Imprint lithography

Abstract

An imprint lithography apparatus is disclosed that has a template holder configured to hold an imprint template, a substrate table, and an optical encoder, the optical encoder having a radiation output, a first diffraction grating, and a detector, the radiation output arranged to illuminate a second diffraction grating and the detector positioned to detect radiation diffracted by the first and second diffraction gratings to provide an alignment signal.

1 . An imprint lithography apparatus comprising a template holder configured to hold an imprint template, a substrate table, and an optical encoder, the optical encoder having a radiation output, a first diffraction grating, and a detector, the radiation output arranged to illuminate a second diffraction grating and the detector positioned to detect radiation diffracted by the first and second diffraction gratings to provide an alignment signal.  
     
     
         2 . The apparatus according to  claim 1 , wherein the second diffraction grating is located on the substrate table.  
     
     
         3 . The apparatus according to  claim 1 , wherein the second diffraction grating is located on a substrate held on the substrate table.  
     
     
         4 . The apparatus according to  claim 1 , wherein the first diffraction grating is fixed to the template holder.  
     
     
         5 . The apparatus according to  claim 1 , wherein the first diffraction grating is provided on the imprint template.  
     
     
         6 . The apparatus according to  claim 1 , wherein the first diffraction grating is a transmissive phase grating.  
     
     
         7 . The apparatus according to  claim 1 , wherein the first diffraction grating is an amplitude grating.  
     
     
         8 . The apparatus according to  claim 1 , wherein the radiation output is configured such that radiation emitted from the radiation output passes through the first diffraction grating before passing to the second diffraction grating.  
     
     
         9 . The apparatus according to  claim 1 , wherein the detector comprises a plurality of spaced apart photodiodes.  
     
     
         10 . The apparatus according to  claim 1 , wherein the period of the second diffraction grating is between 50 nanometers and 10 microns.  
     
     
         11 . The apparatus according to  claim 1 , wherein the period of the first diffraction grating is between 50 nanometers and 10 microns.  
     
     
         12 . The apparatus according to  claim 1 , wherein the second diffraction grating and the first diffraction grating are spaced apart by between 50 nanometers and 10 microns.  
     
     
         13 . The apparatus according to  claim 1 , wherein in addition to the first diffraction grating, the optical encoder is provided with a further diffraction grating, the further diffraction grating having a longer period than the first diffraction grating.  
     
     
         14 . The apparatus according to  claim 1 , wherein the apparatus further comprises an alignment sensor comprising capacitive sensors arranged to detect the presence of capacitor plates.  
     
     
         15 . The apparatus according to  claim 1 , wherein the optical encoder is a linear encoder.  
     
     
         16 . The apparatus according to  claim 1 , wherein the first diffraction grating extends in a predetermined direction, and the second diffraction grating extends in the same direction.  
     
     
         17 . The apparatus according to  claim 1 , wherein the first diffraction grating and the second diffraction grating both extend in two directions.  
     
     
         18 . The apparatus according to  claim 1 , wherein the detected radiation comprises a Moiré pattern.  
     
     
         19 . A method of alignment for an imprint lithography apparatus comprising an imprint template and an optical encoder having a radiation output, a first diffraction grating, and a detector, the method comprising directing radiation from the radiation output onto a second diffraction grating, and detecting radiation diffracted by the first and second diffraction gratings to provide an alignment signal.  
     
     
         20 . The method according to  claim 19 , comprising directing radiation from the radiation output through the first diffraction grating before it is incident upon the second diffraction grating.  
     
     
         21 . The method according to  claim 19 , wherein the second diffraction grating is provided on a substrate table.  
     
     
         22 . The method according to  claim 19 , wherein the second diffraction grating is provided on a substrate.  
     
     
         23 . The method according to  claim 19 , wherein the detected radiation comprises a Moiré pattern.