Pulsed CFE electron source with fast blanker for ultrafast TEM applications.

Abstract

To provide a CPB system that can control X-rays generated by charged particle beams (CPBs).SOLUTION: Charged particle beams (CPBs) 106 are modulated using a beam blanker 112 / deflector 110 and an electrically pulsed extraction electrode 104 in conjunction with a field emitter 102 and a gun lens 108. With such modulation, CPBs can provide both pulsed and continuous mode operation as required for a particular application, while average CPB current is maintained within predetermined levels, such as levels that promote X-ray safe operation. Either the extraction electrode or the beam blanker / deflector can define CPB pulse width, CPB on / off ratio, or both.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to pulsed beam electron microscopes. [Background technology]

[0002] Transmission electron microscopes (TEMs) use continuous electron beams with beam currents generally ranging from about 30-50 pA to a few nA. Higher beam currents are not used because they are associated with dangerous levels of X-ray production. TEM columns can be provided with X-ray shielding, but such shielding is only practical for beam currents of about 150 nA or less. For some applications, high-speed TEMs are required, which can use, for example, picosecond electron beam pulses of a few electrons / ps, or beam pulses of about 10 ns duration. In most high-speed TEM scenarios, the pulsed beam can have peak currents of 1 μA or more at repetition rates of at least 1 MHz. Such pulsed beams are difficult to generate and can produce dangerous levels of X-ray radiation, and improved approaches are needed. Summary of the Invention

[0003] Disclosed herein are methods and apparatus that enable the generation of a charged particle beam (CPB) having pulsed and / or continuous components that can control x-rays generated by the CPB. In an exemplary embodiment, a CPB system includes a CPB source adapted to generate a CPB having a pulsed or continuous CPB component, or both pulsed and continuous CPB components. A CPB lens is disposed to receive the CPB from the CPB source and is coupled to a controller to generate the continuous CPB component by energizing the CPB lens to generate an extended CPB at a beam-limiting aperture such that a portion of the extended CPB is transmitted. Alternatively, the controller energizes the CPB lens to focus the CPB such that a portion of the CPB associated with the pulsed component is substantially transmitted. In some embodiments, an aperture plate defines a beam-limiting aperture, and the CPB source is coupled to a LaB 6The CPB source comprises a field emitter such as a nanorod. In an exemplary embodiment, the CPB source includes an extraction electrode disposed to establish a beam current of at least one of a pulsed CPB component and a continuous CPB component. In some cases, a CPB controller is coupled to the extraction electrode and operable to establish a beam current of at least one of a pulsed CPB component and a continuous CPB component. In yet another embodiment, a beam blanker is disposed to receive the CPB from a beam-limiting aperture, and the CPB controller is operable to energize the beam blanker to selectively deflect the received CPB. In other exemplary embodiments, the blanking aperture plate defines a blanking aperture, and the beam blanker is operable to selectively deflect the CPB into the blanking aperture to block at least a portion of the CPB. In an exemplary embodiment, the beam blanker comprises an electrostatic deflector or an RF resonant cavity. In an exemplary embodiment, the controller is coupled to the CPB lens to focus the CPB into the beam blanker. In other exemplary embodiments, an x-ray shield is disposed about the CPB beam axis and defines an x-ray shielding region, and the beam-limiting aperture is disposed within the x-ray shielding region. In yet another embodiment, the CPB source is positioned to direct the CPB to be blocked by the blanking aperture when the beam blanker is not activated, and the CPB lens is configured to generate a CPB focus located between the beam-limiting aperture and the blanking aperture.

[0004] An exemplary method includes selecting either a first CPB beam focus or a second CPB beam focus, where the first beam focus is arranged to substantially attenuate the CPB by conducting only a portion of the CPB through the beam-limiting aperture and the second CPB focus is arranged such that the CPB is substantially conducted by the beam-limiting aperture. The first CPB focus is selected and the CPB source is operated to generate at least a continuous component of the CPB, and the continuous component is directed to the target. The second CPB focus is selected and a CPB portion associated with the pulsed component is generated and directed to the target.

[0005] In some cases, the continuous component is generated using a field emitter in response to continuous actuation of the extractor, and the pulsed component is generated using pulsed actuation of the field emitter and the extractor. In other examples, the pulsed component is generated using a beam blanker. In additional examples, a CPB portion associated with the pulsed component is directed to a beam blanker and selectively attenuated to define a CPB pulse duration or a CPB contrast ratio, or both a CPB pulse duration and a contrast ratio. In other examples, a second focus is selected and the pulsed component is generated using a beam blanker to have a predetermined pulse duration, contrast ratio, or both a pulse duration and a contrast ratio. In other examples, the beam-limiting aperture is disposed in an x-ray shielded region.

[0006] Yet another method includes providing a CPB source including a field emitter and an extractor and positioning a CPB lens to receive the CPB from the CPB source. A beam-limiting aperture is disposed within the x-ray shielded region. A controller is coupled to the CPB lens to generate a CPB focus at the beam-limiting aperture to generate a pulsed CPB or to generate an expanded beam at the beam-limiting aperture to generate a continuous CPB.

[0007] The charged particle beam system includes a pulseable CPB source adapted to generate a CPB having at least a pulsed CPB component and a CPB blanker disposed to receive at least the pulsed CPB component. A blanking aperture is disposed to receive the pulsed CPB component from the CPB blanker, the CPB blanker operable to selectively direct the pulsed CPB component to the specimen or to block at least a portion of the pulsed CPB component. In representative embodiments, the pulseable CPB source is adapted to generate a CPB having a pulsed component and a stationary component. In some examples, the pulseable CPB source comprises an extraction electrode disposed to establish a beam current of at least one of the pulsed beam component and the stationary beam component. In further examples, a CPB lens disposed to focus the CPB to the beam blanker. In other examples, an x-ray shield is disposed about the CPB beam axis and defines an x-ray shielding region. An aperture is disposed within the x-ray shielding region, and the CPB is configured to focus the CPB such that the extended CPB is incident on the aperture disposed within the x-ray shielding region. In yet another embodiment, the CPB source is arranged to direct at least one of the pulsed and stationary components of the CPB to be blocked by the blanking aperture when the beam blanker is not activated. The controller is operable to select at least one delay between application of one or more voltages to the extractor, the beam blanker drive signal, and the stimulation signal applied to the specimen. In an exemplary embodiment, the pulsed component of the CPB includes pulses of duration less than 100 ns, 50 ns, 10 ns, 1 ns, 100 ps, ​​50 ps, ​​10 ps, ​​or 1 ps at a repetition rate of at least 100 kHz, 1 MHz, 10 MHz, 50 MHz, 100 MHz, 500 MHz, or 1 GHz.

[0008] An exemplary method includes providing a CPB including a pulsed component and a stationary component and directing the CPB to a beam blanker. At least one of the pulsed component and the stationary component is attenuated. Typically, the beam blanker attenuates the stationary component and conducts the pulsed component. In some cases, a ratio of the pulsed component beam current to the stationary beam current is selected and the beam blanker is actuated to direct a beam associated with the selected ratio to the specimen. In some cases, the CPB is optically focused upstream of an x-ray shielding region and the CPB is delivered to the beam blanker with an aperture disposed in the x-ray shielding region. In some embodiments, the pulsed component beam current is generated by applying a pulsed voltage to an extractor. In other embodiments, the pulsed voltage is synchronously applied to the extractor and the beam blanker is actuated. In an exemplary embodiment, the duration of the CPB pulse applied to the specimen is defined by the beam blanker. In an exemplary embodiment, the CPB is an electron beam. In additional embodiments, the image of the specimen is based on the pulsed component of the CPB.

[0009] An additional method includes generating a pulsed CPB by applying a pulse drive to a CPB source to generate a CPB having a pulsed component and a stationary component. The pulsed component is selectively attenuated to reduce the pulse duration or the stationary component is attenuated to generate a predetermined ratio of pulsed current to stationary current. The pulsed CPB is directed at a specimen and a response of the specimen to the pulsed CPB is recorded. The recorded response to the pulsed CPB is a TEM image, a SEM image, or an energy spectrum of charged particles received from the specimen. In other examples, an optical or electrical stimulus is applied to the specimen and the response of the specimen to the optical or electrical stimulus is obtained at two or more relative delays between the optical or electrical stimulus and the pulse of the pulsed CPB.

[0010] An exemplary method for generating a CPB pulse involves directing the CPB to a beam blanker and selectively activating the beam blanker such that the CPB is blocked by an aperture.

[0011] The foregoing and other features of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings. [Brief description of the drawings]

[0012] [Figure 1] 1 illustrates a representative CPB system including a resonant beam deflector. [Figure 2A] 1 illustrates the generation of a typical CPB pulse. [Figure 2B] 1 illustrates the generation of a typical CPB pulse. [Figure 3A] 3A illustrates a representative CPB system for generating CPB pulses. As shown in FIG. 3A, a high brightness pulse and low average beam current are generated. In FIG. 3B, a lower brightness is available, but the average beam current is higher than in FIG. 3A. [Figure 3B] 3A illustrates a representative CPB system for generating CPB pulses. As shown in FIG. 3A, a high brightness pulse and low average beam current are generated. In FIG. 3B, a lower brightness is available, but the average beam current is higher than in FIG. 3A. [Figure 4] 1 illustrates an exemplary embodiment of a method for generating a CPB pulse. [Diagram 5] 1 illustrates another exemplary embodiment of a method for generating a CPB pulse. [Figure 6A] 1 illustrates a representative CPB system including nanorod field emitters. [Figure 6B] 1 illustrates an exemplary CPB system including a field emitter that provides a variable current using a variable drive applied to one or more of the emitter tip, suppressor electrode, or extractor electrode. [Figure 7A] 1 illustrates an exemplary CPB system for generating CPB pulses. [Figure 7B] 1 illustrates an exemplary CPB system for generating CPB pulses. [Figure 8] 1 illustrates another exemplary embodiment of a method for generating a CPB pulse. [Figure 9] 1 illustrates a representative computing environment for implementing any of the disclosed systems and methods. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Disclosed herein is an approach to modulating a charged particle beam (CPB), such as an electron beam, to generate a unique pulsed / continuous beam for use in TEM, SEM, electron spectroscopy, and other applications. With the disclosed modulation strategy, both the time resolution and background suppression can be significantly improved in ultrafast TEM applications, while the average CPB current in the microscope can be easily controlled below the safety limit of X-ray radiation, even in applications using high CPB current or high brightness. Any feature of the examples described below can be combined with features of any other example, and specific embodiments are selected for illustration. In some examples, the pulsed CPB method and apparatus are used in a CPB microscope, and in some cases, parts of the CPB column (CPB lens, astigmatism, specimen stage, vacuum chamber, etc.) are omitted for convenience, although such components and / or SEM or TEM systems are typically included. Additionally, in the disclosed examples, the CPB is directed through an aperture defined in an aperture plate. However, a separate aperture plate is not required, and one or more CPB optical elements, such as a CPB lens, can be used to define the aperture. An aperture is not required, and suitable beam obstruction can be obtained in the component in other ways, such as at the component edge. Furthermore, the aperture does not have to be circular, and can have any shape, such as oval, polygonal, elliptical, etc. The device used to deflect the beam and act as a beam blanker can be coupled to be unenergized, and the average CPB current is maintained at a suitable value outside of the area that is not properly x-ray shielded. For example, to generate a CPB pulse, the beam blanker can be driven to deflect the CPB so that it is conducted to the specimen. In such a configuration, the CPB is normally blanked and then unblanked to generate the CPB pulse. As used herein, a beam blanker selectively allows a portion of the CPB to propagate to a target of interest. Typical examples are electrostatic deflectors, such as deflection plates and resonant RF cavities.With the disclosed methods, systems, and apparatus, the average CPB current can be controlled based on one or more limitations, such as limitations related to x-ray safety.

[0014] Example 1 1, an exemplary CPB system 100 includes a charged particle beam (CPB) emitter 102 proximate to an extractor or extractor electrode 104 positioned to generate or control CPB emission from the CPB emitter 102. In some embodiments, the CPB is generated using field emission, and the CPB emitter 102 and extractor 104 form a field emitter device. For example, the CPB emitter 102 may include a LaB 6 The CPB 106 from the CPB emitter 102 is directed along an axis 105 and focused by a gun lens 108 as controlled by a voltage or other electrical signal from a gun lens drive 123 to form a focused beam 118. The aperture plate 112 includes an aperture 113 disposed along the axis 105 to conduct the focused beam 118 to a resonant cavity deflector 110. The aperture plate 112 is typically disposed in an X-ray shielded region defined by an X-ray shield 109. The resonant cavity driver 126 is disposed to apply a voltage to the resonant cavity deflector 110 at or near a resonant frequency to deflect the focused CPB 118. The aperture plate 120 is disposed to block at least a portion of the focused CPB 118 in response to a deflection produced by the resonant cavity deflector 110. The CPB beam portion transmitted by aperture plate 120 is focused, scanned, or otherwise processed by CPB optics 122 and then delivered to a specimen 124 .

[0015] The controller 130 is coupled to an extractor driver 134, which provides a pulsed extraction signal (typically an extraction voltage) to the extractor 104. The relative phase of the pulsed extraction signal can be set by the controller 130, or a separate phase adjuster 135 can be provided. The controller 130 is also coupled to the resonant cavity driver 126, and a separate phase adjuster 136 can be provided, or the resonant cavity drive signal phase can be established directly by the controller 130. Additionally, the controller 130 is coupled to the CPB optics 122. X-ray interlock logic 131 or other control can be provided such that the CPB is energized or not energized as appropriate for x-ray safe operation, regardless of user or other input.

[0016] In the embodiment of FIG. 1, a pulsed laser 142 is positioned to direct a laser pulse 140 or a continuous or modulated laser beam to the sample 124. A phase adjuster 150 can be provided so that the extractor pulse, the resonant drive signal, and the laser pulse are properly synchronized. In some embodiments, the relative phase of the CPB pulse and the laser pulse is scanned to generate a sample response as a function of relative delay. The relative phase can be conveniently established based on a clock signal provided by either the pulsed laser 142, the controller 130, or the resonant driver 126. In some cases, phase control of a pulsed laser is relatively difficult, and the phase of the electrical drive signals provided to the extractor and the resonant cavity are adjusted.

[0017] In some embodiments, a beam deflector such as resonant cavity beam deflector 110 and associated apertures are positioned such that, without the beam deflector in operation, CPB current in areas lacking adequate x-ray shielding is limited to avoid exposure to dangerous levels of x-rays. For example, the undeflected CPB can be blocked by an aperture plate in the x-ray shielded area and energization of the beam deflector used to direct the CPB through the aperture to the target.

[0018] Example 2 2A, the CPB current 202 as a function of time is graphed, illustrating the pulsed portion 204, pre-pulse portion 206, and post-pulse portion 208 at respective time intervals 205, 207, 209. The CPB current at pulse portion 204 can be substantially higher than the CPB current at pre-pulse portion 206 or post-pulse portion 208. The beam blanking or beam gating signal 210 is timed so that the pulsed portion 204 of CPB remains available or is conducted to additional CPB optics and specimen while the pre-pulse portion 206 and post-pulse portion 208 are decaying as shown at 211, 213, respectively. In this way, the contrast ratio (CPB pulsed current / CPB non-pulsed current) is increased and the CPB pulse duration is nearly unchanged.

[0019] 2B, the CPB current 252 as a function of time is graphed, illustrating the pulsed portion 254, pre-pulse portion 256, and post-pulse portion 258 at respective time intervals 255, 257, 259. A beam blanking or beam gating signal 260 is timed such that the pulsed portion 254 of the CPB is windowed in time to shorten the pulse duration. The CPB pulse portions 262, 264 and the pre- and post-pulse portions 256, 258 are attenuated. In this manner, the CPB pulse duration can be shortened and in some cases the contrast ratio also increased.

[0020] By controlling the beam gating or beam blanking to produce the CPB currents illustrated in FIG. 2A or FIG. 2B, the average beam current is reduced, providing a CPB pulse of shorter duration or a CPB pulse with a higher contrast ratio while increasing x-ray safety.

[0021] Example 3 3A, the CPB system 300 includes a CPB emitter 302 disposed proximate to an extraction electrode 304. A gun lens 306 is disposed to receive the emitted CPB and to form a CPB focus 308, generating an expanded beam 310. The gun lens 306 can also be actuated to generate a focused CPB elsewhere along an axis 305. An aperture plate 312 is disposed within an X-ray shield 314 to receive the expanded beam 310 and to transmit an aperture beam 317 through an aperture 313. The total beam current in the aperture beam 317 is reduced from that of the expanded beam 310, and the portion of the CPB that is not transmitted is directed to the aperture plate within the X-ray shield region. However, the emitted beam current from the CPB emitter 302 can be selected to provide a selected brightness (current / area / steradian), typically high brightness, and by aperturing the expanded beam 310, the average or continuous CPB current can be controlled. In such an arrangement, the average CPB current outside the x-ray shielded region can be reduced and the CPB current is apertured or attenuated within the shielded region, thus improving x-ray safety.

[0022] In addition to providing high CPB brightness in a continuous beam, CPB pulses can also be generated. The aperture beam 317 is directed to a beam blanker 316 which can direct the aperture beam 317 to an aperture plate 318 defining an aperture 319 so that some or all of the aperture beam 317 can be further attenuated and focused or processed by other optical elements such as one or more CPB lenses, deflectors, or objective lenses 320 and directed to a specimen 322.

[0023] In the embodiment of FIG. 3A , the controller 324 controls an extraction voltage V ext, coupled to extraction electrode 304 to apply a lens control voltage V to the CPB source 304. In other embodiments, one or more similar CPB optical elements are positioned and controlled to regulate the current from a CPB source, such as a field emitter, thermal source, pulsed laser-based source, or other CPB source. Controller 324 also controls a lens control voltage V to focus the emitted CPB as needed. gun Apply a voltage V to the gun lens. blanking to the beam blanker 316 to apply a voltage V objective 3A. As shown, control is applied as a control voltage, but can also be provided by other electrical signals. In addition, one or more signal sources (such as voltage sources) are arranged to provide the necessary voltages or other electrical signals, typically as directed by the controller 324, but are not shown in FIG. 3A. However, in some cases, the controller 324 can include a digital-to-analog converter (DAC), which can provide the necessary voltages. The controller 324 can also be coupled to one or more of the aperture plates 312, 318 such that the incident beam current is measured. Alternatively, one or more other CPB detectors can be provided elsewhere along the axis 305.

[0024] The gun lens 306 can be used to condition the CPB current available for delivery to the specimen. A suitable gun voltage V is applied to produce a beam that is significantly attenuated (i.e., sufficiently divergent) by the aperture plate 312. gunWhen is applied, the average beam current outside the X-ray shielding region 315 can be made low enough to reduce X-ray radiation outside the shielding region 315. In other cases, the gun lens 306 produces a CPB that is less divergent or focused at the aperture 313. In addition, the controller 324 can measure the beam current, for example, at the aperture plate 318, to verify that the CPB current is appropriate. One or more of the gun lens 306, the extractor electrode 304, and the beam blanker 316 can be controlled to maintain an appropriate CPB current.

[0025] The beam blanker 316 can be driven to set the CPB pulse duration, increase the CPB on / off ratio (contrast ratio), or otherwise modify the CPB incident on the specimen 322. In the embodiment of Figure 3A, high brightness is available, the average beam current is controlled, and the CPB pulse can be generated and shaped using one or both of the CPB source 302 and the beam blanker 316.

[0026] In yet another embodiment, beam confinement is performed with an aperture plate located along the CPB column prior to significant beam acceleration. In this way, a high average beam current is incident on the aperture plate at a relatively low energy, resulting in reduced x-ray production.

[0027] Example 4 In the embodiment of FIG. 3A, the relatively high CPB current is reduced by expanding the CPB and conducting only a portion of it. In FIG. 3B, the CPB system 350 is configured to generate a lower average beam current and to increase the beam current during a CPB pulse. As shown in FIG. 3B, the CPB system 350 includes a CPB emitter 352 disposed proximate to an extraction electrode 354. A gun lens 356 is disposed to receive the emitted CPB and form a CPB 355 directed through an aperture 358 defined in an aperture plate 360. In this embodiment, the aperture 358 forms the CPB 355 and tends to slightly or moderately attenuate the CPB 355, but substantial attenuation is not necessary to regulate the x-ray emission since the average beam current is appropriately controlled. The aperture plate 360 ​​can be disposed within an x-ray shielded region 362, as defined by an x-ray shield 364. From the aperture 358, the beam propagates to a beam blanker 370, which includes one or more deflection plates. Typically, the CPB 355 is focused near or within the beam blanker 370. An additional aperture 372 defined in the aperture plate 374 and an objective lens 376 form the CPB for delivery to the specimen 380. In the arrangement of FIG. 3B, a relatively low average CPB current is used to reduce x-ray emission, and the CPB current is pulsed using the extractor 354 in response to voltage(s) applied by the beam blanker / extractor driver 382. The beam blanker 370 is driven to increase the on / off ratio, further limit the pulse duration, or both.

[0028] In the embodiment of FIG. 3B , the beam blanker / extractor driver 382 controls the extraction voltage V that regulates the CPB emission from the CPB emitter 352. ext, to the extraction electrode 354 and to the beam blanker 370. In other embodiments, one or more similar CPB optical elements are similarly positioned and controlled to regulate current from a CPB source, such as a field emitter, heat source, or other CPB source. Other lenses and elements can be similarly coupled to appropriate control voltage sources, and each, or some, of the components can use individual driver circuits, as is convenient.

[0029] Either of the CPB systems 300, 350 can be operated to provide a high intensity, low average current CPB.

[0030] Example 5 4, a method 400 of providing pulsed CPB to a specimen includes selecting a pulse duration, repetition rate, and pulse current at 402. A contrast ratio is selected at 404, and a pulse source is selected at 406. For example, a CPB emitter can be selected at 408, and an appropriate CPB extractor pulse amplitude and duration is selected at 410. At 412, the selected CPB extractor pulse is applied and the specimen is exposed to the pulsed CPB.

[0031] Alternatively, the pulse duration is defined at 420 by a selected beam blanker and one or both of the appropriate beam blanker drive amplitude and duration are selected at 422. It is determined at 424 whether the CPB emitter should also be pulsed. If so, an extractor pulse drive amplitude and / or duration is selected at 426 and the selected extractor drive and beam blanker drive are applied at 428 to expose the specimen to the pulsed CPB. If the emitter is not pulsed, then at 430 the selected beam blanker drive is used to deliver the pulsed CPB to the specimen.

[0032] In some cases, the emitter is pulsed and beam blanking is used to set a selected pulse duration and on / off ratio at 440. In this case, an extractor drive amplitude and duration is selected at 442 and a beam blanker drive amplitude and duration is selected at 444. The extractor drive and blanker drive are applied at 446 for exposure of the specimen.

[0033] In further embodiments, the relative timing or phase of the extractor drive and the blanker drive can be selected. For example, if the extractor generates a gradually increasing CPB current, the blanker drive can be applied after the CPB current reaches an appropriate value. In general, the relative timing can be selected to generate current pulses that are substantially the same from pulse to pulse, vary in a predictable manner, or otherwise modulate the CPB.

[0034] Method 400 of FIG. 4 refers to controlling the CPB current by varying an extractor drive, such as an applied voltage. Other CPB current sources can be modulated in other ways, with extractor-based modulation of a field emitter being a convenient and practical example. In addition, the average CPB current can be estimated, and drive values ​​selected, such that the CPB current does not tend to generate undesirable levels of x-ray radiation in any area of ​​the CPB device, particularly not including the x-ray shield.

[0035] Example 6 5, a CPB method 500 includes selecting an operating mode at 502 based on an intended average CPB current. In some cases, a low continuous CPB current is established, such as by an extractor, at 504. An appropriate extraction boost can be selected at 506 to generate a larger pulsed CPB current. If this "boosted" CPB current is associated with an average CPB current that is within predetermined limits, a corresponding CPB current can be generated at 510 such that the sample is exposed to CPB. If not, the beam current or extractor boost can be adjusted at 512 and re-evaluated at 508. If an appropriate CPB current cannot be achieved, a technician can be notified.

[0036] If a relatively high CPB current is selected at 520, the gun lens voltage or other gun controls are adjusted at 522 so that the CPB is attenuated, for example by directing a large area beam into the aperture. At 524, the selection of the continuous CPB current is generally sufficient for x-ray safe operation, but the CPB current can be evaluated to ensure that the average CPB current is within predetermined limits. If so, the sample is exposed at 510. Otherwise, the CPB current and extraction boost are modified at 526. If no suitable value is found, a technician can be notified.

[0037] Example 7 Referring to FIG. 6A, the CPB system 600 includes a CPB emitter 602 having field-emitting nanorods 604 that generate CPB as controlled by an extractor 606. A CPB deflector 608 deflects the CPB so that it is attenuated within an X-ray shielding region 616 defined by a housing 612. The CPB can be partially or completely blocked by an aperture plate 614 based on an applied deflection signal. In this embodiment, a deflected CPB 610 is generated in response to an applied deflection signal. A deflector driver 628 and a beam current driver 626 are coupled to the CPB deflector 608 and the extractor 606, respectively. An electrical or optical signal source 630 provides an electrical or optical stimulation signal 640 to the specimen S, and a phase controller 632 adjusts and controls the relative phase (delay) to provide a CPB pulse with an appropriate delay or advance with respect to the electrical or optical stimulation signal.

[0038] Typical nanorod field emitters have a length of less than 5 μm, such as 4 μm, 3 μm, 2 μm, 1 μm, or 0.5 μm or less, and a diameter of 300 nm or less, such as 200 nm, 150 nm, 100 nm, or 50 nm.

[0039] The beam current drive 626 generally provides a drive signal having a continuous component and a pulsed component. As described above, the CPB deflector 608 can improve the pulse contrast ratio or limit the pulse duration, or both. The increased contrast ratio can be particularly important in low pulse duty cycle applications, since the average CPB current can be substantially much greater than the pulsed CPB current. For example, for a pulsed to continuous current ratio of 100, a duty cycle of 100 can be achieved. -5In this application, the average continuous CPB current is 1000 times greater than the average pulsed current. In most cases, the average CPB current (CPB continuous and pulsed components) is controlled to be below a predetermined limit, such as an x-ray safety limit associated with the configuration of the CPB system 600. In some embodiments, the CPB deflector is not used and the drive signal from the beam current drive 626, and the resulting CPB, is sufficient. In the "high brightness" mode, the average CPB current is limited by expanding the CPB and attenuating the CPB at the aperture. In the "low brightness" mode, the average CPB current is limited by the extractor voltage and an appropriate low continuous current is produced.

[0040] Example 8 Referring to FIG. 6B, a CPB system 650 includes a CPB emitter 652 having a field emitter 654 that generates CPB from an emitter tip 656. The CPB current can be controlled by one or more voltages applied to the field emitter 654 or the emitter tip 656, as provided by an emitter drive 657. A suppressor electrode 658 is typically disposed about the field emitter 654 to suppress stray charged particle emissions, and an extractor electrode 660 is disposed to establish a voltage relative to the emitter tip 656 to induce a selected CPB current. As shown in FIG. 6B, any or all of the suppressor electrode 658, extractor electrode 660, and the field emitter 654 or emitter tip 656 can be controlled with the emitter drive 657 to generate a continuous component of CPB, or to generate a pulsed or other variable CPB component, or to generate both continuous and pulsed components. In some embodiments, one or more additional beam apertures can be disposed along the CPB system axis 699 and used to control one or both of the continuous and pulsed or variable CPB components. For example, an aperture 661 defined in an aperture plate 662 can be controlled with a modulator drive 664 to control the CPB current. Although the beam deflectors, x-ray shields, and other features of the CPB system shown in FIG. 6A can be used after the aperture 661, additional apertures can also be disposed in this portion of the CPB path. The embodiments of FIGS. 6A-6B can also provide beam modulation using a gun lens, although such lenses are not shown. In addition to the CPB modulation provided by driving one or more CPB lenses, deflectors, aperture plates, or other CPB optical elements, pulsed and / or continuous CPB radiation can be generated in response to illumination of an appropriate target with a continuous, pulsed, or modulated light beam or beams. Such CPB can be further modulated using CPB optical elements as needed.

[0041] Example 9 7A, the CPB system 700 includes a CPB source 701 that directs a CPB 702 to a CPB deflector 704, which is operable to generate a deflected CPB 706. A CPB lens 708 defines an aperture 709 through which the CPB 702 is directed to a specimen S. A deflector drive signal applied to the CPB deflector 704 can vary the deflection of the deflected CPB 706 such that the CPB 706 is selectively blocked by the CPB lens 708. The CPB conducted by the aperture 709 is thus modulated, typically on / off modulated, although other modulations can be generated based on the applied deflection signal. A current amplifier 718 is coupled to the specimen S and / or the CPB lens 708 to sense the CPB current. A controller 720 receives an indication of the sensed beam current from the current amplifier 718 and is coupled to generate or initiate drive signals for the beam deflector 704 and the CPB source 701 to control the CPB pulse generation.

[0042] 7B, the CPB system 700 of FIG. 7A is positioned such that the CPB 702 is substantially blocked by the CPB lens 708 and only the deflected beam 706 is transmitted by the aperture 709.

[0043] Example 10 8, an exemplary method 800 includes determining a maximum allowable CPB current at 802, typically a maximum average CPB current based on control of x-ray radiation. A gun lens is adjusted at 804 based on the allowable CPB current. A CPB pulse duration and contrast ratio is selected at 806, and at least one of a CPB blanker or a CPB source is pulsed at 808 to provide an appropriate CPB pulse.

[0044] Example 11 Figure 9 and the following discussion are intended to provide a brief, general description of an exemplary computing environment in which the disclosed technology may be implemented. Moreover, the disclosed technology may be practiced with other computer system configurations, including handheld devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, etc. The disclosed technology may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network.

[0045] 9, an exemplary system for implementing the disclosed technology includes a general purpose computing device in the form of an exemplary conventional PC 900 including one or more processing units 902, a system memory 904, and a system bus 906 coupling the one or more processing units 902 to various system components including the system memory 904. The system bus 906 can be any of a number of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The exemplary system memory 904 includes a read only memory (ROM) 908 and a random access memory (RAM) 910. A basic input / output system (BIOS) 912, containing the basic routines that help to transfer information between elements within the PC 900, is stored in the ROM 908. In the embodiment of FIG. 9, data and processor executable instructions for control, analysis, imaging, and other operational modes of the CPB system, including gun control, extractor drive signals, beam blankers or deflectors, and x-ray limits, are stored in memory portions 910A, 910B, 910C, and 910D, respectively.

[0046] The exemplary PC 900 further includes one or more storage devices 930, such as a hard disk drive for reading from and writing to a hard disk, a magnetic disk drive for reading from and writing to a removable magnetic disk, and an optical disk drive. Such storage devices may be connected to the system bus 906 by a hard disk drive interface, a magnetic disk drive interface, and an optical drive interface, respectively. The drives and associated computer-readable media provide non-volatile storage of computer-readable instructions, data structures, program modules, and other data for the PC 900. Other types of computer-readable media may store data accessible by a PC, such as magnetic cassettes, flash memory cards, digital video disks, and the like.

[0047] A number of program modules may be stored in storage device 930, including an operating system, one or more application programs, other program modules, and program data. A user may enter commands and information into the PC 900 through one or more input devices 940, such as a keyboard and a pointing device, such as a mouse. A monitor 946 or other type of display device is also connected to the system bus 906 via an interface, such as a video adapter.

[0048] The PC 900 may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer 960. In some embodiments, one or more network or communication connections 950 are included and one or more A / D or D / A converters 951, 963 are provided. The remote computer 960 may be another PC, a server, a router, a network PC, or a peer device or other common network node, and typically includes many or all of the elements described above with respect to the PC 900, although only a storage device 962 is illustrated in FIG. 9. The personal computer 900 and / or the remote computer 960 may be connected to logical local area networks (LANs) and wide area networks (WANs).

[0049] General Considerations As used in this application and the claims, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Furthermore, the term "includes" means "comprises." Furthermore, the term "coupled" does not necessarily exclude the presence of intermediate elements between the coupled items.

[0050] The systems, devices, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, both alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and devices are not limited to any particular aspect or feature or combination thereof, nor do the disclosed systems, methods, and devices require that any one or more particular advantages exist or problems be solved. While any theory of operation is for ease of explanation, the disclosed systems, methods, and devices are not limited to such theory of operation.

[0051] Although some operations of the disclosed methods are described in a particular order for convenient presentation, it is to be understood that this method of description encompasses reordering, unless a particular order is required by specific terms described below. For example, operations described in a sequence may in some cases be reordered or performed simultaneously. Furthermore, for simplicity, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and devices may be used with other systems, methods, and devices. In addition, the description may use terms such as "manufacture" and "provide" to describe the disclosed methods. These terms are high-level abstractions of actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible to those of ordinary skill in the art.

[0052] In some instances, values, procedures, or devices may be referred to as "lowest," "best," "smallest," etc. It will be understood that such descriptions are intended to indicate that a selection from among many functional options may be made, and that such a selection is not necessarily better, smaller, or otherwise preferable than other options.

[0053] The examples are described with reference to directions indicated as "above," "below," "upper," "lower," etc. These terms are used for convenience of explanation and do not imply a particular spatial orientation.

[0054] In the disclosed embodiments, the CPB and associated components are referred to as being arranged on-axis. Off-axis arrangements may also be used. The disclosed methods are typically implemented with processor-executable instructions, optionally with user input via a keyboard, mouse or other pointing device, voice recognition, or other types of input. The user's selections may be displayed in one or more menus on the display, and the user may be notified of the need for input via a visual and / or audible alarm on the display.

[0055] As noted in some embodiments, the CPB pulse can be provided using a combination of a CPB source pulse and a beam blanker or beam deflector pulse. The CPB pulse can be synchronized to an external reference signal, such as an optical or electrical signal, or an external signal can be synchronized to the CPB pulse. The CPB pulse can also exhibit a variable delay relative to the external reference signal. In some embodiments, the beam deflector is shown as a lumped circuit element, but a traveling wave beam deflector can also be used.

[0056] A CPB is said to be substantially attenuated for a beam current that is reduced by at least 25%, 10%, 5%, 2.5%, 1%, or less of the incident beam current. A CPB is said to be substantially transmitted for a transmitted beam where the beam current is at least 50%, 60%, 70%, 75%, 89%, 90%, or more of the incident beam current.

[0057] In view of the many possible embodiments to which the principles of the present disclosure may be applied, it should be recognized that the illustrated embodiments are preferred examples only and should not be construed as limiting the scope of the present disclosure.

Claims

1. 1. A charged particle beam (CPB) system comprising: a CPB source adapted to generate a CPB having a pulsed CPB component or a continuous CPB component, or both a pulsed CPB component and a continuous CPB component; a CPB lens positioned to receive the CPB from the CPB source; a controller coupled to the CPB lens, selecting either a first CPB focus or a second CPB focus, the first CPB focus being arranged to substantially attenuate the CPB at a beam-limiting aperture and the second CPB focus being arranged such that the CPB is substantially transmitted by the beam-limiting aperture; if the first CPB focus is selected, activating the CPB source to generate at least a continuous component of the CPB and directing the continuous component to a target; a controller configured to generate at least a pulsed component of the CPB and direct the pulsed component to the target when the second CPB focus is selected.

2. The CPB system of claim 1 , further comprising an aperture plate defining the beam-limiting aperture.

3. The CPB system of claim 1 , wherein the CPB source comprises a field emitter.

4. The CPB system of claim 3 , wherein the field emitters are LaB6 nanorods.

5. The CPB system of claim 3 , wherein the controller is coupled to an extraction electrode, a suppression electrode, or a CPB lens operable to establish a beam current of at least one of the pulsed CPB component and the continuous CPB component.

6. A CPB system as described in any one of claims 1 to 5, wherein the CPB source is operable to establish a beam current of the pulsed CPB component.

7. 7. The CPB system of claim 1, further comprising a beam blanker disposed to receive the CPB from the beam-limiting aperture, the controller operable to energize the beam blanker to selectively deflect the received CPB.

8. 8. The CPB system of claim 7, further comprising a blanking aperture plate defining a blanking aperture, the beam blanker operable to selectively deflect the CPB into the blanking aperture to block at least a portion of the received CPB.

9. The CPB system of claim 7 , wherein the beam blanker comprises an electrostatic deflector.

10. The CPB system of claim 7 , wherein the beam blanker comprises an RF resonant cavity.

11. The CPB system of claim 7 , wherein the controller is coupled to the CPB lens to focus the CPB onto the beam blanker.

12. 8. The CPB system of claim 7, further comprising an x-ray shield disposed about a CPB beam axis and defining an x-ray shielded region, the beam-limiting aperture being disposed within the x-ray shielded region.

13. 13. The CPB system of claim 12, wherein the CPB source is positioned to direct the CPB to be blocked by a blanking aperture when the beam blanker is not activated.

14. The CPB system of claim 12 , wherein the CPB lens is configured to generate a CPB focus disposed between the beam-limiting aperture and a blanking aperture.

15. 1. A CPB method comprising: selecting either a first CPB focus or a second CPB focus, the first CPB focus being positioned to substantially attenuate CPB at a beam-limiting aperture and the second CPB focus being positioned such that the CPB is substantially transmitted by the beam-limiting aperture; if the first CPB focus is selected, activating a CPB source to generate at least a continuous component of the CPB and directing the continuous component to a target; if the second CPB focus is selected, generating at least a pulsed component of the CPB and directing the pulsed component to the target.

16. 16. The method of claim 15, wherein the continuous component is generated using a field emitter in response to continuous actuation of an extractor, and the pulsed component is generated using pulsed actuation of one or more of the field emitter, the extractor, a suppression electrode, or a CPB lens.

17. directing a CPB portion associated with the pulsed component to a beam blanker; 17. The method of claim 16, further comprising selectively attenuating the pulsed components with the beam blanker to define a CPB pulse duration or a CPB contrast ratio, or both a CPB pulse duration and a contrast ratio.

18. 18. The method of any one of claims 15 to 17, further comprising generating a pulsed CPB using a beam blanker to establish a pulsed CPB pulse duration, a contrast ratio, or both a pulse duration and a contrast ratio when the second CPB focusing is selected.

19. The method according to any one of claims 15 to 18, wherein the beam-limiting aperture is arranged in an X-ray shielded area.

20. 1. A CPB method comprising: providing a CPB source including a field emitter and an extractor; positioning a CPB lens to receive CPB from the CPB source; disposing a beam-limiting aperture within the x-ray shielding region; providing a controller coupled to the CPB lens, the controller comprising: selecting either a first CPB focus or a second CPB focus, the first CPB focus being positioned to substantially attenuate CPB at a beam-limiting aperture and the second CPB focus being positioned such that the CPB is substantially transmitted by the beam-limiting aperture; if the first CPB focus is selected, activating a CPB source to generate at least a continuous component of the CPB and directing the continuous component to a target; if the second CPB focus is selected, generating at least a pulsed component of the CPB and directing the pulsed component to the target. A method comprising:

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