Photo-mask acceptance technique
View Patent ↗A technique for calculating a second aerial image associated with a photo-mask that can be used to determine whether or not the photo-mask (which may include defects) is acceptable for use in a photolithographic process is described. In particular, using a first aerial image produced by the photo-mask when illuminated using a source pattern and an inspection image of the photo-mask, a mask pattern corresponding to the photo-mask is determined. For example, the first aerial image may be obtained using an aerial image measurement system, and the inspection image may be a critical-dimension scanning-electron-microscope image of the photo-mask. This image, which has a higher resolution than the first aerial image, may indicate spatial-variations of a magnitude of the transmittance of the photo-mask. Then, the second aerial image may be calculated based on the determined mask pattern using a different source pattern than the source pattern.
1. A computer-implemented method for calculating an aerial image, comprising:
receiving a first aerial image associated with a photo-mask illuminated by a first source pattern, wherein the photo-mask corresponds to a mask pattern, and wherein the photo-mask can include defects;
determining, using a computer, the mask pattern based on the first aerial image and a first inspection image of the photo-mask, wherein the first inspection image has a higher resolution than the first aerial image, and wherein the first inspection image includes a spatial-variation of a magnitude of transmittance of the photo-mask; and
calculating a second aerial image based on the determined mask pattern and a second source pattern that illuminates the determined mask pattern in calculation of the second aerial image, wherein the second source pattern is different from the first source pattern.
2. The method of claim 1 , wherein the first aerial image is associated with an aerial image measurement system.
3. The method of claim 1 , wherein the first aerial image is measured under conditions associated with a photolithographic process; and
wherein the second aerial image is calculated using the conditions.
4. The method of claim 1 , wherein the defects include a deviation in a magnitude of the transmittance of the photo-mask from that associated with a target mask pattern; and
wherein the target mask pattern excludes the defects.
5. The method of claim 1 , wherein the defects include a deviation in a phase of the transmittance of the photo-mask from that associated with a target mask pattern; and
wherein the target mask pattern excludes the defects.
6. The method of claim 1 , wherein the first inspection image includes a critical-dimension scanning-electron-microscope image of the photo-mask.
7. The method of claim 1 , wherein the second source pattern includes a pixilated source pattern.
8. The method of claim 1 , wherein the first source pattern includes one of a predefined group of source patterns; and
wherein the second source pattern includes an arbitrary source pattern.
9. The method of claim 1 , wherein the mask pattern is determined using an inverse optical calculation based on information about an optical path associated with an imaging system that measured the first aerial image.
10. The method of claim 9 , wherein the second aerial image is calculated using a forward optical calculation based on the information about the optical path.
11. The method of claim 1 , wherein the mask pattern is determined based on a target mask pattern that excludes the defects.
12. The method of claim 1 , wherein the method further comprises calculating an estimated resist pattern based on the second aerial image and a model of a photoresist in a photolithographic process.
13. The method of claim 12 , wherein the method further comprises:
identifying differences between the estimated resist pattern and a target pattern; and
determining an acceptance condition of the photo-mask based on the identified differences.
14. The method of claim 1 , wherein the second aerial image is further determined based on a forward optical calculation associated with a recovered inspection image;
wherein the recovered inspection image is determined from a second inspection image associated with the photo-mask and a target mask pattern that excludes the defects; and
wherein the recovered inspection image is characterized by additional spatial frequencies than the second inspection image.
15. The method of claim 14 , wherein the second inspection image has a lower resolution than the first inspection image.
16. The method of claim 14 , wherein the recovered inspection image is determined using an inverse optical calculation based on information about an optical path associated with an imaging system that measured the second inspection image.
17. The method of claim 1 , wherein the method further comprises receiving a set of first aerial images, which include the first aerial image; and
wherein the set of first aerial images are associated with different focal conditions in an imaging system that measured the set of first aerial images; and
wherein the mask pattern is determined using the set of first aerial images.
18. The method of claim 1 , wherein the method further comprises:
identifying differences between the second aerial image and a target pattern; and
determining an acceptance condition of the photo-mask based on the identified differences.
19. A non-transitory computer-program product for use in conjunction with a computer system, the computer-program product comprising a computer-readable storage medium and a computer-program mechanism embedded therein to calculate an aerial image, the computer-program mechanism including:
instructions for receiving a first aerial image associated with a photo-mask illuminated by a first source pattern, wherein the photo-mask corresponds to a mask pattern, and wherein the photo-mask can include defects;
instructions for determining the mask pattern based on the first aerial image and a first inspection image of the photo-mask, wherein the first inspection image has a higher resolution than the first aerial image, and wherein the first inspection image includes a spatial-variation of a magnitude of transmittance of the photo-mask; and
instructions for calculating a second aerial image based on the determined mask pattern and a second source pattern that illuminates the determined mask pattern in calculations of the second aerial image, wherein the second source pattern is different from the first source pattern.
20. A computer system, comprising:
at least one processor;
at least one memory; and
at least one program module, the program module stored in the memory and configured to be executed by the processor to calculate an aerial image, the program module including:
instructions for receiving a first aerial image associated with a photo-mask illuminated by a first source pattern, wherein the photo-mask corresponds to a mask pattern, and wherein the photo-mask can include defects;
instructions for determining the mask pattern based on the first aerial image and a first inspection image of the photo-mask, wherein the first inspection image has a higher resolution than the first aerial image, and wherein the first inspection image includes a spatial-variation of a magnitude of transmittance of the photo-mask; and
instructions for calculating a second aerial image based on the determined mask pattern and a second source pattern that illuminates the determined mask pattern in calculations of the second aerial image, wherein the second source pattern is different from the first source pattern.