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 of measuring a sample by X-ray reflectance scatterometry, the method comprising:
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, wherein the incident X-ray beam is a converging X-ray beam having a converging angle approximately in the range of 2-10 degrees, and wherein a central axis of the converging X-ray beam has a fixed non-zero incident angle and an azimuthal angle of zero relative to the sample;
collecting at least a portion of the scattered X-ray beam, 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;
positioning the central axis of the converging X-ray beam to a 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, 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.
2. The method of claim 1 , wherein impinging the incident X-ray beam comprises impinging a low energy X-ray beam having an energy of approximately 1 keV or less.
3. The method of claim 2 , wherein impinging the low energy X-ray beam comprises generating the low energy X-ray beam from a source selected from the group consisting of carbon (C), molybdenum (Mo) and Rhodium (Rh).
4. The method of claim 2 , further comprising:
prior to impinging the low energy X-ray beam on the sample, focusing the low energy X-ray beam using a toroidal multilayer monochromator that provides an incident angle range of approximately +/−30 degrees and an azimuth angle range of approximately +/−10 degrees.
5. The method of claim 4 , wherein the low energy X-ray beam is not collimated between the focusing and the impinging.
6. The method of claim 4 , wherein focusing the low energy X-ray beam comprises impinging the low energy X-ray beam on the sample at an incident angle range less than the angle of a nominal first-order angle at zero degrees.
7. The method of claim 4 , wherein the toroidal multilayer monochromator provides an incident angle range of approximately +/−20 degrees.
8. The method of claim 1 , wherein collecting the portion of the scattered X-ray beam comprises using a two-dimensional detector to simultaneously sample scattered signal intensity of the portion of the scattered X-ray beam scattered from the plurality of incident angles and the plurality of azimuthal angles.
9. The method of claim 8 , further comprising:
estimating a shape of the periodic structure of the sample by inversion of scattering solutions relative to the sampled scattered signal intensity.
10. The method of claim 1 , wherein impinging the incident X-ray beam on the sample comprises impinging an X-ray beam having a wavelength less than a periodicity of the periodic structure.