Patent Application
20200303156
Embodiments described herein relate to charged particle beam devices, such as scanning electron microscopes configured to inspect specimens such as wafers or other substrates, e.g. to detect pattern defects. Embodiments described herein relate to charged particle beam devices configured to utilize multiple charged particle beams, e.g. a plurality of electron beamlets, particularly for inspection system applications, testing system applications, defect review or critical dimensioning applications, surface imaging applications or the like. Embodiments further relate to a beam splitter for generating multiple beamlets.
There is a high demand for structuring and probing specimens in the nanometer or even in the sub-nanometer scale, particularly in the electronics industry. Micrometer and nanometer scale process control, inspection or structuring is often done with charged particle beams, e.g. electron beams, which are generated, shaped, deflected and focused in charged particle beam devices, such as electron microscopes. For inspection purposes, charged particle beams offer high spatial resolution compared to many optical methods, because electron wavelengths can be significantly shorter than the wavelengths of optical beams.
Inspection devices using charged particle beams such as scanning electron microscopes (SEM) have many functions in industrial fields, including, but not limited to, inspection of electronic circuits, exposure systems for lithography, detecting devices, defect inspection tools, and testing systems for integrated circuits. In charged particle beam systems, fine probes with high current density can be used.
It is attractive to use multiple beams (referred to herein as beamlets) in a charged particle device, to, for example, be able to increase throughput of large scale sample inspection, such as of integrated circuits. Generating, directing, scanning, deflecting, shaping, correcting, and/or focusing beamlets can be technically challenging, in particular when sample structures are to be scanned and inspected in a quick manner with high throughput with nanoscale resolution.
Disclosed herein is a beam splitter for generating a plurality of charged particle beamlets from a charged particle source. The beam splitter includes a plurality of beamlet deflectors which each pass a beamlet. There is a first deflector for passing a first beamlet and a second deflector for passing a second beamlet. Each beamlet deflector includes a low order element and a corresponding higher-order element. Each lower order element has fewer electrodes than each corresponding higher-order element. Each low order element is one of a plurality of low order elements. Each corresponding higher-order element is one of the plurality of higher-order elements.
Disclosed herein is a charged particle beam device that includes a beam splitter that generates charged particle beamlets from a charged particle source. The beam splitter includes a plurality of beamlet deflectors which each pass a beamlet. There is a first deflector for passing a first beamlet and a second deflector for passing a second beamlet. Each beamlet deflector includes a low order element and a corresponding higher-order element. Each lower order element has fewer electrodes than each corresponding higher-order element. Each low order element is one of a plurality of low order elements. Each corresponding higher-order element is one of the plurality of higher-order elements. The charged particle beam device is configured for sample inspection with the plurality of charged particle beamlet. The device includes a charged particle source, followed by a collimating lens and the beam splitter described above. The device also includes a deflector for deflecting the beamlets generated by the beam splitter, the deflector directing the beamlets through a second beam splitter, and a scanner and an objective lens in that order. The objective lens is configured to focus the beamlets on a sample placed on a movable stage of the charged particle beam device, and collect signal charged particles. The second beam splitter directs the collected signal charged particles to a detector. The charged particle beam device further includes a controller which is communicatively coupled to the scanner, deflector, detector, and beam splitter.
Disclosed herein is a method of generating a plurality of charge particle beamlets. The method includes directing a single beam of charged particles through a beam splitter. The beam splitter includes a plurality of beamlet deflectors which each pass a beamlet. There is a first deflector for passing a first beamlet and a second deflector for passing a second beamlet. Each beamlet deflector includes a low order element and a corresponding higher-order element. Each lower order element has fewer electrodes than each corresponding higher-order element. Each low order element is one of a plurality of low order elements. Each corresponding high order element is one of a plurality of high order elements. A low order electrical field is applied to the charged particles with a low order electrostatic element which deflects the charged particles. High order electrical field is applied to the charged particles with the high order electrostatic element to correct aberrations. Charged particle beamlets are generated as the charged particles pass through apertures aligned with the centers of each beamlet deflector.
So that the manner in which the above recited features can be understood in detail, a more particular description, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments and are described in the following:
Herein are used relative terms such as low and high, such as referring to the multipolar order of beam deflecting elements used, for example, to influence the shape and/or trajectory of charged particles, especially in the form of beams or beamlets. The usage of relative terms “high” and “low” is intended to convey comparative meaning, in the sense that a low order element is configured to provide a lower order multipole than a corresponding high order element. This may be manifest in the number of electrodes of the low or high order element.
In an embodiment that may be combined with every embodiment disclosed herein, a low order element has fewer electrodes than a high order element, so that the low order element generates a lower order multipolar field than a high order element. As an example, a low order element could be made of a pair of electrodes that generate a dipole; and a high order element could be made of eight electrodes that generate an octupole. The relative terms high magnitude and low magnitude, likewise, are relative terms which are intended to convey a comparative meaning. For example, a high magnitude low order multipole may have higher magnitude and fewer multipoles than a low magnitude high order multipole.
Herein the term “along the optical axis” is used, such as to convey the beam path of a charged particle beamlet. The usage of “along” in the term is intended to convey that the path is substantially parallel to the optical axis, although some divergence or convergence is possible. Beamlets' respective paths may deviate from being completely parallel from the optical axis of a charged particle device, such as when (or immediately after) the beamlets pass through the beam splitter disclosed herein.
Herein, multipolar beam deflectors are described, with the intended meaning that a dipolar beam deflector generates an electric field which is very well described as a dipolar field, although small perturbations or the like of higher multipoles may exist. Likewise, a quadrupole can generate an electric field that is very well described by no more than a quadrupolar field, although small perturbations or the like of higher multipoles may exist. Extending the concept further, an octupole generates a field that is very well described by no more than an octupolar field; and so on.
Herein, the terms sample and specimen are used interchangeably. Herein, the attachment of one substrate with another may be through the use of an adhesive such as a silicon based adhesive. Attaching substrates together, as described herein, may include steps of aligning respective structures on the substrates, particularly apertures, electrodes, and/or elements of beamlet deflectors.
A plurality of beamlets arranged along a ring which is centered on the optical axis is particularly contemplated. It can be advantageous, yet present technical hurdles, to form multiple beamlets from a single charged particle source 5. For example, a charged particle beam device 100 which uses a single column and a single charged particle source can be made more compact than using multiple columns and multiple sources.
The charged particle source 5 may be an electron source configured to generate an electron beam. Alternatively, the beam source may be an ion source configured to generate an ion beam. In some embodiments, the beam source 105 may include at least one of a cold field emitter (CFE), a Schottky emitter, a thermal field emitter (TFE) or another high current electron beam source, in order to increase the throughput. A high current is considered to be 10 μA in 100 mrad or more, for example up to 5 mA, e.g. 30 μA in 100 mrad to 1 mA in 100 mrad. According to typical implementations, the current is distributed essentially uniformly, e.g. with a deviation of ±10%. According to some embodiments, which can be combined with other embodiments described herein, the beam source can have an emission half angle of about 5 mrad or above, e.g. 50 mrad to 200 mrad. In some embodiments, the beam source may have a virtual source size of 2 nm or more and/or 40 nm or less. For example, if the beam source is a Schottky emitter, the source may have a virtual source size from 10 nm to 40 nm. For example, if the beam source is a cold field emitter (CFE), the source may have a virtual source size from 2 nm to 20 nm.
According to embodiments, which can be combined with other embodiments described herein, a TFE or another high reduced-brightness source capable of providing a large beam current is a source where the brightness does not fall by more than 20% of the maximum value when the emission angle is increased to provide a maximum of 10 μA-100 μA.
The beamlets 10, 20 may propagate toward a sample 8 through a column along the optical axis 0. The beamlets may be operated upon by elements such as one or more deflectors, beam correctors, lens devices, apertures, beam benders and/or beam separators.
The objective lens system 109 may include a combined magnetic-electrostatic objective lens including a magnetic lens portion and an electrostatic lens portion. In some embodiments, a retarding field device may be provided which is configured to reduce the landing energy of the charged particles on the specimen. For example, a retarding field electrode may be arranged upstream of the specimen. The objective lens 80 can also collect signal charge particles and direct them to a second beam splitter 33. The second beam splitter 33 may direct signal charge particles toward a detector 17. Signal charge particles may be secondary electrons and/or backscattered electrons.
A controller can be communicatively coupled to the components, such as the beam splitter 50, detector 17, the stage 7, and the scanner 12. The controller can provide power to lens elements and the like, such as the electrodes of electrostatic lenses.
The detector 17 can include detector elements which can be configured for generation of a measurement signal, e.g. an electronic signal corresponding to detected signal electrons. The controller can receive data generated by the device, such as by the detector.
There are many technical challenges associated with the generation and control of multiple beamlets. Herein is described a beam splitter 50 which can be used to generate multiple beamlets from a charged particle source and/or a single charged particle beam. A beam splitter 50, particularly those described herein, can be made from a monolithic piece, such as from a single piece of silicon or SOI wafer (silicon on insulator). To form the beam splitter 50, various structures such as electrodes, conductive lines, through-holes, etc. can be formed on and/or in a substrate, e.g. a monolith, silicon water, or SOI wafer.
The beam splitter 50 has an optical axis 0 which can be substantially perpendicular to the plane of the beam splitter 50, particularly the at least one substrate 350.
In
The low order elements can be high voltage elements and the high order elements can be low voltage elements. The low order elements can be configured for applying a large deflection to the beamlets, by, for example, applying of a strong (e.g. relatively high magnitude) low order multipole. The high order can be configured for applying an aberration correction, by, for example, applying a weak (e.g. a relatively low magnitude) high order multipole.
For example, each low order element can be a dipole element. Each high order element is configured to generate a higher multipole than the corresponding low order element. For example, the high order elements each generate an octupole, e.g. an electrostatic octupole, to respective beamlets, and the low order element generates a lower order multipolar field, such as a dipole or quadrupole.
The beamlet deflector 70 can have a surface for facing the charged particle source which can be coated with a conductive material, such as a metal film, to reduce charging effects. The substrate 350 which has the surface for facing the charged particle source may have the low order elements 150 or the high order elements 250 on the opposite surface.
As seen in
Each low order element, including the first low order element 110 depicted in
The footprint of each beamlet deflector 70 in the plane perpendicular to the optical axis can be less than 4 mm2, 3 mm2, 2.25 mm2, 2 mm2, 1 mm2, 900 μm2, 800 μm2, or 700 μm2, or approximately 625 μm2. A small footprint can be desirable for allowing for a high density of beamlet deflectors 70 from the same beam splitter 50. The footprint of each beamlet deflector 70 can be from 25 μm×25 μm to 2 mm×2 mm; or from 30 μm×30 μm to 1.5 mm×1.5 mm. A high density of beamlet deflectors 70 can result in a high density of beamlets, which can be desirable, for example, for efficiently using the source energy for a large number of high current charged particle beamlets. It can also be desirable to have discrete, well-separated beamlets with little interaction between neighboring beamlets. It can be technically challenging to produce high spatial density beamlets which are nonetheless well separated in the sense of having manageable (e.g. negligible) beamlet-beamlet interactions. The footprint of an electrode of a beamlet deflector 70 can be less than 10 μm2, 8 μm2, 5 μm2, 4 μm2, or 2 μm2.
As shown in
It is particularly contemplated to have an embodiment in which, along the optical axis, the length of the low order elements is from about 10 μm up to about 2 mm; and the length of the high order elements is less than 200 μm.
In an embodiment that can be combined with any other embodiment, a center-center spacing between the beamlet deflectors 70 in a direction perpendicular to the optical axis can be less than 5 mm, 2 mm, 1 mm, 0.5 mm, or 0.25 mm.
As disclosed herein, it is possible to maintain a small footprint of each beamlet deflector 1, 2 by separating the functions of the beam splitter 50, which generates the plurality of beamlet 10, 20 from a charged particle source 5, into a low order component largely responsible for deflection of the beamlets, and a high order component largely for aberration correction of the beamlets. As disclosed herein, a plurality of low order elements can be high voltage elements for deflection, and a plurality of corresponding high order elements can be low voltage elements for aberration correction.
There can optionally be a plurality of third deflecting elements, such as for fine adjustment, aberration correction, and/or astigmatism correction. A respective third deflecting element, to add to each low order element 150 and corresponding high order element 250, can be a quadrupole, decapole, or tetradecapole, for example. Such a plurality of third deflector elements is particularly envisioned in combination with dipolar low order elements; furthermore, in such an embodiment, the high order elements can each be octupoles. Each third deflecting element can also have an aperture in alignment with the respective apertures of the low and high order elements. A plurality of third deflecting elements may be positioned on another substrate, which can be attached to, such as fixed in alignment with, the substrate(s) of the low and high order elements.
The low order element 110 can be for generating a dipolar field, e.g. for generating a substantially dipolar electric field, with comparatively small, e.g. negligible, higher order field components in comparison to the dipolar field. The low order electrodes 190 can each have the shape of a ring segment. The smaller arc of the ring segment can be adjacent to the aperture, as depicted in
In an embodiment, each low order element 110, 120 has four electrodes 190, including two ground electrodes facing each other with the aperture between. Conductive lines connecting ground electrodes to ground may be present (not shown in
A controller may connect to the low and high voltage conductive lines.
In an embodiment that can be combined with any other embodiment described herein, the cross section of each high voltage conductive line 301 is greater than that of each low voltage conductive line 302. The relatively low cross-section of the low voltage conductive lines 302 can allow a higher density of conductive lines on the substrate surface. A higher density of conductive lines can make it possible to address and/or control more electrodes. A higher density of conductive lines can allow for higher order multipoles for the low order elements, which can be used mainly for aberration correction, and/or it can provide for a higher density of the high order elements themselves, meaning a greater areal density of charged particle beamlets.
By separating the function of the beam splitter 50 into i) low order deflection (with low order elements 150), which may require relatively high voltages which can limit the areal number density of high voltage conductive lines 301, and ii) high order aberration correction (with high order elements 250), which can exploit a higher areal number density of low voltage conductive lines 302 because of the possibility of using lower voltages, it is possible to increase the areal number density of generated charged particle beamlets. In other words, the spacing between neighboring beamlet deflectors 70 can be decreased.
As seen in
In
This disclosure is intended to include the following enumerated embodiments, in which references to reference numerals and/or figures are mentioned to aid in understanding, without the intent of the reference numerals or figures to be limiting:
Various embodiments of the present invention have been described above. It should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein can be used in combination with the features of any other embodiment. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the detailed description.
