Methods for performing model-based lithography guided layout design
View Patent ↗Methods are disclosed to create efficient model-based Sub-Resolution Assist Features (MB-SRAF). An SRAF guidance map is created, where each design target edge location votes for a given field point on whether a single-pixel SRAF placed on this field point would improve or degrade the aerial image over the process window. In one embodiment, the SRAF guidance map is used to determine SRAF placement rules and/or to fine-tune already-placed SRAFs. The SRAF guidance map can be used directly to place SRAFs in a mask layout. Mask layout data including SRAFs may be generated, wherein the SRAFs are placed according to the SRAF guidance map. The SRAF guidance map can comprise an image in which each pixel value indicates whether the pixel would contribute positively to edge behavior of features in the mask layout if the pixel is included as part of a sub-resolution assist feature.
1. A method for placing sub-resolution assist features (“SRAF”) in a mask layout, comprising:
generating an SRAF guidance map for the mask layout, wherein the SRAF guidance map is an image in which each pixel value indicates whether the pixel would contribute positively to edge behavior of features in the mask layout if the pixel is included as part of a sub-resolution assist feature; and
placing sub-resolution assist features in the mask layout according to the SRAF guidance map,
wherein the generating and the placing are performed by using a computer, and
wherein generating an SRAF guidance map comprises:
computing an image gradient map of the mask layout; and
for each field point in the mask layout, computing a total vote sum for a unit source at the field point using the image gradient map.
2. The method of claim 1 , wherein generating an SRAF guidance map comprises:
assigning values in the SRAF guidance map, wherein the value at a pixel in the SRAF guidance map is the total vote sum at a corresponding field point in the mask layout.
3. The method of claim 2 , wherein computing a total vote sum for a unit source at the field point is performed in the frequency domain and includes:
computing the inverse Fourier Transform of a most significant eigenvector of transmission cross-coefficients that represent the optical path of an exposure tool;
computing the Fourier Transform of the mask layout;
multiplying the inverse Fourier Transform by the sum square of frequency and the Fourier Transform of the mask layout to produce a product; and
computing the inverse Fourier Transform of the product to produce the SRAF guidance map.
4. The method of claim 1 , wherein generating an SRAF guidance map comprises:
computing a bilinear SRAF guidance map kernel using the transmission cross-coefficients that represent the optical path of an exposure tool;
computing a linear SRAF guidance map kernel using the transmission cross-coefficients;
computing a partial SRAF guidance map using the bilinear SRAF guidance map kernel and the mask layout;
computing a second partial SRAF guidance map using the linear SRAF guidance map kernel and the mask layout; and
combining the partial SRAF guidance map and the second partial SRAF guidance map.
5. The method of claim 1 , further comprising generating SRAF placement rules using the SRAF guidance map.
6. The method of claim 1 , wherein the mask layout includes optical proximity corrections.
7. A non-transitory computer-readable storage medium including instructions for performing:
generating an SRAF guidance map for the mask layout, wherein the SRAF guidance map is an image in which each pixel value indicates whether the pixel would contribute positively to edge behavior of features in the mask layout if the pixel is included as part of a sub-resolution assist feature; and
placing sub-resolution assist features in the mask layout according to the SRAF guidance map,
wherein the instructions are executed by a computer, and
wherein generating an SRAF guidance map comprises:
computing an image gradient map of the mask layout; and
for each field point in the mask layout, computing a total vote sum for a unit source at the field point using the image gradient map.
8. The computer-readable storage medium of claim 7 , wherein generating an SRAF guidance map comprises:
assigning values in the SRAF guidance map, wherein the value at a pixel in the SRAF guidance map is the total vote sum at a corresponding field point in the mask layout.
9. The computer-readable storage medium of claim 8 , wherein computing a total vote sum for a unit source at the field point is performed in the frequency domain and includes:
computing the inverse Fourier Transform of a most significant eigenvector of transmission cross coefficients that represent the optical path of an exposure tool;
computing the Fourier Transform of the mask layout;
multiplying the inverse Fourier Transform by the sum square of frequency and the Fourier Transform of the mask layout to produce a product; and
computing the inverse Fourier Transform of the product to produce the SRAF guidance map.
10. The computer-readable storage medium of claim 7 , wherein generating an SRAF guidance map comprises:
computing a bilinear SRAF guidance map kernel using the transmission cross-coefficients that represent the optical path of an exposure tool;
computing a linear SRAF guidance map kernel using the transmission cross-coefficients;
computing a partial SRAF guidance map using the bilinear SRAF guidance map kernel and the mask layout;
computing a second partial SRAF guidance map using the linear SRAF guidance map kernel and the mask layout; and
combining the partial SRAF guidance map and the second partial SRAF guidance map.
11. The computer-readable storage medium of claim 7 , further comprising generating SRAF placement rules using the SRAF guidance map.
12. The computer-readable storage medium of claim 7 , wherein the mask layout includes optical proximity corrections.
13. A method for generating mask layout data, comprising:
including sub-resolution assist features in the mask layout data, wherein the sub-resolution assist features were placed according to an SRAF guidance map, wherein the SRAF guidance map is an image in which each pixel value indicates whether the pixel would contribute positively to edge behavior of features in the mask layout if the pixel is included as part of a sub-resolution assist feature, wherein generating an SRAF guidance map is generated by computing an image gradient map of the mask layout and, for each field point in the mask layout, computing a total vote sum for a unit source at the field point using the image gradient map.
14. The method for generating mask layout data of claim 13 , wherein the SRAF guidance map is generated by:
computing the inverse Fourier Transform of a most significant eigenvector of transmission cross coefficients that represent the optical path of an exposure tool;
computing the Fourier Transform of the mask layout;
multiplying the inverse Fourier Transform by the sum square of frequency and the Fourier Transform of the mask layout to produce a product; and
computing the inverse Fourier Transform of the product to produce the SRAF guidance map.
15. The method for generating mask layout data of claim 14 , wherein the initial mask layout includes optical proximity corrections.
16. A mask having a mask layout that includes sub-resolution assist features, wherein the sub-resolution assist features were placed according to an SRAF guidance map, wherein the SRAF guidance map is an image in which each pixel value indicates whether the pixel would contribute positively to through-focus and through-dose edge behavior of features in the mask layout if the pixel is included as part of a sub-resolution assist feature, wherein generating an SRAF guidance map is generated by computing an image gradient map of the mask layout and, for each field point in the mask layout, computing a total vote sum for a unit source at the field point using the image gradient map.