Metrology method and apparatus
Disclosed is a method for measuring alignment on an alignment mark, and associated apparatuses. The method comprises illuminating the alignment mark with illumination comprising at least one wavelength; capturing the scattered radiation scattered from the alignment mark as a result of said illumination step, and determining at least one position value for said alignment mark from an angularly resolved representation of said scattered radiation, wherein said alignment mark, or a feature thereof, is smaller than said at least one wavelength in at least one dimension of a substrate plane.
1 . A method for measuring alignment on an alignment mark, the method comprising:
illuminating the alignment mark with illumination comprising at least one wavelength, wherein the illumination comprises coherent illumination;
capturing scattered radiation scattered from the alignment mark as a result of the illumination, wherein the scattered radiation, includes a zeroth order component and is directed to a balanced detector or differential detector; and
determining at least one position value for the alignment mark from an angle-resolved scatterometry measurement using the scattered radiation;
wherein the alignment mark, or a feature thereof, is smaller than the at least one wavelength in at least one dimension of a substrate plane.
2 . The method as claimed in claim 1 , wherein the determining at least one position value comprises determining the at least one position value from measurement of balance or symmetry in the angle-resolved scatterometry measurement.
3 . The method as of claim 1 , further comprising:
scanning the illumination over the alignment mark, and
determining the at least one position value from a zero crossing of an alignment signal determined from the angle-resolved scatterometry measurement.
4 . The method of claim 1 , wherein the determining at least one position value comprises determining a first position value for a first dimension of the substrate plane and a second position value for a second dimension of the substrate plane.
5 . The method of claim 4 , further comprising:
scanning the illumination obliquely over the alignment mark;
determining the first position value from a zero crossing of a first alignment signal determined from the angle-resolved scatterometry measurement; and
determining the second position value from a zero crossing of a second alignment signal determined from the angle-resolved scatterometry measurement.
6 . The method of claim 5 , wherein the first alignment signal is determined from a first combination of quadrants of the angle-resolved scatterometry measurement and the second alignment signal is determined from a second combination of quadrants of the angle-resolved scatterometry measurement.
7 . The method of claim 1 , wherein the alignment mark is a functional product structure.
8 . The method of claim 1 , wherein the alignment mark is surrounded by a contrasting region, the contrasting region optically contrasting the alignment mark.
9 . The method of claim 8 , wherein the alignment mark comprises a structure.
10 . The method of claim 9 , wherein the contrasting region is an empty region.
11 . The method of claim 8 , wherein the alignment mark is an empty region.
12 . The method of claim 11 , wherein the contrasting region comprises exposed dummy structure.
13 . The method of claim 1 , wherein the alignment mark is partially or completely surrounded by auxiliary features.
14 . The method of claim 1 , wherein a target is smaller than the wavelength in both dimensions of the substrate plane.
15 . The method of claim 1 , wherein the alignment mark comprises a line, or a pair of orthogonal lines.
16 . The method of claim 1 , wherein the alignment mark comprises a periodic alignment mark comprising repetitions of features, wherein each feature is smaller than the wavelength in at least one dimension of the substrate plane.
17 . The method of claim 16 , wherein one or more features of the alignment mark comprise broken features having one or more gaps.
18 . The method of claim 16 , wherein the alignment mark mimics actual product structure.
19 . The method of claim 1 , wherein the alignment mark is symmetrical in at least one dimension of the substrate plane.
20 . The method of claim 1 , wherein the alignment mark is located within-die.
21 . The method of claim 1 , wherein the at least one dimension of the alignment mark is no more than two orders of magnitude different to a critical dimension of product structure on a same substrate as the alignment mark.
22 . The method of claim 1 , wherein the at least one dimension of the alignment mark is of the same order of magnitude as a critical dimension of product structure on a same substrate as the alignment mark.
23 . The method of claim 1 , further comprising measuring a plurality of the alignment marks simultaneously.
24 . The method of claim 23 , further comprising illuminating each of the alignment marks with a respective beam of the illumination; and
capturing and processing respective scattered radiation from each alignment mark to determine a respective position value.
25 . A coherent Fourier scatterometer being operable to perform the method of claim 1 .
26 . An alignment sensor configured to perform the method of claim 1 .
27 . A lithographic apparatus comprising the alignment sensor of claim 26 .