Lateral shift measurement using an optical technique
Alignment of layers during manufacture of a multi-layer sample is controlled by applying optical measurements to a measurement site in the sample. The measurement site includes two diffractive structures located one above the other in two different layers, respectively. The optical measurements include at least two measurements with different polarization states of incident light, each measurement including illuminating the measurement site so as to illuminate one of the diffractive structures through the other. The diffraction properties of the measurement site are indicative of a lateral shift between the diffractive structures. The diffraction properties detected are analyzed for the different polarization states of the incident light to determine an existing lateral shift between the layers.
1. A structure configured for overlay measurement on a multi-layer sample, said structure comprising first and second test sites, each comprising a pair of diffractive structures of predetermined geometries located in different layers one above the other, wherein
each of the diffractive structures comprises a pattern of features aligned in a spaced-apart relationship along at least one X-axis and Y-axis,
the two diffractive structures in each of said first and second test sites are arranged with a predetermined lateral shift between the patterns in said diffractive structures, such that the diffractive structures in the first test site are arranged with a lateral shift of a predetermined value Δ in a first direction along one of said X-axis and Y-axes, and the diffractive structures in the second test site are arranged with a lateral shift of said value Δ along said one of the X- and Y-axes in a second opposite direction;
a difference between first and second measured diffraction signatures from the first and second test sites, respectively, providing an overlay measurement indicative of a lateral shift between said layers in the sample.
2. The structure according to claim 1 , wherein the patterns of features in said diffractive structures have same periodicity.
3. The structure according to claim 1 , wherein the diffractive structures of the pair located in a top layer of said different layers comprise the patterns of features formed by spaced-apart photoresist-containing regions, and the diffractive structures of the pair located in an underneath layer of said different layers comprise the patterns of features formed by spaced-apart aluminum-containing regions.
4. A multi-layer sample comprising a test structure configured as the structure of claim 1 .
5. A semiconductor wafer sample comprising a test structure configured as the structure of claim 1 .
6. The structure according to claim 1 , wherein the diffractive structures of the first and second test sites in the different layers comprise the patterns of features of different first and second materials, respectively.
7. A method for use in overlay measurements of a lateral shift between layers in a patterned region of a multi-layer sample, the method comprising: during manufacture of the patterned region in the sample, creating at least one test structure located in the sample outside said patterned region, and being configured as the structure of claim 1 with the predetermined intentionally induced lateral shift between the first and second test sites; such that a lateral shift between the layers in the patterned region introduced as an error in the manufacture of the sample is identifiable as a difference between diffraction signatures measured from the first and second test sites enhanced by said intentionally induced lateral shift between the first and second test sites.
8. The structure according to claim 6 , wherein each of the diffractive structures of the pair located in a top layer of said different layers comprises the pattern of features formed by spaced-apart photoresist-containing regions.
9. The structure according to claim 8 , wherein each of the diffractive structures of the pair located in an underneath layer of said different layers comprises the pattern of features formed by spaced-apart metal regions.
10. The method according to claim 7 , wherein the diffraction signature is formed by electromagnetic radiation diffracted from the pattern of features in the respective diffractive structure.
11. The method according to claim 10 , wherein said electromagnetic radiation is optical radiation.
12. The method according to claim 7 , wherein said multi-layer sample is a semiconductor wafer.
13. A multi-layer sample comprising at least one test structure configured for overlay measurement in said sample, the test structure comprising first and second test sites, each comprising a pair of diffractive structures of predetermined geometries located in different layers one above the other in said sample, each of the diffractive structures comprising a pattern of features aligned in a spaced-apart relationship along at least one X-axis and Y-axis, wherein
the two diffractive structures in each of said first and second test sites are arranged with a predetermined lateral shift between the patterns in said diffractive structures, such that the diffractive structures in the first test site are arranged with a lateral shift of a predetermined value Δ in a first direction along one of said X-axis and Y-axes, and the diffractive structures in the second test site are arranged with a lateral shift of said value Δ along said one of the X- and Y-axes in a second opposite direction, a difference between first and second measured diffraction signatures from the first and second test sites, respectively, providing an overlay measurement of a lateral shift between said layers in the sample.
14. The multi-layer sample according to claim 13 , comprising a patterned region, said at least one test structure being located outside said patterned region and being configured for the overlay measurements to correct alignment of the layers of the sample within said patterned region.
15. The multi-layer sample according to claim 13 , being a semiconductor wafer.