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EP-4111472-B1 - SOFT X-RAY OPTICS WITH IMPROVED FILTERING

EP4111472B1EP 4111472 B1EP4111472 B1EP 4111472B1EP-4111472-B1

Inventors

  • KUZNETSOV, ALEXANDER
  • CHEN, Boxue
  • ARTEMIEV, Nikolay

Dates

Publication Date
20260506
Application Date
20210323

Claims (14)

  1. A multilayer X-ray reflecting optic (130) comprising: a substrate (11); a multilayer x-ray reflecting structure (12) disposed above the substrate; and an integrated optical filter (131) disposed above the substrate, the integrated optical filter including one layer of silicon dioxide (132) fabricated on top of the multilayer x-ray reflecting structure and one layer of Tellurium (133) deposited on top of the silicon dioxide later, said integrated optical filter being configured to absorb radiation having wavelengths above 10 nanometers.
  2. The multilayer X-ray reflecting optic of Claim 1, wherein the integrated optical filter (131) includes more than two different radiation absorbing material layers.
  3. The multilayer X-ray reflecting optic of Claim 1, wherein the integrated optical filter (131) is disposed over the multilayer reflecting structure (12).
  4. The multilayer X-ray reflecting optic of Claim 1, wherein the integrated optical filter (131) is disposed between the substrate (11) and the multilayer x-ray reflecting structure (12).
  5. The multilayer X-ray reflecting optic of Claim 1, further comprising: a diffusion barrier layer (192), the diffusion barrier layer disposed between the integrated optical filter (131) and the multilayer x-ray reflecting structure (12), disposed between the substrate (11) and the multilayer x-ray reflecting structure (12), or disposed over the integrated optical filter.
  6. The multilayer X-ray reflecting optic of Claim 1, wherein an optical surface of the substrate (11) is curved.
  7. The multilayer X-ray reflecting optic of Claim 1, wherein a thickness of the integrated optical filter (131) varies as a function of location on an optical surface of the substrate (11).
  8. The multilayer X-ray reflecting optic of Claim 1, wherein the multilayer x-ray reflecting structure (12) reflects incoming light over a range of wavelengths.
  9. A metrology system (200), comprising: an x-ray illumination source configured to generate an amount of soft x-ray radiation including multiple illumination wavelengths within a desired photon energy range from 80 electronvolts to 3,000 electronvolts and an undesired photon energy range below 80 electronvolts; an x-ray detector configured to detect an amount of x-ray radiation scattered from a semiconductor wafer in response to the amount of soft x-ray radiation; a plurality of multilayer x-ray reflecting optics (130) as recited in claim 1; 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.
  10. The metrology system of Claim 9, wherein the metrology system is a soft x-ray reflectometry system.
  11. The metrology system of Claim 10, wherein the soft x-ray reflectometry system operates in a grazing incidence mode; or wherein the metrology system operates in an imaging mode.
  12. The metrology system of Claim 11, wherein the integrated optical filter is disposed over a multilayer x-ray reflecting structure fabricated over the optical surface of the at least one of the plurality of x-ray optical elements.
  13. The metrology system of Claim 12, further comprising: a diffusion barrier layer, the diffusion barrier layer disposed between the material layers of the integrated optical filter and the multilayer x-ray reflecting structure, disposed between the optical surface and the multilayer x-ray reflecting structure, or disposed over the material layers of the integrated optical filter.
  14. The metrology system of Claim 13, wherein the optical surface of the at least one of the plurality of x-ray optical elements is curved; or wherein a thickness of the integrated optical filter varies as a function of location on the optical surface of the at least one of the plurality of x-ray optical elements; or further comprising: a stand-alone optical filter disposed in the optical path between the x-ray illumination source and the detector.

Description

TECHNICAL FIELD The described embodiments relate to x-ray optics, and more particularly to thin film optical layers employed to filter out of band radiation in optical systems. BACKGROUND INFORMATION Semiconductor devices such as logic and memory devices are typically fabricated by a sequence of processing steps applied to a specimen. The various features and multiple structural levels of the semiconductor devices are formed by these processing steps. For example, lithography among others is one semiconductor fabrication process that involves generating a pattern on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated on a single semiconductor wafer and then separated into individual semiconductor devices. Metrology processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield. A number of metrology based techniques including scatterometry and reflectometry implementations, and associated analysis algorithms are commonly used to characterize critical dimensions, film thicknesses, composition and other parameters of nanoscale structures. Traditionally, scatterometry critical dimension measurements are performed on targets consisting of thin films and/or repeated periodic structures. During device fabrication, these films and periodic structures typically represent the actual device geometry and material structure or an intermediate design. As devices (e.g., logic and memory devices) move toward smaller nanometer-scale dimensions, characterization becomes more difficult. Devices incorporating complex three-dimensional geometry and materials with diverse physical properties contribute to characterization difficulty. Metrology systems based on x-ray based scatterometry and reflectometry measurements have emerged as suitable tools for dimensional metrology of semiconductor structures. X-ray based metrology systems have exhibited measurement capability for both low and high aspect ratio structures. In some applications, x-ray based metrology systems feature an illumination beam spot size compatible with scribe-line targets. X-ray based metrology systems have made it possible to efficiently develop and validate measurement recipes for challenging measurement applications and operate in a high volume manufacturing (HVM) environment without substantial prior dimensional and material composition information. Highly reflective multilayer optics are a critical component of the optical systems of x-ray based measurement and processing systems. Highly reflective multilayer optics typically employ repeating pairs of different material film layers. Each pair of layers includes an absorber material layer and a spacer material layer. Common absorber materials include Tungsten (W), Tungsten disilicide (WSi2), Ruthenium (Ru), Vanadium (V), Lanthanum (La), Molybdenum (Mo), Titanium dioxide (TiO2), Nickel (Ni), etc. Common spacer materials include Carbon (C), Boron nitride (BN), Boron Carbide (B4C), Silicon (Si), etc. FIG. 1 depicts an illustration of a cross-sectional view of a multilayer optic 10 used in soft x-ray applications. A set of repeated pairs of multilayer coatings 12 is fabricated over a Silicon substrate 11. The top four repeated pairs of multilayer coatings 13A-D are illustrated. Each repeated pair of multilayer coatings includes a spacer layer (e.g., layer 15 of repeated pair 13A) and an absorber layer (e.g., layer 14 of repeated pair 13A). In the embodiment depicted in FIG. 1, the spacer layer is fabricated from Scandium (Sc), and the absorber layer is fabricated from Chromium (Cr). In one embodiment, the set of multilayer coatings 12 includes four hundred repeated pairs of multilayer coatings. The spatial period, P, of the set of multilayer coatings (i.e., thickness of each repeated material pair) is 1.56 nanometers to satisfy the Bragg condition. Additional description of the multilayer optic depicted in FIG. 1 is presented in "14.5% near-normal incidence reflectance of Cr Sc x-ray multilayer mirrors of the water window," by Eriksson, Fredrik, et al., Optics letters 28-24 (2003): 2494-2496. The reflectivity of multilayer optic 10 is typically extremely sensitive to incident angle and beam energy (i.e., wavelength). FIG. 2 is a plot 20 illustrative of a simulation of the reflectivity of multilayer optic 10 as a function of beam energy for an angle of incidence of five degrees. The simulation employs the Fresnel equations assuming ideal, flat interfaces. The optical constants associated with each material (i.e., delta and beta constants) are derived using scattering factor tables from the Center For X-Ray Optics (CXRO) of the materials science division of the Lawrence Berkeley National Laboratory (accessible via Internet at http://henke.lbl.gov/optical_constants/.