CN108292583B - Arrangement of a plurality of charged particle beams - Google Patents

Arrangement of a plurality of charged particle beams Download PDF

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Publication number
CN108292583B
CN108292583B CN201680026508.6A CN201680026508A CN108292583B CN 108292583 B CN108292583 B CN 108292583B CN 201680026508 A CN201680026508 A CN 201680026508A CN 108292583 B CN108292583 B CN 108292583B
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CN
China
Prior art keywords
electron
micro
lens
source
optical axis
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CN201680026508.6A
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Chinese (zh)
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CN108292583A (en
Inventor
任伟明
李帅
刘学东
陈仲玮
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Asml 荷兰有限公司
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Priority to PCT/US2016/027267 priority Critical patent/WO2016145458A1/en
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/28Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02Details
    • H01J37/04Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/10Lenses
    • H01J37/12Lenses electrostatic
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02Details
    • H01J37/04Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/147Arrangements for directing or deflecting the discharge along a desired path
    • H01J37/1472Deflecting along given lines
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/04Means for controlling the discharge
    • H01J2237/049Focusing means
    • H01J2237/0492Lens systems
    • H01J2237/04924Lens systems electrostatic
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/06Sources
    • H01J2237/083Beam forming
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/10Lenses
    • H01J2237/12Lenses electrostatic
    • H01J2237/1205Microlenses
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/15Means for deflecting or directing discharge
    • H01J2237/151Electrostatic means
    • H01J2237/1516Multipoles
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/26Electron or ion microscopes
    • H01J2237/28Scanning microscopes
    • H01J2237/2813Scanning microscopes characterised by the application
    • H01J2237/2817Pattern inspection

Abstract

A multi-beam apparatus for viewing a sample with high resolution and high throughput is presented. In the apparatus, a source conversion unit changes a single electron source into a virtual multi-source array, a main projection imaging system projects the array to form a plurality of detection points on a sample, and a condenser lens adjusts currents of the plurality of detection points. In the source conversion unit, the image forming device is upstream of the beamlet limitation device, and thereby generates less scattered electrons. The image forming device not only forms a virtual multi-source array, but also compensates for off-axis aberrations of the plurality of probe points.

Description

Arrangement of a plurality of charged particle beams

Priority declaration

This application claims priority to U.S. provisional application No.62/130,819 to Ren et al, entitled "Apparatus of Positive Charge-Particle Beams" filed on 10/3/2015, the entire disclosure of which is incorporated herein by reference.

Technical Field

The present invention relates to a charged particle device having a plurality of charged particle beams. More particularly, the present invention relates to an apparatus for simultaneously acquiring images of a plurality of scanning areas of an observation area on a sample surface using a plurality of charged particle beams. Thus, the apparatus can be used to inspect and/or evaluate defects on wafers/masks with high resolution and high throughput in the semiconductor manufacturing industry.

Background

In order to manufacture semiconductor IC chips, pattern defects and/or undesirable particles (residues) inevitably occur on the surface of the wafer/mask during the manufacturing process, which greatly reduces the yield. To meet the increasing demands on IC chip performance, patterns with smaller and smaller critical feature sizes are employed. As a result, conventional yield management tools with beams are becoming increasingly inadequate due to diffraction effects, and yield management tools with electron beams are increasingly being employed. The electron beam has a shorter wavelength than the photon beam, and thus it is possible to provide excellent spatial resolution. Currently, yield management tools with electron beams employ the principles of Scanning Electron Microscopy (SEM) with a single electron beam, which can therefore provide higher resolution, but cannot provide throughput adequate for mass production. Although higher and higher beam currents can be used to increase throughput, the coulomb effect will fundamentally degrade excellent spatial resolution.

To alleviate the yield limitations, instead of using a single electron beam with a large current, one promising solution is to use multiple electron beams each with a small current. The multiple electron beams form multiple probe points on an inspected or observed surface of the sample. For a sample surface, multiple probe points may scan multiple small scan areas within a large observation area on the sample surface, respectively and simultaneously. The electrons of each probe point generate secondary electrons from the surface of the sample where they land. The secondary electrons include slow secondary electrons (energy ≦ 50eV) and backscattered electrons (energy close to the landing energy of the electron). Secondary electrons from multiple small scan areas can be collected separately and simultaneously by multiple electron detectors. Therefore, an image of a large observation area including all small scanning areas can be obtained more quickly than scanning the large observation area with a single beam.

The multiple electron beams may each be from multiple electron sources, or from a single electron source. With the former, a plurality of electron beams are generally focused onto and scanned over a plurality of small scanning areas through a plurality of columns, respectively, and secondary electrons from each scanning area are detected by one electron detector within the corresponding column. Thus, the device is generally referred to as a multi-column device. The multiple columns may be independent or share a multi-axis magnetic or electromagnetic compound objective lens (such as US8,294,095). The beam separation between two adjacent beams is typically as large as 30 to 50mm on the sample surface.

For the latter, a source conversion unit is used to virtually change a single electron source into a plurality of sub-sources. The source conversion unit includes a beamlet forming device and an image forming device. The beamlet-forming means basically comprise a plurality of beam-limiting openings which divide the primary electron beam generated by the single electron source into a plurality of sub-beams or beamlets, respectively. The image forming apparatus basically includes a plurality of electron optical elements that focus or deflect the plurality of beamlets to form a plurality of parallel images of the electron source, respectively. Each of the plurality of parallel images may be considered to be a sub-source emitting a respective one of the sub-beams. The beamlet intervals, i.e., the beam limiting opening intervals, are in the order of micrometers in order to make more beamlets available, and thus the source conversion unit may be manufactured by a semiconductor manufacturing process or a MEMS (micro electro mechanical system) process. Of course, one main projection imaging system and one deflection scanning unit in one single column are used to project a plurality of parallel images to and scan a plurality of small scanning areas, respectively, and a plurality of secondary electron beams from the plurality of small scanning areas are detected by a plurality of detecting elements of one electron detecting device in one single column, respectively. The plurality of detection elements may be a plurality of electron detectors placed side by side or a plurality of pixels of one electron detector. Thus, the device is often referred to as a multi-beam device.

In the source conversion unit 20-1 in fig. 1A, the image forming apparatus 22-1 is constituted by a plurality of lenses (22_1L to 22_ 3L). The substantially parallel primary electron beams 2 from one single electron source are divided into a plurality of sub-beams (2_1 to 2_3) by the plurality of beam limiting openings (21_1 to 21_3) of the sub-beam forming device 21, and the plurality of lenses focus the plurality of sub-beams to form a plurality of parallel images (2_1r to 2_3r) of the single electron source, respectively. The plurality of parallel images are usually real images, but may be virtual images under certain conditions in the case where each of the plurality of lenses is an aperture lens. US7,244,949 and US7,880,143 each propose a multi-beam apparatus having one image forming apparatus of this type. In the source conversion unit 20-2 in fig. 1B, the image forming device 22-2 is constituted by a plurality of deflectors (22_2D and 22_ 3D). The diverging primary electron beam 2 from one single electron source is divided into a plurality of sub-beams (2_2 and 2_3) by a plurality of beam limiting openings (21_2 and 21_3) of the sub-beam forming device 21, and a plurality of deflectors respectively deflect the plurality of sub-beams to form a plurality of parallel virtual images (2_2v and 2_3v) of the single electron source.

As early as The 50 s of The 20 th century, The concept of using deflectors to form virtual images of Electron sources was used in The well-known Two-Slit Electron Interference experiments, in which Electron biprisms were employed to form Two virtual images as shown in FIG. 2 (FIG. 1 of The Merli-Missiroli-Pozzi Two-SlElectron-Interference Experiment, published by Rodolfo Rosa in "Physics in Perfect, 14(2012) 178-" As shown in FIG. 2). The electronic biprism basically comprises two parallel plates at ground potential and a very thin wire F between them. When a potential not equal to the ground potential is applied to the line F, the electron biprism becomes two deflectors having deflection directions opposite to each other. The primary electron beam from the electron source S passes through the two deflectors and becomes two deflected sub-beams forming virtual images S1 and S2 of the electron source S. If the potential is positive, the two sub-beams overlap each other, and interference fringes occur in the overlapping region.

Since then, the above concept has been adopted in a number of ways in multi-beam devices. JP- cA-10-339711 and US8,378,299 directly use cA conventional electron biprism to form two probe spots on the sample surface. US6,943,349 uses one annular deflector (fig. 5 thereof) or correspondingly one deflector array (fig. 12 thereof) to form more than two probing points on the sample surface and can therefore provide higher throughput. The annular deflector includes an inner annular electrode and an outer annular electrode. If the potentials of the two ring electrodes are not equal to each other, an electric field in a local radial direction will occur in the annular gap between them, and thus the ring deflector may deflect more than two beamlets together in different directions. Furthermore, the deflecting function of the annular deflector may be performed by one respective deflector array having a plurality of multi-pole type deflectors arranged along the annular gap.

In the conventional source conversion unit 20-2 in fig. 1B, due to the divergence of the primary electron beam 2, a plurality of sub-beams pass through a plurality of beam limiting openings at different incident angles and are thus subject to strong and different electron scattering. Scattered electrons in each beamlet will enlarge the detection spot and/or become background noise and thus deteriorate the image resolution of the corresponding scan area.

In US6,943,349, the current of the plurality of beamlets can only be changed by changing the size of the emission or beam-limiting opening of the single electron source. A single electron source takes a long time to become stable when its emission changes. The beamlet-forming device needs to have more than one set of openings, and the openings in this set are of a different size than the other sets. Changing the groups in use is very time consuming. Furthermore, under certain operating conditions of the objective lens, the secondary electron beam can only be focused onto a plurality of detector elements of the in-lens detector. The available applications are limited.

It is therefore desirable to provide a multi-beam apparatus capable of simultaneously acquiring images of multiple small scan areas within a large observation area on a sample surface with high image resolution and high throughput. In particular, there is a need for a multi-beam apparatus that can inspect and/or evaluate defects on wafers/masks with high resolution and high throughput to match the roadmap of the semiconductor manufacturing industry.

Disclosure of Invention

It is an object of the present invention to provide a new multi-beam apparatus capable of providing high resolution and high throughput for viewing samples and in particular for use as a yield management tool to inspect and/or assess defects on wafers/masks in the semiconductor manufacturing industry. The multi-beam apparatus employs a new source conversion unit to first form a plurality of parallel virtual images of a single electron source and to second limit the current of a corresponding plurality of beamlets, employs a condenser lens to adjust the current of the plurality of beamlets, employs a primary projection imaging system to project the plurality of parallel virtual images to form a plurality of detection points on an observed surface of a sample, employs a beam splitter to deflect a plurality of secondary electron beams from the observed surface away from paths of the plurality of beamlets, and employs a secondary projection imaging system to focus the plurality of secondary electron beams to be detected by a plurality of detection elements of an electron detection device, respectively.

Accordingly, the present invention therefore provides a source conversion unit comprising an image forming device comprising an upper layer having a plurality of upper 4-pole structures and a lower layer having a plurality of lower 4-pole structures, and a beamlet confinement device below the image forming device and comprising a plurality of beam-confinement openings. Each upper 4-pole structure is above and aligned with a respective one of the lower 4-pole structures, and both have an azimuthal difference of about 45 ° and form a pair of 4-pole structures. Thus, the plurality of upper 4-pole structures and the plurality of lower 4-pole structures form a plurality of pairs of 4-pole structures. A plurality of beam limiting openings are respectively aligned with the plurality of pairs of 4-pole structures. A pair of 4-pole structures serves as a micro-deflector to deflect one beamlet of an electron beam generated by an electron source to form a virtual image thereof, as a micro-lens to focus the one beamlet to a desired degree, and/or as a micro-stigmator to add a desired amount of astigmatic aberration to the one beamlet.

The invention also provides a multi-beam apparatus for observing the surface of a sample, comprising an electron source, a condenser lens below the electron source, a source converting unit below the condenser lens, a main projection imaging system below the source converting unit and including an objective lens, a deflection scanning unit inside the main projection imaging system, a sample stage below the main projection imaging system, a beam splitter above the objective lens, a subsidiary projection imaging system above the beam splitter, and an electronic detection device having a plurality of detection elements. The source conversion unit includes an image forming device having a plurality of micro-deflectors and a beamlet confinement device having a plurality of beam confinement openings, wherein the image forming device is above the beamlet confinement device. The electron source, condenser lens, source conversion unit, main projection imaging system, deflection scanning unit and beam splitter are aligned with the main optical axis of the apparatus. The sample stage holds the sample so that the surface faces the objective lens. The secondary projection imaging system and the electronic detection device are aligned with a secondary optical axis of the apparatus, the secondary optical axis being non-parallel to the primary optical axis. The electron source generates a primary electron beam along a primary optical axis, and the plurality of micro-deflectors deflect the primary electron beam to form a plurality of parallel virtual images of the electron source. Thus, a virtual multi-source array is converted from the electron source, and a plurality of beamlets comprising the virtual multi-source array pass through the plurality of beam-limiting openings, respectively. Thus, the current of each beamlet is limited by a respective one of the beam limiting openings, and the current of the plurality of beamlets can be varied by adjusting the condenser lens. The main projection imaging system images a virtual multi-source array onto a surface, and a plurality of detection points are thus formed on the surface. The deflection scanning unit deflects the plurality of beamlets to scan a plurality of detection points respectively over a plurality of scan areas within an observation area on the surface. The plurality of secondary electron beams are generated by a plurality of probe points from a plurality of scanning areas, respectively, and are focused by the objective lens while passing. Then, the beam splitter deflects the plurality of secondary electron beams to the auxiliary projection imaging system, and the auxiliary projection imaging system focuses the plurality of secondary electron beams and keeps the plurality of secondary electron beams detected through the plurality of detection elements, respectively. Thus, each detection element provides an image signal of a corresponding one of the scanning areas.

The multi-beam arrangement may further comprise a main aperture plate below the electron source, the main aperture plate having a main opening aligned with the main optical axis and serving as a beam-limiting aperture for the primary electron beam. The main projection imaging system may further comprise a transfer lens above the objective lens, the transfer lens focusing the plurality of beamlets to land vertically on the surface. Each of the plurality of micro-deflectors has a 4-pole structure that can generate a deflection field in any radial direction. The multi-beam apparatus may further comprise a single-beam electron detector above the beam splitter, which may be used in single-beam mode. The multi-beam apparatus may further comprise an in-lens electron detector having a beamlet pass-through aperture aligned with the primary optical axis, the in-lens electron detector being below the beam splitter and being usable in the single beam mode.

The invention also provides a multi-beam apparatus for observing the surface of a sample, comprising an electron source, a condenser lens below the electron source, a source converting unit below the condenser lens, a main projection imaging system below the source converting unit and including an objective lens, a deflection scanning unit inside the main projection imaging system, a sample stage below the main projection imaging system, a beam splitter above the objective lens, a subsidiary projection imaging system above the beam splitter, and an electronic detection device having a plurality of detection elements. The source conversion unit comprises an image forming device with a plurality of micro-deflector and compensator elements and a beamlet limitation device with a plurality of beam limiting openings, and each micro-deflector and compensator element comprises a micro-deflector and a micro-compensator with a micro-lens and a micro-stigmator. The image forming device is above the beamlet confinement device. The electron source, condenser lens, source conversion unit, main projection imaging system, deflection scanning unit and beam splitter are aligned with the main optical axis of the apparatus. The sample stage holds the sample so that the surface faces the objective lens. The secondary projection imaging system and the electronic detection device are aligned with a secondary optical axis of the apparatus, the secondary optical axis being non-parallel to the primary optical axis. The electron source generates a primary electron beam along a primary optical axis, and the plurality of micro-deflectors deflect the primary electron beam to form a plurality of parallel virtual images of the electron source. Thus, a virtual multi-source array is converted from an electron source. A plurality of beamlets comprising a virtual multi-source array respectively pass through a plurality of beam-limiting openings, so that the current of each beamlet is limited by a respective one of the beam-limiting openings. The current of the plurality of beamlets may be varied by adjusting the condenser lens. The main projection imaging system images the virtual multi-source array onto a surface so that a plurality of detection points are formed on the surface. One microlens and one micro-stigmator of one micro-compensator compensate for the field curvature and astigmatic aberration, respectively, of a corresponding one of the probe points, and the deflecting scanning unit deflects the plurality of beamlets to sweep the plurality of probe points, respectively, over a plurality of scan areas within an observation area on the surface. A plurality of secondary electron beams are generated by a plurality of probe points from a plurality of scanning areas, respectively, and are focused by an objective lens while passing, and then deflected by a beam splitter to enter a secondary projection imaging system. The auxiliary projection imaging system focuses the plurality of secondary electron beams and maintains the plurality of secondary electron beams to be detected through the plurality of detecting elements, respectively, so that each detecting element provides an image signal of a corresponding one of the scanning areas.

The multi-beam arrangement may further comprise a main aperture plate below the electron source, the main aperture plate having a main opening aligned with the main optical axis and serving as a beam-limiting aperture for the primary electron beam. Each of the plurality of micro-deflector and compensator elements may have an 8-pole structure, the 8-pole structure acting as one micro-deflector by generating the desired deflection field and as one micro-compensator by generating the desired quadrupole field and the desired circular lens field. Each of the plurality of micro-deflector and compensator elements comprises an upper 4-pole structure and a lower 4-pole structure in an upper layer and a lower layer, respectively, the upper layer being above the lower layer, the upper 4-pole structure and the lower 4-pole structure being aligned with each other and having an azimuthal angle difference of 45 °. The upper 4-pole structure and the lower 4-pole structure can be used as a micro-deflector by generating the desired deflection field and as a micro-compensator by generating the desired quadrupole field and the desired circular lens field. The main projection imaging system may further comprise a transfer lens above the objective lens, the transfer lens focusing the plurality of beamlets to land vertically on the surface. The multi-beam apparatus may further comprise a single-beam electron detector above the beam splitter, which may be used in single-beam mode. The multi-beam apparatus may further comprise an in-lens electron detector having a beamlet pass-through aperture aligned with the primary optical axis, the in-lens electron detector being below the beam splitter and being usable in the single beam mode.

The invention also provides a method for configuring a source conversion unit for forming a virtual multi-source array from an electron source, comprising the steps of: an image forming apparatus including an upper layer having a plurality of upper 4-pole structures and a lower layer having a plurality of lower 4-pole structures, and a beamlet limitation device provided below the image forming apparatus and including a plurality of beam limitation openings are provided. Each upper 4-pole structure is above and aligned with a respective one of the lower 4-pole structures, and they all have an azimuthal difference of 45 ° and form a pair of 4-pole structures. Thus, the plurality of upper 4-pole structures and the plurality of lower 4-pole structures form a plurality of pairs of 4-pole structures. A plurality of beam limiting openings are respectively aligned with the plurality of pairs of 4-pole structures. A pair of 4-pole structures serves as a micro-deflection to deflect one beamlet of an electron beam generated by an electron source to form a virtual image thereof, as a micro-lens to focus the one beamlet to a desired degree, and/or as a micro-stigmator to add a desired amount of astigmatic aberration to the one beamlet.

The source conversion unit may include an upper conductive plate having a plurality of upper vias respectively aligned with the plurality of pairs of 4-pole structures. The source conversion unit may further include a lower conductive plate having a plurality of lower vias respectively aligned with the plurality of pairs of 4-pole structures.

The invention also provides a method for forming a virtual multi-source array from an electron source, comprising the steps of: deflecting an electron beam from an electron source into a plurality of beamlets by using an upper layer having a plurality of upper 4-pole structures and a lower layer having a plurality of lower 4-pole structures, and confining the plurality of beamlets by using a plurality of openings. Each upper 4-pole structure is above and aligned with a respective one of the lower 4-pole structures, and both have an azimuthal difference of 45 ° and form a pair of 4-pole structures.

The invention also provides a charged particle beam apparatus comprising a single charged particle source for providing a primary beam, means for converting the primary beam into a plurality of sub-beams, a first projection system for forming a plurality of probe points on a sample from the plurality of sub-beams, a deflection scanning unit for scanning the plurality of probe points on the sample, means for separating the plurality of signal electron beams away from the plurality of sub-beams, a detection device for receiving the plurality of signal electron beams, and a second projection system for forming a plurality of signal points from the plurality of signal electron beams on a plurality of electron detection elements of the detection device, respectively. The conversion component comprises a plurality of deflectors for deflecting the plurality of beamlets and a plurality of beam limiting openings below the plurality of deflectors. The plurality of signal electron beams are each generated as a result of a plurality of beamlets impinging on the sample.

The charged particle beam device may further comprise a condenser lens for adjusting the current of the plurality of detection points. The conversion section includes a plurality of compensators for compensating for aberrations of the plurality of detection points, respectively.

Other advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which certain embodiments of the invention are set forth by way of illustration and example.

Drawings

The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:

fig. 1A and 1B are schematic diagrams of a conventional source conversion unit, respectively.

Fig. 2 is a schematic diagram of an electron interference experiment with an electron biprism.

Fig. 3A is a schematic diagram of one configuration of the novel multi-beam apparatus in accordance with one embodiment of the present invention.

Fig. 3B to 3D are schematic views of the operation modes of the new multi-beam apparatus of fig. 3A, respectively.

Fig. 4 is a schematic diagram of another configuration of the novel multi-beam apparatus according to another embodiment of the present invention.

Fig. 5A to 5C are schematic diagrams of the configuration of the image forming apparatus in fig. 3A according to another embodiment of the present invention, respectively.

Fig. 6A to 6D are schematic diagrams of the configuration of the image forming apparatus in fig. 3A according to another embodiment of the present invention, respectively.

Fig. 7 is a schematic diagram of a configuration of the advanced image forming apparatus in fig. 4 according to another embodiment of the present invention.

Fig. 8A to 8D are schematic diagrams of a configuration of the advanced image forming apparatus in fig. 4 according to another embodiment of the present invention.

Fig. 9A is a schematic diagram of another configuration of the novel multi-beam apparatus according to another embodiment of the present invention.

Fig. 9B and 9C are schematic diagrams of the operation modes of the new multi-beam apparatus of fig. 9A, respectively.

Fig. 10 is a schematic diagram of one mode of operation of the novel multi-beam apparatus of fig. 4.

Fig. 11A is a schematic diagram of another configuration of the novel multi-beam apparatus and one mode of operation thereof, according to another embodiment of the present invention.

Fig. 11B is a schematic diagram of another configuration of the novel multi-beam apparatus and one mode of operation thereof, according to another embodiment of the present invention.

Detailed Description

Various example embodiments of the present invention will now be described more fully with reference to the accompanying drawings, in which some example embodiments of the invention are shown. Without limiting the scope of protection of the invention, all the description and drawings of the embodiments will refer to electron beams. However, these examples are not intended to limit the invention to specific charged particles.

In the drawings, the relative sizes of each component and among components may be exaggerated for clarity. In the following description of the drawings, the same or similar reference numerals refer to the same or similar parts or entities, and only the differences with respect to the respective embodiments are described. For clarity, only three beamlets are available in the figure, but the number of beamlets may be any one.

Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intention to limit example embodiments of the invention to the specific forms disclosed, but on the contrary, example embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the scope of the invention.

In the present invention, "axial" means "in the direction of the optical axis of a lens (circle or multipole), an imaging system or device", "radial" means "in the direction perpendicular to the optical axis", "on-axis" means "on or aligned with the optical axis", and "off-axis" means "not on or misaligned with the optical axis".

In the present invention, "the imaging system is aligned with the optical axis" means "all the electron optical elements (such as a circular lens and a multipole lens) are aligned with the optical axis".

In the present invention, X, Y and the Z axis form Cartesian coordinates. The optical axis of the main projection imaging system is on the Z-axis, and the primary electron beam travels along the Z-axis.

In the present invention, "primary electrons" mean "electrons emitted from an electron source and incident on a surface of a sample to be observed or inspected", and "secondary electrons" mean "electrons generated from the surface by the primary electrons".

In the present invention, "signal electrons" mean "electrons generated from the surface of the sample to be observed or inspected by the primary charged particle beam".

In the present invention, "single beam mode" means that only one beamlet is being used.

In the present invention, all terms referring to through holes, openings and apertures mean an opening or hole through one plate.

Next, the present invention will provide some embodiments of new multi-beam apparatus. A multi-beam apparatus employs a new source conversion unit to first form a plurality of parallel virtual images of a single electron source and to second limit the current of a plurality of beamlets, a condenser lens to adjust the current of the plurality of beamlets, a primary projection imaging system to project the plurality of parallel virtual images to form a plurality of detection spots on an observed surface of a sample, a beam splitter to deflect a plurality of secondary electron beams from the surface away from the paths of the plurality of beamlets, and a secondary projection imaging system to focus the plurality of secondary electron beams to be detected by a plurality of detection elements of an electron detection device, respectively.

The new source conversion unit comprises an image forming device having a plurality of micro-deflectors and a beamlet confinement device having a plurality of beam confinement openings, and the image forming device is upstream of the beamlet confinement device. The primary electron beam from the single electron source is first deflected by the plurality of micro-deflectors to form a plurality of parallel virtual images of the single electron source, and the plurality of beamlets forming the plurality of parallel virtual images will pass vertically or substantially vertically through the plurality of beam limits. In this way, the plurality of beam limiting openings will not only generate less scattered electrons than in the prior art, but also cut off scattered electrons generated upstream and thereby eliminate image resolution deterioration due to electron scattering. The image forming apparatus may further include a plurality of micro-compensators to compensate for off-axis aberrations (curvature of field and astigmatism) of the plurality of probe points, respectively, and thereby further improve image resolution of the observed surface.

One embodiment of the new multi-beam apparatus 100A is shown in fig. 3A. The single electron source 101 is on the main optical axis 100_ 1. The common condenser lens 110, the main aperture plate 171, the new source conversion unit 120, the main projection imaging system 130, the deflection scanning unit 132 and the beam splitter 160 are placed along the main optical axis 100_1 and aligned with the main optical axis 100_ 1. The secondary projection imaging system 150 and the electronic detection device 140 are positioned along the secondary optical axis 150_1 and aligned with the secondary optical axis 150_ 1.

The main aperture plate 171 may be placed over the common condenser lens 9 or just above the new source conversion unit 120, as shown here. The new source conversion unit 120 comprises a micro-deflector array 122 with two micro-deflectors 122_2 and 122_3 and a beamlet confinement plate 121 with three beam confinement openings 121_1, 121_2 and 121_3, wherein the beam confinement opening 121_1 is aligned with the main optical axis 100_ 1. If the beam limiting opening 121_1 is not aligned with the main optical axis 100_1, there will be another micro-deflector 122_1 (as shown in fig. 5C). The main projection imaging system 130 includes a transfer lens 133 and an objective lens 131. The deflection scanning unit 132 includes at least one deflector. The beam splitter 160 is a wien filter. The auxiliary projection imaging system 150 includes an anti-scan deflector 151, a zoom lens 152 (including at least two lenses 152_1 and 152_2), and an anti-rotation magnetic lens 154. The electronic detection device 140 includes three detection elements 140_1, 140_2, and 140_ 3. Each of the above lenses may be an electrostatic lens, a magnetic lens, or an electromagnetic compound lens.

Fig. 3B-3D show three modes of operation of the new multi-beam apparatus 100A. The single electron source 101 comprises a cathode, an extraction and/or an anode, wherein primary electrons are emitted from the cathode and extracted and/or accelerated to form a primary electron beam 102, the primary electron beam 102 having a high energy (such as 8 to 20keV), a high angular intensity (such as 0.5 to 5mA/sr) and a cross (virtual or actual) 101s, here shown with an on-axis elliptical mark. Therefore, it is convenient to consider that the primary electron beam 102 is emitted from the crossover 101s, and the single electron source 101 is simplified to the crossover 101 s.

In fig. 3B, the condenser lens 110 is off. The primary electron beam 102 passes through the condenser lens 110 without focusing influence, and its peripheral electrons are cut off by the main aperture of the main aperture plate 171. Micro-deflectors 122_2 and 122_3 deflect sub-beams 102_2 and 102_3, respectively, of primary electron beam 102. The deflected beamlets 102_2 and 102_3 form off-axis virtual images 102_2v and 102_3v, respectively, of the intersection 101s of the single electron source 101. The deflected beamlets 102_2 and 102_3 are parallel or substantially parallel to the main optical axis 100_1 and are thus perpendicularly incident on the beamlet confinement plate 121. The beam limiting openings 121_1, 121_2 and 121_3 cut off peripheral electrons of the central portion 102_1 of the primary electron beam 102 and of the deflected beamlets 102_2 and 102_3, respectively, and thereby limit their current. Thus, one virtual multi-source array 101v is formed, which comprises the intersection 101s and its two parallel off-axis virtual images 102_2v and 102_3 v. A virtual image may avoid the coulomb effect at a real image in fig. 1A. To further reduce the coulomb effect, a main aperture plate 171 may be placed over the condenser lens 110 to cut off peripheral electrons as early as possible.

Next, the intersection 101S and its two parallel off-axis virtual images 102_2v and 102_3v are imaged onto the surface 7 to be observed through the transfer lens 133 and the objective lens 131, and their images form three detection points 102_1S, 102_2S, and 102_3S on the surface 7 to be observed. In order to land the two off-axis beamlets 102_2 and 102_3 perpendicularly on the observed surface 7, a transfer lens 133 focuses them through the front focal point of the objective lens 131. If the objective lens 131 comprises one magnetic lens, the two off-axis beamlets 102_2 and 102_3 may not pass through the front focus exactly due to the influence of the magnetic rotation and this is very helpful for reducing the coulomb effect at the beamlet intersection CS. The deflection scanning unit 132 deflects the three beamlets 102_1 to 102_3, and thus the three detection points 102_1S to 102_3S scan three separate areas on the observed surface 7.

The secondary electron beams 102_1se, 102_2se, and 102_3se emitted from the three scanning areas are focused by the objective lens 131, and deflected by the beam splitter 160 to enter the secondary projection imaging system 150 along the secondary optical axis 150_ 1. The lenses 152 and 153 focus the secondary electron beams onto the three detection elements 140_1 to 140_3, respectively. Thus, each detection element will provide an image signal of a corresponding one of the scan areas. If some secondary electrons of the secondary electron beam from one scanning area enter an adjacent detection element, the image signal of the adjacent detection element will also comprise extrinsic information from that scanning area, and for that adjacent detection element the extrinsic information is crosstalk from this scanning area. To avoid cross talk between the detection elements, the zoom lens 152 makes the spot size of each secondary electron beam smaller than the corresponding detection element, and the anti-scan deflector 151 will synchronously deflect the secondary electron beams 102_1se to 102_3se to keep them within the corresponding detection elements during deflection of the beamlets 102_1 to 102_3 by the deflection scanning unit 132.

Different samples typically require different viewing conditions, such as landing energy and current of the beamlets. This is particularly true for the inspection and/or evaluation of defects on wafers/masks in the semiconductor manufacturing industry. The focusing energy of the objective lens 131 will vary with landing energy, which will affect the position of the secondary electron beam on the electron detection device 140 and induce crosstalk. In this case, the zoom lens 152 will be adjusted to eliminate the radial displacement of the secondary electron beam. If the objective lens 131 comprises a magnetic lens, the anti-rotation magnetic lens 154 will be adjusted to eliminate the rotation of the secondary electron beam.

Each of the two off-axis probe points 102_2S and 102_3S includes off-axis aberrations generated by the objective lens 131, the transfer lens 133, and the condenser lens when turned on. The off-axis aberrations of each off-axis probe point can be reduced by individually optimizing the trajectories of the respective beamlets. The static part of the off-axis aberrations can be reduced by adjusting the deflection capabilities of the respective micro-deflectors. The dynamic part of the off-axis aberrations can be reduced by optimizing the performance of the deflecting scanning unit 132, which deflecting scanning unit 132 may thus comprise more than one deflector.

Unlike fig. 3B, the condenser lens 110 in fig. 3C is turned on, which focuses the primary electron beam 102 to form an on-axis virtual image 101sv of the intersection 101s of the single electron source 101. The micro-deflectors 122_2 and 122_3 deflect the beamlets 102_2 and 102_3, respectively, of the focused primary electron beam 102 and form two off-axis virtual images 102_2v and 102_3v of the crossover 101 s. The deflected beamlets 102_2 and 102_3 are parallel or substantially parallel to the main optical axis 100_1 and are thus perpendicularly incident on the beamlet confinement plate 121. The beam limiting openings 121_1, 121_2 and 121_3 cut off the peripheral electrons of the central portion 102_1 of the focused primary electron beam 102 and the peripheral electrons of the deflected beamlets 102_2 and 102_3, respectively, and thereby limit the current thereof. The focusing function of the condenser lens 110 increases the current density of the focused primary electron beam 102 and thus increases the current of the beamlets 102_1 to 102_3 to be higher than in fig. 3B. Thus, the current of all the beamlets can be continuously adjusted by the condenser lens 110.

Similar to a conventional SEM, the size of each probe spot can be minimized by balancing geometric and diffractive aberrations, gaussian image size, and coulombic effects. The focusing function of the condenser lens 110 changes the imaging magnification from the intersection 101s to the observed surface 7, which affects the balance and thus can increase the size of each detection point. To avoid that the size of the detection spot increases too much when the current of the beamlets varies greatly, the size of the beam limiting openings 121_1 to 121_3 may be changed accordingly. Therefore, the beamlet confinement plate 121 preferably has multiple sets of beam confinement openings. The beam limiting openings in one group are of a different size than in the other group. Alternatively, the focusing power of the transfer lens 133 may be changed to reduce the variation in imaging magnification. The trajectories of the off-axis beamlets 102_2 and 102_3 will be affected by the variation of the focusing power of the transfer lens 133, and the deflection power of the micro-deflectors 122_2 and 122_3 can be adjusted accordingly to maintain the trajectories. In this manner, the sub-beams 102_2 and 102_3 may be slightly non-parallel to the primary optical axis 100_1, as shown in fig. 3D.

Another embodiment 110A of the new multi-beam apparatus is shown in fig. 4. Unlike embodiment 100A, the new source conversion unit 120-1 includes one micro-deflector and compensator array 122-1 having three micro-deflector and compensator elements 122_1dc, 122_2dc, and 122_3 dc. Each of the micro-deflector and compensator elements comprises a micro-deflector and a micro-compensator, a micro-compensator having a micro-lens and a micro-stigmator. The micro-deflectors are used to form a virtual multi-source array, and have the same function as the micro-deflectors 122_2 and 122_3 shown in fig. 3B to 3D. As is well known, the condenser lens 110, the transfer lens 133 and the objective lens 131 will generate off-axis aberrations. As described above, the effect of off-axis aberrations on the probe spot size can be reduced by individually optimizing the trajectories of the beamlets. Thus, the micro-lens and the micro-stigmator will be used to compensate for the residual field curvature and astigmatic aberration of the probe point, respectively. In contrast to the micro-deflector array 122 in fig. 3A, the micro-deflector and compensator array 122-1 is an advanced image forming apparatus.

Each of the micro-deflectors 122_2 and 122_3 in fig. 3A may simply comprise two parallel electrodes perpendicular to the required deflection direction of the respective beamlet, as shown in fig. 5A. For example, the micro-deflector 122_2 has two parallel electrodes 122_2_ e1 and 122_2_ e2 perpendicular to the X-axis, and thereby deflects the beamlet 102_2 in the X-axis direction. Fig. 5B shows an embodiment in which micro-deflector array 122 deflects 8 beamlets. Since each micro-deflector has a particular orientation, it is difficult to manufacture one micro-deflector array 122 including a large number of micro-deflectors. From a manufacturing point of view, all micro-deflectors preferably have the same configuration and the same orientation in terms of geometry. Therefore, a micro-deflector with a quadrupole or 4-pole configuration can meet this requirement, as shown in fig. 5C. The four electrodes of each micro-deflector may form two deflectors which can deflect one electron beamlet in any direction. The micro-deflector 122_1 may be used if the corresponding beam limiting opening 121_1 is not correctly aligned with the main optical axis 101.

In order to operate a micro-deflector, a drive circuit needs to connect each electrode thereto. In order to prevent the driving circuit from being damaged by the primary electron beam 102, it is preferable to place a conductive plate above the electrodes of all the micro-deflectors in fig. 5A to 5C. Taking fig. 5C as an example, in fig. 6A, an upper conductive plate 122-CL1 having a plurality of upper through holes and an upper insulating plate 122-IL1 having a plurality of upper apertures are placed over the electrodes of the micro-deflectors 122_1 to 122_ 3. The electrodes of the micro-deflectors 122_1 to 122_3 may be attached to the upper insulating plate 122-IL 1. The upper through hole and upper aperture are aligned with the optical axis of the micro-deflector, respectively, such as upper through hole CL1_2 and upper aperture IL1_2 on the optical axis 122_2_1 of the micro-deflector 122_ 2. Each upper through hole has a radial dimension equal to or smaller than the internal radial dimension of the electrode of the corresponding micro-deflector for protecting its driving circuit, while each upper aperture has a radial dimension greater than that of the corresponding upper through hole to avoid charging on its inner side wall. In this way, the deflection fields of all micro-deflectors will have a short edge extent on the upper side, which will reduce their deflection aberrations.

Based on fig. 6A, the micro-deflector array 122 in fig. 6B also includes a lower conductive plate 122-CL2 having a plurality of lower vias. Each lower via is aligned with the optical axis of one micro-deflector, such as lower via CL2_2 being on the optical axis 122_2_1 of micro-deflector 122_ 2. In this way, the deflection fields of all micro-deflectors will have a short edge extent both on the upper and lower side, which will reduce their deflection aberrations. Unlike fig. 6B, the micro-deflector array 122 in fig. 6C employs a lower insulating plate 122-IL2 with a plurality of lower apertures to support the electrodes of the micro-deflectors 122_1 to 122_ 3. Each lower aperture is aligned with the optical axis of one micro-deflector, such as the lower aperture IL2_2 being on the optical axis 122_2_1 of the micro-deflector 122_ 2. The radial dimension of each lower orifice is greater than the inner radial dimension of the electrode of the corresponding micro-deflector. The micro deflector array 122 in fig. 6D is a combination of fig. 6B and 6C, which is more stable in configuration.

Fig. 7 illustrates one embodiment of the micro-deflector and compensator element 122_2dc of the micro-deflector and compensator array 122-1 in fig. 4, having an 8-pole configuration. The eight electrodes 122_2dc _ e1 to 122_2dc _ e8 may be driven to generate dipole fields (deflection fields) having a basic amount for generating virtual images of the electron source 1 and an additional amount for compensating distortion in any direction, quadrupole fields (astigmatism fields) for compensating astigmatism in any direction, and circular lens fields for compensating field curvature.

FIG. 8A illustrates another embodiment of the micro-deflector and compensator array 122-1 of FIG. 4. Each micro-deflector and compensator element comprises a pair of 4-pole lenses, which are placed in two layers, aligned with each other, and have an azimuthal or azimuthal difference of 45 °. The micro deflector and compensator elements 122_1dc, 122_2dc and 122_3dc are respectively composed of a pair of upper and lower 4-pole lenses 122_1dc-1 and 122_1dc-2, a pair of upper and lower 4-pole lenses 122_2dc-1 and 122_2dc-2, and a pair of upper and lower 4-pole lenses 122_3dc-1 and 122_3 dc-2. The upper 4-pole lenses 122_1dc-1, 122_2dc-1, and 122_3dc-1 are placed in the upper layer 122-1-1, and the lower 4-pole lenses 122_1dc-2, 122_2dc-2, and 122_3dc-2 are placed in the lower layer 122-1-2 and aligned with the upper 4-pole lenses 122_1dc-1, 122_2dc-1, and 122_3dc-1, respectively. As an example, with respect to the X-axis, the azimuth angle of the upper 4-pole lenses 122_1dc-1, 122_2dc-1, and 122_3dc-1 is 0 ° as shown in fig. 8B, and the azimuth angle of the lower 4-pole lenses 122_1dc-2, 122_2dc-2, and 122_3dc-2 is 45 ° as shown in fig. 8C. In FIG. 8D, the upper and lower layers are shielded by the upper and lower conductive plates 122-CL1 and 122-CL2 and supported by the upper and lower insulating plates 122-IL1 and 122-IL2 and the middle insulating plate 122-IL3 with a plurality of middle apertures, similar to FIG. 6D. For each of the micro-deflector and compensator elements, the deflection field in any desired direction, as well as the circular lens field, may be generated by either or both of the upper and lower 4-pole lenses, and the quadrupole field in any direction may be generated by the upper and lower 4-pole lenses.

Another embodiment 200A of the new multi-beam apparatus is shown in fig. 9A. In contrast to embodiment 110A in FIG. 4, the transfer lens 133 is removed from the main projection imaging system. Fig. 9B shows an operation mode in which the off-axis beamlets 102_2 and 102_3 are deflected parallel to the main optical axis 200_1 by the micro-deflector and compensator elements 122_2dc and 122_3dc, respectively, and land obliquely on the observed surface 7. This mode can be used for viewing applications where there is no strict requirement on the incidence of the beamlets or stereoscopic imaging is required. The micro-deflector and compensator elements 122_2dc and 122_3dc may compensate for large off-axis aberrations of the two off-axis beamlets 102_2 and 102_3 due to passing through the objective 131 with large radial offset. Fig. 9C shows another mode of operation, in which the off-axis beamlets 102_2 and 102_3 are further deflected towards the main optical axis 200_1 by micro-deflector and compensator elements 102_2dc and 102_3dc, respectively, and thus land less obliquely on the observed surface 7. If the micro-deflector and compensator elements 122_2dc and 122_3dc deflect the off-axis beamlets 102_2 and 102_3, respectively, to pass through the front focal point of the objective lens 131, the off-axis beamlets 102_2 and 102_3 will be normally incident on the surface 7 to be observed. To avoid that the off-axis beamlets 102_2 and 102_3 pass through the beam limiting openings at large angles of incidence, it is preferred to keep a long distance between the front focal point of the objective 131 and the micro-deflector and compensator array 122-1.

It is well known that the more beamlets are scanned across the viewed surface 7, the more charge may build up on the viewed surface 7. Thus, some of the beamlets may not be needed for a particular viewing application. In this case, the sub-beams may be directed to be hidden by the sub-beam limiting plate. Fig. 10 shows this mode of operation of embodiment 110A in fig. 4, in which the micro-deflector and compensator 122_2dc is turned off and the beamlet 102_2 is switched off by beamlet limit plate 121. The micro-deflector and compensator 122_2dc may need to be turned on to direct the beamlet 102_2 to be cut off by the beamlet limit plate 121, depending on the detailed structure of the source switching unit 120-1.

Based on the embodiment 110A in fig. 4, another embodiment 111A of the new multi-beam apparatus is proposed in fig. 11A, in which a single beam electron detector 141 is added. When only one beamlet is required for some reason, such as searching for optimistic imaging conditions (landing energy and probe current) for viewing applications, then the device will operate in single beam mode. In this case, the beam splitter 160 may deflect the respective secondary electron beam to the single-beam electron detector 141. Here, the beamlet 102_1 is used as the beamlet in use. The secondary electron beams 102_1se generated by the beamlets 102_1 are deflected to be detected by a single beam electron detector 141. The use of the single-beam electron detector 141 avoids the process of adjusting the secondary projection imaging system 150 with respect to changes in the focusing power of the objective 131. As described above, when the landing energy and/or current of the in-use beamlets changes, the focusing power of the objective lens 131 will change. In addition, fig. 11B shows another embodiment 112A of the new multibeam device, in which an in-lens electron detector 142 having beamlet passing apertures is placed below the beam splitter 160. When the apparatus is operated in single beam mode, secondary electrons having a large emission angle within the secondary electron beam with respect to the in-use beamlet may be detected by the in-lens electron detector 142, and secondary electrons having a small emission angle will pass through the beamlet pass-through aperture and be detected by the corresponding detection element of the electron detection device 140. Here, the beamlet 102_1 is used as the beamlet in use. Within the secondary electron beam 102_1se generated by the beamlet 102_1, secondary electrons 102_1se _2 having a large emission angle strike the in-lens electron detector 142, and secondary electrons 102_1se _1 having a small emission angle are deflected to be detected by the electron detection device 140. The single-beam electron detector 141 and the in-lens electron detector 142 may be used in combination. In this case, the secondary electrons 102_1se _2 having a large emission angle may be detected by the in-lens electron detector 142, and the secondary electrons 102_1se _1 having a small emission angle may be deflected by the beam splitter 160 to be detected by the single-beam electron detector 141. Although not shown here, the in-lens electron detector 142 may also be placed above the beam splitter 160. In this case, the in-lens electron detector 142 may detect an outer portion of the secondary electron beam 102_1se when the beam splitter is closed.

In summary, the present invention proposes a new multi-beam apparatus for observing a sample with high resolution and high throughput. The new multi-beam apparatus may be used as a yield management tool to inspect and/or evaluate defects on wafers/masks in the semiconductor manufacturing industry. The multi-beam apparatus employs a new source conversion unit to form a plurality of parallel virtual images of a single electron source, employs a condenser lens to adjust the currents of a plurality of sub-beams, employs a primary projection imaging system to project the plurality of parallel virtual images to form a plurality of detection points on an observed surface of a sample, employs a beam splitter to deflect a plurality of secondary electron beams therefrom away from paths of the plurality of sub-beams, and employs a secondary projection imaging system to focus the plurality of secondary electron beams to be detected by a plurality of detection elements of an electron detection device, respectively. In the new source conversion unit, the image forming means is upstream of the beamlet limitation means, and thereby image resolution degradation due to electron scattering is mitigated. The image forming apparatus includes a plurality of micro-deflectors for forming a plurality of parallel virtual images, or a plurality of micro-deflectors and compensator elements for forming a plurality of parallel virtual images and compensating for off-axis aberrations of a plurality of detection points.

While the invention has been explained in relation to its preferred embodiments, it is to be understood that other modifications and variations may be made without departing from the spirit and scope of the invention as hereinafter claimed.

Claims (19)

1. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source;
a condenser lens below the electron source;
a source conversion unit under the condenser lens;
a main projection imaging system below the source conversion unit and including an objective lens;
a deflection scanning unit inside the main projection imaging system;
a sample stage below the main projection imaging system;
a beam splitter above the objective lens;
a secondary projection imaging system above the beam splitter; and
an electronic test device having a plurality of test elements,
wherein the source conversion unit comprises an image forming device having a plurality of micro-deflectors and a beamlet confinement device having a plurality of beam confinement openings, and the image forming device is above the beamlet confinement device,
wherein the electron source, the condenser lens, the source conversion unit, the primary projection imaging system, the deflection scanning unit and the beam splitter are aligned with a primary optical axis of the apparatus, the sample stage holds the sample such that the surface faces the objective lens, the secondary projection imaging system and the electronic detection device are aligned with a secondary optical axis of the apparatus, and the secondary optical axis is not parallel to the primary optical axis,
wherein the electron source generates primary electron beams along the primary optical axis, the plurality of micro-deflectors deflect the primary electron beams to form a plurality of parallel virtual images of the electron source and so a virtual multi-source array is converted from the electron source, a plurality of beamlets comprising the virtual multi-source array pass through the plurality of beam limiting openings, respectively, the current of each beamlet is thus limited by a respective one of the beam limiting openings, and the currents of the plurality of beamlets can be changed by adjusting the condenser lens,
wherein the main projection imaging system images the virtual multi-source array onto the surface, a plurality of detection points are thus formed on the surface, and the deflection scanning unit deflects the plurality of beamlets to scan the plurality of detection points respectively over a plurality of scan areas within an observation area on the surface,
wherein a plurality of secondary electron beams are respectively generated by the plurality of probe points from the plurality of scan areas and are focused by the objective lens upon passage, the beam splitter then deflects the plurality of secondary electron beams to the secondary projection imaging system, which focuses the plurality of secondary electron beams and keeps the plurality of secondary electron beams respectively detected by the plurality of detection elements, and each detection element thus provides an image signal of a corresponding one of the scan areas.
2. The multi-beam apparatus according to claim 1, further comprising a main aperture plate below the electron source, the main aperture plate having a main opening aligned with the main optical axis and serving as a beam limiting aperture for the primary electron beam.
3. The multi-beam apparatus of claim 2, wherein the main projection imaging system comprises a transfer lens above the objective lens, the transfer lens focusing the plurality of beamlets to land vertically on the surface.
4. The multi-beam device of claim 3, wherein each of the plurality of micro-deflectors has a 4-pole structure, the 4-pole structure being capable of generating a deflection field in any radial direction.
5. The multibeam device of claim 4, further comprising a single-beam electron detector above the beam splitter, the single-beam electron detector being usable in a single-beam mode.
6. The multi-beam apparatus according to claim 4, further comprising an in-lens electron detector having beamlet passing apertures aligned with the primary optical axis, the in-lens electron detector being usable in single beam mode.
7. The multi-beam apparatus according to claim 5, further comprising an in-lens electron detector having a beamlet pass aperture aligned with the primary optical axis, the in-lens electron detector being below the beam splitter and being usable in the single beam mode.
8. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source;
a condenser lens below the electron source;
a source conversion unit under the condenser lens;
a main projection imaging system below the source conversion unit and including an objective lens;
a deflection scanning unit inside the main projection imaging system;
a sample stage below the main projection imaging system;
a beam splitter above the objective lens;
a secondary projection imaging system above the beam splitter; and
an electronic test device having a plurality of test elements,
wherein the source conversion unit comprises an image forming device having a plurality of micro-deflector and compensator elements and a beamlet limitation device having a plurality of beam limiting openings, each micro-deflector and compensator element comprising one micro-deflector and one micro-compensator, the one micro-compensator having one micro-lens and one micro-stigmator, and the image forming device being above the beamlet limitation device,
wherein the electron source, the condenser lens, the source conversion unit, the primary projection imaging system, the deflection scanning unit and the beam splitter are aligned with a primary optical axis of the apparatus, the sample stage holds the sample such that the surface faces the objective lens, the secondary projection imaging system and the electronic detection device are aligned with a secondary optical axis of the apparatus, and the secondary optical axis is not parallel to the primary optical axis,
wherein the electron source generates primary electron beams along the primary optical axis, the plurality of micro-deflectors deflect the primary electron beams to form a plurality of parallel virtual images of the electron source and so a virtual multi-source array is converted from the electron source, a plurality of beamlets comprising the virtual multi-source array pass through the plurality of beam limiting openings, respectively, the current of each beamlet is thus limited by a respective one of the beam limiting openings, and the currents of the plurality of beamlets can be changed by adjusting the condenser lens,
wherein the main projection imaging system images the virtual multi-source array onto the surface and a plurality of probe points are thus formed on the surface, the one micro lens and the one micro stigmator of the one micro compensator compensate for a field curvature and an astigmatic aberration, respectively, of a corresponding one of the probe points, and the deflection scanning unit deflects the plurality of beamlets to scan the plurality of probe points, respectively, over a plurality of scan regions within an observation region on the surface,
wherein a plurality of secondary electron beams are respectively generated by the plurality of probe points from the plurality of scan areas and are focused by the objective lens upon passage, the beam splitter then deflects the plurality of secondary electron beams to enter the secondary projection imaging system, the secondary projection imaging system focuses the plurality of secondary electron beams and maintains the plurality of secondary electron beams respectively detected by the plurality of detection elements, and each detection element thus provides an image signal of a corresponding one of the scan areas.
9. The multi-beam apparatus according to claim 8, further comprising a main aperture plate below the electron source, the main aperture plate having a main opening aligned with the main optical axis and serving as a beam limiting aperture for the primary electron beam.
10. The multi-beam apparatus according to claim 9, wherein each of the plurality of micro-deflector and compensator elements has an 8-pole structure, the 8-pole structure serving as the one micro-deflector by generating a desired deflection field and serving as the one micro-compensator by generating a desired quadrupole field and a desired circular lens field.
11. The multi-beam device of claim 9, wherein each of the plurality of micro-deflector and compensator elements comprises an upper 4-pole structure and a lower 4-pole structure in an upper layer and a lower layer, respectively, the upper layer being above the lower layer, and the upper 4-pole structure and the lower 4-pole structure being aligned with each other and having an azimuthal angle difference of 45 °.
12. The multi-beam apparatus according to claim 11, wherein the upper 4-pole structure and the lower 4-pole structure function as the one micro-deflector by generating a desired deflection field and function as the one micro-compensator by generating a desired quadrupole field and a desired circular lens field.
13. The multi-beam apparatus of claim 12, wherein the main projection imaging system comprises a transfer lens above the objective lens, the transfer lens focusing the plurality of beamlets to land vertically on the surface.
14. The multibeam device of claim 13, further comprising a single-beam electron detector above the beam splitter, the single-beam electron detector being usable in a single-beam mode.
15. The multi-beam apparatus of claim 13, further comprising an in-lens electron detector having beamlet passing apertures aligned with the primary optical axis, the in-lens electron detector being usable in a single beam mode.
16. The multi-beam apparatus according to claim 14, further comprising an in-lens electron detector having a beamlet pass aperture aligned with the primary optical axis, the in-lens electron detector being below the beam splitter and being usable in the single beam mode.
17. A charged particle beam device, comprising:
a single charged particle source for providing a primary beam;
means for converting the primary beam into a plurality of beamlets, the means for converting comprising a plurality of deflectors for deflecting the plurality of beamlets and a plurality of beam limiting openings below the plurality of deflectors;
a first projection system for forming a plurality of probe points on a sample from the plurality of beamlets;
a deflection scanning unit for scanning the plurality of probe points on the sample;
means for splitting a plurality of signal electron beams generated as a result of the plurality of beamlets, respectively, bombarding the sample away from the plurality of beamlets;
a detection device for receiving the plurality of signal electron beams; and
a second projection system for forming a plurality of signal points from the plurality of signal electron beams on a plurality of electron detection elements of the detection device, respectively,
wherein the single charged particle source, the means for converting, the first projection system, the deflection scanning unit and the means for separating are aligned with a main optical axis of the apparatus, the sample faces the first projection system, the second projection system and the detection device are aligned with a secondary optical axis of the apparatus, and the secondary optical axis is not parallel to the main optical axis.
18. The charged particle beam device of claim 17, further comprising a condenser lens for adjusting the current of the plurality of probe points.
19. The charged particle beam device of claim 18, wherein the means for converting comprises a plurality of compensators for compensating aberrations of the plurality of detection points, respectively.
CN201680026508.6A 2015-03-10 2016-04-13 Arrangement of a plurality of charged particle beams CN108292583B (en)

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