Lithography system and projection method

Abstract

The present invention relates a probe forming lithography system for generating a pattern on to a target surface such as a wafer, using a black and white writing strategy, i.e. writing or not writing a grid cell, thereby dividing said pattern over a grid comprising grid cells, said pattern comprising features of a size larger than that of a grid cell, in each of which cells said probe is switched “on” or “off, wherein a probe on said target covers a significantly larger surface area than a grid cell, and wherein within a feature a position dependent distribution of black and white writings is effected within the range of the probe size as well as to a method upon which such system may be based.

The invention claimed is: 
     
       1. Method of operating a writing beam probe forming lithography system for projecting a pattern on to a target surface, comprising:
 using an “on” and “off” writing strategy to operate said writing beam probe based on dividing said pattern over a grid comprising grid cells, wherein said pattern includes features having a size larger than that of each one of said grid cells, 
 in each of said grid cells, switching said writing beam probe “on” or “off”, wherein the writing beam probe on said target is set to cover a surface area that covers a plurality of grid cells, and 
 wherein during a single pass of a writing beam 
 effecting a position dependent distribution of “on” and “off” switching within a range of the writing beam probe size wherein said writing strategy is completed during said single pass. 
 
     
     
       2. Method according to  claim 1 , wherein said position dependent distribution is performed near an edge of a feature to be written on said target. 
     
     
       3. Method according to  claim 1 , wherein said position dependent distribution is performed for effecting a sub grid cell placement of a feature edge on said target. 
     
     
       4. Method according to  claim 1 , wherein positioning of a feature edge is effected by not writing part or parts of a line of grid cells oriented parallel to said edge, and located at a distance from said edge. 
     
     
       5. Method according to  claim 1 , wherein grid cells are written in at least one line of said grid adjacent a feature edge outside of said feature, whereby said line of grid cells is oriented in parallel to said edge. 
     
     
       6. Method according to the  claim 5 , wherein at least one set of a number of grid cells is additionally written in said line. 
     
     
       7. Method according to  claim 1 , wherein an overall dose modulation is effected for said feature, by switching on and off said writing beam probe in a regular pattern. 
     
     
       8. Method according to the  claim 7 , in which edges of said feature are shifted with respect to said grid. 
     
     
       9. Method according to  claim 1 , wherein on/off switching of a writing beam probe is slower than the pixel rate. 
     
     
       10. Method according to  claim 1 , in which an effective edge position of a feature of said pattern is controlled by not writing one or a set of grid cells within a range of the writing beam probe size from the edge. 
     
     
       11. Method according to  claim 1 , wherein the writing beam probe comprises a Gaussian probe, wherein a full exposure of a certain grid cell also causes a partial exposure in the grid cells adjacent to the exposed grid cell. 
     
     
       12. A writing beam probe forming lithography system for generating a pattern on to a target surface, comprising:
 using a writing strategy based on dividing said pattern over a grid comprising grid cells and wherein said writing beam probe is switched “on” or “off” in each one of said grid cells for writing or not writing each one of said grid cells, said pattern comprising features of a size larger than that of one of said grid cells, 
 wherein the writing beam probe on said target is larger than the size of one of said grid cells in that said writing beam probe covers a plurality of grid cells, and 
 wherein within a feature, a position dependent distribution of writing and not writing of grid cells is effected within a range of the writing beam probe size wherein said writing strategy is completed during a single pass of said writing beam probe. 
 
     
     
       13. System according to  claim 12 , in which the writing beam probe size is of a value within a range from 5 to 20 times the grid cell size. 
     
     
       14. System according to  claim 12 , wherein the writing beam probe comprises a Gaussian probe, wherein a full exposure of a certain grid cell also causes a partial exposure in the grid cells adjacent to the exposed grid cell. 
     
     
       15. Method for operating a lithography system in which a pattern is to be projected on to a target surface, comprising:
 using a plurality of writing beams in the form of probe forming beams, generated in a charged particle beams column part of said system, and scanned over said target surface for writing said pattern, 
 modulating the writing beams in said column by blanking each writing beam individually within the column or not, 
 writing said pattern being performed by scanning each individual writing beam in a direction transverse to a mechanical movement of said target relative to said column, 
 positioning pattern features on said target using a virtual grid divided into grid cells of a dimension such that each probe forming beam covers a plurality of grid cells, and 
 locating, an edge of a feature of a size larger than that of one of said grid cells virtually independent from said grid size by not writing at least one set of grid cells in at least the last scan line for writing said feature, which set is larger than a number of grid cells and smaller than the number of grid cells required for writing the dimension of each said probe forming beam, 
 wherein said writing is completed during a single pass of said probe forming beams. 
 
     
     
       16. Method of operating a writing electron beam forming maskless lithography system for writing a desired pattern on to a target surface, using an “on” and “off” writing strategy using a combination of relative movement of the target surface and a timed “on” and “off” switching of the writing beam, said method comprising:
 dividing said desired pattern over a virtual grid comprising grid cells, wherein said desired pattern comprising features having a size larger than that of said grid cells, wherein a feature comprises an edge, 
 altering the content of grid cells to obtain an adapted rasterized pattern wherein at least one of part of the grid cells near the edge inside the feature are not written and additional grid cells near the edge outside the feature are written, 
 wherein the writing beam on said target is larger than the size of a grid cell in that said writing beam is set to cover a surface area that covers a multiplicity of grid cells, 
 wherein, for the writing of said adapted rasterized pattern on to the target surface, a position dependent distribution of “on” and “off” switching is effected within a range of the writing beam size, wherein in each of said grid cells said writing beam is switched “on” or “off” according to the adapted rasterized pattern, and wherein the patterning of features is attained without multiple passages for writing said pattern. 
 
     
     
       17. Method according to claim 16, wherein additional grid cells immediately near the edge of the feature are added with an interruption of two or more not written grid cells between each pair of added cells. 
     
     
       18. Method according to claim 16, wherein said altering the content of grid cells is performed for effecting a sub grid cell placement of a feature edge on said target. 
     
     
       19. Method according to claim 16, wherein positioning of the feature edge is effected by not writing part or parts of a line of grid cells oriented parallel to said edge, and located at a distance from said edge. 
     
     
       20. Method according to claim 16, wherein the additional grid cells are written in at least one line of said grid adjacent the feature edge outside of said feature, whereby said line of grid cells is oriented in parallel to said edge. 
     
     
       21. Method according to claim 20, wherein at least one set of a number of grid cells is additionally written in said line. 
     
     
       22. Method according to claim 16, wherein an overall dose modulation is effected for said feature, by switching on and off said writing beam in a regular pattern. 
     
     
       23. Method according to the claim 22, in which edges of said feature are shifted with respect to said grid. 
     
     
       24. Method according to claim 16, wherein the timed on/off switching of the writing beam is slower than a pixel rate. 
     
     
       25. Method according to claim 16, in which an effective edge position of the feature of said pattern is controlled by not writing one or a set of grid cells within a range of the writing beam size from the edge. 
     
     
       26. Method according to claim 16, in which the writing beam size is of a value within a range from 5 to 20 times the size of said grid cells. 
     
     
       27. Method according to claim 16, wherein a diameter of the writing beam on said target is at least a length of about ten grid cells of said grid. 
     
     
       28. A writing beam forming lithography system for generating a pattern on to a target surface, comprising:
 a beam generator for generating a electron beam,   an aperture array for splitting up said beam into a plurality of substantially parallel writing beams,   a modulation array, for modulating said writing beams, and   a control unit adapted for controlling the modulation array for modulating the writing beams for writing a desired pattern on to the target surface, using an “on” and “off” writing strategy using a combination of relative movement of the target surface and a timed “on” and “off” switching of the writing beam, wherein said control unit is adapted for:   dividing said desired pattern over a virtual grid comprising grid cells, wherein said desired pattern comprising features having a size larger than that of said grid cells, wherein a feature comprises an edge,   altering the content of grid cells to obtain an adapted rasterized pattern wherein at least one of part of the grid cells near the edge inside the feature are not written and additional grid cells near the edge outside the feature are written,   wherein the writing beam on said target is larger than the size of a grid cell in that said writing beam is set to cover a surface area that covers a multiplicity of grid cells,   wherein, for the writing of said adapted rasterized pattern on to the target surface, a position dependent distribution of “on” and “off” switching is effected within a range of the writing beam size, wherein in each of said grid cells said writing beam is switched “on” or “off” according to the adapted rasterized pattern, and wherein the patterning of features is attained without multiple passages for writing said pattern.   
     
     
       29. System according to claim 28, in which the writing beam size is of a value within a range from 5 to 20 times the grid cell size. 
     
     
       30. System according to claim 28, wherein the writing beam comprises a Gaussian writing beam, wherein a full exposure of a certain grid cell also causes a partial exposure in the grid cells adjacent to the exposed grid cell, wherein a diameter of the writing beam on said target is at least a length of about ten grid cells of said grid. 
     
     
       31. Method for operating a lithography system in which a pattern is to be projected on to a target surface, comprising:
 using a plurality of writing beams in the form of probe forming beams, generated in a charged particle beams column part of said system, and scanned over said target surface for writing said pattern,   modulating the writing beams in said column by blanking each writing beam individually within the column or not,   writing said pattern being performed by scanning each individual writing beam in a direction transverse to a mechanical movement of said target relative to said column,   positioning pattern features on said target using a virtual grid divided into grid cells of a dimension such that each probe forming beam covers a plurality of grid cells, and   locating, an edge of a feature of a size larger than that of one of said grid cells virtually independent from said grid size by at least one of not writing grid cells inside the feature and writing additional pixels near the edge of said feature at the outside of said feature,   wherein said writing is completed during a single pass of said probe forming beams.