Method for calibrating a scanning charged particle microscope
A method for calibrating a scanning charged particle microscope, such as a scanning electron microscope (SEM), is provided. The method includes dividing a wafer into a plurality of regions; preparing, on each of the plurality of regions, a pattern including a first periodic structure interleaved with a second periodic structure, the first and second periodic structures having an induced offset; determining an actual pitch the first and second periodic structures and thereby determining actual induced offset on each of the plurality of regions; selecting a plurality of regions from among the plurality of regions; measuring, by the SEM, a pitch of first and second periodic structures on each of the plurality of regions; and performing linearity calibration on the SEM based on the determining and the measuring.
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.