherein adaptation of the sensor comprises adaptation of the sub-layer. 
     
     
         8 . The sensor according to  claim 7 , wherein the adaptation of the sub-layer comprises an adaptation of one or more of the thickness, material, composition, or refractive index of the sub-layer. 
     
     
         9 . A detection system for detecting contamination in an application system, the detection system comprising:
 a sensor adapted for receiving an irradiation beam from an irradiation source and adapted for reflecting a modified irradiation beam to a radiation detector, 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 a top layer of the reflective multi-layer coating and/or the capping layer is adapted to cause a first reflectivity change upon initial formation of a first contamination layer on the top layer of the reflective multi-layer coating and/or the capping layer when the sensor is provided in the application system, the first reflectivity change being larger than an average reflectivity change upon formation of a thicker contamination layer on the capping layer, 
   and   a processing system for deriving a contamination level as a function of a detected reflectivity of the sensor.   
     
     
         10 . The detection system according to  claim 9 , wherein the processing system for deriving a contamination level is adapted for taking into account a correlation between the change in reflectivity and the thickness of the contamination layer formed on the sensor. 
     
     
         11 . The detection system according to  claim 9 , wherein the processing system is adapted for taking into account a calibration measurement providing information regarding the initial reflectivity of the reflective substrate. 
     
     
         12 . The detection system according to  claim 9 , the detection system further comprising a feedback providing system for providing feedback regarding the contamination to the application system. 
     
     
         13 . The detection system according to  claim 9 , the detection system further comprising a contamination removal system for removing the contamination from the capping layer. 
     
     
         14 . An extreme ultraviolet lithographic system comprising:
 a plurality of mirrors, at least one of the mirrors comprising a reflective substrate and a capping layer provided on the reflective substrate, wherein the capping layer of the at least one mirror is adapted so as to cause a mirror reflectivity change upon initial formation of a first contamination layer on the capping layer of the at least one mirror; and   a 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 a top layer of the reflective multi-layer coating and/or the capping layer is adapted to cause a first reflectivity change upon initial formation of a first contamination layer on the top layer of the reflective multi-layer coating and/or the capping layer, the first reflectivity change being larger than an average reflectivity change upon formation of a thicker contamination layer on the capping layer,   wherein the mirror reflectivity change is substantially smaller than the first reflectivity change for the sensor.   
     
     
         15 . An application system according to  claim 14 , further comprising:
 a processing system for deriving a contamination level as a function of a detected reflectivity of the sensor; and   a feedback providing system for providing feedback regarding the contamination to the lithographic system and controlling an irradiation source of the lithographic system.   
     
     
         16 . A method of sensing contamination in an application system, the method comprising:
 providing a sensor comprising a capping layer, and   sensing a first reflectivity change of the sensor upon initial formation of a first contamination layer on the capping layer when the sensor is provided in an application system, the first reflectivity change being larger than an average reflectivity change upon formation of a thicker contamination layer on the capping layer.   
     
     
         17 . The method according to  claim 16 , the method further comprising determining a contamination quantity based on the sensed first reflectivity change. 
     
     
         18 . The method according to  claim 17 , the method further comprising controlling the application system based on the determined contamination quantity. 
     
     
         19 . A method of manufacturing a sensor for sensing contamination in an application system, the method comprising
 obtaining a substrate; and   providing a capping layer on the substrate thus forming a sensor, the sensor being adapted to cause a first reflectivity change upon initial formation of a first contamination layer on the capping layer when the sensor is provided in the system, the first reflectivity change being larger than an average reflectivity change upon formation of a thicker contamination layer on the capping layer.