Methods and systems for measuring periodic structures using multi-angle X-ray reflectance scatterometry (XRS)
Methods and systems for measuring periodic structures using multi-angle X-ray reflectance scatterometry (XRS) are disclosed. For example, a method of measuring a sample by X-ray reflectance scatterometry involves impinging an incident X-ray beam on a sample having a periodic structure to generate a scattered X-ray beam, the incident X-ray beam simultaneously providing a plurality of incident angles and a plurality of azimuthal angles. The method also involves collecting at least a portion of the scattered X-ray beam.
1. A method to characterize a sample using an X-ray reflectance scatterometry, the method comprising:
impinging an incident low energy X-ray beam having an energy of 1keV or less on a sample having a periodic structure to generate a first scattered X-ray beam, wherein the incident low energy X-ray beam is converging in an incidence and azimuth planes thereby providing simultaneously a plurality of incident angles and a plurality of azimuthal angles and having a range of incident angles that is greater than a range of azimuthal angles; and
collecting at least a portion of the first scattered X-ray beam.
2. The method of claim 1 , wherein the range of incident angles is from +30 degrees to −30 degrees, and the range of azimuthal angles is from +10 degrees to −10 degrees.
3. The method of claim 1 , wherein the converging incident X-ray beam has a converging angle in a range of from 20 degrees to 40 degrees.
4. The method of claim 1 , wherein a central axis of the converging X-ray beam has a fixed azimuthal angle of zero relative to the sample.
5. The method of claim 1 , wherein a central axis of the converging X-ray beam has a fixed non-zero incident angle in a range of 10 degrees to 15degrees from a horizontal plane.
6. The method of claim 2 , wherein a central axis of the converging X-ray beam has a fixed non-zero azimuthal angle relative to the sample.
7. The method of claim 2 , wherein a central axis of the converging X-ray beam has a fixed non-zero incident angle in a range of 10 degrees to 15degrees from a horizontal plane.
8. The method of claim 7 , wherein the central axis of the converging X-ray beam has a fixed non-zero azimuthal angle relative to the sample.
9. The method of claim 8 , further comprising:
positioning the central axis of the converging X-ray beam to the fixed non-zero azimuthal angle at the fixed non-zero incident angle relative to the sample; and, subsequently,
impinging the converging X-ray beam on the sample to generate a second scattered X-ray beam; and
collecting at least a portion of the second scattered X-ray beam.
10. The method of claim 9 , wherein collecting the portion of the scattered X-ray beam comprises collecting 0 th order but not 1 st order diffraction data for the sample, and wherein collecting the portion of the second scattered X-ray beam comprises collecting 1 st order but not 0 th order diffraction data for the sample.
11. The method of claim 1 , further comprising
generating the incident X-ray beam from a source selected from the group consisting of carbon (C), molybdenum (Mo) and Rhodium (Rh).
12. The method of claim 1 , further comprising:
prior to the impinging, focusing the incident X-ray beam using a multilayer monochromator to generate the converging incident X-ray beam.
13. The method of claim 12 , wherein the incident X-ray beam is not collimated between the focusing and the impinging.
14. The method of claim 1 , the range of incident angles is less than the angle of a nominal first-order angle at zero degrees.
15. The method of claim 1 , wherein the range of incident angles of from +20 degrees to −20 degrees is provided using a toroidal multilayer monochromator.
16. The method of claim 1 , further comprising:
estimating a shape of the periodic structure of the sample by inversion of scattering solutions relative to the sampled scattered signal intensity.
17. The method of claim 1 , wherein the converging incident X-ray beam has a wavelength that is less than a periodicity of the periodic structure.
18. A method to measure a sample using an X-ray reflectance scatterometry, the method comprising:
impinging an incident low energy X-ray beam having an energy of 1keV or less on a sample having a periodic structure to generate a scattered X-ray beam, wherein the incident low energy X-ray beam is converging in an incidence and azimuth planes thereby providing simultaneously a plurality of incident angles and a plurality of azimuthal angles and having a range of incident angles that is greater than a range of azimuthal angles; and
collecting at least a portion of the scattered X-ray beam using a two-dimensional detector to simultaneously sample a scattered signal intensity of the at least the portion of the scattered X-ray beam that is scattered from the range of incident angles and the range of azimuthal angles.
19. A system to measure a sample using an X-ray reflectance scatterometry, the system comprising:
an X-ray source for generating an X-ray beam having an energy of 1 keV or less;
a sample holder for positioning a sample having a periodic structure;
a monochromator positioned between the X-ray source and the sample holder, the monochromator for focusing the X-ray beam to impinge an incident low energy X-ray beam on the sample to generate a scattered X-ray beam, wherein the incident low energy X-ray beam is converging in an incident angles and a plurality of azimuthal angles and having a range of incident angles that is greater than a range of azimuthal angles; and
a 2-D detector for collecting at least a portion of the scattered X-ray beam from the sample.
20. The system of claim 19 , wherein the X-ray source comprises an electron gun directed at an anode comprising a material selected from the group consisting of carbon (C), molybdenum (Mo) and Rhodium (Rh).
21. The system of claim 19 , wherein the monochromator is a toroidal monochromator to provide the range of incident angles from +20 degrees to −20degrees.
22. The system of claim 19 , wherein there is no intervening collimator between the monochromator and the sample holder.
23. The system of claim 19 , wherein the sample holder is rotatable to change an azimuth angle of a central axis of the X-ray beam relative to the periodic structure of the sample.
24. The system of claim 19 , wherein the sample holder is rotatable to provide an orthogonal operation with an eucentric rotation enabling two or more sample rotations per measurement.
25. The system of claim 19 , further comprising:
a processor coupled to the two-dimensional detector, the processor for estimating a shape of the periodic structure by inversion of scattering solutions relative to the sampled scattered signal intensity.