Lithographic apparatus, device manufacturing method and energy sensor

Abstract

An energy sensor, e.g. as part of a transmission image sensor comprises: a radiation-sensitive detector arranged to receive a pulsed radiation beam and to generate a current in response thereto; a circuit equivalent to an RC network connected across the radiation-sensitive detector; and an analog to digital converter connected across a resistive component of the circuit and arranged to output digital samples measuring the voltage across the resistive component at a sampling rate that is greater than the pulse repetition rate of the pulsed radiation beam.

1 . A lithographic apparatus having sensor system comprising: 
 a radiation-sensitive detector arranged to receive a pulsed radiation beam and to generate a current in response thereto;    a circuit equivalent to an RC network connected across the radiation-sensitive detector; and    an analog to digital converter connected across a resistive component of the circuit and arranged to output digital samples measuring voltage across the resistive component at a sampling rate that is greater than a pulse repetition rate of the pulsed radiation beam.    
   
   
       2 . The apparatus according to  claim 1 , wherein the sampling rate is greater than 5 times the pulse repetition rate.  
   
   
       3 . The apparatus according to  claim 1 , wherein the sampling rate is greater than 10 times the pulse repetition rate  
   
   
       4 . The apparatus according to  claim 1 , wherein the sampling rate is greater than 20 times the pulse repetition rate  
   
   
       5 . The apparatus according to  claim 1 , wherein the sampling rate is greater than 50 times the pulse repetition rate  
   
   
       6 . The apparatus according to  claim 1 , wherein the radiation sensitive detector has an equivalent resistance Rs and an equivalent capacitance Cp, and the sampling rate f satisfies the following inequality:  
         f>n (1/( RsCp ))  
     where n is a positive real number greater than 1.  
   
   
       7 . The apparatus according to  claim 6 , wherein n is greater than 50.  
   
   
       8 . The apparatus according to  claim 1  wherein the circuit has an equivalent resistance Ri and an equivalent capacitance Ci and the sampling rate f satisfies the following inequality:  
         f>p (1/( RiCi ))  where p is a positive real number greater than 1.    
   
   
       9 . The apparatus according to  claim 8 , wherein p is greater than 50.  
   
   
       10 . The apparatus according to  claim 1 , further comprising a digital signal processor connected to the analog to digital converter to receive the digital samples and configured and arranged to calculate therefrom a measure of the energy of a pulse of the radiation beam.  
   
   
       11 . Apparatus according to  claim 1 , wherein the radiation beam is electromagnetic radiation having a wavelength of less than or equal to about 365 nm.  
   
   
       12 . Apparatus according to  claim 1 , wherein the radiation-sensitive detector is part of a transmission image sensor system.  
   
   
       13 . Apparatus according to  claim 1 , wherein the radiation sensitive detector is part of an interferometric aberration sensor.  
   
   
       14 . A device manufacturing method using a lithographic apparatus which has a radiation-sensitive detector arranged to receive a pulsed radiation beam and to generate a current in response thereto connected to a circuit equivalent to an RC network, the method comprising: 
 digitally sampling the voltage across a resistive component of the circuit at a sampling rate that is greater than the pulse repetition rate of the pulsed radiation beam.    
   
   
       15 . A method according to  claim 14 , wherein the sampling rate is greater than 5 times the pulse repetition rate.  
   
   
       16 . A method according to  claim 14 , wherein the sampling rate is greater than 10 times the pulse repetition rate.  
   
   
       17 . A method according to  claim 14 , wherein the sampling rate is greater than 20 times the pulse repetition rate.  
   
   
       18 . A method according to  claim 14 , wherein the sampling rate is greater than 50 times the pulse repetition rate.  
   
   
       19 . A method according to  claim 14  wherein the radiation sensitive detector has an equivalent resistance Rs and an equivalent capacitance Cp, and the sampling rate f satisfies the following inequality:  
         f>n (1/( RsCp ))  
     where n is a positive real number greater than 1.  
   
   
       20 . The apparatus according to  claim 19 , wherein n is greater than 50.  
   
   
       21 . A method according to  claim 14 , wherein the circuit has an equivalent resistance Ri and an equivalent capacitance Ci and the sampling rate f satisfies the following inequality:  
         f>p (1/( RiCi ))  where p is a positive real number greater than 1.    
   
   
       22 . The apparatus according to  claim 21 , wherein p is greater than 50.  
   
   
       23 . An energy sensor comprising: 
 a radiation-sensitive detector arranged to receive a pulsed radiation beam and to generate a current in response thereto;    a circuit equivalent to an RC network connected across the radiation-sensitive detector; and    an analog to digital converter connected across a resistive component of the circuit and arranged to output digital samples measuring the voltage across the resistive component at a sampling rate that is greater than the pulse repetition rate of the pulsed radiation beam.