Method for measuring a sample and microscope implementing the method
The present invention relates to a method for measuring a sample with a microscope, the method comprising scanning the sample using a focusing plane having a first angle with respect to a top surface of the sample and computing a confidence distance based on the first angle. The method further comprises selecting at least one among a plurality of alignment markers on the sample for performing a lateral alignment of the scanning step and/or for performing a lateral alignment of an output of the scanning step. In particular, the at least one alignment marker selected at the selecting step is chosen among the alignment markers placed within the confidence distance from an intersection of the focusing plane with the top surface.
1. A method for measuring a sample with a microscope, the method comprising the steps of:
scanning the sample using a charged particle beam focused at a focusing plane having a first angle with respect to a top surface of the sample,
computing a confidence distance based on the first angle,
selecting at least one among a plurality of alignment markers on the sample for performing a lateral alignment of the scanning step and/or for performing a lateral alignment of an output of the scanning step,
wherein the at least one alignment marker selected at the selecting step is chosen among the alignment markers placed within the confidence distance from an intersection of the focusing plane with the top surface.
2. The method of claim 1 , wherein the first angle is bigger than 5 degrees, and/or smaller than 70 degrees.
3. The method of claim 1 ,
wherein the sample comprises at least a region with a slanted surface, the slanted surface having a second angle with respect to the top surface,
wherein the first angle and the second angle differ for at most 10 degrees and/or 10%.
4. The method of claim 1 ,
wherein the confidence distance is measured in a direction perpendicular to the intersection.
5. The method of claim 1 ,
wherein the confidence distance is measured in a direction parallel to the top surface.
6. The method of claim 1 ,
wherein the step of computing the confidence distance is based on a maximum tolerable defocusing value.
7. The method of claim 6 ,
wherein the maximum tolerable defocusing value is a maximum tolerable defocusing height.
8. The method of claim 1 ,
wherein the step of computing comprises computing
ConfDist= f (ϕ)
wherein
ϕ is the first angle,
ConfDist is the confidence distance,
f is a function which increases as ϕ decreases.
9. The method of claim 1 , further comprising the step of
marking the sample with one or more alignment markers.
10. The method of claim 9 ,
wherein the marking step comprises realizing one or more alignment markers within the confidence distance from the intersection.
11. The method of claim 9 ,
wherein the marking step comprises realizing one or more alignment markers such that a separation distance between two neighbouring alignment markers is
D≤ 2× h MAX /tan(ϕ)
wherein
D is the separation distance
ϕ is the first angle,
h MAX is a maximum tolerable defocusing height.
12. The method of claim 9 ,
wherein the marking step comprises realizing one or more alignment markers such that a separation distance between two neighbouring alignment markers is
D ≤2×ConfDist
wherein
D is the separation distance,
ConfDist is the confidence distance.
13. The method of claim 1 , further comprising the step of
milling the sample so as to realize one or more slanted surfaces in the sample.
14. The method of claim 13 , further comprising the step of marking the sample with one or more alignment markers, wherein the milling step and the marking step are implemented with the same component.
15. A microscope comprising
a controller, and
a memory,
wherein the memory stores instructions configured to cause the controller to control the microscope so as to execute the method of claim 1 .
16. A software product for a microscope, the product comprising instructions configured to cause a controller to control the microscope so as to execute the method of claim 1 .
17. The microscope of claim 15 , wherein the first angle is bigger than 5 degrees, and/or smaller than 70 degrees.
18. The microscope of claim 15 , wherein the sample comprises at least a region with a slanted surface, the slanted surface having a second angle with respect to the top surface,
wherein the first angle and the second angle differ for at most 10 degrees and/or 10%.
19. The microscope of claim 15 , wherein the confidence distance is measured in a direction perpendicular to the intersection.
20. The microscope of claim 15 , wherein the confidence distance is measured in a direction parallel to the top surface.
21. A method for measuring a sample with a microscope that has a focusing plane, the method comprising the steps of:
positioning the sample relative to the microscope such that the focusing plane has a first angle with respect to a top surface of the sample,
scanning the sample using the microscope with the focusing plane having the first angle with respect to the top surface of the sample,
computing a confidence distance based on the first angle, and
selecting at least one among a plurality of alignment markers on the sample for performing a lateral alignment of the scanning step and/or for performing a lateral alignment of an output of the scanning step,
wherein the at least one alignment marker selected at the selecting step is chosen among the alignment markers placed within the confidence distance from an intersection of the focusing plane with the top surface.
22. The method of claim 21 , wherein the microscope comprises an atomic force microscope.
23. The method of claim 1 , wherein the microscope comprises a scanning electron microscope or a helium-ion microscope.
24. The method of claim 2 , wherein the first angle is at least one of (i) bigger than 15 degrees, or (ii) smaller than 50 degrees.
25. The microscope of claim 17 , wherein the first angle is at least one of (i) bigger than 15 degrees, or (ii) smaller than 50 degrees.