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NL2020465B1 - Apparatus and method for inspecting a surface of a sample, using a multi-beam charged particle column - Google Patents

Apparatus and method for inspecting a surface of a sample, using a multi-beam charged particle column Download PDF

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Publication number
NL2020465B1
NL2020465B1 NL2020465A NL2020465A NL2020465B1 NL 2020465 B1 NL2020465 B1 NL 2020465B1 NL 2020465 A NL2020465 A NL 2020465A NL 2020465 A NL2020465 A NL 2020465A NL 2020465 B1 NL2020465 B1 NL 2020465B1
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NL
Netherlands
Prior art keywords
electron
charged particle
photon
primary charged
sample
Prior art date
Application number
NL2020465A
Other languages
Dutch (nl)
Inventor
Kruit Pieter
Naftali Ron
Original Assignee
Univ Delft Tech
Applied Materials Israel Ltd
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Priority to NL2020465A priority Critical patent/NL2020465B1/en
Application granted granted Critical
Publication of NL2020465B1 publication Critical patent/NL2020465B1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
    • H01J37/147—Arrangements for directing or deflecting the discharge along a desired path
    • H01J37/1472—Deflecting along given lines
    • H01J37/1474—Scanning means
    • H01J37/1475—Scanning means magnetic
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/244—Detectors; Associated components or circuits therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/15—Means for deflecting or directing discharge
    • H01J2237/1508—Combined electrostatic-electromagnetic means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/244—Detection characterized by the detecting means
    • H01J2237/2445—Photon detectors for X-rays, light, e.g. photomultipliers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/244—Detection characterized by the detecting means
    • H01J2237/2448—Secondary particle detectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/245—Detection characterised by the variable being measured
    • H01J2237/24592—Inspection and quality control of devices

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Measurement Of Radiation (AREA)

Abstract

Apparatus and method for inspecting a surface of a sample. Said. apparatus comprises a multi—beam charged particle column comprising a source for creating multiple primary beams directed. towards the sample, an objective lens for focusing' said. primary beams on said. sample, an electron—photon converter unit comprising an array of electron to photon converter sections, each section is located next to a primary beam within a distance equal to a pitch of the primary beams at the electro—photon converter unit, a photon transport unit for transporting light from said electron to photon converter sections to a photo detector, and an electron collection unit for guiding secondary electrons created in the sample, towards the electron—photon converter unit. The electron collection unit is arranged to project secondary electrons created in the sample by one of said primary beams to at least one of said electron to photon converter sections.

Description

BACKGROUND
One of the routine steps of integrated circuits is surfaces, i substantial in the production of check for especially part of defects the inspection starting up a the whole 300 mm wafer when new is for in the pattern and the pattern or on top of the wafer.
of inspection is presently performed by highoptical microscopy in dedicated instruments.
With the progress in lithography, it is desirable that instruments detect smaller and smaller defects imbedded in throughput and from
A problem is that the light scattering rapidly decreases when the particle's so the signal-to-background (and noise) ratio is size
In order to solve this problem, electron beam inspection machines have been used and for some purposes are still in use. Electron beam inspection machines can have a much higher resolution than optical system. However, electron beam inspection machines are limited in the speed at which the electron beam inspection machines can inspect a wafer. In order to increase the speed, multi-beam electron beam systems have been proposed.
US 2007/0272856, described a method and an apparatus for inspecting a specimen surface. The method comprises the steps of generating a plurality of primary beams directed towards the specimen surface, focusing the plurality of primary beams onto respective loci on the specimen surface, collecting a plurality of secondary beams of charged particles originating from the specimen surface upon incidence of the primary beams, converting at least one of the collected secondary beams into an optical beam, and detecting the optical beam. The apparatus described in this Patent Publication comprises a screen with fluorescent material, which screen is disposed between an emitter for generating a plurality of primary beams and the specimen surface, the primary beams are focused at the level of the screen and which screen is constructed such that the primary beams can travers through holes in the screen. The secondary beams from the specimen surface are directed from the specimen surface towards the screen and are defocused on the screen to provide a spot which covers an area around the holes in the screen. At these spots, the secondary beams are converted into optical beams, which optical beams are then imaged through free space onto a plane in which the optical detector is located.
SUMMARY
A disadvantage of the system described in US 2007/0272856 is, that the spots of secondary beams on the relatively large and spots of adjacent secondary partially large spots which results screen are beams are relatively detector, detector .
In addition, the onto the optical large spots on the of the primary large .
of this system are imaged through free space
Accordingly, the specimen
A the optical overlapping .
are imaged in relatively the pitch surface is relatively further disadvantage beams beams on is, that onto the optical detector via an optical lens. Typically the optical lens is arranged next to the array of primary beams so that said optical lens does not obstruct the trajectory of the primary beams. The optical lens is therefore arranged remote from the screen of fluorescent material where the secondary electrons are converted into light, and the numerical aperture and thus the light-gathering ability of the lens is relatively small, which makes the detection of the secondary electrons inefficient.
It is an object to least partially solve at least one of the above identified disadvantages and/or to provide an alternative inspection apparatus, which allows for high throughput inspection of samples, in particular semiconductor wafers.
According to a first aspect, a multi-beam charged particle column for inspecting a surface of a sample is provided, which multi-beam charged particle column comprising:
one or more emitters which are arranged for creating multiple primary charged particle beams directed along trajectories towards the surface of the sample, an objective lens unit for focusing said multiple primary charged particle beams on said sample, an electron-photon converter unit comprising a plurality of electron to photon converter sections, wherein at least one electron to photon converter section of said plurality of electron to photon converter sections is located next to a trajectory of a primary charged particle beam and within a distance equal to a pitch of trajectories of the primary charged particle beams at the electronphoton converter unit, a photon transport unit for transporting light from said electron to photon converter sections to a light detector, and an electron collection unit comprising multi aperture plates for guiding secondary electrons created in the sample upon incidence of the primary charged particle beams, towards the electron to photon converter sections of the electron-photon converter unit, wherein the electron collection unit is configured for projecting secondary electrons created in the sample by one of said primary charged particle beams to at least one of said electron to photon converter sections arranged at one side with respect to the trajectory of said one of the primary charged particle beams.
According to embodiments of the present invention, the secondary electrons created in the sample by one of the primary charged particle beams are directed to a position at one side with respect to said one of the primary charged particle beam. By configuring the electron collection unit to project the secondary electrons to a position at one side with respect to the primary charged particle beam which produced the secondary electrons, an overlap of the secondary electrons created by multiple primary charged particle beams can at least substantially be prevented, in particular when the electron collection unit is configured for projecting secondary electrons all at a same side with respect to the corresponding primary charged particle beams that created the secondary electrons in the sample. In a preferred embodiment, the secondary electrons created in the sample by one of the primary charged particle beams are directed onto the electron to photon converter section arranged adjacent to or neighboring the trajectory of said one of said primary charged particle beams.
It is noted that in the apparatus described in US 2007/0272856, the secondary beams from the sample are directed towards a screen and are defocused on the screen to provide a spot which covers an area around the holes in the screen. Contrarily to the arrangement in the prior art, the electron collection unit according to embodiments of the present invention, is arranged for projecting the secondary electrons to one side next to the primary charged particle beam. In the apparatus of embodiments of the present invention, an overlap of the spots of secondary electrons from adjacent primary charged particle beams can be prevented, which makes it easier to detect and distinguish the secondary electrons coming from adjacent primary charged particle beams. Accordingly, the detection and evaluation of the secondary electrons from the surface of the sample can be faster, and thus the surface of the sample can be inspected more quickly, which increases the throughput for the inspection of samples.
It is further noted that in the apparatus described in WO 2016/036246, the multi-sensor detector system is arranged at a position which is spaced apart from the array primary electron beams, in a direction perpendicular to an optical axis of the primary electron beams. According to embodiments of the present invention, the electron-photon converter unit comprises an array of electron to photon converter sections, wherein each electron to photon converter section is located next to a primary charged particle beam and within a distance equal to a pitch of the primary charged particle beams at the electro-photon converter unit. In the apparatus of embodiments of the present invention, the electron to photon converter sections are arranged close to the primary charged particle beams. Preferably, at least one electron to photon converter section of said array of electron to photon converter sections is arranged between two adjacent primary charged particle beams. By arranged the each electron to photon converter section close to a primary beam or even between two adjacent primary beams, the width of the multi-beam charged particle column can be reduces, which makes it easier to arranged multiple multi-beam charged particle column close to each other and to arrange more multi-beam charged particle columns within a certain area above the sample. Accordingly, the surface of the sample can be inspected more quickly, which increase the throughput for the inspection of samples.
It is possible to use a free space optical imaging for transporting light from said electron to photon converter section to a light detector, as for example described in US 2007/0272856, or to arrange the light detector directly above or on top of the electron to photon converter section. When the light detector is arranged directly above or on top of the electron to photon converter section, the photon transport unit does not need to have extra or separate component and is essentially established by the configuration of the array of electron to photon converter sections and the photo detectors.
In an embodiment, the photon transport unit comprises a plurality of optical fibers. In an embodiment, at least one optical fiber of said plurality of optical fibers has a first end, wherein the first end is arranged adjacent or attached to one of said electron to photon converter sections for coupling light from said electron to photon converter section into the optical fiber. In an embodiment, the at least one optical fiber of said plurality of optical fibers has a second end, wherein the second end is configured to project light from said optical fiber onto the photon detector or light detector. In an embodiment, at least the first end of said at least one optical fiber of said array of optical fibers is arranged between the trajectories of two adjacent primary charged particle beams of said multiple primary charged particle beams .
In an embodiment, at least one of the plurality of optical fibers is at least partially coated with a photo-reflecting layer. When using optical fibers which are coated with a photo-reflecting layer, the acceptance cone of the optical fibers is not limited by the conditions of total internal reflection, and the acceptance cone can be much larger. The acceptance cone represents all angles with respect to the longitudinal axis of the optical fiber at which photons may enter the optical fiber such that the photons will convey along the optical fiber. When using optical fibers with a photo-reflecting coating, the maximum angle at which light may enter the optical fiber so that the light will propagate along the optical fiber is much larger. An example of such a photo-reflecting layer is a mirror coating, for example using an aluminum coating which may be enhanced by dielectric coatings.
In an embodiment, at least one of the plurality of optical fibers is tapered towards the first end. In an embodiment, the at least one optical fiber is cut at said first end at an angle between 10° and 90° with respect to an central axis of said at least one optical fiber. When using a tapered optical fiber, the optical fiber can be more easily inserted in between and arranged next to the trajectories of the primary charged particle beams of the multi-beam charged particle column.
In an embodiment, at least one electron to photon converter section of said plurality of electron to photon converter sections is arranged between the trajectories of two adjacent primary charged particle beams of said multiple primary charged particle beams. Accordingly this embodiment advantageously utilizes the area between the trajectories of two adjacent primary charged particle beams to arrange the electron to photon converter section inside the plurality of primary charged particle beams. This provides a very compact multi-beam charged particle column and/or allows to arrange at least two multi-beam charged particle columns close to each other for inspecting adjacent parts of the surface of a sample.
In an embodiment, said plurality of electron to photon converter sections comprises a plurality of strips of luminescent material, wherein at least one strip of said plurality of strips is located next to the trajectory of a primary charged particle beam and within to the pitch of the trajectories of tb particle beams at the electron-photon Preferably said plurality of strips ai plane, wherein said plane is arrange!
a distance equal primary charged converter unit.
arranged in a such that the trajectories of the primary charged particle beams traverse said plane in a said plane.
In an direction substantially perpendicular to photon converter plate or a layer the plate or layer of passage openings for Preferably said plate arranged that the embodiment, the plurality of sections comprises or are a of luminescent material. In an electron to traverse in a plane, trajectories said part of embodiment, luminescent material is provided with the primary or layer of wherein the charged particle beams, luminescent material is a direction arranged such particle beams substantially plane is of the primary charged plane in perpendicular to said plane.
In an embodiment, the material of an carrier, layer of layer of luminescent optically transparent In an embodiment, the is arranged on top such as a glass carrier, luminescent material is preferably arranged at a side of said optically transparent carrier which is facing the electron collection unit. The electron to photon converter sections comprises any converting material having the property that converts an incident electrons into one or more photons. Examples are scintillating materials, for instance crystal scintillators such as YAG, YAP, Nal, etc..., or plastic scintillators, or a fluorescent or phosphorescent materials. Within the meaning of this application such materials are also called luminescent materials .
In an embodiment, said electron to photon converter sections, in particular said strips of luminescent material, are coated with a photo-reflecting layer. Preferably the photo-reflecting layer is arranged at a side of said electron to photon converter sections which is facing away from the photon transport unit. Preferably the photo-reflecting layer is at least partially transparent for secondary electrons. This allows at least part of the secondary electrons reflecting layer. The secondary the photo-reflecting layer are to pass through the photoelectrons that pass through converted into photons by the converting material of the electron to photon converter sections. Only a part of the generated photons will be traveling in a direction towards the photon transport unit, which part may be transported by said photon transport unit to the photo detector. The part of the generated photons that is traveling opposite to the direction towards the photon transport unit, is reflected by the photo-reflecting layer and is substantially re-directed toward the photon transport unit after said reflection. Accordingly, the part of the generated photons that can be collected by the photon transport unit for transporting towards the photo detector can be increased.
In an embodiment, the multi-beam charged particle column comprises an optical axis, wherein the trajectories of the multiple primary charged particle beams are arranged in multiple rows, wherein each row extends in a first direction substantially perpendicular to the optical axis, wherein the rows are arranged next to each other in a second direction substantially perpendicular to said first direction and said optical axis. Accordingly the multi-beam charged particle column according to this embodiment comprises an array of charged particle beam trajectories which are arranged in multiple rows, which rows are arranged next to each other in a direction substantially perpendicular to the direction of the rows. Preferably the pitch between adjacent trajectories of the primary charged particle beams is substantially constant. Preferably the pitch between the rows of trajectories of the primary charged particle beams is substantially equal to the pits between adjacent trajectories of the primary charged particle beams in the rows .
In an embodiment, at least one of the plurality optical fibers of said photon transport unit is arranged at least partially in between two adjacent rows. Accordingly the space between the rows of the multiple primary charged particle beams is used to accommodate at least part of the optical fibers, in particular to arrange the first end of said optical fibers adjacent or attached to one of said electron to photon converter sections, in particular adjacent or attached to one of said strips of luminescent material.
In an embodiment, the emitter comprises a single thermal field emission source, preferably of the Schottky type, for emitting a diverging electron beam towards a beam splitter, wherein the beam splitter comprises a plate with multiple apertures which are arranged for creating multiple primary beams, one primary beam per aperture. In this embodiment, the multiple primary charged particle beams are primary electron beams.
In an embodiment, the multi-beam charged particle column comprises a collimator lens for substantially collimating the primary charged particle beams from the emitter. In an embodiment, the electron-photon converter is preferably arranged between the collimator lens and the sample holder, more preferably arranged between the collimator and the objective lens unit.
In an embodiment, the electron collection unit comprises a Wien deflector unit for providing a magnetic field to disentangle the primary charged particle beams from the secondary electron beams coming from the surface of the sample upon incidence of the primary charged particle beams. In an embodiment, such a Wien deflector unit in use comprise perpendicular electric and magnetic fields which are configured so that a deflection of the primary charged particle beams by the electric field is substantially equal to but in an opposite direction of a deflection of the primary charged particle beams by the magnetic field. In addition the electric and magnetic fields are configured so that the deflection of the secondary electrons by the electric field is substantially in the same direction as the deflection of the secondary electrons by the magnetic field.
According to a second aspect, a method for inspecting a surface of a sample using a multi-beam charged particle column is provided, wherein said method comprises the steps of:
operating one or more emitters for creating multiple primary charged particle beams directed along trajectories towards the surface of the sample, collimating the primary charged particle beams, focusing said multiple primary charged particle beams on said sample, guiding secondary electrons created in the charged unit upon incidence of the primary towards an electron-photon converter electron collection unit, least part means of particle by means sample beams of an converting at electrons into photons converter unit, wherein comprising a plurality sections, wherein at least section of said plurality sections by the of is located next of the one of the secondary electron-photon converter unit electron-photon electron to photon electron to photon electron to photon a trajectory of converter converter converter a primary within a distance equal to a to charged pitch of at the electron-photon converter unit collection unit is configured for particle beam and trajectories of the primary charged particle beams , wherein the electron projecting secondary electrons created in the sample by one of said primary charged particle beams to at least one of said electron to photon converter sections arranged at one side with respect to the trajectory of said one of the primary charged particle beams, and transporting light from said electron to photon converter sections to a photo detector.
In an embodiment, the method is performed by means of a multi-beam charged particle column or an embodiment thereof, as described above.
In an embodiment, the multi-beam charged particle column comprises at least one optical fiber wherein said at least one optical fiber has a first end, wherein the first end is arranged adjacent to or attached to one of said electron to photon converter sections, wherein the method comprises the step of:
coupling light from said electron to photon converter section into the optical fiber.
In an embodiment, the at least one optical fiber has a second end, wherein the method comprises the step of:
projecting light from the second end of said at least one optical fiber onto the photo detector.
The various aspects and in the specification can be wherever possible, the aspects and dependent claims, applications .
features described and shown applied, aspects, features described in
These individual individually, in particular the attached can be made subject of divisional patent
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings, in which:
Figure 1 schematically shows an example of a multi-beam charged particle column;
Figure 2 schematically shows a first detailed view in the XZ plane of a part of the multi-beam charged particle column according to embodiments of the invention;
Figure 3 schematically shows a first detailed view in the YZ plane of a part of the multi-beam charged particle column of figure 2;
Figure 4 schematically shows a first detailed view in the XY plane of a part of the multi-beam charged particle column of figures 2 and 3;
Figure 5 schematically shows detailed view of a part of a second example of a photon transport unit, and
Figure 6 schematically shows a detailed view in the XZ plane of a part of the multi-beam charged particle column according to a second example of a multi-beam charged particle column according to embodiments of the invention .
DETAILED DESCRIPTION
Figure 1 shows a schematic representation of a multi-beam charged particle column 1 comprising an emitter 2, which is arranged substantially on an optical axis OA, for generating a diverging charged particle beam 3 which extends along said optical axis OA. Preferably, said emitter 2 comprises a Schottky source.
Downstream from said emitter 2, a lens array 4 is provided, which lens array 4 is provided with an aperture array for splitting the diverging charged particle beam 3 in multiple primary charged particle beams 5; each aperture of said aperture array provides one primary charged particle beam 5. In addition the lenses of the lens array 4 focusses each individual primary charged particle beam 5 at or near a collimator lens 6, which is arranged at a side of the lens array 4 facing away from the emitter 2.
Accordingly, the emitter 2 and the lens array 4 constitutes an arrangement for creating multiple primary charged particle beams 5, which multiple primary charged particle beams 5 are directed towards the surface of a sample 11.
The collimator lens 6 is arranged for substantially collimating the primary charged particle beams 5 from the emitter 2, in particular to direct each primary charged particle beam 5 substantially parallel to the optical axis OA. In embodiment, the collimator lens 6 comprises a deflector array which is arranged for deflecting the individual primary charged particle beams 5, in order to produce an array of primary charged particle beams 7 which are arranged substantially parallel to the optical axis OA as schematically shown in figure 1.
not strictly necessary, it makes components at the side of the from the emitter
2, such as the
Although a collimator is the positioning of the collimator 6 facing away objective lens unit, much less critical, direction along the optical axis OA.
Subsequently, axis OA, more detail the optical described in below.
at least in a detector array 8 which detector array 8 figures
1, the charged with reference to schematically shown in figure array 8 is arranged to allow beams 7 to travel through the objective lens unit 10.
The objective focusing each one of said beams 7 on said sample 11.
the
As lens is at will be
2, 3 and detector the primary detector array 8 towards an multiple primary particle
In between
Wien detector array 8, a array, is arranged, provides at least < primary charged particle beams coming from the incidence of the primary be explained in more
Figures 2, of an example of
In objective filter 9, the use, a magnetic beams surface lens
e.g.
Wien unit 10 and the a Wien deflector deflector array disentangle the and secondary of the sample particle beams 7, field to electron charged detail below.
and 4 show different a multi-beam charged according to embodiments of the invention, in figures 2, 3 and 4 corresponds to part of the multi-beam charged particle 1, below the collimator lens 6. The figures 2, 3 and 4, comprises the same as upon will views of part column particle
The part the particular the column 1 of figure example shown in upper part of the shown charged particle column of figure 1, in particular the part above the detector array 8 for producing an array of primary charged particle beams 7 which are arranged substantially parallel to the optical axis OA.
According to the example shown in the figures 2, 3 and 4, the multi-beam charged particle column 1' comprises an electron-photon converter unit 81 comprising an array electron to photon converter sections, in particular an array of fluorescent strips 82. Each fluorescent strip 82 is located in the plane of the electron-photon converter unit 81, next to a primary beam 7 and within a distance d equal to a pitch of the primary beams 7 at the electron-photon converter unit 81. As shown in the figures 2 and 3 in particular, the multiple primary charged particle beams 7 traverses the plane of the electron-photon converter unit 81 which plane extends in a XY direction, substantially perpendicular to the optical axis OA.
It is noted that at least one strip of said array of fluorescent strips 82 is arranged between two adjacent primary charged particle beams 7 of said multiple primary charged particle beams.
It is further noted that in the example shown in figures 2, 3 and 4, the electron-photon converter unit 81 comprises a series of parallel arranged fluorescent strips which extend substantially in the Y-direction. However, the electron-photon converter unit may alternatively also a plate of a fluorescent material with through holes or openings 83 for the primary charged particle beams 7, which plate of fluorescent material extends in the XY direction. The parts of such a plate which extend in the X or Y direction in between the through holes for the primary charged particle beams 7, are also considered to be fluorescent strips in accordance with embodiments of the present invention.
As schematically indicated in figure 2, the primary charged particle beams 7 travel through the plane of the electron-photon converter unit 81, via the openings between the fluorescent strips 82, towards the Wien filter 9. The Wien filter comprises a combination of a magnetic deflector 91 and an electrostatic deflector 92. In use, the electrostatic deflector 92 is arranged to at least substantially counteract the deflection of the magnetic deflector 91 for the primary charged particle beams 7.
Accordingly, the primary charged particle beams 7' which have traversed the Wien filter, are shifted to a small extend in the X-direction, but are still arranged substantially parallel to the optical axis OA, and thus substantially parallel to the primary charged particle beams 7 above the Wien filter 9.
Subsequently, the primary charged particle beams 7' are focused onto a sample 11 via an objective lens unit
10.
The objective lens unit 10 comprises an electron collection unit comprising multi aperture plates for, in use, guiding secondary electrons 12 created in the sample 11 upon incidence of the primary charged particle beams 7', towards the Wien filter 9. For the secondary electrons 12, which travel in opposite direction with respect to the primary charged particle beams 7, 7', the electrostatic deflector 92 does not counteract the deflection of the magnetic deflector 91, but now the deflections of the secondary electrons 12 by the electrostatic deflector 92 and the magnetic deflector 91 add up. Accordingly, the secondary electrons 12' which have passed the Wien filter are no longer traveling substantially parallel to the optical axis OA, but are deflected to travel at an angle with respect to the optical axis OA in order to project the secondary electrons 12^ onto the fluorescent strips 82 of the electron-photon converter unit 81, as schematically shown in figure 2.
At the fluorescent strips 82 of the electronphoton converter unit 81, photons are created upon incidence of the secondary electrons 12' . At least a part of said photons are transported from the fluorescent strip 82 to a photo detector 13 via a photon transport unit. In the example as shown in figures 2 and 3 and according to embodiments of the present invention, said photon transport unit comprises an array of optical fibers 14. Each optical fiber 14 comprises a first end 15 which is arranged adjacent or attached to one of said fluorescent strips 82 for coupling light (photons) from said fluorescent strip 82 into the optical fiber 14, and a second end 16 which is arranged to project light from said optical fiber 14 onto the photo detector 13.
As schematically shown in figure 2, the first end 15 of the optical fibers 14 of said array of optical fibers is arranged between two adjacent primary charged particle beams 7 of said multiple primary charged particle beams.
Figure 4 shows a schematic top view at the plane of the electron-photon converter unit 81, in particular in the XY plane which extends substantially perpendicular to the optical axis OA, as indicated in Figure 2 by the reference IV - IV. As shown in figure 4, the multiple primary charged particle beams 7 are arranged in multiple rows 71, 72, wherein each row 71, 72 extends in a first direction, in this example in the Y-direction, substantially perpendicular to the optical axis OA as schematically shown in figure 3. The rows 71, 72 of primary charged particle beams 7 are arranged next to each other in a second direction, in this example in the Xdirection, substantially perpendicular to said first direction and said optical axis OA. The fluorescent strips 82 of the electron-photon converter unit 81, are arranged next to a row 71, 72 of primary charged particle beams 7 and within a distance equal to a pitch d of the rows 71, 72 of the primary charged particle beams 7 at the electronphoton converter unit 81. As schematically indicated in figure 4, the openings 83 between the fluorescent strips 82 are arranged to allow passage of the primary charged particle beams 7 through the plane of the electron-photon converter unit 81.
In use, secondary electrons 12' created in the sample 11 upon incidence of the primary charged particle beams 7, are deflected by the Wien filter 9 in the Xdirection and are projected onto the fluorescent strips 82 of the electron-photon converter unit 81, as schematically shown in figure 4. The secondary electrons 12' incident on the fluorescent strips 82 at a side facing the Wien filter 9, are converted by fluorescent material of the fluorescent strips 82 into photons (light) . At a side of the fluorescent strips 82 facing away from the Wien filter, in particular at or near the position where the secondary electrons 12' are deflected to, optical fibers 14 are arranged to collect at least part of the created photons and to guide the collected photons a photo detector 13, as schematically shown in figure 3. All the optical fibers 14 which are arranged to collect the photons from the various spots of secondary electrons 12' on a specific fluorescent strip 82, are arranged above said fluorescent strip 82, in particular in a ZY plane, at least the parts of the optical fibers 14 which is arranged next to or in between the rows 71, 72 of primary charged particle beam 7. As schematically shown in figure 3, the optical fibers 14 are bent or curved in the YZ plane in order to arranged the second end 16 of the fibers at least out of the area of the primary charged particle beams 7 to project light from said optical fiber 14 onto the photo detector 13. The bended or curved optical fibers 14 are substantially confined to the area above the fluorescent strips 82 in order to circumvent that the optical fibers 14 get in the way of the primary charged particle beams 7. The assembly of optical fibers 14 constitute a photon transport unit according to embodiments of the present invention.
The photons created by the conversion of the secondary electrons 12' in the fluorescent strips 82 may also be emitted in a direction away from the first end 15 of the optical fibers 14. In order to redirect these photons back towards the first end 15 of the optical fibers 14, the fluorescent strips 82 may be coated with a photoreflecting layer 21 at a side of said fluorescent strips 82 facing away from the first end 15 of the optical fibers 14, as schematically indicated in figure 3. Preferably, the photo-reflecting layer 21 is substantially transparent for the secondary electrons 12' , so that at least a substantial amount of the secondary electrons 12' reach the fluorescent material of the fluorescent strips photons .
An alternative of the and curved fibers 14, is shown in figure example, the optical fibers 14' first end 15' . The first end 15' are cut at an angle an central axis CA
5. In or bent optical this alternative are tapered towards the of the optical fibers 14' a between 10° and 90° with respect to of said optical fibers 14' . At the tapered first end fluorescent plate or which in use may be arranged instead of and at of the fluorescent strips 82 in the example of
12' which are projected onto fluorescent
15' and 4. The secondary electrons the fluorescent plate or converted into photons 20. At photons 20 are coupled optical fibers 14' and said optical fiber 14' photons 20 are total internal optical fibers may be at layer 22, as 14' in figure
As into confined >ers 14' , a is arranged, the position figures 2, 3 least part the first are conveyed or towards a layer 82' are of the generated end 15' of the directed through photo-detector .
inside optical fiber 14' due reflection at the side surface of
The to
14' . Alternatively, the least partially coated with schematically indicated at .
discussed above, it is arrange the photo detector 130 directly the electron to photon converter sections (e.g.
the
14' also possible to above or on top of fluorescent strip 82), as schematically shown in a second example shown in figure 6. According to this example, the photo detector 130 comprises an array of through holes 131 for the primary charged particle beams 7. The photo detector 130 preferably comprises an array of photo detector sections 132, each of said photo detector section 132 is arranged directly above or on top of one of the electron to photon converter sections (e.g. fluorescent strip 82). Accordingly, the photon transport unit does not need to have extra or separate components, such as optical fibers, and is essentially established by the configuration of the array of electron to photon converter sections and the array of photo detector sections 132.
It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the spirit and scope of the present invention .
It is noted that in use the charged particle beams, in particular the primary charged particle beams, travel along the corresponding trajectories of the charged particle beams, and the representation of the charged particle beams in the enclosed figures also depict the corresponding trajectories of the charged particle beams. When not in use, the charged particle beams are not present in the multi-beam charged particle column. However, the trajectories, which represent the path the charged particle beams follow when the multi-beam charged particle column is in use, can be defined even if the multi-beam charged particle column is not in use.
In summary, embodiments of the present invention relates to an apparatus and method for inspecting a surface of a sample. Said apparatus comprises a multi-beam charged particle column comprising arranged source for creating multiple primary beams directed towards the sample, an objective lens for focusing said primary beams on said sample, an electron-photon converter unit comprising an array of electron to photon converter sections, each section is located next to a primary beam within a distance equal to a pitch of the primary beams at the electro-photon converter unit, a photon transport unit for transporting light from said electron to photon converter sections to a photo detector, and an electron collection unit for guiding secondary electrons created in the sample, towards the electron-photon converter unit . The electron collection unit is arranged to project secondary electrons created in the sample by one of said primary beams to at least one of 5 said electron to photon converter sections.

Claims (19)

CONCLUSIESCONCLUSIONS 1. 1. Een A kolom met column with meerdere multiple geladen loaded deeltjes particles bundels bundles voor in front of het it inspecteren inspect van een of a oppervlak surface van from een a monster, sample, waarbij at which de kolom met the column with meerdere multiple : geladen : loaded deeltjes particles bundels bundles omvat includes één a of meer emitters or more emitters die zijn they are ingericht furnished voor in front of het it creëren to create van from meer more dere primaire primary geladen loaded deeltjes particles bundels bundles welke langs banen which run along zijn gericht are targeted naar het to the oppervlak surface van from het it
monster, een ob jectief-lens-eenheid voor het op het monster focusseren van de meerdere primaire geladen deeltjes bundels, een elektron-foton omzet eenheid omvattende meerdere elektron-naar-foton omzet segmenten, waarbij ten minste één elektron-naar-foton omzet segment van de meerdere elektron-naar-foton omzet segmenten naast een baan van een primaire geladen deeltjes bundel geplaatst is binnen een afstand gelijk aan een steek van de banen van de primaire geladen deeltjes bundels bij de elektron-foton omzet eenheid, een fotontransporteenheid voor het transporteren van licht van de elektron-naar-foton omzet segmenten naar een lichtdetector, en een elektron-verzamel-eenheid omvattende meerdere apertuurplaten voor het geleiden van secundaire elektronen die bij het invallen van de primaire geladen deeltjes bundels in het monster worden gecreëerd, naar de elektronnaar-foton omzet segmenten van de elektron-foton omzet eenheid, waarbij de elektron-verzamel-eenheid is geconfigureerd voor het projecteren van secundaire elektronen die in het monster worden gecreëerd door één van de primaire geladen deeltjes bundels naar ten minste één van de elektron-naar-foton omzet segmenten die aan één zijde ten opzichte van de baan van die ene van de primaire geladen deeltjes bundels geplaatst is.sample, an objective lens unit for focusing the multiple primary charged particle beams on the sample, an electron-photon conversion unit comprising a plurality of electron-to-photon conversion segments, wherein at least one electron-to-photon conversion segment of the plurality of electron-to-photon converting segments disposed adjacent to a trajectory of a primary charged particle beam within a distance equal to a pitch of the trajectories of the primary charged particle beams at the electron-photon converting unit, a photon transport unit for transporting of light from the electron-to-photon converting segments to a light detector, and an electron-collecting unit comprising a plurality of aperture plates for guiding secondary electrons that are created upon incident of the primary charged particle beams in the sample, to the electronon photon-converting segments of the electron-photon-converting unit, the electron-collecting unit being configured for the t projecting secondary electrons created in the sample by one of the primary charged particle beams to at least one of the electron-to-photon converting segments that bundle on one side relative to the trajectory of that one of the primary charged particle beams is placed. 2. De kolom met meerdere geladen deeltjes bundels volgens conclusie 1, waarbij ten minste één elektron-naarfoton omzet segment van de meerdere elektron-naar-foton omzet segmenten is geplaatst tussen de banen van twee aangrenzende primaire geladen deeltjes bundels van de meerdere primaire geladen deeltjes bundels.The multi-charged particle beam column according to claim 1, wherein at least one electron-to-photon converting segment of the multiple electron-to-photon converting segments is disposed between the trajectories of two adjacent primary charged particle bundles of the plurality of primary charged particles bundles. 3. De kolom met meerdere geladen deeltjes bundels volgens conclusie 1 of 2, waarbij de fotontransporteenheid meerdere optische vezels omvat.The multi-particle beam bundle according to claim 1 or 2, wherein the photo transport unit comprises a plurality of optical fibers. 4. De kolom met meerdere geladen deeltjes bundels volgens conclusie 3, waarbij ten minste één optische vezel van de meerdere optische vezels een eerste uiteinde heeft, waarbij het eerste uiteinde geplaatst is naast of bevestigd is aan één van de elektron-naar-foton omzet segmenten voor het inkoppelen van licht van het elektron-naar-foton omzet segment in de optische vezel.The multi-particle beam bundle column according to claim 3, wherein at least one optical fiber of the plurality of optical fibers has a first end, the first end being located adjacent to or attached to one of the electron-to-photon converting segments for coupling light from the electron-to-photon conversion segment into the optical fiber. 5. De kolom met meerdere geladen deeltjes bundels volgens conclusie 4, waarbij de ten minste ene optische vezel van de meerdere optische vezels een tweede uiteinde heeft, waarbij het tweede uiteinde is geconfigureerd voor het projecteren van licht van de optische vezel op een fotodetector.The multi-particle beam bundle according to claim 4, wherein the at least one optical fiber of the plurality of optical fibers has a second end, the second end being configured to project light from the optical fiber onto a photo-detector. 6. De kolom met meerdere geladen deeltjes bundels volgens conclusie 3, waarbij ten minste één optische vezel van de meerdere optische vezels een eerste uiteinde heeft, waarbij het eerste uiteinde tussen de banen van twee aangrenzende primaire geladen deeltjes bundels van de meerdere geladen deeltjes bundels geplaatst is.The multi-charged particle bundle column according to claim 3, wherein at least one optical fiber of the plurality of optical fibers has a first end, the first end placed between the webs of two adjacent primary charged particle bundles of the plurality of charged particle bundles is. 7. De kolom met meerdere geladen deeltjes bundels volgens één van de conclusies 3-6, waarbij ten minste één van de meerdere optische vezels ten minste gedeeltelijk bekleed is met een foto-reflecterende laag.The multi-particle beam bundle column according to any of claims 3-6, wherein at least one of the plurality of optical fibers is at least partially coated with a photo-reflective layer. 8. De kolom met meerdere geladen deeltjes bundels volgens één van de conclusies 1-7, waarbij ten minste één van de meerdere optische vezel naar het eerste uiteinde spits toeloopt.The multi-particle beam bundle according to any of claims 1-7, wherein at least one of the plurality of optical fibers tapers to the first end. 9. De kolom met meerdere geladen deeltjes bundels volgens conclusie 8, waarbij de ten minste ene optische vezel aan het eerste uiteinde onder een hoek tussen 10e en 902 ten opzichte van een centrale as van de ten minste ene optische vezel is gesneden.The multi-particle beam bundle according to claim 8, wherein the at least one optical fiber at the first end is cut at an angle between 10 th and 90 2 relative to a central axis of the at least one optical fiber. 10. De kolom met meerdere geladen deeltjes bundels volgens één van de conclusies 1-9, waarbij de meerdere elektron-naar-foton omzet segmenten meerder stroken van luminescent materiaal omvatten, waarbij ten minste één strook van de meerdere stroken naast de baan van een primaire geladen deeltjes bundel geplaatst is binnen een afstand gelijk aan de steek van de banen van de primaire geladen deeltjes bundels bij de elektron-foton omzet eenheid.The multi-particle beam bundle according to any of claims 1-9, wherein the multiple electron-to-photon converting segments comprise multiple strips of luminescent material, at least one strip of the plurality of strips adjacent to the trajectory of a primary charged particle beam is placed within a distance equal to the pitch of the orbits of the primary charged particle beams at the electron-photon conversion unit. 11. De kolom met meerdere geladen deeltjes bundels volgens één van de conclusies 1 - 10, waarbij de meerder elektron-naar-foton omzet segmenten een plaat of een laag van luminescent materiaal omvatten.The multi-particle beam bundle column according to any of claims 1 to 10, wherein the multiple electron-to-photon conversion segments comprise a plate or a layer of luminescent material. 12. De kolom met meerdere geladen deeltjes bundels volgens conclusie 11, waarbij de plaat of de laag van luminescent materiaal is voorzien van doorgaande openingen voor de primaire geladen deeltjes bundels.The multi-charged particle bundle column according to claim 11, wherein the plate or layer of luminescent material is provided with through openings for the primary charged particle bundles. 13. De kolom met meerdere geladen deeltjes bundels volgens één van de conclusies 1 - 12, waarbij de genoemde meerdere elektron-naar-foton omzet segmenten ten minste gedeeltelijk zijn bekleed met een foto-reflecterende laag.The multi-particle beam bundle according to any one of claims 1 to 12, wherein said multiple electron-to-photon conversion segments are at least partially coated with a photo-reflective layer. 14. De kolom met meerdere geladen deeltjes bundels volgens één van de conclusies 1 - 13, waarbij de kolom met meerdere geladen deeltjes bundels een optische as omvat, waarbij de banen van de meerdere primaire geladen deeltjes bundels in meerdere rijen geplaatst zijn, waarbij elke rij zich uitstrekt in een eerste richting in hoofdzaak loodrecht op de optische as, waarbij de rijen naast elkaar geplaatst zijn in een tweede richting in hoofdzaak loodrecht op de eerste richting en de optische as.The multi-charged particle bundle column according to any one of claims 1 to 13, wherein the multi-charged particle bundles column comprises an optical axis, wherein the paths of the plurality of primary charged particle bundles are arranged in a plurality of rows, each row extending in a first direction substantially perpendicular to the optical axis, the rows being arranged side by side in a second direction substantially perpendicular to the first direction and the optical axis. 15. De kolom met meerdere geladen deeltjes bundels volgens conclusie 14, indien afhankelijk van één van de conclusies 3-9, waarbij ten minste één van de meerdere optische vezels ten minste gedeeltelijk tussen twee aangrenzende rijen geplaatst is.The multi-particle beam bundle according to claim 14, if dependent on any of claims 3-9, wherein at least one of the plurality of optical fibers is placed at least partially between two adjacent rows. 16. De kolom met meerdere geladen deeltjes bundels volgens één van de conclusies 1 - 15, waarbij de één of meer emitters een enkele thermische veld-emissiebron omvat voor het uitzenden van een divergerende geladen deeltjes bundel naar een bundel-splits-inrichting, waarbij de bundel-splits-inrichting een plaat met meerdere aperturen omvat die is ingericht voor het creëren van meerdere primaire geladen deeltjes bundels, één primaire geladen deeltjes bundel per apertuur.The multi-charged particle beam column according to any of claims 1 to 15, wherein the one or more emitters comprise a single thermal field emission source for transmitting a diverging charged particle beam to a beam splitter, the bundle splitter comprises a plate with a plurality of apertures that is adapted to create a plurality of primary charged particle bundles, one primary charged particle bundle per aperture. 17. De kolom met meerdere geladen deeltjes bundels volgens één van de conclusies 1 - 16, waarbij de elektron-verzamel-eenheid een Wien-afbuig-eenheid omvat voor het verschaffen van een magnetisch veld voor het ontwarren van de primaire geladen deeltjes bundels van de secundaire elektronen bundels die van het oppervlak van het monster komen na het invallen van de primaire geladen deeltjes bundels.The multi-charged particle beam column according to any one of claims 1 to 16, wherein the electron-collecting unit comprises a Wien deflection unit for providing a magnetic field for disentangling the primary charged particle beams from the secondary electron beams coming from the surface of the sample after the incident of the primary charged particle beams. 18. Werkwijze voor het inspecteren van een oppervlak van een monster gebruik makend van een kolom met meerdere geladen deeltjes bundels, waarbij de werkwijze de stappen omvat van:A method of inspecting a surface of a sample using a column with a plurality of charged particle bundles, the method comprising the steps of: het in werking stellen van één of meer emitters voor het creëren van meerdere primaire gelanden deeltjes bundels die langs banen naar het oppervlak van het monster zijn gericht, het focusseren van de meerder primaire geladen deeltjes bundels op het monster, het door een elektron-verzamel-eenheid naar een elektron-foton omzet eenheid geleiden van secundaire elektronen die in het monster zijn gecreëerd na inval van de primaire geladen deeltjes bundels, het omzetten van ten minste een deel van de secundaire elektronen in fotonen door middel van de elektron-foton omzet eenheid, waarbij de elektron-foton omzet eenheid meerdere elektron-naar-foton omzet segmenten omvat, waarbij ten minste één elektron-naar-foton omzet segment van de meerdere elektron-naar-foton omzet segmenten naast een baan van een primaire geladen deeltjes bundel geplaatst is binnen een afstand gelijk aan een steek van de banen van de primaire geladen deeltjes bundels bij de elektron-foton omzet eenheid, waarbij de elektron-verzameleenheid is geconfigureerd voor het projecteren van secundaire elektronen die in het monster worden gecreëerd door één van de primaire geladen deeltjes bundels naar ten minste één van de elektron-naar-foton omzet segmenten die aan één zijde ten opzichte van de baan van die ene van de primaire geladen deeltjes bundels geplaatst is, en het transporteren van licht van de elektron-naarfoton omzet segmenten naar een licht-detector.activating one or more emitters to create a plurality of primary landed particle bundles directed along paths to the surface of the sample, focusing the plurality of primary charged particle bundles on the sample, electron-collecting unit to an electron-photon conversion unit guiding secondary electrons created in the sample after raid of the primary charged particle beams, converting at least a part of the secondary electrons into photons by means of the electron-photon conversion unit, wherein the electron-photon converting unit comprises a plurality of electron-to-photon converting segments, wherein at least one electron-to-photon converting segment of the multiple electron-to-photon converting segments is disposed within a trajectory of a primary charged particle beam a distance equal to one pitch of the trajectories of the primary charged particle beams at the electron-photon conversion unit, the e The electron collection unit is configured to project secondary electrons created in the sample through one of the primary charged particle beams to at least one of the electron-to-photon converting segments that are on one side relative to the orbit of that one of the primary charged particle bundles, and transporting light from the electron-to-photon converting segments to a light detector. 19. De werkwijze volgens conclusie 18, waarbij de kolom met meerdere geladen deeltjes bundels ten minste één optische vezel omvat waarbij de genoemde ten minste ene optische vezel een eerste uiteinde heeft, waarbij het eerste uiteinde aangrenzend geplaatst is aan of bevestigd is met één van de elektron-naar-foton omzet segmenten, waarbij de werkwijze de stap omvat van:The method of claim 18, wherein the multi-particle beam bundle column comprises at least one optical fiber wherein said at least one optical fiber has a first end, the first end being adjacent to or attached to one of the electron-to-photon conversion segments, the method comprising the step of: het koppelen van licht van het elektron-naarfoton omzet segment in de optische vezel.coupling light from the electron-to-photon conversion segment in the optical fiber. 5 20. De werkwijze volgens conclusie 19, waarbij de ten minste ene optische vezel een tweede uiteinde heeft, waarbij de werkwijze de stap omvat van:20. The method of claim 19, wherein the at least one optical fiber has a second end, the method comprising the step of: het projecteren van licht van het tweede uiteinde van de genoemde ten minste ene optische vezel op een licht10 detector.projecting light from the second end of said at least one optical fiber onto a light detector. □A □A□ A □ A 71 72 πι—*· □A71 72 πι— * · □ A
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