Method and apparatus for photomask fabrication

Abstract

The invention provides methods and apparatuses for controlling critical dimension (CD) uniformity of a photomask by neutralizing CD variation associated with pattern density and process fluctuation.

1 . An apparatus comprising; 
 a chamber enclosing a substrate mount to receive and mount a substrate;    a source of reactive species operative to direct a flow of the reactive species in the chamber toward the substrate, wherein the source and the mount are movable relative to each other; and    a data processing device operable to 
 receive information describing local pattern density at a collection of different locations on a substrate, and  
 control a period of time for which each of the locations is exposed to the reactive species flow based on the local pattern density at that location.  
   
   
   
       2 . The apparatus of  claim 1 , wherein the data processing device is further operable to control continuous relative movement between the source of the reactive species and the mount.  
   
   
       3 . The apparatus of  claim 1 , wherein the data processing device is further operable to control discontinuous relative movement between the source of the reactive species and the mount.  
   
   
       4 . The apparatus of  claim 1 , wherein the data processing device is further operable to receive a map of local critical dimension (CD) measurements of the substrate.  
   
   
       5 . The apparatus of  claim 1 , wherein the data processing device is further operable to receive pattern information used to direct the writing of a photomask pattern.  
   
   
       6 . The apparatus of  claim 1 , wherein the data processing device is further operable to receive image data from which a number of structures per unit area can be determined.  
   
   
       7 . The apparatus of  claim 1 , wherein the data processing device is further operative to determine a distribution of the reactive species flow.  
   
   
       8 . The apparatus of  claim 7 , wherein the distribution of reactive species flow is equal to the impact range of the etch loading effect.  
   
   
       9 . The apparatus of  claim 7 , wherein the distribution of reactive species flow is less than the impact range of the etch loading effect.  
   
   
       10 . The apparatus of  claim 1 , wherein the data processing device is further operative to generate a velocity map based on the received information describing the local pattern density.  
   
   
       11 . The apparatus of  claim 1 , wherein the source of reactive species comprises a plasma source.  
   
   
       12 . The apparatus of  claim 1 , wherein the source of reactive species comprises an radio frequency (RF) source.  
   
   
       13 . The apparatus of  claim 1 , wherein the substrate mount comprises a movable substrate mount.  
   
   
       14 . The apparatus of  claim 1 , wherein the source of reactive species is operative to direct a Gaussian distribution of the reactive species toward the substrate.  
   
   
       15 . An article comprising a machine-readable medium including machine-executable instructions operative to cause a machine to perform operations, the operations comprising: 
 receiving information describing local pattern density at a collection of different locations on a photomask; and    controlling a differential etching of the locations in the collection based on the local pattern density at that location.    
   
   
       16 . The article of  claim 15 , wherein controlling the differential etching comprises controlling a period of time for which each of the locations is exposed to the reactive species flow based on the local pattern density at that location.  
   
   
       17 . The article of  claim 16 , wherein controlling the period of time for which each of the locations is exposed to the reactive species flow comprises controlling relative movement between a source of the reactive species flow and the substrate.  
   
   
       18 . The article of  claim 17 , wherein controlling the relative movement between the source and the substrate comprises controlling a velocity of continuous movement between the source and the substrate.  
   
   
       19 . The article of  claim 18 , wherein: 
 the operations further comprise generating a velocity map based upon the local pattern density at the collection of locations; and    the velocity of continuous movement between the source and the substrate is controlled based upon the velocity map.    
   
   
       20 . The article of  claim 15 , wherein receiving information describing local pattern density comprises receiving critical dimension (CD) measurements of a pattern on the photomask.  
   
   
       21 . The article of  claim 15 , wherein receiving the information describing the local pattern density comprises receiving local critical dimension (CD) measurements made at the different locations in the collection.  
   
   
       22 . The article of  claim 15 , wherein receiving the local critical dimension (CD) measurements comprises sampling the local critical dimension (CD) at the different locations in the collection.  
   
   
       23 . An apparatus comprising; 
 a mount to receive and mount a photomask comprising at least one of a photoresist and an absorber;    an etchant source operative to direct an etchant of the at least one of the photoresist and the absorber toward a surface of the photomask, the directed etchant having a spatial distribution that is smaller than the size of the surface of the photomask; and    a data processing device operable to 
 receive information describing local pattern density at a collection of different locations on the photomask, the pattern being in the at least one of a photoresist and an absorber, and  
 control a differential etching of the locations in the collection with the directed etchant based on the local pattern density at that location.