Particle-induced x-ray emission using light and heavy particle beams

Abstract

To provide an improved method of particle-induced X-ray emission (PIXE) analysis at relatively low ion beam energy.SOLUTION: A method of PIXE analysis comprises: (a) delivering a first ion beam from a first ion source onto an area of a sample, where the first ion beam comprises ions having a first composition and having kinetic energy of 50 kilo-electron-Volts (keV) or less; (b) simultaneously with the delivery of the first ion beam onto the sample area, delivering a second ion beam from a second ion source onto the sample area, where the second ion beam comprises ions having a second composition and having kinetic energy of 50 keV or less; and (c) detecting X-rays that are emitted from the sample area in response to the simultaneous delivery of the first and second ion beams to the sample area.SELECTED DRAWING: Figure 7A

Description

Technical Field

[0001] The present invention relates to a focused ion beam apparatus and a method of using such an apparatus. More particularly, the present invention relates to elemental analysis of a sample using a method of particle-induced X-ray emission by two or more ion beams, wherein the first beam contains protons or other light ions and the second beam contains a different ion species, and both beams are directed at the specimen simultaneously or essentially simultaneously. The present invention may be implemented in a focused ion beam apparatus including both a stand-alone focused ion beam apparatus and a dual beam apparatus that also includes a scanning electron microscope function.

Background Art

[0002] Focused Ion Beam (FIB) instruments are important for sample preparation, nanofabrication, and materials analysis. Standalone FIB systems are well-known, but they are typically combined with Scanning Electron Microscope (SEM) components [1], and more recently, with femtosecond laser ablation system components, as components of dual-beam or triple-beam microscopes [2]. FIB instruments are advantageous in semiconductor manufacturing and processing applications, occupying a position intermediate between small-scale electron beam processing and large-scale bulk processing. The focused beam enables maskless processing of small-sized feature shapes that are inaccessible in bulk processing such as Reactive Ion Etching (RIE). In such applications, FIB systems offer significantly higher throughput than that provided by processing using electron beams, such as electron beam lithography and Focused Electron Beam Induced Processing (FEBIP) [3,4]. For this reason, FIB instruments are typically used in industrial applications such as semiconductor failure analysis, where cross-section formation, tomography, or TEM lamella preparation is required on a relatively small scale and high throughput is fundamental for cost reasons. Focused ion beam systems are also finding their way into research and development in applications such as the preparation of biological samples for cryo-TEM analysis, the preparation of samples for atom probe tomography, or the manufacture of optical elements such as solid immersion lenses. Thus, FIB instruments are ubiquitous and can be found in numerous factories and laboratories around the world [3,5,6,7].

[0003] The FIB device is similar to a scanning electron microscope and may be used in a similar manner to a scanning electron microscope. In any operation of such a device, a tightly focused beam of charged particles is scanned or rastered across the surface of the target sample. The impact of the beam's energy on the surface of the sample induces either backscattering of particles from each respective focus or the emission of secondary charged particles (ions or electrons). The particles backscattered or emitted from each respective point may be detected by a particle detector that provides a measure of the relative amount of particles detected from each point. The number of such particles that can be detected, and thus the signal intensity, may depend on the topography (microstructure, topography) and composition of the sample. In this way, a map of the topography and / or composition of the sample may be developed. However, while an SEM uses a focused electron beam to image a sample, an FIB instead uses a focused beam of ions. Due to this difference in beam composition, an FIB device generates an image with somewhat lower resolution than an SEM image and, in contrast to an SEM device, may cause damage to the sample through the sputtering process. Nevertheless, the sputtering process may be advantageously used in micro-etching or micro-milling applications. Thus, many dual-beam systems comprise both FIB components or subsystems and SEM components or subsystems. In such dual-beam systems, the SEM portion may be used to monitor the micro-etching or micro-milling procedures performed by the FIB portion by its imaging capabilities.

[0004] Particularly interesting for the present disclosure is the technique of Particle Induced X-Ray Emission (PIXE). This technique is ideal for trace element analysis and, in particular, at a sensitivity of 100 - 500 ppm, for energy dispersive spectroscopy performed in a scanning electron When compared to similar X-ray spectroscopy techniques such as scanning electron microscope (SEM-EDS)

[10] , the sample composition can be determined to be within 1 ppm (parts per million). The PIXE analytical technique can be determined with a sensitivity of less than 1000 x 10 ...

[0005] Typically, the PIXE analysis technique uses a few megaelectron volts. PIXE is typically performed with incident particle energies of 1000 to 2000 electron-Volts (MeV) because the x-ray production cross section increases significantly at such high energies.

[13] The optimal energy range for PIXE has been found to be 3 MeV, where the x-ray production cross section is maximized while background contributions remain sufficiently low.

[14] However, these high primary ion energies have so far restricted the use of the PIXE technique to particle accelerator facilities, which are limited in terms of availability and cost. As a result, the PIXE technique may currently be somewhat inaccessible to the general laboratory user.

[0006] The ability to perform PIXE on a clustered ion beam device represents a major step in the advancement of PIXE technology, opening up PIXE's availability to a variety of additional equipment and providing a complementary technology to SEM-EDS, thereby giving significantly improved sensitivity to trace elements. U.S. Patent Application No. 17 / 728,869, filed on April 25, 2022, by the same applicant and co-pending, describes a new method of particle-induced X-ray emission called Very Low Energy PIXE (VLE-PIXE). The inventors of this co-pending application have made the surprising discovery that the number of X-ray photons emitted from a patch of a sample irradiated with a flux of hydrogen ions (H + ) is significantly enhanced by irradiating the same patch of the sample simultaneously or nearly simultaneously with a flux of heavy ions (Ar + , Kr + , Xe + , etc.), and that it may thus be detected, with the kinetic energy of the incident particles being ≦50 keV. This very low energy range makes PIXE analysis available for standard commercially available FIB equipment. The inventors of U.S. Patent Application No. 17 / 728,869 have shown that X-ray signal enhancement requires the simultaneous interaction of both light and heavy ions with the sample. However, the exact electronic mechanism by which the X-ray signal is enhanced remains an area of active research.

[0007] To demonstrate the VLE-PIXE phenomenon, the inventors of U.S. Patent Application No. 17 / 728,869 utilized a well-known FIB apparatus as described in U.S. Patents Nos. 8,076,650 and 8,822,913, which is equipped with an inductively-coupled plasma (ICP) ion source and a gas mixing device. Such an apparatus may be referred to as a Plasma Focused Ion Beam (PFIB) apparatus. According to the method taught in U.S. Patent Application No. 17 / 728,869, the ion source was modified for use with hydrogen.

[0008] Figures 1A to 1C are reproduced from the aforementioned co-pending U.S. patent application, and schematically show an example of an apparatus and a device capable of performing VLE-PIXE, as described in this application. In both apparatus 1a (FIG. 1A) and apparatus 1b (FIG. 1B), the FIB column 6 housed in the vacuum chamber 13 receives a mixture of ions including at least hydrogen ions (i.e., protons) 2 and ions 3 heavier than protons from an inductively coupled high-frequency plasma ion source 4 including a coiled electrode 5 to which a radio-frequency (RF) voltage waveform is applied during operation. The ions are generated from a gas received from the gas inlet pipe 11 and including a mixture of hydrogen containing hydrogen molecules 2m and at least one other non-hydrogen gas containing molecules 3m. These different gases may be provided in a purified form and mixed in appropriate proportions in a gas mixing manifold (see FIG. 1C) before being introduced into the gas inlet pipe 11. Alternatively, the gas may be provided in a pre-mixed form, thereby eliminating the need for a gas mixing manifold and any metering valves required for proportional mixing. When an appropriate RF voltage is applied to the coiled electrode 5, a plasma is ignited in the ion source 4 by a well-known method.

[0009] Continuing to refer to FIGS. 1A and 1B, ions 2, 3 are focused into beam 7 and guided along the length of FIB column 6 toward the beam focus on the surface of sample 8 by an electric and / or magnetic field applied to a series of ion optics 15 that may include ion lenses and ion guides. The ion optics accelerates the ions toward the sample and causes the ion beam, a mixture of light and heavy ions, to impact the sample surface with a kinetic energy of 50 keV or less. When both protons 2 and heavier ions 3 impact on the same area of sample 8, a measurable amount of X-ray photons 9 are generated, and these X-ray photons are derived by a well-known method of ejecting inner shell electrons of the sample's atoms and filling the resulting electron holes with electrons from high energy electron shells. The resulting X-rays are detected by energy dispersive X-ray detector 10 and recorded as an energy dispersive spectrum. In this way, the elemental composition of the sample may be determined. Apparatus 1b further includes a scanning electron microscope (SEM) column 12 within the vacuum chamber that is used to direct and focus an electron beam onto the sample. Images of areas of the sample may be created in a well-known manner using detection of secondary electrons or backscattered electrons by an electron detector (not shown).

[0010] FIG. 1C is a schematic diagram of an ion source 100 used in such a PFIB apparatus (see also U.S. Pat. No. 8,076,650 and U.S. Pat. No. 8,822,913). A predetermined gas mixture is provided by a gas mixing system 220. The gas mixture is provided from an external gas supply line 104 through a gas filter 106 into a plasma chamber 102 in a source tube 103 and then to a capillary 108 having a flow restrictor 110. Energy is supplied from an RF power supply 113 to the plasma chamber 102 by an antenna coil 114, and ions are extracted by an extraction electrode 120 through a source electrode aperture 116 in a source electrode 118. A split Faraday shield 121 reduces the capacitive coupling between the coil 114 and the plasma in the chamber 102 and reduces the energy spread of the extracted ions in the chamber 102. The power supply 113 preferably drives the antenna 114 in a “balanced” mode, i.e., the electrical phase shift across the antenna is adjusted to reduce the modulation of the plasma potential as described in U.S. Pat. No. 7,670,455. The balanced antenna preferably provides a null point in the radio frequency energy field in the plasma, which reduces the energy spread of the ions extracted from the plasma chamber 102.

[0011] The gas conductance into and out of the plasma chamber 102 passes through the flow restrictor 110 in the capillary (at the top of the source tube 103) and the aperture 116 (typically less than 1 / 4 mm in diameter) in the source electrode 118. A pump 122 connected to the gas supply line 104 via a valve 123 removes gas from the plasma chamber 102 via the capillary 108 and the gas supply line 104. An ion column pump (not shown) extracts gas from the plasma chamber 102 through the source electrode aperture 116.

[0012] The gas mixing system 220 receives gases from multiple gas sources, such as gas reservoir 130A, gas reservoir 130B, gas reservoir 130C, and gas reservoir 130D, and supplies the gases to the gas supply line 104 via corresponding valves 131A-131D. The valves 131A-131D are adjusted to provide a desired gas mixture to the gas supply line 104 to provide gases to the plasma chamber 106. Multiple valves 131A-131D may be opened simultaneously to provide multiple gas species to the plasma chamber simultaneously. The valves 131A-131D are preferably metering valves that control the ratio of gases to the gas inlet 104. The beam voltage source 132 provides a high voltage to the plasma in the chamber 102, and the extraction voltage source 134 provides a voltage to the extraction electrode 120. The extracted ions or electrons are focused by the focusing electrode 136. Further details of the focusing column and the sample chamber are not shown.

[0013] 2A and 2B show a comparison of the VLE-PIXE spectrum of the NIST standard reference material SRM654b using the method of U.S. Patent Application Serial No. 17 / 728,869 with a conventional SEM-EDS spectrum. Spectrum 351 in FIG. 2A is a 5 keV SEM-EDS spectrum of the same sample. This is the Xe + Ion-doped proton (H + 2A, which is a portion of a 24 keV VLE-PIXE spectrum of the same sample obtained using a single focused ion beam (shown as H / Xe ion beam) containing 10 keV ions. FIG. 2B shows the VLE-PIXE and SEM-EDS spectra of the same sample using a higher accelerating voltage. Spectrum 353 is the 30 keV SEM-EDS spectrum of the sample. Spectrum 354 is another portion of the 24 keV H / Xe VLE-PIXE spectrum. The SEM-EDS spectrum continues up to a value of 30 keV. However, only bremsstrahlung background is observed in the SEM-EDS spectrum at energies greater than 10 keV, and therefore the spectrum has been truncated for clarity.

[0014] Figures 3A and 3B show a comparison of the VLE-PIXE spectra and the conventional SEM-EDS spectra of NIST Standard Reference Material SRM1242 using the method of U.S. Patent Application No. 17 / 728,869. Spectrum 355 in Figure 3A is the 5 keV SEM-EDS spectrum of the sample. This is compared with spectrum 356 in Figure 3A, which is part of the 24 keV VLE-PIXE spectrum of the same sample obtained using a single beam containing doped protons. Figure 3B shows the VLE-PIXE spectra and the SEM-EDS spectra of the same sample using a larger acceleration voltage. Spectrum 357 is the 30 keV SEM-EDS spectrum of the sample, and spectrum 358 is another part of the 24 keV H / Xe VLE-PIXE spectrum. + Qualitatively, the VLE-PIXE spectra of Figures 2A and 2B, and Figures 3A and 3B can be characterized by the near-complete absence of bremsstrahlung background, as opposed to the broad and strong bremsstrahlung background typical of SEM-EDS spectra. An example of this bremsstrahlung background is labeled in Figure 2A. As a result, several peaks that cannot be identified in the SEM-EDS spectra are present in the VLE-PIXE spectra, leading to the identification of two additional minor components, Ni and Cu. Ni can be identified in the VLE-PIXE spectra based on the presence of the Ni Lα peak, as well as the Ni K

[0015] peak, and the K α peak. Cu can be identified in the VLE-PIXE spectra based on the Cu L β peak. α Based on the peak, it can be identified in the VLE-PIXE spectra.

[0016] Figures 4 to 6 show the analytical effectiveness of the VLE-PIXE technique described in US Patent Application No. 17 / 728,869. Figure 4 is a graphical representation of the X-ray signal enhancement factor for several X-ray peaks of the NIST Standard Reference Material SRM654b observed for light doping of the beam with nitrogen dopants, argon dopants, and xenon dopants, with respect to an ion beam consisting of more than 99% hydrogen. Figure 5 is a plot of the measured intensities of several prominent X-ray peaks generated by repeatedly exposing a sample of the NIST Standard Reference Material SRM654b to a hydrogen ion beam with a gradually decreasing proportion of Ar dopant, where the proportion of Ar is controlled by repeated plasma source evacuation cycles. Figure 6 is a histogram comparing the lower limits of detection of several elements in the NIST Standard Reference Material SRM654b determined by SEM-EDS with the lower limits of detection of the same elements determined by Xe-doped hydrogen ion VLE PIXE.

[0017] Based on the results of US Patent Application No. 17 / 728,869, the newly recognized ability to perform VLE-PIXE on a FIB microscope with a sensitivity comparable to that of conventional PIXE performed at much higher energies represents a significant leap forward in PIXE analysis. Nevertheless, the inventors recognized that additional modifications could reveal the full advantages of the VLE-PIXE technique. For example, the aforementioned patent application describes an experimental procedure by which a well-known FIB system comprising an inductively coupled high-frequency plasma ion source, an associated gas mixing manifold, and a FIB column can be modified to generate a single ion beam containing both light and heavy ion species focused on the sample surface. However, this document does not mention the possibility of using alternative ion delivery methods. Furthermore, H +Using hydrogen as a reagent gas to generate ions poses safety concerns. Proton beams are commonly used to induce X-ray emission during PIXE analysis, but Lestiani et al.

[15] recently demonstrated that helium particle-induced X-ray emission is more suitable for the detection of Na, Mg, Al, and Si than conventional proton-induced X-ray emission using a 4 MV Van de Graaff particle accelerator. Therefore, there is still a need for the development of further methods, devices, and gas compositions for the improvement of PIXE X-ray analysis at relatively low ion beam energies (e.g., up to 50 kilo-electron-volts) that are generally available using existing focused ion beam devices and dual beam devices including an electron microscope column in addition to a focused ion beam column.

Summary of the Invention

[0018] In light of the above background, the present inventors have addressed the above need in the art through the development of alternative beam delivery configurations and additional ion beam compositions. When PIXE signals are collected during FIB milling, this leads to the possibility of endpoint detection and real-time elemental mapping that can be utilized in 3D tomography workflows.

[0019] According to a first aspect of the present invention, there is provided a particle-induced X-ray emission (PIXE) analysis method, the method comprising: delivering, onto a region of a sample, a first ion beam comprising ions having a first composition and having a kinetic energy of the ions of 50 kilo-electron-volt (keV) or less from a first ion source; simultaneously with the delivery of the first ion beam onto the sample region, delivering, onto the sample region, a second ion beam comprising ions having a second composition and having a kinetic energy of the ions of the second ion beam of 50 kilo-electron-volt (keV) or less from a second ion source; Detecting X-rays emitted from the sample region in response to the simultaneous delivery of the first and second ion beams to the sample region.

[0020] According to a second aspect of the present invention, a second method of particle-induced X-ray emission (PIXE) analysis is provided, the second method comprising: Delivering a plurality of pulses of first ions having a first composition from a first ion source, the first ions being incident on a region of the sample, the kinetic energy of the first ions being 50 kiloelectron volts (keV) or less; Simultaneously with the delivery of the plurality of pulses of first ions onto the sample region, delivering a plurality of pulses of second ions from a second ion source, the second ions having a second composition, the kinetic energy of the ions in the second ion beam being 50 keV or less, the second ion beam being incident on the sample region; Detecting and measuring X-rays emitted from the sample region in response to the collision of the pulses of the first and second ions with the sample region.

[0021] According to a third aspect of the present invention, an analytical apparatus is provided, the analytical apparatus comprising: A first ion beam column configured to deliver a first ion beam including ions having a first composition from a first ion source onto a region of a sample, such that the delivered ions have a kinetic energy of 50 kiloelectron volts (keV) or less; A second ion beam column configured to deliver a second ion beam including ions having a second composition from a second ion source onto the sample region simultaneously with the delivery of the first ion beam onto the sample region, such that the delivered ions of the second ion beam have a kinetic energy of 50 keV or less; An X-ray detector configured to detect X-rays emitted from the sample region in response to the simultaneous delivery of the first and second ion beams to the sample region. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and various other aspects of the present invention will become apparent from the following description with reference to the accompanying drawings, which are given by way of example only and are not necessarily drawn to scale.

Figure 1A

Figure 1B

Figure 1C

Figure 2A

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Figure 3A

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Figure 7A

Figure 7B

Figure 8A

Figure 8B

DETAILED DESCRIPTION OF THE INVENTION

[0023] The following description is presented to enable a person skilled in the art to make and use the invention and is provided in the context of a particular application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art, and the general principles herein may be applied to other embodiments. Accordingly, the invention is not intended to be limited to the embodiments and examples shown, but is to be accorded the widest possible scope consistent with the features and principles shown and described. To gain a more thorough and complete understanding of the features of the invention, reference should be made to FIGS. 1A-18 in conjunction with the following description.

[0024] In the description of the invention herein, unless otherwise understood or stated implicitly or explicitly, words in the singular form shall include their plural equivalents, and words in the plural form shall include their singular equivalents. Further, unless otherwise understood or stated implicitly or explicitly, for any given component or embodiment described herein, any of the possible candidates or alternatives listed for that component may generally be used individually or in combination with one another. Additionally, it should be understood that the figures shown herein are not necessarily drawn to scale, and some of the elements may be drawn merely to clarify the invention. Also, reference numerals may be repeated in the various figures to indicate corresponding or similar elements. Additionally, unless otherwise understood or stated implicitly or explicitly, any listing of candidates or alternatives is merely illustrative and not limiting.

[0025] FIG. 7A is a schematic diagram of a first system 200a for performing ultra-low energy particle-induced X-ray emission (VLE-PIXE) measurements according to the present teachings. System 200a includes a first ion beam column 206a and a second ion beam column 206b disposed within a vacuum chamber 213. Each ion beam column includes a respective ionization source (not shown) that generates ions from a received reagent material. For example, FIG. 7A shows delivering two gaseous reagent materials 202m, 203m having different compositions to ion beam columns 206a, 296b, respectively, through gas inlet tubes 211a and 211b. In some embodiments, gaseous reagent material 202m may be selected from hydrogen, helium, and mixtures thereof, and gaseous reagent material 203m may be selected from nitrogen, noble gases, and various mixtures thereof. The non-shown ion sources of the two columns generate ions 202 and 203 from reagent materials 203m and 202m, respectively. Each ion source may include any suitable type of ion source, such as an inductively coupled high frequency plasma ion source, an electron impact ionization source, etc. The two ion sources need not be of the same type.

[0026] Each ion beam column, in addition to an ion source, directs each set of generated ions 202, 203 as respective ion beams 207a, 207b through respective columns 206a, 206b toward a common target area on a sample 208, and includes a plurality of accelerator electrodes, ion condenser lenses, apertures, and / or deflection lenses. Further, the ion optics of each ion beam column 206a, 206b may be operated to remove ions other than a desired charge state from each ion beam 207a, 207b. Generally, though not necessarily, the ion beam column includes a focused ion beam (FIB) column. In such a case, each ion beam column also includes one or more objective lenses that may be operated to focus the ion beam onto the target area. Otherwise, when the column is not an FIB column, the beam directed at the sample may be collimated (parallelized) or divergent, and need not be focused. By not operating the focusing lens, the same effect can be achieved using an FIB column. A parallel or divergent ion beam may be used to interact one or more ion beams with a specific area of interest on the sample surface. The beam density of ions delivered onto a given sample area may also be controlled using a parallel or divergent beam.

[0027] System 200a (FIG. 7A) also includes an X-ray detector 210 configured to detect X-ray radiation from a target area of a sample 208 stimulated by simultaneous or near-simultaneous collisions of ion beams 207a, 207b of different compositions onto the target area. As described by the inventors of the aforementioned U.S. Patent Application No. 17 / 728,869, the amount of X-ray photons detected during such operation is generally significantly greater than that detected by colliding either one of the two beams separately. Further, the amount of X-ray photons detected during simultaneous or near-simultaneous collisions of the two beams 207a, 207b is significantly greater than the algebraic sum of the X-ray photons detected by separate collisions of the two ion beams with the sample.

[0028] To investigate the X-ray spectral effects of "near-simultaneous" collisions of two ion beams onto a target area, the two ion beams 207a, 207b may be pulsed, and each ion beam pulse includes a packet of ions in which the irradiation from the ion beam column is temporally separated from both the previous leading packet and the subsequent trailing packet. The pulses may be generated by operating deflection electrodes (not shown) within each ion beam column so as to periodically blank each ion beam. Considering the travel time from the ion exit of each column to the target area, the emission times of the packets from the two columns to the target area may completely overlap, partially overlap, or not overlap at all. By varying the timing of the two sets of pulses, various phase shifts of the pulse arrival waveforms may be introduced. These phase shifts may be adjusted to maximize the resulting X-ray emission signal.

[0029] System 200a further includes one or more computers or electronic controllers 230 that are electrically coupled to a column (e.g., to an ion source, ion lenses, and other electrodes thereof), to an X-ray detector 210, and to other components not shown (e.g., an actuator for moving a sample stage, a vacuum pump, etc.) for the purpose of performing an analysis procedure. In particular, the one or more computers or electronic controllers 230 may include or have access to software or firmware that enables the system to perform VLE-PIXE analysis according to the methods taught herein. Thus, the one or more computers or electronic controllers 230 may include or have access to a non-transitory computer-readable medium that includes instructions that, when executed by one or more hardware processors, operate to perform the method. For example, the instructions may, when executed, control, among other things, the phase shift between the pulse arrival time waveforms of two pulsed ion beams delivered to a common area of a sample. Further, the instructions may, when executed, receive and analyze signals received from detector 210 and adjust the phase shift to maximize the signal.

[0030] FIG. 7B is a schematic diagram of a second system 200b for performing VLE-PIXE measurements according to the present teachings. System 200b differs from system 200a (FIG. 7A) in that it further includes an electron microscope column 212 within a vacuum system 213. System 200b provides an additional capability over system 200a to mill a sample using at least one of ion beam columns 206a, 206b and then examine the progress of the milling at high magnification using electron microscope column 212.

[0031] FIG. 8A is a flowchart of a first method 300 for performing VLE-PIXE measurements according to the present teachings. Step 302 of method 300, which is the first step, includes delivering a beam of first ions (e.g., ion beam 207a shown in FIG. 7A) from a first ion beam column (e.g., column 206a shown in FIG. 7A) onto an area of the sample surface with an incident kinetic energy of 50 keV or less. In step 304, a beam of second ions (e.g., ion beam 207b) from a second ion beam column (e.g., column 206b) is delivered onto the same area of the sample surface with an incident kinetic energy of 50 keV or less. Thus, steps 302 and 304 are performed simultaneously. The two ion beams may include different respective ion compositions and may also include different ion charge states.

[0032] Step 306 includes detecting X-rays emitted from the sample area simultaneously with the delivery of the first and second ion beams to the sample area. Thus, steps 302, 304, and 306 are all performed simultaneously. Steps 308 and 310 are optional adjustment steps that may be performed either simultaneously with or subsequent to the performance of steps 302, 304, and 306. In step 308, at least one of the first and second ion beams is focused and / or defocused to maximize the detected X-ray signal. In step 310, the angle between the first ion beam 207a and the second ion beam 207b may be adjusted to maximize the detected X-ray signal. This step may be performed manually. Alternatively, step 310 may be performed automatically if at least one of the ion beam columns is fixed to a movable mounting structure (not shown) positioned under the control of a motor or actuator under the control of one or more computers or electronic controllers 230. Following the adjustment, the execution of the method may be restarted (or continued) with the adjusted settings to perform further simultaneous execution of steps 302, 304, and 306.

[0033] FIG. 8B is a flowchart of a second method 350 for performing VLE-PIXE measurements according to the present teachings. Method 350 differs from method 300 (FIG. 8A) in that method 350 is associated with the delivery of a first and second plurality of ion pulses (i.e., pulsed ion beams) to a sample region. Thus, method 350 includes one additional optional adjustment step 359, where this adjustment is related to the phase difference between a waveform corresponding to the first plurality of pulses and another waveform corresponding to the second plurality of pulses.

[0034] The description included in this application is intended to serve as a basic description. The present invention is not intended to be limited by the specific embodiments described herein, which are intended as a single illustration of the individual aspects of the present invention. Functionally equivalent methods and components are within the scope of the present invention. Various other modifications of the present invention will become apparent to those skilled in the art from the foregoing description and the accompanying drawings, in addition to those shown and described herein. The specific numerical values of the device operation parameters presented herein are provided as typical operation parameters that are determined for a particular device and are not intended to be limiting in any way.

[0035] List of References [1] Young, Richard J., and Mary V. Moore. Dual-beam (FIB-SEM) systems. Introduction to focused ion beams. Springer, Boston, MA, 2005. 247-268. [2] McLean P Echlin, Marcus Straw, Steven Randolph, Jorge Filevich, and Tresa M Pollock. The TriBeam system: Femtosecond laser ablation in situ SEM. Materials Characterization, 100:1-12, 2015. [3] Yongqi Fu and Kok Ann Bryan Ngoi. Focused ion beam direct fabrication of micro-optical elements: features compared with laser beam and electron beam direct writing, 2004. [4] Lucille A Giannuzzi et al., Introduction to focused ion beams: instrumentation, theory, techniques and practice. Springer Science & Business Media, 2004. [5] Lucille A Giannuzzi and Frederick A Stevie. A review of focused ion beam milling techniques for TEM specimen preparation. Micron, 30(3):197 - 204, 1999. [6] Richard Young, C Rue, S Randolph, C Chandler, G Franz, R Schampers, A Klumpp, and L Kwakman. A comparison of xenon plasma FIB technology with conventional gallium LMIS FIB: imaging, milling, and gas - assisted applications. Microscopy and Microanalysis, 17(S2):652 - 653, 2011. [7] TL Burnett, Kelley, B Winiarski, L Contreras, M Daly, A Gholinia, MG Burke, and PJ Withers. Large volume serial section tomography by Xe Plasma FIB dual beam microscopy. Ultramicroscopy, 161:119 - 129, 2016. [8] Sven AE Johansson and Thomas B Johansson. Analytical application of particle induced X-ray emission. Nuclear Instruments and Methods, 137(3):473-516, 1976. [9] CG Ryan. Quantitative trace element imaging using PIXE and the nuclear microprobe. International Journal of Imaging Systems and Technology, 11(4):219-230, 2000.

[10] Dale Newbury, Nicholas Ritchie, Michael Mengason, and Keana Scott. SEM / EDS Trace Analysis: Limits Imposed by Fluorescence of the Detector. Microscopy and Microanalysis, 23(S1):1026-1027, 2017.

[11] Rainer Siegele, David D Cohen, and Nick Dytlewski. The ANSTO high energy heavy ion microprobe. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 158(14):31-38, 1999.

[12] A Denker, J Opitz Coutureau, M Griesser, R Denk, and H Winter. Nondestructive analysis of coins using high-energy PIXE. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 226(1-2):163-171, 2004.

[13] K Ishii and S Morita. Theoretical estimation of PIXE detection limits. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 34(2):209-216, 1988.

[14] Keizo Ishii and Susumu Morita. Continuous backgrounds in PIXE. International Journal of PIXE, 1(01):1-29, 1990.

[15] Lestiani, Diah Dwiana, Sung Kijin, Muhayatun Santoso, and Ikuji Takagi. "Helium and Proton Particle-Induced X-Ray Emission (PIXE) for Characterization of PM2.5 from Surabaya, Indonesia." Analytical Letters 2023, 1-14.

Claims

1. 1. A particle induced x-ray emission (PIXE) analysis method comprising: delivering a first ion beam from a first ion source onto a sample region, the first ion beam including ions having a first composition, the ions having a kinetic energy of 50 kiloelectron volts (keV) or less; concurrently with the delivery of the first ion beam onto the sample region, delivering a second ion beam from a second ion source onto the sample region, the second ion beam comprising ions having a second composition, the kinetic energy of the ions of the second ion beam being less than or equal to 50 kiloelectron volts (keV); and detecting x-rays emitted from the sample region in response to the simultaneous delivery of the first and second ion beams to the sample region.

2. The PIXE analysis method of claim 1 , further comprising focusing at least one of the first and second ion beams onto the sample region.

3. 2. The PIXE analysis method of claim 1, further comprising adjusting an angle between the first ion beam and the second ion beam, whereby a magnitude of a detected X-ray signal is maximized by said adjusting.

4. 4. The PIXE analysis method according to claim 1, wherein the first ion beam comprises either protons or helium ions, or a mixture thereof, and the second ion beam comprises ions having a larger mass than the ions of the first ion beam.

5. 5. The PIXE analysis method of claim 4, wherein the second ion beam comprises ions of any of nitrogen, argon, or xenon, or a mixture thereof.

6. 4. The PIXE analysis method according to claim 1, wherein the first ion beam is delivered from a first focused ion beam column and the second ion beam is delivered from a second focused ion beam column.

7. 1. A particle induced x-ray emission (PIXE) analysis method comprising: delivering a plurality of pulses of first ions from a first ion source onto a sample region, the first ions including ions having a first composition, the kinetic energy of the first ions being less than or equal to 50 kiloelectron volts (keV); concurrently with the delivery of the multiple pulses of the first ions onto the sample region, delivering multiple pulses of second ions from a second ion source onto the sample region, a second ion beam having a second composition and the kinetic energy of the ions of the second ion beam being less than or equal to 50 keV; detecting and measuring x-rays emitted from the sample region in response to the impingement of the pulses of the first and second ions on the sample region.

8. The PIXE analysis method of claim 7 further comprising focusing at least one of a plurality of pulses of first ions and a plurality of pulses of second ions onto the sample region.

9. 8. The PIXE analysis method of claim 7, further comprising adjusting an angle of incidence of at least one ion of the plurality of pulses of first and second ions onto the sample region, whereby a magnitude of a detected X-ray signal is maximized by said adjusting.

10. 10. The PIXE analysis method of claim 7, further comprising adjusting a phase difference between the multiple pulses of the first ions and the multiple pulses of the second ions, whereby a magnitude of a detected X-ray signal is maximized by said adjusting.

11. 10. The PIXE analysis method of claim 7, wherein the ions of the multiple pulses of first ions comprise either protons or helium ions, or a mixture thereof, and the ions of the multiple pulses of second ions have a greater mass than the ions of the multiple pulses of first ions.

12. 12. The PIXE analysis method of claim 11, wherein the ions of the plurality of pulses of second ions comprise ions of any of nitrogen, argon, or xenon, or mixtures thereof.

13. 1. An analytical apparatus comprising: a first ion beam column comprising a first ion source and configured to deliver a first ion beam comprising ions having a first composition onto a sample region, whereby the delivered ions have a kinetic energy of 50 kiloelectron volts (keV) or less; a second ion beam column comprising a second ion source and configured to deliver a second ion beam onto the sample region concurrently with the delivery of the first ion beam onto the sample region, the second ion beam comprising ions having a second composition, whereby the delivered ions of the second ion beam have a kinetic energy of 50 keV or less; an x-ray detector configured to detect x-rays emitted from the sample region in response to simultaneous delivery of the first and second ion beams to the sample region.

14. The analytical device is electrically coupled to a non-transitory computer-readable medium containing instructions that, when executed by one or more hardware processors, 14. The analytical apparatus of claim 13, further operable to cause an ion lens of the first or second ion beam column to adjust a focal point of at least one of the first and second ion beams at the sample region, whereby a magnitude of a detected X-ray signal is maximized by said adjustment.

15. The analytical device is electrically coupled to a non-transitory computer-readable medium containing instructions that, when executed by one or more hardware processors, 14. The analytical apparatus of claim 13, further operable to cause an ion lens of the first or second ion beam column to adjust an angle of incidence of at least one of the ions of the first and second ion beams onto the sample region, whereby a magnitude of a detected X-ray signal is maximized by said adjustment.

16. The analytical apparatus of any one of claims 13 to 15, wherein at least one of the first and second ion beam columns is a focused ion beam column.

17. 16. The analytical apparatus of claim 13, wherein the first ion beam column and the first ion beam source are configured to deliver either protons or helium ions, or a mixture thereof, to the sample region, and the second ion beam column is configured to deliver ions having a larger mass than the protons or helium ions to the sample region.

18. 20. The analytical apparatus of claim 17, wherein the second ion beam column and the second ion source are configured to deliver ions comprising any of nitrogen, argon, or xenon, or a mixture thereof, to the sample region.

19. 1. An analytical apparatus comprising: a first ion beam column comprising a first ion source and configured to deliver a first plurality of pulses of ions having a first composition onto a sample region, whereby the delivered ions have a kinetic energy of 50 kiloelectron volts (keV) or less; a second ion beam column comprising a second ion source and configured to deliver a second plurality of pulses onto the sample region comprising ions having a second composition simultaneously with the delivery of a first plurality of pulses of ions having the first composition onto the sample region, whereby the delivered ions of the second plurality of pulses have a kinetic energy of 50 keV or less; an x-ray detector configured to detect x-rays emitted from the sample region in response to simultaneous delivery of the first and second ion beams to the sample region.

20. The analytical device is electrically coupled to a non-transitory computer-readable medium containing instructions that, when executed by one or more hardware processors, 20. The analyzer of claim 19, operative to cause the first and second ion beam columns to control timing of the first and second plurality of pulses such that a phase difference between the first and second plurality of pulses is adjusted.

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