Method of assessing a model of a substrate, an inspection apparatus and a lithographic apparatus
A method of assessing a model of a substrate is presented. A scatterometry measurement is taken using radiation at a first wavelength. The wavelength of the radiation is then changed and a further scatterometry measurement taken. If the scatterometry measurements are consistent across a range of wavelengths then the model is sufficiently accurate. However, if the scatterometry measurements change as the wavelength changes then the model of the substrate is not sufficiently accurate.
1. A method comprising:
taking a first scatterometry measurement of a substrate using a first characteristic value of radiation comprising a known characteristic;
determining a first value of a characteristic of a feature of the substrate or a first residual using the first scatterometry measurement;
taking a second scatterometry measurement using a second characteristic value of the radiation;
determining a second value of the characteristic of the feature of the substrate or a second residual using the second scatterometry measurement; and
comparing the first value and the second value of the characteristic of the feature or the first residual and the second residual to determine an accuracy of a model of the feature of the substrate.
2. The method according to claim 1 , further comprising changing a value of the characteristic of the radiation to a third value.
3. The method according to claim 1 , further comprising:
taking a third scatterometry measurement using the third characteristic value of the radiation; and
determining a third value of the characteristic of the feature using the third scatterometry measurement;
comparing the first, second, and third values of the characteristic of the feature of the substrate.
4. The method according to claim 2 , further comprising changing the value of the characteristic of the radiation to a fourth value.
5. The method according to claim 1 , wherein the radiation characteristic to be changed is a wavelength of the radiation.
6. The method according to claim 1 , wherein the radiation characteristic to be changed is a polarization of the radiation.
7. The method according to claim 1 , wherein the radiation characteristic to be changed is an angle of incidence on the substrate.
8. The method according to claim 1 , wherein the radiation characteristic to be changed is an illumination mode of the radiation.
9. The method according to claim 1 , wherein the comparing comprises determining whether the second value of the characteristic of the feature is within a predetermined range of the first value of the characteristic of the feature.
10. An inspection apparatus comprising:
a radiation projector configured to project radiation onto a substrate, the radiation comprising a characteristic that comprises a plurality of values;
a high numerical aperture lens; and
a detector configured to detect the radiation reflected from a surface of the substrate,
wherein the detector is configured to separate the detected radiation into a plurality of sub-divisions, each sub-division of the plurality of sub-divisions comprising a different value for the characteristic of the radiation.
11. The inspection apparatus according to claim 10 , wherein the characteristic that differs between the sub-divisions is a wavelength.
12. The inspection apparatus according to claim 10 , further comprising:
an imaging spectrometer configured to separate the detected radiation into a plurality of sub-divisions, each sub-division of the plurality of sub-divisions comprising a different value for the characteristic of the radiation.
13. A lithographic apparatus comprising:
an illumination system arranged to illuminate a pattern;
a projection system arranged to project an image of the pattern on to a substrate; and
an inspection apparatus configured to measure a target on the substrate, the inspection apparatus comprising;
a radiation projector configured to project radiation onto the substrate, the radiation comprising a characteristic that comprises a plurality of values;
a high numerical aperture lens; and
a detector configured to detect the radiation reflected from a surface of the substrate,
wherein the detector is configured to separate the detected radiation into a plurality of sub-divisions, each sub-division of the plurality of sub-divisions comprising a different value for the characteristic of the radiation.
14. The inspection apparatus according to claim 13 , wherein the characteristic that differs between the sub-divisions is a wavelength.
15. The inspection apparatus according to claim 13 , further comprising:
an imaging spectrometer configured to separate the detected radiation into a plurality of sub-divisions, each sub-division of the plurality of sub-divisions comprising a different value for the characteristic of the radiation.