Inspection apparatus and method
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithographic apparatus has an inspection apparatus with an EUV radiation source. The radiation source emits a radiation beam that includes coherent radiation of a specific wavelength. The beam propagates to illumination optical system, which focuses the radiation beam into a focused beam of illuminating radiation. The illumination optical system illuminates a three-dimensional product structure on the substrate, which scatters the illuminating radiation. On the surface of a detector, the radiation scattered by the product structure forms a diffraction pattern that is used to reconstruct data describing the three-dimensional product structure.
1. A method of obtaining data describing a three-dimensional product structure, the method comprising:
illuminating the three-dimensional product structure with illuminating radiation, the illuminating radiation having at least one controllable characteristic;
capturing a plurality of diffraction patterns formed by said radiation after scattering by the three-dimensional product structure, wherein each diffraction pattern is formed by illuminating radiation, the illuminating radiation having a specific value of the at least one controllable characteristic; and
reconstructing the data describing the three-dimensional product structure based on the captured plurality of diffraction patterns.
2. The method of claim 1 , wherein the reconstructing comprises performing phase retrieval on the captured diffraction patterns.
3. The method of claim 1 , wherein the illuminating radiation comprises radiation with a first wavelength spectrum, the first wavelength spectrum comprising a first plurality of wavelengths.
4. The method of claim 3 , wherein the capturing comprises using an optical element to progressively capture one diffraction pattern of the plurality of diffraction patterns at each of the wavelengths of the first plurality of wavelengths.
5. The method of claim 4 , wherein the optical element comprises a rotating filter wheel, a scanning monochromator, or an acousto-optic filter.
6. The method of claim 3 , wherein:
the illuminating comprises providing first and second coherent radiation pulses, the second radiation pulse having one of a plurality of time delays, and
the capturing comprises:
receiving first and second scattered radiation pulses formed by the first and second coherent radiation pulses after scattering by the product surface;
reconstructing a diffraction pattern based on the first and second scattered radiation pulses; and
repeating the receiving and reconstructing for each time delay in the plurality of time delays.
7. The method of claim 1 , wherein the illuminating comprises adapting a radiation source to output illuminating radiation having a single wavelength,
and further comprising repeating the illuminating and capturing for each wavelength in a second plurality of wavelengths.
8. The method of claim 1 , further comprising reconstructing a three-dimensional image of the three-dimensional product structure based on the data.
9. An inspection apparatus comprising:
an illuminator configured to illuminate a three-dimensional product structure with illuminating radiation, the illuminating radiation having at least one controllable characteristic;
a sensor configured to capture a plurality of diffraction patterns formed by said radiation after scattering by the three-dimensional product structure, wherein each diffraction pattern is formed by illuminating radiation, the illuminating radiation having a specific value of the at least one controllable characteristic; and
a reconstruction device configured to reconstruct the data describing the three-dimensional product structure based on the captured plurality of diffraction patterns.
10. A method of manufacturing devices wherein device features and metrology targets are formed on a series of substrates by a lithographic process, wherein properties of the metrology targets on one or more processed substrates are measured by a method comprising:
illuminating a three-dimensional product structure with illuminating radiation, the illuminating radiation having at least one controllable characteristic;
capturing a plurality of diffraction patterns formed by said radiation after scattering by the three-dimensional product structure, wherein each diffraction pattern is formed by illuminating radiation, the illuminating radiation having a specific value of the at least one controllable characteristic;
reconstructing the data describing the three-dimensional product structure based on the captured plurality of diffraction patterns; and
using the measured properties to adjust parameters of the lithographic process for the processing of further substrates.
11. A computer program product comprising machine-readable instructions for causing a processor to perform operations comprising:
illuminating a three-dimensional product structure with illuminating radiation, the illuminating radiation having at least one controllable characteristic;
capturing a plurality of diffraction patterns formed by said radiation after scattering by the three-dimensional product structure, wherein each diffraction pattern is formed by illuminating radiation, the illuminating radiation having a specific value of the at least one controllable characteristic;
reconstructing the data describing the three-dimensional product structure based on the captured plurality of diffraction patterns.
12. The computer program product of claim 11 , further comprising instructions for causing a processor to reconstruct a diffraction pattern based on the first and second scattered radiation pulses.