Lithographic projection apparatus, device manufacturing methods and mask for use in a device manufacturing method

Abstract

During an alignment calibration process in a lithographic apparatus using a sensor to detect a property of a projected image at substrate level, a diffuser is inserted into the illumination beam to increase the range of angles of radiation incident on the substrate. Thereby it can be ensured that sufficient radiation enters the sensor even when the is a mismatch between the illumination mode used and the acceptance NA of the sensor.

1 . A lithographic projection apparatus comprising: 
 an illumination system arranged to illuminate a patterning device with an illumination beam of radiation having a defined illumination profile;    a projection system arranged to project an image of the patterning device onto a substrate;    a sensor selectively positionable in place of said substrate and arranged to measure a property of the image projected by the projection system; and    a diffuser selectively positionable in the path of said illumination beam and arranged to increase the range of angles at which radiation of the illumination beam is incident on the patterning device.    
   
   
       2 . Apparatus according to  claim 1  wherein the illumination system includes a pupil plane that is a Fourier transform of an object plane containing the patterning device and wherein the diffuser is selectively positionable in a plane that is not conjugate with either the pupil plane or the object plane.  
   
   
       3 . Apparatus according to  claim 2  wherein the illumination system comprises moveable masking blades arranged to define the area of the patterning device that is illuminated by the illumination beam and wherein the diffuser is proximate the moveable masking blades.  
   
   
       4 . Apparatus according to  claim 1  wherein the diffuser is proximate the patterning device.  
   
   
       5 . Apparatus according to  claim 1  wherein the diffuser is arranged to be movable into and out of the illumination beam faster that the illumination system can change the illumination profile of the illumination beam.  
   
   
       6 . Apparatus according to  claim 1  wherein said sensor is arranged to accept radiation arriving at a predetermined range of angles of incidence and wherein said diffuser is arranged to diffuse light such that light arrives at said sensor across substantially all of said predetermined range of angles of incidence.  
   
   
       7 . Apparatus according to  claim 1  wherein the sensor comprises a transmission image sensor.  
   
   
       8 . Apparatus according to  claim 1  wherein the sensor comprises a reflection image sensor.  
   
   
       9 . Apparatus according to  claim 1  wherein the sensor comprises an interferometric alignment sensor.  
   
   
       10 . A device manufacturing method using a lithographic projection apparatus having an illumination system arranged to illuminate a patterning device with an illumination beam, a projection system arranged to project an image of the patterning device onto a substrate and a sensor arranged to detect a property of an image projected by the projection system, the method comprising: 
 setting the illumination system to illuminate the patterning device with an illumination beam having an illumination profile;    inserting a diffuser into the path of the illumination beam so as to increase the range of angles at which radiation of the illumination beam is incident on a marker on the patterning device; and    using the sensor to detect a property of an image of the marker projected by the projection system.    
   
   
       11 . A method according to  claim 10  further comprising: 
 removing the diffuser from the path of the illumination beam after the step of using the sensor; and    exposing a substrate to a pattern defined by said patterning device.    
   
   
       12 . A method according to  claim 10  wherein the patterning device is a mask and wherein said diffuser is attached to said mask.  
   
   
       13 . A method according to  claim 10  wherein the patterning device is a mask and wherein said apparatus further comprises a mask table arranged to hold the mask, the method comprising loading the mask onto the mask table, positioning the diffuser over the marker on the mask and moving the mask table holding the mask and diffuser to insert the mask and diffuser into the path of the illumination beam  
   
   
       14 . A mask for use in a device manufacturing method of a lithographic apparatus, the mask comprising: 
 a substrate;    a pattern layer having a first area in which is defined at least one device pattern and a second area not overlapping said first area in which is defined at least one marker pattern; and    a diffuser at least partly covering said second area and arranged to increase the range of angles of incidence of radiation illuminating the second area.    
   
   
       15 . A mask according to  claim 14  wherein the substrate has a first side and a second side opposite thereto, the pattern layer being provided on the first side and the diffuser on the second side.  
   
   
       16 . A mask according to  claim 14  wherein the diffuser comprises an additional piece of material adhered to the substrate.  
   
   
       17 . A mask according to  claim 14  wherein the diffuser comprises a surface relief on the substrate.  
   
   
       18 . A mask according to  claim 14  wherein the diffuser comprises a part of the substrate having scattering centers implanted therein.