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Patexia Research
Patent No. US 11280749
Issue Date Mar 22, 2022
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Patent 11280749 - Holes tilt angle measurement using FIB diagonal cut > Claims

  • 1. A method of evaluating a region of a sample that includes a plurality of holes, the method comprising: taking a first image of the region of the sample that includes the plurality of holes by scanning the region with a first charged particle beam;evaluating the first image to determine a first center-to-center distance between first and second holes in the plurality of holes;milling a diagonal cut in an area within the region that includes the second hole at an angle such that an upper surface of the sample in the milled area where the second hole is located is recessed with respect to an upper surface of the sample where the first hole is located;thereafter, taking a second image of the region of the sample that includes the first and second holes by scanning the region with the first charged particle beam;evaluating the second image to determine a second center-to-center distance between first and second holes in the plurality of holes; andcomparing the second center-to-center distance to the first center-to-center distance.
    • 2. The method of claim 1 further comprising determining an angle θ at which the holes are tilted.
      • 3. The method of claim 2 further comprising rejecting the sample from a manufacturing line if the angle θ is greater than a predetermined value.
    • 4. The method of claim 1 further comprising determining an angle β at which the holes are tilted according to the following formula:tanβ=tanα(xΔx+cosθ)where α is the angle of diagonal cut, x is the center-to-center distance between the first and second holes as measured in the first image, and βx is a difference in the exact positions of the second hole before and after the diagonal cut and θ is the angle between a first imaginary line bisecting centers of the first and second holes in the first image and a second imaginary line bisecting a center of the second hole as initially imaged and the center of the second hole in the second image.
    • 5. The method of claim 1 wherein the first hole is outside the area of the region milled at an angle.
    • 6. The method of claim 1 wherein the plurality of holes are etched at an angle tilted in a first horizontal plane and the sample is milled in the first horizontal plane.
      • 7. The method of claim 6 further comprising determining an angle β at which the holes are tilted at which the plurality of holes are tilted according to the following formula:tanβ=tanα(1+xΔx)where α is the angle of diagonal cut, x is the center-to-center distance between the first and second holes as measured in the first image, and βx is a difference in the center-to-center measurements of the second image and the first image.
    • 8. The method of claim 1 wherein the sample is positioned within in a vacuum chamber of an evaluation tool that includes a scanning electron microscope (SEM) column and a focused ion beam (FIB) column and the first and second images are taken with the SEM column and the milling is performed with the FIB column.
      • 9. The method of claim 8 wherein the sample is a semiconductor wafer.
  • 10. A system for evaluating a region of a sample that includes a plurality of holes, the system comprising: a vacuum chamber;a sample support configured to hold a sample within the vacuum chamber during a sample evaluation process;a scanning electron microscope (SEM) column configured to direct a first charged particle beam into the vacuum chamber;a focused ion beam (FIB) column configured to direct a second charged particle beam into the vacuum chamber;a processor and a memory coupled to the processor, the memory including a plurality of computer-readable instructions that, when executed by the processor, cause the system to: take a first image of the region of the sample that includes the plurality of holes by scanning the region with a first charged particle beam;evaluate the first image to determine a first center-to-center distance between first and second holes in the plurality of holes;mill a diagonal cut in an area within the region that includes the second hole at an angle such that an upper surface of the sample in the milled area where the second hole is located is recessed with respect to an upper surface of the sample where the first hole is located;thereafter, take a second image of the region of the sample that includes the first and second holes by scanning the region with the first charged particle beam;evaluate the second image to determine a second center-to-center distance between first and second holes in the plurality of holes; andcompare the second center-to-center distance to the first center-to-center distance.
    • 11. The system for evaluating a sample set forth in claim 10 wherein the processor further causes the system to determine an angle θ at which the holes are tilted.
    • 12. The system for evaluating a sample set forth in claim 10 wherein the first hole is outside the area of the region milled at an angle.
    • 13. The system for evaluating a sample set forth in claim 10 wherein the processor further causes the system to determine an angle β at which the holes are tilted according to the following formula:tanβ=tanα(xΔx+cosθ)where α is the angle of diagonal cut, x is the center-to-center distance between the first and second holes as measured in the first image, and βx is a difference in the exact positions of the second hole before and after the diagonal cut and θ is the angle between a first imaginary line bisecting centers of the first and second holes in the first image and a second imaginary line bisecting a center of the second hole as initially imaged and the center of the second hole in the second image.
    • 14. The system for evaluating a sample set forth in claim 10 wherein the plurality of holes are etched at an angle tilted in a first horizontal plane and the processor further causes the system to mill the sample in the first horizontal plane.
      • 15. The system for evaluating a sample set forth in claim 14 wherein the processor further causes the system to determine an angle β at which the holes are tilted at which the plurality of holes are tilted according to the following formula:tanβ=tanα(1+xΔx)where α is the angle of diagonal cut, x is the center-to-center distance between the first and second holes as measured in the first image, and βx is a difference in the center-to-center measurements of the second image and the first image.
  • 16. A non-transitory computer-readable memory that stores instructions for evaluating a region of a sample that includes a plurality of holes by: taking a first image of the region of the sample that includes the plurality of holes by scanning the region with a first charged particle beam;evaluating the first image to determine a first center-to-center distance between first and second holes in the plurality of holes;milling a diagonal cut in an area within the region that includes the second hole at an angle such that an upper surface of the sample in the milled area where the second hole is located is recessed with respect to an upper surface of the sample where the first hole is located;thereafter, taking a second image of the region of the sample that includes the first and second holes by scanning the region with the first charged particle beam;evaluating the second image to determine a second center-to-center distance between first and second holes in the plurality of holes; andcomparing the second center-to-center distance to the first center-to-center distance.
    • 17. The non-transitory computer-readable memory set forth in claim 16 wherein the instructions for evaluating the region further include instructions to determine an angle β at which the holes are tilted.
    • 18. The non-transitory computer-readable memory set forth in claim 16 wherein the first hole is outside the area of the region milled at an angle.
    • 19. The non-transitory computer-readable memory set forth in claim 16 wherein the instructions for evaluating the region further include instructions to determine an angle β at which the holes are tilted according to the following formula:tanβ=tanα(xΔx+cosθ)where α is the angle of diagonal cut, x is the center-to-center distance between the first and second holes as measured in the first image, and βx is a difference in the exact positions of the second hole before and after the diagonal cut and θ is the angle between a first imaginary line bisecting centers of the first and second holes in the first image and a second imaginary line bisecting a center of the second hole as initially imaged and the center of the second hole in the second image.
    • 20. The non-transitory computer-readable memory set forth in claim 16 wherein the plurality of holes are etched at an angle tilted in a first horizontal plane and the instructions for evaluating the region further include instructions to determine an angle β at which the holes are tilted at which the plurality of holes are tilted according to the following formula:tanβ=tanα(1+xΔx)where α is the angle of diagonal cut, x is the center-to-center distance between the first and second holes as measured in the first image, and βx is a difference in the center-to-center measurements of the second image and the first image.
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