U.S. patent application number 15/879611 was filed with the patent office on 2019-07-25 for position feedback for multi-beam particle detector.
The applicant listed for this patent is KLA-Tencor Corporation. Invention is credited to Alan D. Brodie, Christopher Sears.
Application Number | 20190227010 15/879611 |
Document ID | / |
Family ID | 67069531 |
Filed Date | 2019-07-25 |
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United States Patent
Application |
20190227010 |
Kind Code |
A1 |
Brodie; Alan D. ; et
al. |
July 25, 2019 |
POSITION FEEDBACK FOR MULTI-BEAM PARTICLE DETECTOR
Abstract
A multi-beam metrology system includes an illumination source
configured to generate a beam array, an illumination sub-system to
direct the beam array to a sample at an array of measurement
locations, an imaging sub-system to image the array of measurement
locations as an array of imaged spots in a detection plane, and a
detection assembly to generate detection signal channels associated
with each of the imaged spots. The detection assembly includes an
array of detection elements configured to receive the imaged spots
with separate detection elements, and one or more position
detectors to measure positions of the imaged spots in the detection
plane. The detection assembly further generates feedback signals
for the imaging sub-system based on the measured positions of the
imaged spots to adjust the positions of one or more of the imaged
spots in the detection plane to maintain alignment of the array of
detection elements.
Inventors: |
Brodie; Alan D.; (Palo Alto,
CA) ; Sears; Christopher; (Fremont, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KLA-Tencor Corporation |
Milpitas |
CA |
US |
|
|
Family ID: |
67069531 |
Appl. No.: |
15/879611 |
Filed: |
January 25, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 23/203 20130101;
G01N 23/2251 20130101; G01N 2223/6116 20130101; H01J 2237/2445
20130101; H01J 2237/2446 20130101; G01N 23/2255 20130101; H01J
37/265 20130101; H01J 37/28 20130101; H01J 37/244 20130101 |
International
Class: |
G01N 23/2251 20060101
G01N023/2251; G01N 23/2255 20060101 G01N023/2255 |
Claims
1. A multi-beam metrology system, comprising: an illumination
source configured to generate a beam array; an illumination
sub-system including one or more focusing elements configured to
direct the beam array to a sample at an array of measurement
locations; an imaging sub-system configured to image the array of
measurement locations as an array of imaged spots in a detection
plane, the imaging sub-system including at least one of an
adjustable lens, an adjustable deflector, or an adjustable
stigmator, the one or more adjustable beam control elements
configured to adjust positions of one or more of the imaged spots
in the detection plane; and a detection assembly configured to
generate detection signal channels associated with at least some of
the imaged spots, the detection assembly comprising: an array of
detection elements configured to receive the imaged spots with
separate detection elements; and one or more position detectors
configured to measure positions of the imaged spots in the
detection plane, wherein the detection assembly generates feedback
signals indicative of alignment of the imaged spots on the array of
detection elements based on the positions of the imaged spots in
the detection plane, wherein the imaging sub-system adjusts the
positions of one or more of the imaged spots in the detection plane
based on the feedback signals to maintain alignment of the imaged
spots on the array of detection elements.
2. The multi-beam metrology system of claim 1, wherein the
illumination source comprises: one or more particle beam sources,
wherein the beam array includes a particle beam array.
3. The multi-beam metrology system of claim 2, wherein the particle
beam array comprises: an array of at least one of electron beams or
ion beams.
4. The multi-beam metrology system of claim 2, wherein the
detection assembly comprises: a scintillator located at the
detection plane, the scintillator configured to generate optical
radiation in response to receiving particles associated with the
imaged spots; and one or more detector lenses configured to image
the optical radiation generated by the scintillator onto the array
of detection elements.
5. The multi-beam metrology system of claim 4, wherein the array of
detection elements comprises: an array of optical fibers, wherein
the one or more detector lenses provide an image of the optical
radiation generated by the scintillator to input faces of the array
of optical fibers; and one or more optical detectors coupled to
output faces of the array of optical fibers and configured to
receive the optical radiation generated by the scintillator and
propagating through the array of optical fibers.
6. The multi-beam metrology system of claim 5, wherein the
detection assembly further comprises: a beamsplitter located
between the one or more detector lenses and the one or more
position detectors configured to provide a secondary image of the
optical radiation generated by the scintillator to the one or more
position detectors, wherein the feedback signals maintain alignment
of the imaged spots on the input faces of the array of optical
fibers based on the secondary image.
7. The multi-beam metrology system of claim 6, wherein the one or
more position detectors comprises: a camera.
8. The multi-beam metrology system of claim 7, wherein the camera
comprises: at least one of a charge-coupled device or a
complementary metal oxide semiconductor device.
9. The multi-beam metrology system of claim 1, wherein the array of
detection elements comprises: an array of diodes located at the
detection plane.
10. The multi-beam metrology system of claim 9, wherein a diode of
the array of diodes includes two or more pixels, wherein the one or
more position detectors includes the two or more pixels, wherein a
position of an imaged spot of the array of imaged spots on the
diode is determined based on a relative signal strength of the two
or more pixels, wherein the feedback signals maintain alignment of
the imaged spots on the array of diodes.
11. The multi-beam metrology system of claim 10, wherein the two or
more pixels comprises: three pixels.
12. The multi-beam metrology system of claim 9, wherein the array
of diodes comprises: an array of PIN diodes.
13. The multi-beam metrology system of claim 1, wherein the imaging
sub-system is configured to adjust a focal position of at least one
imaged spot with respect to the detection plane based on the
feedback signals.
14. The multi-beam metrology system of claim 1, wherein the imaging
sub-system is configured to adjust a transverse position of at
least one imaged spot in the detection plane based on the feedback
signals.
15. The multi-beam metrology system of claim 1, wherein the imaging
sub-system is configured to provide at least one of astigmatism
correction or near-edge correction based on the feedback
signals.
16. A detection assembly, comprising: an array of detection
elements configured to receive one or more imaged spots at a
detection plane with separate detection elements, wherein the one
or more imaged spots include radiation emanating from a sample in
response to a beam array from a multi-beam illumination source and
imaged to the detection plane by an imaging sub-system, wherein the
imaging sub-system includes at least one of an adjustable lens, an
adjustable deflector, or an adjustable stigmator; and one or more
position detectors configured to measure positions of the imaged
spots in the detection plane, wherein the detection assembly
generates feedback signals indicative of alignment of the imaged
spots on the array of detection elements based on the positions of
the imaged spots in the detection plane, wherein the imaging
sub-system adjusts the positions of one or more of the imaged spots
in the detection plane based on the feedback signals to maintain
alignment of the imaged spots on the array of detection
elements.
17. The detection assembly of claim 16, wherein the beam array
comprises: an array of at least one of electron beams or ion
beams.
18. The detection assembly of claim 16, wherein the detection
assembly further comprises: a scintillator located at the detection
plane, the scintillator configured to generate optical radiation in
response to receiving particles associated with the imaged spots;
and one or more detector lenses configured to image the optical
radiation generated by the scintillator onto the array of detection
elements.
19. The detection assembly of claim 18, wherein the array of
detection elements comprises: an array of optical fibers, wherein
the one or more detector lenses provide an image of the optical
radiation generated by the scintillator to input faces of the array
of optical fibers; and one or more optical detectors coupled to
output faces of the array of optical fibers and configured to
receive the optical radiation generated by the scintillator and
propagating through the array of optical fibers.
20. The detection assembly of claim 19, wherein the detection
assembly further comprises: a beamsplitter located between the one
or more detector lenses and the one or more position detectors
configured to provide a secondary image of the optical radiation
generated by the scintillator to the one or more position
detectors, wherein the feedback signals maintain alignment of the
imaged spots on the input faces of the array of optical fibers
based on the secondary image.
21. The detection assembly of claim 20, wherein the one or more
position detectors comprises: a camera.
22. The detection assembly of claim 21, wherein the camera
comprises: at least one of a charge-coupled device or a
complementary metal oxide semiconductor device.
23. The detection assembly of claim 16, wherein the array of
detection elements comprises: an array of diodes located at the
detection plane.
24. The detection assembly of claim 23, wherein a diode of the
array of diodes includes two or more pixels, wherein the one or
more position detectors includes the two or more pixels, wherein a
position of an imaged spot of the array of imaged spots on the
diode is determined based on a relative signal strength of the two
or more pixels, wherein the feedback signals maintain alignment of
the imaged spots on the array of diodes.
25. The detection assembly of claim 24, wherein the two or more
pixels comprises: three pixels.
26. The detection assembly of claim 23, wherein the array of diodes
comprises: an array of PIN diodes.
27. The detection assembly of claim 16, wherein the imaging
sub-system is configured to adjust a focal position of at least one
imaged spot with respect to the detection plane based on the
feedback signals.
28. The detection assembly of claim 16, wherein the imaging
sub-system is configured to adjust a transverse position of at
least one imaged spot in the detection plane based on the feedback
signals.
29. The detection assembly of claim 16, wherein the imaging
sub-system is configured to provide at least one of astigmatism
correction or near-edge correction based on the feedback
signals.
30. A method for detecting positions of multiple particle beams,
comprising: generating a particle beam array with an illumination
source; directing the particle beam array to an array of
measurement locations on a sample; imaging the array of measurement
locations to an array of imaged spots at a detection plane with an
imaging sub-system including at least one of an adjustable lens, an
adjustable deflector, or an adjustable stigmator; receiving the
imaged spots with separate detection elements of an array of
detection elements; measuring, with one or more position detectors,
positions of the imaged spots at the detection plane; and
generating feedback signals for the imaging sub-system based on the
measured positions of the imaged spots to adjust the positions of
the one or imaged spots in the detection plane to maintain
alignment of the imaged spots on the array of detection
elements.
31. The method of claim 30, further comprising: adjusting the
positions of the imaged spots in the detection plane with the
imaging sub-system based on the feedback signals to maintain
alignment of the array of detection elements.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to particle beam
detection and, more particularly, to position detection of multiple
particle beams.
BACKGROUND
[0002] Inspection systems identify and classify defects on
semiconductor wafers to generate a defect population on the sample.
Further, inspection systems may identify defects on unprocessed
wafers (e.g., prior to one or more fabrication steps) or at any
time during sample fabrication. A given semiconductor wafer
including one or more fabricated layers may include hundreds of
chips, each chip containing thousands of components of interest,
and each component of interest may have millions of instances on a
given layer of a chip. As a result, inspection systems may generate
vast numbers of data points (e.g., hundreds of billions of data
points for some systems) on a given wafer. Further, the demand for
ever-shrinking devices leads to increased demands on inspection
systems, which may negatively impact the throughput. Therefore, it
would be desirable to provide a system and method for curing
shortcomings such as those identified above.
SUMMARY
[0003] A multi-beam metrology system is disclosed in accordance
with one or more illustrative embodiments of the present
disclosure. In one illustrative embodiment, the system includes an
illumination source configured to generate a beam array. In another
illustrative embodiment, the system includes an illumination
sub-system configured to direct the beam array to a sample at an
array of measurement locations. In another illustrative embodiment,
the system includes an imaging sub-system configured to image the
array of measurement locations as an array of imaged spots in a
detection plane, the imaging sub-system further configured to
adjust positions of one or more of the imaged spots in the
detection plane. In another illustrative embodiment, the system
includes a detection assembly configured to generate detection
signal channels associated with each of the imaged spots. In one
illustrative embodiment, the detection assembly includes an array
of detection elements configured to receive the imaged spots with
separate detection elements. In another illustrative embodiment,
the detection assembly includes one or more position detectors
configured to measure positions of the imaged spots in the
detection plane. In another illustrative embodiment, the detection
assembly generates feedback signals for the imaging sub-system
based on the measured positions of the imaged spots to adjust the
positions of one or more of the imaged spots in the detection plane
to maintain alignment of the array of detection elements.
[0004] A detection assembly is disclosed in accordance with one or
more illustrative embodiments of the present disclosure. In one
illustrative embodiment, the detection assembly includes an array
of detection elements configured to receive one or more imaged
spots at a detection plane with separate detection elements. In
another illustrative embodiment, the one or more imaged spots
include radiation emanating from a sample in response to a beam
array from a multi-beam illumination source and imaged to the
detection plane by an imaging sub-system, of an imaging sub-system.
In another illustrative embodiment, the detection assembly includes
one or more position detectors configured to measure positions of
the imaged spots in the detection plane. In another illustrative
embodiment, the detection assembly generates feedback signals for
the imaging sub-system based on the measured positions of the
imaged spots in the detection plane to adjust the positions of one
or more of the imaged spots in the detection plane to maintain
alignment of the array of detection elements.
[0005] A method for detecting positions of multiple particle beams
is disclosed in accordance with one or more illustrative
embodiments of the present disclosure. In one illustrative
embodiment, the method includes generating a particle beam array
with an illumination source. In one illustrative embodiment, the
method includes directing the particle beam array to an array of
measurement locations on a sample with an illumination sub-system.
In one illustrative embodiment, the method includes imaging the
array of measurement locations to an array of imaged spots at a
detection plane with an imaging sub-system. In another illustrative
embodiment, the method includes receiving the imaged spots with
separate detection elements of an array of detection elements. In
another illustrative embodiment, the method includes measuring,
with one or more position detectors, positions of the imaged spots
at the detection plane. In another illustrative embodiment, the
method includes generating feedback signals for the imaging
sub-system based on the measured positions of the imaged spots to
adjust the positions of the one or imaged spots in the detection
plane to maintain alignment of the array of detection elements.
[0006] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not necessarily restrictive of the
invention as claimed. The accompanying drawings, which are
incorporated in and constitute a part of the specification,
illustrate embodiments of the invention and together with the
general description, serve to explain the principles of the
invention.
BRIEF DESCRIPTION OF DRAWINGS
[0007] The numerous advantages of the disclosure may be better
understood by those skilled in the art by reference to the
accompanying figures in which:
[0008] FIG. 1 is a conceptual view of a multi-beam inspection
system, in accordance with one or more embodiments of the present
disclosure.
[0009] FIG. 2 is a plan view of a detection plane including a 2D
array of imaged spots, in accordance with one or more embodiments
of the present disclosure.
[0010] FIG. 3 is a conceptual view of a detection assembly in which
the array of imaged spots at a detection plane is reimaged as a
secondary image to a secondary detection plane, in accordance with
one or more embodiments of the present disclosure.
[0011] FIG. 4 is a conceptual view of a portion of a detection
assembly including a solid immersion lens, in accordance with one
or more embodiments of the present disclosure.
[0012] FIG. 5A is a top view of a detection assembly including an
array of detection elements, in accordance with one or more
embodiments of the present disclosure.
[0013] FIG. 5B is a side view of a detection assembly including an
array of PIN detection elements fabricated on a common substrate
layer, in accordance with one or more embodiments of the present
disclosure.
[0014] FIG. 6A is a conceptual view of a detection element
including three pixels for position detection, in accordance with
one or more embodiments of the present disclosure.
[0015] FIG. 6B is a top view of an array of detection elements in
which each individual detection element includes three pixels
operating as position detectors, in accordance with one or more
embodiments of the present disclosure.
[0016] FIG. 7A is a conceptual side view of a tilted sample
illustrating incident illumination beams (solid arrows) and
resultant particles (dashed arrows) emanating from the sample, in
accordance with one or more embodiments of the present
disclosure.
[0017] FIG. 7B is a conceptual top view of the detection plane in
response to a tilted sample, in accordance with one or more
embodiments of the present disclosure.
[0018] FIG. 8A is a conceptual side view of a sample exhibiting
uniform charging in response to incident illumination beams and
resultant particles emanating from the surface, in accordance with
one or more embodiments of the present disclosure.
[0019] FIG. 8B is a conceptual top view of the detection plane in
response to uniform sample charging, in accordance with one or more
embodiments of the present disclosure.
[0020] FIG. 9A is a conceptual side view of a sample exhibiting
non-uniform charging, in accordance with one or more embodiments of
the present disclosure.
[0021] FIG. 9B is a conceptual top view of the detection plane in
response to non-uniform sample charging, in accordance with one or
more embodiments of the present disclosure.
[0022] FIG. 10A is a conceptual view of a particle-based multi-beam
inspection system, in accordance with one or more embodiments of
the present disclosure.
[0023] FIG. 10B is a conceptual view of adjustable beam-control
elements suitable for modifying the positions of one or more imaged
spots in the detection plane, in accordance with one or more
embodiments of the present disclosure.
[0024] FIG. 11 is a flow diagram illustrating steps performed in a
method for simultaneously detecting positions of multiple particle
beams, in accordance with one or more embodiments of the present
disclosure.
DETAILED DESCRIPTION
[0025] Reference will now be made in detail to the subject matter
disclosed, which is illustrated in the accompanying drawings. The
present disclosure has been particularly shown and described with
respect to certain embodiments and specific features thereof. The
embodiments set forth herein are taken to be illustrative rather
than limiting. It should be readily apparent to those of ordinary
skill in the art that various changes and modifications in form and
detail may be made without departing from the spirit and scope of
the disclosure.
[0026] Embodiments of the present disclosure are directed to a
multi-beam inspection system including an illumination sub-system
to direct a beam array to a sample at an array of measurement
locations, an imaging sub-system to image the measurement locations
as an array of imaged spots at a detection plane, and a detection
assembly to generate detection signal channels associated with each
of the imaged spots. In this regard, multiple portions of the
sample may be interrogated in parallel (e.g., the array of
measurement locations), which may provide increased throughput
relative to a system without arrays of beams.
[0027] Sample inspection may generally be performed using any type
of illumination beam known in the art such as, but not limited to,
particle beams (e.g., electron beams, ion beams, or the like), or
beams of electromagnetic radiation (e.g., X-rays, optical beams, or
the like). For example, a particle beam inspection system may
typically have a higher resolution, but a lower throughput, than an
optical beam inspection system. Accordingly, inspection systems
with different types of illumination beams may be utilized
individually or in combination to take advantage of complementary
advantages.
[0028] As used throughout the present disclosure, the term sample
generally refers to any sample suitable for inspection. For
example, a sample may include an unprocessed semiconductor or
non-semiconductor material (e.g., a wafer, or the like). A
semiconductor or non-semiconductor material may include, but is not
limited to, monocrystalline silicon, gallium arsenide, and indium
phosphide. By way of another example, a sample may include a
semiconductor device at any stage of fabrication. For instance, a
semiconductor device may be formed as one or more layers of
patterned or unpatterned material. Such layers may include, but are
not limited to, a resist, a dielectric material, a conductive
material, and a semiconductive material. Many different types of
such layers are known in the art, and the term sample as used
herein is intended to encompass a sample on which all types of such
layers may be formed. Many different types of devices may be formed
on a sample, and the term sample as used herein is intended to
encompass a sample on which any type of device known in the art is
being fabricated. By way of another example, a sample may include
one or more elements used in a fabrication process such as, but not
limited to, a reticle or a photomask.
[0029] For example, a sample may include a plurality of dies, each
having repeatable patterned features. Formation and processing of
such layers of material may ultimately result in completed devices.
Further, for the purposes of the present disclosure, the term
sample and wafer should be interpreted as interchangeable. In
addition, for the purposes of the present disclosure, the terms
patterning device, mask, and reticle should be interpreted as
interchangeable.
[0030] Additional embodiments of the present disclosure are
directed to a detection assembly including an array of detection
elements configured to receive each of the imaged spots with a
separate detection element. For example, the array of detection
elements may generate a separate detection channel associated with
each of the imaged spots, which are in turn associated with each
beam of the beam array. In this regard, an image of the sample may
be formed by combining the detection channel signals associated
with each of the imaged spots on the sample. Further, the sample
and/or the beam array may be translated to build up a sample image
of any arbitrary size.
[0031] Additional embodiments of the present disclosure are
directed to a detection assembly including position detectors to
measure positions of the imaged spots at the detection plane. In
this regard, the positions of the imaged spots on the individual
detection elements may be monitored.
[0032] The detector assembly may be configured in various ways to
simultaneously image the sample and monitor the positions of each
imaged spot in the detection plane. For example, the detector
assembly may include an array of multi-pixel detection elements
located at the detection plane to directly receive the imaged
spots. Further, the one or more position detectors may include one
or more pixels of the multi-pixel detection elements. The position
of an imaged spot on a multi-pixel detection element may thus be
determined based on the relative signal strengths of each pixel. By
way of another example, the detector assembly may include a
detector imaging system to provide a first image at the detection
plane onto input faces of an optical fiber array coupled to
detection elements and a second image (e.g., via a beamsplitter) to
a position-monitoring camera. Such a configuration may be suitable
for any type of illumination beam. For instance, the detector
assembly for a particle beam inspection system may include a
scintillator located at the detection plane to generate photons in
response to absorbed secondary electrons from the sample associated
with the imaged spots. The detector imaging system may then image
the light generated by the scintillator onto the array of optical
fibers as well as the position monitoring camera.
[0033] Additional embodiments of the present disclosure are
directed to providing feedback signals to the imaging sub-system to
adjust the positions of the imaged spots in the detection plane to
maintain alignment of the array of detection elements based on the
output of the position detectors. For example, the imaging
sub-system may include one or more adjustable beam-control elements
(e.g., focusing elements, aberration correcting elements, or the
like) suitable for modifying the positions of one or more of the
imaged spots at the detection plane.
[0034] It is recognized herein that accurate alignment of the array
of imaged spots and the array of detection elements is essential
not only for initial system alignment, but also for continued
operation. For example, alignment of the array of imaged spots and
the array of detection elements may reduce and/or minimize
cross-talk between detection elements. By way of another example,
the sensitivity of a detection element may vary as a function of
position across an input face. For instance, in the case that the
array of detection elements includes an array of optical fibers
coupled to optical detectors, the relative positions of the imaged
spots on the input faces of the fibers will strongly influence the
coupling efficiency of light into the fibers.
[0035] It is further recognized herein that the positions of imaged
spots in the detection plane may shift due to a variety of sample
variations such as, but not limited to, variations of physical
properties, electrical properties, chemical properties, or optical
properties. For example, sample tilt may cause all imaged spots to
shift in a common direction. By way of another example, charging
effects in a particle beam inspection system may cause some imaged
spots to shift relative to others leading to asymmetric distortions
at the sample plane.
[0036] Additional embodiments of the present disclosure are
directed to providing feedback signals to the imaging sub-system to
compensate for measured deviations of the imaged spots at the
detection plane. In this regard, the feedback signals may maintain
alignment of the detector elements in response to variations on the
sample.
[0037] Additional embodiments of the present disclosure are
directed to utilizing the positions of the imaged spots as
supplemental inspection data. In this regard, the positions of the
imaged spots in the detection plane may provide diagnostic
information about variations on the sample (e.g., sample tilt, a
distribution of charging effects, or the like) that may supplement
the image generated by the detection elements.
[0038] FIG. 1 is a conceptual view of a multi-beam inspection
system 100, in accordance with one or more embodiments of the
present disclosure. In one embodiment, the multi-beam inspection
system 100 includes a multi-beam illumination source 102 to
generate an array of illumination beams (e.g., a beam array, a
beamlet array, or the like), an illumination sub-system 104 to
illuminate a sample with the beam array at an array of measurement
locations (e.g., located at an image plane of the illumination
sub-system 104), an imaging sub-system 106 to image the array of
measurement locations to a detection plane as an array of imaged
spots, and a detection assembly 108 to receive the array of imaged
spots at the detection plane and generate detection signal channels
associated with each imaged spot. In this regard, the multi-beam
inspection system 100 may simultaneously interrogate a sample with
each illumination beam. In another embodiment, the multi-beam
inspection system 100 includes a controller 110 including one or
more processors 112 configured to execute program instructions
maintained on a memory medium 114. In this regard, the one or more
processors 112 of controller 110 may execute any of the various
process steps described throughout the present disclosure.
[0039] The one or more processors 112 of a controller 110 may
include any processing element known in the art. In this sense, the
one or more processors 112 may include any microprocessor-type
device configured to execute algorithms and/or instructions. In one
embodiment, the one or more processors 112 may consist of a desktop
computer, mainframe computer system, workstation, image computer,
parallel processor, or any other computer system (e.g., networked
computer) configured to execute a program configured to operate the
multi-beam inspection system 100, as described throughout the
present disclosure. It is further recognized that the term
"processor" may be broadly defined to encompass any device having
one or more processing elements, which execute program instructions
from a non-transitory memory medium 114.
[0040] The memory medium 114 may include any storage medium known
in the art suitable for storing program instructions executable by
the associated one or more processors 112. For example, the memory
medium 114 may include a non-transitory memory medium. By way of
another example, the memory medium 114 may include, but is not
limited to, a read-only memory ROM), a random access memory (RAM),
a magnetic or optical memory device (e.g., disk), a magnetic tape,
a solid state drive, and the like. It is further noted that memory
medium 114 may be housed in a common controller housing with the
one or more processors 112. In one embodiment, the memory medium
114 may be located remotely with respect to the physical location
of the one or more processors 112 and controller 110. For instance,
the one or more processors 112 of controller 110 may access a
remote memory (e.g., server), accessible through a network (e.g.,
internet, intranet and the like). Therefore, the above description
should not be interpreted as a limitation on the present invention
but merely an illustration.
[0041] The imaging sub-system 106 may collect any type of particles
and/or radiation emanating from the sample from the array of
measurement locations to generate the array of imaged spots at the
detection plane. For example, in response to the incident
illumination beams, the sample may radiate electromagnetic
radiation (e.g., X-rays, optical radiation, or the like) and/or
particles (e.g., secondary electrons, backscattered electrons,
ions, neutral particles, or the like). Accordingly the imaged spots
may include electromagnetic radiation and/or particles collected by
the imaging sub-system 106.
[0042] In another embodiment, the detection assembly 108 includes
an array of detection elements 116. For example, the detection
assembly 108 may receive each imaged spot (e.g., the
electromagnetic radiation and/or particles emanating from the
sample in response to the illumination beams) with a separate
detection element 116. In this regard, the detection assembly 108
may generate a separate data signal (e.g., a detection channel
signal) associated with each measurement location on the sample
illuminated by an illumination beam. Further the controller 110 may
receive the detection channel signals from the detection elements
116.
[0043] In another embodiment, the detection assembly 108 includes
one or more position detectors 118 to measure the positions of the
imaged spots at the detection plane. The positions of the imaged
spots at the detection plane may thus be representative of the
positions of the alignment of imaged spots on the detection
elements 116. Further, the controller 110 may receive position
signals from the position detectors 118.
[0044] In another embodiment, the imaging sub-system 106 includes
one or more adjustable beam control elements suitable for
manipulating the positions of one or more illumination beams of the
beam array at the detection plane. Accordingly, the controller 110
may generate feedback signals based on the position signals from
the position detectors 118 and provide the feedback signals to the
imaging sub-system 106. In this regard, the imaging sub-system 106
may continually adjust the positions of the imaged spots in the
detection plane to maintain alignment of the detection elements
116.
[0045] Referring now to FIGS. 2-4, embodiments of the detection
assembly 108 for simultaneously generating detection signal
channels for an array of imaged spots at a detection plane and
monitoring the positions of the array of imaged spots at the
detection plane are described.
[0046] FIG. 2 is a plan view of a detection plane 202 including a
2D array of imaged spots 204, in accordance with one or more
embodiments of the present disclosure. As described previously
herein, the imaged spots 204 may include particles and/or
electromagnetic radiation emanating from a sample generated in
response to an array of illumination beams. It is to be understood
that number and distribution of the imaged spots 204 illustrated in
FIG. 2 is provided solely for illustrative purposes and should not
be interpreted as limiting. The detection assembly 108 may be
configured to generate detection channel signals and determine
positions of imaged spots 204 in any distribution known in the
art.
[0047] FIG. 3 is a conceptual view of a detection assembly 108 in
which the array of imaged spots 204 at a detection plane 202 is
reimaged as a secondary image to a secondary detection plane 302,
in accordance with one or more embodiments of the present
disclosure. In one embodiment, the detection assembly 108 includes
a scintillator 304 located at the detection plane 202 to absorb
particles emanating from the sample and subsequently emit
electromagnetic radiation (e.g., light). The scintillator 304 may
include any type of scintillator known in the art suitable for
generating light in response to absorbed particles. For example,
the scintillator 304 may, but is not required to, include emit
light a fluorescent material through fluorescence in response to
the absorption of particles emitted by the camera 312 and captured
by the imaging sub-system 106. Accordingly, the scintillator 304
may include any type of such fluorescent material including, but
not limited to, organic or inorganic crystals or liquids. In one
embodiment, the scintillator 304 includes a plastic scintillator
including a polymer matrix that itself generates fluorescence in
response to absorbed particles or includes fluorophores suspended
within the polymer matrix.
[0048] In another embodiment, the scintillator 304 absorbs
particles generated from a sample associated with the imaged spots
204 and subsequently emits light with visible wavelengths. In one
instance, the scintillator 304 emits light with an approximately 20
nanometer bandwidth centered at approximately 400 nanometers.
[0049] In another embodiment, the scintillator 304 is selected to
provide a rapid florescent decay time of the scintillator 304 to
facilitate fast scanning of the sample and high throughput
detection. For example, the fluorescent decay time of the
scintillator 304 may be less than approximately 20 nanoseconds. By
way of another example, the fluorescent decay time of the
scintillator 304 may be less than approximately 10 nanoseconds. By
way of another example, the fluorescent decay time of the
scintillator 304 may be less than approximately 5 nanoseconds.
[0050] Further, the intensity of the light generated by the
scintillator 304 may be proportional to the absorbed energy from
the particles making up the imaged spots 204. In this regard,
detection of the optical image at the secondary detection plane 302
may provide substantially the same information about the sample as
detection of the imaged spots 204 including particles at the
detection plane 202.
[0051] In another embodiment, the detection assembly 108 includes a
detector imaging sub-system 306 to image light generated by the
scintillator 304 in response to the imaged spots 204 to the
secondary detection plane 302 as a secondary image. The detector
imaging sub-system 306 may include any number of optical elements
to capture light from the scintillator 304 and generate the
secondary image at the secondary detection plane 302. For example,
as illustrated in FIG. 3, the detector imaging sub-system 306 may
include one or more detector lenses 308. In one instance, a
detector lens 308 may include a high numerical aperture (high NA)
lens (e.g., an objective lens, or the like).
[0052] In another embodiment, a detector imaging sub-system 306
includes a solid immersion lens (SIL) placed in contact with the
scintillator 304 (or a substrate material in contact with the
scintillator 304). For example, a SIL may include, but is not
limited to a hemispherical lens or a truncated spherical lens
(e.g., a Weierstrauss SIL or a superhemispherical SIL). FIG. 4 is a
conceptual view of a portion of the detection assembly 108
including a solid immersion lens, in accordance with one or more
embodiments of the present disclosure. In one embodiment, the
detector imaging sub-system 306 includes a Weierstrauss SIL 402 in
contact with the scintillator 304. The SIL 402 may provide a high
NA for efficient collection of light from the scintillator 304.
Further, the refractive index of the SIL 402 may be selected to,
but is not required to be selected to, be similar to the refractive
index of the scintillator 304 to limit refraction at the interface
between the scintillator 304 and the SIL 402. In another
embodiment, the detector imaging sub-system 306 includes one or
more additional detector lenses 404 to collect light captured by
the SIL 402 and generate the image of the detection plane 202 at
the secondary detection plane 302.
[0053] In one embodiment, the detection assembly 108 includes an
array of optical fibers 310 (e.g., a fiber bundle) positioned with
input faces at the secondary detection plane 302. In this regard,
the detector imaging sub-system 306 may couple light from the
scintillator 304 associated with the imaged spots 204 into the
optical fibers 310. For example, the spatial distribution of the
optical fibers 310 may correspond to a scaled version of the
distribution of illumination beams within the beam array 1002. In
this regard, the light associated with each imaged spot 204 may be
coupled into a different optical fiber 310.
[0054] In another embodiment, the detector imaging sub-system 306
magnifies the detection plane 202 such that the secondary images of
the imaged spots 204 match the core diameter of the optical fibers
310 to provide efficient coupling of light into the optical fibers
310. Further, it may be the case that the imaging sub-system 106
provides additional magnification of the sample when generating the
imaged spots 204 at the detection plane 202. Accordingly, the size
of the secondary image on the secondary detection plane 302 may
include the combined magnification of the illumination sub-system
104 and the detector imaging sub-system 306 stages.
[0055] The optical fibers 310 may include any type of optical
fibers with any core size available in the art. In one embodiment,
the optical fibers 310 include multimode optical fibers. Cores of
multimode optical fibers may typically range from approximately 200
micrometers to 1,600 micrometers. In one instance, an array of
multimode optical fibers 310 having a 400 micrometer core diameter
may require approximately 35.times. total magnification to image an
illuminated spot on the sample onto a core of an optical fiber 310
for efficient coupling. Accordingly, the required 35.times.
magnification can be split between the imaging sub-system 106 and
the detector imaging sub-system 306. For example, the spot imaging
sub-system 106 may provide, but is not required to provide,
approximately 3.5.times. magnification such that the detector
imaging sub-system 306 may provide 10.times. magnification.
[0056] In another embodiment, the array of detection elements 116
within the detection assembly 108 may be coupled to output faces of
the optical fibers 310 to detect light coupled into the optical
fibers 310. Accordingly, the detection assembly 108 may provide
separate detection signal channels for light associated with each
imaged spot 204 (associated with portions of the sample illuminated
by each illumination beam).
[0057] The detection elements 116 may include any type of optical
detectors known in the art suitable for detecting light generated
by the scintillator 304. In one embodiment, the detection elements
116 include light-sensitive diodes. In another embodiment, the
detection assembly 108 includes one or more amplifiers to increase
the detection sensitivity. For example, the detection elements 116
may include, but are not required to include, avalanche photodiodes
providing internal analog gain. By way of another example, the
detection assembly 108 may include electronic amplifiers to amplify
the electronic detection signals provided by the detection elements
116.
[0058] It is recognized herein that the output faces of the optical
fibers 310 may be arranged in any distribution and need not
correspond to the distribution of the input faces. For example, the
output faces of the optical fibers 310 may be separated from each
other to provide physical space required for the detection elements
116.
[0059] In another embodiment, a least a portion of the multi-beam
inspection system 100 is contained within a vacuum chamber.
Further, the detection assembly 108 may be located either within
the chamber, outside of the chamber, or partially inside the
chamber. For example, the a scintillator 304 may be integrated with
a window of the vacuum chamber such that at least a portion of the
detection assembly 108 may be located outside of the vacuum
chamber. In one instance, the scintillator 304 is mounted inside a
window flange in the place of or alongside a transparent window
material. In this regard, one face of the scintillator 304 may face
the vacuum chamber and be exposed to particles emanating from the
sample associated with the imaged spots 204. Further, the light
emitted by scintillator 304 the may propagate outside the chamber
for collection with the detector imaging sub-system 306.
[0060] In another instance, a SIL 402 may be directly mounted to
the vacuum chamber window (e.g., the scintillator 304 or a
transparent window material proximate to the scintillator 304) with
optical grease to collect the light from the scintillator 304.
Further, the additional detector lenses 404 of the detector imaging
sub-system 306 may be mounted to the SIL 402 in a fixed position to
generate the secondary image of the imaged spots 204.
[0061] In another embodiment, the array of detection elements 116
is located directly at the secondary detection plane 302 (e.g., in
place of the array of optical fibers 310 illustrated in FIGS. 3 and
4). For example, the spatial distribution of the array of detection
elements 116 may correspond to a scaled version of the distribution
of illumination beams within the beam array 1002 such that the
light associated with each imaged spot 204 may be directed to a
separate detection element 116.
[0062] In another embodiment, as illustrated in FIG. 3, the one or
more position detectors 118 of the detection assembly 108 may
include a camera 312 positioned to receive conjugate image of the
secondary detection plane 302. For example, the detector imaging
sub-system 306 may include a beamsplitter 314 positioned such that
the detector imaging sub-system 306 may generate conjugate images
at the secondary detection plane 302 and a camera detection plane
316. Further, the inclusion of the beamsplitter 314 in the context
of FIG. 3 is provided solely for illustrative purposes and should
not be interpreted as limiting. Rather, the beamsplitter 314 may be
included in any design of the detector imaging sub-system 306 In
one instance, a beamsplitter 314 may be incorporated into the
detector imaging sub-system 306 illustrated in FIG. 4. In this
regard, the beamsplitter 314 may generate conjugate images at the
secondary image plane and a camera detection plane 316 based on
light collected by a SIL 402.
[0063] In another embodiment, the camera 312 generates position
data for each of the imaged spots 204 in the detection plane. For
example, the position data may derived from the pixel locations on
the camera 312 receiving light from the scintillator 304 associated
with each of the imaged spots 204. Further, the position data may
track deviations of the positions of each of the imaged spots 204
in response to variations on the sample.
[0064] In another embodiment, position data generated by the camera
312 may be calibrated to a desired alignment of the detection
elements 116 with respect to the imaged spots 204. For example,
calibration may include determining nominal positions of the
secondary images of the imaged spots 204 on the camera 312 that
correspond to an alignment of the secondary images of the imaged
spots 204 with the cores of the optical fibers 310. Accordingly,
deviations of the positions of the imaged spots 204 measured by the
camera may indicate misalignments of the optical fibers 310 and
thus reduced signal on the detection elements 116 at the output
faces of the optical fibers 310.
[0065] The camera 312 may include any type of measurement detector
suitable for detecting light emitted from the scintillator 304. For
example, the camera may include, but is not limited to, a
charge-coupled device (CCD) or a complementary metal-oxide
semiconductor (CMOS) device.
[0066] Referring now to FIGS. 5A through 6B, embodiments of a
detection assembly 108 including a multi-pixel array of detection
elements 116 for simultaneously measuring the intensities and
positions of the imaged spots 204 are described. In this regard,
the array of detection elements 116 may be positioned at the
detection plane 202 and may directly detect the particles and/or
electromagnetic radiation emanating from the sample associated with
the imaged spots 204.
[0067] FIG. 5A is a top view of a detection assembly 108 including
an array of detection elements 116, in accordance with one or more
embodiments of the present disclosure. In one embodiment, the
spatial distribution of the detection elements 116 may correspond
to a scaled version of the distribution of illumination beams
within the beam array 1002 array of detection elements 116.
Accordingly, each imaged spot 204 may be received by a separate
detection element 116. Further, the dots in FIG. 5A indicate the
nominal positions of the imaged spots 204 on the detection elements
116.
[0068] The detection elements 116 of FIG. 5A may include any type
of detectors known in the art suitable for detecting particles
and/or electromagnetic radiation emanating from the sample. In one
embodiment, the detection elements 116 include diodes sensitive to
electrons (e.g., secondary electrons and/or backscattered
electrons). For example, the detection elements 116 may include PIN
diodes. It is noted that avalanche gain (e.g., such as generated in
APDs) may not be necessary and may, in some applications, induce
excessive heating and/or excessive gain.
[0069] The detection elements 116 may further be fabricated and
packaged using various techniques. FIG. 5B is a side view of a
detection assembly 108 including an array of PIN detection elements
116 fabricated on a common substrate layer 502, in accordance with
one or more embodiments of the present disclosure. In one
embodiment, each detection element 116 includes at least one
separate bond pad such that each detection element 116 may generate
a separate detection signal channel. In another embodiment, as
illustrated in FIG. 5B, the bond pads of the detection elements 116
may be connected to an external substrate 504 by filled vias 506
through the common substrate layer 502 such the detection signal
channels may be connected to additional circuitry (e.g., to one or
more amplifies, the controller 110, or the like). Further, the
common substrate layer 502 may be, but is not required to be,
back-thinned to provide both mechanical stability and short
connections to the external substrate 504 for high-speed
performance.
[0070] In another embodiment, the detection assembly 108 includes
position detectors 118 integrated with each detection element 116
to determine the positions of the imaged spots 204 on the detection
elements 116. For example, each detection element 116 may include
two or more pixels. In this regard, the relative position of an
imaged spot 204 on a detection element 116 may be determined based
on the relative energy absorbed by the pixels with respect to the
total energy absorbed by the detection element 116.
[0071] FIG. 6A is a conceptual view of a detection element 116
including three pixels 602 for position detection, in accordance
with one or more embodiments of the present disclosure. In one
embodiment, the detection element 116 includes a first pixel 602a,
a second pixel 602b, and a third pixel 602c arranged such that the
energy associated with a circular imaged spot 204 nominally
centered on the detection element 116 will be equally divided
between the three pixels 602a,b,c. However, deviations of the
imaged spot 204 from the nominal position will result in unequal
distribution of energy absorbed by the three pixels 602a,b,c.
Accordingly, position data including the magnitude and direction of
a deviation of the imaged spot 204 from the nominal position may be
calculated given a known energy distribution of the imaged spot
204.
[0072] In another embodiment, each pixel 602 (e.g., pixels 602a,b,c
of FIG. 6A) of the detection elements 116 may have a separate
electrical connection to the external substrate 504 such that the
absorbed energy of all pixels 602 may be separately accessed for
the calculation of position data.
[0073] FIG. 6B is a top view of an array of detection elements 116
in which each individual detection element 116 includes three
pixels 602 operating as position detectors 118, in accordance with
one or more embodiments of the present disclosure. In this regard,
the positions of each imaged spot 204 with respect to the detection
elements 116 may be determined.
[0074] It is to be understood that the description of detection
elements 116 having three pixels 602 provided in FIGS. 6A and 6B,
along with the associated descriptions, are provided solely for
illustrative purposes and should not be interpreted as limiting.
The detection elements 116 of a detection assembly 108 may include
any number of pixels for the generation of position data for
incident imaged spots 204. It is recognized herein that the number
and distribution of pixels 602 may influence the accuracy with
which position data may be generated. For example, a detection
element 116 including two pixels oriented symmetrically may
determine position data along a single direction. By way of another
example, a detection element 116 including four quadrants of the
active area of the detection element 116 may determine position
data based on the relative energy absorbed in each quadrant.
Additionally, pixels 6023 may be arranged in any geometry such as,
but not limited to, an annular geometry.
[0075] In another embodiment, position signals including the
positions of the imaged spots 204 in the detection plane 202 may be
utilized as feedback signals to the imaging sub-system 106 to
maintain alignment of the detection elements 116. For example, the
imaging sub-system 106 may include one or more adjustable elements
suitable for adjusting the positions of one or more of the imaged
spots 204 in the detection plane 202 such as, but not limited to,
adjustable focusing elements or aberration correcting elements.
[0076] Feedback signals including positions of the imaged spots 204
in the detection plane 202 may be utilized for a variety of
purposes during the operation of a multi-beam inspection system
100. In one embodiment, the feedback signals are utilized to align
the detection assembly 108 prior to runtime. In another embodiment,
feedback signals are utilized to maintain alignment of the
detection assembly 108 during runtime. For example, variations of
the sample such as, but not limited to, physical, chemical,
mechanical, or optical properties may lead to misalignments of one
or more imaged spots 204 with respect to the detection elements
116. Accordingly, the feedback signals may provide a means to
mitigate the misalignments.
[0077] FIGS. 7A through 9B illustrate several examples of sample
variations and the impacts on the alignment of the detection
elements 116.
[0078] FIG. 7A is a conceptual side view of a tilted sample 700
illustrating incident illumination beams 702 (solid arrows) and
resultant particles 704 (dashed arrows) emanating from the sample
700, in accordance with one or more embodiments of the present
disclosure. A tilted sample 700 will induce a uniform mismatch
between the locations at which the array of illumination beams 702
impinge on the sample 706 and the array of measurement locations
imaged by the imaging sub-system 106 along the direction of the
tilt. FIG. 7B is a conceptual top view of the detection plane 202
in response to a tilted sample, in accordance with one or more
embodiments of the present disclosure. In FIG. 7B, the imaged spots
204 are uniformly deflected from nominal positions on each of the
detection elements 116. Accordingly, feedback signals generated by
the position data may direct the imaging sub-system 106 to
uniformly deflect (e.g., with a deflector) the imaged spots
204.
[0079] FIG. 8A is a conceptual side view of a sample 800 exhibiting
uniform charging in response to incident illumination beams 802
(solid arrows) and resultant particles 804 (dashed arrows)
emanating from the surface, in accordance with one or more
embodiments of the present disclosure. For example, insulating
structures and/or structures that are not connected to a ground
source may develop a charge (e.g., a positive charge or a negative
charge) in a region 806 in response to depletion of particles
(e.g., secondary electrons, ions, or the like) induced by the beam
array. Accordingly, the induced charge may deflect the trajectories
of secondary electrons and thus the positions of the imaged spots
204 in the detection plane 202. FIG. 8B is a conceptual top view of
the detection plane 202 in response to uniform sample charging, in
accordance with one or more embodiments of the present disclosure.
In FIG. 8B, the imaged spots 204 are non-uniformly, buy
symmetrically, deflected from nominal positions on each of the
detection elements 116. For example, the uniform charging effects
may induce lensing and higher-order aberration effects that cause
the imaged spots 204 near the edges of the beam array 1002 to
deflect with respect to those near the center. Accordingly,
feedback signals generated by the position data may direct the
imaging sub-system 106 to mitigate the lensing effect through focal
adjustments and/or aberration corrections.
[0080] FIG. 9A is a conceptual side view of a sample 900 exhibiting
non-uniform charging in response to incident illumination beams 902
(solid arrows) and resultant particles 904 (dashed arrows)
emanating from the surface, in accordance with one or more
embodiments of the present disclosure. For example, variations in
sample properties and/or the presence of patterned features may
induce non-uniform charging effects (e.g., in region 906) that may
non-uniformly deflect the trajectories of some imaged spots 204
with respect to others. FIG. 9B is a conceptual top view of the
detection plane 202 in response to non-uniform sample charging, in
accordance with one or more embodiments of the present disclosure.
In FIG. 9B, the imaged spots 204 are non-uniformly and
asymmetrically deflected from nominal positions on each of the
detection elements 116. Accordingly, feedback signals generated by
the position data may direct the imaging sub-system 106 to mitigate
the lensing effect through asymmetric aberration corrections and/or
deflections of some of the imaged spots 204.
[0081] It is to be understood that the examples of sample-induced
misalignments and associated feedback corrections illustrated in
FIGS. 7A through 9B are provided solely for illustrative purposes
and should not be interpreted as limiting. It is recognized herein
that misalignment of the detection assembly 108 may be induced by a
complex variety of factors including sample-induced effects, beam
drift, and the like. Further, it may be the case that feedback
signals based on position data from the position detectors 118 may
partially, rather than completely, mitigate the misalignment.
[0082] In another embodiment, position data of the imaged spots 204
generated by the position detectors 118 is used to supplement the
intensity of the imaged spots 204 captured by the detection
elements 116. For example, observed deflections of one or more
imaged spots 204 may itself serve as diagnostic information
relevant to the inspection of a sample. For example, as described
previously herein and illustrated in FIGS. 8A through 9B, the
relative positions of the imaged spots 204 in the detection plane
202 may be indicative of charging effects due to known structures
as well as aberrant structures (e.g., defects).
[0083] Referring again to FIG. 1, the detection assembly 108 may be
utilized in combination with any type of multi-beam inspection
system 100 known in the art such as, but not limited to,
particle-based or optical inspection systems.
[0084] Further, defects in a sample die may be characterized by
comparing a voltage contrast image of the sample die with a voltage
contrast image of a reference die (e.g., die-to-die (D2D)
inspection, standard reference die (SRD) inspection, or the like)
or by comparing a voltage contrast image of the sample die with an
image based on design characteristics (e.g., die-to-database (D2DB)
inspection). Inspection systems using persistent data (e.g., stored
data) is generally described in U.S. Pat. No. 8,126,255, issued on
Feb. 28, 2012, which is incorporated herein by reference in its
entirety. Inspection systems using design data of a sample to
facilitate inspection is generally described in U.S. Pat. No.
7,676,077, issued on Mar. 9, 2010, and U.S. Pat. No. 6,154,714,
issued on Nov. 28, 2000, and U.S. Pat. No. 8,041,103, issued on
Oct. 18, 2011, which are incorporated herein by reference in their
entirety. The determination of defect and fault sources are
generally described in U.S. Pat. No. 6,920,596, issued on Jul. 19,
2005, U.S. Pat. No. 8,194,968, issued on Jun. 5, 2015, and U.S.
Pat. No. 6,995,393, issued on Feb. 7, 2006, which are incorporated
herein by reference in their entirety. Device property extraction
and monitoring is generally described in U.S. Pat. No. 8,611,639,
issued on Dec. 17, 2013. Sample device designs suitable for VCI are
generally described in U.S. Pat. No. 6,509,197, issued on Jan. 21,
2003, U.S. Pat. No. 6,528,818, issued on Mar. 4, 2003, U.S. Pat.
No. 6,576,923, issued on Jun. 10, 2003, and U.S. Pat. No.
6,636,064, issued on Oct. 21, 2003, which are incorporated herein
by reference in their entirety. The use of reticles in inspection
systems is generally described in U.S. Pat. No. 6,529,621, issued
on Mar. 4, 2003, U.S. Pat. No. 6,748,103, issued on Jun. 8, 2004,
and U.S. Pat. No. 6,966,047, issued on Nov. 15, 2005, which are
incorporated herein by reference in their entirety. Generating an
inspection process or inspection target is generally described in
U.S. Pat. No. 6,691,052, issued on Feb. 10, 2004, U.S. Pat. No.
6,921,672, issued on Jul. 26, 2005, and U.S. Pat. No. 8,112,241,
issued on Feb. 7, 2012, which are incorporated herein by reference
in their entirety. Determination of critical areas of semiconductor
design data is generally described in U.S. Pat. No. 6,948,141,
issued on Sep. 20, 2005, which is incorporated by reference herein
in its entirety.
[0085] The use of dual-energy electron flooding for neutralization
of a charged substrate is generally described in U.S. Pat. No.
6,930,309, issued on Aug. 16, 2005, which is incorporated herein by
reference in its entirety. The use of particle beams with different
energies are generally described in U.S. Pat. No. 6,803,571, issued
on Oct. 12, 2004, and U.S. Pat. No. 7,217,924, issued on May 15,
2007, which are incorporated herein by reference in their entirety.
The use of multiple particle beams for sample inspection are
generally described in U.S. Pat. No. 6,774,646, issued on Aug. 10,
2004, U.S. Pat. No. 7,391,033, issued on Jun. 24, 2008, and U.S.
Pat. No. 8,362,425, issued on Jan. 29, 2013, which are incorporated
herein by reference in their entirety. Multiple-column particle
beam systems and methods are generally described in U.S. Pat. No.
8,455,838, issued on Jun. 4, 2013, which is incorporated herein by
reference in its entirety.
[0086] FIG. 10A is a conceptual view of a particle-based multi-beam
inspection system 100, in accordance with one or more embodiments
of the present disclosure. In one embodiment, the multi-beam
illumination source 102 generates a beam array 1002 including two
or more illumination beams 1002a. The multi-beam illumination
source 102 may include any type of particle source known in the art
suitable for generating illumination beams 1002a including any type
of particles. For example, the multi-beam illumination source 102
may include an electron source such that one or more illumination
beams 1002a include electron beams. By way of another example, the
multi-beam illumination source 102 may include an ion source such
that the one or more illumination beams 1002a may include ion
beams. Further, the multi-beam illumination source 102 may include,
but is not limited to, one or more electron guns, one or more ion
guns, one or more cathode sources, one or more emitter tips, one or
more anodes, or one or more gate valves suitable for generating
particle radiation.
[0087] As described previously herein, the multi-beam illumination
source 102 may include one or more additional illumination sources
(e.g., optical sources, or the like) suitable for illuminating a
sample for the purposes of sample inspection and/or sample
alignment. For example, the multi-beam illumination source 102 may
generate electromagnetic radiation having any wavelength including,
but not limited to X-rays, visible light (e.g., ultraviolet (UV)
wavelengths, visible wavelengths, infrared (IR) wavelengths, and
the like). Further, the illumination beams 1002a may exhibit any
selected degree of spatial or temporal coherence.
[0088] The multi-beam illumination source 102 may generate the beam
array 1002 using any method known in the art. In one embodiment, as
illustrated in FIG. 10A, the multi-beam illumination source 102 may
include an emission source 1004 and a gun lens 1006 to collect
particles emitted from the emission source 1004 and direct them to
a beam lens array 1008. For example, the beam lens array 1008 may
include a series of apertures and/or lenses arranged to split the
particles from the gun lens 1006 into the array of illumination
beams 1002a. The multi-beam illumination source 102 may further
include a current-control aperture 1010 (e.g., a current-control
aperture) to limit the size and/or current of particles directed to
the beam lens array 1008. In one embodiment, the current-control
aperture 1010 may control the spatial extent of particles incident
on the beam lens array 1008 and may thus control the number of
illumination beams 1002a in the beam array 1002.
[0089] In another embodiment, though not shown, one or more of the
illumination beams 1002a may be generated by a separate emission
source 1004 the multi-beam illumination source 102 may two or more
emission sources 1004 to generate the illumination beams 1002a of
the beam array 1002.
[0090] The illumination sub-system 104 may include any number of
focusing elements and/or beam-shaping elements to direct the beam
array 1002 to a sample plane 1012 at which a sample 1014 is
located. In this regard, the array of locations in the sample plane
1012 represent an array of measurement locations (e.g., on the
sample 1014) interrogated by the multi-beam inspection system
100.
[0091] In one embodiment, the illumination sub-system 104 includes
one or more illumination sub-system focusing elements 1016 (e.g.,
lenses). For example, as illustrated in FIG. 10A, the illumination
sub-system focusing elements 1016 may include a transfer lens 1018
and an objective lens 1020 forming a compound system to direct the
beam array 1002 to the sample plane 1012 (e.g., to the sample
1014). In one instance, the illumination sub-system focusing
elements 1016 image the beam lens array 1008 to the sample plane
1012. In another instance (not shown), the beam lens array 1008
focuses each illumination beam 1002a to a virtual source plane, and
the illumination sub-system focusing elements 1016 then image the
virtual source plane on the sample 1014. Such a configuration may
facilitate additional control over the focal properties of the
illumination beams 1002a.
[0092] In another embodiment, the illumination sub-system 104
includes beam-shaping elements to further modify the
characteristics of the illumination beams 1002a. For example, the
illumination sub-system 104 may include aberration-correcting
components such as, but not limited to, stigmators for mitigating
astigmatism.
[0093] Accordingly, the illumination sub-system 104 may be selected
and/or adjusted to provide selected focal characteristics of the
illumination beams 1002a on the sample 1014. For example, the
spacing between illumination beams 1002a may be adjusted based on a
magnification of the illumination sub-system focusing elements
1016. By way of another example, the numerical aperture of the
illumination beams 1002a may be adjusted based on the focal powers
of the illumination sub-system focusing elements 1016.
[0094] Further, the illumination sub-system focusing elements 1016
may include any type of lenses known in the art including, but not
limited to, electrostatic, magnetic, uni-potential, or
double-potential lenses. Additionally, the illumination sub-system
104 may include one or more elements held at a controlled
electrical potential with respect to the sample 1014 to modify the
landing energies of the illumination beams 1002a.
[0095] The imaging sub-system 106 may include any number of
focusing elements and/or beam-shaping elements to image the array
of measurement spots to a detection plane 202 for detection with
the detection assembly 108. In one embodiment, the imaging
sub-system 106 includes one or more particle lenses (e.g.,
electrostatic, magnetic, uni-potential, double potential lenses, or
the like) to capture and image particles such as, but not limited
to secondary electrons or backscattered electrons from the sample
1014 in response to the illumination beams 1002a. In another
embodiment, the imaging sub-system 106 includes one or more optical
lenses to capture and image electromagnetic radiation emanating
from the sample 1014 in response to the illumination beams
1002a.
[0096] In one embodiment, as illustrated in FIG. 10A, the imaging
sub-system 106 includes a Wien filter 1022 to separate particles
(e.g., electrons) emanating from the sample 1014 from the
illumination beams 1002a. For example, the Wien filter 1022 may be
located above the objective lens 1020 to redirect particles
collected by the objective lens 1020 towards the detection assembly
108. Further, the imaging sub-system 106 may include one or more
imaging sub-system focusing elements 1024 to image the array of
measurement locations onto the detection plane 202.
[0097] In another embodiment, though not shown, the imaging
sub-system 106 includes a secondary electron bender to further
deflect particles redirected by the Wien filter 1022. For example,
a secondary electron bender may include, but is not required to
include, charged plates with different applied voltages through
which collected electrons propagate. In this regard, the secondary
electron bender may facilitate the inclusion of the adjustable
beam-control elements 1026.
[0098] In another embodiment, the imaging sub-system 106 includes
one or more adjustable beam-control elements 1026 suitable for
modifying the positions of one or more imaged spots 204 in the
detection plane 202 based on feedback signals. For example, the
adjustable beam-control elements 1026 may receive feedback signals
from the detection assembly 108 (e.g., the position detectors 118
of the detection assembly 108) indicating a misalignment of one or
more detection elements 116. In response, the adjustable
beam-control elements 1026 may selectively modify positions of the
relevant imaged spots 204 to maintain alignment of the detection
elements 116.
[0099] FIG. 10B is a conceptual view of adjustable beam-control
elements 1026 suitable for modifying the positions of one or more
imaged spots 204 in the detection plane 202, in accordance with one
or more embodiments of the present disclosure. In one embodiment,
the adjustable beam-control elements 1026 include one or more
adjustable focusing elements 1028 having an adjustable focal power
and/or rotation adjustment. For example, the adjustable focusing
elements 1028 may adjust the magnification of the imaged spots 204
and thus the size and spacing between the imaged spots 204. In
another embodiment, the adjustable beam-control elements 1026
include one or more deflectors 1030 configured to deflect the
imaged spots 204 in one or more selected directions. For example,
the adjustable beam-control elements 1026 may include two
deflectors 1030 configured to deflect the imaged spots 204 along
orthogonal directions. In another embodiment, the adjustable
beam-control elements 1026 includes one or more stigmators 1032
suitable for introducing and/or mitigating aberrations such as
astigmatism into the imaged spots 204. In another embodiment, the
adjustable beam-control elements 1026 provide near-edge correction
as a means of adjusting positions of one or more imaged spots 204.
For example, the stigmators 1032 may uniformly modify the imaged
spots 204.
[0100] The multi-beam inspection system 100 may generate an
extended image of the sample 1014 based on scanning the sample 1014
and/or the beam array 1002 and generating a composite image based
on signals received from the detection assembly 108. In one
embodiment, the multi-beam inspection system 100 includes a sample
stage 1034 to secure and translate the sample 1014. The sample
stage 1034 may include any device suitable for positioning and/or
scanning the sample 1014 within the multi-beam inspection system
100. For example, the sample stage 1034 may include any combination
of linear translation stages, rotational stages, tip/tilt stages,
or the like.
[0101] In another embodiment, the multi-beam inspection system 100
includes one or more particle scanning elements 1036. The particle
scanning elements 1036 may include, but are not limited to, one or
more scanning coils or deflectors suitable for controlling a
position of the illumination beams 1002a relative to the surface of
the sample 1014. In this regard, particle scanning elements 1036
may scan the illumination beams 1002a across the sample 1014 in a
selected pattern. It is noted herein that the multi-beam inspection
system 100 may operate in any scanning mode known in the art. For
example, the multi-beam inspection system 100 may operate in a
step-and-scan mode when scanning the illumination beams 1002a
across the surface of the sample 1014. In this regard, the
multi-beam inspection system 100 may scan an illumination beam
1002a across the sample 1014, which may be nominally stationary
with respect to the illumination beam 1002a or in synchronous
motion with the illumination beam 1002a.
[0102] Further, the multi-beam illumination source 102 may generate
a beam array 1002 having any selected number of illumination beams
1002a with any distribution for illuminating the sample 1014. For
example, the multi-beam inspection system 100 may illuminate a
sample 1014 with a 1-D array (e.g., a line array) of illumination
beams 1002a distributed along a first direction to generate a line
image and may further translate the sample 1014 mounted on a sample
stage 1034 along an orthogonal direction to generate a line-scan
image of any desired length. By way of another example, the
multi-beam inspection system 100 may illuminate the sample 1014
with a 2D array of illumination beams 1002a and may translate the
sample 1014 and/or the beam array 1002 in a coordinated pattern to
generate an image of the sample 1014.
[0103] FIG. 11 is a flow diagram illustrating steps performed in a
method 1100 for simultaneously detecting positions of multiple
particle beams, in accordance with one or more embodiments of the
present disclosure. Applicant notes that the embodiments and
enabling technologies described previously herein in the context of
multi-beam inspection system 100 should be interpreted to extend to
method 1100. It is further noted, however, that the method 1100 is
not limited to the architecture of multi-beam inspection system
100.
[0104] In one embodiment, the method 1100 includes a step 1102 of
generating a particle beam array with an illumination source. The
particle beam may include any type of particles such as, but not
limited to, electrons, ions, or neutral particles. In another
embodiment, the method 1100 includes a step 1104 of directing the
particle beam array to an array of measurement locations on a
sample with an illumination sub-system. In another embodiment, the
method 1100 includes a step 1106 of imaging the array of
measurement locations to an array of imaged spots at a detection
plane with an imaging sub-system. For example, the imaging
sub-system may collect particles emanating from the sample in
response to the particle beam array such as, but not limited to,
secondary electrons or backscattered electrons.
[0105] In another embodiment, the method 1100 includes a step 1108
of receiving the imaged spots with separate detection elements of
an array of detection elements. For example, a detection assembly
may include an array of detection elements suitable for generating
a separate detection signal channel for each received imaged spot.
In another embodiment, the method 1100 includes a step 1110 of
measuring, with one or more position detectors, positions of the
imaged spots at the detection plane. For example, the detection
assembly may further include position detectors configured to
measure and continually monitor the positions of the imaged spots
at the detection plane. Further, the position detectors may be
calibrated to the array of detection elements such that the
position detectors may monitor the accuracy of the alignment of the
imaged spots on the array of detection elements.
[0106] Simultaneous detection of the intensities of the imaged
spots and the positions of the imaged spots on the array of
detection elements may be achieved in various ways. In one
embodiment, a scintillator is located at the detection plane to
absorb the particles from the sample (e.g., associated with the
imaged spots) and subsequently emit electromagnetic radiation
(e.g., light) in response. Further, the detection plane (and thus
the light from the scintillator associated with the imaged spots)
may be re-imaged to two conjugate secondary image planes. In this
regard, the detection elements may be located at one of the
conjugate secondary image planes and a position detector (e.g., a
camera) may be located at the other conjugate secondary image
plane. Accordingly, deviations of the positions of the imaged spots
at the detection plane result in simultaneous modifications of the
secondary image on both the detection elements and the position
detector.
[0107] Additionally, the array of detection elements may be coupled
to an optical fiber bundle. In this regard, the input faces of the
fiber bundle may be located at one of the conjugate secondary image
planes and may be further arranged as a scaled version of the array
of imaged spots. Accordingly, the secondary images of the detection
plane may be adjusted such that secondary images of the imaged
spots are each collected by a different optical fiber.
[0108] In another embodiment, an array of multi-pixel detection
elements that are directly sensitive to particles from the sample
may be located at the detection plane and arranged as a scaled
version of the array of imaged spots such that each imaged spot is
captured by a separate multi-pixel detection element. The positions
of the imaged spots on a multi-pixel detection element may be
determined based on the energies absorbed by each pixel relative to
the aggregate energy absorbed by the entire multi-pixel detection
element.
[0109] In another embodiment, the method 1100 includes a step 1112
of generating feedback signals for the imaging sub-system based on
the measured positions of the imaged spots to adjust the positions
of the one or imaged spots in the detection plane to maintain
alignment of the array of detection elements. For example, the
imaging sub-system may include adjustable beam control elements
such as, but not limited to, adjustable lenses, deflectors,
stigmators, or the like suitable for modifying the positions of the
imaged spots at the detection plane. Accordingly, the imaging
sub-system may continually adjust the positions of the imaged spots
at the detection plane to maintain alignment of the detection
elements.
[0110] The herein described subject matter sometimes illustrates
different components contained within, or connected with, other
components. It is to be understood that such depicted architectures
are merely exemplary, and that in fact many other architectures can
be implemented which achieve the same functionality. In a
conceptual sense, any arrangement of components to achieve the same
functionality is effectively "associated" such that the desired
functionality is achieved. Hence, any two components herein
combined to achieve a particular functionality can be seen as
"associated with" each other such that the desired functionality is
achieved, irrespective of architectures or intermedial components.
Likewise, any two components so associated can also be viewed as
being "connected" or "coupled" to each other to achieve the desired
functionality, and any two components capable of being so
associated can also be viewed as being "couplable" to each other to
achieve the desired functionality. Specific examples of couplable
include but are not limited to physically interactable and/or
physically interacting components and/or wirelessly interactable
and/or wirelessly interacting components and/or logically
interactable and/or logically interacting components.
[0111] It is believed that the present disclosure and many of its
attendant advantages will be understood by the foregoing
description, and it will be apparent that various changes may be
made in the form, construction, and arrangement of the components
without departing from the disclosed subject matter or without
sacrificing all of its material advantages. The form described is
merely explanatory, and it is the intention of the following claims
to encompass and include such changes. Furthermore, it is to be
understood that the invention is defined by the appended
claims.
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