Technique for measuring overlay between layers of a multilayer structure
A method for determining overlay between layers of a multilayer structure may include obtaining a given image representing the multilayer structure, obtaining expected images for layers of the multilayer structure, providing a combined expected image of the multilayer structure as a combination of the expected images of said layers, performing registration of the given image against the combined expected image, and providing segmentation of the given image, thereby producing a segmented image, and maps of the layers of said multilayered structure. The method may further include determining overlay between any two selected layers of the multilayer structure by processing the maps of the two selected layers together with the expected images of said two selected layers.
1. A method for determining overlay between layers of a multilayer structure, the method comprising:
obtaining a given image representative of the multilayer structure;
obtaining expected images of layers of the multilayer structure;
generating, based on the expected images, a combined expected image of the multilayer structure;
registering the given image against the combined expected image;
generating segmentation data for the given image;
computing an overlay measurement between two layers of the multilayer structure; and
correcting the segmentation data based on the computed overlay measurement.
2. The method according to claim 1 , further comprising:
re-computing the overlay measurement using the corrected segmentation data.
3. The method according to claim 1 , wherein one or more of the expected images of the layers or the combined expected image are design images processed by simulation.
4. The method according to claim 1 , further comprising:
determining safe areas on the expected images based on probable occlusions and distortions between the expected images and the given image.
5. The method according to claim 4 , wherein the overlay measurement is computed based on the determined safe areas.
6. The method according to claim 1 , wherein the computing the overlay measurement comprises, for each of the two layers:
performing per-layer registration between a map of a specific layer with the corresponding expected image of the specific layer;
measuring a shift of a specific layer by comparing the map of the specific layer with the corresponding expected image of the specific layer to determine two shifts of the two layers respectively; and
computing the overlay measurement between the two layers as a difference between the two shifts.
7. The method according to claim 1 , wherein the multilayer structure is a three-dimensional integrated circuit, and wherein the given image is a scanning electron micrograph of the three-dimensional integrated circuit.
8. A system for image processing comprising:
a memory to store a given image of a multilayer structure and expected images of layers of the multilayer structure; and
a processor to:
obtain a given image representative of the multilayer structure;
obtain expected images of layers of the multilayer structure;
generate, based on the expected images, a combined expected image of the multilayer structure;
register the given image against the combined expected image;
generate segmentation data for the given image;
compute an overlay measurement between two layers of the multilayer structure; and
correct the segmentation data based on the computed overlay measurement.
9. The system according to claim 8 , wherein the processor is further to:
re-compute the overlay measurement using the corrected segmentation data.
10. The system according to claim 8 , wherein one or more of the expected images of the layers or the combined expected image are design images processed by simulation.
11. The system according to claim 8 , wherein the processor is further to:
determine safe areas on the expected images based on probable occlusions and distortions between the expected images and the given image.
12. The system according to claim 11 , wherein the overlay measurement is to be computed based on the determined safe areas.
13. The system according to claim 8 , wherein to compute the overlay measurement, the processor is further to, for each of the two layers:
perform per-layer registration between a map of a specific layer with the corresponding expected image of the specific layer;
measure a shift of a specific layer by comparing the map of the specific layer with the corresponding expected image of the specific layer to determine two shifts of the two layers respectively; and
compute the overlay measurement between the two layers as a difference between the two shifts.
14. The system according to claim 8 , wherein the multilayer structure is a three-dimensional integrated circuit, and wherein the given image is a scanning electron micrograph of the three-dimensional integrated circuit.
15. A non-transitory computer-readable medium on which program instructions are stored, which instructions, when read by a processor, cause the processor to:
obtain a given image representative of a multilayer structure;
obtain expected images of layers of the multilayer structure;
generate, based on the expected images, a combined expected image of the multilayer structure;
register the given image against the combined expected image;
generate segmentation data for the given image;
compute an overlay measurement between two layers of the multilayer structure; and
correct the segmentation data based on the computed overlay measurement.
16. The non-transitory computer-readable medium according to claim 15 , wherein the program instructions further cause the processor to:
re-compute the overlay measurement using the corrected segmentation data.
17. The non-transitory computer-readable medium according to claim 15 , wherein one or more of the expected images of the layers or the combined expected image are design images processed by simulation.
18. The non-transitory computer-readable medium according to claim 15 , wherein the program instructions further cause the processor to:
determine safe areas on the expected images based on probable occlusions and distortions between the expected images and the given image, wherein the overlay measurement is to be computed based on the determined safe areas.
19. The non-transitory computer-readable medium according to claim 15 , wherein to compute the overlay measurement, the program instructions further cause the processor to, for each of the two layers:
perform per-layer registration between a map of a specific layer with the corresponding expected image of the specific layer;
measure a shift of a specific layer by comparing the map of the specific layer with the corresponding expected image of the specific layer to determine two shifts of the two layers respectively; and
compute the overlay measurement between the two layers as a difference between the two shifts.
20. The non-transitory computer-readable medium according to claim 15 , wherein the multilayer structure is a three-dimensional integrated circuit, and wherein the given image is a scanning electron micrograph of the three-dimensional integrated circuit.