Methods and systems for semiconductor metrology based on polychromatic soft X-Ray diffraction
Methods and systems for performing measurements of semiconductor structures based on high-brightness, polychromatic, reflective small angle x-ray scatterometry (RSAXS) metrology are presented herein. RSAXS measurements are performed over a range of wavelengths, angles of incidence, and azimuth angles with small illumination beam spot size, simultaneously or sequentially. In some embodiments, RSAXS measurements are performed with x-ray radiation in the soft x-ray (SXR) region at grazing angles of incidence in the range of 5-20 degrees. In some embodiments, the x-ray illumination source size is 10 micrometers or less, and focusing optics project the source area onto a wafer with a demagnification factor of 0.2 or less, enabling an incident x-ray illumination spot size of less than two micrometers. In another aspect, active focusing optics project programmed ranges of illumination wavelengths, angles of incidence, and azimuth angles, or any combination thereof, onto a metrology area, either simultaneously or sequentially.
1. A metrology system comprising:
an x-ray illumination source configured to generate an amount of soft x-ray radiation including multiple illumination wavelengths within a photon energy range from 80 electronvolts to 3,000 electronvolts;
one or more x-ray illumination optical elements disposed in an illumination optical path between the x-ray illumination source and a semiconductor wafer, wherein the one or more x-ray illumination optical elements focus the amount of soft x-ray radiation including the multiple illumination wavelengths onto the semiconductor wafer as an x-ray illumination beam incident on the semiconductor wafer at a nominal grazing incidence angle between 5 and 20 degrees;
an x-ray detector configured to detect an amount of x-ray radiation scattered from the semiconductor wafer in response to the incident x-ray illumination beam; and
a computing system configured to determine a value of a parameter of interest characterizing a structure disposed on the semiconductor wafer based on the detected amount of x-ray radiation.
2. The metrology system of claim 1 , wherein the one or more x-ray illumination optical elements simultaneously focus the amount of soft x-ray radiation including the multiple illumination wavelengths onto the semiconductor wafer as an x-ray illumination beam incident on the semiconductor wafer at a plurality of angles of incidence, a plurality of wavelengths, and a plurality of azimuth angles.
3. The metrology system of claim 1 , wherein the one or more x-ray illumination optical elements select a subset of the multiple illumination wavelengths and focus the selected subset of the multiple wavelengths onto the semiconductor wafer as an x-ray illumination beam incident on the semiconductor wafer.
4. The metrology system of claim 3 , wherein the one or more x-ray illumination optical elements simultaneously focus the selected subset of the multiple wavelengths onto the semiconductor wafer at a plurality of angles of incidence and a plurality of azimuth angles.
5. The metrology system of claim 3 , wherein the one or more x-ray illumination optical elements are graded multi-layer optical elements that select the subset of the multiple illumination wavelengths.
6. The metrology system of claim 5 , the one or more x-ray illumination optical elements are elliptically shaped optical elements arranged in a toroidal configuration that simultaneously focuses the x-ray illumination beam incident on the semiconductor wafer at a plurality of angles of incidence and a plurality of azimuth angles.
7. The metrology system of claim 1 , wherein the one or more x-ray illumination optical elements focus the amount of soft x-ray radiation onto a metrology target disposed on the semiconductor wafer, wherein the metrology target includes an array of nominally periodic unit cells, wherein one or more cells of the nominally periodic array are deleted, displaced, or structurally modified at programmed or random locations within the array.
8. The metrology system of claim 1 , wherein the parameter of interest is any of an overlay error, a critical dimension, and an edge placement error.
9. The metrology system of claim 1 , wherein a source area of the x-ray illumination source is characterized by a lateral dimension of 10 micrometers or less.
10. The metrology system of claim 1 , wherein the one or more x-ray illumination optical elements focus the amount of soft x-ray radiation onto the semiconductor wafer with a magnification factor of 0.2 or less.
11. The metrology system of claim 1 , further comprising:
a first vacuum chamber enveloping a significant portion of an illumination optical path between the x-ray illumination source and the semiconductor wafer.
12. The metrology system of claim 1 , further comprising:
a first vacuum chamber enveloping a significant portion of a collection beam path between the semiconductor wafer and the x-ray detector.
13. The metrology system of claim 1 , further comprising:
a specimen positioning system configured to position the specimen with respect to the x-ray illumination beam such that the x-ray illumination beam is incident on the surface of the specimen at any location on the surface of the specimen and rotate the specimen with respect to the x-ray illumination beam about an axis of rotation such that the x-ray illumination beam is incident on the surface of the specimen at any location at a plurality of angles of incidence and rotate the specimen about an azimuth axis of rotation such that the x-ray illumination beam is incident on the surface of the specimen at any location at a plurality of azimuth angles.
14. A method comprising:
generating an amount of soft x-ray radiation including multiple illumination wavelengths within a photon energy range from 80 electronvolts to 3,000 electronvolts;
focusing the amount of soft x-ray radiation including the multiple illumination wavelengths onto a semiconductor wafer as an x-ray illumination beam incident on the semiconductor wafer at a nominal grazing incidence angle between 5 and 20 degrees;
detecting an amount of x-ray radiation scattered from the semiconductor wafer in response to the incident x-ray illumination beam; and
determining a value of a parameter of interest characterizing a structure disposed on the semiconductor wafer based on the detected amount of x-ray radiation.
15. The method of claim 14 , further comprising:
simultaneously focusing the amount of soft x-ray radiation including the multiple illumination wavelengths onto the semiconductor wafer as an x-ray illumination beam incident on the semiconductor wafer at a plurality of angles of incidence, a plurality of wavelengths, and a plurality of azimuth angles.
16. The method of claim 14 , further comprising:
selecting a subset of the multiple illumination wavelengths and focusing the selected subset of the multiple wavelengths onto the semiconductor wafer.
17. The method of claim 16 , further comprising:
simultaneously focusing the selected subset of the multiple wavelengths onto the semiconductor wafer at a plurality of angles of incidence and a plurality of azimuth angles.
18. The method of claim 14 , wherein the amount of soft x-ray radiation is focused onto a metrology target disposed on the semiconductor wafer, wherein the metrology target includes an array of nominally periodic unit cells, wherein one or more cells of the nominally periodic array are deleted, displaced, or structurally modified at programmed or random locations within the array.
19. The method of claim 14 , wherein the parameter of interest is any of an overlay error, a critical dimension, and an edge placement error.
20. A metrology system comprising:
an x-ray illumination source configured to generate an amount of soft x-ray radiation including multiple illumination wavelengths within a photon energy range from 80 electronvolts to 3,000 electronvolts;
one or more x-ray illumination optical elements disposed in an illumination optical path between the x-ray illumination source and a semiconductor wafer, wherein the one or more x-ray illumination optical elements focus the amount of soft x-ray radiation including the multiple wavelengths onto a metrology target disposed on the semiconductor wafer as an x-ray illumination beam incident on the metrology target at a nominal grazing incidence angle between 5 and 20 degrees, wherein the metrology target includes an array of nominally periodic unit cells, wherein one or more structural elements of each nominally periodic unit cell is deleted at a programmed or random location within each of the unit cells;
an x-ray detector configured to detect an amount of x-ray radiation scattered from the semiconductor wafer in response to the incident x-ray illumination beam; and
a computing system configured to determine a value of a parameter of interest characterizing a structure disposed on the semiconductor wafer based on the detected amount of x-ray radiation.
21. The metrology system of claim 20 , wherein the one or more x-ray illumination optical elements simultaneously focus the amount of soft x-ray radiation including the multiple illumination wavelengths onto the metrology target as an x-ray illumination beam incident on the metrology target at a plurality of angles of incidence, a plurality of wavelengths, and a plurality of azimuth angles.
22. The metrology system of claim 20 , wherein the one or more x-ray illumination optical elements select a subset of the multiple illumination wavelengths and focus the selected subset of the multiple wavelengths onto the metrology target.
23. The metrology system of claim 22 , wherein the one or more x-ray illumination optical elements simultaneously focus the selected subset of the multiple wavelengths onto the semiconductor wafer at a plurality of angles of incidence and a plurality of azimuth angles.
24. The metrology system of claim 22 , wherein the one or more x-ray illumination optical elements are graded multi-layer optical elements that select the subset of the multiple illumination wavelengths.
25. The metrology system of claim 24 , the one or more x-ray illumination optical elements are elliptically shaped optical elements arranged in a toroidal configuration that simultaneously focuses the x-ray illumination beam incident on the semiconductor wafer at a plurality of angles of incidence and a plurality of azimuth angles.
26. The metrology system of claim 20 , wherein a source area of the x-ray illumination source is characterized by a lateral dimension of 10 micrometers or less.
27. The metrology system of claim 20 , wherein the one or more x-ray illumination optical elements focus the amount of soft x-ray radiation onto the semiconductor wafer with a magnification factor of 0.2 or less.