JP7305826B2 - Multiple charged particle beam device - Google Patents

Description

PRIORITY CLAIM This application claims priority to U.S. Provisional Application Serial No. 62/130,819, entitled "Multiple Charged Particle Beam Apparatus," filed March 10, 2015, to Len et al. , which is incorporated herein by reference in its entirety.

The present invention relates to charged particle devices having multiple charged particle beams, and more particularly to devices that use multiple charged particle beams to simultaneously acquire images of multiple scan regions of an observation area on a sample surface. Thus, the apparatus can be used to inspect and/or investigate defects on wafers/masks with high resolution and high throughput in the semiconductor manufacturing industry.

During the manufacture of semiconductor IC chips, pattern defects and/or unwanted particles (residues) inevitably appear on the wafer/mask surface during the manufacturing process, which greatly reduces yield. Patterns with smaller and smaller critical feature dimensions are being employed to meet the performance requirements of ever-evolving IC chips. Therefore, conventional yield control tools using optical beams are gradually becoming unqualified due to diffraction effects, and yield control tools using electron beams are increasingly used. Electron beams have shorter wavelengths than photon beams and can provide superior spatial resolution. Currently, yield control tools using electron beams use scanning electron microscope (SEM) principles with a single electron beam, which can provide high resolution but not throughput suitable for mass production. Although it is possible to use larger and larger beam currents to increase throughput, the excellent spatial resolution is fundamentally degraded by the Coulomb effect.

A promising solution, rather than using a single electron beam with a large current, to alleviate the constraint on throughput is to use multiple electron beams, each with a small current. Multiple electron beams form multiple probe spots on one inspected or observed surface of the specimen. On the sample surface, multiple probe spots can simultaneously scan multiple small scan regions within a large observation area on the sample surface. The electrons of each probe spot generate secondary electrons from where they impinge on the sample surface. Secondary electrons include slow secondary electrons (energy less than 50 eV) and backscattered electrons (energy close to the energy of the incident electrons). Secondary electrons from multiple small scan areas can be collected simultaneously by multiple electron detectors, respectively. Therefore, an image of a large viewing area containing all sub-scanned regions can be acquired much faster than scanning that large viewing area with a single beam.

Multiple electron beams may be obtained from each of multiple electron sources or from a single electron source. In the former, multiple electron beams are usually focused and scanned respectively by multiple columns into multiple small scanning areas, and the secondary electrons from each scanning area are detected by one electron detector inside the corresponding column. be. Therefore, this device is commonly referred to as a multi-column device. Multiple columns can be independent or share a multi-axis magnetic or electromagnetic compound objective lens (eg US Pat. No. 8,294,095). The beam spacing of two adjacent beams on the sample surface is usually of the order of 30-50 mm.

In the latter, a source transformation unit is used to virtually transform a single electron source into multiple sub-sources. The source transformation unit comprises one beamlet forming means and one image forming means. The beamlet forming means basically comprise a plurality of beam-limiting apertures each dividing a primary electron beam produced by a single electron source into a plurality of sub-beams or beamlets. The imaging means basically comprises a plurality of electro-optical elements that either focus or deflect the plurality of beamlets respectively to form a plurality of parallel images of the electron source. Each of the multiple parallel images can be viewed as a sub-source emitting a corresponding beamlet. Since the beamlet spacing or beam limiting aperture spacing is on the order of micrometers, more beamlets are available, so the source conversion unit can be made by semiconductor manufacturing processes or MEMS (micro-electro-mechanical systems) processes. . Naturally, one primary projection imaging system and one deflection scanning unit in one single column are used to respectively project and scan a plurality of parallel images onto a plurality of sub-scanning areas and obtain therefrom. A plurality of secondary electron beams generated are respectively detected by a plurality of detector elements of an electron detection device within a single column. The multiple detector elements may be multiple electron detectors arranged in parallel or multiple pixels of an electron detector. This device is therefore commonly referred to as a multibeam device.

In the source conversion unit 20-1 of FIG. 1A, the image forming means 22-1 consists of a plurality of lenses (22_1L to 22_3L). A substantially parallel primary electron beam 2 from one single electron source is split into a plurality of beamlets (2_1-2_3) by a plurality of beam limiting apertures (21_1-21_3) of the beamlet forming means 21, and a plurality of lenses respectively focus the multiple beamlets to form multiple parallel images (2_1r-2_3r) of a single electron source. The multiple parallel images are typically real images, but may be virtual images under certain conditions where each of the multiple lenses is an aperture lens. US 7,244,949 and US 7,880,143 propose multi-beam devices with one imaging means of this type. In the source transform unit 20-2 of FIG. 1B, the imaging means 22-2 consists of a plurality of deflectors (22_2D and 22_3D). A divergent primary electron beam 2 from one single electron source is split into multiple beamlets (2_2 and 2_3) by multiple beam limiting apertures (21_2 and 21_3) of the beamlet forming means 21, and multiple deflectors are single beamlets (2_2 and 2_3). A plurality of beamlets are each deflected to form a plurality of parallel virtual images (2_2v and 2_3v) of one electron source.

The idea of using deflectors to form a virtual image of the electron source was used in the famous double-slit electron interference experiment as early as the 1950's. As shown here in Figure 2 (Figure 1 of "Merli-Missiloli-Podge Double Slit Electron Interference Experiment", published in Physics in Perspective, 14 (2012), 178-195, by Rodolfo Rosa) An electron beam biprism is used to form two virtual images. An electron beam biprism basically comprises two parallel plates at ground potential and a very thin wire F between them. When a potential unequal to ground potential is applied to wire F, the electron beam biprism becomes two deflectors with opposite deflections. A primary electron beam from an electron source S passes through these two deflectors into two deflected beamlets that form virtual images of the electron source S S1 and S2. When the potential is positive, the two beamlets overlap each other and interference fringes appear in the overlapping area.

Since then, the aforementioned ideas have been used in many ways in multibeam devices. JP-A-10-339711 and US Pat. No. 8,378,299 directly use one conventional electron biprism to form two probe spots on the sample surface. US 6,943,349 uses one annular deflector (Id. Fig. 5) or one corresponding deflector array (Id. Fig. 12) to form more than two probe spots on the sample surface. and thereby provide high 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 will appear in the ring gap in the local radial direction, thus the ring deflector will deflect more than two beamlets together in different directions. be able to. Furthermore, the deflection function of the annular deflector can also be performed by a corresponding deflector array having multiple multi-pole deflectors arranged along the annular gap.

In the conventional source conversion unit 20-2 of FIG. 1B, due to the divergence of the primary electron beam 2, multiple beamlets pass through multiple beam-limiting apertures at different angles of incidence, resulting in different electron intensities. suffer from clutter. Scattered electrons in each beamlet magnify the probe spot and/or become background noise, thus degrading the image resolution of the corresponding scanned area.

In US 6,943,349 the current of multiple beamlets can only be deflected by changing either the emission of a single electron source or the size of the beam limiting aperture. A single electron source takes a long time to reach a stable state when its emission is changed. The beamlet forming means should have a plurality of groups of apertures, and the size of apertures in one group should be different from those in other groups. Changing groups in use is very time consuming. In addition, the secondary electron beam can only be focused on a large number of detector elements of the in-lens detector at some specific operating conditions of the objective lens. Therefore, the available fields of application are limited.

Therefore, there is a need 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 resolution and high throughput. In particular, a multi-beam tool capable of inspecting and/or investigating defects on wafers/masks with high resolution and high throughput is needed to meet the roadmap of the semiconductor manufacturing industry.

It is an object of the present invention to be able to provide both high resolution and high throughput for viewing specimens, particularly as a yield control tool to inspect and/or investigate defects on wafers/masks in the semiconductor manufacturing industry. The object of the present invention is to provide a novel multi-beam device for The multi-beam device first forms multiple parallel virtual images of a single electron source, then a new source transformation unit to limit the current of the corresponding multiple beamlets, and the current of the multiple beamlets to a primary projection imaging system for projecting a plurality of parallel virtual images to form a plurality of probe spots on the surface to be observed of the specimen; A beam separator is employed to deflect the beams out of the path of the electrons and a secondary projection imaging system to focus the secondary electron beams so that they are each detected by a plurality of detector elements of the electronic detection device.

Accordingly, the present invention provides a source conversion unit, which comprises an upper layer having a plurality of upper quadrupole structures and a lower layer having a plurality of lower quadrupole structures; a beamlet limiting means comprising a plurality of beam limiting apertures. Each upper quadrupole structure is above and aligned with one corresponding lower quadrupole structure, which are azimuthally different by 45° and form a pair of quadrupole structures. Thus, the multiple upper quadrupole structures and the multiple lower quadrupole structures form a set of multiple quadrupole structures. A plurality of beam limiting apertures are respectively aligned with a plurality of sets of quadrupole structures. a set of quadrupole structures a micro-deflector for deflecting a beamlet of the electron beam produced by the electron source to form a virtual image of the electron source; a micro-lens for converging the beamlet to a desired degree; and/or act as a microstigmator to add a desired amount of astigmatism to a single beamlet.

The invention also provides a multi-beam device for observing the surface of a specimen, which comprises an electron source, a condenser lens below the electron source, a source conversion unit below the condenser lens, a source a primary projection imaging system with an objective below the transformation unit, a deflection scanning unit inside the primary projection imaging system, a specimen stage below the primary projection imaging system, and above the objective A beam separator, a secondary projection imaging system above the beam separator, and an electronic detection device having a plurality of detector elements. The source transformation unit comprises an imaging means having a plurality of microdeflectors and a beamlet limiting means having a plurality of beam limiting apertures, the imaging means being above the beamlet limiting means. The electronic source, condenser lens, source transformation unit, primary projection imaging system, deflection scanning unit and beam separator are aligned with the primary optical axis of the apparatus. The sample stage supports the sample with its surface facing the objective lens. The secondary projection imaging system and the electronic detection device are aligned with the secondary optical axis of the apparatus, the secondary optical axis being non-parallel to the primary optical axis. An electron source produces a primary electron beam along a primary optical axis, and multiple microdeflectors deflect the primary electron beam to form multiple parallel virtual images of the electron source. A virtual multi-source array is thereby converted from the electron source, and a plurality of beamlets comprising the virtual multi-source array pass through a plurality of beam-limiting apertures, respectively. The current of each beamlet is thereby limited by one corresponding beam-limiting aperture, and the current of multiple beamlets can be varied by adjusting the condenser lens. A primary projection imaging system images a virtual multi-source array onto the surface such that multiple probe spots are formed on the surface. A deflection scanning unit deflects the plurality of beamlets to cause the plurality of probe spots to respectively scan a plurality of scanning regions within an observation area on the surface. A plurality of secondary electron beams are respectively generated from a plurality of scan regions by a plurality of probe spots and focused as they pass through the objective lens. A beam separator deflects the plurality of secondary electron beams to a secondary projection imaging system, which focuses the plurality of secondary electron beams for respective detection by a plurality of detector elements. and maintain. Each detector element thereby provides an image signal for one corresponding scan area.

The multi-beam device may further comprise a main aperture plate below the electron sources and having a main aperture aligned with the primary optical axis and acting as a beam limiting aperture for the primary electron beams. The primary projection imaging system may comprise a transfer lens above the objective lens that focuses the beamlets to be incident normal to the surface. Each of the plurality of microdeflectors has a quadrupole structure capable of generating a deflection field in any radial direction. The multi-beam device may further comprise a single-beam electron detector above the beam separator and operable in single-beam mode. The multi-beam device may further comprise an in-lens electron detector that has a beamlet passage hole aligned with the primary optical axis and is below the beam separator and is usable in single beam mode.

The invention also provides a multi-beam device for observing the surface of a specimen, which comprises an electron source, a condenser lens below the electron source, a source conversion unit below the condenser lens, a source a primary projection imaging system with an objective below the transformation unit, a deflection scanning unit inside the primary projection imaging system, a specimen stage below the primary projection imaging system, and above the objective A beam separator, a secondary projection imaging system above the beam separator, and an electronic detection device having a plurality of detector elements. The source transform unit comprises imaging means having a plurality of microdeflector compensator elements and beamlet limiting means having a plurality of beam limiting apertures, each microdeflector compensator element comprising one microdeflector and one microlens and a microcompensator with a microstigmator. The imaging means is above the beamlet limiting means. The electronic source, condenser lens, source transformation unit, primary projection imaging system, deflection scanning unit and beam separator are aligned with the primary optical axis of the apparatus. The sample stage supports the sample with its surface facing the objective lens. The secondary projection imaging system and the electronic detection device are aligned with the secondary optical axis of the apparatus, the secondary optical axis being non-parallel to the primary optical axis. An electron source produces a primary electron beam along a primary optical axis, and multiple microdeflectors deflect the primary electron beam to form multiple parallel virtual images of the electron source. A virtual multi-source array is thereby transformed from the electron sources. A plurality of beamlets comprising a virtual multi-source array pass through each of the plurality of beam limiting apertures such that the current of each beamlet is limited by a corresponding beam limiting aperture. The current of multiple beamlets can be changed by adjusting the condenser lens. A primary projection imaging system images a virtual multi-source array onto the surface such that multiple probe spots are formed on the surface. One microlens and one microstigmator of one microcompensator respectively compensate field curvature and astigmatism of one corresponding probe spot, and the deflection scanning unit provides multiple A plurality of beamlets are deflected to respectively scan the scan region with a plurality of probe spots. A plurality of secondary electron beams are respectively generated from a plurality of scanning regions by a plurality of probe spots and converged as they pass through an objective lens, and a beam separator is arranged to enter a plurality of secondary electron beams into a secondary projection imaging system. deflects the secondary electron beam of A secondary projection imaging system focuses and maintains a plurality of secondary electron beams for respective detection by a plurality of detector elements, whereby each detector element provides an image signal for a corresponding scan area. .

The multi-beam device may further comprise a main aperture plate below the electron sources and having a main aperture aligned with the primary optical axis and acting as a beam limiting aperture for the primary electron beams. Each of the plurality of microdeflector compensator elements acts as a microdeflector by generating the desired deflection field and as a microcompensator by generating the desired quadrupole field and the desired circular lens field. It may have an octapole structure that works. Each of the plurality of microdeflector compensator elements has an upper quadrupole structure on the upper layer and a lower quadrupole structure on the lower layer, the upper layer above the lower layer, the upper quadrupole structure and the lower quadrupole structure The structures are aligned with each other and differ in azimuth angle by 45°. The upper and lower quadrupole structures are combined as one micro-deflector by producing the desired deflection field and as one micro-compensator by producing the desired quadrupole field and the desired circular lens field. may function. The primary projection imaging system may comprise a transfer lens above the objective lens that focuses the beamlets to be incident normal to the surface. The multi-beam device may further comprise a single-beam electron detector above the beam separator and operable in single-beam mode. The multi-beam device may further comprise an in-lens electron detector that has a beamlet passage hole aligned with the primary optical axis and is below the beam separator and is usable in single beam mode.

The present invention also provides a method of constructing a source conversion unit for forming a virtual multi-source array from electron sources, which comprises an upper layer having a plurality of upper quadrupole structures and a plurality of lower quadrupole structures. and providing a beamlet limiting means below the imaging means and comprising a plurality of beam limiting apertures. Each upper quadrupole structure is above and aligned with one corresponding lower quadrupole structure, which are azimuthally different by 45° and form a pair of quadrupole structures. A plurality of upper quadrupole structures and a plurality of lower quadrupole structures thereby form a set of a plurality of quadrupole structures. A plurality of beam limiting apertures are respectively aligned with a plurality of sets of quadrupole structures. A set of quadrupole structures is a micro-deflector that deflects a beamlet of an electron beam produced by an electron source to form a virtual image of the electron source, a micro-deflector that focuses the beamlet to a desired degree. It functions as a lens and/or a microstigmator that adds a desired amount of astigmatism to the single beamlet.

The source conversion unit may comprise an upper electrically conducting plate having a plurality of upper through-holes respectively aligned with the sets of quadrupole structures. The source conversion unit may further comprise a lower electrically conductive plate having a plurality of lower through-holes respectively aligned with the sets of quadrupole structures.

The present invention also provides a method for forming a virtual multi-source array from electron sources, which uses an upper layer with a plurality of upper quadrupole structures and a lower layer with a plurality of lower quadrupole structures. deflecting an electron beam from an electron source into a plurality of beamlets by using a plurality of apertures to restrict the plurality of beamlets. Each upper quadrupole structure is above and aligned with one corresponding lower quadrupole structure, which are azimuthally different by 45° and form a pair of quadrupole structures.

The present invention also provides a charged particle beam device comprising a single charged particle source for providing a primary beam, means for transforming the primary beam into a plurality of beamlets, and from the plurality of beamlets onto a specimen. a deflection scanning unit for scanning the plurality of probe spots on the specimen; means for separating the plurality of signal electron beams from the plurality of beamlets; and the plurality of signal electron beams. and a second projection system for forming a plurality of signal spots from the plurality of signal electron beams respectively on a plurality of electron detector elements of the detection device. The transforming means comprises a plurality of deflectors for deflecting the plurality of beamlets and a plurality of beam limiting apertures below the plurality of deflectors. A plurality of signal electron beams are each generated by the impingement of the plurality of beamlets on the specimen.

The charged particle beam device may further comprise a condenser lens for adjusting the current of the multiple probe spots. The transformation means comprises a plurality of compensators for compensating aberrations of the plurality of probe spots respectively.

Other advantages of the present invention will become apparent from the accompanying drawings and the following description, which set forth, by way of example, several embodiments of the invention.

The present invention will be readily understood from the accompanying drawings and the detailed description that follows. Like reference numerals in each drawing indicate like structural elements.

1 is a schematic diagram of a conventional source transformation unit; FIG. 1 is a schematic diagram of a conventional source transformation unit; FIG.

It is a schematic diagram of an electron interference experiment using an electron beam biprism.

1 is a schematic diagram of one configuration of a novel multi-beam device according to one embodiment of the present invention; FIG.

3B is a schematic diagram of the mode of operation of the novel multi-beam device of FIG. 3A; FIG. 3B is a schematic diagram of the mode of operation of the novel multi-beam device of FIG. 3A; FIG. 3B is a schematic diagram of the mode of operation of the novel multi-beam device of FIG. 3A; FIG.

Fig. 3 is a schematic diagram of another configuration of a novel multi-beam device according to another embodiment of the invention;

3B is a schematic diagram of the configuration of the imaging means of FIG. 3A according to another embodiment of the present invention; FIG. 3B is a schematic diagram of the configuration of the imaging means of FIG. 3A according to another embodiment of the present invention; FIG. 3B is a schematic diagram of the configuration of the imaging means of FIG. 3A according to another embodiment of the present invention; FIG.

3B is a schematic diagram of the configuration of the imaging means of FIG. 3A according to another embodiment of the present invention; FIG. 3B is a schematic diagram of the configuration of the imaging means of FIG. 3A according to another embodiment of the present invention; FIG. 3B is a schematic diagram of the configuration of the imaging means of FIG. 3A according to another embodiment of the present invention; FIG. 3B is a schematic diagram of the configuration of the imaging means of FIG. 3A according to another embodiment of the present invention; FIG.

Figure 5 is a schematic diagram of the configuration of the advanced imaging means of Figure 4 according to another embodiment of the present invention;

Figure 5 is a schematic diagram of the configuration of the advanced imaging means of Figure 4 according to another embodiment of the present invention; Figure 5 is a schematic diagram of the configuration of the advanced imaging means of Figure 4 according to another embodiment of the present invention; Figure 5 is a schematic diagram of the configuration of the advanced imaging means of Figure 4 according to another embodiment of the present invention; Figure 5 is a schematic diagram of the configuration of the advanced imaging means of Figure 4 according to another embodiment of the present invention;

Fig. 3 is a schematic diagram of another configuration of a novel multi-beam device according to another embodiment of the invention;

9B is a schematic diagram of the mode of operation of the new multi-beam device of FIG. 9A; FIG. 9B is a schematic diagram of the mode of operation of the new multi-beam device of FIG. 9A; FIG.

Figure 5 is a schematic diagram of one mode of operation of the new multi-beam device of Figure 4;

Fig. 3 is a schematic diagram of another configuration of a novel multi-beam device and one of its modes of operation according to another embodiment of the present invention;

Fig. 3 is a schematic diagram of another configuration of a novel multi-beam device and one of its modes of operation according to another embodiment of the present invention;

Various exemplary embodiments of the invention are described more fully hereinafter with reference to the accompanying drawings, which show some exemplary embodiments of the invention. Without limiting the scope of protection of the invention, the descriptions and drawings of those embodiments all refer to electron beams by way of example, but they are used to limit the invention to specific charged particles. shouldn't.

In the drawings, each component and relative dimensions between components may be exaggerated for clarity. In the following description of the drawings, same or similar reference numbers refer to same or similar components or entities, and only differences with respect to individual embodiments are described. For clarity, only three beamlets are available in the drawing, but any number of beamlets is possible.

Accordingly, while example embodiments of the invention are susceptible to various modifications and alternative forms, embodiments are shown by way of example in the drawings and will herein be described in detail. There is no intention, however, to limit the exemplary embodiments of the invention to the particular forms disclosed, and on the contrary, the exemplary embodiments of the invention include all variations that fall within the scope of the invention. , equivalents, and alternatives.

In the present invention, "axial direction" means "optical axis direction of a lens (circular or multipolar), imaging system, or device", and "radial direction" means "direction perpendicular to the optical axis". “On-axis” means “on or aligned with the optical axis” and “off-axis” means “not on or aligned with the optical axis”. No.

In the present invention, "the imaging system is aligned with the optical axis" means "all electron optical elements (circular lenses, multipole lenses, etc.) are aligned with the optical axis".

In the present invention, the X, Y and Z axes form a Cartesian coordinate system. The optical axis of the primary projection imaging system lies on the Z-axis and the primary electron beam travels along the Z-axis.

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

In the present invention, "signal electrons" refer to "electrons generated by a primary charged particle beam from the observed or inspected surface of a specimen".

In this invention, "single beam mode" means that only one beamlet is used.

In this invention, all terms relating to through-holes, apertures, and orifices refer to apertures or holes passing through a single plate.

Subsequently, the present invention provides several embodiments of new multi-beam devices. The multi-beam device first forms multiple parallel virtual images of a single electron source, then a new source transformation unit to limit the current of the multiple beamlets, and the multiple beamlets a primary projection imaging system for projecting a plurality of parallel virtual images to form a plurality of probe spots on the observed surface of the specimen; and a plurality of secondary electron beams from the surface. out of the path of the plurality of beamlets, and a secondary projection imaging system for converging the plurality of secondary electron beams to be respectively detected by the plurality of detector elements of the electronic detection device. adopt.

This new source transformation unit comprises an imaging means comprising a plurality of micro-deflectors and a beamlet limiting means comprising a plurality of beam limiting apertures, the imaging means being upstream of the beamlet limiting means. A primary electron beam from a single electron source is first deflected by multiple micro-deflectors to form multiple parallel virtual images of the single electron source, and then multiple beams to form multiple parallel virtual images. A let passes vertically or substantially vertically through a plurality of beam limits. In this way, the multiple beam-limiting apertures not only produce less scattered electrons than in the prior art, but also block scattered electrons produced upstream, thus reducing image resolution due to electron scattering. disappears. The imaging means further comprises a plurality of micro-compensators for respectively compensating off-axis aberrations (field curvature and astigmatism) of the plurality of probe spots, thus further improving the image resolution of the observed surface.

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

The main aperture plate 171 can be placed above the common condenser lens 9 or directly above the new source conversion unit 120 as shown. The new source conversion unit 120 comprises a micro-deflector array 122 with two micro-deflectors 122_2, 122_3, and a beamlet limiting plate 121 with three beam limiting apertures 121_1, 121_2, 121-3, the beam limiting apertures 121_1 is aligned with the primary optical axis 100_1. There may be another micro-deflector 122_1 (as shown in FIG. 5C) if the beam limiting aperture 121_1 is not aligned with the primary optical axis 100_1. Primary projection imaging system 130 comprises transfer lens 133 and objective lens 131 . Deflection scanning unit 132 comprises at least one deflector. Beam separator 160 is a Wien filter. The secondary projection imaging system 150 comprises a counter-scan deflector 151 , a zoom lens 152 (comprising at least two lenses 152_1, 152_2) and a counter-rotating magnetic lens 154 . The electronic sensing device 140 comprises three sensing elements 140_1, 140_2, 140_3. Each of the lenses described above may be an electrostatic lens, a magnetic lens, or an electromagnetic compound lens.

Figures 3B-3D show three modes of operation of the new multi-beam device 100A. The single electron source 101 comprises a cathode, an extractor and/or an anode, and primary electrons are emitted from the cathode with high energy (eg 8-20 keV), high angular intensity (eg 0.5-5 mA/sr ), and (imaginary or real) crossover 101s (illustrated by an on-axis ellipse), so that the primary electron beam 102 crosses It is convenient to think of the single electron source 101 simplistically as the crossover 101s emanating from the over 101s.

In FIG. 3B, condenser lens 110 is off. The primary electron beam 102 passes through the condenser lens 110 without convergence effects, and its peripheral electrons are blocked by the main aperture of the main aperture plate 171 . Micro-deflectors 122_2 and 122_3 deflect beamlets 102_2 and 102_3 of primary electron beam 102, respectively. The deflected beamlets 102_2, 102_3 form off-axis virtual images 102_2v, 102_3v of the crossover 101s of the single electron source 101, respectively. The deflected beamlets 102_2, 102_3 are parallel or substantially parallel to the primary optical axis 100_1 and are therefore incident on the beamlet limiting plate 121 perpendicularly. Beam limiting apertures 121_1, 121_2, 121_3 block the electrons at the center 102_1 of the primary electron beam 102 and the peripheral electrons of the deflected beamlets 102_2, 102_3, respectively. As a result, one virtual multi-source array 101v is formed, which includes the crossover 101s and its two parallel off-axis virtual images 102_2v, 102_3v. One virtual image can avoid the Coulomb effect in one real image in FIG. To further reduce the Coulomb effect, the main aperture plate 171 may be placed above the condenser lens 110 to block the peripheral electrons as early as possible.

Subsequently, the crossover 101s and its two parallel off-axis virtual images 102_2v, 102_3v are imaged onto the observed surface 7 by the transfer lens 133 and the objective lens 131, and their images are projected onto three probe spots 102_1s. , 102_2s, 102_3s. In order to make the two off-axis beamlets 102_2, 102_3 perpendicularly incident on the observed surface 7, the transfer lens 133 converges them through the front focal point of the objective lens 131. FIG. If the objective lens 131 comprises one magnetic lens, the two off-axis beamlets 102_2, 102_3 may not pass the front focal point exactly due to the effect of magnetic rotation, which is the beamlet crossover Very helpful in reducing the Coulomb effect in CS. The deflection scanning unit 132 deflects the three beamlets 102_1-102_3 so that the three probe spots 102_1s-102_3s scan three separate regions on the surface 7 to be observed.

The secondary electron beams 102_1se, 102_2se, 102_3se emitted from the three scanning regions are converged by the objective lens 131 and directed by the beam separator 160 to enter the secondary projection imaging system 150 along the secondary optical axis 150_1. biased towards. Lenses 152 and 153 converge the secondary electron beams onto three detection elements 140_1 to 140_3, respectively. Each detector element thereby provides an image signal for one corresponding scan area. If some secondary electrons of a secondary electron beam from one scan area are directed to an adjacent detector element, the image signal of the adjacent detector element will contain irrelevant information from that scan area and its adjacent detector elements. The irrelevant information for the detector element being scanned is the crosstalk from the scan area. To avoid cross-talk between detector elements, zoom lens 152 makes the spot size of each secondary electron beam smaller than the corresponding detector element, and inverse scan deflector 151 allows deflection scan unit 132 to focus on beamlets 102_1-102_3. , the secondary electron beams 102_1se-102_3se are synchronously deflected so as to remain within the corresponding detector elements while deflecting .

Different samples usually require different viewing conditions, such as beamlet incident energy and current. This is particularly true for inspection and/or investigation of wafer/mask defects in the semiconductor manufacturing industry. The focusing power of the objective lens 131 changes with the incident energy, which affects the position of the secondary electron beam on the electron detection device 140 and causes crosstalk. In this case, the zoom lens 152 is adjusted to eliminate radial displacement of the secondary electron beam. If objective lens 131 comprises a single magnetic lens, counter-rotating magnetic lens 154 is adjusted to eliminate rotation of the secondary electron beam.

Each of the two off-axis probe spots 102_2s, 102_3s comprises off-axis aberrations produced 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 spot can be reduced by individually optimizing the trajectories of the corresponding beamlets. The static portion of off-axis aberration can be reduced by adjusting the deflection power of the corresponding microdeflectors. The dynamic portion of off-axis aberration can be reduced by optimizing the performance of deflection scanning unit 132 . Therefore, the deflection scanning unit 132 may comprise multiple deflectors.

Unlike FIG. 3B, in FIG. 3C the condenser lens 110 is switched on. A condenser lens 110 converges the primary electron beam 102 to form an on-axis virtual image 101sv of the single electron source 101 crossover 101s. Micro-deflectors 122_2 and 122_3 deflect beamlets 102_2 and 102_3 of the focused primary electron beam 102, respectively, to form off-axis virtual images 102_2v and 102_3v of crossover 101s. The deflected beamlets 102_2, 102_3 are parallel or substantially parallel to the primary optical axis 100_1 and are therefore incident on the beamlet limiting plate 121 perpendicularly. The beam-limiting apertures 121_1, 121_2, 121_3 block the electrons at the center 102_1 of the focused primary electron beam 102 and the peripheral electrons of the deflected beamlets 102_2, 102_3, respectively, thereby limiting their currents. The focusing function of condenser lens 110 increases the current density of focused primary electron beam 102, thereby increasing the current of beamlets 102_1-102_3 higher than in FIG. 3B. Therefore, the current of all beamlets can be adjusted continuously by condenser lens 110 .

As with conventional SEMs, the size of each probe spot is minimized by balancing geometric aberrations, diffraction aberrations, Gaussian image size, and Coulomb effect. The focusing function of the condenser lens 110 changes the imaging magnification from the crossover 101s to the observed surface 7, which affects the balance and thus can increase the size of each probe spot. To avoid large enlargements of the probe spot size when the beamlet current is varied significantly, the size of the beam limiting apertures 121_1-121_3 may be varied considerably. As a result, beamlet limiting plate 121 preferably has multiple groups of beam limiting apertures. The beam limiting aperture size in one group is different from that in the other group. Alternatively, the converging power of transfer lens 133 may be varied to reduce variations in imaging magnification. Since the trajectories of the off-axis beamlets 102_2, 102_3 are affected by the focusing power variation of the transfer lens 133, substantial adjustments may be made to the deflection forces of the micro-deflectors 122_2, 122_3 so that they maintain their trajectories. . In this way, beamlets 102_2, 102_3 may be slightly non-parallel to primary optical axis 100_1, as shown in FIG. 3D.

Another embodiment 110A of the new multi-beam device is shown in FIG. Unlike embodiment 100A, the new source conversion unit 120-1 comprises a microdeflector compensator array 122-1 having three microdeflector compensator elements 122_1dc, 122_2dc, 122_3dc. Each micro-deflector compensator element comprises one micro-deflector and one micro-compensator with one micro-lens and one micro-stigmator. The micro-deflectors are used to form one virtual multi-source array, similar to the function of micro-deflectors 122_2, 122_3 shown in Figures 3B-3D. As is well known, condenser lens 110, transfer lens 133, and objective lens 131 produce off-axis aberrations. As mentioned above, the effect of off-axis aberrations on the size of the probe spot can be reduced by individually optimizing the trajectories of the beamlets. Microlenses and microstigmators are then used to compensate for field curvature and astigmatism, respectively, remaining in the probe spot. Compared to the microdeflector array 122 of FIG. 3A, the microdeflector compensator array 122-1 is an advanced imaging means.

Each of the microdeflectors 122_2, 122_3 of FIG. 3A may simply include two parallel electrodes perpendicular to the required deflection direction of the corresponding beamlet, as shown in FIG. 5A. For example, micro-deflector 122_2 has two parallel electrodes 122_2_e1, 122-2_e2 perpendicular to the X-axis, thereby deflecting beamlet 102_2 in the X-axis direction. FIG. 5B shows one embodiment of a micro-deflector array 122 that deflects eight beamlets. Because each micro-deflector has a spatial orientation, it is difficult to make a single micro-deflector array 122 with a large number of micro-deflectors. From a manufacturing point of view it is desirable that all micro-deflectors have the same geometrical configuration and the same orientation. Hence, a microdeflector with a quadrupole or quadrupole configuration can meet this requirement, as shown in FIG. 5C. The four electrodes of each microdeflector can form two deflectors capable of deflecting one beamlet in any direction. A micro-deflector 122_1 can be used when the corresponding beam-limiting aperture 121_1 is not exactly aligned with the primary optical axis 101 .

In order to operate one micro-deflector, a drive circuit is required to connect to each of its electrodes. To prevent the drive circuitry from being damaged by the primary electron beam 102, it is preferable to place one electrically conductive plate above all the microdeflector electrodes of FIGS. 5A-5C. Taking FIG. 5C as an example, FIG. 6 shows an upper electrically conductive plate 122-CL1 having a number of upper through-holes and an upper insulator plate 122-IL1 having a number of upper orifices for the electrodes of the microdeflectors 122_1-122_3. placed above. The electrodes of the microdeflectors 122_1-122_3 can be attached to the upper insulator plate 122-IL1. The upper through-hole and upper orifice are respectively aligned with the optical axis of the microdeflector, eg, the upper through-hole CL1_2 and upper orifice IL1_2 are on the optical axis 122_2_1 of the microdeflector 122_2. The radial size of each upper through-hole is equal to or smaller than the inner diameter dimension of the corresponding microdeflector electrode to protect the drive circuit, and the radial size of each upper orifice avoids charging of the inner sidewall. larger than the radial size of the corresponding upper through hole. In this way, the deflection field of every microdeflector has a shorter edge extent on its upper side, thus reducing deflection aberrations.

Based on FIG. 6A, the micro-deflector array 122 of FIG. 6B further comprises a lower electrically conductive plate 122-CL2 with multiple lower through-holes. Each lower through-hole is aligned with the optical axis of one micro-deflector, for example, lower through-hole CL2_2 is on optical axis 122_2_1 of micro-deflector 122_2. In this way, the deflection field of every microdeflector has a reduced edge extent both on its upper and lower sides, thus reducing deflection aberrations. Unlike FIG. 6B, the micro-deflector array 122 of FIG. 6C employs a bottom insulator plate 122-IL2 with multiple bottom orifices to support the electrodes of micro-deflectors 122_1-122_3. Each bottom orifice is aligned with the optical axis of one microdeflector, eg, bottom orifice IL2_2 is on optical axis 122_2_1 of microdeflector 122_2. The radial size of each lower orifice is greater than the inner diameter dimension of the corresponding microdeflector electrode. The micro-deflector array 122 of Figure 6D is a combination of Figures 6B and 6C, resulting in a more stable configuration.

FIG. 7 shows one embodiment of microdeflector compensator element 122_2dc of microdeflector compensator array 122-1 of FIG. 4, which has an 8-pole configuration. The eight electrodes 122_2dc_e1 to 122_2dc_e8 are composed of a dipole field (deflection field) having a basic amount for generating a virtual image of the electron source 1 in any direction and an additional amount for correcting distortion, and a four-field field for correcting astigmatism in any direction. It can be driven to produce a heavy pole field (astigmatism field) and a circular lens field that corrects field curvature.

FIG. 8A shows another embodiment of the microdeflector compensator array 122-1 of FIG. Each microdeflector compensator element comprises a pair of quadrupole lenses arranged in two layers, aligned with each other, and differing in azimuth or pose by 45°. The micro-deflector compensator elements 122_1dc, 122_2dc, 122_3dc are respectively a set of upper and lower quadrupole lenses 122_1dc-1, 122_1dc-2, a set of upper and lower quadrupole lenses 122_2dc-1, 122_2dc-2, and an upper and a pair of lower quadrupole lenses 122_3dc-1 and 122_3dc-2. The upper quadrupole lenses 122_1dc-1, 122_2dc-1 and 122_3dc-1 are arranged on the upper layer 122-1-1, and the lower quadrupole lenses 122_1dc-2, 122_2dc-2 and 122_3dc-2 are arranged on the lower layer 122-1-2. and aligned with the upper quadrupole lenses 122_1dc-1, 122_2dc-1 and 122_3dc-1, respectively. As an example, with respect to the X-axis, the azimuth angles of the upper quadrupole lenses 122_1dc-1, 122_2dc-1, 122_3dc-1 are 0° as shown in FIG. The azimuth angle of 122_3dc-2 is 45° as shown in FIG. 8C. In FIG. 8D, similar to FIG. 6D, the upper and lower layers are shielded by an upper electrically conductive plate 122-CL1 and a lower electrically conductive plate 122_CL2, and an upper insulator plate 122-IL1 and a lower insulator plate 122-IL2. It is supported by an intermediate insulator plate 122-IL3 having a number of intermediate orifices. For each microdeflector compensator element, any desired directional deflection field and circular lens field are generated by either or both the upper and lower quadrupole lenses, and an arbitrarily oriented quadrupole field is generated by the upper quadrupole lens. It can be produced by both a quadrupole lens and a lower quadrupole lens.

Another embodiment of the new multi-beam device is shown in FIG. 9A. Compared to embodiment 110A of FIG. 4, transfer lens 133 has been removed from the primary projection imaging system. FIG. 9B illustrates one mode of operation in which off-axis beamlets 102_2 and 102_3 are deflected parallel to primary optical axis 200_1 by microdeflector compensator elements 122_2dc and 122_3dc, respectively, and deflected at an oblique angle to observed surface 7. FIG. is incident. This mode can be used for fields of observation that do not have strict requirements on the beamlet incidence situation or that require stereo imaging. The micro-deflector compensator elements 122_2dc, 122_3dc can compensate for large off-axis aberrations of the two off-axis beamlets 102_2, 102_3 due to passing through the objective lens 131 with large radial misalignment. FIG. 9C shows another mode of operation in which the off-axis beamlets 102_2, 102_3 are further deflected by microdeflector compensator elements 102_2dc, 102_3dc, respectively, toward the primary optical axis 200_1, correspondingly 7 at a smaller oblique angle. If the microdeflector compensator elements 122_2dc and 122_3dc respectively deflect the off-axis beamlets 102_2 and 102_3 to pass through the front focus of the objective lens 131, then the off-axis beamlets 102_2 and 102_3 are perpendicular to the observed surface 7. Incident. To avoid the off-axis beamlets 102_2, 102_3 from passing through the beam-limiting aperture at large angles of incidence, it is preferable to keep a long distance between the front focus of the objective lens 131 and the microdeflector compensator array 122-1. .

As is well known, the more beamlets that scan the observed surface 7, the more charging can occur there. Therefore, some beamlets may not be needed in a particular field of view. In this case, the beamlets may be directed to be blanked by the beamlet limiting plate. FIG. 10 shows such a mode of operation for embodiment 110A of FIG. The micro-deflector compensator element 122_2dc may need to be switched on to direct the beamlet 102_2 blocked by the beamlet limiting plate 121, which is the detailed structure of the source transform unit 120-1. depends on

Based on the embodiment 110A of FIG. 4, another embodiment 111A of a new multi-beam device is proposed in FIG. 11A, in which a single beam electron detector 141 is added. If for some reason only one beamlet is needed, such as searching for the optimum imaging conditions (incident energy and probe current) for a field of view, the apparatus operates in single beam mode. In this case, beam separator 160 can deflect the corresponding secondary electron beam to single-beam electron detector 141 . A beamlet 102_1 is used here as the beamlet. A secondary electron beam 102_1se generated by beamlet 102_1 is deflected to be detected by single-beam electron detector 141 . By using the single beam electron detector 141, the process of adjusting the secondary projection imaging system 150 for variations in the focusing power of the objective lens 131 can be avoided. As mentioned above, the focusing power of the objective lens 131 changes if the incident energy and/or current of the beamlets used change. Further, FIG. 11B shows another embodiment 112 A of the new multi-beam device, in which an in-lens electron detector 142 with beamlet passage holes is positioned below the beam separator 160 . When the apparatus operates in single beam mode, secondary electrons with large emission angles of the secondary electron beam associated with the beamlets used are detected by the in-lens electron detector 142 and secondary electrons with small emission angles are detected by the in-lens electron detector 142 . can pass through the beamlet passage holes and be detected by corresponding detector elements of the electronic detection device 140 . A beamlet 102_1 is used here as the beamlet. Of the secondary electron beam 102_1se generated by the beamlet 102_1, the secondary electrons 102_1se_2 with a large radiation angle collide with the in-lens electron detector 142, and the secondary electrons 102_1se_1 with a small radiation angle are detected by the electron detection device 140. are biased as A combination of the single beam electron detector 141 and the in-lens electron detector 142 can also be used. In this case, the secondary electrons 102_1se_2 with large emission angles are detected by the in-lens electron detector 142, and the secondary electrons 102_1se_1 with small emission angles are deflected by the beam separator 160 so as to be detected by the single-beam electron detector 141. can Although not shown here, the in-lens electron detector 142 may also be positioned above the beam separator 160 . In this case, the in-lens electron detector 142 can detect the outer portion of the secondary electron beam 102_1se when the beam separator is off.

In summary, the present invention proposes a new multi-beam device for observing specimens with high resolution and high throughput. This new multi-beam tool can serve as a yield control tool to inspect and/or investigate defects on wafers/masks in the semiconductor manufacturing industry. The multi-beam instrument includes a new source transformation unit that forms multiple parallel virtual images of a single electron source, a condenser lens that adjusts the currents of the multiple beamlets, and multiple probe spots on the surface of the sample to be observed. a primary projection imaging system for projecting a plurality of parallel virtual images so as to form a plurality of parallel virtual images; a beam separator for deflecting a plurality of secondary electron beams from the surface away from the paths of the plurality of beamlets; and a plurality of electronic detection devices. a secondary projection imaging system for converging the plurality of secondary electron beams to be respectively detected by the detector elements of . In this new source transform unit, the imaging means is upstream of the beamlet limiting means, thus mitigating image resolution degradation due to electron scattering. The imaging means comprises a plurality of micro-deflectors for forming a plurality of parallel virtual images or a plurality of micro-deflector compensators for forming a plurality of parallel virtual images and compensating for off-axis aberrations of the plurality of probe spots. have elements.

Although the invention has been described in relation to preferred embodiments thereof, it should be understood that other modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed. .

Claims (14)

a charged particle source configured to provide a primary beam;
an imaging unit configured to form multiple images of the charged particle source with multiple beamlets of the primary beam;
a transfer lens and an objective lens, the transfer lens configured to focus the plurality of beamlets, the objective lens receiving the focused beamlets and providing a plurality of probe spots on a sample; from the plurality of beamlets; and
a deflection scanning unit configured to reduce off-axis aberrations for each off-axis probe spot by individually optimizing the trajectory of the corresponding beamlet;
a second projection system configured to focus a plurality of secondary beams generated by the plurality of probe spots on the specimen;
a detection device having a plurality of detection elements configured to receive the plurality of secondary beams;
A charged particle beam device, wherein the second projection system includes a counter-rotating magnetic lens configured to minimize rotation of the plurality of secondary beams towards the detection device. Charged particle beam device according to claim 1, wherein the transfer lens is configured to focus the plurality of beamlets for normal incidence on the specimen. Charged particle beam device according to claim 1 or 2, wherein the transfer lens is arranged to focus the plurality of beamlets through a front focus of the objective lens. Charged particle beam device according to any one of claims 1 to 3, wherein the transfer lens is configured to reduce variations in imaging magnification by adjusting the focusing power of the transfer lens. Charged particle beam device according to claim 4, wherein the transfer lens is arranged to optimize the trajectory of the corresponding beamlet by adjusting the focusing power. Charged particle beam device according to any of claims 1 to 5 , wherein the deflection scanning unit is arranged to scan the plurality of probe spots on the specimen. The deflection scanning unit comprises a plurality of deflectors, each deflector of the plurality of deflectors configured to reduce off-axis aberrations of each off-axis probe spot by individually optimizing the trajectory of the corresponding beamlet. Charged particle beam device according to any one of claims 1 to 6 , wherein The second projection system is configured to synchronously deflect the plurality of secondary beams to maintain them within corresponding detector elements while the deflection scanning unit deflects the plurality of beamlets. Charged particle beam device according to any of claims 1 to 7 , comprising an inverse scan deflector. Charged particle beam device according to any of claims 1 to 8 , further comprising a beam limiting element having a plurality of beam limiting apertures for limiting said plurality of beamlets. Charged particle beam device according to any of claims 1 to 9 , further comprising a condenser lens configured to focus the primary beam so as to vary the current of the plurality of probe spots on the specimen. Charged particle beam device according to any of the preceding claims, wherein said second projection system comprises a zoom lens arranged to minimize radial displacement of said plurality of secondary beams. Charged particle beam device according to claim 11 , wherein the zoom lens comprises a plurality of lenses. Charged particle beam device according to claim 11 or 12 , wherein the zoom lens and the counter-rotating magnetic lens are arranged to focus the plurality of secondary beams onto the detection device. Charged particle beam device according to any of the preceding claims, further comprising a beam separator configured to separate said plurality of beamlets and said plurality of secondary beams.

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