CN220473342U - Optical detection system - Google Patents
Optical detection system Download PDFInfo
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- CN220473342U CN220473342U CN202321819594.XU CN202321819594U CN220473342U CN 220473342 U CN220473342 U CN 220473342U CN 202321819594 U CN202321819594 U CN 202321819594U CN 220473342 U CN220473342 U CN 220473342U
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- light
- detection system
- optical detection
- mirror
- detector
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- 238000001514 detection method Methods 0.000 title claims abstract description 95
- 230000003287 optical effect Effects 0.000 title claims abstract description 88
- 238000009304 pastoral farming Methods 0.000 claims abstract description 26
- 230000007547 defect Effects 0.000 description 38
- 238000007689 inspection Methods 0.000 description 20
- 238000000034 method Methods 0.000 description 8
- 238000003384 imaging method Methods 0.000 description 6
- 238000002310 reflectometry Methods 0.000 description 5
- 238000009826 distribution Methods 0.000 description 4
- 230000035945 sensitivity Effects 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 3
- 238000001459 lithography Methods 0.000 description 3
- 238000000206 photolithography Methods 0.000 description 3
- 230000004075 alteration Effects 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- GALOTNBSUVEISR-UHFFFAOYSA-N molybdenum;silicon Chemical compound [Mo]#[Si] GALOTNBSUVEISR-UHFFFAOYSA-N 0.000 description 1
- 238000001259 photo etching Methods 0.000 description 1
- 238000004626 scanning electron microscopy Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
Abstract
The utility model discloses an optical detection system. An optical detection system includes a scanning stage, a Wolter mirror, and a detector. The scanning stage is for carrying a sample to be measured and is arranged to enable the sample to be illuminated by incident light to produce reflected and scattered light. The Wolter mirror is arranged such that reflected and scattered light grazing incidence to the Wolter mirror and the grazing incidence light is reflected. The detector is arranged to receive light reflected from the Wolter mirror.
Description
Technical Field
The present utility model relates generally to the field of optical inspection, and in particular to optical inspection of defects in lithographic technology.
Background
Defect-free masks are one of the key elements to ensure yield in chip manufacturing processes using photolithography. Therefore, defect detection (e.g., mask defect detection, wafer detection, etc.) in photolithography is one of the core technologies of photolithography processes.
Some lithographic techniques use masks that act as reflective optical elements, which can result in more complex defect structures (e.g., phase defects (phase defects) being added, etc.) on the mask. Further, since these masks often have a structure of a multilayer film, part of defects may be buried in the multilayer film, making it difficult to detect with an atomic force microscope, a scanning electron microscope (Scanning Electron Microscopy, SEM), an electron beam, or the like.
Current optical inspection methods for inspecting these masks require the use of inspection light sources similar to those used for photolithographic exposure, for example, the actinic method. The active method employs an ultraviolet light source and is typically a dark field defect detection method based on Schwarzschild optics. Fig. 1 shows an optical inspection system 100 for dark field defect inspection of a mask using a Schwarzschild optical system 130. The optical inspection system 100 includes a mask 110, a Schwarzschild optical system 130, and a detector 150. In inspection, light from a light source (not shown) is incident on the mask 110 (for clarity, the incident light is not shown) to produce scattered light that is reflected by the Schwarzschild optical system 130 to the detector 150 (shown in solid and dashed light paths in fig. 1). The Schwarzschild optical system 130 may be composed of two spherical mirrors, which may eliminate many higher order aberrations, and thus may achieve a high imaging resolution. However, in the optical inspection system 100 using the Schwarzschild optical system 130, scattered light generated due to defects of the mask 110 is incident on the mirror surface of the Schwarzschild optical system 130 near normal incidence, which results in that the signal indicating the scattered light of the defects, which is finally collected by the detector 150, is greatly limited by the reflectivity and bandwidth of the inspection system (e.g., the Schwarzschild optical system 130).
Since mask defect detection needs to ensure both detection speed and detection sensitivity, it is important to improve the collection ability of scattered light, i.e., to improve the signal-to-noise ratio of the imaging system in the detection system. There is a need in the art for an optical detection system that can greatly increase the scattered light signal collection capability while ensuring sufficient imaging resolution to simultaneously increase detection speed and detection sensitivity.
Disclosure of Invention
The present utility model provides a technique capable of improving the detection speed and detection sensitivity for defect detection in a lithography technique.
According to the present utility model, there is provided an optical detection system comprising: a scanning stage for carrying a sample to be measured, the scanning stage being arranged to enable the sample to be illuminated by incident light to produce reflected and scattered light; a Wolter mirror arranged to at least grazing the scattered light to the Wolter mirror and reflect the grazing light; and a detector arranged to receive light reflected from the Wolter mirror.
The optical detection system as described above, further comprising: a light source for emitting incident light for illuminating the sample.
An optical detection system according to any preceding claim, wherein the light source comprises an ultraviolet light source.
An optical detection system according to any preceding claim wherein the detector comprises an ultraviolet charge coupled device camera.
An optical detection system according to any one of the preceding claims, wherein the light source comprises an X-ray light source.
The optical detection system of any one of the preceding claims, further comprising: a mirror arranged to graze light from the light source to the mirror and reflect the grazing light to illuminate the sample.
The optical detection system of any one of the preceding claims, further comprising: and the vacuum cavity is used for accommodating the scanning table, the Wolter mirror, the light source and the detector.
The optical detection system of any one of the preceding claims, further comprising: an aperture stop for limiting a beam diameter of scattered and/or reflected light that can be grazing incidence to the Wolter mirror and/or a beam diameter of light reflected from the Wolter mirror.
An optical detection system according to any preceding claim, wherein the scanning stage is arranged to bring the sample parallel to the detection face of the detector and the scanning stage is arranged to move the sample in a plane parallel to and/or perpendicular to the detection face.
The optical inspection system of any preceding claim, wherein the sample is a reticle and the scanning stage is arranged to cause light illuminating the reticle to be incident on the reticle near normal incidence.
An optical inspection system according to any preceding claim, wherein the sample is a wafer and the scanning stage is arranged to graze light illuminating the wafer to the wafer.
The optical detection system provided by the utility model can effectively overcome the limitation of reflectivity and bandwidth of the optical system in defect detection aiming at defect detection in the photoetching technology, so that the detection speed and the detection sensitivity are improved.
Drawings
Various non-limiting embodiments of the present utility model are described in connection with the accompanying drawings, in which:
fig. 1 shows an optical inspection system for dark field defect inspection of a mask using a Schwarzschild optical system.
Fig. 2 shows an optical detection system according to an embodiment of the utility model.
Fig. 3 shows an optical detection system according to another embodiment of the utility model.
Fig. 4 shows an optical detection system according to another embodiment of the utility model.
Fig. 5 shows an optical detection system according to another embodiment of the utility model.
Detailed Description
In this application, the term "near normal incidence" refers to incidence having an angle of incidence in the range of 0-10 °. As known to those skilled in the art, the term "Wolter lens" refers to an optical system lens comprising two coaxial confocal conic surfaces of revolution (e.g., ellipsoidal, hyperbolic, parabolic) that may include Wolter type I, wolter type II and Wolter type III optical system lenses.
Fig. 2 shows an optical detection system 200 according to one embodiment of the utility model. The optical inspection system 200 shown in fig. 2 may be used to optically inspect reticle 210 for defects.
As an example, the reticle 210 may be a reticle for Ultraviolet (e.g., deep Ultraviolet (DUV), extreme Ultraviolet (Extreme Ultraviolet, EUV), etc.) lithography techniques.
The optical detection system 200 may include a scanning stage (not shown), a Wolter mirror 230, and a detector 250. The scanning stage may be used to carry a reticle 210 to be inspected. The scanning stage is arranged to enable reticle 210 to be illuminated by incident light 220 to produce reflected light (not shown) and scattered light 240, wherein scattered light 240 may contain information reflecting defects of reticle 210. Specifically, the scanning stage is arranged such that incident light 220 is incident on reticle 210 near normal incidence.
The Wolter mirror 230 is arranged to at least grazing incidence of scattered light 240 from reticle 210 to Wolter mirror 230 and reflect the grazing incidence light to form reflected light 260. In some embodiments, wolter mirror 230 may also be arranged to grazing incidence of reflected light from reticle 210 to Wolter mirror 230 and reflect the grazing incidence of light. Specifically, wolter mirror 230 may collect the above-described scattered light 240 (and optionally reflected light) within a certain numerical aperture for imaging onto detector 250. The detector 250 may be arranged to receive reflected light 260 reflected from the Wolter mirror 230, and the detector 250 may acquire a defect distribution image on the reticle 210 by detecting the reflected light 260, since the reflected light 260 is reflected from the scattered light 240 described above, and the scattered light 240 contains information indicative of defects of the reticle 210. By way of example, wolter mirror 230 may be a Wolter type I, wolter type II or Wolter type III optical system lens.
In some embodiments, the scanning stage may be movable. In some embodiments, the scanning stage is arranged to move the reticle 210 parallel to the detection plane of the detector 250, and the scanning stage is arranged to move the reticle 210 in a plane parallel to the detection plane (e.g., in an up-down direction and/or in a direction perpendicular to the page in fig. 2) so that defect detection can be performed for various locations on the reticle 210.
In some embodiments, the scanning stage is arranged to move the reticle 210 in a direction perpendicular to the detection plane (e.g., in a side-to-side direction in fig. 2), such that the distance between the reticle 210 and the Wolter mirror 230 may be adjusted to adjust the angle of incidence of the scattered light 240 grazing the Wolter mirror 230. In some embodiments, the scanning stage is arranged to move the reticle 210 in a direction perpendicular to the detection plane in response to the intensity of the reflected light 260 received by the detector 250. In some embodiments, detector 250 may detect the intensity of reflected light 260 in real time while reticle 210 is moving in a direction perpendicular to the detection plane, thereby determining an optimal angle of incidence of scattered light 240 with the maximum intensity of reflected light 260.
The current dark field defect detection system based on the Schwarzschild optical system is limited by the peak value of the reflectivity curve and the bandwidth of the multilayer film reflector, the theoretical value of the reflectivity peak value is only about 40%, and the actual measurement value on literature materials is only 10-20%. In contrast, an optical detection system (e.g., optical detection system 200) according to embodiments of the present utility model may have an average reflectivity of several times more than a dark field defect detection system based on grazing incidence reflective Wolter mirrors.
Furthermore, for dark field defect detection systems based on Schwarzschild optical systems, the bandwidth of the commonly used molybdenum-silicon multilayer film mirrors is typically 0.5nm, and multiple reflections can lead to further narrowing of the bandwidth. In contrast, the bandwidth of an optical detection system (e.g., optical detection system 200) according to embodiments of the present utility model is not limited in the corresponding ultraviolet band. These will greatly increase the signal strength of the dark field defect detection system and more importantly make possible the use of wide bandwidth uv light sources.
It can be seen that by utilizing the grazing incidence reflection imaging system of the Wolter mirror 230, a wide bandwidth light source can be allowed to illuminate the reticle 210 to be tested, thereby improving the signal intensity and the signal-to-noise ratio; while allowing scanning imaging at wavelengths within a wide range of wavelengths, thereby increasing the means of identifying signals indicative of defects on reticle 210.
In some embodiments, the optical detection system 200 may include a light source (not shown). The light source emits incident light 220 that irradiates reticle 210. In some embodiments, the light source may include an ultraviolet (e.g., DUV, EUV, etc.) light source. In some embodiments, the ultraviolet light source may comprise an ultraviolet light source of any bandwidth. Accordingly, the detector 250 may include an ultraviolet charge coupled device (Charge Coupled Device, CCD) camera. In alternative embodiments, the light source may comprise an X-ray light source. Accordingly, the surface of the Wolter mirror 230 may be coated such that only light (e.g., ultraviolet light or X-rays) within a wavelength range of light emitted from the light source is reflected, thereby further improving reflection efficiency and signal acquisition efficiency.
In some embodiments, optical detection system 200 may include an aperture stop 270. The aperture stop 270 may be used to limit the beam diameter of scattered and/or reflected light that can be grazing incidence to the Wolter mirror 230. That is, wolter mirror 230 is caused to collect the above-described scattered light 240 and/or reflected light within a certain numerical aperture. Alternatively or additionally, the optical detection system 200 may include an aperture stop 280. An aperture stop 280 may be used to limit the beam diameter of the reflected light 260 reflected from the Wolter mirror 230. That is, the detector 250 is caused to detect reflected light 260 reflected from the Wolter mirror 230 within a certain numerical aperture.
In some embodiments, optical detection system 200 may include a vacuum chamber (not shown) that may house the scanning stage, reticle 210, wolter mirror 230, light source, and detector 250.
Fig. 3 shows an optical detection system 300 according to another embodiment of the utility model. Similar to optical inspection system 200 of FIG. 2, optical inspection system 300 of FIG. 3 may be used to optically inspect reticle 310 for defects.
As an example, reticle 310 may be a reticle for ultraviolet (e.g., DUV, EUV, etc.) lithography.
Optical detection system 300 may include a scanning stage (not shown), a Wolter mirror 330, and a detector 350, which may be similar to scanning stage, wolter mirror 230, and detector 250, respectively, of optical detection system 200 in FIG. 2. Optical detection system 300 may also include a mirror 370. Mirror 370 is arranged to grazing light from a light source (not shown) to mirror 370 and reflect the grazing light to illuminate reticle 310. Since the reflected light striking the detector 350 is reflected by the scattered light generated on the Wolter mirror 330, which contains information indicating defects of the reticle 310, the detector 350 can acquire a defect distribution image on the reticle 310 by detecting the reflected light. By illuminating reticle 310 with both grazing incidence and reflected light, the signal strength and signal-to-noise ratio of the optical signal received by detector 350 may be further improved.
Other aspects of the optical detection system 300 may be similar to the optical detection system 200 of fig. 2.
Fig. 4 shows an optical detection system 400 according to another embodiment of the utility model. The optical inspection system 400 shown in fig. 4 may be used to optically inspect a wafer 410 for defects.
The optical detection system 400 may include a scanning stage (not shown), a Wolter mirror 430, and a detector 450. The scanning stage may be used to carry a wafer 410 to be inspected. The scanning stage is arranged to enable the wafer 410 to be illuminated by incident light 420 to produce reflected light and scattered light, wherein the scattered light may contain information reflecting defects of the wafer 410. Since the reflected light irradiated to the detector 450 is reflected by the scattered light generated on the Wolter mirror 430, which contains information indicating defects of the wafer 410, the detector 450 can acquire a defect distribution image on the wafer 410 by detecting the reflected light. Specifically, the scanning stage is arranged to grazing incidence of the incident light 420 to the wafer 410. In some embodiments, the scanning stage may be movable such that defect detection may be performed for various locations on the wafer 410.
In some embodiments, the scanning stage may be movable. In some embodiments, the scanning stage is arranged such that the wafer 410 is parallel to the detection plane of the detector 450, and the scanning stage is arranged such that the wafer 410 is moved in a plane parallel to the detection plane (e.g., in the up-down direction and/or in a direction perpendicular to the paper plane in fig. 4) so that defect detection can be performed for various locations on the wafer 410.
In some embodiments, the scanning stage is arranged to move the wafer 410 in a direction perpendicular to the detection plane (e.g., in a side-to-side direction in fig. 4) such that the distance between the wafer 410 and the Wolter mirror 430 can be adjusted to adjust the angle of incidence of the scattered light grazing incidence to the Wolter mirror 430. In some embodiments, the scanning stage is arranged to move the wafer 410 in a direction perpendicular to the detection plane in response to the intensity of the reflected light received by the detector 450. In some embodiments, the detector 450 may detect the intensity of the reflected light in real time while the wafer 410 is moving in a direction perpendicular to the detection plane, thereby determining an optimal incident angle of the scattered light with the maximum intensity of the reflected light.
Other aspects of the optical detection system 400 may be similar to the optical detection system 200 of fig. 2.
Fig. 5 shows an optical detection system 500 according to another embodiment of the utility model. Similar to the optical inspection system 400 of fig. 4, the optical inspection system 500 shown in fig. 5 may be used to optically inspect a wafer 510 for defects.
Optical detection system 500 may include a scanning stage (not shown), a Wolter mirror 530, and a detector 550, which may be similar to scanning stage, wolter mirror 230, and detector 250, respectively, of optical detection system 200 in FIG. 2. The optical detection system 500 may also include a mirror 570. The mirror 570 is arranged to grazing incidence of light emitted by a light source (not shown) to the mirror 570 and to reflect the grazing incidence of light to illuminate the wafer 510. Since the reflected light striking the detector 550 is reflected from scattered light generated on the Wolter mirror 530, which contains information indicating defects of the wafer 510, the detector 550 can acquire a defect distribution image on the wafer 510 by detecting the reflected light. By illuminating the wafer 510 with both grazing incidence and reflected light, the signal strength and signal-to-noise ratio of the optical signal received by the detector 550 may be further improved.
Other aspects of the optical detection system 500 may be similar to the optical detection system 200 of fig. 2.
Various embodiments of the present utility model have been described with reference to the accompanying drawings. The embodiments are exemplary and not limiting.
Claims (11)
1. An optical detection system, comprising:
a scanning stage for carrying a sample to be detected, the scanning stage being arranged to enable the sample to be illuminated by incident light to produce reflected and scattered light;
a Wolter mirror arranged to at least grazing the scattered light to the Wolter mirror and reflect the grazing light; and
a detector arranged to receive light reflected from the Wolter mirror.
2. The optical detection system of claim 1, further comprising:
a light source that emits incident light that irradiates the sample.
3. The optical detection system of claim 2, wherein the light source comprises an ultraviolet light source.
4. The optical detection system of claim 3, wherein the detector comprises an ultraviolet charge coupled device camera.
5. The optical detection system of claim 2, wherein the light source comprises an X-ray light source.
6. The optical detection system of claim 2, further comprising:
a mirror arranged to graze light from the light source to the mirror and reflect the grazing light to illuminate the sample.
7. The optical detection system of claim 2, further comprising:
and the vacuum cavity is used for accommodating the scanning table, the Wolter mirror, the light source and the detector.
8. The optical detection system of claim 1, further comprising:
an aperture stop for limiting a beam diameter of scattered and/or reflected light that can be grazing incidence to the Wolter mirror and/or a beam diameter of light reflected from the Wolter mirror.
9. The optical detection system of claim 1, wherein,
the scanning stage is arranged such that the sample is parallel to the detection face of the detector, and
the scanning stage is arranged to move the sample in a plane parallel to the detection face and/or perpendicular to the detection face.
10. The optical detection system of claim 1, wherein,
the sample is a reticle, and
the scanning stage is arranged to cause light illuminating the reticle to be incident to the reticle near normal incidence.
11. The optical detection system of claim 1, wherein,
the sample is a wafer, and
the scanning stage is arranged to graze light illuminating the wafer to the wafer.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202321819594.XU CN220473342U (en) | 2023-07-11 | 2023-07-11 | Optical detection system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202321819594.XU CN220473342U (en) | 2023-07-11 | 2023-07-11 | Optical detection system |
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| Publication Number | Publication Date |
|---|---|
| CN220473342U true CN220473342U (en) | 2024-02-09 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202321819594.XU Active CN220473342U (en) | 2023-07-11 | 2023-07-11 | Optical detection system |
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| CN (1) | CN220473342U (en) |
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- 2023-07-11 CN CN202321819594.XU patent/CN220473342U/en active Active
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