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 sample, said structure comprising a pair of diffractive structures having predetermined geometries and being arranged at locations relative to each other corresponding to alignment of layers in the sample, wherein
each of the diffractive structures of the pair comprises a diffractive pattern formed by features aligned along at least one axis,
the diffractive structures of the pair are arranged such that the features of one of the diffractive structures of the pair are located either above or between the features of the other diffractive structure of said pair, with a predetermined lateral shift between the diffractive patterns in the diffractive structures in accordance with a predetermined model of simulated diffraction effects from incident electromagnetic radiation interaction with laterally shifted diffractive structures of a pair of such structures of said predetermined geometries, thereby enabling direct overlay measurement of a lateral shift between the layers in the sample from diffraction of incident electromagnetic radiation from said pair of diffractive structures.
2. The structure according to claim 1 , wherein the features of said diffractive structures include lines.
3. The structure according to claim 1 , wherein each of said diffractive patterns includes a two-dimensional grating.
4. The structure according to claim 1 , wherein the diffractive patterns in the diffractive structures of the pair have same periodicity of the features.
5. The structure according to claim 1 , wherein each of the diffractive structures of the pair has a square profile.
6. The structure according to claim 1 , wherein the diffractive pattern of at least one of the diffractive structures of the pair comprises spaced-apart photoresist regions.
7. The structure according to claim 1 , wherein said predetermined lateral shift and said patterns in the diffractive structures which are selected in accordance with the predetermined model of simulated diffraction effects are based on Rigorous Couple Wave Theory.
8. The structure according to claim 1 , wherein said predetermined lateral shift and said patterns in the diffractive structures which are selected in accordance with the predetermined model of simulated diffraction effects are based on simulated parameters including critical dimensions of patterns in the sample, heights of said patterns, and additional parameters characterizing an individual pattern in layers of the sample.
9. The structure according to claim 1 , wherein said sample is a semiconductor wafer.
10. The structure according to claim 1 , wherein said sample is a multi-layer wafer, the structure being configured for overlay measurement between layers in the wafer sample.
11. The structure according to claim 1 , comprising at least one additional diffractive structure configured for measuring parameters of at least one of said diffractive structures of said pair.
12. The structure according to claim 1 , comprising at least one additional pair of diffractive structures.
13. The structure according to claim 11 , wherein the features of said diffractive structures include lines.
14. The structure according to claim 12 , wherein the features of said diffractive structures include lines.