JP7066779B2 - Multi-charged particle beam device - Google Patents

Description

Priority Claim This application is the right of Ren et al. And claims the priority of US Provisional Application Nos. 62 / 130,819 entitled "Multiple Charged Particle Beam Devices" filed on March 10, 2015. , All of which is incorporated herein by reference.

The present invention relates to a charged particle device having a plurality of charged particle beams, and more particularly to a device using a plurality of charged particle beams so as to simultaneously acquire images of a plurality of scanning regions of an observation area on a sample surface. Therefore, the device can be used in the semiconductor manufacturing industry to inspect and / or investigate defects on wafers / masks with high resolution and high throughput.

During the manufacture of semiconductor IC chips, pattern defects and / or uninvited particles (residues) inevitably appear on the surface of the wafer / mask during the manufacturing process, which greatly reduces yield. Patterns with smaller and smaller critical feature dimensions are used to meet the performance requirements of ever-evolving IC chips. Therefore, conventional yield management tools that use optical beams are gradually becoming unsuitable due to the diffraction effect, and yield management tools that use electron beams are increasingly being used. Since the electron beam has a shorter wavelength than the photon beam, it can provide excellent spatial resolution. Currently, yield management tools using electron beams use the principle of scanning electron microscopy (SEM) with a single electron beam, so that they can provide high resolution but not throughput suitable for mass production. It is possible to use larger and larger beam currents to increase the throughput, but the excellent spatial resolution is essentially degraded by the Coulomb effect.

A promising solution, rather than using a single electron beam with a large current, to ease the constraints 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 a sample. On the sample surface, a plurality of probe spots can simultaneously scan a plurality of small scanning areas within a large observation area on the sample surface. The electrons in each probe spot generate secondary electrons from the incident location on the sample surface. Secondary electrons include slow secondary electrons (energy of 50 eV or less) and backscattered electrons (energy close to the energy of incident electrons). Secondary electrons from a plurality of small scanning regions can be simultaneously recovered by a plurality of electron detectors. Therefore, an image of a large observation area including all the small scan areas can be obtained much faster than scanning the large observation area with a single beam.

Multiple electron beams are obtained from multiple electron sources, respectively, or from a single electron source. In the former, multiple electron beams are usually converged and scanned into multiple small scanning regions by multiple columns, and secondary electrons from each scanning region are detected by one electron detector inside the corresponding column. To. 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 composite objective (eg US8,294,095). The distance between two adjacent beams on the sample surface is usually about 30 to 50 mm.

In the latter, a source conversion unit is used to virtually transform a single electronic source into multiple subsources. The source conversion unit includes one beamlet forming means and one image forming means. The beamlet forming means basically comprises a plurality of beam limiting apertures that divide the primary electron beam generated by a single electron source into a plurality of subbeams or beamlets, respectively. The image forming means basically comprises a plurality of electron optics elements that either converge or deflect the plurality of beamlets so as to form a plurality of parallel images of the electron source. Each of the multiple parallel images can be considered as one subsource emitting one corresponding beamlet. Since the beamlet spacing or beam limiting aperture spacing is at the micrometer level, more beamlets are available, so the source conversion unit can be manufactured by a semiconductor manufacturing process or a MEMS (Micro Electro Mechanical Systems) process. .. Naturally, one primary projection imaging system and one deflection scanning unit in one single column are used to project and scan multiple parallel images into multiple small scanning areas, respectively, from which they are obtained. The plurality of secondary electron beams to be generated are detected by the plurality of detection elements of one electron detection device inside a single column. The plurality of detection elements may be a plurality of electron detectors arranged in parallel, or a plurality of pixels of one electron detector. Therefore, this device is commonly referred to as a multi-beam device.

In the source conversion unit 20-1 of FIG. 1A, the image forming means 22-1 is composed of a plurality of lenses (22_1L to 22_3L). Substantially parallel primary electron beams 2 from one single electron source are divided into a plurality of beamlets (2_1 to 2_3) by a plurality of beam limiting apertures (21_1 to 21_3) of the beamlet forming means 21. Lenses converge multiple beamlets, respectively, to form multiple parallel images (2_1r-2_3r) of a single electron source. The plurality of parallel images is typically a real image, but can be a virtual image under certain conditions where each of the plurality of lenses is an aperture lens. US7, 244, 949 and US 7, 880, 143 propose a multi-beam device having one image forming means of this type. In the source conversion unit 20-2 of FIG. 1B, the image forming means 22-2 is composed of a plurality of deflectors (22_2D and 22_3D). The divergent primary electron beam 2 from one single electron source is divided into a plurality of beamlets (2_2 and 2_3) by a plurality of beam limiting apertures (21_2 and 21_3) of the beamlet forming means 21, and the plurality of deflectors are single. Each of the beamlets is deflected to form multiple parallel virtual images (2_2v and 2_3v) of an electron source.

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

Since then, the above ideas have been used in many ways in multi-beam devices. JP-A-10-339711 and US8,378,299 directly use one conventional electron beam biprism to form two probe spots on the sample surface. US6,943,349 uses one annular deflector (FIG. 5 of the same) or one corresponding deflector array (FIG. 12 of the same) to form more than two probe spots on the sample surface. And it can provide high throughput. The annular deflector includes an inner annular electrode and an outer annular electrode. If the potentials of the two annular electrodes are not equal to each other, one electric field will appear in the annular gap in the local radial direction, so the annular deflector will deflect more than two beamlets together in different directions. be able to. Further, the deflection function of the annular deflector can also be performed by one corresponding deflector array having a plurality of multipolar deflectors arranged along the annular gap.

In the conventional source conversion unit 20-2 of FIG. 1B, a plurality of beamlets pass through a plurality of beam limiting apertures at various incident angles due to the divergence of the primary electron beam 2, thereby causing electrons of various intensities. I suffer from scattering. Scattered electrons in each beamlet enlarge the probe spot and / or become background noise, thus degrading the image resolution of the corresponding scan area.

In US 6,943,349, the currents of multiple beamlets can only be deflected by varying 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 stabilize when its emission amount is changed. The beamlet forming means needs to have a plurality of groups of openings and to make the size of the openings of one group different from that of the other groups. It takes a lot of time to change the group when using it. In addition, the secondary electron beam can only converge to a large number of detector elements in the in-lens detector under some specific operating conditions of the objective lens. Therefore, the available application fields are limited.

Therefore, it is necessary to provide a multi-beam device capable of simultaneously acquiring images of a plurality of small scanning regions in a large observation area on the sample surface with high resolution and high throughput. In particular, multi-beam equipment 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.

An object of the present invention is to be able to provide both high resolution and high throughput for observing a sample, especially as a yield management tool for inspecting and / or investigating defects on wafers / masks in the semiconductor manufacturing industry. The purpose is to provide a new multi-beam device. The multi-beam device first forms multiple parallel virtual images of a single electron source, then a new source conversion unit that limits the current of the corresponding multiple beamlets, and the current of the multiple beamlets. A condenser lens to be adjusted, a primary projection imaging system that projects multiple parallel virtual images so as to form multiple probe spots on the observed surface of the sample, and multiple beams of multiple secondary electron beams from the surface. It employs a beam separator that deflects to deviate from the path of the let, and a secondary projection imaging system that converges a plurality of secondary electron beams so that they are each detected by a plurality of detection elements of the electron detection device.

Therefore, the present invention provides a source conversion unit, which comprises an image forming means including an upper layer having a plurality of upper quadrupole structures and a lower layer having a plurality of lower quadrupole structures, and a lower portion of the image forming means. It is provided with a beamlet limiting means having a plurality of beam limiting openings. Each upper quadrupole structure is above and aligned with one corresponding lower quadrupole structure, both forming a set of quadrupole structures with different azimuths of 45 °. Therefore, the plurality of upper quadrupole structures and the plurality of lower quadrupole structures form a set of a plurality of quadrupole structures. The plurality of beam limiting apertures are aligned with a plurality of sets of quadrupole structures, respectively. A set of quadrupole structures, a microdeflector that deflects one beamlet of an electron beam generated by an electron source to form a virtual image of the electron source, a microlens that converges one beamlet to the desired degree. And / or functions as a microstigmeter that adds a desired amount of astigmatism to a single beamlet.

The present invention also provides a multi-beam device for observing the surface of a sample, which includes an electron source, a condenser lens below the electron source, a source conversion unit below the condenser lens, and a source. Below the conversion unit, the primary projection imaging system with the objective lens, the deflection scanning unit inside the primary projection imaging system, the sample stage below the primary projection imaging system, and above the objective lens. It comprises a beam separator, a secondary projection imaging system above the beam separator, and an electron detection device having a plurality of detection elements. The source conversion unit comprises an image forming means having a plurality of microdeflectors and a beamlet limiting means having a plurality of beam limiting openings, and the image forming means is above the beamlet limiting means. The electronic source, condenser lens, source conversion unit, primary projection imaging system, deflection scanning unit, and beam separator are aligned with the primary optical axis of this device. The sample stage supports the sample so that the surface faces the objective lens. The secondary projection imaging system and electron detection device are aligned with the secondary optical axis of the device, and the secondary optical axis is non-parallel to the primary optical axis. The electron source produces a primary electron beam along the primary optical axis, and the plurality of microdeflectors deflect the primary electron beam to form multiple parallel virtual images of the electron source. Thereby, the virtual multi-source array is converted from the electronic source, and the plurality of beamlets including the virtual multi-source array pass through the plurality of beam limiting openings, respectively. Thereby, the current of each beamlet is limited by one corresponding beam limiting aperture, and the current of multiple beamlets can be changed by adjusting the condenser lens. The primary projection imaging system forms a virtual multi-source array on a surface, whereby multiple probe spots are formed on the surface. The deflection scanning unit deflects a plurality of beamlets so that the plurality of scanning areas in the observation area on the surface are scanned by the plurality of probe spots, respectively. A plurality of secondary electron beams are generated from a plurality of scanning regions by a plurality of probe spots, and are converged as they pass through an objective lens. The beam separator deflects multiple secondary electron beams into a secondary projection imaging system, which converges the multiple secondary electron beams so that they are each detected by multiple detection elements. And maintain. Thereby, each detection element provides an image signal of one corresponding scanning region.

The multi-beam device may further include a main aperture plate that is below the electron source, has a main aperture aligned with the primary optical axis, and acts as a beam limiting aperture for the primary electron beam. The primary projection imaging system may include a transfer lens that is above the objective lens and converges a plurality of beamlets so that they are perpendicular 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 include a single-beam electron detector that is above the beam separator and can be used in single-beam mode. The multi-beam device may further include an in-lens electron detector that has a beamlet passage hole aligned to the primary optical axis, is below the beam separator, and can be used in a single beam mode.

The present invention also provides a multi-beam device for observing the surface of a sample, which includes an electron source, a condenser lens below the electron source, a source conversion unit below the condenser lens, and a source. Below the conversion unit, the primary projection imaging system with the objective lens, the deflection scanning unit inside the primary projection imaging system, the sample stage below the primary projection imaging system, and above the objective lens. It comprises a beam separator, a secondary projection imaging system above the beam separator, and an electron detection device having a plurality of detection elements. The source conversion unit comprises image forming means having a plurality of micro deflector compensator elements and beamlet limiting means having a plurality of beam limiting apertures, and each micro deflector compensator element has one micro deflector and one. It comprises one micro-compensator with one micro-lens and one micro-stig meter. The image forming means is above the beamlet limiting means. The electron source, condenser lens, source conversion unit, primary projection imaging system, deflection scanning unit, and beam separator are aligned with the primary optical axis of the device. The sample stage supports the sample so that the surface faces the objective lens. The secondary projection imaging system and electron detection device are aligned with the secondary optical axis of the device, and the secondary optical axis is non-parallel to the primary optical axis. The electron source produces a primary electron beam along the primary optical axis, and the plurality of microdeflectors deflect the primary electron beam to form multiple parallel virtual images of the electron source. This transforms the virtual multi-source array from the electronic source. Multiple beamlets, including a virtual multi-source array, pass through each of the beam limiting apertures, thereby limiting the current of each beamlet by one corresponding beam limiting aperture. The currents of multiple beamlets can be changed by adjusting the condenser lens. The primary projection imaging system forms a virtual multi-source array on a surface, whereby multiple probe spots are formed on the surface. One microlens and one microstigmeter in one microcompensator compensate for curvature of field and astigmatism in one corresponding probe spot, respectively, and the deflection scanning unit is a plurality of observation areas within the observation area on the surface. The plurality of beamlets are deflected so that the scanning area is scanned by the plurality of probe spots. Multiple secondary electron beams are generated from multiple scanning regions by multiple probe spots and converge as they pass through the objective, and multiple beam separators are incident on the secondary projection imaging system. Deflection of the secondary electron beam of. The secondary projection imaging system converges and maintains a plurality of secondary electron beams to be detected by a plurality of detection elements, whereby each detection element provides an image signal of one corresponding scanning region. ..

The multi-beam device may further include a main aperture plate that is below the electron source, has a main aperture aligned with the primary optical axis, and acts as a beam limiting aperture for the primary electron beam. Each of the multiple microdeflector compensator elements is a microdeflector by generating the desired deflection field, and as a microcompensator by producing the desired quadrupole field and the desired circular lens field. It may have a functioning octapole structure. Each of the multiple microdeflector compensator elements has an upper quadrupole structure in the upper layer and a lower quadrupole structure in the lower layer, with 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 by 45 °. The upper quadrupole structure and the lower quadrupole structure are as one microdeflector by generating the desired deflection field, and as one microcompensator by creating the desired quadrupole field and the desired circular lens field. It may work. The primary projection imaging system may include a transfer lens that is above the objective lens and converges a plurality of beamlets so that they are perpendicular to the surface. The multi-beam device may further include a single-beam electron detector that is above the beam separator and can be used in single-beam mode. The multi-beam device may further include an in-lens electron detector that has a beamlet passage hole aligned to the primary optical axis, is below the beam separator, and can be used in a single beam mode.

The present invention also provides a method of constructing a source conversion unit for forming a virtual multi-source array from an electronic source, which is an upper layer having a plurality of upper quadrupole structures and a plurality of lower quadrupole structures. It is provided with a step of providing an image forming means including a lower layer having the above, and a step of providing a beamlet limiting means below the image forming means and having a plurality of beam limiting openings. Each upper quadrupole structure is above and aligned with one corresponding lower quadrupole structure, both forming a set of quadrupole structures with different azimuths of 45 °. As a result, the plurality of upper quadrupole structures and the plurality of lower quadrupole structures form a set of the plurality of quadrupole structures. The plurality of beam limiting apertures are aligned with a plurality of sets of quadrupole structures, respectively. A set of quadrupole structures is a microdeflector that deflects one beamlet of an electron beam generated by an electron source to form a virtual image of the electron source, a micro that converges the one beamlet to the desired degree. It functions as a lens and / or a microstigmeter that adds a desired amount of astigmatism to the single beamlet.

The source conversion unit may include a set of a plurality of quadrupole structures and an upper electrical conduction plate having a plurality of upper through holes aligned with each other. The source conversion unit may further include a set of quadrupole structures and a lower electrical conduction plate with a plurality of bottom through holes aligned with each other.

The present invention also provides a method for forming a virtual multi-source array from an electron source, which uses an upper layer with a plurality of upper quadrupole structures and a lower layer with a plurality of lower quadrupole structures. This comprises deflecting the electron beam from the electron source to the plurality of beamlets and limiting the plurality of beamlets by using the plurality of openings. Each upper quadrupole structure is above and aligned with one corresponding lower quadrupole structure, both forming a set of quadrupole structures with different azimuths of 45 °.

The invention also provides a charged particle beam device, which is a single charged particle source that provides a primary beam, a means of converting the primary beam into multiple beamlets, and a sample from multiple beamlets. A first projection system that forms multiple probe spots, a deflection scanning unit that scans multiple probe spots on a sample, means for separating multiple signal electron beams from multiple beamlets, and multiple signal electron beams. It comprises a detection device that receives a receiver and a second projection system that forms a plurality of signal spots from a plurality of signal electron beams on a plurality of electron detection elements of the detection device. The conversion means includes a plurality of deflectors that deflect the plurality of beamlets and a plurality of beam limiting openings below the plurality of deflectors. Multiple signal electron beams are each generated by the collision of multiple beamlets with a specimen.

The charged particle beam device may further include a condenser lens that regulates the currents of the plurality of probe spots. The conversion means includes a plurality of compensators for compensating for aberrations of the plurality of probe spots.

Other advantages of the invention will become apparent from the accompanying drawings illustrating some embodiments of the invention for purposes of illustration and the following description.

The present invention will be readily understood by reference to the accompanying drawings and the detailed description below. Similar reference numerals in each drawing point to similar structural elements.

It is a schematic diagram of the conventional source conversion unit. It is a schematic diagram of the conventional source conversion unit.

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

It is a schematic diagram of one configuration of a new multi-beam apparatus which concerns on one Embodiment of this invention.

It is a schematic diagram of the operation mode of the new multi-beam apparatus of FIG. 3A. It is a schematic diagram of the operation mode of the new multi-beam apparatus of FIG. 3A. It is a schematic diagram of the operation mode of the new multi-beam apparatus of FIG. 3A.

It is a schematic diagram of the other configuration of the new multi-beam apparatus which concerns on other embodiments of this invention.

FIG. 3 is a schematic diagram of the configuration of the image forming means of FIG. 3A according to another embodiment of the present invention. FIG. 3 is a schematic diagram of the configuration of the image forming means of FIG. 3A according to another embodiment of the present invention. FIG. 3 is a schematic diagram of the configuration of the image forming means of FIG. 3A according to another embodiment of the present invention.

FIG. 3 is a schematic diagram of the configuration of the image forming means of FIG. 3A according to another embodiment of the present invention. FIG. 3 is a schematic diagram of the configuration of the image forming means of FIG. 3A according to another embodiment of the present invention. FIG. 3 is a schematic diagram of the configuration of the image forming means of FIG. 3A according to another embodiment of the present invention. FIG. 3 is a schematic diagram of the configuration of the image forming means of FIG. 3A according to another embodiment of the present invention.

FIG. 5 is a schematic diagram of the configuration of the advanced image forming means of FIG. 4 according to another embodiment of the present invention.

FIG. 5 is a schematic diagram of the configuration of the advanced image forming means of FIG. 4 according to another embodiment of the present invention. FIG. 5 is a schematic diagram of the configuration of the advanced image forming means of FIG. 4 according to another embodiment of the present invention. FIG. 5 is a schematic diagram of the configuration of the advanced image forming means of FIG. 4 according to another embodiment of the present invention. FIG. 5 is a schematic diagram of the configuration of the advanced image forming means of FIG. 4 according to another embodiment of the present invention.

It is a schematic diagram of the other configuration of the new multi-beam apparatus which concerns on other embodiments of this invention.

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

It is a schematic diagram of one operation mode of the new multi-beam apparatus of FIG.

It is the schematic of another configuration of the new multi-beam apparatus which concerns on other embodiment of this invention, and one operation mode thereof.

It is the schematic of another configuration of the new multi-beam apparatus which concerns on other embodiment of this invention, and one operation mode thereof.

Hereinafter, various exemplary embodiments of the invention will be described more fully with reference to the accompanying drawings showing some exemplary embodiments of the invention. Without limiting the scope of protection of the invention, all description and drawings of those embodiments refer to electron beams by way of example, but those embodiments are used to limit the invention to specific charged particles. Should not be.

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

Accordingly, where exemplary embodiments of the invention are possible in a variety of variants and alternatives, embodiments are shown in the drawings for illustrative purposes and are described in detail herein. However, there is no intention to limit the exemplary embodiments of the invention to the particular embodiments disclosed, in contrast, the exemplary embodiments of the invention are any variation within the scope of the invention. , Equals, and alternatives.

In the present invention, the "axial direction" means the "optical axis direction of the lens (circular or multipolar), imaging system, or device", and the "radial direction" means the "direction perpendicular to the optical axis". "On axis" means "on the optical axis or aligned with the optical axis", and "off axis" means "not on the optical axis or aligned with the optical axis". There is no such thing.

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

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

In the present invention, the "primary electron" means an "electron emitted from an electron source and incident on the observed or inspected surface of the sample", and the "secondary electron" means "primary electron" from the surface. "Electrons generated by".

In the present invention, the "signal electron" means "an electron generated by a primary charged particle beam from an observed or inspected surface of a sample".

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

In the present invention, all terms relating to through holes, openings, and orifices refer to openings or holes that penetrate a plate.

Subsequently, the present invention provides some embodiments of a new multi-beam device. The multi-beam device is a multi-beam device that first forms multiple parallel virtual images of a single electron source, then a new source conversion unit that limits the current of multiple beamlets, and multiple beamlets. A condenser lens that adjusts the current of the sample, a primary projection imaging system that projects multiple parallel virtual images so as to form multiple probe spots on the observed surface of the sample, and multiple secondary electron beams from the surface. A beam separator that deflects to deviate from the path of multiple beamlets, and a secondary projection imaging system that converges multiple secondary electron beams to be detected by multiple detection elements of the electron detection device, respectively. adopt.

The new source conversion unit comprises image forming means having a plurality of microdeflectors and beamlet limiting means having a plurality of beam limiting apertures, the image forming means being upstream of the beamlet limiting means. The primary electron beam from a single electron source is first deflected by multiple microdeflectors to form multiple parallel virtual images of a single electron source, and then multiple beams forming multiple parallel virtual images. The let passes through multiple beam limits vertically or substantially vertically. In this way, the plurality of beam limiting apertures not only generate low-scattered electrons as compared with the prior art, but also block the scattered electrons generated upstream, and thus the deterioration of image resolution due to electron scattering. Is gone. The image forming means further comprises a plurality of micro-compensators that compensate for the off-axis aberrations (field curvature and astigmatism) of the plurality of probe spots, respectively, thereby further improving the image resolution of the observed surface.

FIG. 3A shows an embodiment 100A of a new multi-beam device. The single electron source 101 is on the primary optical axis 100_1. The common condenser lens 110, main aperture plate 171, new source conversion unit 120, primary projection imaging system 130, deflection scanning unit 132, and beam separator 160 are arranged along the primary optical axis 100_1 and the primary optical axis. It is aligned to 100_1. The secondary projection imaging system 150 and the electron detection device 140 are arranged along the secondary optical axis 150_1 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 microdeflector array 122 with two microdeflectors 122_2,122_3 and a beamlet limiting plate 121 with three beam limiting apertures 121_1, 121_2, 121-3 and a beam limiting aperture. 121_1 is aligned with the primary optical axis 100_1. If the beam limiting aperture 121_1 is not aligned with the primary optical axis 100_1, there may be another microdeflector 122_1 (as shown in FIG. 5C). The primary 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 separator 160 is a Viennese filter. The secondary projection imaging system 150 includes a reverse scan deflector 151, a zoom lens 152 (equipped with at least two lenses 152_1 and 152_2), and a reverse rotation magnetic lens 154. The electronic detection device 140 includes three detection elements 140_1, 140_2, 140_3. Each of the above lenses may be an electrostatic lens, a magnetic lens, or an electromagnetic composite lens.

3B-3D show three operating modes of the new multi-beam device 100A. The single electron source 101 comprises a cathode, a drawer, and / or an anode, and primary electrons are emitted from the cathode to have high energy (eg 8-20 keV) and high angular intensity (eg 0.5-5 mA / sr). ), And / or accelerated to form a primary electron beam 102 with (imaginary or real) crossover 101s (illustrated by an elliptical symbol on the axis), thus crossing the primary electron beam 102. It is convenient to think that the single electron source 101 originates from the over 101s and is simplified to be the crossover 101s.

In FIG. 3B, the condenser lens 110 is off. The primary electron beam 102 passes through the condenser lens 110 without the influence of convergence, and the electrons at the periphery thereof are blocked by the main aperture of the main aperture plate 171. The micro deflectors 122_2, 122_3 deflect the beamlets 102_2, 102_3 of the 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 perpendicular to the beamlet limiting plate 121. The beam limiting openings 121_1, 121_2, 121_3 block electrons in the central portion 102_1 of the primary electron beam 102 and the peripheral edges 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. In order to further reduce the Coulomb effect, the main aperture plate 171 may be placed above the condenser lens 110 so as to block peripheral electrons as soon as possible.

Subsequently, the crossover 101s and its two parallel off-axis virtual images 102_2v, 102_3v are imaged on the observed surface 7 by the transfer lens 133 and the objective lens 131, and these images are imaged there by the three probe spots 102_1s. , 102_2s, 102_3s. In order to make the two off-axis beamlets 102_2, 102_3 perpendicular to the observed surface 7, the transfer lens 133 converges them so that they pass through the anterior focal point of the objective lens 131. If the objective lens 131 includes one magnetic lens, the two off-axis beamlets 102_2, 102_3 do not have to accurately pass the anterior focal point due to the effects of magnetic rotation, which is a beamlet crossover. Very useful for reducing the Coulomb effect in CS. The deflection scanning unit 132 deflects the three beamlets 102_1 to 102_3 so that the three probe spots 102_1s to 102_3s scan three separate regions on the observed surface 7.

The secondary electron beams 102_1se, 102_2se, 102_3se emitted from the three scanning regions are converged by the objective lens 131, and enter the secondary projection imaging system 150 along the secondary optical axis 150_1 by the beam separator 160. Is biased to. The lenses 152 and 153 converge the secondary electron beam on the three detection elements 140_1 to 140_3, respectively. Thereby, each detection element provides an image signal of one corresponding scanning region. When some secondary electrons of the secondary electron beam from one scanning region are directed to the adjacent detection element, the image signal of the adjacent detection element contains irrelevant information from the scanning region and is adjacent to the secondary electron beam. The information irrelevant to the detecting element is the crosstalk from the scanning region. In order to avoid crosstalk 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 reverse scan deflector 151 has the deflection scan unit 132 of the beamlets 102_1 to 102_13. The secondary electron beams 102_1se to 102_3se are synchronously deflected so as to be maintained in the corresponding detection element while deflecting.

Various samples usually require different observation conditions such as beamlet incident energy and current. This is especially true for wafer / mask defect inspection and / or investigation in the semiconductor manufacturing industry. The converging force of the objective lens 131 changes depending on 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 the radial displacement of the secondary electron beam. When the objective lens 131 includes one magnetic lens, the counter-rotating magnetic lens 154 is adjusted to eliminate the rotation of the secondary electron beam.

Each of the two off-axis probe spots 102_2s, 102_3s comprises an off-axis aberration 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 aberrations can be reduced by adjusting the deflection force of the corresponding microdeflector. The dynamic portion of off-axis aberrations can be reduced by optimizing the performance of the deflection scanning unit 132. Therefore, the deflection scanning unit 132 may include a plurality of deflectors.

Unlike FIG. 3B, the condenser lens 110 is switched on in FIG. 3C. The condenser lens 110 converges the primary electron beam 102 so as to form an axial virtual image 101sv of the crossover 101s of the single electron source 101. The microdeflectors 122_2 and 122_3 deflect the focused primary electron beam 102 beamlets 102_2 and 102_3, respectively, to form off-axis virtual images 102_2v and 102_3v of the crossover 101s. The deflected beamlets 102_2, 102_3 are parallel or substantially parallel to the primary optical axis 100_1 and are therefore perpendicular to the beamlet limiting plate 121. The beam limiting apertures 121_1, 121_2, 121_3 block electrons at the center 102_1 of the converged primary electron beam 102 and at the periphery of the deflected beamlet 102_2, 102_3, respectively, thereby limiting their currents. The convergence function of the condenser lens 110 increases the current density of the converged primary electron beam 102, thereby increasing the currents of the beamlets 102_1 to 102_3 higher than in FIG. 3B. Therefore, the currents of all beamlets can be continuously adjusted by the 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 the Coulomb effect. The convergence function of the condenser lens 110 changes the image magnification from the crossover 101s to the observed surface 7, which affects the balance, and thus can increase the size of each probe spot. In order to avoid a large increase in the size of the probe spot when the current of the beamlet is changed significantly, the size of the beam limiting openings 121_1 to 121_3 may be changed considerably. As a result, the beamlet limiting plate 121 preferably has a large number of groups of beam limiting openings. The size of the beam limiting aperture in one group is different from that in the other group. Alternatively, the focusing force of the transfer lens 133 may be changed so as to reduce the fluctuation of the image magnification. Since the orbit of the off-axis beamlet 102_2,102_3 is affected by the fluctuation of the focusing force of the transfer lens 133, a considerable adjustment may be made to the deflection force so that the deflection force of the microdeflector 122_2,122_3 maintains the orbit. .. In this way, the beamlets 102_2, 102_3 may be slightly non-parallel to the primary optical axis 100_1, as shown in FIG. 3D.

FIG. 4 shows another embodiment 110A of the new multi-beam device. Unlike the embodiment 100A, the new source conversion unit 120-1 comprises a microdeflector compensator array 122-1 with three microdeflector compensator elements 122_1dc, 122_2dc, 122_3dc. Each microdeflector compensator element comprises one microdeflector and one microcompensator with one microlens and one microstigmeter. The microdeflectors are used to form a single virtual multi-source array, similar to the functions of the microdeflectors 122_2, 122_3 shown in FIGS. 3B-3D. As is well known, the condenser lens 110, the transfer lens 133, and the 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 orbit of the beamlet. Therefore, the microlens and the microstigmeter are used to compensate for the curvature of field and astigmatism remaining in the probe spot, respectively. Compared to the microdeflector array 122 of FIG. 3A, the microdeflector compensator array 122-1 is an advanced image forming 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, the microdeflector 122_2 has two parallel electrodes 122_2_e1, 122-2_e2 perpendicular to the X-axis, thereby deflecting the beamlet 102_2 in the X-axis direction. FIG. 5B shows one embodiment of the microdeflector array 122 that deflects eight beamlets. Since each microdeflector has a spatial orientation, it is difficult to make one microdeflector array 122 with a large number of microdeflectors. From a manufacturing point of view, it is desirable that all microdeflectors have the same geometrical configuration and the same orientation. Therefore, 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. The microdeflector 122_1 can be used when the corresponding beam limiting aperture 121_1 is not precisely aligned with the primary optical axis 101.

In order to operate one micro deflector, the drive circuit needs to be connected to each electrode. In order to prevent the drive circuit from being damaged by the primary electron beam 102, it is preferable to place one electrical conduction plate above the electrodes of all the microdeflectors in FIGS. 5A-5C. Taking FIG. 5C as an example, in FIG. 6, the upper electrical conduction plate 122-CL1 having a large number of upper through holes and the upper insulator plate 122-IL1 having a large number of upper orifices are the electrodes of the microdeflectors 122_1 to 122_3. It is located above. The electrodes of the micro deflectors 122_1 to 122_3 can be attached to the upper insulator plate 122-IL1. The upper through hole and the upper orifice are aligned with each other on the optical axis of the micro deflector. For example, the upper through hole CL1_2 and the upper orifice IL1_2 are on the optical axis 122_2 of the micro deflector 122_2. The radial size of each top through hole is equal to or smaller than the inner diameter of the corresponding microdeflector electrode to protect the drive circuit, and the radial size of each top orifice avoids charging the inner sidewall. Therefore, it is larger than the radial size of the corresponding upper through hole. In this way, the deflection field of all microdeflectors has a shorter edge range above it, thus reducing deflection aberrations.

Based on FIG. 6A, the microdeflector array 122 of FIG. 6B further comprises a lower electrical conduction plate 122-CL2 with a large number of lower through holes. Each lower through hole is aligned with the optical axis of one microdeflector, for example, the lower through hole CL2_2 is on the optical axis 122_2 of the microdeflector 122_2. In this way, the deflection field of all microdeflectors has a shorter edge range both above and below it, thus reducing deflection aberrations. Unlike FIG. 6B, the microdeflector array 122 of FIG. 6C employs a lower insulator plate 122-IL2 having a large number of lower orifices to support the electrodes of the microdeflectors 122_1 to 122_3. Each lower orifice is aligned with the optical axis of one microreflector, for example, the lower orifice IL2_2 is on the optical axis 122_2_1 of the microdeflector 122_2. The radial size of each lower orifice is greater than the inner diameter of the corresponding microdeflector electrode. The micro deflector array 122 of FIG. 6D is a combination of FIGS. 6B and 6C, and has a more stable configuration.

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

FIG. 8A shows another embodiment of the microdeflector compensator array 122-1 of FIG. Each microdeflector compensator element is arranged in two layers and comprises a set of quadrupole lenses that are aligned with each other and differ in azimuth or orientation by 45 °. The microdeflector compensator elements 122_1dc, 122_2dc, 122_3dc are a set of upper and lower quadrupole lenses 122_1dc-1, 122_1dc-2, a set of upper and lower quadrupole lenses 122_1, 122_2dc-2, and an upper part, respectively. It consists of a pair of lower 4-pole lenses 122_3dc-1 and 122_3dc-2. The upper quadrupole lenses 122_1dc-1, 122_2dc-1, 122_3dc-1 are arranged in the upper layer 122-1-1, and the lower quadrupole lenses 122_1dc-2, 122_2dc-2, 122_3dc-2 are in the lower layer 122-1-2. It is arranged in the upper quadrupole lens 122_1dc-1, 122_2dc-1, 122_3dc-1, respectively. As an example, with respect to the X-axis, the azimuth of the upper quadrupole lenses 122_1dc-1, 122_2dc-1, 122_3dc-1 is 0 ° as shown in FIG. 8B, and the lower quadrupole lenses 122_1dc-2, 122_2dc-2, The azimuth of 122_3dc-2 is 45 ° as shown in FIG. 8C. In FIG. 8D, similarly to FIG. 6D, the upper layer and the lower layer are shielded by the upper electric conduction plate 122-CL1 and the lower electric conduction plate 122_CL2, and the upper insulator plate 122-IL1 and the lower insulator plate 122-IL2 are formed. It is supported by an intermediate insulator plate 122-IL3 with a large number of intermediate orifices. For each microdeflector compensator element, a deflection field and circular lens field in any desired direction are generated by either or both of the upper quadrupole lens and the lower quadrupole lens, and the quadrupole field in any direction is the top. It can be produced by both a quadrupole lens and a lower quadrupole lens.

FIG. 9A shows another embodiment of the new multi-beam device. Compared to the 110A embodiment of FIG. 4, the transfer lens 133 has been removed from the primary projection imaging system. FIG. 9B shows one mode of operation in which the off-axis beamlets 102_2, 102_3 are deflected in parallel with the primary optical axis 200_1 by the microdeflector compensator elements 122_2dc and 122_3dc, respectively, at an oblique angle to the observed surface 7. It is incident. This mode can be used in observation areas where there are no strict requirements for beamlet incidence or where stereo imaging is required. The microdeflector compensator elements 122_2dc, 122_3dc can compensate for the large off-axis aberrations of the two off-axis beamlets 102_2, 102_3 due to passing through the objective lens 131 with a large radial misalignment. FIG. 9C shows another mode of operation in which the off-axis beamlets 102_2, 102_3 are further deflected by the microdeflector compensator elements 102_2dc, 102_3dc toward the primary optical axis 200_1, respectively, and the observed surface accordingly. It is incident on 7 at a smaller oblique angle. When the off-axis beamlets 102_2, 102_3 are deflected so that the microdeflector compensator elements 122_2dc and 122_3dc pass through the front focal point of the objective lens 131, the off-axis beamlets 102_2, 102_3 are perpendicular to the observed surface 7. Incident. It is preferable to maintain a long distance between the anterior focal point of the objective lens 131 and the microdeflector compensator array 122-1 to prevent the off-axis beamlets 102_2, 102_3 from passing through the beam limiting aperture at a large incident angle. ..

As is well known, the more beamlets that scan the observed surface 7, the more charge can occur there. Therefore, some beamlets may not be needed in certain areas of observation. In this case, the beamlets may be oriented to be blanked by the beamlet limiting plate. FIG. 10 shows such an operating mode of embodiment 110A of FIG. 4, with the microdeflector compensator element 122_2dc turned off and the beamlet 102_2 blocked by the beamlet limiting plate 121. The microdeflector compensator element 122_2dc may need to be switched on to orient the beamlet 102_2 blocked by the beamlet limiting plate 121, which is the detailed structure of the source conversion unit 120-1. Depends on.

Based on embodiment 110A of FIG. 4, another embodiment 111A of the new multi-beam device is proposed in FIG. 11A, with the addition of a single-beam electron detector 141. The device operates in single beam mode when only one beamlet is required for some reason, such as searching for optimal imaging conditions (incident energy and probe current) for a field of observation. In this case, the beam separator 160 can deflect the corresponding secondary electron beam to the single beam electron detector 141. As the beamlet, the beamlet 102_1 is used here. The secondary electron beam 102_1se generated by the beamlet 102_1 is deflected to be detected by the single beam electron detector 141. By using the single-beam electron detector 141, it is possible to avoid the process of adjusting the secondary projection imaging system 150 with respect to the fluctuation of the focusing force of the objective lens 131. As mentioned above, the convergence force of the objective lens 131 changes as the incident energy and / or current of the beamlet used changes. Further, FIG. 11B shows another embodiment 112A of the new multi-beam device, in which an in-lens electron detector 142 with a beamlet pass hole is located below the beam separator 160. When the device operates in single beam mode, of the secondary electron beams related to the beamlets used, the secondary electrons with a large radiation angle are detected by the in-lens electron detector 142, and the secondary electrons with a small radiation angle are detected. Can pass through the beamlet passage hole and be detected by the corresponding detection element of the electron detection device 140. As the beamlet, the beamlet 102_1 is used here. Of the secondary electron beams 102_1se generated by the beamlet 102_1, the secondary electrons 102_1se_2 having a large radiation angle collide with the in-lens electron detector 142, and the secondary electrons 102_1se_1 having a small radiation angle are detected by the electron detection device 140. It is biased to. A single beam electron detector 141 and an in-lens electron detector 142 can also be used in combination. In this case, the secondary electrons 102_1se_1 having a large radiation angle are detected by the in-lens electron detector 142, and the secondary electrons 102_1se_1 having a small radiation angle are deflected by the beam separator 160 so as to be detected by the single beam electron detector 141. Can be. Although not shown here, the in-lens electron detector 142 may also be located 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 samples with high resolution and high throughput. This new multi-beam device can serve as a yield management tool for inspecting and / or investigating defects on wafers / masks in the semiconductor manufacturing industry. The multi-beam device forms a new source conversion unit that forms multiple parallel virtual images of a single electron source, a condenser lens that adjusts the current of multiple beamlets, and multiple probe spots on the observed surface of the sample. A primary projection imaging system that projects multiple parallel virtual images in such a way, a beam separator that deflects multiple secondary electron beams from the surface so as to be out of the path of multiple beamlets, and a plurality of electron detection devices. A secondary projection imaging system that converges a plurality of secondary electron beams so as to be detected by each of the detection elements of the above is adopted. In this new source conversion unit, the image forming means is upstream of the beamlet limiting means, and thus the deterioration of image resolution due to electron scattering is mitigated. The image forming means is 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 a plurality of probe spots. It has an element.

Although the invention has been described in connection with its preferred embodiments, it should be understood that other modifications and variations may be made without departing from the spirit and scope of the invention as claimed below. ..

Claims (12)

With a charged particle source configured to provide a primary beam,
An image forming unit configured to form a plurality of images of the charged particle source using a plurality of beamlets of the primary beam.
A first projection system having an objective lens and configured to form a plurality of probe spots from the plurality of beamlets on a sample.
A second projection system configured to converge a plurality of secondary beams generated by the plurality of probe spots on the sample.
A beam separator configured to separate the plurality of beamlets and the plurality of secondary beams,
A detection device having a plurality of detection elements configured to receive the plurality of secondary beams, and a detection device.
A condenser lens configured to converge the primary beam so as to change the currents of the plurality of probe spots on the sample.
A deflection scanning unit that deflects the plurality of beamlets such that the plurality of probe spots scan the sample .
The second projection system includes a counter-rotating magnetic lens configured to eliminate rotation of the plurality of secondary beams in the detection device.
The second projection system is configured to synchronously deflect the plurality of secondary beams while maintaining the plurality of beamlets in the corresponding detection element while the deflection scanning unit deflects the plurality of beamlets. A charged particle beam device that includes a reverse scan deflector . The charged particle beam apparatus according to claim 1, wherein the first projection system includes a transfer lens that converges the plurality of beamlets so as to be vertically incident on the sample. The charged particle beam apparatus according to claim 1 or 2, further comprising a deflection scanning unit configured to scan the plurality of probe spots on the sample. The charged particle beam apparatus according to any one of claims 1 to 3, further comprising a beam limiting element that limits the plurality of beamlets by a plurality of beam limiting openings. The charged particle beam device according to any one of claims 1 to 4, wherein the condenser lens is arranged between the charged particle source and the image forming unit. One of claims 1 to 5, wherein the second projection system includes a zoom lens configured to make the spot size of each of the plurality of secondary beams smaller than the corresponding detection element of the plurality of detection elements. The charged particle beam device described in. The charged particle beam device according to claim 6, wherein the zoom lens is configured to remove radial displacements of the plurality of secondary beams in the detection device. The image forming unit is
A first layer with a set of first multipolar structures,
Includes a second layer with a second set of multipolar structures,
The first set of multipolar structures is aligned with the second set of multipolar structures to function as multiple microdeflectors, with each microreflector being a charged particle produced by the charged particle source. The charged particle beam apparatus according to any one of claims 1 to 7 , wherein the beamlet of the above is deflected to form an imaginary image of the charged particle source. With a charged particle source configured to provide a primary beam,
An image forming unit configured to form a plurality of images of the charged particle source using a plurality of beamlets of the primary beam.
A first projection system having an objective lens and configured to form a plurality of probe spots from the plurality of beamlets on a sample.
A second projection system configured to converge a plurality of secondary beams generated by the plurality of probe spots on the sample.
A beam separator configured to separate the plurality of beamlets and the plurality of secondary beams,
A detection device having a plurality of detection elements configured to receive the plurality of secondary beams.
The second projection system includes a counter-rotating magnetic lens configured to eliminate rotation of the plurality of secondary beams in the detection device.
The image forming unit is
A first layer with a set of first multipolar structures,
Includes a second layer with a second set of multipolar structures,
The first set of multipolar structures is aligned with the second set of multipolar structures to function as multiple microdeflectors, with each microreflector being a charged particle produced by the charged particle source. A charged particle beam device that deflects a beamlet of a charged particle beam to form an imaginary image of the charged particle source. It comprises an image forming element comprising a first layer having a first set of multipolar structures and a second layer having a second set of multipolar structures.
The first set of multipolar structures is aligned with the second set of multipolar structures to function as multiple microdeflectors, with each microdeflector of the charged particles produced by the charged particle source. The beamlet is deflected to form an imaginary image of the charged particle source.
The plurality of microdeflectors form a plurality of beamlets that exit the source conversion unit so as to allow multiple probe spots on the surface of the sample. The source conversion unit according to claim 10 , wherein the charged particle source and a plurality of imaginary images of the charged particle source form a multi-source array. A multi-beam device comprising the source conversion unit according to claim 10 or 11 .

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