Apparatus and methods for detecting overlay errors using scatterometry
Disclosed is a scatterometry mark for determining an overlay error, critical dimension, or profile of the mark. The mark includes a first plurality of periodic structures on a first layer, a second plurality of periodic structures on a second layer, and a third plurality of periodic structures on a third layer that is underneath the first and second layer. The third periodic structures are perpendicular to the first and second structures, and the third periodic structures have one or more characteristics so as to result in a plurality of lower structures beneath the third periodic structures being screened from significantly affecting at least part of a spectrum of a plurality of scattered signals detected from the first and second periodic structures for determining an overlay error, critical dimension, or profile of the first and second periodic structures or at least one of such detected scattered signals.
1. A scatterometry mark for determining an overlay error, critical dimension, or profile of the mark, comprising:
a first plurality of periodic structures on a first layer;
a second plurality of periodic structures on a second layer; and
a third plurality of periodic structures on a third layer that is underneath the first and second layer, wherein the third periodic structures are perpendicular to the first and second structures, and wherein the third periodic structures have one or more characteristics so as to result in a plurality of lower structures beneath the third periodic structures being screened from significantly affecting at least part of a spectrum of a plurality of scattered signals detected from the first and second periodic structures for determining an overlay error, critical dimension, or profile of the first and second periodic structures or at least one of such detected scattered signals.
2. A target as recited in claim 1 , wherein the third periodic structures comprise copper damascene materials.
3. The target of claim 2 , wherein the one or more characteristics of the third periodic structures comprise a pitch and line width that have values selected so as to result in the lower structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals.
4. The target of claim 2 , wherein the one or more characteristics of the third periodic structures comprise a pitch value selected so as to result in the third periodic structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals.
5. The target of claim 2 , wherein the one or more characteristics of the third periodic structures comprise a line width value selected so as to result in the lower structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals.
6. The target of claim 2 , wherein the one or more characteristics of the third periodic structures comprise a height value selected so as to result in the lower structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals.
7. The target of claim 2 , wherein the one or more characteristics of the third periodic structures comprise a pitch, line width, and line height that have values selected so as to result in the lower structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals.
8. The target of claim 1 , wherein there are a plurality of different predefined offsets between different sets of the first and second periodic structures so that overlay error between the first and second periodic structures is determinable by analyzing a plurality of scattered signals from the different sets of the first and second structures, wherein the detected scattered signals comprise +1st and −1 st diffraction orders.
9. The target of claim 1 , wherein the first periodic structures have a first center of symmetry (COS) and the second periodic structures have a second COS, and wherein the difference between the first COS and the second COS corresponds to an overlay error between the first and second periodic structures, and wherein the first and second periodic structures have a 180° rotational symmetry, without having a 90° rotational symmetry, with respect to the first and second COS, respectively.
10. A target structure for measuring an overlay error between a first periodic structure and a second periodic structure both disposed above a third periodic structure, wherein the third periodic structure is oriented in a first direction and the first and second periodic structures are oriented in a second direction, the second direction being substantially orthogonal to the first direction, wherein the third periodic structure is arranged to form a barrier over lower structures beneath the third periodic structures so that such lower structures do not significantly affect scattered radiation from the first and second periodic structures for measuring the overlay error.
11. The target of claim 10 , wherein the third periodic structures have a pitch and line width that have values selected so as to cause the third periodic structure to form the barrier over lower structures beneath the third periodic structures so that such lower structures do not significantly affect scattered radiation from the first and second periodic structures for measuring the overlay error.
12. The target of claim 10 , wherein there are a plurality of different predefined offsets between different sets of the first and second periodic structures so that overlay error between the first and second periodic structures is determinable by analyzing a plurality of scattered signals from the different sets of the first and second structures, wherein the detected scattered signals comprise +1st and −1 st diffraction orders.
13. A metrology system for measuring an overlay error, critical dimension (CD), or profile of a target, comprising:
a scatterometry module for directing radiation towards a plurality of targets and detecting scattered signals from the targets; and
a processor configured to analyze the detected scattered signals to thereby determine an overlay error, critical dimension (CD), or profile of such targets, wherein the targets comprise a first periodic structure and a second periodic structure both disposed above a third periodic structure, wherein the third periodic structure is oriented in a first direction and the first and second periodic structures are oriented in a second direction, the second direction being substantially orthogonal to the first direction, wherein the third periodic structure is arranged to form a barrier over lower structures beneath the third periodic structures so that such lower structures do not significantly affect the scattered signals from the first and second periodic structures and analyzed by the processor.
14. The system of claim 13 , wherein the targets from which the processor analyzes the detected scattered signals have one or more characteristics comprising a pitch and line width that have values selected so as to result in the lower structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals and analyzed by the processor.
15. The system of claim 14 , wherein the one or more characteristics of the third periodic structures comprise a pitch value selected so as to result in the third periodic structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals and analyzed by the processor.
16. The system of claim 14 , wherein the one or more characteristics of the third periodic structures comprise a line width value selected so as to result in the lower structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals and analyzed by the processor.
17. The system of claim 14 , wherein the one or more characteristics of the third periodic structures comprise a height value selected so as to result in the lower structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals and analyzed by the processor.
18. The system of claim 14 , wherein the one or more characteristics of the third periodic structures comprise a pitch, line width, and line height that have values selected so as to result in the lower structures being screened by the third periodic structures from significantly affecting at least part of a spectrum of the detected scattered signals or at least one of the detected scattered signals and analyzed by the processor.
19. The system of claim 14 , wherein the one or more materials of the third periodic structures include a copper damascene material.
20. The system of claim 13 , wherein there are a plurality of different predefined offsets between different sets of the first and second periodic structures so that overlay error between the first and second periodic structures is determinable by analyzing a plurality of scattered signals from the different sets of the first and second structures, wherein the detected scattered signals comprise +1st and −1 st diffraction orders.
21. A method of determining an overlay error, critical dimension, or profile of a scatterometry target, comprising:
providing a scatterometry target having a first plurality of periodic structures on a first layer, a second plurality of periodic structures on a second layer, and a third plurality of periodic structures on a third layer that is underneath the first and second layer, wherein the third periodic structures are perpendicular to the first and second structures and have one or more characteristics such that a scattered signal detected from the first and second periodic structures for determining an overlay error, critical dimension, or profile of the first and second periodic structures is substantially less sensitive to a plurality of lower structures beneath the third periodic structures, as compared with a plurality of scattered signals detected from the first and second periodic targets in the absence of such third structures;
using a metrology tool, directing radiation towards the target;
using a metrology tool, detecting scattered signals from the target so that the third periodic structures form a barrier over the lower structures beneath the third periodic structures so that such lower structures do not significantly affect the detected scattered signals from the first and second periodic structures; and
determining the overlay error, critical dimension, or profile of the first and second periodic structures based on the detected scattered signals.