Method for coarse wafer alignment in a lithographic apparatus

Abstract

A method for alignment of a substrate, in which the substrate includes a mark in a scribe lane, and the scribe lane extends along a longitudinal direction as a first direction. The mark has a periodic structure in the first direction. The method includes providing an illumination beam for scanning the mark in a direction perpendicular to a direction of the mark's periodic structure along a first scan path across the mark, scanning the spot of the illumination beam along a second scan path across the mark, the second scan path being parallel to the first scan path, wherein the second scan path is shifted relative to the first scan path over a first shift that corresponds to a fraction of the repeating distance of the periodic structure.

1 . A method for aligning a substrate in a lithographic apparatus, the substrate comprising a mark in a scribe lane, the scribe lane extending along a longitudinal direction as a first direction, the mark having a first structure in the first direction and a second structure extending in a second direction perpendicular to the first direction, the method comprising:
 providing an illumination beam for scanning the mark in the second direction during an optical alignment scan;   obtaining a first scan signal coming from the mark by scanning a spot of the illumination beam in the second direction along a first scan path across the mark;   obtaining a second scan signal coming from the mark by scanning the spot of the illumination beam in the second direction along a second scan path across the mark; and   determining a differential alignment signal from a difference between the first and second scan signals to distinguish the mark.   
     
     
         2 . The method according to  claim 1 , further including:
 using the differential alignment signal to determine a position of the substrate in a substrate alignment procedure.   
     
     
         3 . The method according to  claim 2 , wherein obtaining the first scan signal includes:
 obtaining first alignment data from the first scan signal, wherein the first alignment data is a representative of a measured intensity at a measured position within the scribe lane along the first scan path in the second direction,   wherein obtaining the second scan signal includes:
 obtaining second alignment data from the second scan signal, wherein the second alignment data is a representative of a measured intensity at a measured position within the scribe lane along the second scan path in the second direction. 
   
     
     
         4 . The method according to  claim 3 , wherein determining the differential alignment signal includes:
 determining the differential alignment signal based on the first alignment data of the first scan signal and the second alignment data of the second scan signal, wherein the second scan path being parallel to the first scan path.   
     
     
         5 . The method according to  claim 1 , wherein the mark having a periodic structure in the first direction and a mark structure extending in a second direction perpendicular to the first direction, the periodic structure having a repeating distance in the first direction. 
     
     
         6 . The method according to  claim 5 , wherein the second scan path is shifted along the first direction relative to the first scan path over a first shift, the first shift corresponding to a fraction of the repeating distance of the periodic structure in the first direction. 
     
     
         7 . The method according to  claim 1 , wherein providing an illumination beam for scanning the mark includes:
 providing the illumination beam of a self referencing interferometer as the spot on the substrate.   
     
     
         8 . The method according to  claim 1 , wherein the mark comprises a plurality of lines, the lines extending in the first direction and being arranged parallel to each other, each one of the plurality of lines being divided in a plurality of blocks in a substantially identical manner, the repeating distance of the periodic structure being defined by a spacing of the blocks in each line in the first direction; the mark structure in the second direction being defined by an interspace between each pair of lines selected from the plurality of lines. 
     
     
         9 . The method according to  claim 8 , wherein the plurality of lines comprises at least three lines. 
     
     
         10 . The method according to  claim 8 , wherein, the plurality of lines comprises a set of oblique lines which are each ranked under an oblique angle relative to the first direction; the repeating distance of the periodic structure being defined by a spacing between each pair of lines in the first direction, and wherein the mark structure in the second direction is defined by an interspace between the lines in the second direction. 
     
     
         11 . The method according to  claim 1 , further comprising:
 registering by a self referencing interferometer of a first interferometry signal obtained during the scanning along the first scan path;   registering by the self referencing interferometer of a second interferometry signal obtained during the scanning along the second scan path; and   determining a first differential interferometry signal from the first interferometry signal and the second interferometry signal.   
     
     
         12 . The method according to  claim 11 , further comprising:
 matching a pattern of the first differential interferometry signal with an expected pattern corresponding to the mark,   wherein the second scan path is shifted along the first direction relative to the first scan path over a first shift, the first shift corresponding to a fraction of the repeating distance of the periodic structure in the first direction.   
     
     
         13 . The method according to  claim 12 , wherein: if the pattern in the first differential interferometry signal does not match with the expected pattern of the mark, the method further comprises:
 scanning a spot of the illumination beam along a third scan path across the mark, the third scan path being parallel to the first scan path and is shifted relative to the first scan path over a second shift, the second shift corresponding a second fraction of the repeating distance of the periodic structure in the first direction, and registering by the self referencing interferometer of a third interferometry signal obtained during the scanning along the third scan path.   
     
     
         14 . The method according to  claim 13 , wherein the substrate is a wafer and the first differential interferometry signal is used for determining the position of the wafer in a wafer alignment procedure in the lithographic apparatus. 
     
     
         15 . The method according to  claim 13 , further comprising:
 determining a second differential interferometry signal from the first interferometry signal and the third interferometry signal; matching a pattern of the second differential interferometry signal with the expected pattern corresponding to the mark; and if the pattern in the second differential interferometry signal does not match with expected pattern of the mark: determining a third differential interferometry signal from the first interferometry signal and the third interferometry signal; matching a pattern of the third differential interferometry signal with the expected pattern corresponding to the mark.   
     
     
         16 . The method according to  claim 15 , wherein the substrate is a wafer and one interferometry signal selected from the second and third differential interferometry signals is used for determining a position of the wafer in a wafer alignment procedure in the lithographic apparatus. 
     
     
         17 . A lithographic apparatus comprising: 
       a substrate table constructed to hold a substrate, the substrate comprising a mark in a scribe lane, the scribe lane extending along a longitudinal direction as a first direction, the mark having a first structure in the first direction and a second structure extending in a second direction perpendicular to the first direction;
 a scanning device for providing an illumination beam for scanning the mark in the second direction; and 
 a control system coupled to the substrate table and the scanning device for controlling an action of the substrate table and the scanning device, respectively, 
 wherein the control system is configured to control:
 providing an illumination beam for scanning the mark in the second direction during an optical alignment scan; 
 obtaining a first scan signal coming from the mark by scanning a spot of the illumination beam in the second direction along a first scan path across the mark; 
 obtaining a second scan signal coming from the mark by scanning the spot of the illumination beam in the second direction along a second scan path across the mark; and 
 determining a differential alignment signal from a difference between the first and second scan signals to distinguish the mark. 
 
 
     
     
         18 . The lithographic apparatus according to  claim 17 , wherein the control system further comprises a self referencing interferometer constructed for registering of a signal obtained by the scanning device, the control system being coupled to the self referencing interferometer for controlling an action of the self referencing interferometer, wherein the control system is configured to control:
 obtaining first alignment data from the first scan signal, wherein the first alignment data is a representative of a measured intensity at a measured position within the scribe lane along the first scan path in the second direction;   obtaining second alignment data from the second scan signal, wherein the second alignment data is a representative of a measured intensity at a measured position within the scribe lane along the second scan path in the second direction;   determining the differential alignment signal based on the first alignment data of the first scan signal and the second alignment data of the second scan signal, wherein the second scan path being parallel to the first scan path; and   using the differential alignment signal to determine a position of the substrate in a substrate alignment procedure.   
     
     
         19 . A computer program stored on a non-transitory medium to be loaded by a computer, the computer comprising a processor, memory, the memory being connected to the processor, the computer being part of a lithographic apparatus, the lithographic apparatus comprising:
 a substrate table constructed to hold a substrate, the substrate comprising a mark in a scribe lane, the scribe lane extending along a longitudinal direction as a first direction, the mark having a first structure in the first direction and a second structure extending in a second direction perpendicular to the first direction;   a scanning device for providing an illumination beam for scanning the mark in the second direction; and   the computer being arranged as a control system coupled to the substrate table and the scanning device for controlling actions of the substrate table and the scanning device, respectively;   the computer program after being loaded allowing the processor to carry out:
 providing an illumination beam for scanning the mark in the second direction during an optical alignment scan; 
 obtaining a first scan signal coming from the mark by scanning a spot of the illumination beam in the second direction along a first scan path across the mark; 
 obtaining a second scan signal coming from the mark by scanning the spot of the illumination beam in the second direction along a second scan path across the mark; and 
 determining a differential alignment signal from a difference between the first and second scan signals to distinguish the mark. 
   
     
     
         20 . The computer program stored on a non-transitory medium according to  claim 19 , wherein the computer program further includes machine-executable instructions for:
 obtaining first alignment data from the first scan signal, wherein the first alignment data is a representative of a measured intensity at a measured position within the scribe lane along the first scan path in the second direction;   obtaining second alignment data from the second scan signal, wherein the second alignment data is a representative of a measured intensity at a measured position within the scribe lane along the second scan path in the second direction;   determining the differential alignment signal based on the first alignment data of the first scan signal and the second alignment data of the second scan signal, wherein the second scan path being parallel to the first scan path; and   using the differential alignment signal to determine a position of the substrate in a substrate alignment procedure.