Method for correlating a structural parameter of a plurality of gratings and method for determining a structural parameter value of an unknown grating using the same
View Patent ↗A method for correlating a structural parameter of a plurality of gratings acquires images from a plurality of gratings, which have different structural parameters. A focus metrics algorithm is then performed to find the off-focus offset of the orders of each grating from the intensity variation of these images, and the variation ratio of the off-focus offset to the order for each grating is calculated later. Consequently, the structural parameters of these gratings can be correlated based on the variation ratio of the off-focus offset to the order. The present method acquires images from an unknown grating at different off-focus offsets, and performs a focus metrics algorithm to find the off-focus offset of the orders of the unknown grating. The variation ratio is calculated and the structural parameter of the unknown grating is determined based on the variation ratio.
1. A method for correlating a structural parameter of a plurality of predetermined gratings, comprising steps of:
acquiring a plurality of images from the predetermined gratings at a plurality of predetermined off-focus offsets, wherein the predetermined gratings have different structural parameter values;
performing a focus metrics algorithm to find the off-focus offsets corresponding to orders for each of the predetermined gratings;
calculating a variation ratio of the off-focus offsets to the orders for each of the predetermined gratings; and
correlating the variation ratio with the structural parameters of the predetermined gratings.
2. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 1 , wherein the step of acquiring a plurality of images from the predetermined gratings at a plurality of predetermined off-focus offsets uses a through focus image acquisition technique.
3. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 1 , wherein the focus metrics algorithm uses a standard variation method to calculate an intensity standard variation for each of the images.
4. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 3 , wherein the orders possess a local minimum value of the intensity standard variation.
5. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 1 , wherein the step of correlating the variation ratio with the structural parameter of the predetermined gratings is performed using a least square method.
6. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 1 , wherein the structural parameter is periodicity.
7. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 1 , wherein the structural parameter is pitch.
8. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 1 , wherein the structural parameter is thickness.
9. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 1 , wherein the structural parameter is line-to-space ratio.
10. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 1 , wherein the structural parameter is width.
11. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 10 , wherein the width is line width.
12. The method for correlating a structural parameter of a plurality of predetermined gratings according to claim 10 , wherein the width is critical dimension.
13. A method for determining a structural parameter value of an unknown grating, comprising steps of:
generating a relation formula of a structural parameter to a variation ratio from a plurality of predetermined gratings by correlating the structural parameter with the variation ratio of off-focus offsets to orders of the predetermined gratings having different structural parameter values;
acquiring a plurality of images from the unknown grating at a plurality of predetermined off-focus offsets;
performing a focus metrics algorithm on the images to find the off-focus offsets corresponding to the orders of the unknown gratings;
calculating a target variation ratio of the off-focus offsets to the orders of the unknown grating; and
deciding the structural parameter value of the unknown grating by substituting the target variation ratio into the relation formula.
14. The method for determining a structural parameter value of an unknown grating according to claim 13 , wherein the step of acquiring a plurality of images from the unknown grating at a plurality of predetermined off-focus offsets is performed uses focus image acquisition technique.
15. The method for determining a structural parameter value of an unknown grating according to claim 13 , wherein the focus metrics algorithm uses a standard variation method to calculate an intensity standard variation for each of the images.
16. The method for determining a structural parameter value of an unknown grating according to claim 15 , wherein the orders possess a local minimum value of the intensity standard variation.
17. The method for determining a structural parameter value of an unknown grating according to claim 13 , wherein the structural parameter is pitch.
18. The method for determining a structural parameter value of an unknown grating according to claim 13 , wherein the structural parameter is periodicity.
19. The method for determining a structural parameter value of an unknown grating according to claim 13 , wherein the structural parameter is thickness.
20. The method for determining a structural parameter value of an unknown grating according to claim 13 , wherein the structural parameter is line-to-space ratio.
21. The method for determining a structural parameter value of an unknown grating according to claim 13 , wherein the structural parameter is width.
22. The method for determining a structural parameter value of an unknown grating according to claim 21 , wherein the structural parameter is line width.
23. The method for determining a structural parameter value of an unknown grating according to claim 21 , wherein the structural parameter is critical dimension.
24. The method for determining a structural parameter value of an unknown grating according to claim 13 , wherein the step of generating a relation formula of a structural parameter to a variation ratio from a plurality of predetermined grating comprises:
acquiring a plurality of images from the predetermined gratings at a plurality of off-focus offsets;
performing a focus metrics algorithm on the images to find the off-focus offsets corresponding to the orders for each of the predetermined gratings;
calculating the variation ratio of the off-focus offsets to the orders for each of the predetermined gratings; and
correlating the structural parameter with the variation ratio to generate the relation formula.