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

Abstract

The invention relates to particle-induced X-ray emission using a light particle beam and a heavy particle beam. A particle induced X-ray emission (PIXE) analysis method, the method comprising: (a) delivering a first ion beam from a first ion source and comprising ions having a first component, where the ions have a kinetic energy of no greater than 50 kiloelectron volts (keV), onto a region of a sample; (b) transporting a second ion beam from a second ion source onto the sample region while transporting the first ion beam onto the sample region, the second ion beam comprising ions having a second component wherein the ions of the second ion beam have a kinetic energy of no greater than 50 keV; and (c) detecting X-rays emitted from the sample region in response to simultaneous delivery of the first ion beam and the second ion beam to the sample region.

Description

Technical Field

[0001] The present invention relates to focused ion beam devices and methods of using such devices. More particularly, the present invention relates to methods of using particle induced x-ray emission to perform elemental analysis of a sample by means of two or more ion beams, a first beam comprising protons or other light ions and a second beam comprising a different ion species, wherein both beams are redirected to the sample simultaneously or substantially simultaneously. The present invention may be embodied in focused ion beam devices, including both stand-alone focused ion beam devices and dual beam devices that also include scanning electron microscope functionality. Background Art

[0002] Focused ion beam (FIB) instruments are an important part of sample preparation, nanofabrication, and materials analysis. Although stand-alone FIB devices are known, they are often 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 dominate semiconductor manufacturing and processing applications in the middle ground between small-scale electron beam processing and large-scale batch processing, where the focused beam allows maskless processing of small features that are not achievable with batch processing such as reactive ion etching (RIE). In such applications, FIB devices provide 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 often used in industrial applications such as semiconductor failure analysis, where relatively small-scale cross-sectioning, tomography, or TEM lamella preparation is required and high throughput is necessary for cost reasons. Focused ion beam devices also have a place in research and development, such applications include: preparation of biological samples for cryo-TEM analysis, preparation of samples for atom probe tomography, or the manufacture of optical components such as solid immersion lenses. As a result, FIB instruments are ubiquitous and can be found in a large number of factories and laboratories throughout the world. [3,5,6,7]

[0003] The FIB device is similar to a scanning electron microscope and can be used in a similar manner. In the operation of such devices, a tightly focused charged particle beam is scanned or rasterized across the surface of the sample of interest. From each respective focus, the energy of the beam strikes the surface of the sample causing the backscattering of particles or the emission of secondary charged particles (ions or electrons). The particles backscattered or emitted from each respective point can be detected by a particle detector, which provides a measurement of the relative amount of particles detected from each point. The number of such particles that can be detected and therefore the signal intensity can depend on the sample morphology and composition. In this way, a mapping map of the sample morphology and / or composition can be formed. However, SEM utilizes a focused electron beam to image the sample, while FIB utilizes a focused ion beam. Due to this difference in beam composition, the FIB device generates an image with a resolution slightly lower than that of the SEM image, and in contrast to the SEM device, the FIB device can damage the sample by a sputtering process. However, the sputtering process can be advantageously used in micro-etching or micro-grinding applications. Therefore, many dual-beam systems include FIB components or subsystems and SEM components or subsystems. In such dual beam systems, the SEM portion can be used to monitor the micro-etching or micro-milling procedure performed by the FIB portion through its imaging capabilities.

[0004] Of particular interest to the present invention is the particle induced X-ray emission (PIXE) technique. This technique is ideal for trace element analysis, where sample composition can be determined with sensitivities equal to or less than 1 part per million, [8, 9] particularly when compared to similar X-ray spectroscopic techniques such as energy dispersive spectroscopy (SEM-EDS) performed in a scanning electron microscope with sensitivities of 100 ppm to 500 ppm.

[10] PIXE analysis is typically performed by bombarding the sample surface with an ion beam while detecting the emitted X-rays. In theory, the beam can include any type of ion. However, in practice, very light ions such as protons are used due to their high velocity at a given acceleration potential, since the X-ray production cross section (XRPCS) is proportional to the ion velocity. Although heavier ions can be used, extremely high accelerating potentials would be required to match the proton velocity

[11] and significant sample damage may result

[12] .

[0005] Typically, PIXE analysis techniques are performed at incident particle energies of several megaelectronvolts (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 the background contribution remains sufficiently low.

[14] However, these high primary ion energies have so far limited 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 is currently somewhat inaccessible to general laboratory users.

[0006] Being able to perform PIXE on a focused ion beam instrument would represent a major step forward in the advancement of PIXE technology, opening up the availability of PIXE to a range of additional facilities and providing a complementary technique to SEM-EDS, significantly increasing sensitivity to trace elements. Co-pending and commonly assigned U.S. patent application Ser. No. 17 / 728,869, filed April 25, 2022, describes a new approach to particle induced X-ray emission known as Very Low Energy PIXE (VLE-PIXE). The inventors of the co-pending patent application surprisingly discovered that by using hydrogen ions (H + ) stream and simultaneously or almost simultaneously with heavy ions (such as Ar + , Kr + 、Xe + ) stream bombarding the same block of the sample can greatly increase and thereby detect the number of X-ray photons emitted from the sample block, where the kinetic energy of the incident particles is ≤50keV. This extremely low energy range makes PIXE analysis applicable to standard commercial FIB instruments. The inventors of U.S. patent application No. 17 / 728,869 showed that X-ray signal enhancement requires both light and heavy ions to interact with the sample simultaneously. However, the exact electronic mechanism of the enhanced X-ray signal 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 known FIB apparatus as described in U.S. Patent No. 8,076,650 and U.S. Patent No. 8,822,913, which is equipped with an inductively coupled plasma (ICP) ion source and a gas mixing device. Such an apparatus is sometimes referred to as a plasma focused ion beam (PFIB) apparatus. According to the method proposed in U.S. Patent Application No. 17 / 728,869, the ion source was modified for use with hydrogen.

[0008] The present invention is reproduced herein based on the aforementioned co-pending U.S. patent application Figures 1A to 1CSchematically illustrates an example of a device and apparatus that can implement VLE-PIXE, as described in the application. In device 1a ( Figure 1A ) and device 1b( Figure 1B ) in both, a FIB column 6 housed within a vacuum chamber 13 receives an ion mixture comprising at least hydrogen ions (i.e., protons) 2 and ions heavier than protons 3 from an inductively coupled plasma ion source 4 comprising a coiled electrode 5 to which, in operation, a radio frequency (RF) voltage waveform is applied. The ions are generated from a gas received from an inlet tube 11 and comprising a mixture of hydrogen including hydrogen molecules 2m and at least one other non-hydrogen gas including molecules 3m. The different gases may be provided in purified form and mixed in a gas mixing manifold (see Figure 1C ) in appropriate proportions. Alternatively, the gases may be provided in premixed form, thereby obviating the need for a gas mixing manifold and any metering valves required for proportioned mixing. Application of a suitable RF voltage to the coiled electrode 5 causes ignition of the plasma within the ion source 4 in a known manner.

[0009] Continue to refer Figure 1A to Figure 1B , the ions 2, 3 are focused into a beam 7 and directed along the length of the FIB column 6 toward the beam focus on the surface of the sample 8 by electric and / or magnetic fields applied to a series of ion optical devices 15, which may include ion lenses and ion guides. The ion optical device accelerates the ions toward the sample and causes a mixture of light ions and heavy ions of the ion beam to collide with the sample surface with a kinetic energy less than or equal to 50 keV. Both the protons 2 and the heavier ions 3 impact the same area on the sample 8 to generate a measurable amount of X-ray photons 9, which are derived in a known manner by the ejection of inner shell electrons of the atoms of the sample and by the filling of the resulting electron holes by electrons from higher energy electron shells. The resulting X-rays are detected by an energy dispersive X-ray detector 10 and recorded as an energy dispersive spectrum. In this way, the elemental composition of the sample can be determined. The device 1b also includes a scanning electron microscope (SEM) column 12 in the vacuum chamber, which is used to guide and focus the electron beam onto the sample. Detection of secondary or backscattered electrons by an electron detector (not shown) can be used to form an image of the sample area in a known manner.

[0010] Figure 1C8,822,913). A predetermined gas mixture is provided by a gas mixing system 220. The gas mixture is provided from an external gas feed line 104 through a gas filter 106 to a plasma chamber 102 within a source tube 103 and then to a capillary 108 having a current restrictor 110. Energy is fed from an RF power source 113 into the plasma chamber 102 through an antenna coil 114, and ions are extracted through a source electrode hole 116 in a source electrode 118 by an extractor electrode 120. A split Faraday cage 121 reduces the capacitive coupling between the coil 114 and the plasma in the chamber 102, where the capacitive coupling reduces the energy spread of the extracted ions. Power source 113 preferably drives antenna 114 in a "balanced" manner, i.e., adjusting the electrical phase shift across the antenna to reduce modulation of the plasma potential, as described in U.S. Pat. No. 7,670,455. A balanced antenna preferably provides a null in the RF energy field within the plasma, which reduces the energy spread of ions extracted from plasma chamber 102.

[0011] Gas conduction into and out of the plasma chamber 102 passes through a restrictor 110 in the capillary (at the top of the source tube 103) and an 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 through a valve 123 removes gas from the plasma chamber 102 through 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 gas from a plurality of gas sources, such as gas storage device 130A, gas storage device 130B, gas storage device 130C, and gas storage device 130D, which are supplied into the gas supply line 104 through corresponding valves 131A to 131D. The valves 131A to 131D are adjusted to provide a desired gas mixture into the gas feed line 104 to provide the gas to the plasma chamber 106. Multiple valves of the valves 131A to 131D can be opened simultaneously to provide multiple gas species to the plasma chamber simultaneously. The valves 131A to 131D are preferably metering valves that control the ratio of gases entering the gas inlet 104. The beam voltage source 132 supplies a high voltage to the plasma in the chamber 102, and the extraction voltage source 134 supplies a voltage to the extraction electrode 120. The extracted ions or electrons are focused by the focusing electrode 136. Additional details of the focusing column and the sample chamber are not shown.

[0013] FIG. 2A to FIG. 2BShown is a comparison of conventional SEM-EDS and VLE-PIXE spectra of NIST Standard Reference Material SRM 654b using the method of US Patent Application No. 17 / 728,869. Figure 2A Spectrum 351 is the 5keVSEM-EDS spectrum of the same sample. This can be compared with Figure 2A 352, which is a spectrum of the same sample doped with Xe + The proton of the ion (H + ions) (denoted as H / Xe ion beam). Figure 2B VLE-PIXE spectra and SEM-EDS spectra of the same sample using a larger accelerating voltage are shown. Spectrum 353 is a 30 keV SEM-EDS spectrum of the sample. Spectrum 354 is another portion of the 24 keV H / Xe VLE-PIXE spectrum. The values ​​of the SEM-EDS spectrum continue to 30 keV. However, only the bremsstrahlung background is observed in the SEM-EDS spectrum at energies greater than 10 keV; therefore, the spectrum is truncated for clarity.

[0014] FIG. 3A to FIG. 3B Shown is a comparison of conventional SEM-EDS spectra and VLE-PIXE spectra of NIST Standard Reference Material SRM 1242 using the method of US Patent Application No. 17 / 728,869. Figure 3A Spectrum 355 is the 5keVSEM-EDS spectrum of the sample. This can be compared with Figure 3A 356, which is a spectrum of the same sample doped with Xe + Part of a 24keV VLE-PIXE spectrum acquired with a single beam of protons. Figure 3B A VLE-PIXE spectrum and a SEM-EDS spectrum of the same sample using a higher accelerating voltage are shown. Spectrum 357 is a 30 keV SEM-EDS spectrum of the sample, while spectrum 358 is another portion of the 24 keV H / Xe VLE-PIXE spectrum.

[0015] Quantitatively, FIG. 2A to FIG. 2B and FIG. 3A to FIG. 3B The VLE-PIXE spectra can be characterized by the almost complete absence of a bremsstrahlung background, in contrast to the broad and intense bremsstrahlung background that is typical of SEM-EDS spectra. Figure 2A An example of this bremsstrahlung background is marked in . Therefore, there are several peaks in the VLE-PIXE spectrum that are not identifiable in the SEM-EDS spectrum, leading to the identification of two additional minor components; Ni and Cu.α and K β Ni can be identified in the VLE-PIXE spectrum based on the presence of a Cu L α The Cu peak was identified in the VLE-PIXE spectrum.

[0016] Figures 4 to 6 The analytical results of the VLE-PIXE technique described in US Patent Application No. 17 / 728,869 are shown. Figure 4 A graphical representation of the X-ray signal enhancement factors for several X-ray peaks of NIST Standard Reference Material SRM 654b relative to an ion beam composed of >99% hydrogen, as observed when the beam is lightly doped with nitrogen, argon, and xenon dopants. Figure 5 is a graph of the measured intensities of some prominent X-ray peaks generated by repeatedly exposing samples of NIST Standard Reference Material SRM 654b to hydrogen ion beams having decreasing percentages of Ar dopant, where the percentage of Ar is controlled by repeated plasma source pump-down cycles. Figure 6 is a bar graph comparing the lower limits of detection for several elements in NIST Standard Reference Material SRM 654b as determined by SEM-EDS with the lower limits of detection for the same elements as determined by Xe doped hydrogen ion VLE PIXE.

[0017] Based on the results of U.S. Patent Application No. 17 / 728,869, it has been newly recognized that VLE-PIXE can be performed on a FIB microscope with a sensitivity comparable to conventional PIXE performed at much higher energies, representing a significant breakthrough in PIXE analysis. Nevertheless, the inventors have recognized that additional modifications may reveal the full benefits of the VLE-PIXE technique. For example, the aforementioned patent application describes an experimental procedure in which a known FIB system including an inductively coupled plasma ion source, an associated gas mixing manifold, and a FIB column may be modified to generate a single ion beam including both light ion species and heavy ion species to be focused onto a sample surface. However, the document does not mention the possibility of employing alternative ion transport methods. Further, the use of hydrogen bodies as a source for generating H +Ion reagent gases present safety risks. Although proton beams are commonly used to induce X-ray emission during PIXE analysis (Lestiani et al.),

[15] it has recently been demonstrated that helium particle-induced X-ray emission is more suitable for detecting Na, Mg, Al and Si than conventional proton-induced X-ray emission using a 4MV VandeGraaff particle accelerator. Therefore, there is still a need to develop additional methods, devices and gas compositions for enhancing PIXE X-ray analysis at relatively low ion beam energies (e.g., maximum 50 keV), which can generally be obtained using existing focused ion beam devices and dual beam devices, wherein, in addition to the focused ion beam column, the dual beam device also includes an electron microscope column. Summary of the invention

[0018] In light of the above background, the inventors have addressed the above needs in the art by developing alternative beam delivery configurations and additional ion beam components. If PIXE signals are collected during FIB milling, this raises the possibility of endpoint detection and real-time elemental mapping that can be exploited 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:

[0020] delivering a first ion beam from a first ion source and including ions having a first composition onto a region of the sample, wherein the ions have a kinetic energy no greater than 50 kiloelectronvolts (keV);

[0021] delivering a second ion beam from a second ion source onto the sample region simultaneously with delivering the first ion beam onto the sample region, the second ion beam comprising ions having a second composition, wherein the kinetic energy of the ions of the second ion beam is no greater than 50 kiloelectronvolts (keV); and

[0022] X-rays emitted from the sample region are detected in response to simultaneously delivering the first ion beam and the second ion beam to the sample region.

[0023] According to a second aspect of the present invention, there is provided a second method of particle induced X-ray emission (PIXE) analysis, the second method comprising:

[0024] delivering a plurality of pulses of first ions from a first ion source and comprising ions having a first composition to a region of the sample, wherein the first ions have a kinetic energy no greater than 50 kiloelectronvolts (keV);

[0025] delivering a plurality of pulses of second ions from a second ion source onto the sample region simultaneously with delivering the plurality of pulses of first ions onto the sample region, the second ion beam comprising ions having a second composition, wherein the kinetic energy of the ions of the second ion beam is no greater than 50 kiloelectronvolts (keV); and

[0026] X-rays emitted from the sample region are detected and measured in response to causing the pulse of the first ions and the pulse of the second ions to impinge upon the sample region.

[0027] According to a third aspect of the present invention, there is provided an analysis device, the device comprising:

[0028] 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 region of the sample such that the kinetic energy of the delivered ions is no greater than 50 kiloelectronvolts (keV);

[0029] a second ion beam column comprising a second ion source and configured to deliver a second ion beam comprising ions having a second composition onto the sample region simultaneously with delivering the first ion beam onto the sample region, such that the kinetic energy of the delivered ions of the second ion beam is no greater than 50 keV; and

[0030] An X-ray detector is configured to detect X-rays emitted from the sample region in response to simultaneously delivering the first ion beam and the second ion beam to the sample region. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and various other aspects of the invention will become apparent from the following description, given by way of example only and with reference to the accompanying drawings, which are not necessarily drawn to scale, in which:

[0032] Figure 1A is a schematic diagram of an apparatus as previously described for performing very low energy particle induced X-ray emission (VLE-PIXE) measurements, the apparatus comprising a focused ion beam (FIB) column, a plasma ion source adapted to generate ions from a gas mixture and to provide the ions to the FIB column, and an X-ray detector;

[0033] Figure 1B is a schematic diagram of a dual beam setup as previously described for performing VLE-PIXE measurements, the setup comprising a FIB column, a scanning electron microscope column, a plasma ion source adapted to generate ions from a gas mixture and to provide the ions to the FIB column, and an X-ray detector;

[0034] Figure 1Cis a schematic diagram of a known inductively coupled plasma ion source for generating ions and providing the generated ions to a FIB column;

[0035] Figure 2A Comparison between the 24keV VLE-PIXE spectrum of NIST standard reference material SRM 654b and the 5keV SEM-EDS spectrum of the same sample;

[0036] Figure 2B Comparison results between the 24keVVLE-PIXE spectrum of NIST standard reference material SRM654b and the 30keVSEM-EDS spectrum of the same sample;

[0037] Figure 3A Comparison between the 24keV VLE-PIXE spectrum of NIST standard reference material SRM 1242 and the 5keV SEM-EDS spectrum of the same sample;

[0038] Figure 3B Comparison between the 24keVVLE-PIXE spectrum of NIST standard reference material SRM 1242 and the 30keVSEM-EDS spectrum of the same sample;

[0039] Figure 4 is a graphical representation of the X-ray signal enhancement factors for several X-ray peaks of NIST Standard Reference Material SRM 654b relative to an ion beam composed of >99% hydrogen, as observed for beams lightly doped with nitrogen, argon, and xenon dopants;

[0040] Figure 5 is a graph of measured intensities of some prominent X-ray peaks generated by repeatedly exposing a sample of NIST standard reference material SRM654b to a hydrogen ion beam having a decreasing percentage of its Ar dopant, wherein the percentage of Ar is controlled by repeated plasma source pump-down cycles;

[0041] Figure 6 is a bar graph comparing the lower limits of detection of several elements in NIST Standard Reference Material SRM 654b as determined by SEM-EDS with the lower limits of detection of the same elements as determined by Xe doped hydrogen ion VLE PIXE;

[0042] Fig. 7A is a schematic diagram of a first apparatus for performing very low energy particle induced X-ray emission (VLE-PIXE) measurements in accordance with the teachings of the present invention;

[0043] Figure 7B is a schematic diagram of a second apparatus for performing VLE-PIXE measurements according to the teachings of the present invention;

[0044] Fig. 8A is a flow chart of a first method for performing VLE-PIXE measurements according to the teachings of the present invention; and

[0045] Figure 8B is a flow chart of a second method for performing VLE-PIXE measurements in accordance with the teachings of the present invention. DETAILED DESCRIPTION

[0046] The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a specific application and its requirements. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments and examples shown, but should be consistent with the widest possible scope based on the features and principles shown and described. In order to fully understand the features of the present invention in more detail, please refer to the following description in conjunction with the present invention. Figures 1A-8B .

[0047] In the description of the present invention herein, it should be understood that, unless otherwise implicitly or explicitly understood or stated, words appearing in the singular encompass their plural counterparts, and words appearing in the plural encompass their singular counterparts. In addition, it should be understood that, unless otherwise implicitly or explicitly understood or stated, for any given component or embodiment described herein, any possible candidate or alternative listed for that component may generally be used individually or in combination with each other. In addition, it should be understood that the drawings as shown herein may not be drawn to scale, where only some elements may be drawn for the clarity of the present invention. And, reference numerals may be repeated in various figures to show corresponding or similar elements. In addition, it should be understood that, unless otherwise implicitly or explicitly understood or stated, any list of candidates or alternatives is merely illustrative, not restrictive.

[0048] Fig. 7A 2 is a schematic diagram of a first system 200a for performing very low energy particle induced X-ray emission (VLE-PIXE) measurements according to the teachings of the present invention. The 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 corresponding ionization source (not shown) that generates ions from a received reagent material. For example, Fig. 7AShown are two kinds of gaseous reagent materials 202m, 203m with different compositions being transported to ion beam columns 206a, 296b by gas inlet pipes 211a and 211b respectively.In some embodiments, gaseous reagent material 202m can be selected from hydrogen, helium and their mixture, and gaseous reagent material 203m can be selected from nitrogen, inert gas and their various mixtures.The unshown ion sources of two columns generate ions 202 and 203 from reagent materials 202m and 203m respectively.Each ion source can include the ion source of any suitable type, such as inductively coupled plasma ion source, electron impact ionization source etc.These two ion sources do not need to be the ion sources of the same type.

[0049] In addition to the ion source, each ion beam column also includes a plurality of accelerator electrodes, ion focusing lenses, orifices and / or deflector lenses, which guide each group of generated ions 202, 203 through corresponding columns 206a, 206b as corresponding ion beams 207a, 207b toward a common target area on a sample 208. In addition, the ion optics of each ion beam column 206a, 206b can be operated to remove ions in each ion beam 207a, 207b that are different from the desired charge state. Ion beam columns typically include but do not necessarily include focused ion beam (FIB) columns. In such cases, each ion beam column also includes one or more objective lenses, which can be operated to focus the ion beam on the target area. Otherwise, if the column is not a FIB column, the beam directed to the sample can be collimated or even diverged but not focused. By preventing the activation of the focusing lens, the same effect can be achieved using the FIB column. Collimated or divergent ion beams can be used to interact one or more ion beams with a specific area of ​​interest on the same sample. Collimated or divergent beams may also be employed to control the flux density of ions delivered to a given sample area.

[0050] System 200a( Fig. 7A ) also includes an X-ray detector 210 that is configured to detect X-ray emissions from a target region of the sample 208 that are stimulated by simultaneously or nearly simultaneously impinging the compositionally different ion beams 207a, 207b on the target region. As noted 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 typically significantly greater than the amount of X-ray photons detected by impinging either of the two beams separately. Furthermore, the amount of X-ray photons detected during simultaneous or nearly simultaneous impingement of the two beams 207a, 207b is significantly greater than the algebraic sum of the X-ray photons that would otherwise be detected by impinging the two ion beams separately on the sample.

[0051] In order to study the X-ray spectral effects of having two ion beams "almost simultaneously" impinge on a target area, the two ion beams 207a, 207b can be pulsed, wherein each ion beam pulse includes an ion packet that is emitted from the ion beam column at a time separated from the earlier previous packet and the subsequent subsequent packet. Pulses can be generated by operating deflector electrodes (not shown) within each ion beam column to periodically blank each ion beam. While allowing travel time from the ion outlet of each column to the target area, the transport time of each packet from the two columns to the target area may overlap completely, partially, or may not overlap. By making the timing of the two sets of pulses different, various phase shifts of the pulse arrival waveforms can be introduced. These phase shifts can be adjusted to maximize the resulting X-ray emission signal.

[0052] The system 200a also includes one or more computers or electronic controllers 230, which are electrically coupled to the column (e.g., to its ion source, ion lens, and other electrodes), to the X-ray detector 210, and to other components not shown (e.g., actuators for moving the sample stage, vacuum pumps, etc.) to achieve the purpose of executing the analysis procedure. Specifically, 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 method proposed herein. Therefore, the one or more computers or electronic controllers 230 may include or have access to a non-transitory computer-readable medium including instructions that are operated to execute the method when executed by one or more hardware processors. For example, the instructions, when executed, may (among other things) control the phase shift between the pulse arrival time waveforms of two pulsed ion beams delivered to a common region of the sample. Further, the instructions, when executed, may receive and analyze the signals received from the detector 210 and adjust the phase shift to maximize the signal.

[0053] Figure 7B 2 is a schematic diagram of a second system 200b for performing VLE-PIXE measurements according to the teachings of the present invention. Fig. 7A ) is that an electron microscope column 212 is additionally included in the vacuum system 213. Compared to the system 200a, the system 200b provides an additional function of using at least one of the ion beam columns 206a, 206b to mill the sample and then using the electron microscope column 212 to check the milling progress at a high magnification.

[0054] Fig. 8A 3 is a flow chart of a first method 300 for performing a VLE-PIXE measurement according to the teachings of the present invention. The first step of the method 300, step 302, includes directing a beam of first ions (e.g., Fig. 7AThe ion beam 207a is shown as being emitted from a first ion beam column (e.g., Fig. 7A 304, a second ion beam (e.g., ion beam 207b) from a second ion beam column (e.g., column 206b) is delivered to the same area of ​​the sample surface at an incident kinetic energy of ≤50 keV. Thus, steps 302 and 304 are performed simultaneously. The two ion beams include different corresponding ion components and may also include different ion charge states.

[0055] Step 306 includes detecting X-rays emitted from the sample area while delivering the first ion beam and the second ion beam to the sample area. Therefore, all steps 302, 304 and 306 are performed simultaneously. Steps 308 and 310 are optional adjustment steps, which may occur simultaneously with or after the execution of steps 302, 304 and 306. In step 308, focusing and / or defocusing of at least one of the first ion beam and the second ion beam is performed to maximize the detected X-ray signal. In step 310, the angle between the first ion beam 207a and the second ion beam 207b can be adjusted to maximize the detected X-ray signal. This step can be performed manually. Alternatively, if at least one ion beam column is attached to a movable mounting structure (not shown), step 310 can be performed automatically, wherein the position of the movable mounting structure is controlled by a motor or actuator, and the motor or actuator is controlled by one or more computers or electronic controllers 230. After the adjustment, execution of the method may be resumed (or may continue), further performing steps 302 , 304 , and 306 simultaneously using the adjusted settings.

[0056] Figure 8B is a flow chart of a second method 350 for performing VLE-PIXE measurements according to the teachings of the present invention. Method 350 is similar to method 300 ( Fig. 8A ) in that method 350 involves delivering a first plurality of ion pulses and a second plurality of ion pulses (i.e., a pulsed ion beam) to a sample region. Thus, method 350 includes an additional optional adjustment step, step 359, wherein the adjustment involves a phase difference between a waveform corresponding to the first plurality of pulses and another waveform corresponding to the second plurality of pulses.

[0057] The discussion contained in this application is intended to serve as a basic description. The scope of the present invention is not limited to the specific embodiments described herein, which are intended to be single illustrations of separate 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, in addition to those shown and described herein, will become apparent to those skilled in the art based on the foregoing description and drawings. The specific values ​​of the device operating parameters presented herein are provided as typical operating parameters as determined for a specific device, and are not intended to be limited in any way.

[0058] References

[0059] [1] Young, Richard J., and Mary V. Moore. Dual-beam (FIB-SEM) systems. Introduction to focused ion beams. Springer, Boston, MA, 2005.247-268.

[0060] [2]McLean P Echlin, Marcus Straw, Steven Randolph, Jorge Filevich, and Tresa M Pollock. The TriBeam system: Femtosecond laser ablation in situSEM. Materials Characterization, 100:1–12, 2015.

[0061] [3] Yongqi Fu and Kok Ann Bryan Ngoi. Focused ion beam directfabrication of micro-optical elements: features compared with laser beam and electron beam direct writing, 2004.

[0062] [4]Lucille A Giannuzzi et al. Introduction to focused ion beams: instrumentation, theory, techniques and practice. Springer Science&BusinessMedia, 2004.

[0063] [5]Lucille A Giannuzzi and Frederick A Stevie.A review of focused ionbeam milling techniques for TEM specimen preparation.Micron,30(3):197–204,1999.

[0064] [6]RichardYoung,C Rue,S Randolph,C Chandler,GFranz,R Schampers,AKlumpp,and L Kwakman.A comparison of xenon plasma FIB technology withconventional gallium LMIS FIB:imaging,milling,and gas-assistedapplications.Microscopy and Microanalysis,17(S2):652–653,2011.

[0065] [7]TL Burnett,R Kelley,B Winiarski,L Contreras,M Daly,A Gholinia,MGBurke,and PJ Withers.Large volume serial section tomography by Xe Plasma FIBdual beam microscopy.Ultramicroscopy,161:119–129,2016.

[0066] [8]Sven AE Johansson and Thomas B Johansson.Analytical application ofparticle induced X-ray emission.Nuclear Instruments and Methods,137(3):473–516,1976.

[0067] [9]CG Ryan.Quantitative trace element imaging using PIXE and thenuclear microprobe.International Journal of Imaging Systems and Technology,11(4):219–230,2000.

[0068]

[10] Dale Newbury,Nicholas Ritchie,Michael Mengason,and KeanaScott.SEM / EDS Trace Analysis:Limits Imposed by Fluorescence of theDetector.Microscopy andMicroanalysis,23(S1):1026–1027,2017.

[0069]

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

[0070]

[12] A Denker,J Opitz Coutureau,M Griesser,R Denk,and HWinter.Nondestructive analysis of coins using high-energy PIXE.NuclearInstruments and Methods in Physics Research Section B:Beam Interactions withMaterials andAtoms,226(1-2):163–171,2004.

[0071]

[13] K Ishii and S Morita.Theoretical estimation of PIXE detectionlimits.Nuclear Instruments and Methods in Physics Research Section B:BeamInteractions with Materials andAtoms,34(2):209–216,1988.

[0072]

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

[0073]

[15] Lestiani,Diah Dwiana,Sung Kijin,Muhayatun Santoso,and IkujiTakagi.“Helium and Proton Particle-Induced X-Ray Emission(PIXE)forCharacterization of PM2.5 from Surabaya,Indonesia.”Analytical Letters(2023):1-14.

Claims

1. A particle induced X-ray emission (PIXE) analysis method, the method comprising: delivering a first ion beam from a first ion source and including ions having a first composition onto a region of the sample, wherein the ions have a kinetic energy no greater than 50 kiloelectronvolts (keV); delivering a second ion beam from a second ion source onto the sample region simultaneously with delivering the first ion beam onto the sample region, the second ion beam comprising ions having a second composition, wherein the kinetic energy of the ions of the second ion beam is no greater than 50 kiloelectronvolts (keV); and X-rays emitted from the sample region are detected in response to simultaneously delivering the first ion beam and the second ion beam to the sample region. 2 . The PIXE analysis method according to claim 1 , further comprising focusing at least one of the first ion beam and the second ion beam onto the sample area. 3 . The PIXE analysis method according to claim 1 , further comprising adjusting an angle between the first ion beam and the second ion beam so that the amplitude of the detected X-ray signal is maximized by the adjustment.

4. The PIXE analysis method according to any one of claims 1 to 3, wherein: The first ion beam comprises protons or helium ions or a mixture thereof, and wherein the second ion beam comprises ions having a mass greater than the mass of the ions of the first ion beam.

5. The PIXE analysis method according to claim 4, wherein: The second ion beam includes nitrogen ions, argon ions or xenon ions or a mixture thereof.

6. The PIXE analysis method according to any one of claims 1 to 3, 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. A particle induced X-ray emission (PIXE) analysis method, the method comprising: delivering a plurality of pulses of first ions from a first ion source and comprising ions having a first composition onto a region of the sample, wherein the first ions have a kinetic energy no greater than 50 kiloelectronvolts (keV); delivering a plurality of pulses of second ions from a second ion source onto the sample region simultaneously with delivering the plurality of pulses of the first ions onto the sample region, the second ion beam comprising ions having a second composition, wherein the kinetic energy of the ions of the second ion beam is no greater than 50 keV; and X-rays emitted from the sample region are detected and measured in response to causing the pulse of the first ions and the pulse of the second ions to impinge upon the sample region. 8 . The PIXE analysis method of claim 7 , further comprising focusing at least one of the first plurality of ion pulses and the second plurality of ion pulses onto the sample region.

9. The PIXE analysis method according to claim 7, further comprising adjusting an angle at which ions of at least one of the first plurality of pulses and the second plurality of pulses are incident on the sample area, such that the amplitude of the detected X-ray signal is maximized by the adjustment. 10 . The PIXE analysis method according to claim 7 , further comprising adjusting a phase difference between the first plurality of pulses and the second plurality of pulses such that the amplitude of the detected X-ray signal is maximized by the adjustment.

11. The PIXE analysis method according to any one of claims 7 to 9, wherein: The ions of the first plurality of pulses include protons or helium ions or a mixture thereof, and wherein the mass of the ions of the second plurality of pulses is greater than the mass of the ions of the first plurality of pulses.

12. The PIXE analysis method according to claim 11, wherein: The ions of the second plurality of pulses include nitrogen ions, argon ions, or xenon ions, or mixtures thereof.

13. An analysis device, 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 region of a sample such that a kinetic energy of the delivered ions is no greater than 50 kiloelectronvolts (keV); a second ion beam column comprising a second ion source and configured to deliver a second ion beam comprising ions having a second composition onto the sample region simultaneously with delivering the first ion beam onto the sample region, such that the kinetic energy of the delivered ions of the second ion beam is no greater than 50 keV; and An X-ray detector is configured to detect X-rays emitted from the sample region in response to simultaneously delivering the first ion beam and the second ion beam to the sample region.

14. The analysis device according to claim 13, wherein: The apparatus is electrically coupled to a non-transitory computer-readable medium comprising instructions that, when executed by one or more hardware processors, are operable to: An ion lens of the first ion beam column or the second ion beam column is caused to adjust a focus of at least one of the first ion beam and the second ion beam at the sample region so that an amplitude of a detected X-ray signal is maximized by the adjustment.

15. The analysis device according to claim 13, wherein: The apparatus is electrically coupled to a non-transitory computer-readable medium comprising instructions that, when executed by one or more hardware processors, are operable to: An ion lens of the first ion beam column or the second ion beam column is caused to adjust an angle at which ions of at least one of the first ion beam and the second ion beam are incident on the sample area, so that the amplitude of the detected X-ray signal is maximized by the adjustment.

16. The analysis device according to any one of claims 13 to 15, wherein: At least one of the first ion beam column and the second ion beam column is a focused ion beam column.

17. The analysis device according to any one of claims 13 to 15, wherein: The first ion beam column and the first ion beam source are configured to deliver protons or helium ions or a mixture thereof to the sample region, and wherein the second ion beam column is configured to deliver ions having a mass greater than the protons or the helium ions to the sample region.

18. The analysis device according to claim 17, wherein The second ion beam column and the second ion source are configured to deliver ions comprising nitrogen, argon or xenon, or mixtures thereof, to the sample region.

19. An analysis device, comprising: a first ion beam column comprising a first ion source and configured to deliver a first plurality of ion pulses having a first composition onto a region of a sample such that the kinetic energy of the delivered ions is no greater than 50 kiloelectronvolts (keV); a second ion beam column comprising a second ion source and configured to deliver a second plurality of pulses comprising ions having a second composition onto the sample region simultaneously with delivering the first plurality of ion pulses having the first composition onto the sample region, such that the kinetic energy of the delivered ions of the second plurality of pulses is no greater than 50 keV; and An X-ray detector is configured to detect X-rays emitted from the sample region in response to simultaneously delivering the first ion beam and the second ion beam to the sample region.

20. The analysis device according to claim 19, wherein The apparatus is electrically coupled to a non-transitory computer-readable medium comprising instructions that, when executed by one or more hardware processors, are operable to: The first ion beam column and the second ion beam column are caused to control the timing of the first plurality of pulses and the second plurality of pulses such that a phase difference between the first plurality of pulses and the second plurality of pulses is adjusted.

Images