Single-cell scatterometry overlay with sensitivity calibration
A metrology system may receive metrology data for a first set of overlay targets including at least two cells with different intended offsets. The system may further receive metrology data for a second set of overlay targets, where the metrology data for the second set of overlay targets is based on fewer cells than for the first set of overlay targets. The system may further generate sensitivity metrics at locations of the first set of overlay targets based on the metrology data for the first set of overlay targets, generate overlay measurements for the first set of overlay targets based on the sensitivity metrics and the metrology data from the first set of overlay targets, and generate overlay measurements for the first and second sets of overlay targets based on the sensitivity metrics and the metrology data from the second set of overlay targets.
1 . A metrology system comprising:
a controller communicatively coupled to a metrology sub-system, the metrology sub-system configured to illuminate a sample with an illumination beam and collect measurement light from the sample, the controller including one or more processors configured to implement a metrology recipe by executing program instructions causing the one or more processors to:
generate, via the metrology sub-system in accordance with the metrology recipe, metrology data associated with a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells with different intended offsets between overlapping features on two layers of a sample, wherein the metrology data associated with the first set of overlay targets is associated with separate pupil-plane measurements of intensities of two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets;
generate, via the metrology sub-system in accordance with the metrology recipe, metrology data associated with a second set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets;
generate sensitivity metrics at locations of the first set of overlay targets based on the metrology data associated with the first set of overlay targets, wherein the sensitivity metrics are generated per pixel associated with the pupil plane of the metrology sub-system based on one or more difference signals associated with differences between the pupil-plane measurements of the intensities of the two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets;
determine sensitivity metrics at locations of the second set of overlay targets, wherein the sensitivity metric for a particular location of a particular one of the second set of overlay targets is generated based on N nearest overlay targets in the first set of overlay targets, wherein a value of N is determined based on at least one of a rate of change of the sensitivity metric across the sample or a density of the first set of overlay targets; and
generate overlay measurements for the first set of overlay targets based on the metrology data associated with the first set of overlay targets; and
generate overlay measurements for the second set of overlay targets based on the metrology data associated with the second set of overlay targets and the sensitivity metrics at the locations of the second set of overlay targets.
2 . The metrology system of claim 1 , wherein the cells of at least one of the first or second sets of overlay targets are 180-degree rotationally symmetric.
3 . The metrology system of claim 1 , wherein the first set overlay targets includes two cells with different intended offsets, wherein the second set of overlay targets includes a single cell.
4 . The metrology system of claim 3 , wherein the cells of the first and second sets of overlay targets include grating-over-grating structures, wherein the metrology data for the first and second sets of overlay targets includes first-order diffraction from the respective cells.
5 . The metrology system of claim 1 , wherein the first set overlay targets includes four cells with different intended offsets, wherein the second set of overlay targets includes two of the cells with different intended offsets.
6 . The metrology system of claim 5 , wherein the cells of the first and second sets of overlay targets include grating-over-grating structures, wherein the metrology data for the first and second sets of overlay targets includes zero-order light from the respective cells.
7 . The metrology system of claim 1 , wherein the first set overlay targets and the second set of overlay targets have a common number of cells, wherein the metrology data associated with the second set of overlay targets is based on a subset of the cells.
8 . The metrology system of claim 1 , wherein the generating the overlay measurements for the first and second sets of overlay targets based on the sensitivity metrics and the metrology data from the second set of overlay targets comprises:
calculating the sensitivity metrics at locations of the second set of overlay targets based on the sensitivity metrics at the locations of the first set of overlay targets.
9 . The metrology system of claim 1 , wherein the cells of the first and second sets of overlay targets include grating-over-grating structures, wherein constituent gratings of the grating-over-grating structures have a common pitch.
10 . The metrology system of claim 9 , wherein the metrology data associated with any of the grating-over-grating structures includes metrology data associated with positive first-order diffraction (I +1 ) and negative first-order diffraction (I −1 ).
11 . The metrology system of claim 10 , wherein the metrology data associated with the positive first-order diffraction (I +1 ) and the negative first-order diffraction (I −1 ) is captured in the pupil plane.
12 . The metrology system of claim 1 , wherein each of the first set of overlay targets includes a first grating-over-grating structure with a first intended offset (f 1 ) and a second grating-over-grating structure with a second intended offset (f 2 ), wherein the metrology data associated with each of the first set of overlay targets includes positive first-order diffraction
(
I
+
1
f
1
)
from the first grating-over-grating structure, negative first-order diffraction
(
I
-
1
f
1
)
from the first grating-over-grating structure, positive first-order diffraction
(
I
+
1
f
2
)
from the second grating-over-grating structure, and negative first-order diffraction
(
I
-
1
f
2
)
from the second grating-over-grating structure.
13 . The metrology system of claim 12 , wherein the first intended offset (f 1 ) and the second intended offset (f 2 ) have equal magnitudes and opposite directions such that f 1 =f 0 and f 2 =−f 0 .
14 . The metrology system of claim 13 , wherein the sensitivity metric (G) for a particular one of the first set of overlay targets is calculated as
G
=
D
+
f
0
-
D
-
f
0
2
f
0
,
where
D
+
f
0
=
I
+
1
+
f
0
-
I
-
1
+
f
0
2
and
D
-
f
0
=
I
+
1
-
f
0
-
I
-
1
-
f
0
2
based on the metrology data associated with the particular one of the first set of overlay targets.
15 . The metrology system of claim 14 , wherein an overlay measurement (OVL) for the particular one of the first set of overlay targets is calculated as
OVL
=
P
2
π
tan
-
1
(
K
G
tan
(
2
π
f
0
P
)
)
,
where
K
=
D
+
f
0
+
D
-
f
0
2
.
16 . The metrology system of claim 1 , wherein the sensitivity metrics are independent of physical overlay at the locations of the first set of overlay targets.
17 . The metrology system of claim 16 , wherein the sensitivity metrics correspond to a linear response of the metrology data in response to variations of the physical overlay at the locations of the first set of overlay targets.
18 . The metrology system of claim 1 , wherein the second set of overlay targets is larger than the first set of overlay targets.
19 . The metrology system of claim 1 , wherein the program instructions are further configured to cause the one or more processors to provide correctibles for controlling an exposure tool based on the overlay measurements for the first and second sets of overlay targets.
20 . A metrology system comprising:
a metrology sub-system configured to generate metrology data associated with a sample, wherein the metrology sub-system is configured to illuminate a sample with at least one illumination beam from an illumination source and direct measurement light from the sample onto one or more detectors using one or more lenses; wherein the metrology sub-system is configured to implement a metrology recipe by:
generating metrology data associated with a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells with different intended offsets between overlapping features on two layers of the sample, wherein the metrology data associated with the first set of overlay targets is associated with separate pupil-plane measurements of intensities of two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets; and
generating metrology data associated with a second set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets; and
a controller communicatively coupled to the metrology sub-system, the controller including one or more processors configured to execute program instructions causing the one or more processors to:
receive, from the metrology sub-system in accordance with the metrology recipe, metrology data associated with the first set of overlay targets;
receive metrology data associated with the second set of overlay targets;
generate sensitivity metrics at locations of the first set of overlay targets based on the metrology data associated with the first set of overlay targets, wherein the sensitivity metrics are generated per pixel associated with the pupil plane of the metrology sub-system based on one or more difference signals associated with differences between the pupil-plane measurements of the intensities of the two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets;
determine sensitivity metrics at locations of the second set of overlay targets, wherein the sensitivity metric for a particular location of a particular one of the second set of overlay targets is generated based on N nearest overlay targets in the first set of overlay targets, wherein a value of N is determined based on at least one of a rate of change of the sensitivity metric across the sample or a density of the first set of overlay targets;
generate overlay measurements for the first set of overlay targets based on the sensitivity metrics and the metrology data associated with the first set of overlay targets; and
generate overlay measurements for the second set of overlay targets based on the metrology data associated with the second set of overlay targets and the sensitivity metrics at the locations of the second set of overlay targets.
21 . The metrology system of claim 20 , wherein the generating the overlay measurements for the first and second sets of overlay targets based on the sensitivity metrics and the metrology data from the second set of overlay targets comprises:
calculating the sensitivity metrics at locations of the second set of overlay targets based on the sensitivity metrics at the locations of the first set of overlay targets.
22 . The metrology system of claim 20 , wherein the cells of the first and second sets of overlay targets include grating-over-grating structures, wherein the grating-over-grating structures have a common pitch.
23 . The metrology system of claim 22 , wherein the metrology data associated with any of the grating-over-grating structures includes data associated with positive first-order diffraction (I +1 ) and negative first-order diffraction (I −1 ).
24 . The metrology system of claim 23 , wherein the metrology data associated with the positive first-order diffraction (I +1 ) and the negative first-order diffraction (I −1 ) is resolved in the pupil plane.
25 . The metrology system of claim 20 , wherein the program instructions are further configured to cause the one or more processors to provide correctibles for controlling an exposure tool based on the overlay measurements for the first and second sets of overlay targets.
26 . A method comprising:
generating, with a metrology sub-system in accordance with a metrology recipe, metrology data associated with a first set of overlay targets and a second set of overlay targets on a sample, wherein each of the first set of overlay targets includes at least two cells with different intended offsets between overlapping features on two layers of the sample, wherein the metrology data associated with the first set of overlay targets is associated with separate pupil-plane measurements of intensities of two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets;
generating sensitivity metrics at locations of the first set of overlay targets based on the metrology data associated with the first set of overlay targets, wherein the sensitivity metrics are generated per pixel associated with the pupil plane of the metrology sub-system based on one or more difference signals associated with differences between the pupil-plane measurements of the intensities of the two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets;
determining sensitivity metrics at locations of the second set of overlay targets, wherein the sensitivity metric for a particular location of a particular one of the second set of overlay targets is generated based on N nearest overlay targets in the first set of overlay targets, wherein a value of N is determined based on at least one of a rate of change of the sensitivity metric across the sample or a density of the first set of overlay targets;
generating overlay measurements for the first set of overlay targets based on the sensitivity metrics and the metrology data associated with the first set of overlay targets; and
generating overlay measurements for the second set of overlay targets based on the metrology data associated with the second set of overlay targets and the sensitivity metrics at the locations of the second set of overlay targets.
27 . The metrology method of claim 26 , further comprising:
providing correctibles for controlling an exposure tool based on the overlay measurements for the first and second sets of overlay targets.
28 . A sample comprising:
a plurality of overlay targets distributed across a plurality of fields, wherein the plurality of overlay targets comprises:
a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells with different intended offsets between overlapping features on two layers of the sample; and
a second set of overlay targets, wherein each of the second set of overlay targets includes fewer cells than the first set of overlay targets
wherein the first set of overlay targets and the second set of overlay targets are distributed across the sample such that a sensitivity metric for a particular location of a particular one of the second set of overlay targets is determinable based on N nearest overlay targets in the first set of overlay targets, wherein a value of N is based on at least one of a rate of change of the sensitivity metric across the sample or a density of the first set of overlay targets;
wherein a distribution of the first set of overlay targets and the second set of overlay targets is configured to provide that overlay measurements for the second set of overlay targets are determinable based on metrology data associated with the second set of overlay targets and sensitivity metrics generated per pixel associated with a pupil plane of a metrology sub-system based on metrology data associated with separate pupil-plane measurements of intensities by the metrology sub-system of two or more diffraction orders of an illumination beam by the first set of overlay targets provides overlay measurements at locations of the first set of overlay targets; and
wherein metrology data associated with diffraction by the second set of overlay targets and sensitivity metrics from the metrology data associated with the first set of overlay targets provides overlay measurements at locations of the second set of overlay targets, wherein the sensitivity metrics are generated per pixel associated with a pupil plane of a metrology sub-system based on metrology data associated with separate pupil-plane measurements of intensities by the metrology sub-system of two or more diffraction orders of an illumination beam by the first set of overlay targets provides overlay measurements at locations of the first set of overlay targets.