Arc scanning method for laser-induced breakdown spectroscopy applications

Abstract

The present invention relates to a method for compositional analysis, in particular laser-induced breakdown spectroscopy (LIBS), the method comprising: providing a sample, the sample having a surface; moving an ablation spot to a plurality of locations on the surface along an arc path defined by a plurality of arcs, wherein the plurality of arcs extend from one edge of a region to another edge of the region, wherein the arc path follows adjacent arcs of the plurality of arcs; applying a pulse to an energy source to provide a beam of electromagnetic energy to ablate material at the ablation spot; collecting an emission spectrum in response to applying the pulse to the energy source; and analyzing the emission spectrum to determine a composition at the surface.

Description

Technical Field

[0001] This disclosure relates in its entirety to systems and methods for performing laser-induced breakdown spectroscopy. Background Technology

[0002] Elemental analysis techniques help determine the elemental composition of materials in various forms. The range of elemental analysis techniques extends from destructive (e.g., materials are destroyed during testing) to semi-destructive (e.g., materials are sampled or their surfaces are damaged) to fully non-destructive (e.g., materials remain intact). Exemplary techniques may include inductively coupled plasma atomic emission spectrometry (e.g., ICP-AES), ICP-mass spectrometry (e.g., ICP-MS), electrothermal atomization atomic absorption spectrometry (e.g., ETA-AAS), X-ray fluorescence spectrometry (e.g., XRF), X-ray diffraction (e.g., XRD), and laser-induced breakdown spectroscopy (e.g., LIBS). Elemental analysis can be qualitative or quantitative and typically requires calibration against known standards.

[0003] Laser-induced breakdown spectroscopy (LIBS) is an analytical technique used to analyze a wide range of materials, including metals, semiconductors, polymers, glasses, ceramics, and minerals. LIBS can detect and quantify elements in the periodic table with very high precision. LIBS can analyze both large and small samples, requires almost no sample preparation, and can be used for large-scale elemental analysis and microscanning for imaging. LIBS relies on the emission of pulsed energy (such as pulsed laser emission) towards the sample to ablate, atomize, and ionize the material. Each laser pulse impacts and ablates the material on the sample surface, followed by atomization and ionization to generate a plasma plume. The light from this plasma plume can be analyzed to perform qualitative and quantitative spectroscopic measurements. Therefore, LIBS offers easy-to-use, rapid in-situ chemical analysis with high accuracy, desired detection limits, and low cost.

[0004] The interaction of lasers with matter is based on quantum mechanics, which describes how photons are absorbed or emitted by atoms. If an atom absorbs a photon, one or more electrons move from the ground state to a higher energy quantum state. Electrons tend to occupy the lowest possible energy level, and during cooling / decay, the atom emits a photon to return to the lower energy level. Different energy levels of different atoms produce different photon energies for each atom, resulting in narrowband light emission due to their quantization. These emissions correspond to spectral emission lines present in the LIBS spectrum.

[0005] Plasma lifetime has three basic phases. The first phase is the ignition process, which includes initial bond breaking and plasma formation during the laser pulse. This is influenced by the laser type, laser power, and pulse duration. The second phase of plasma lifetime is most critical for optimizing LIBS spectral acquisition and measurement because the plasma induces atomic emission during cooling. After ignition, the plasma continues to expand and cool. Simultaneously, the temperature and density of electrons change. This process depends on the ablation quality, spot size, energy coupled to the sample, and environmental conditions (sample state, pressure, etc.).

[0006] The final stage of the plasma lifetime is of little use for LIBS measurements. A certain amount of ablation mass is not excited into vapor or plasma; therefore, this amount of material is ablated into particles, and these particles generate non-radiative condensed vapor, liquid sample ejection, and solid sample ablation. Furthermore, the ablated atoms decrease in temperature and generate nanoparticles during plasma recombination. Summary of the Invention

[0007] In a first embodiment, a method for compositional analysis includes: providing a sample having a surface encompassing a region to be analyzed; and moving an ablation point to one of a plurality of locations on the surface along an arc path defined by a plurality of arcs. The plurality of arcs extend from one edge of the region to another edge of the region. The arc path follows adjacent arcs among the plurality of arcs. The method further includes: applying a pulse to an energy source to provide an electromagnetic energy beam to ablate material at the ablation point; collecting an emission spectrum in response to the pulse applied to the energy source; and analyzing the emission spectrum to determine the composition at the surface. The emission spectrum is a spectrum of light emission.

[0008] In an example of the first embodiment, the method further includes moving the ablation point along the arc path to a second location on the surface, the second location being adjacent to the first location along the arc path.

[0009] In another example of the first embodiment and in the example above, moving the ablation point includes moving the sample using a translation plate.

[0010] In another example of the first implementation scheme and in the example above, the moving ablation point includes a positioning reflector.

[0011] In the additional example of the first implementation scheme and the example above, the energy source includes a laser.

[0012] In another example of the first embodiment and in the examples described above, collecting the emission spectrum includes collecting the emission spectrum using a solid-state device or a photomultiplier tube.

[0013] In another example of the first implementation scheme and in the example above, the arc path follows the adjacent arcs along the plurality of arcs at different angular directions.

[0014] In the additional example of the first embodiment and the examples described above, the plurality of arcs have a common center point and are distributed with different radii. For example, the common center point is located at the edge of the surface. In one example, the common center point is located at the intersection of two edges of the surface. In another example, the common center point is located outside the boundary of the surface. In yet another example, moving the ablation point involves continuously scanning the arcs among the plurality of arcs in a direction toward the common center point. In the additional example, each of the plurality of arcs is equidistant from adjacent arcs along a radial direction from the common center point.

[0015] In another example of the first embodiment and in the examples described above, the plurality of arcs have two common foci. For example, moving the ablation point involves continuously scanning the arcs among the plurality of arcs along a direction toward the common foci. In another example, each of the plurality of arcs is equidistant from the adjacent arcs along a direction from the common foci.

[0016] In another example of the first implementation scheme and in the example above, each of the plurality of positions within one of the plurality of arcs is linearly equidistant.

[0017] In the additional example of the first embodiment and the example above, each of the plurality of positions within one of the plurality of arcs is equidistantly distributed along the arc.

[0018] In another example of the first embodiment and in the example above, a position on one of the plurality of arcs is equidistant from another position on that arc and yet another position on an adjacent arc among the plurality of arcs.

[0019] In another example of the first implementation and the example above, the method further includes selecting a sampling density and determining the number of arcs limiting the plurality of arcs based at least in part on the selected sampling density.

[0020] In the additional example of the first implementation scheme and the example above, the analysis includes: determining the composition at the location, and averaging the composition with other compositions determined at other locations among the plurality of locations.

[0021] In another example of the first embodiment and the example above, the analysis includes determining the composition at the location and generating an image that includes the positional resolution of the composition displayed at a relative location and other compositions displayed at other relative locations.

[0022] In another example of the first implementation scheme and in the example above, each of the plurality of arcs has a non-zero and non-infinite radius of curvature.

[0023] In a second example, a system includes: an energy source for providing an energy beam; and a positioning mechanism for relatively positioning a surface of a sample and the energy beam to provide an ablation point at one of a plurality of locations on the surface. The surface contains an area to be analyzed. The system also includes: a light-collecting lens guided to collect emission spectra from the ablation point; a spectrometer optically connected to the light-collecting lens; and a controller communicating with the positioning mechanism. The controller guides the movement of the ablation point on the surface along an arcuate path defined by a plurality of arcs extending from one edge of the area to another edge of the area to the plurality of locations.

[0024] In an example of the second embodiment, the system also includes an F-θ lens in the path of the energy beam.

[0025] In another example of the second implementation scheme and the example above, the positioning mechanism includes an adjustable reflector.

[0026] In another example of the second implementation scheme and the example above, the arc path follows the adjacent arcs along the plurality of arcs at different angular directions.

[0027] In the additional example of the second embodiment and the example above, the plurality of arcs have a common center point and are distributed with different radii. For example, the common center point is located at a corner of the surface. In one example, the controller is used to guide the movement of the ablation point to continuously scan the arcs among the plurality of arcs in a direction toward the common center point. In another example, each of the plurality of arcs is equidistant from the adjacent arcs along a radial direction from the common center point.

[0028] In another example of the second embodiment and the example described above, the plurality of arcs have two common foci. For example, the controller is used to guide the movement of the ablation point to continuously scan the arcs among the plurality of arcs along a direction toward the common foci. In one example, each of the plurality of arcs is equidistant from the adjacent arcs along a direction from the common foci.

[0029] In another example of the second implementation scheme and in the example above, each of the plurality of arcs has a non-zero and non-infinite radius of curvature.

[0030] In the additional example of the second implementation scheme and the example above, each of the plurality of positions within one of the plurality of arcs is linearly equidistant.

[0031] In another example of the second implementation scheme and the example above, one of the multiple positions on one of the multiple arcs is equidistant from another of the multiple positions on the same arc and yet another of the multiple positions on an adjacent arc. Attached Figure Description

[0032] This disclosure will be better understood by referring to the accompanying drawings, and many features and advantages of this disclosure will become apparent to those skilled in the art.

[0033] Figure 1 and Figure 2 Examples include exemplary laser-induced breakdown spectroscopy systems.

[0034] Figures 3, 4, 5 and 6 illustrate prior art scanning patterns and their associated arrays of ablation points.

[0035] Figure 7 includes an example of a compositional diagram with exemplary location resolution.

[0036] Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 and Figure 13 This includes an exemplary arc path and its associated array of ablation points.

[0037] Figure 14 , Figure 15 , Figure 16 and Figure 17 Includes an exemplary arc and its associated center point.

[0038] Figure 18 and Figure 19 This includes exemplary arcs with non-circular configurations.

[0039] Figure 20 Includes a flowchart illustrating an exemplary method for laser-induced breakdown spectroscopy.

[0040] Figure 21 Examples include exemplary arc paths that cover irregular shapes.

[0041] Figure 22 Examples of exemplary arc paths composed of test specimens at different depths are included.

[0042] Figure 23 A flowchart of an exemplary method for performing laser-induced breakdown spectroscopy is included.

[0043] Figure 24 , Figure 25 , Figure 26 , Figure 27 and Figure 28Examples of sample images including those indicating positional resolution.

[0044] Using the same reference numerals in different figures indicates similar or identical items. Detailed Implementation

[0045] In one embodiment, the system for compositional analysis includes an energy source to provide an energy beam directed at an ablation point on a sample surface. The energy source may be, for example, a laser. The ablation point may be moved sequentially along an arc path or arc pathway to a location on the surface. In one example, the arc path is defined by multiple arcs, where the path follows adjacent arcs at different angular directions. In one example, the multiple arcs may be circular and may have a common center point, while being distributed from that center point with different radii. In another example, the multiple arcs may have two common focal points. Each of the multiple arcs has a radius of curvature, but the radius of curvature may vary across the arcs. In one example, each arc is concave in the scanning direction, for example, on the side facing the common center point or focal point. The system may include a controller that guides the movement of the ablation point along the arc path to these locations. The system may also include lenses and mirrors, or optionally a linear stage platform, to facilitate the movement of the ablation point. The energy beam ablates material from the sample surface at the ablation point. The ablated material produces an emission spectrum. The system may include a collection system to collect the emission spectrum. In one example, the collection system includes a light-collecting lens optically connected to a spectrometer or spectrometer to determine the wavelengths emitted by the ablated material. The system can use the emission spectrum to determine which elements are present and, optionally, the amount of each element present.

[0046] In another example, the method for compositional analysis includes providing a sample having a surface. At each location sequentially along an arc path, an emission spectrum is collected from the surface ablated material at that location, and the emission spectrum is analyzed to determine the composition at that surface. Optionally, the emission spectrum is converted into a digital signal for further analysis to determine the composition. The composition can be analyzed, for example, by averaging, to determine an average surface composition. In another example, the compositions at these locations can be used to form a position-resolved image or graph of the composition.

[0047] It has been found that conventional scanning methods leave artifacts when displayed as position-resolved images or graphs. These artifacts can manifest as blurring or smearing tails on the image. Specifically, the presence of these artifacts leads to problems with the accuracy of the image and the accuracy of any averages derived from compositional measurements. These artifacts are believed to be caused by previously ejected material, and conventional scanning methods have been found to exacerbate the blurring problem due to the strong material transport effect when moving the pulsed laser along a single direction (i.e., along a substantially straight path). In contrast, it has been found that using arc paths that traverse positions on the surface reduces the effects of material transport and, specifically, eliminates the appearance of artifacts such as blurring or smearing tails. Furthermore, when using galvanometers, arc paths provide movement between points along each arc in the same direction, where directional variation is limited, thus restricting stress and strain on the mechanical aspects of the system, particularly the galvanometers.

[0048] Figure 1 This diagram includes a system 100 for compositional analysis, for example, by laser-induced breakdown spectroscopy. A sample 102 is placed on a platform 104. At an ablation point 112 located on the surface of the sample 102, an energy source 106 directs an energy beam 108 through an optical system, such as a lens 110. Material is ablated from the surface of the sample 102, and at least a portion of the ablated material is atomized or ionized, thereby generating an emission spectrum 114, which is collected by a light-collecting lens 116 optically connected to a spectrometer 118, for example, using an optical fiber cable.

[0049] The energy source 106 may be a laser. In one example, the energy source may be a pulsed laser with a typical wavelength in the range of 200 nm to 1100 nm (such as 1064 nm, 532 nm, or 266 nm). Furthermore, the energy source may have a wavelength of 0.5 MW / cm². 2 Up to 2GW / cm 2 Within the range (such as at least 1MW / cm) 2 The peak power is sufficient to ablate material from the sample surface and probe elemental composition. For example, the laser pulse can have an energy range of 100 μJ to 100 mJ and a pulse width in the femtosecond, picosecond, or nanosecond range, with pulse repetition rates up to the MHz range. The laser can be a mode-locked laser or a Q-switched laser. For example, the laser can be a passive Q-switched laser or an active Q-switched laser.

[0050] Lens 110 may include a spherical lens, a flat-field scanning lens, such as an F-tan(θ) scanning lens or an F-θ scanning lens. Specifically, lens 110 is an F-θ scanning lens.

[0051] The collection system may include a light-collecting lens 116 and a spectrometer 118. In one example, the spectrometer includes an imaging device such as a solid-state device (e.g., a charge-coupled device (CCD) imaging device) or a photomultiplier.

[0052] Specifically, system 100 includes controller 120. In one example, controller 120 can control the relative movement of the position of ablation point 112 to the surface of sample 102. For example, controller 120 can control a linear stage translation stage (such as platform 104) to move sample 102 relative to a fixed beam 108. In another example, mirrors such as galvanometers, prisms, or lenses can be used to change the relative position of the ablation point on the fixed sample. Controller 120 can control the relative movement of the ablation point 112 to the sequential position along an arc path on the surface of sample 102. Based on the set of emission spectra at each position on the surface of sample 102, a compositional map of the scanned surface can be constructed.

[0053] The controller 120 can also control the timing of the laser 106 to ablate the material only at desired locations on the sample surface. Furthermore, the controller 120 can control a collection system (such as a spectrometer 118) to collect emission spectra over a delay from the start of laser 106 activation.

[0054] In another example, Figure 2 A system 200 for performing compositional analysis is schematically illustrated. System 200 includes an electromagnetic energy source 204 that emits an electromagnetic energy beam 206. A set of one or more fixed reflectors 208 and movable positioning reflectors (such as galvanometers 210) can guide the electromagnetic energy beam through a lens 212 to an ablation point 214 on the surface of a sample 202. In one example, the motor-driven reflector 210 can be automatically adjusted to guide the ablation point to a position sequentially positioned along an arc path on the surface of the sample 202. Lens 212 can be a spherical lens, a flat-field scanning lens, or an F-θ scanning lens. In one example, lens 212 is a flat-field scanning lens or an F-θ scanning lens. Specifically, lens 212 is an F-θ scanning lens.

[0055] When the material is ablated at ablation point 214 by electromagnetic energy beam 206, an emission spectrum 216 is generated. The emission spectrum 216 can be guided to spectrometer 220 by one or more mirrors 218.

[0056] In one example, the electromagnetic energy source 204 is a laser. In another example, the energy source in 204 can be a pulsed laser with a typical wavelength in the range of 200 nm to 1100 nm (such as 1064 nm, 532 nm, or 266 nm). Furthermore, the energy source can have a wavelength of 0.5 MW / cm². 2 Up to 2GW / cm 2Within the range (such as at least 1MW / cm) 2 The laser pulse can have a peak power sufficient to ablate material from the sample surface and probe elemental composition. For example, the laser pulse can have an energy in the range of 100 μJ to 100 mJ and a pulse width in the femtosecond, picosecond, or nanosecond range, with pulse repetition rates up to the MHz level. The laser can be a mode-locked laser or a Q-switched laser. For example, the laser can be a passive Q-switched laser or an active Q-switched laser.

[0057] The spectrometer 220 may include various optical components, such as one or more mirrors, lenses, apertures, gratings, prisms, and emission collection devices. In one example, the emission collection device is a solid-state device, such as a charge-coupled device (CCD) imaging device. In other examples, other emission detectors such as photomultipliers may be employed.

[0058] System 200 may include controller 222. In one example, controller 222 controls adjustable mirror 210 to adjust the position of ablation point 214 on the surface of sample 202. Specifically, controller 222 is configured, for example, to move the ablation point to a position sequentially set along an arc path by controlling a motor driving adjustable mirror 210. Furthermore, controller 222 may control the activation of energy source 204 and may control the time for spectrometer 220 to collect or analyze emission spectra.

[0059] Controller 222 or 120 may include a computer (not shown): for example, including a storage medium, memory, processor, and one or more interfaces (such as a user output interface, a user input interface, and a network interface) linked together. The storage medium may be one or more of any form of non-volatile storage device, such as a hard disk drive, a magnetic disk, an optical disk, ROM, etc. The storage medium may store one or more computer programs for causing controller 222 to adjust the position of ablation point 214 on the surface of sample 202. The memory may be any random access memory suitable for storing data or computer programs. The processor may be any processing unit suitable for executing one or more computer programs (such as those stored on the storage medium or in memory). The processor may include a single processing unit or multiple processing units operating in parallel, individually, or cooperatively with each other. In performing processing operations, the processor may store data to or from the storage medium or memory. An interface may be provided, which is any unit for providing an interface between the computer and the movable reflector 210 and the energy source 204. The user input interface may be arranged to receive input from a user or operator. The user can provide input via one or more input devices of the controller (such as a mouse (or other pointing device) or a keyboard), which are connected to or communicate with the user input interface. However, it should be understood that the user can provide input to the computer via one or more additional or alternative input devices (such as a touchscreen). The computer can store the input received from the input device via the user input interface in memory for subsequent access and processing by the processor, or it can pass it directly to the processor so that the processor can respond accordingly to the user input. The user output interface can be arranged to provide graphical / visual output to the user or operator. For example, the emission spectrum collected from a sample can be provided to the user or operator as graphical / visual output. Thus, the processor can be arranged to instruct the user output interface to form an image / video signal representing the desired graphical output and to provide that signal to a video display unit (VDU), such as a monitor (or screen or display unit) connected to the user output interface. It should be understood that the above computer architecture is merely exemplary, and other computer systems with different architectures (e.g., with fewer components or with additional or alternative components) can be used. As an example, a computer may include one or more of the following: a personal computer; a server computer; a laptop computer; and so on.

[0060] Figures 3 and 4 illustrate conventional scanning patterns. For example, Figure 3 shows a conventional raster scanning pattern. Figure 4 shows a conventional serpentine scanning pattern. Figures 5 and 6 show the distribution of positions, such as a grid or array of positions, at which ablation is performed against conventional raster and serpentine scanning patterns. These conventional scanning patterns are based on dividing the image into horizontal bars, also known as scan lines. Each scan line can then be divided into a set of discrete positions to serve as ablation points, where each point represents a single ablation location. In the examples shown in Figures 5 and 6, the positions are distributed at regular intervals. It has been found that such conventional scanning methods or patterns shown in Figures 3 and 4 result in artifacts in the position-resolved composition image and lead to questionable average composition when averaging across the grid or array of positions. Therefore, conventional scanning methods are problematic in that they introduce errors into the measurement of uniformly distributed positions on the sample surface, especially when the scanning pattern causes the laser to scan primarily in a single direction. Since the galvanometer or linear stage cannot be stopped abruptly and can be moved beyond the end of each scan line, another problem may be the sampling of the surface beyond the boundary of the area under study at the end of each scan line due to the inertial characteristics of the galvanometer or linear stage.

[0061] To illustrate artifacts caused by conventional scanning methods, laser-induced breakdown spectroscopy using different scanning patterns was employed to test for the presence of elemental nickel on the surface of a printed circuit board (PCB). A 532nm laser with an energy of 2 mJ / pulse and a repetition rate of 1 kHz was used for each scanning pattern. This laser has a power of 2 MW / pulse and a beam width of 4 mm, thus providing 16 MW / cm². 2 As shown in Figure 7, the serpentine scanning method generates artifacts such as smudges, additional marks, or blurring effects. Serpentine scanning utilizes a single galvanometer for rapid scanning in the X-direction. After one row has been scanned, a second galvanometer varies its length at the end of each row in the Y-axis with an offset. Therefore, the laser scan is focused in a single direction, resulting in a strong material transport effect as the laser scans above the sample surface.

[0062] In contrast, it has been found that scanning along an arc path to sequentially move ablation points to locations along the arc path allows for the collection of emission spectra without artifacts associated with conventional scanning methods. For example, the arc path can be defined by multiple arcs, where the path follows adjacent arcs in different or opposite directions. In one example, these arcs may have a common center point (i.e., the same center point) and be distributed with different radii. In another example, the arcs may have two common center points (i.e., the same focus). It is believed that during conventional scanning methods, the ejected material follows a linear path to subsequent ablation points, while during arc path scanning methods, the ejected material moves in a direction tangential to the arc, thus limiting the reanalysis of the same material and therefore limiting blurring or smudge artifacts.

[0063] An arc path comprises multiple arcs. A scan through an arc path involves moving sequentially along the arcs through adjacent positions, then moving to an adjacent arc, and then sequentially moving along the adjacent arcs through adjacent positions. In one example, the scan of an arc is performed along a first angular direction, while the scans of adjacent arcs are performed along the opposite angular direction. In a particular example, the scans of consecutive arcs are performed alternately along angular directions. Alternatively, the scans through arcs may be performed along the same angular direction.

[0064] In one example, the arcs lie at different radii but share a common center point—that is, the same center point. The arcs extend from one edge of the surface to another. For example, Figure 8 The surface on which the arc path is defined is shown. The arcs can be distributed with equal radius differences.

[0065] In the example of circular arcs, the maximum radius can be identified as the extension across the selected surface, and the arcs can be spaced apart from each other at equal distances along the radius. For example, the number of arcs can be selected, and the spacing between the arcs can be determined by dividing the maximum radius by the number of arcs.

[0066] In the example where μ is a non-negative real number and υ is in an elliptical coordinate system ranging from 0 to 2π, an arc can be formed by keeping μ constant and changing υ to form an arc. The arcs can be distributed arithmetically with μ as a unit. In other examples, other coordinate systems (e.g., biangular coordinates, hyperbolic coordinates, etc.) can be used to define multiple arcs. Furthermore, each arc can be identical and spaced equidistant across the surface.

[0067] Arc paths can include moving across an arc, moving to an adjacent arc, and moving across adjacent arcs. Once the ablation point has moved across an arc and reached the end of the arc at its angular boundary (typically at the edge of the surface area), the ablation point can move to the beginning of an adjacent arc to begin moving across that arc. In an example where the ablation point moves across adjacent arcs in opposite angular directions, the ablation point can move from the end of the arc along the edge of the surface area to the beginning of a subsequent arc. Thus, the ablation point moves across arcs from edge to edge.

[0068] An arc path can begin with the arc furthest from the center point or focus and move sequentially to adjacent arcs closer to the center point or focus, such as... Figure 8 As shown. For example, as shown in Equation 1 below, an arc path consisting of segments of a circle can be defined as a sine function, where the boundary is typically located at θ greater than 0 and less than π / 2, and is set according to the position of the edge of the arc contact surface region. The radius of each subsequent arc gradually decreases from the radius of the previous arc. Any sprayed material may move tangentially to the arc, thus limiting the reanalysis of the same material. Alternatively, the arc path can start from the arc closest to the center point and move sequentially to adjacent arcs with larger radii.

[0069] (Equation 1) [x; y] = [rcosθ; r sinθ], where θ Edge1 ≤θ≤θ Edge2 and

[0070]

[0071] Where r is the radius, r max The maximum radius is given by step_num, which is the number of steps and has a maximum value of step_num. max And θ is a value θ at the first edge of the surface. Edge1 And it has a value θ at the second edge. Edge2 The angle.

[0072] An arc can be defined as having a different shape in other coordinate systems, such as a biangular coordinate system or an elliptical coordinate system. In an elliptical coordinate system, an arc path can be a segment of an ellipse. For example, as shown in Equation 2, elliptical coordinates can be used to define an arc path.

[0073] (Equation 2) Where a is a constant, μ is a non-negative real number, and the range of υ is from the first edge of the surface. Edge1 to the second edge υ Edge1 Each arc can be a segment of an ellipse defined by the constant value of μ. Multiple arcs can be defined by segments of an ellipse having equal differences in units of μ.

[0074] To further define the arc path, specify positions along each arc. For example, Figure 9 It shows along Figure 8 The locations of the arc paths are distributed along the arc. In one example, these locations may be equidistant from each other along the arc. For example, these locations may be linearly equidistant (e.g., Equation 3). In another example, these locations may be equidistant along the arc (e.g., Equation 4).

[0075] (Equation 2)

[0076] (Equation 3) Where x and y are functions of time, the ablation point is at the first position at t1 and at the adjacent position at t2. And Δl is along the straight line... Or along the arc The distance between positions.

[0077] To specify the sampling density or the number of sampling locations, and thus the density or number of ablation points, the number of arcs or the spacing between arcs can be selected, or the distance between locations along the arcs can be selected. Alternatively, the system can determine the number of arcs and the spacing between adjacent points based on the desired density.

[0078] For example, such as Figure 10 , Figure 11 , Figure 12 and Figure 13 As shown, increasing the number of arcs and decreasing the distance between positions on the arcs increases the density of positions, and thus increases the density of measurable ablation points. This increased position density provides an increase in the spatial resolution of the composed image.

[0079] Optionally, the arcs can be spaced apart and their positions distributed along the arcs to form a grid or array of positions uniformly distributed across the surface. In one example, a position on an arc is equidistant from another position on the arc and yet another position on an adjacent arc. For example, these positions can form a grid or array in a polar coordinate system. In one example, these positions are arranged equidistantly along the arcs and equidistantly along the radius. A position can be equidistant from an adjacent position within the arc and equidistant from the adjacent position along a radius from the center point. In another example, these positions can form a grid or array in a biangular or elliptical coordinate system.

[0080] like Figure 14 As shown, adjacent arcs are positioned at different radial distances (R1 or R2) from the same center point (CP). The radii of curvature of adjacent arcs can be equal to their distance from the center point. In one example, the arc path may scan along the arc of radius R1 in the first angular direction and then along the arc of radius R2 in the opposite angular direction. Alternatively, the arc path may scan the arc of radius R2 before the arc of radius R1. In yet another alternative example, the arc path may scan both arcs in the same angular direction.

[0081] like Figure 14 As shown, the center point is set at the corner of the surface. In one example, the center point (CP) can be set at the edge of the surface, such as... Figure 15 As shown. In another example, the center point (CP) can be set at the intersection of the two edges of the surface (e.g., a corner), as shown. Figure 16 As shown. In Figure 17In another example shown, the center point (CP) may be located outside the boundary of the surface. Alternatively, the center point (CP) may be located on or within the boundary of the surface. Depending on the shape of the surface boundary, different locations of the center point (CP) may offer advantages over other optional locations of the center point (CP).

[0082] exist Figure 18 In another example shown, each of the multiple arcs may have two common foci (i.e., two identical foci). For example, the arc may be a segment of an ellipse. Such an elliptical segment defines the arc path along which the locations of the ablation points are distributed. Such arcs may be defined in an elliptical coordinate system or a biangular coordinate system. Foci may be located at the edges of the surface region. In another example, foci may be located at different edges of the surface region. In yet another example, foci may be located at different corners of the surface region. In an additional example, foci may be located outside the surface region.

[0083] In the additional example, each arc can have the same shape and be uniformly distributed across the surface, such as... Figure 19 As shown. Generally speaking, an arc has a radius of curvature that is neither zero (e.g., a point) nor infinite (e.g., a straight line). For example, when the arc is a segment of an ellipse or other non-circular curve, the radius of curvature can vary across the arc.

[0084] In one example, each of these arcs has a concave side facing the end of the scan and a convex side facing away from the end and towards the start of the scan. As noted herein, the curve is concave in the scan direction.

[0085] Figure 20 This includes an example of an exemplary method 2000 for performing compositional analysis. For example, the method includes inserting a sample into a compositional analysis system, as shown in box 2002. Generally, the sample has a surface at which it will be ablated to produce an emission spectrum that can be used for compositional analysis.

[0086] As shown in box 2004, the system can move ablation points to sequential locations along an arc path. The ablation points can be positioned at various locations along the arc path. The configuration of the arc path (e.g., the location of the center point, the distance between arcs, the corner boundaries of the arcs, the distance between points on the arcs, etc.) can be selected to provide the desired sample density across the surface.

[0087] At selected time intervals, an energy source such as a laser can be activated, as shown in box 2006. For example, the laser can be activated at rates ranging from 1 Hz to several MHz (such as 100 Hz to 1000 Hz). When activated, the material is ablated from the surface at the ablation point, thereby promoting the generation of an emission spectrum.

[0088] By moving the sample relative to a fixed electromagnetic energy beam, for example, using a linear stage platform, the ablation point can be moved sequentially between locations along an arc path. In another example, the ablation point can be moved by changing the path of the energy beam relative to a fixed sample surface, such as by using an adjustable or movable lens, prism, or mirror (e.g., a galvanometer).

[0089] As shown in box 2008, the emission spectrum can be collected. For example, an optical system such as a set of focusing lenses can be used to collect the emission spectrum emitted from the ablation point. The emission spectrum can be optically provided to a spectrometer, which collects the emission spectrum and converts it into a digital signal, as shown in box 2010. This digital signal can indicate the intensity of the light received at various wavelengths, which can be used to determine the composition.

[0090] As shown in box 2012, the system determines whether the end of the arc path has been reached. If not, the system moves the ablation point along the arc path to a subsequent location, as shown in box 2004, activates the energy source, collects the emission spectrum, and converts the emission spectrum into a signal.

[0091] As shown in box 2014, the system can analyze the converted signal or digital signal to qualitatively and optionally quantitatively determine the composition. In one example, the analysis can be performed after measurements are taken at each ablation point across the ablation points. Alternatively, the analysis can be performed simultaneously with the measurement of the emission spectrum. This analysis can result in averaging of the composition across the positions along the arc path. In another example, the analysis can provide a position-resolved image or graph indicating the composition at various locations on the sample surface. The analysis can be performed by a computer associated with the spectrometer. In some embodiments, the computer used to perform the analysis can be as described above. Figure 2 The computer with controller 222 in it.

[0092] Depending on the nature of the desired analysis, the resolution of the image constituting the sample, or other factors, the number or density of measurement locations across a selected sample region can be adjusted. The nature of the arc path allows for adjustment of the density or number of measurement locations by changing the location of the center point or focal point, the number of arcs, the spacing between arcs, and the distance between locations along the arcs.

[0093] Various arc paths can be used to cover test areas of different shapes. For example, Figures 8 to 13 An arc path configured for a square surface region is shown. Similar arc paths can be used to test rectangular shapes. Arc paths can be envisioned for testing regular shapes such as squares, rectangles, other parallelograms, other quadrilateral shapes (such as trapezoids or kites), other polygons, and combinations or cascades thereof. Furthermore, arc paths can be used to test irregular shapes. For example, Figure 21An exemplary 2-D surface with an irregular shape is shown, along with an associated arc path for testing a surface with such an irregular shape. A center point with a radial vector extending through the surface can be selected. The center point can be located on an edge or outside the boundary of the surface.

[0094] Arc paths can also be used to test the same area at different depths. For example, the same location within a pattern of positions can be tested more than once to reach subsurface depths. The surface of the sample is analyzed by a first arc pattern scan using a laser, and each subsequent arc pattern scan is etched into the sample to an additional depth. By continuing this process, multiple layers can be analyzed according to depth. By combining the analysis of these layers in three dimensions, the system can produce a three-dimensional map, meaning the composition of the sample can be analyzed in three dimensions. In one example, Figure 22 Examples include using arc patterns generated from arc paths on the same test area to test composition as a function of depth. In the illustrated example, a first arc path traversing the array of test locations is used to perform surface analysis at test (1). Additional arc paths can be used in each of tests (2), (3), or (4), etc., to test composition at etch depths 1, 2, or 3, etc. Figure 20 In the example shown, the same arc path can be used in each of the subsequent tests (2), (3), or (4) to test the composition at different depths at the same test point. In an alternative example, different arc paths can be used in one or more additional tests, as long as the arc path passes through the same measurement position pattern. The scanning direction of the laser along the arc path can be the same for each test depth 1, 2, 3, etc., or it can be different between test depths. In one example, at the first test depth, the laser moves along the arc path in a first direction, and at the second test depth, the laser moves along the arc path in a second direction or the opposite direction, with the laser movement passing through the same measurement position array regardless of the scanning direction.

[0095] Generally, when selecting a test area, various geometries, arc patterns, and arc distributions can be used to define the arc path across the test area. Specifically, the geometry may include cascading arc patterns, adjustments to step size and different dimensions, or subsequent tracking across previously tested points to generate a compositional measurement based on depth. Furthermore, the density of selected locations, the distance between arcs, the distance between locations, the location of a common center point or focal point, and other factors define the number or density of measurement locations within a grid or array (e.g., a 2-D array in a polar or elliptical coordinate system) within a portion of the test area.

[0096] exist Figure 23In the example shown, method 2300 for performing compositional analysis includes inserting a sample into a testing system, as shown in box 2302. The sample comprises a surface of the composition to be tested. For example, the sample can be a metal, semiconductor, polymer, glass, ceramic, or mineral sample.

[0097] As shown in box 2304, a test area can be selected on the surface of the inserted sample. In one example, the test area is a square area. Alternatively, the test area can be a rectangular shape or other geometry, as described above. For example, the geometry can be an irregular shape.

[0098] Depending on the nature and shape of the test area, the system can determine the geometry to be used when defining an arc path through a measurement location defined within the test area, as shown in box 2306. For example, defining the geometry may include defining a cascade of various arc patterns, adjusting the step size between arcs, selecting a common center point or focus, determining the angular boundaries of the arc, or selecting an arc pattern at measurement locations to be tested multiple times.

[0099] The method may also include defining the density of the grid or array of measurement locations by selecting factors that provide a desired density for the array of measurement locations, such as the step size between arcs or the distance between locations, as shown in box 2308. Smaller step sizes and distances between points provide a larger number of measurement locations within the array and a higher density of measurement locations for a given area. Alternatively, the density can be selected, and the system can determine the arc pattern or the distance between locations to achieve the selected density.

[0100] Once the geometry is selected, an arc path is defined along which measurements can be performed. For example, as shown in box 2310, the ablation point can be moved along the arc path to a sequential location within a grid or array of measurement locations (e.g., a 2-D array or grid in polar coordinates). At the desired location, a pulse can be applied to an energy source (such as a laser), as shown in box 2312. The pulse causes ablation of the material at the ablation point or location on the sample surface, thereby generating an emission spectrum.

[0101] As shown in box 2314, the emission spectrum can be collected, for example, using a light-collecting lens or other optical system. The collected emission spectrum can be converted into a digital signal, for example, using a spectrometer, as shown in box 2316.

[0102] After collecting the emission spectrum, the system can determine whether the end of the arc path along the selected geometry has been reached, as shown in box 2318. If not, the system can move the ablation point along the arc path to a subsequent location and repeat the pulse application of the laser and the collection of the emission spectrum.

[0103] If the end of the path is reached, the system can determine whether the end of the geometry has been reached, as shown in box 2320. For example, the system can determine whether all depths have been tested or whether there are additional arc patterns to be tested. If the end of the geometry has not been reached, the system can select the next geometry, as shown in box 2322.

[0104] Depending on the properties of the geometry, the system can reset the focus of the energy source (e.g., a laser), as shown in box 2326. For example, when testing an additional depth, the focus can be adjusted for the next depth. The system can then move the ablation point sequentially along the arc path, apply pulses to the laser, and collect the emission spectrum at each location.

[0105] The system can analyze the converted signal to determine its composition, as shown in box 2324. For example, the system can average the composition at these locations to determine the average value across the test area on the surface. In another example, the system can provide a location-resolved plot or image indicating the composition at different locations.

[0106] The implementation of the aforementioned system and method offers technical advantages over conventional systems. Specifically, the implementation overcomes the material transport effects observed in conventional systems and testing methods, thereby reducing errors and artifacts (such as blurring or smearing caused by position) in position-resolved plots that indicate composition based on location. Such errors are also reduced when compositions collected from a set of locations are averaged. High accuracy is achieved in position-resolved plots when galvanometer (or linear stage) movement is minimized. Furthermore, the durability of system components is increased due to the limited number of abrupt changes in the orientation of the galvanometer (or linear stage).

[0107] Example

[0108] Example 1

[0109] Printed circuit boards (PCBs) are tested to determine the presence of elemental copper, nickel, tin, and barium on their surfaces. Laser-induced breakdown spectroscopy (LAS) utilizing an arc path is used to test the same areas of the PCB. A 532nm laser with an energy of 2 mJ / pulse and a repetition rate of 1 kHz is used for the scanning pattern. This laser has a power of 2 MW / pulse and a beam width of 4 mm, thus providing 16 MW / cm². 2 . Figure 24 (copper), Figure 25 (nickel), Figure 26 (tin) and Figure 27 (Barium) shows a position-resolved map of the composition measured using an arc path.

[0110] like Figures 24 to 27As shown, compared to the smudges or blurry artifacts shown in Figure 7, the use of an arc path provides a precise and visually clear image. The arc has a concave curvature relative to the scanning direction, which can cause the ejected material to lie outside the continuous scanning area, thus avoiding reanalysis of the ablated material. For example, as the laser scans along the arc path, the ejected material experiences a centripetal force that pushes the material perpendicular to the arc curve function. Furthermore, any remaining material ejected tangentially relative to the scanning direction will not be superimposed on the continuous ablation site. The curvature of the arc path maps to points on the grid away from the tangent and therefore away from the next point where material superimposes.

[0111] Example 2

[0112] The presence of chromium in a two-euro coin was tested using laser-induced breakdown spectroscopy with an arc path. A 532nm laser with an energy of 2 mJ / pulse and a repetition rate of 1 kHz was used for the scanning pattern. This laser has a power of 2 MW / pulse and a beam width of 4 mm, thus providing 16 MW / cm². 2 . Figure 28 A position-resolved map of the composition (chromium) measured using an arc path is shown.

[0113] Figure 28 As shown, chemical mapping distinguishes the elements used to coat the letters from the substrate immediately surrounding them. Therefore, each letter has a sharp boundary, with minimal mass transport effect after ablation, which would otherwise result in blurring or smudge artifacts.

[0114] It should be noted that not all activities described above in the general description or examples are required. Some activities may not be required, and one or more additional activities may be performed besides those described. Furthermore, the order in which the activities are listed is not necessarily the order in which they are performed.

[0115] In the foregoing specification, the concepts have been described with reference to specific embodiments. However, those skilled in the art will understand that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims. Therefore, the specification and drawings should be considered illustrative rather than restrictive, and all such modifications are intended to be included within the scope of the invention.

[0116] As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof are intended to cover non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of features is not necessarily limited to those features, but may include other features not expressly listed or inherent to such a process, method, article, or apparatus. Furthermore, unless expressly stated otherwise, “or” means inclusive “or” rather than exclusive “or.” For example, conditions A or B satisfy any of the following: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); and both A and B are true (or exist).

[0117] Furthermore, the terms "a" or "an" are used to describe the elements and components described herein. This is done merely for convenience and to give a general meaning regarding the scope of the invention. The description should be understood to include one or at least one, and the singular includes the plural, unless it is obvious otherwise.

[0118] The benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. However, the benefits, advantages, solutions to problems, and any features that may cause any benefit, advantage, or solution to occur or become more significant should not be construed as key, essential, or necessary features of any or all claims.

[0119] Upon reading this specification, those skilled in the art will understand that, for clarity, certain features described herein in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, for brevity, various features described in the context of a single embodiment may also be provided individually or in any sub-combination. Furthermore, references to values ​​within a scope include every value within that scope.

Claims

1. A method for laser-induced breakdown spectroscopy, the method comprising: A sample is provided, the sample having a surface containing the region to be analyzed; The ablation point is moved to a first position among a plurality of positions on the surface along an arc path defined by a plurality of arcs, wherein the plurality of arcs extend from one edge of the region to the other edge of the region and each arc is concave in the scanning direction, wherein the arc path follows adjacent arcs among the plurality of arcs; A pulse is applied to the energy source to provide an electromagnetic energy beam to ablate the material at the ablation point; The emission spectrum is collected in response to the application of a pulse to the energy source; as well as The emission spectrum is analyzed to determine the composition at the surface.

2. The method of claim 1, further comprising moving the ablation point along the path to a second position on the surface, the second position being adjacent to the first position along the path.

3. The method according to claim 1 or claim 2, wherein moving the ablation point comprises moving the sample using a translation plate.

4. The method according to claim 1 or claim 2, wherein moving the ablation point includes positioning a reflector.

5. The method according to claim 1 or claim 2, wherein the energy source comprises a laser.

6. The method of claim 1 or claim 2, wherein collecting the emission spectrum comprises collecting the emission spectrum using a solid-state device or a photomultiplier.

7. The method of claim 1 or claim 2, wherein the arc path follows adjacent arcs along the plurality of arcs at different angular directions.

8. The method according to claim 1 or claim 2, wherein the plurality of arcs have a common center point and are distributed with different radii.

9. The method of claim 8, wherein the common center point is located at the edge of the surface.

10. The method of claim 8, wherein the common center point is located at the intersection of two edges of the surface.

11. The method of claim 8, wherein the common center point is located outside the boundary of the surface.

12. The method of claim 8, wherein moving the ablation point comprises continuously scanning the arcs of the plurality of arcs in a direction toward the common center point.

13. The method of claim 8, wherein each of the plurality of arcs is equidistant from the adjacent arcs along a radial direction from the common center point.

14. The method according to claim 1 or claim 2, wherein the plurality of arcs have two common focal points.

15. The method of claim 14, wherein moving the ablation point comprises continuously scanning the arcs of the plurality of arcs in a direction toward the common focal point.

16. The method of claim 14, wherein each of the plurality of arcs is equidistant from adjacent arcs along a direction from the common focus.

17. The method according to claim 1 or claim 2, wherein each of the plurality of positions within one of the plurality of arcs is linearly equidistant.

18. The method according to claim 1 or claim 2, wherein each of the plurality of positions within one of the plurality of arcs is equidistantly distributed along the arc.

19. The method according to claim 1 or claim 2, wherein a position on one of the plurality of arcs is equidistant from another position on the same arc and yet another position on an adjacent arc of the plurality of arcs.

20. The method of claim 1 or claim 2, further comprising selecting a sampling density and determining the number of arcs defining the plurality of arcs based at least in part on the selected sampling density.

21. The method according to claim 1 or claim 2, wherein the analysis comprises: The composition at the stated location is determined, and the stated composition is averaged with other compositions determined at other locations among the plurality of locations.

22. The method according to claim 1 or claim 2, wherein the analysis comprises: The composition at the stated location is determined, and an image is generated that includes a position-resolved image of the composition displayed at a relative location and other compositions displayed at other relative locations.

23. The method according to claim 1 or claim 2, wherein each of the plurality of arcs has a non-zero and non-infinite radius of curvature.

24. A system for laser-induced breakdown spectroscopy, the system comprising: An energy source, which provides an energy beam; A positioning mechanism for relatively positioning the surface of a sample and the energy beam to provide an ablation point at one of a plurality of locations on the surface, the surface containing the area to be analyzed; A light-collecting lens, which is guided to collect the emission spectrum from the ablation point; A spectrometer, wherein the spectrometer is optically connected to a light-collecting lens; and A controller, which communicates with the positioning mechanism, is used to guide the movement of the ablation point on the surface along an arc path defined by a plurality of arcs to the plurality of locations, the plurality of arcs extending from one edge of the region to the other edge of the region and each arc being concave in the scanning direction.

25. The system of claim 24, further comprising an F-θ lens in the path of the energy beam.

Images