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1. WO2020141071 - METHOD FOR CALIBRATING A SCANNING CHARGED PARTICLE MICROSCOPE

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[ EN ]

CLAIMS:

1. A method for calibrating a scanning electron microscope (SEM), comprising:

providing a reference sample including a first periodic structure interleaved with a second periodic structure, each of the first periodic structure and second periodic structure having a period along a measurement direction;

measuring, by the SEM, an offset between the first periodic structure and the second periodic structure;

comparing the measured offset with an induced offset; and

calibrating the SEM based on the comparison.

2. The method of claim 1, wherein the induced offset comprises an offset predefined for the reference sample.

3. The method of claim 2, wherein the induced offset further comprises an offset caused by an overlay error during a manufacturing process of the reference sample.

4. The method of claim 1 , wherein the induced offset is obtained by tracing using a laser interferometer.

5. The method of claim 1, wherein the offset measured by the SEM is based on an image of the reference sample obtained by the SEM, and wherein a left edge and a right edge of the first and second periodic structures on the image are asymmetrical.

6. The method of claim 1, wherein the first periodic structure and the second periodic structure are on different layers of the reference sample.

7. The method of claim 1, wherein each of the first periodic structure and the second periodic structure comprise a set of periodic lines.

8. The method of claim 1, further comprising:

tracing a critical dimension of the first and second periodic structures; and

measuring, by the SEM, the critical dimension of the first and second periodic structures, wherein calibrating the SEM further comprises calibrating the SEM based on a correlation between the measured critical dimension and the traced critical dimension of the first and second periodic structures.

9. The method claim 1, further comprising:

tracing a line width of the first periodic structure or the second periodic structure; and measuring, by the SEM, the line width of the first periodic structure or the second periodic structure,

wherein calibrating the SEM further comprises calibrating the SEM based on a correlation between the measured line width and the traced line width of the first periodic structure or the second periodic structure.

10. The method of claim 1, wherein:

the first periodic structure includes a first set of lines extending in a first direction and a second set of lines that are connected with the first set of lines and extending in a second direction; and

the second periodic structure includes a third set of lines extending in the first direction and a fourth set of lines that are connected with the third set of lines and extending in the second direction.

11. The method of claim 1 , wherein:

the first periodic structure further comprises a plurality of first periodic sub-structures disposed on different areas of the reference sample;

the second periodic structure further comprises a plurality of second periodic sub-structures disposed on different areas of the reference sample; and

each of the plurality of first periodic sub-structures is paired with a corresponding one of the plurality of second periodic sub-structures to form a plurality of pairs of first and second periodic sub structures for calibration.

12. A system for calibrating a scanning electron microscope (SEM), the system comprising: a stage configured to support a reference sample including a first periodic structure interleaved with a second periodic structure, the first and second periodic structures having an induced offset therebetween;

a laser interferometer;

the SEM; and

a controller configured to:

cause the laser interferometer to trace the induced offset between the first and second periodic structures;

cause the scanning electron microscope to measure the induced offset between the first and second periodic structures; and

compare the measured induced offset with the traced induced offset to perform the calibration.

13. The system of claim 12, wherein the induced offset comprises an offset predefined for the reference sample and an offset caused by an overlay error during a manufacturing process of the reference sample.

14. The system of claim 12, wherein the first periodic structure and the second periodic structure are on different layers of the reference sample

15. The system of claim 12, wherein the measured induced offset is obtained based on an image of the reference sample obtained by the SEM, and wherein a left edge and a right edge of the first and second periodic structures on the image are asymmetrical.