U.S. patent application number 16/106272 was filed with the patent office on 2020-09-03 for photocathode emitter system that generates multiple electron beams.
The applicant listed for this patent is KLA-TENCOR CORPORATION. Invention is credited to Gildardo R. Delgado, Rudy Garcia, Frances A. Hill, Katerina Ioakeimidi, Gary V. Lopez Lopez, Zefram Marks, Michael E. Romero.
Application Number | 20200279713 16/106272 |
Document ID | / |
Family ID | 1000005031117 |
Filed Date | 2020-09-03 |
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United States Patent
Application |
20200279713 |
Kind Code |
A1 |
Delgado; Gildardo R. ; et
al. |
September 3, 2020 |
PHOTOCATHODE EMITTER SYSTEM THAT GENERATES MULTIPLE ELECTRON
BEAMS
Abstract
The system includes a photocathode electron source, diffractive
optical element, and a microlens array to focus the beamlets. A
source directs a radiation beam to the diffractive optical element,
which produces a beamlet array to be used in combination with a
photocathode surface to generate an array of electron beams from
the beamlets.
Inventors: |
Delgado; Gildardo R.;
(Livermore, CA) ; Ioakeimidi; Katerina; (San
Francisco, CA) ; Garcia; Rudy; (Union City, CA)
; Marks; Zefram; (Fremont, CA) ; Lopez Lopez; Gary
V.; (Sunnyvale, CA) ; Hill; Frances A.;
(Sunnyvale, CA) ; Romero; Michael E.; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KLA-TENCOR CORPORATION |
Milpitas |
CA |
US |
|
|
Family ID: |
1000005031117 |
Appl. No.: |
16/106272 |
Filed: |
August 21, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62630429 |
Feb 14, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 37/28 20130101;
H01J 37/22 20130101; G01N 23/20058 20130101; H01J 37/073
20130101 |
International
Class: |
H01J 37/073 20060101
H01J037/073; H01J 37/22 20060101 H01J037/22; G01N 23/20058 20060101
G01N023/20058 |
Claims
1. A system comprising: a diffractive optical element configured to
receive an incident radiation beam, wherein the diffractive optical
element forms a plurality of beamlets from the incident radiation
beam, and wherein the beamlets each have a spot size from 10 .mu.m
to 100 .mu.m; an extractor plate; a microlens array that provides
collimation and focus of the beamlets, wherein the microlens array
is disposed between the diffractive optical element and the
extractor plate along a path of the beamlets; a condenser lens
disposed between the diffractive optical element and the microlens
array along the path of the beamlets; and a photocathode surface
disposed between the microlens array and the extractor plate along
the path of the beamlets, wherein the photocathode surface
generates a plurality of electron beams from the beamlets, and
wherein the electron beams generated by the photocathode surface
each have a spot size from 10 .mu.m to 100 .mu.m.
2. The system of claim 1, further comprising a laser light source
that generates the incident radiation beam.
3. The system of claim 1, wherein the beamlets are in an array.
4. The system of claim 1, wherein the electron beams range from 2
nA to 5 nA.
5. The system of claim 1, wherein the plurality of electron beams
includes from 100 to 1000 of the electron beams.
6. The system of claim 1, further comprising an electron beam
column, wherein the electron beams are directed at the electron
beam column from the extractor plate.
7. The system of claim 6, further comprising a plurality of the
electron beam columns, and wherein each of the electron beams is
directed at one of the electron beam columns.
8. The system of claim 1, wherein the electron beams have a spatial
separation from 50 .mu.m to 10 mm.
9. (canceled)
10. The system of claim 1, wherein the incident radiation beam is
ultraviolet radiation.
11. The system of claim 1, further comprising a voltage source in
electronic communication with the extractor plate.
12. A wafer inspection tool comprising the system of claim 1.
13. A method comprising: generating a radiation beam; receiving the
radiation beam at a diffractive optical element; forming a
plurality of beamlets from the radiation beam using the diffractive
optical element, wherein the beamlets each have a spot size from 10
.mu.m to 100 .mu.m; directing the beamlets through a condenser
lens; collimating and focusing the beamlets with a microlens array
downstream of the condenser lens with respect to a direction the
beamlets are projected; directing the beamlets from the microlens
array to a photocathode surface; generating a plurality of electron
beams from the beamlets using the photocathode surface, wherein the
electron beams generated by the photocathode surface each have a
spot size from 10 .mu.m to 100 .mu.m; and extracting the electron
beams from the photocathode surface.
14. The method of claim 13, wherein the beamlets are in an array
ranging from 4.times.6 to 48.times.48
15. The method of claim 13, wherein the electron beams range from 2
nA to 5 nA.
16. The method of claim 13, wherein the plurality of electron beams
includes from 100 to 1000 of the electron beams.
17. The method of claim 13, wherein the electron beams have a
spatial separation from 50 .mu.m to 10 mm.
18. (canceled)
19. The method of claim 13, wherein the radiation beam is
ultraviolet radiation.
20. The method of claim 13, wherein a pattern of the beamlets is
transmitted to the electron beams.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to the provisional patent
application filed Feb. 14, 2018 and assigned U.S. App. No.
62/630,429, the disclosure of which is hereby incorporated by
reference.
FIELD OF THE DISCLOSURE
[0002] This disclosure relates to electron beam emitters.
BACKGROUND OF THE DISCLOSURE
[0003] Evolution of the semiconductor manufacturing industry is
placing ever greater demands on yield management and, in
particular, on metrology and inspection systems. Critical
dimensions continue to shrink, yet the industry needs to decrease
time for achieving high-yield, high-value production. Minimizing
the total time from detecting a yield problem to fixing it
determines the return-on-investment for a semiconductor
manufacturer.
[0004] Fabricating semiconductor devices, such as logic and memory
devices, typically includes processing a semiconductor wafer using
a large number of fabrication processes to form various features
and multiple levels of the semiconductor devices. For example,
lithography is a semiconductor fabrication process that involves
transferring a pattern from a reticle to a photoresist arranged on
a semiconductor wafer. Additional examples of semiconductor
fabrication processes include, but are not limited to,
chemical-mechanical polishing (CMP), etch, deposition, and ion
implantation. Multiple semiconductor devices may be fabricated in
an arrangement on a single semiconductor wafer and then separated
into individual semiconductor devices.
[0005] Inspection processes are used at various steps during a
semiconductor manufacturing process to detect defects on wafers to
promote higher yield in the manufacturing process and, thus, higher
profits. Inspection has always been an important part of
fabricating semiconductor devices such as integrated circuits
(ICs). However, as the dimensions of semiconductor devices
decrease, inspection becomes even more important to the successful
manufacture of acceptable semiconductor devices because smaller
defects can cause the devices to fail. For instance, as the
dimensions of semiconductor devices decrease, detection of defects
of decreasing size has become necessary since even relatively small
defects may cause unwanted aberrations in the semiconductor
devices.
[0006] As semiconductor devices become smaller, it becomes more
important to develop enhanced inspection and review tools and
procedures to increase the resolution, speed, and throughput of
wafer and photomask/reticle inspection processes. One inspection
technology includes electron beam based inspection such as use of a
scanning electron microscope (SEM). An SEM uses an electron source.
Electron sources can be divided into two broad groups: thermionic
sources and field emission sources. Thermionic sources are usually
made of tungsten or lanthanum hexaboride (LaB.sub.6). In thermionic
emission, electrons are boiled off the material surface when the
electron thermal energy is high enough to overcome the surface
potential barrier. Even though thermionic emitters are widely used,
they typically require elevated temperatures (e.g., >1300 K) to
operate, and may have several drawbacks such as inefficient power
consumption, wide energy spread, short lifetime, low current
density, and limited brightness. The demand for more efficient
electron sources has driven the research and development of
Schottky emitters and cold electron sources such as electron field
emitters.
[0007] In the Schottky emitters, thermionic emission is enhanced by
effective potential barrier lowering due to the image charge effect
under an applied external electric field. Schottky emitters are
typically made of a tungsten wire having a tip coated with a layer
of zirconium oxide (ZrO.sub.x), which exhibits a low work function
(e.g., approximately 2.9 eV). Schottky emitters are currently used
in some electron beam systems. Despite being quite successful,
thermally-assisted Schottky emitters still need to be operated at
high temperature (e.g., >1000 K) and high vacuum (e.g.,
approximately 10.sup.-9 mbar), and have wider than desirable
electron emission energy spread due to the high operating
temperature.
[0008] Cold electron sources, particularly electron field emitters,
have been used in field emission displays, gas ionizers, x-ray
sources, electron beam lithography, and electron microscopes, among
other applications. Field emission takes place when the applied
electric field is high enough to reduce the potential barrier on
the tip-vacuum interface so that electrons can tunnel through this
barrier at a temperature close to room temperature (e.g.,
quantum-mechanical tunneling). A typical field-emitter comprises a
conical emitter tip with a circular gate aperture. A potential
difference is established across the emitter cathode, the gate and
the anode under an applied external field, resulting in high
electric field at the surface of the tip. Electrons tunnel through
the narrow surface barrier and travel towards an anode, which is
biased at a higher potential than the gate. The emission current
density can be estimated by a modified version of the
Fowler-Nordheim theory, which takes into account the field
enhancement factor due to the field emitters.
[0009] Field emitters, because they can operate near room
temperature, have lower energy spread than Schottky and thermionic
emitters, and can have higher brightness and electron current than
thermionic emitters. However, in practical use, the output current
of a field emitter is less stable because contaminants can easily
stick to the tip of the emitter and raise its work function, and
hence lower the brightness and current. Periodic flashing (i.e.,
temporarily raising the tip temperature) is required to remove
those contaminants. While the tip is being flashed, the instrument
is not available for operation. Instruments in the semiconductor
industry are required to operate continuously and stably without
interruption, so Schottky emitters are usually used in preference
to cold field emitters.
[0010] Previous field emitter arrays (FEAs) had multiple conically
shaped electron emitters arranged in a two-dimensional periodic
array. These field emitter arrays can be broadly categorized by the
material used for fabrication into two broad categories: metallic
field emitters and semiconductor field emitters.
[0011] Thermal field emitters (TFE) were previously used to
generate electron beams. An individual electron source was used to
form an array. Each electron source requires expensive XYZ stages.
The cost of each individual electron source system was expensive
and cost-prohibitive for a large array. In addition, the electron
current density was low.
[0012] Photocathodes also have been used to generate electron
beams. A single light beam incident on a photocathode system can
generate a single electron beam with high brightness that is
capable of delivering high electron current density. However, a
problem with single electron beam systems is that even with high
brightness systems, single electron beam systems still have
relative low throughput for inspection. Low throughput is a
drawback to electron beam inspection. With current available
electron beam sources, thousands of beams would be required.
[0013] Splitting the single electron beam into numerous beams for a
multi-beam SEM system required an array of aperture lenses and/or
micro-lenses. The array of aperture lenses and/or micro-lenses are
set in small, electrically-charged apertures that are substantially
round in design to create lens fields. If the apertures are
out-of-round, astigmatism is introduced in the lens fields, which
results in a distorted image plane.
[0014] Therefore, what is needed is an improved system to generate
electron beams.
BRIEF SUMMARY OF THE DISCLOSURE
[0015] A system is provided in a first embodiment. The system
comprises a diffractive optical element configured to receive an
incident radiation beam, an extractor plate, a microlens array that
provides collimation and focus of the beamlets, a condenser lens
disposed between the diffractive optical element and the microlens
array along the path of the beamlets, and a photocathode surface
disposed between the microlens array and the extractor plate along
the path of the beamlets. The diffractive optical element forms the
beamlets from the incident radiation beam. The microlens array is
disposed between the diffractive optical element and the extractor
plate along a path of the beamlets. The photocathode surface
generates a plurality of electron beams from the beamlets.
[0016] The system can further include a laser light source that
generates the incident radiation beam.
[0017] The beamlets may be in an array.
[0018] The electron beams can have a density from 2 nA to 5 nA.
[0019] The electron beams can have a spatial separation from 50
.mu.m to 10 mm.
[0020] 100 to 1000 of the electron beams may be included.
[0021] The system can further include an electron beam column. In
an instance, the electron beams are directed from the extractor
plate at the electron beam column.
[0022] The system can include a plurality of the electron beam
columns. In an instance, each of the electron beams is directed at
one of the electron beam columns.
[0023] The beamlets each can have a spot size from 10 .mu.m to 100
.mu.m. The electron beams generated by the photocathode surface
each can have a spot size from 10 .mu.m to 100 .mu.m.
[0024] The incident radiation beam may be ultraviolet
radiation.
[0025] The system can further include a voltage source in
electronic communication with the extractor plate.
[0026] A wafer inspection tool can include the system of the first
embodiment.
[0027] A method is provided in a second embodiment. A radiation
beam is generated and received at a diffractive optical element. A
plurality of beamlets are formed from the radiation beam using the
diffractive optical element. The beamlets are directed through a
condenser lens. The beamlets are collimated and focused with a
microlens array downstream of the condenser lens with respect to a
direction the beamlets are projected. The beamlets from the
microlens array are directed to a photocathode surface. A plurality
of electron beams are generated from the beamlets using the
photocathode surface. The electron beams are extracted from the
photocathode surface.
[0028] The beamlets can be in an array ranging from 4.times.6 to
48.times.48
[0029] The electron beams can have a density from 2 nA to 5 nA.
[0030] 100 to 1000 of the electron beams may be included.
[0031] The electron beams can have a spatial separation from 50
.mu.m to 10 mm.
[0032] The beamlets each can have a spot size from 10 .mu.m to 100
.mu.m. The electron beams generated by the photocathode surface
each can have a spot size from 10 .mu.m to 100 .mu.m.
[0033] The radiation beam may be ultraviolet radiation.
[0034] A pattern of the beamlets can be transmitted to the electron
beams.
DESCRIPTION OF THE DRAWINGS
[0035] For a fuller understanding of the nature and objects of the
disclosure, reference should be made to the following detailed
description taken in conjunction with the accompanying drawings, in
which:
[0036] FIG. 1 is a view of a diffractive optical element
photocathode array system to produce multiple electron beams;
[0037] FIG. 2 illustrates electron beams that are extracted from
the photocathode surface by providing voltage to an extractor plate
creating an extraction field;
[0038] FIG. 3 is an embodiment of a method in accordance with the
present disclosure; and
[0039] FIG. 4 is block diagram of an embodiment of a system in
accordance with the present disclosure.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0040] Although claimed subject matter will be described in terms
of certain embodiments, other embodiments, including embodiments
that do not provide all of the benefits and features set forth
herein, are also within the scope of this disclosure. Various
structural, logical, process step, and electronic changes may be
made without departing from the scope of the disclosure.
Accordingly, the scope of the disclosure is defined only by
reference to the appended claims.
[0041] The system is designed for electron beam inspection of
semiconductor wafers with high throughput. The system includes a
photocathode electron source, diffractive optical element (DOE),
lens system to parallelize the beamlets, and microlens array to
focus the beamlets. Using a DOE with microlens array to produce
collimated parallel beamlets on a photocathode surface can produce
a patterned electron beam.
[0042] A photocathode system can provide high electron density per
beam, which reduces the number of beams required. A multiple
electron beam system can achieve high resolution with increased
throughput. High speed and high resolution electron beams can be
provided with a DOE lens system coupled to a photocathode element
to generate a multi-electron beam system. A multiple electron beam
inspection system using parallel data acquisition may increase the
throughput and shorten the time to inspect a wafer or reticle.
[0043] FIG. 1 is a view of a diffractive optical element
photocathode array system 100 to produce a multi-electron beam. A
source directs a radiation beam 101 on the DOE 102, which will
produce a beamlet array to be used in combination with a
photocathode 111 surface to generate an array of electron beams
110. In particular, the radiation beam 101 impinging on DOE 102
forms an array of light beamlets 107 that impinge a microlens array
104. The microlens array 104 focuses the focused parallelized
beamlets 109 to a photocathode surface 111. The photocathode
surface 111 generates a multi-electron-beam pattern.
[0044] The light source that generates the incident radiation beam
may be, for example, lasers, diodes, lamps, or broadband (BB) light
sources. BB sources can be obtained from, for example,
laser-produced plasmas, laser-sustained plasmas, laser-produced
supercontinuum sources, white lasers, or largely tunable optical
parametric sources. These sources can be continuous-wave (CW) or
pulsed and can have wavelengths that range from vacuum ultraviolet
(VUV) to the infrared (IR). A single wavelength can be selected
with a suitable spectrometer or narrow or wide bands of wavelengths
can be selected by filters or other methods.
[0045] In an embodiment, the light source is a laser light source
or a diode. The incident radiation beam may be ultraviolet
radiation. In an instance, the radiation beam 101 is light with a
wavelength of 266 nm. The radiation beam may be generated such that
it has low noise.
[0046] In another embodiment, the light source is a CW light
source.
[0047] The system 100 includes a DOE 102, a condenser lens 103, a
microlens array 104, a photocathode element 105 with a photocathode
surface 111, and an extractor plate 106. Radiation from the source
passes through the DOE 102, the condenser lens 103, and the
microlens array 104 before being projected on the photocathode
surface 111. The electron beams can be extracted from the
photocathode surface 111 using the extractor plate 106.
[0048] Optical alignment of the microlens array 104 may impact
output of the electron beams 110. Uniformity across the entire
photocathode surface 111 and/or equivalent spot size in the focused
parallelized beamlets 109 can affect performance. A light beam may
be larger than the electron emitting aperture. A light beam also
may be smaller than the electron beam limiting aperture. If the
light beam is smaller than the electron beam limiting aperture,
then a metrology alignment may be performed.
[0049] The DOE 102 receives an incident radiation beam 101. The DOE
102 forms a plurality of beamlets 107 from the incident radiation
beam 101. The number of beamlets 107 produced by the DOE 102 may be
the same as the number of beamlets exiting the condenser lens 103
or the number of electron beams 110 that are produced. Four
beamlets 107 are illustrated exiting the condenser lens 103 for
simplicity. Thus, the number of beamlets 107 can vary from that
illustrated in FIG. 1. The number of beamlets 107 (and electron
beams 110) can form an array. The array may include, for example,
4.times.6, 6.times.6, 1.times.10, 10.times.10, 10.times.100,
30.times.100, or other configurations of beamlets 107 and electron
beams 110.
[0050] The condenser lens 103 is disposed between the DOE 102 and
the microlens array; 104. The condenser lens 103 may adjust
trajectory of the beamlets 107 and can be configured to provide an
output of parallelized beamlets 108. The number of parallelized
beamlets 108 equals the number of beamlets 107.
[0051] The microlens array 104 can provide collimation and focus of
the parallelized beamlets 108. The microlens array 104 is disposed
between the DOE 102 and the extractor plate 106. The parallelized
beamlets 108 leaving the microlens array 104 are focused
parallelized beamlets 109, which are focused at the cathode surface
111.
[0052] The photocathode surface 111 in the photocathode element 105
is disposed between the microlens array 104 and the extractor plate
106. The photocathode surface 111 generates a plurality of electron
beams 110 from the focused parallelized beamlets 109. The
photocathode surface 111 may be or may include a photosensitive
compound. When struck by a photon, the photocathode surface 111 can
cause electron emission due to the photoelectric effect.
[0053] In an embodiment, the photocathode element 105 can include
bare metals, coated metals, cesium metal or alloys thereof,
negative electron affinity (NEA) materials, a Zintl salt
photocathode material, or alkali photocathode materials.
[0054] While twelve of the electron beams 110 are illustrated, the
photocathode surface 111 can generate from 100 to 1000 or from 100
to 2500 the electron beams 110. The number of electron beams 110
can be scaled depending on the system design or the
application.
[0055] The extractor plate 106 is opposite the DOE 102 with respect
to a direction of travel of the beamlets 107. In an instance, the
extractor plate 106 includes 20 .mu.m diameter apertures, though
other size apertures are possible. The extractor plate 106 can be
in electronic communication with a voltage source 112. The voltage
range can be from 0.1 KV to 50 KV. For high resolution inspection,
the voltage range can be from 0.1 KV to 5 KV. Other voltages are
possible, and these ranges are merely examples.
[0056] The DOE 102 can be designed to generate a desired number of
beamlets with a desired spatial separation and pattern. Optical
lenses can be used to form parallelized beamlets, but also to form
and shape the light beams. The beamlets can be aligned to a
microlens array 104 optics. The combination of DOE 102, optical
elements, and the microlens array 104 can provide multiple beams of
electrons having a desired spatial separation, spot size, and
pattern.
[0057] In an example, radiation, such as ultraviolet radiation, in
a collimated beam is directed onto the DOE 102. A focusing lens can
be used to collimate individual beamlets and a microlens array 104
can focus the beamlets on the photocathode surface 111.
[0058] The design of the DOE 102 can define the number of the
beamlets, a size of the array, and a desired spatial separation and
pattern. The pattern imposed onto the beamlets is transmitted to
the multiple electron beams 110 as these electron beams 110 are
generated by the photocathode surface 111. Previous designs had
difficulty producing an array of electron beams with the same size,
arrangement, or other properties as the electron beams 110.
[0059] The beamlets, such as the parallelized beamlets 108 or the
focused parallelized beamlets 109, can be in an array. The pattern
of the beamlets can be transmitted to the electron beams 110. Thus,
an array of beamlets can be transmitted to an array of electron
beams 110.
[0060] The beamlets, such as the parallelized beamlets 108 or the
focused parallelized beamlets 109, each can have a spot size from
10 .mu.m to 100 .mu.m. The electron beams 110 generated by the
photocathode surface 111 each can have a spot size from 10 .mu.m to
100 .mu.m.
[0061] The electron beams 110 can have a density from 2 nA to 5
nA.
[0062] The electron beams 110 can have a spatial separation from 50
.mu.m to 10 mm or more. Spatial separation of the electron beams
110 in the 10's of mm is possible.
[0063] The system 100 can include an electron beam column, which
may be downstream of the extractor plate 106 relative to the
direction of travel of the electron beams 110. The electron beam
column can include components such as, for example, apertures,
deflectors, scan coils, electromagnetic lenses, magnetic lenses, or
detectors. The configuration of the electron beam column can vary
with the particular application of the system.
[0064] The electron beams 110 can be directed at the electron beam
column. In an instance, there are multiple electron beam columns.
Each of the electron beams 110 can be directed at one of the
electron beam columns. Each electron beam column can individually
control one of the electron beams. Simultaneous use of multiple
individually-controlled electron beams allows for corrections of
each beam.
[0065] Embodiments disclosed herein allow formation of multiple
beams of electrons by directing a small spot size (e.g., 10-100
.mu.m) radiation (e.g., ultraviolet light) onto a suitable
photocathode surface 111. The photocathode surface 111 can produce
a small electron spot size (e.g., 10-100 .mu.m). The electrons
produced from the photocathode surface 111 can be accelerated by
voltage applied to the extractor plate 106. The final spot of each
electron beam 110 can be controlled by the electron optics.
[0066] Multi-electron beams from photocathodes using DOE with a
microlens array can enable inspection of a mask or wafer in a few
hours. Conventional methods may take months to perform the same
inspection.
[0067] The photocathode surface 111 may be configured for the
wavelength of the radiation beam 101. For example, the photocathode
surface 111 may have different coatings or substrate materials
depending on the wavelength of the radiation beam 101. For UV
wavelengths down to 248 nm, fused silica or sapphire may be used as
the substrate material. For wavelengths below 193 nm, MgF.sub.2 or
CaF.sub.2 may be used. The material of the photocathode surface 111
can be chosen for optimal quantum efficiency (QE) and energy spread
at a given wavelength.
[0068] Design of the DOE 102 may vary depending on the wavelength
of the radiation beam 101 or the pitch of the beamlets 107.
Material in the DOE 102 can be selected based on the wavelength
that is used in the diffractive optical element photocathode array
system 100. For UV wavelengths down to 248 nm, fused silica or
sapphire may be used a material in the DOE 102. For wavelengths
below 193 nm, MgF.sub.2 or CaF.sub.2 may be used.
[0069] Design of the condenser lens 103 or microlens array 104 can
vary depending on the wavelength of the radiation beam 101 or the
spot sizes of the beamlets 107 or parallelized beamlets 108.
Material in the condenser lens 103 or microlens array 104 can be
selected based on the wavelength that is used in the diffractive
optical element photocathode array system 100. For UV wavelengths
down to 248 nm, fused silica or sapphire may be used a material in
the condenser lens 103 or microlens array 104. For wavelengths
below 193 nm, MgF.sub.2 or CaF.sub.2 may be used.
[0070] The system 100 can increase throughput. A larger array of
the electron beams 110 and/or a larger spot size of the electron
beams 110 can increase throughput.
[0071] FIG. 2 illustrates electron beams 110 that are extracted
from the photocathode surface 111 by providing voltage to an
extractor plate 106 creating an extraction field (shown by the
arrow 113). The extractor plate 106 defines a plurality of
extraction apertures 114. As seen in FIG. 1, the electron beams 110
are formed from the focused parallelized beamlets 109.
[0072] FIG. 3 is an embodiment of a method 200. At 201, a radiation
beam is generated. The radiation beam may be ultraviolet radiation
or another wavelength of radiation. The radiation beam is received
at a DOE at 202. A plurality of beamlets are formed from the
radiation beam using the DOE at 203. The beamlets are directed
through a condenser lens at 204. The beamlets are collimated and
focused downstream of the condenser lens with a microlens array at
205. The downstream position may be with respect to a direction the
beamlets are projected. At 206, the beamlets are directed from the
microlens array to a photocathode surface. A plurality of electron
beams are generated from the beamlets using the photocathode
surface at 207. The electron beams are extracted from the
photocathode surface at 208.
[0073] The beamlets can be in an array ranging from, for example,
4.times.6 to 48.times.48. Other array configurations are possible.
The array may depend on the pitch of the beamlets.
[0074] The electron beams can have a density from 2 nA to 5 nA.
There may be from 100 to 1000 or from 100 to 2500 electron beams.
The electron beams can have a spatial separation from 50 .mu.m to
10 mm or more. Spatial separation of the electron beams 110 in the
10's of mm is possible.
[0075] In an instance, the beamlets each have a spot size from 10
.mu.m to 100 .mu.m, and the electron beams generated by the
photocathode each have a spot size from 10 .mu.m to 100 .mu.m.
[0076] A pattern of the beamlets can be transmitted to the electron
beams. Thus, the electron beams can have the same pattern as the
beamlets impinging the photocathode surface.
[0077] Embodiments disclosed herein enable designs of multiple
electron beams and patterning targets with multiple beams of
electrons. Any type of light can be used depending on the
photocathode material. For inspection, a CW laser or radiation from
lamps, diodes, or laser-produced plasmas may be used as light
sources. For most photocathode material with high QE, an
ultraviolet light source may be used.
[0078] Embodiments disclosed herein can be used in reticle or wafer
inspection, review, or metrology systems, such as those that use a
single electron source or multiple electron sources. Embodiments
disclosed herein can be used in systems that use electron sources
for generation of x-rays using single or multiple electron sources
for use of wafer or reticle, metrology, review or inspection.
[0079] FIG. 4 is a block diagram of an embodiment of a system 300.
The system 300 includes a wafer inspection tool (which includes the
electron column 301) configured to generate images of a wafer
304.
[0080] The wafer inspection tool includes an output acquisition
subsystem that includes at least an energy source and a detector.
The output acquisition subsystem may be an electron beam-based
output acquisition subsystem. For example, in one embodiment, the
energy directed to the wafer 304 includes electrons, and the energy
detected from the wafer 304 includes electrons. In this manner, the
energy source may be an electron beam source. In one such
embodiment shown in FIG. 4, the output acquisition subsystem
includes electron column 301, which is coupled to computer
subsystem 302. A chuck (not illustrated) may hold the wafer
304.
[0081] As also shown in FIG. 4, the electron column 301 includes an
electron beam source 303 configured to generate electrons that are
focused to wafer 304 by one or more elements 305. The electron beam
source 303 may include, for example, an embodiment of the
diffractive optical element photocathode array system 100 of FIG.
1. The one or more elements 305 may include, for example, a gun
lens, an anode, a beam limiting aperture, a gate valve, a beam
current selection aperture, an objective lens, and a scanning
subsystem, all of which may include any such suitable elements
known in the art. The components of the electron beam column also
may be part of the elements 305.
[0082] Electrons returned from the wafer 304 (e.g., secondary
electrons) may be focused by one or more elements 306 to detector
307. One or more elements 306 may include, for example, a scanning
subsystem, which may be the same scanning subsystem included in
element(s) 305.
[0083] The electron column also may include any other suitable
elements known in the art.
[0084] Although the electron column 301 is shown in FIG. 4 as being
configured such that the electrons are directed to the wafer 304 at
an oblique angle of incidence and are scattered from the wafer 304
at another oblique angle, the electron beam may be directed to and
scattered from the wafer 304 at any suitable angles. In addition,
the electron beam-based output acquisition subsystem may be
configured to use multiple modes to generate images of the wafer
304 (e.g., with different illumination angles, collection angles,
etc.). The multiple modes of the electron beam-based output
acquisition subsystem may be different in any image generation
parameters of the output acquisition subsystem.
[0085] Computer subsystem 302 may be coupled to detector 307 such
that the computer subsystem 302 is in electronic communication with
the detector 307 or other components of the wafer inspection tool.
The detector 307 may detect electrons returned from the surface of
the wafer 304 thereby forming electron beam images of the wafer 304
with the computer subsystem 302. The electron beam images may
include any suitable electron beam images. The computer subsystem
302 includes a processor 308 and an electronic data storage unit
309. The processor 308 may include a microprocessor, a
microcontroller, or other devices.
[0086] It is noted that FIG. 4 is provided herein to generally
illustrate a configuration of an electron beam-based output
acquisition subsystem that may be used in the embodiments described
herein. The electron beam-based output acquisition subsystem
configuration described herein may be altered to optimize the
performance of the output acquisition subsystem as is normally
performed when designing a commercial output acquisition system. In
addition, the systems described herein may be implemented using an
existing system (e.g., by adding functionality described herein to
an existing system). For some such systems, the methods described
herein may be provided as optional functionality of the system
(e.g., in addition to other functionality of the system).
Alternatively, the system described herein may be designed as a
completely new system.
[0087] The computer subsystem 302 may be coupled to the components
of the system 300 in any suitable manner (e.g., via one or more
transmission media, which may include wired and/or wireless
transmission media) such that the processor 308 can receive output.
The processor 308 may be configured to perform a number of
functions using the output. The wafer inspection tool can receive
instructions or other information from the processor 308. The
processor 308 and/or the electronic data storage unit 309
optionally may be in electronic communication with another wafer
inspection tool, a wafer metrology tool, or a wafer review tool
(not illustrated) to receive additional information or send
instructions.
[0088] The computer subsystem 302, other system(s), or other
subsystem(s) described herein may be part of various systems,
including a personal computer system, image computer, mainframe
computer system, workstation, network appliance, internet
appliance, or other device. The subsystem(s) or system(s) may also
include any suitable processor known in the art, such as a parallel
processor. In addition, the subsystem(s) or system(s) may include a
platform with high speed processing and software, either as a
standalone or a networked tool.
[0089] The processor 308 and electronic data storage unit 309 may
be disposed in or otherwise part of the system 300 or another
device. In an example, the processor 308 and electronic data
storage unit 309 may be part of a standalone control unit or in a
centralized quality control unit. Multiple processors 308 or
electronic data storage unit 309 may be used.
[0090] The processor 308 may be implemented in practice by any
combination of hardware, software, and firmware. Also, its
functions as described herein may be performed by one unit, or
divided up among different components, each of which may be
implemented in turn by any combination of hardware, software and
firmware. Program code or instructions for the processor 308 to
implement various methods and functions may be stored in readable
storage media, such as a memory in the electronic data storage unit
309 or other memory.
[0091] The system 300 of FIG. 4 is merely one example of a system
that can use the diffractive optical element photocathode array
system 100 of FIG. 1. Embodiments of the diffractive optical
element photocathode array system 100 of FIG. 1 may be part of a
defect review system, an inspection system, a metrology system, or
some other type of system. Thus, the embodiments disclosed herein
describe some configurations that can be tailored in a number of
manners for systems having different capabilities that are more or
less suitable for different applications.
[0092] Each of the steps of the method may be performed as
described herein. The methods also may include any other step(s)
that can be performed by the processor and/or computer subsystem(s)
or system(s) described herein. The steps can be performed by one or
more computer systems, which may be configured according to any of
the embodiments described herein. In addition, the methods
described above may be performed by any of the system embodiments
described herein.
[0093] Although the present disclosure has been described with
respect to one or more particular embodiments, it will be
understood that other embodiments of the present disclosure may be
made without departing from the scope of the present disclosure.
Hence, the present disclosure is deemed limited only by the
appended claims and the reasonable interpretation thereof.
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