Method and system for determining a charged particle beam exposure for a local pattern density
Methods for exposing a desired shape in an area on a surface using a charged particle beam system include determining a local pattern density for the area, based on an original set of exposure information. A pre-proximity effect correction (PEC) maximum dose for the local pattern density is determined, based on a pre-determined target post-PEC maximum dose. The pre-PEC maximum dose is calculated near an edge of the desired shape. Methods also include modifying the original set of exposure information with the pre-PEC maximum dose to create a modified set of exposure information.
1 . A method for exposing a desired shape in an area on a surface using a charged particle beam system, the method comprising:
determining a local pattern density for the area, based on an original set of exposure information;
determining a pre-proximity effect correction (PEC) maximum dose for the local pattern density, based on a pre-determined target post-PEC maximum dose, wherein the pre-PEC maximum dose is calculated near an edge of the desired shape; and
modifying the original set of exposure information with the pre-PEC maximum dose to create a modified set of exposure information;
wherein the pre-determined target post-PEC maximum dose is based on a maximum write time.
2 . The method of claim 1 , wherein the modified set of exposure information is refined by PEC resulting in adjusted dosages that are less than the pre-determined target post-PEC maximum dose.
3 . The method of claim 1 , wherein a portion of a width of the desired shape exceeds a pre-determined width.
4 . The method of claim 1 , wherein at a location where a width of a portion of the desired shape is below a pre-determined width, the pre-PEC maximum dose is calculated near a center of the desired shape.
5 . The method of claim 1 , further comprising calculating a backscatter for a sub area of the area, based on the local pattern density for the area.
6 . The method of claim 5 , further comprising increasing a dosage for at least one pixel in a plurality of pixels in the sub area, in a location where the backscatter of the sub area is below a pre-determined threshold, thereby increasing the backscatter of the sub area.
7 . The method of claim 6 , wherein the dosage for the at least one pixel in the plurality of pixels in the sub area is increased so that the backscatter is increased to a pre-determined value.
8 . The method of claim 6 , wherein the dosage for the at least one pixel in the plurality of pixels in the sub area is increased only if the at least one pixel is more than a pre-determined distance from the edge of the desired shape in the area on the surface.
9 . The method of claim 6 , wherein the increased dosage of the at least one pixel in the plurality of pixels in the sub area is applied closer than a pre-determined distance from an inner edge of the desired shape in the area on the surface.
10 . The method of claim 6 , wherein the increase in dosage comprises an artificial background dose.
11 . The method of claim 6 , wherein the original set of exposure information comprises information for multiple exposure passes, and wherein the increasing of the backscatter of the sub area only occurs in one exposure pass of the multiple exposure passes.
12 . The method of claim 5 , wherein the sub area is subdivided into partitions, wherein an artificial background dose is determined for each partition.
13 . The method of claim 12 , wherein the artificial background dose for any location within an individual partition is interpolated across the individual partition.
14 . The method of claim 13 , wherein the interpolation is based on the artificial background doses for adjacent partitions.
15 . The method of claim 1 , wherein a mask exposure is performed inline with one or more steps selected from the group consisting of determining the local pattern density, determining the pre-PEC maximum dose, determining an artificial background dose, and creating the modified set of exposure information.
16 . The method of claim 1 , further comprising inputting a target dose margin, wherein the target dose margin is used to set the pre-determined target post-PEC maximum dose.
17 . The method of claim 1 , further comprising calculating a dose margin for the desired shape to be exposed.
18 . The method of claim 17 , further comprising calculating a target minimum dose margin at a pre-determined edge location of a pre-determined pattern in a pre-determined backscatter area;
wherein the pre-PEC maximum dose is determined to achieve the dose margin below the target minimum dose margin for the desired shape to be exposed.
19 . The method of claim 1 , further comprising exposing the surface with the modified set of exposure information.