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CN-122003578-A - Interferometer configured to measure small structures

CN122003578ACN 122003578 ACN122003578 ACN 122003578ACN-122003578-A

Abstract

An interferometer is configured to characterize a plurality of structures in a sample, including high aspect ratio structures. The interferometer irradiates the sample with illumination optics having a numerical aperture smaller than that of the collection optics collecting the reflected light in order to increase the amount of light penetrating the depth of the structure and to improve the signal-to-noise ratio. During measurement, the focal position of the collection optics relative to the sample is fixed while the optical path difference between the sample light and the reference light is varied to scan the coherent fringes across the depth of the structure. Images of the region of the sample are collected at different optical path differences between the reference light and the sample light and analyzed to characterize the structure in the sample.

Inventors

  • J. SCHMIDT
  • H AB Mustafa

Assignees

  • 昂图创新有限公司

Dates

Publication Date
20260508
Application Date
20240905
Priority Date
20230907

Claims (17)

  1. 1. A method of characterizing a region of a sample comprising a plurality of structures with an interferometer, the method comprising: Dividing illumination light into sample light to be incident on and reflected by the sample and reference light to be incident on and reflected by a reference mirror; Illuminating the region of the sample with the sample light using illumination optics having a first numerical aperture; focusing collection optics at a focal location relative to the sample, the collection optics having a second numerical aperture that is greater than the first numerical aperture; Changing an optical path difference between the sample light and the reference light without changing the focal position of the collection optics relative to the sample; Imaging reflected sample light from the sample with reflected reference light from the reference mirror with the collection optics at a plurality of optical path differences to produce a plurality of images, and The plurality of images of the region of the sample including the plurality of structures are analyzed to characterize the region of the sample.
  2. 2. The method of claim 1, further comprising providing the illumination light into an optical path of the interferometer between the collection optics and the sample.
  3. 3. The method of claim 1, wherein changing the optical path difference between the sample light and the reference light without changing the focal position of the collection optics relative to the sample comprises at least one of moving the reference mirror and moving a beam splitter that splits the illumination light into the sample light and the reference light.
  4. 4. The method of claim 1, the method further comprising: Splitting the reference light to produce a second reference light to be incident on and to be reflected by a second reference mirror; changing a second optical path difference between the sample light and the second reference light without changing the focal position of the collection optics relative to the sample; Imaging reflected sample light from the sample interfering at a plurality of second optical path differences with reflected second reference light from the second reference mirror using the collection optics to produce a second plurality of images, and The second plurality of images of the region of the sample including the plurality of structures is analyzed to characterize the region of the sample.
  5. 5. The method of claim 4, wherein the second optical path difference is different from the optical path difference, and wherein reflected sample light from the sample that interferes with reflected reference light from the reference mirror in the plurality of images at the optical path difference creates a top interference fringe corresponding to a top surface of the sample, and reflected sample light from the sample that interferes with reflected second reference light from the second reference mirror in the second plurality of images at the second optical path difference creates a bottom interference fringe corresponding to a bottom of the plurality of structures.
  6. 6. The method of claim 1, the method further comprising: Reducing the numerical aperture of a light source generating the illumination light; Providing the illumination light into an optical path of the interferometer using a beam splitter that directs the illumination light into an objective lens, and Wherein the illumination optics having the first numerical aperture comprises the numerical aperture of the light source and the objective lens; wherein the collection optics having the second numerical aperture greater than the first numerical aperture comprises the objective lens.
  7. 7. The method of claim 1, wherein the plurality of structures comprises at least one of trenches, holes, and High Aspect Ratio (HAR) structures, wherein the HAR structures have a width of 5 μιη or less and a depth of 30 μιη or more.
  8. 8. The method of claim 1, the method further comprising: detecting a top interference fringe corresponding to a top surface of the sample in the plurality of images; Detecting bottom interference fringes corresponding to bottoms of the plurality of structures in the plurality of images, and The depth of the plurality of structures is determined based on a distance between the top interference fringe and the bottom interference fringe.
  9. 9. An interferometer configured to characterize a region of a sample comprising a plurality of structures, the interferometer comprising: means for dividing illumination light into sample light to be incident on and reflected by the sample and reference light to be incident on and reflected by a reference mirror; means for illuminating the region of the sample with the sample light using illumination optics having a first numerical aperture; Means for focusing collection optics at a focal location relative to the sample, the collection optics having a second numerical aperture that is greater than the first numerical aperture; Means for changing an optical path difference between the sample light and the reference light without changing the focal position of the collection optics relative to the sample; Means for imaging reflected sample light from the sample with reflected reference light from the reference mirror with the collection optics interfering at a plurality of optical path differences to produce a plurality of images, and Means for analyzing the plurality of images of the region of the sample including the plurality of structures to characterize the region of the sample.
  10. 10. The interferometer of claim 9, wherein the means for separating the illumination light into sample light and reference light is positioned between the collection optics and the sample.
  11. 11. The interferometer of claim 9, wherein said means for changing the optical path difference between the sample light and the reference light without changing the focus positioning of the collection optics relative to the sample performs at least one of moving the reference mirror and moving a beam splitter that splits the illumination light into the sample light and the reference light.
  12. 12. The interferometer of claim 9, said interferometer further comprising: means for dividing the reference light to produce a second reference light to be incident on and to be reflected by a second reference mirror; Means for changing a second optical path difference between the sample light and the second reference light without changing the focal position of the collection optics relative to the sample; Means for imaging reflected sample light from the sample interfering at a plurality of second optical path differences with reflected second reference light from the second reference mirror using the collection optics to produce a second plurality of images, and Means for analyzing the second plurality of images of the region of the sample comprising the plurality of structures to characterize the region of the sample.
  13. 13. The interferometer of claim 12, wherein the second optical path difference is different than the optical path difference, and wherein reflected sample light from the sample that interferes with reflected reference light from the reference mirror in the plurality of images at the optical path difference produces a top interference fringe corresponding to a top surface of the sample, and reflected sample light from the sample that interferes with reflected second reference light from the second reference mirror in the second plurality of images at the second optical path difference produces a bottom interference fringe corresponding to a bottom of the plurality of structures.
  14. 14. The interferometer of claim 9, said interferometer further comprising: means for reducing the numerical aperture of a light source generating said illumination light; Means for providing the illumination light to the interferometer, directing the illumination light into an optical path of an objective lens, and Wherein the illumination optics having the first numerical aperture comprises the numerical aperture of the light source and the objective lens; wherein the collection optics having the second numerical aperture greater than the first numerical aperture comprises the objective lens.
  15. 15. The interferometer of claim 9, wherein the plurality of structures comprises at least one of trenches, holes, and High Aspect Ratio (HAR) structures, wherein the HAR structures have a width of 5 μιη or less and a depth of 30 μιη or more.
  16. 16. The interferometer of claim 9, said interferometer further comprising: Means for detecting a top interference fringe in the plurality of images corresponding to a top surface of the sample; means for detecting bottom interference fringes corresponding to bottoms of the plurality of structures in the plurality of images, and Means for determining the depth of the plurality of structures based on a distance between the top interference fringe and the bottom interference fringe.
  17. 17. An interferometer configured to characterize a region of a sample comprising a plurality of structures, the interferometer comprising: A beam splitter configured to split illumination light into sample light to be incident on and reflected by the sample and reference light to be incident on and reflected by a reference mirror; Illumination optics having a first numerical aperture and configured to illuminate the region of the sample with the sample light; Collection optics configured to focus at a focal location relative to the sample, the collection optics having a second numerical aperture that is greater than the first numerical aperture; An actuator configured to change an optical path difference between the sample light and the reference light without changing the focal position of the collection optics relative to the sample; a detector configured to image reflected sample light from the sample with reflected reference light from the reference mirror with the collection optics at a plurality of optical path differences to produce a plurality of images, and At least one processor configured to analyze the plurality of images of the region of the sample including the plurality of structures to characterize the region of the sample.

Description

Interferometer configured to measure small structures Technical Field The subject matter described herein relates to interferometry, and more particularly to methods and apparatus for measuring deep and narrow structures. Background Interferometry is a well-known method for accurately measuring various physical parameters, including the shape or contour of the surface of a solid object. A plurality of data frames are acquired, each data frame being at a different relative phase shift between the reference beam and the test beam, and the data is processed by a computer to determine the relative path difference between the reference beam and the test beam with high accuracy. The semiconductor and other similar industries are producing smaller and more complex structures that require non-contact evaluation during fabrication. For example, one type of structure being produced is Through Silicon Vias (TSVs), which are used to connect devices and chips in advanced packaging of integrated circuits. For example, a TSV may include both trenches and holes. Structures such as TSVs are sometimes referred to as High Aspect Ratios (HARs) due to their large depth and narrow width. As the depth of complex structures such as TSVs continues to increase and the width narrows, it becomes increasingly difficult if not impossible to measure the profile of these devices using conventional optical metrology methods. For example, with conventional interferometers, insufficient amounts of light can penetrate the depth of the structure and return to the detector to provide adequate signals. Disclosure of Invention The interferometer is configured to characterize a plurality of structures in a sample, including structures having a high aspect ratio. The interferometer illuminates the sample with illumination optics having a numerical aperture smaller than the collection optics for collecting reflected light from the sample, thereby increasing the amount of light penetrating the depth of the structure to improve the signal-to-noise ratio. In addition, the collection optics are focused at a fixed focal position relative to the sample while varying the optical path difference between the sample light and the reference light, or modulating the periodicity of the spectrum of the light to scan a coherent stripe across the depth of the structure during measurement. Images of the region of the sample are collected at different optical path differences between the reference light and the sample light and analyzed to characterize the structure in the sample. In one implementation, a method of characterizing an area of a sample including a plurality of structures with an interferometer includes dividing illumination light into sample light to be incident on and reflected by the sample and reference light to be incident on and reflected by a reference mirror. The method includes illuminating an area of the sample with sample light using illumination optics having a first numerical aperture, and focusing collection optics at a focal position relative to the sample, the collection optics having a second numerical aperture that is greater than the first numerical aperture. One or more coherence envelopes resulting from interference of reflected sample light from the sample with reflected reference light from the reference mirror are scanned through the depth of the sample without altering the focal position of the collection optics relative to the sample. The method further includes imaging, with the collection optics, reflected sample light from the sample interfering with reflected reference light from the reference mirror at a plurality of depths of one or more coherence envelopes to produce a plurality of images. Multiple images of a region of the sample including multiple structures are analyzed to characterize the region of the sample. In one implementation, an interferometer configured for characterizing a region of a sample comprising a plurality of structures includes means for separating illumination light into sample light to be incident on and reflected by the sample and reference light to be incident on and reflected by a reference mirror. The interferometer further comprises means for illuminating an area of the sample with the sample light using illumination optics having a first numerical aperture, and means for focusing collection optics at a focal position relative to the sample, the collection optics having a second numerical aperture that is greater than the first numerical aperture. The interferometer further comprises means for scanning one or more coherence envelopes generated by interference of reflected sample light from the sample with reflected reference light from the reference mirror through the depth of the sample without changing the focal position of the collection optics relative to the sample. The interferometer further includes means for imaging, with the collection optics, reflected sample light from the sample in