Metrology methods and targets are provided, that expand metrological procedures beyond current technologies into multi-layered targets, quasi-periodic targets and device-like targets, without having to introduce offsets along the critical direction of the device design. Machine learning algorithm application to measurements and/or simulations of metrology measurements of metrology targets are disclosed for deriving metrology data such as overlays from multi-layered target and corresponding configurations of targets are provided to enable such measurements. Quasi-periodic targets which are based on device patterns are shown to improve the similarity between target and device designs. Offsets are introduced only in non-critical direction and/or sensitivity is calibrated to enable, together with the solutions for multi-layer measurements and quasi-periodic target measurements, direct device optical metrology measurements.

A method of determining a measurement subset of metrology point locations which includes a subset of potential metrology point locations on a substrate. The method including identifying a plurality of candidate metrology point locations from the potential metrology point locations. A change in the level of informativity imparted by the measurement subset of metrology point locations which is attributable to the inclusion of that candidate metrology point location into the measurement subset of metrology point locations is evaluated for each of the candidate metrology point locations. The candidate metrology point locations which have the greatest increase in the level of informativity attributed thereto are selected for inclusion into the measurement subset of metrology point locations.

A structure in semiconductor fabrication includes at least a first periodic asymmetric feature and a periodic asymmetric second feature. The first feature contains a plurality of periodically distributed first elements. The first feature has a first asymmetric profile such that the first feature no longer has the same first asymmetric profile when it is rotated by 180 degrees. The second feature contains a plurality of periodically distributed second elements. The second feature has a second asymmetric profile such that the second feature no longer has the same second asymmetric profile when it is rotated by 180 degrees. The second asymmetric profile is different from the first asymmetric profile.

According to one embodiment, wafer lithography equipment includes an exposure unit transferring a circuit pattern onto a wafer, a measurement unit measuring a dimension of the circuit pattern and a calculator. The calculator includes calculating a first difference. The first difference is the difference between a first dimension and a second dimension. The first dimension is obtained by substituting a first exposure amount and a first focus distance into an approximate response surface function. The second dimension is measured by the measurement unit. The calculator also includes calculating a second difference. The second difference is the sum total of the first difference for all of the circuit patterns. The calculator also includes calculating a second exposure amount and a second focus distance causing the difference between the approximate response surface function and the second difference to be a minimum. The calculator also includes calculating a correction exposure amount.

A method of determining overlay of a patterning process, the method including: illuminating a substrate with a radiation beam such that a beam spot on the substrate is filled with one or more physical instances of a unit cell, the unit cell having geometric symmetry at a nominal value of overlay; detecting primarily zeroth order radiation redirected by the one or more physical instances of the unit cell using a detector; and determining, by a hardware computer system, a non-nominal value of overlay of the unit cell from values of an optical characteristic of the detected radiation.

A diffraction measurement target that has at least a first sub-target and at least a second sub-target, and wherein (1) the first and second sub-targets each include a pair of periodic structures and the first sub-target has a different design than the second sub-target, the different design including the first sub-target periodic structures having a different pitch, feature width, space width, and/or segmentation than the second sub-target periodic structure or (2) the first and second sub-targets respectively include a first and second periodic structure in a first layer, and a third periodic structure is located at least partly underneath the first periodic structure in a second layer under the first layer and there being no periodic structure underneath the second periodic structure in the second layer, and a fourth periodic structure is located at least partly underneath the second periodic structure in a third layer under the second layer.

Disclosed is a method of measuring focus performance of a lithographic apparatus. The method comprises using the lithographic apparatus to print at least one focus metrology pattern on a substrate, the printed focus metrology pattern comprising at least a first periodic array of features, and using inspection radiation to measure asymmetry between opposite portions of a diffraction spectrum for the first periodic array in the printed focus metrology pattern. A measurement of focus performance is derived based at least in part on the asymmetry measured. The first periodic array comprises a repeating arrangement of a space region having no features and a pattern region having at least one first feature comprising sub-features projecting from a main body and at least one second feature; and wherein the first feature and second feature are in sufficient proximity to be effectively detected as a single feature during measurement. A patterning device comprising said first periodic array is also disclosed.

A method of determining overlay of a patterning process, the method including: obtaining a detected representation of radiation redirected by one or more physical instances of a unit cell, wherein the unit cell has geometric symmetry at a nominal value of overlay and wherein the detected representation of the radiation was obtained by illuminating a substrate with a radiation beam such that a beam spot on the substrate was filled with the one or more physical instances of the unit cell; and determining, from optical characteristic values from the detected radiation representation, a value of a first overlay for the unit cell separately from a second overlay for the unit cell that is also obtainable from the same optical characteristic values, wherein the first overlay is in a different direction than the second overlay or between a different combination of parts of the unit cell than the second overlay.

An overlay alignment mark, a method for measuring overlay error, and a method for overlay alignment are provided in the embodiments of the present disclosure. the overlay alignment mark is formed on a wafer to be detected and comprises a first pattern and a second pattern, the first pattern being located in a first layer of the wafer and comprising two first solid sub-patterns which are provided opposite to each other in a first direction and extend in a second direction perpendicular to the first direction, respectively, and the second pattern being located in a second layer above the first layer of the wafer and comprising two first hollowed sub-patterns which are provided opposite to each other in the first direction and two to second hollowed sub-patterns which are provided opposite to each other in the second direction; and two opposite side edges of each of the two first solid sub-patterns extending in the second direction are at least partially exposed from a respective one of the two first hollowed sub-patterns.

An overlay alignment mark located in a patterned wafer and a method for measuring overlay error are provided, the patterned wafer having a lower-layer pattern in a first layer thereof and an upper-layer pattern in a second layer thereof above the first layer, the overlay alignment mark comprising: a first pattern, which is a portion of the lower-layer pattern and comprises a pair of solid features formed in the first layer; and a second pattern, which is a portion of the upper-layer pattern and comprises two pairs of hollowed features formed in the second layer, with two imaginary lines connecting between geometric centers of respective pairs in the two pairs of hollowed features extending in two mutually orthogonal directions, respectively; an orthographic projection of the pair of solid features on the wafer at least partially overlaps with an orthographic projection of a respective pair of hollowed features on the wafer.