Improved EDS calibration

Abstract

The present invention relates to improved EDS calibration and provides a method wherein the method comprises: providing reference data indicative of at least one reference energy dispersive X-ray spectrum; providing measurement data indicative of at least one measured energy dispersive X-ray spectrum obtained from the sample; and determining a transformation based on a comparison of the measurement data and the reference data. The invention also relates to a system configured to perform the method.

Description

Technical Field

[0001] The present invention generally relates to methods and structures for identifying the composition of a sample using an energy dispersive spectroscopy system. Background Art

[0002] Mineral analysis systems, such as those from FEI Company (the assignee of the present invention) (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) and MLA (Mineral Dissociation Analyzer) have been used for many years to determine the presence of valuable minerals in mines. Such systems direct an electron beam to a sample and measure the energy of X-rays from the material in response to the electron beam. One such process is called "energy dispersive X-ray analysis" or "EDS", which can be used for elemental analysis or chemical characterization of a sample. Determining the elements present in a mineral sample is called "elemental decomposition". Beams other than electron beams can also be used to excite the sample. For example, an X-ray beam or an ion beam can be used as an alternative.

[0003] EDS systems rely on the emission of X-rays from a sample to perform elemental analysis. Each element has a unique atomic structure, so the X-rays that are characteristic of the element's atomic structure are unique to that element. To stimulate the emission of X-rays from a sample, a beam is directed onto the sample so that electrons from an inner shell are ejected. Electrons from the outer shell manage to fill the electron hole, and the energy difference between the higher energy shell and the lower energy shell is released as X-rays, which can be detected by a suitable detector.

[0004] By using an energy dispersive spectrometer to measure the number and energy of X-rays emitted from a sample and comparing the measured spectrum with a reference library, the unknown elemental composition of the sample can be determined. The reference library may include reference features of known components. The reference features may, for example, include reference spectra and / or reference element intensity values. EDS analysis, especially when combined with backscattered electron (BSE) analysis, can be used to quantify a wide range of mineral properties, such as mineral abundance, particle size, and degree of dissociation, i.e., how easily the desired mineral is separated from the background material. Existing EDS analysis systems include QEM / SEM technology, which is assigned to FEI Company, Inc, the assignee of the present invention.

[0005] A mineral classification system must be able to compare each unknown measured spectrum to a library of known mineral signatures and then select a known mineral based on which of the known minerals is most similar to the measured spectrum. Typically, in order to [TP386530EPPRI1]

[0006] Finding the most similar known mineral requires using a metric that represents the degree of similarity between the measured data and the known material.

[0007] This type of mineral analysis system is also used in the oil and gas industry. Drill cuttings (rock cuttings induced by the drill bit) and diamond drill cores can be analyzed to allow geologists to determine the exact nature of the materials encountered during drilling, which in turn allows more accurate predictions about the materials still before drilling, thus reducing risks in exploration and production. During drilling, a liquid called "mud" is injected into the well to lubricate the drill rig and remove the drill cuttings from the well. Samples can be taken from the mud including the cuttings from the drill rig. Recording drill cuttings and drill cores as accurately as possible during and after drilling is an important aspect of analyzing the drilling process. The information obtained from cutting and coring samples allows characterization of downhole lithologic changes in reservoir sequences, a key requirement in exploration and production wells, and mineralogical and petrographic studies reinforce the basic understanding of reservoir and seal characteristics. Traditional optical, scanning electron microscope (SEM), electron probe microanalyzer (EPMA) and X-ray diffraction (XRD) analysis methods are well established and widely used in the industry.

[0008] Mineral analysis attempts to identify what minerals are present and their relative proportions at whatever point the electron beam is pointed at. Analytical instruments typically measure the X-ray signal, determine what elements are present, and then use a database of mineral definitions to convert the element list into a mineral identification.

[0009] Specific minerals always have peaks at certain energies in the X-ray spectrum. In order to accurately determine which peaks correspond to which minerals, it is necessary to calibrate the instrument before it can identify the unknown mineral. For this reason, instrument calibration techniques are particularly important for meaningful analysis.

[0010] EDS instruments are typically calibrated using either standards-based calibration or standardless calibration. In standards-based calibration, known materials called "standards" are analyzed and the results are used to build a reference library. The unknown sample is then compared to the reference library to determine what elements are present. The calibration standards must be analyzed under the same conditions as those used to analyze the unknown material. Because the conditions in the measuring instrument depend on many factors, conventional standards-based calibration requires a full set of standards to be measured every day when the machine is in use. For example, the QemScan instrument described above currently identifies up to 72 different elements found in mineral samples. Conventional standards-based calibration would require each instrument to have a set of 72 element / mineral standards to generate a complete set of elemental signatures. This type of calibration is very expensive both in terms of the cost of supplying a standard block containing a complete set of element and mineral standards, as well as in terms of the operator time required and the reduced instrument throughput. Additionally, because there are several elements that are only present in minerals and cannot be measured individually, it is not possible to perform this type of calibration for these elements.

[0011] Factory calibration using prior art methods is not practical because conventional standards-based decomposition requires that all elements be obtained on the same machine under the same conditions as the X-ray spectrum of the mineral being analyzed [TP386530EPPRI1]

[0012] Standard X-ray Spectra. Prior art suggests that elemental X-ray spectra need to be measured on the same machine and cannot be taken from another machine based on standard elemental analysis requirements. This is because variations in the way a user sets up a particular instrument (including, for example, specific sample geometry, height, etc.) will change the properties of the X-ray spectrum and affect the calibration.

[0013] With standardless EDS analysis, analysis of a specific mineral sample can be performed without comparison to known standards. Based on the characteristics of the collected spectrum, the element list is narrowed down and one element is finally selected. Standardless analysis is much more complex and has greater inaccuracies than standard-based analysis, but it provides the user with an easy setup since it does not require the instrument to be calibrated using certain parameters for all possible elements.

[0014] Therefore, there is a need for an effective calibration method and apparatus that is less expensive, simpler and easier to implement, and allows for faster measurement of samples. Summary of the invention

[0015] The present invention relates to a method comprising: providing reference data indicating at least one reference energy-dispersive X-ray spectrum; providing measurement data indicating at least one measured energy-dispersive X-ray spectrum obtained from a sample; and determining a transformation based on a comparison of the measurement data with the reference data.

[0016] An object of the invention may be to increase the match between the measured data and the reference data via the determined transformation. This in turn may provide a better identification of the material constituting the sample.

[0017] It is particularly advantageous to align the measured data and the reference data. This means that the X-ray emission lines of the elements in the reference data and the measured data have the same energy. Typically, the X-ray emission lines of the elements may be represented by corresponding spectrum peaks in the measured data and the reference data. Ideally, for the same X-ray emission line, the peaks in the measured spectrum and the peaks in the reference spectrum should be identical. However, this may not be the case for various reasons. Namely, there may be differences in how the X-ray emission lines are represented in the reference data and how they are represented in the measured data.

[0018] There are several reasons for this difference or mismatch. One such reason may be related to hardware inaccuracies. Different hardware devices may introduce different errors when obtaining measurement data or reference data. Even if the same hardware device is used to obtain reference data and measurement data, hardware drift may still cause differences between reference data and measurement data. Another reason may be related to the process of obtaining measurement data. Due to efficiency reasons, the accuracy of measurement data acquisition may be reduced, resulting in measurement data with inherent inaccuracies. Other reasons may involve inefficient alignment or calibration algorithms and / or user errors.

[0019] [TP386530EPPRI1]

[0020] Additionally, when the sample is analyzed, for example, with an EDS instrument, such differences may lead to misidentification of the materials that make up the sample. This is often the case with materials with similar chemical properties, which can easily be confused for each other.

[0021] Therefore, the present invention can alleviate these problems by determining the transformation between the measured data and the reference data.

[0022] The measurement data may include measurement spectrum peaks. The measurement spectrum peaks may generally have a bell curve shape. They may generally resemble a Gaussian function. The measurement spectrum peaks may indicate a specific energy level at which a sample emits a large number of X-rays. In addition, each measurement spectrum peak may provide information about the number of X-rays detected at that specific energy level. In general, each measurement spectrum peak may indicate, for a series of consecutive energy levels, a corresponding count of X-rays emitted within the series.

[0023] Each measured peak can indicate the corresponding element in the sample.

[0024] Specifically, each measured spectral peak may be indicative of a specific X-ray emission line of a corresponding element in the sample.

[0025] The method may include detecting measured spectrum peaks on the measurement data. The detection process typically includes identifying portions of the measured spectrum where the X-ray counts exceed a predetermined detection threshold for background radiation and any other noise sources.

[0026] Throughout the specification, the terms "X-ray counts" and "X-ray intensity" are used interchangeably.

[0027] The reference data may include reference spectral peaks. The above discussion of measuring spectral peaks applies mutatis mutandis to reference spectral peaks.

[0028] Each reference spectrum peak can indicate a corresponding element.

[0029] Each reference spectrum peak may indicate a specific X-ray emission line of the corresponding element.

[0030] The method may further comprise detecting calibration peaks on the measurement data. The calibration peaks may be peaks in the measured spectrum which may be used for calibration, i.e. for increasing the match between the measurement data and the reference data. In particular, the calibration peaks may be used to determine the transformation. It may be advantageous that the calibration peaks may be such that they may clearly indicate how a particular X-ray emission line was detected during the acquisition of the measurement data. Thus, the calibration peaks may be used as ground truth about how a particular instrument (i.e. the instrument used to obtain the measurement data) may detect a particular X-ray emission line represented by the calibration peak. This information may be used to perform a corresponding modification of the reference data.

[0031] The calibration peak may include an intensity that may be higher than the intensity of the background radiation. In this way, it can be ensured that the calibration peak indicates the elements present in the sample. That is, it can be ensured that the calibration peak indicates the X-rays emitted by the sample and not other sources.

[0032] [TP386530EPPRI1]

[0033] The intensity of a calibration peak may refer to the maximum intensity of the calibration peak.

[0034] Additionally, the term "intensity" may refer to X-ray counts.

[0035] The background radiation intensity may refer to the intensity of background radiation including an energy similar to the energy of the calibration peak. That is, for different calibration peaks, the background radiation intensity may be different depending on the energy of the calibration peak. For example, an energy region containing the calibration peak may be defined for determining the intensity of the background radiation. This may, for example, be an average value of the intensity of the background radiation in the energy region.

[0036] Furthermore, background radiation intensity may be used herein to refer to the intensity of radiation generated by any source other than the sample.

[0037] For each calibration peak, the ratio of the intensity of the calibration peak to the intensity of the background radiation may be above an intensity ratio threshold. The intensity ratio threshold may be a user defined parameter. Furthermore, the intensity ratio threshold may be adjustable.

[0038] The intensity ratio thresholds can be configured so that it can be ensured that the calibration peaks are indeed likely to be caused by X-rays emitted by the sample. In addition, the intensity ratio thresholds can be configured so that they are caused by elements in the sample that have a significant weight percentage in the sample. In this way, the calibration peaks can be well-defined peaks that can allow their energy levels to be read more accurately.

[0039] Each calibration peak may be unblocked such that any other spectral peak in the measurement data that is present in the same measured spectrum as the calibration peak has an energy difference from the calibration peak that is greater than a blockage threshold.

[0040] The calibration peaks may be a subset of the measured spectrum peaks. As described above, it may be advantageous to have calibration peaks such that they may clearly indicate how a particular X-ray emission line was detected during the acquisition of the measurement data. That is, it may be advantageous for the calibration peaks to be well-defined peaks. Thus, not every measured spectrum peak in the measurement data may be used as a calibration peak, but rather a subset thereof. The subset may consist of measured spectrum peaks that meet predefined criteria.

[0041] Detecting calibration peaks on the measurement data may include classifying at least some of the measurement spectrum peaks as calibration peaks.

[0042] Classifying at least some of the measured spectrum peaks as calibration peaks may be based on respective intensities of the measured spectrum peaks.

[0043] Classifying at least some of the measured spectrum peaks as calibration peaks may be based on the intensity of the measured spectrum peaks relative to the intensity of background radiation.

[0044] If the ratio of the intensity of the measured spectrum peak to the background radiation intensity may be above an intensity ratio threshold, the measured spectrum peak may be classified as a calibration peak.

[0045] Classifying at least some of the measured spectrum peaks as calibration peaks may be based on the energy of the measured spectrum peaks.

[0046] [TP386530EPPRI1]

[0047] A specific measurement peak may be classified as a calibration peak if it is unobstructed such that the energy difference between any other measurement peak in the measurement data present in the same measurement spectrum as the specific measurement peak and the specific measurement peak exceeds a blocking threshold.

[0048] If at least one measured spectral peak may be the highest peak among the measured spectral peaks corresponding to the same X-ray emission line within the measurement data, it may be classified as a calibration peak.

[0049] In some embodiments, detecting calibration peaks on the measurement data may include, for each measurement spectrum in the measurement data, detecting all measurement spectrum peaks in the measurement spectrum. The method may also include, for each measurement spectrum in the measurement data, rejecting measurement spectrum peaks in the measurement spectrum that include a peak-to-background ratio that is less than an intensity ratio threshold, wherein the peak-to-background ratio is the ratio of the intensity of the measurement spectrum peak to the intensity of background radiation. Alternatively or in addition, the method may include, for each measurement spectrum, rejecting measurement spectrum peaks in the measurement spectrum that overlap with other measurement spectrum peaks in the measurement spectrum, wherein two peaks in the measurement spectrum overlap if they include an energy difference that is less than a blocking threshold.

[0050] The non-rejected measured spectral peaks can be grouped according to the X-ray emission lines they indicate. That is, each group includes non-rejected measured spectral peaks that may indicate the same X-ray emission line.

[0051] In each group, the non-rejected measured spectrum peak with the highest peak-to-background ratio can be determined as the calibration peak. Therefore, if there are multiple non-rejected measured spectrum peaks in the measurement data, the most clearly defined peak can be determined as the calibration peak. In other words, generally any non-rejected measured spectrum peak can be a calibration peak. However, if there are multiple non-rejected measured spectrum peaks for the same X-ray emission line, only one of them may be sufficient. In such cases, the peak with the highest peak-to-background ratio can be determined as the calibration peak, which can be selected as the calibration peak.

[0052] Determining the transformation may include determining at least one piecewise transformation based on the calibration peaks and the reference data.

[0053] The piecewise transformation can allow for fine alignment between the reference data and the measured data. It can be particularly advantageous because it can mitigate non-linear misalignment between the reference data and the measured data. That is, it is often the case that the misalignment between the reference data and the measured data can be a non-linear function of energy. Therefore, in such cases, simply performing a linear transformation of the entire reference data may not be sufficient. The piecewise transformation addresses this by allowing different transforms to be applied over different energy regions.

[0054] The at least one piecewise transformation may be applicable to a portion of the total energy range of the reference data. The portion may be between (inclusive of) the minimum energy and the maximum energy of the calibration peak. In other words, the at least one piecewise transformation as a whole may be applicable to a portion of the total energy range of the reference data. Assuming that the piecewise transformation can be determined based on the calibration peak, the portion to which the piecewise transformation is applicable may be bounded by the minimum energy and the maximum energy of the calibration peak.

[0055] [TP386530EPPRI1]

[0056] Outside of said parts, transforms other than piecewise transforms may be applied.

[0057] Each of the at least one piecewise transform may be determined based on a corresponding pair of consecutive calibration peaks, wherein the two calibration peaks may be consecutive provided that no other calibration peak of the measurement data includes an energy between the energies of the two consecutive calibration peaks.

[0058] Each of the at least one piecewise transform may be selectively applied to a corresponding piecewise energy region of the reference data containing energies between or equal to corresponding energies of a corresponding pair of calibration peaks.

[0059] In short, a piecewise transformation can be determined using two consecutive calibration peaks, and the piecewise transformation can be applicable to an energy region bounded by the energies of the two consecutive calibration peaks. Outside the energy region bounded by the energies of the two consecutive calibration peaks, other piecewise transformations and / or transformations other than the piecewise transformation can be applicable. The above is true for any pair of consecutive calibration peaks.

[0060] Determining the transformation may include determining a plurality of piecewise transformations, wherein each piecewise transformation may be determined based on a corresponding pair of consecutive calibration peaks, wherein the two calibration peaks may be consecutive provided that no other calibration peaks of the measurement data may exist between the two calibration peaks.

[0061] Each of the piecewise transforms may be selectively applied to a corresponding piecewise energy region of the reference data containing energies between or equal to corresponding energies of a corresponding pair of target measurement peaks.

[0062] Each of the at least one piecewise transform may be a linear transform.

[0063] The method may include storing the segmented transformation in a memory device.

[0064] The method may include storing coefficients indicative of the piecewise transform in a memory device.

[0065] Each piecewise transform of the at least one piecewise transform may be a sub-function of a piecewise function.

[0066] The method may include respectively calculating reference peak width parameters for a plurality of reference spectral peaks.

[0067] Each reference peak width parameter may indicate an energy range encompassed by a corresponding reference spectral peak.

[0068] Each reference peak width parameter may indicate the spread of a corresponding reference spectral peak along an energy axis.

[0069] Each reference peak width parameter may indicate the standard deviation of the corresponding reference spectral peak.

[0070] Each reference peak width parameter may include a variance of a corresponding reference spectral peak.

[0071] The method may include calculating measured peak width parameters for the plurality of measured spectral peaks, respectively.

[0072] The method may include calculating a measurement peak width parameter only for unobstructed measurement peaks, wherein a particular measurement peak may be unobstructed if any other peak in the measurement data present in the same measurement spectrum as the particular measurement peak has an energy difference of more than a blocking threshold from the particular measurement peak. It may be advantageous to utilize measurement peak width parameters only for unobstructed measurement peaks. These measurement peaks may clearly indicate [TP386530EPPRI1]

[0073] How specific X-ray emission lines were detected during the acquisition of the measurement data. Therefore, these measurement spectrum peaks can be used as ground truth about how a specific instrument (i.e., the instrument used to obtain the measurement data) can detect specific X-ray emission lines. This information can be used to perform corresponding modifications to the reference data.

[0074] Each measured peak width parameter may indicate an energy range encompassed by a corresponding measured spectral peak.

[0075] Each measured peak width parameter may indicate the spread of a corresponding measured spectral peak along an energy axis.

[0076] Each measured peak width parameter may indicate the standard deviation of the corresponding measured spectral peak.

[0077] Each measured peak width parameter may include the variance of the corresponding measured spectral peak.

[0078] Determining the transformation may include determining the peak width transformation based on the reference peak width parameters and the measured peak width parameters.

[0079] Peak width transformation may be advantageous because it may allow the shape, in particular the width, of the peaks of the reference data to be adjusted so that they may better match the measured data.

[0080] The peak width transformation can be applied to the entire energy range of the reference data.

[0081] The method may include fitting a reference peak width function on the reference peak width parameters, and fitting a measured peak width function on the measured peak width parameters. Thus, the reference peak width function may represent the reference peak width parameters. Similarly, the measured peak width function may therefore represent the measured peak width parameters.

[0082] The reference peak width function and the measured peak width function may be extrapolated over the entire range of energies of the reference data.

[0083] The peak width shift may be determined based on the reference peak width function and the measured peak width function.

[0084] The peak width shift may be determined based on a difference between a reference peak width function and a measured peak width function.

[0085] The peak width shift may be determined based on the square root of the square difference between the reference peak width function and the measured peak width function.

[0086] The method may include storing the peak width transformation in a memory device.

[0087] The method may include storing a function indicative of a peak width transition in a memory device.

[0088] Peak width shifts can be energy related.

[0089] Applying the peak width transformation may include adjusting a reference peak width parameter of at least one reference spectral peak using the peak width transformation. In this way, the width of the reference spectral peak may be adjusted to better match the width of the measured data.

[0090] Determining the transformation may include determining an end-to-end transformation based on the first measured spectral peak, the second measured spectral peak and the reference data. That is, the end-to-end transformation may utilize only two measured spectral peaks.

[0091] The end-to-end transformation can be applied to the entire energy range of the reference data.

[0092] The end-to-end transformation may be a linear transformation.

[0093] The first measured spectrum peak may be a first unobstructed measured spectrum peak having the lowest energy in the measured data, and the second measured spectrum peak may be a second unobstructed measured spectrum peak having the highest energy in the measured data [TP386530EPPRI1]

[0094] spectral peaks, wherein a particular measured spectral peak may be unobstructed if any other spectral peak in the measured data present in the same measured spectrum as the particular measured spectral peak has an energy difference of more than a blocking threshold from the particular measured spectral peak. In other words, the unobstructed peaks with the lowest energy and the highest energy of the measured data may be used to determine the end-to-end transformation.

[0095] Applying the end-to-end transformation may include applying the end-to-end transformation in an energy region that includes energies less than a minimum energy of the calibration peak and energies greater than a maximum energy of the calibration peak. In other words, application of the end-to-end transformation may be limited to energy regions that fall outside a range defined by the calibration peaks having the lowest energy and the highest energy. In short, in energy regions where a piecewise transformation may be applied, an end-to-end transformation may not be necessary.

[0096] The method may further comprise applying the transformation to the reference data to generate calibrated reference data. The calibrated reference data may thus better match the measured data. That is, the calibrated reference data may comprise smaller differences from the reference data.

[0097] Applying the transformation to the reference data to generate calibrated reference data may include modifying the reference data based on the transformation.

[0098] Applying the transform may include applying the at least one piecewise transform.

[0099] Applying the transformation may include applying a peak width transformation.

[0100] Applying the transformation may include applying an end-to-end transformation.

[0101] Applying the transform may include applying a peak width transform prior to applying the at least one piecewise transform.

[0102] Applying the transformation may include applying the at least one piecewise transformation in an energy region containing energies between (including the end values) a minimum energy and a maximum energy of the calibration peak, and applying an end-to-end transformation in an energy region containing energies less than the minimum energy of the calibration peak and energies greater than the maximum energy of the calibration peak.

[0103] The method may also include determining elements contained in the sample by comparing the measurement data to calibrated reference data.

[0104] The method may further include determining the elemental composition of the sample by elemental decomposition based on a comparison of the measured data with calibrated reference data.

[0105] Providing reference data may include: using a source instrument, generating reference data by the following steps: using a beam source of the source instrument to emit a beam toward one or more element standards; using an X-ray detector of the source instrument to obtain an energy dispersive X-ray spectrum of the one or more element standards; and generating reference data from the spectrum of the one or more element standards.

[0106] [TP386530EPPRI1]

[0107] Obtaining a spectrum of the elemental standard may include obtaining a spectrum of the elemental standard with a high resolution instrument setting that can detect at least one million X-ray counts.

[0108] Obtaining spectra of elemental standards may include obtaining spectra of all naturally occurring elements in a mineral analysis.

[0109] Providing reference data may include: using an on-site instrument to generate measurement data by: using a beam source of the on-site instrument to emit a beam toward a sample; using an X-ray detector of the on-site instrument to obtain at least one energy-dispersive X-ray spectrum of the sample; and generating measurement data from at least one energy-dispersive X-ray spectrum of the sample.

[0110] Obtaining at least one energy dispersive X-ray spectrum of the sample may include obtaining at least one energy dispersive X-ray spectrum of the sample at a lower resolution instrument setting than a high resolution instrument setting used to generate the reference data.

[0111] The method may also include identifying the sample.

[0112] The invention may also relate to a method of calibrating an instrument for analysis, comprising the method in question.

[0113] The present invention may also relate to a system comprising: a beam source for emitting a beam onto a sample; an X-ray detector for detecting X-rays emitted from the sample when the beam hits it; a computer-readable memory storing reference data indicating at least one reference energy-dispersive X-ray spectrum and computer instructions for: obtaining measurement data indicating at least one measured energy-dispersive X-ray spectrum obtained from the sample; and determining a transformation based on a comparison of the measurement data with the reference data.

[0114] The computer readable memory may also store computer instructions for applying the transformation to the reference data to generate calibrated reference data.

[0115] The computer readable memory may also store computer instructions for comparing the measurement data to calibrated reference data to determine elements contained in the sample.

[0116] The system may also include a data processing system configured to receive computer instructions from the computer readable memory and execute the computer instructions.

[0117] The system may be configured to perform any of the method embodiments discussed above and below.

[0118] The present disclosure also relates to the following numbered embodiments.

[0119] M1. A method comprising:

[0120] providing reference data indicative of at least one reference energy dispersive X-ray spectrum;

[0121] [TP386530EPPRI1]

[0122] providing measurement data indicative of at least one measured energy dispersive X-ray spectrum obtained from the sample;

[0123] A transformation is determined based on a comparison of the measurement data with the reference data.

[0124] M2. A method according to any of the preceding embodiments, wherein the measurement data comprises measurement of spectral peaks.

[0125] M3. A method according to the previous embodiment, wherein each measured spectrum peak indicates a corresponding element in the sample.

[0126] M4. A method according to any one of the preceding two embodiments, wherein each measured spectral peak indicates a specific X-ray emission line of a corresponding element in the sample.

[0127] M5. A method according to any of the preceding embodiments, wherein the method comprises detecting measurement spectrum peaks on the measurement data.

[0128] M6. A method according to any of the preceding embodiments, wherein the reference data comprises reference spectral peaks.

[0129] M7. The method according to the preceding embodiment, wherein each reference spectral peak indicates a corresponding element. M8. The method according to any one of the preceding 2 embodiments, wherein each reference spectral peak indicates a specific X-ray emission line of a corresponding element.

[0130] M9. A method according to any of the preceding embodiments, further comprising detecting a calibration peak on the measurement data.

[0131] M10. A method according to the previous embodiment, wherein the calibration peak includes an intensity higher than the background radiation intensity.

[0132] M11. A method according to any one of the preceding two embodiments, wherein for each calibration peak, the ratio of the intensity of the calibration peak to the background radiation intensity is higher than an intensity ratio threshold.

[0133] M12. A method according to any one of the preceding three embodiments, wherein each calibration peak is unobstructed, so that any other spectral peak in the measurement data present in the same measurement spectrum as the calibration peak has an energy difference with the calibration peak that is greater than a blocking threshold.

[0134] M13. A method according to any one of the preceding 4 embodiments and having the features of embodiment M2, wherein the calibration peaks are a subset of the measured spectrum peaks.

[0135] M14. A method according to any one of the preceding five embodiments and having the features of embodiment M2, wherein detecting calibration peaks on the measurement data comprises classifying at least some of the measurement spectrum peaks as calibration peaks.

[0136] [TP386530EPPRI1]

[0137] M15. A method according to the previous embodiment, wherein the classification of at least some of the measured spectral peaks as calibration peaks is based on the corresponding intensities of the measured spectral peaks.

[0138] M16. A method according to any one of the preceding two embodiments, wherein classification of at least some of the measured spectral peaks as calibration peaks is based on the intensity of the measured spectral peaks relative to the intensity of background radiation.

[0139] M17. A method according to any one of the preceding three embodiments, wherein if the ratio of the intensity of the measured spectral peak to the background radiation intensity is higher than an intensity ratio threshold, the measured spectral peak is classified as a calibration peak.

[0140] M18. A method according to any of the preceding 4 embodiments, wherein classification of at least some of the measured spectral peaks as calibration peaks is based on the energy of the measured spectral peaks.

[0141] M19. A method according to any one of the foregoing five embodiments, wherein if a specific measurement spectral peak is unobstructed so that the energy difference between any other measurement spectral peak in the measurement data present in the same measurement spectrum as the specific measurement spectral peak and the specific measurement spectral peak exceeds a blocking threshold, then the specific measurement spectral peak is classified as a calibration peak.

[0142] M20. A method according to any one of the foregoing six embodiments, wherein at least one measured spectral peak is classified as a calibration peak if the at least one measured spectral peak is the highest peak among the measured spectral peaks corresponding to the same X-ray emission line in the measurement data.

[0143] M21. A method according to any of the preceding embodiments and having the features of embodiment M9, wherein detecting a calibration peak on the measurement data comprises

[0144] (a) For each measured spectrum in the measurement data:

[0145] (a1) detecting all measurement peaks in the measurement spectrum;

[0146] (a2) rejecting a measured spectrum peak in the measured spectrum that includes a peak-to-background ratio that is less than an intensity ratio threshold, wherein the peak-to-background ratio is a ratio of the intensity of the measured spectrum peak to the intensity of background radiation;

[0147] (a3) rejecting measured peaks in the measured spectrum that overlap with other measured peaks in the measured spectrum, wherein two peaks in the measured spectrum overlap if they comprise an energy difference that is less than a blockade threshold;

[0148] (b) grouping all non-rejected measured peaks from (a) according to the X-ray emission lines they indicate;

[0149] (c) In each of the groups, the non-rejected measured spectrum peak having the highest peak-to-background ratio is determined as the calibration peak.

[0150] [TP386530EPPRI1]

[0151] M22. A method according to any of the preceding embodiments and having the features of embodiment M9, wherein determining a transformation comprises determining at least one piecewise transformation based on the calibration peak and the reference data.

[0152] M23. A method according to the previous embodiment, wherein the at least one piecewise transformation is capable of being applied to a portion of the total energy range of the reference data.

[0153] M24. A method according to the previous embodiment, wherein the portion is between the minimum energy and the maximum energy of the calibration peak, including the end values.

[0154] M25. A method according to any one of the preceding 3 embodiments, wherein each of the at least one segmented transformation is determined based on a corresponding pair of consecutive calibration peaks,

[0155] Wherein two calibration peaks are consecutive, the proviso is that no other calibration peak of the measurement data includes an energy between the energies of the two consecutive calibration peaks.

[0156] M26. The method of the preceding embodiment, wherein each of the at least one piecewise transform is selectively applied to a corresponding piecewise energy region of the reference data, the corresponding piecewise energy region containing energies between or equal to the corresponding energies of the corresponding pair of calibration peaks. M27. The method of any of the preceding embodiments and having the features of embodiment M9, wherein the determining the transform comprises determining a plurality of piecewise transforms,

[0157] Each segmented transformation is determined based on a corresponding pair of consecutive calibration peaks.

[0158] Two calibration peaks are continuous if no other calibration peaks of the measurement data are located between the two calibration peaks.

[0159] M28. A method according to the previous embodiment, wherein each of the segmented transformations is selectively applied to a corresponding segmented energy region of the reference data, and the corresponding segmented energy region contains energies between or equal to the corresponding energies of a corresponding pair of target measurement peaks.

[0160] M29. A method according to any one of the preceding 7 embodiments, wherein each of the at least one segmented transform is a linear transform.

[0161] M30. A method according to any of the preceding 8 embodiments, wherein the method comprises storing the segmented transformation in a memory device.

[0162] [TP386530EPPRI1]

[0163] M31. A method according to any one of the preceding 9 implementations, wherein the method includes storing coefficients indicating the segmented transformation in a memory device.

[0164] M32. A method according to any one of the preceding 10 implementations, wherein each of the at least one piecewise transformation is a sub-function of a piecewise function.

[0165] M33. A method according to any of the preceding embodiments, wherein the method comprises separately calculating reference peak width parameters of a plurality of reference spectral peaks.

[0166] M34. A method according to the previous embodiment, wherein each reference peak width parameter indicates an energy range encompassed by the corresponding reference spectral peak.

[0167] M35. A method according to any one of the preceding two embodiments, wherein each reference peak width parameter indicates an extension of the corresponding reference spectral peak along an energy axis.

[0168] M36. A method according to any one of the preceding three embodiments, wherein each reference peak width parameter indicates the standard deviation of the corresponding reference spectral peak.

[0169] M37. A method according to any one of the preceding 4 embodiments, wherein each reference peak width parameter comprises the variance of the corresponding reference spectral peak.

[0170] M38. A method according to any of the preceding embodiments, wherein the method comprises separately calculating the measured peak width parameters of a plurality of measured spectral peaks.

[0171] M39. A method according to the preceding embodiment, wherein the method comprises calculating the measurement peak width parameter only for unobstructed measurement peaks, wherein the specific measurement peak is unobstructed if the energy difference between any other peak in the measurement data present in the same measurement spectrum as the specific measurement peak and the specific measurement peak exceeds a blocking threshold. M40. A method according to any one of the preceding 2 embodiments, wherein each measurement peak width parameter indicates an energy range encompassed by the corresponding measurement peak.

[0172] M41. A method according to any one of the preceding three embodiments, wherein each measured peak width parameter indicates an extension of the corresponding measured spectral peak along an energy axis.

[0173] M42. A method according to any one of the preceding 4 embodiments, wherein each measured peak width parameter indicates a standard deviation of the corresponding measured spectral peak.

[0174] M43. A method according to any one of the preceding five embodiments, wherein each measured peak width parameter comprises the variance of the corresponding measured spectral peak.

[0175] M44. A method according to any one of the preceding embodiments and having the features of embodiments M33 and M38, wherein determining the transformation comprises determining the peak width transformation based on the reference peak width parameters and the measured peak width parameters.

[0176] [TP386530EPPRI1]

[0177] M45. A method according to the previous embodiment, wherein the peak width transformation can be applied to the entire energy range of the reference data.

[0178] M46. A method according to any one of the preceding two embodiments, wherein the method comprises fitting a reference peak width function on the reference peak width parameters, and fitting a measured peak width function on the measured peak width parameters.

[0179] M47. A method according to the previous embodiment, wherein the peak width transformation is determined based on the reference peak width function and the measured peak width function.

[0180] M48. A method according to any one of the preceding two embodiments, wherein the peak width transformation is determined based on the difference between the reference peak width function and the measured peak width function.

[0181] M49. A method according to any one of the preceding three embodiments, wherein the peak width transformation is determined based on the square root of the square difference between the reference peak width function and the measured peak width function.

[0182] M50. A method according to any one of the preceding six embodiments, wherein the method comprises storing the peak width transformation in a memory device.

[0183] M51. A method according to any one of the preceding 7 embodiments, wherein the method comprises storing a function indicative of the peak width transformation in a memory device.

[0184] M52. A method according to any one of the preceding 8 embodiments, wherein the peak width change is energy-related.

[0185] M53. A method according to any one of the preceding 9 embodiments, wherein applying the peak width transform comprises using the peak width transform to adjust the reference peak width parameter of at least one reference spectral peak.

[0186] M54. A method according to any one of the preceding embodiments,

[0187] Wherein determining the transformation comprises determining an end-to-end transformation based on the first measured spectrum peak, the second measured spectrum peak and the reference data.

[0188] M55. A method according to the previous embodiment, wherein the end-to-end transformation can be applied to the entire energy range of the reference data.

[0189] M56. A method according to any one of the preceding 2 embodiments,

[0190] wherein the first measured spectrum peak is the first unobstructed measured spectrum peak having the lowest energy in the measured data, and

[0191] The second measured spectrum peak is a second unobstructed measured spectrum peak having the highest energy in the measured data,

[0192] [TP386530EPPRI1]

[0193] If the energy difference between any other spectral peak in the measurement data present in the same measurement spectrum as the specific measurement spectral peak and the specific measurement spectral peak exceeds a blocking threshold, the specific measurement spectral peak is unblocked.

[0194] M57. A method according to any one of the preceding three embodiments and having the features of embodiment M9, wherein applying the end-to-end transformation includes applying the end-to-end transformation in an energy region comprising energies less than a minimum energy of the calibration peak and energies greater than a maximum energy of the calibration peak.

[0195] M58. A method according to any of the preceding embodiments, the method further comprising applying the transformation to the reference data to generate calibrated reference data.

[0196] M59. A method according to the previous embodiment, wherein applying the transformation to the reference data to generate calibrated reference data includes modifying the reference data based on the transformation.

[0197] M60. The method according to any one of the preceding 2 embodiments and having the features of embodiment M22, wherein applying the transformation comprises applying the at least one piecewise transformation. M61. The method according to any one of the preceding 3 embodiments and having the features of embodiment M44, wherein applying the transformation comprises applying the peak width transformation.

[0198] M62. A method according to any one of the preceding 4 embodiments and having the features of embodiment M54, wherein applying the transformation includes applying the end-to-end transformation.

[0199] M63. A method according to any one of the preceding five embodiments and having the features of embodiments M22 and M44, wherein applying the transformation includes applying the peak width transformation before applying the at least one piecewise transformation.

[0200] M64. A method according to any one of the preceding 6 embodiments and having the features of embodiments M22 and M54, wherein applying the transformation comprises

[0201] applying the at least one piecewise transformation over an energy region containing energies between a minimum energy and a maximum energy of the calibration peak, the energy region including the minimum energy and the maximum energy of the calibration peak, and

[0202] The end-to-end transformation is applied over an energy region that includes energies less than the minimum energy of the calibration peak and energies greater than the maximum energy of the calibration peak.

[0203] M65. A method according to any one of the preceding 7 embodiments, further comprising determining the elements contained in the sample by comparing the measurement data with the calibrated reference data.

[0204] [TP386530EPPRI1]

[0205] M66. A method according to any one of the preceding eight embodiments, further comprising determining the elemental composition of the sample by elemental decomposition based on comparison of the measurement data with the calibrated reference data.

[0206] M67. A method according to any one of the preceding embodiments, wherein providing reference data comprises:

[0207] Using the source instrument, generate the reference data by following these steps:

[0208] emitting a beam toward one or more element standards using a beam source of the source instrument;

[0209] obtaining an energy dispersive X-ray spectrum of the one or more elemental standards using an X-ray detector of the source instrument;

[0210] The reference data is generated from the spectra of the one or more element standards. M68. The method according to the preceding embodiment, wherein obtaining spectra of element standards comprises obtaining spectra of element standards with a high resolution instrument setting that detects at least one million X-ray counts.

[0211] M69. A method according to any of the preceding two embodiments, wherein obtaining a spectrum of an elemental standard comprises obtaining spectra of all naturally occurring elements in a mineral analysis.

[0212] M70. A method according to any of the preceding embodiments, wherein providing measurement data comprises:

[0213] Using the field instrument, the measurement data is generated by the following steps:

[0214] emitting a beam toward the sample using a beam source of the in-situ instrument;

[0215] obtaining at least one energy dispersive X-ray spectrum of the sample using an X-ray detector of the in situ instrument; and

[0216] The measurement data is generated from the at least one energy dispersive X-ray spectrum of the sample.

[0217] M71. A method according to the previous embodiment, wherein obtaining at least one energy-dispersive X-ray spectrum of the sample includes obtaining at least one energy-dispersive X-ray spectrum of the sample with a resolution instrument setting lower than the high-resolution instrument setting used to generate the reference data.

[0218] M72. According to any of the preceding embodiments, the method also includes identifying the sample.

[0219] M73. A method according to any of the preceding embodiments and having the features of embodiment M54, wherein the end-to-end transformation is a linear transformation.

[0220] [TP386530EPPRI1]

[0221] M74. A method for calibrating an instrument for sample analysis, the method comprising a method according to any one of the preceding embodiments.

[0222] S1. A system, comprising:

[0223] a beam source for emitting a beam onto a sample;

[0224] an X-ray detector for detecting X-rays emitted from the sample upon impact of the beam;

[0225] A computer readable memory storing reference data indicative of at least one reference energy dispersive X-ray spectrum and computer instructions for:

[0226] obtaining measurement data indicative of at least one measured energy dispersive X-ray spectrum obtained from the sample;

[0227] A transformation is determined based on a comparison of the measurement data with the reference data.

[0228] S2. The system according to the preceding embodiment, wherein the computer readable memory further stores computer instructions for:

[0229] The transformation is applied to the reference data to generate calibrated reference data.

[0230] S3. The system according to the preceding embodiment, wherein the computer readable memory further stores computer instructions for:

[0231] The measured data is compared to the calibrated reference data to determine the elements contained in the sample.

[0232] S4. According to any one of the preceding three embodiments, the system further comprises a data processing system configured to receive the computer instructions from the computer readable memory and execute the computer instructions.

[0233] S5. A system according to any one of the preceding 4 embodiments, wherein the system is configured to perform a method according to any one of the preceding method embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0234] Figure 1 is a plot of the measured spectrum and the corresponding reference spectrum;

[0235] Figure 2 is a diagram showing misidentification of phases in a mineral;

[0236] Figure 3 The standard deviations of a plurality of reference spectral peaks and a plurality of measured spectral peaks and their corresponding fits are shown;

[0237] Figure 4 Shown is applied to Figure 3 Extrapolation of the standard deviation of

[0238] Figure 5 Shown based on Figure 4 Example of peak width transformation determined by extrapolation;

[0239] [TP386530EPPRI1]

[0240] Figure 6 The calibration peaks in the spectrum are shown;

[0241] Figure 7shows segmented energy portions along a spectrum, where corresponding segmented transforms may be selectively applied;

[0242] Figure 8 Shows the application Figure 7 The corresponding piecewise transformation of the piecewise energy part of ;

[0243] Fig. 9 is a plot of the measured spectrum and the corresponding reference spectrum and calibrated reference spectrum;

[0244] Fig.10 is a diagram indicating different phases in a mineral sample identified using the teachings of the present disclosure;

[0245] Fig.11 shows the peak energy differences between 3 different measurement data and corresponding reference data for scenarios where the reference data is not calibrated, the reference data is calibrated using the prior art, and the reference data is calibrated using the teachings of the present disclosure;

[0246] Fig.12 A method that can be used to calibrate reference data is shown;

[0247] Fig.13 A scanning electron beam with an X-ray detector suitable for analyzing a standard according to a preferred embodiment of the present invention is shown. DETAILED DESCRIPTION

[0248] A preferred embodiment of the present invention provides a method for calibrating a local energy dispersive spectroscopy (EDS) instrument using measurement data indicating at least one measured energy dispersive X-ray spectrum obtained from a sample. Preferably, the local EDS instrument may have stored reference data that may contain high-quality spectra of all elements analyzed. The measurement data is compared with the reference data, and the comparison is used to define a transformation. The transformation may then be applied to the reference data to generate calibrated reference data, which may include a calibration spectrum for each spectrum in the original reference data. Therefore, the spectrum contained in the reference data may be closer to the spectrum that would be produced if the corresponding element was analyzed using the same instrument settings on the same local instrument. The spectrum generated by the local EDS instrument may then be compared with the calibrated reference data to determine the elements in the sample. This can be used to greatly improve the accuracy of element identification.

[0249] Figure 1is a graph of a measured spectrum 14 and a corresponding reference spectrum 12. It should be understood that throughout the disclosure, unless the context implies otherwise, the term "spectrum" refers to an energy dispersive X-ray spectrum, i.e., a spectrum obtained using energy dispersive X-ray spectroscopy. In the accompanying drawings, the horizontal axis indicates the energy in keV (kiloelectron volts) of the detected X-rays emitted from the sample, and the vertical axis indicates the number of X-rays collected at each energy level, i.e., the number of photons or photon counts. Therefore, each spectrum indicates the number of X-rays detected at different energy levels. The number of X-rays can also be referred to as intensity.

[0250] [TP386530EPPRI1]

[0251] The measurement spectrum 14 may be part of the measurement data and may be obtained when analyzing a sample using an EDS instrument. Those skilled in the art will appreciate that each peak in the measurement spectrum 14 and in particular the energy of each peak indicates a corresponding chemical element. Throughout the disclosure, the terms "chemical element" and "element" are used interchangeably unless the context implies otherwise.

[0252] The corresponding reference spectrum 12 can be part of the reference data. As any spectrum in the reference data, it can usually be obtained by analyzing an element standard (i.e., a reference material of known composition) using an EDS instrument. In addition, the reference data can usually be obtained using a high-resolution setting of the EDS instrument. In addition, the reference data can preferably be obtained on the same type of EDS detector and / or using the same beam voltage as that used to obtain the measurement data. That is, it can be preferred to use similar conditions to obtain the reference data and the measurement data. This can increase the similarity between the measurement data and the corresponding reference data, thereby increasing the identification of the elements or phases in the sample.

[0253] However, since ensuring precise conditions for obtaining reference and measured data can be challenging, discrepancies between reference and measured data can be expected. Figure 1 , which also depicts a measured spectrum 14 and a corresponding reference spectrum 12, both indicating the same material, in this example quartz (SiO2). A first difference 15 is shown as being approximately 0.5 keV, indicating that there may be an offset 15 between the detected energy of the measured spectrum peak and the energy of the corresponding reference spectrum peak. In this example, both peaks indicate oxygen. A second difference 17, 19 is shown between 1.5 keV and 2 keV, indicating that there may be a difference between the width 17 of the measured spectrum peak and the width 19 of the reference spectrum peak. As used herein, the width of a peak indicates the spread of the peak along the energy axis.

[0254] This difference may lead to errors in identifying unknown elements or phases in the sample. Such misidentifications may typically occur in the case of phases with similar elemental compositions, such as chalcopyrite (CuFeS2), covellite (CuS), chalcocite (Cu2S), and bornite (Cu5FeS4). In particular, misidentifications may occur at the boundaries between phases with similar elemental compositions.

[0255] Figure 2 is a diagram illustrating phase misidentification in a mineral sample. In the accompanying figure, the materials contained in each zone of the sample are represented by the corresponding hatching. In particular, EDS analysis of the sample shows that it contains bornite 26, chalcopyrite 22, chalcocite 24, covellite 27, tetrahedrite 25, and other materials 29. The sample area represented by the thick outline represents at least a portion of the sample's composition that has been misidentified. Specifically, the area is located in the boundary between chalcopyrite 22 and chalcocite 24 and is misidentified as being composed of bornite 26. This misidentification occurs because the elemental composition of these materials is highly similar, which in turn means that they contain similar spectra. Therefore, differences between the measured data and the reference data (e.g., Figure 1 ) can lead to misidentification between these phases.

[0256] [TP386530EPPRI1]

[0257] The present disclosure provides various techniques for mitigating the difference between measured data and reference data and thereby mitigating phase misidentification. Specifically, the present disclosure teaches the calculation of peak width transformation ( Figures 3 to 5 ) and at least one piecewise transform ( Figures 6 to 8 ). The present disclosure teaches applying a peak width transformation to reference data to adjust the reference spectrum peak 19 (see Figure 1 ) width, and applying at least one piecewise transform to a selective energy portion of the reference data to reduce or remove an offset between the detected energy of the measured spectrum peak and the energy of the corresponding reference spectrum peak 15 (see Figure 1 ).

[0258] Figure 3A scatter plot of the standard deviations 32, 37 of the measured spectrum peaks and the reference spectrum peaks is depicted. Specifically, the square 32 indicates the standard deviation of the measured spectrum peak and the circle 37 indicates the standard deviation of the reference spectrum peak present in the reference data. As can be noted, the standard deviation of the reference spectrum peak can be greater in number than the standard deviation of the measured spectrum peak. In this figure, the horizontal axis depicts energy in keV and the vertical axis is unitless and depicts the standard deviation values. As noted, in this example, the standard deviation of the measured spectrum peak is higher than the corresponding standard deviation of the reference spectrum peak. Those skilled in the art will understand that if the measured spectrum peak and the reference measured peak include similar energy levels and therefore indicate the same material, they are corresponding. It should also be understood that the measured spectrum peak and its corresponding reference measured peak ideally include the same energy level.

[0259] Although the graph only indicates the standard deviation of reference spectrum peaks up to 10 keV, it should be understood that the standard deviation of each reference spectrum peak present in the reference data may be used.

[0260] In addition, a corresponding function 34, 35 can be fitted to each set of standard deviations 32, 37. Specifically, the reference peak width function 35 can be fitted to the standard deviation of the reference spectrum peak, and the measured peak width function 34 can be fitted to the standard deviation of the measured spectrum peak. By way of example only, a weighted least squares function can be used to calculate the functions 34, 35. The weights can be calculated based on the concentration of the elements in the sample. The concentration can be obtained by comparing the measured data with the reference data (i.e., with the reference data before calibration). Likewise, the reference peak width function 35 can extend beyond the depicted energy range, and can actually extend throughout the entire energy range of the reference data.

[0261] Figure 4 Shown is applied to Figure 3 Specifically, the calculated functions 34, 35 can be used to extrapolate the standard deviations 32, 37 of the measured and reference spectral peaks over a wider range and at higher density energy levels. As can be noted, Figure 3 In , the standard deviation of the measured spectrum peak lies between 0 keV and about 8 keV and is extrapolated to a wider range of 0 keV to 20 keV. In addition, other values ​​of the standard deviation of the measured spectrum peak and the reference spectrum peak can be calculated, which result in a more dense distribution of the standard deviations over the energy range.

[0262] [TP386530EPPRI1]

[0263] More specifically, if Figure 4As shown, the measured peak width function 34 can be used to calculate the corresponding standard deviation of each energy bin defined between the total energy range of the reference data, which in this example is 0 keV to 20 keV. Similarly, the reference peak width function 35 can be used to calculate the corresponding standard deviation of each energy bin defined between the total energy range of the reference data.

[0264] Figure 5 Shown based on Figure 4 50 determined by extrapolation of . In this example, for each energy bin defined between the total energy range of the reference data, a corresponding peak width transform value can be calculated based on the difference between the standard deviation 32 of the measured spectrum peak of the energy bin and the standard deviation 37 of the reference spectrum peak of the energy bin. The calculated peak width transform values ​​can be stored in a memory device for future use. Alternatively or in addition, a function such as a polynomial function can be fit to the peak width transform values ​​and the function can be stored in a memory device for future use.

[0265] It should be understood that although Figures 3 to 5 In the example shown, the standard deviation is used to determine the peak width transformation 50, but in general any other measure of the width of the spectrum peak can be used. That is, in general, a peak width parameter of the spectrum peak can be used. The peak width parameter can indicate the spread of the spectrum peak along the energy axis. In some embodiments (such as Figures 3 to 5 ), the peak width parameter may indicate the standard deviation of the spectral peak 32, 37. Alternatively or in addition, the peak width parameter may indicate the variance of the spectral peak.

[0266] Figure 6 A calibration peak 60 in the spectrum is shown. The calibration peak 60 may be a subset of all spectral peaks present in the spectrum. The calibration peak 60 may be a spectral peak that meets predefined requirements. The calibration peak 60 may be detected by first detecting spectral peaks in the measured spectrum, then determining which spectral peaks meet one or more predefined requirements, and then classifying the spectral peaks that meet the one or more requirements as calibration peaks 60. Alternatively or in addition, the calibration peak 60 may be detected by storing descriptive data of the calibration peak 60 in a memory device, and then searching for the calibration peak 60 on the measured spectrum using the data describing the calibration peak. The descriptive data of the calibration peak 60 may include at least one predefined requirement.

[0267] The calibration peak 60 may preferably be an unobstructed spectral peak.

[0268] Furthermore, if multiple spectral peaks are detected in the sample for a particular element or for a particular energy level, it may be advantageous to select the highest spectral peak (i.e., the spectral peak with the highest photon count) as the calibration peak 60. For example, if the sample has various phases that all contain silicon, the silicon peak of the phase with the highest silicon peak may be selected as the calibration peak 60. Alternatively or in addition, if the sample has various phases that all contain silicon, the silicon peak of the phase that does not contain other materials that interfere with silicon will be selected as the calibration peak 60. It should be understood that silicon is used herein only as an example, and the definition of selecting a calibration peak applies to any particular element.

[0269] [TP386530EPPRI1]

[0270] exist Figure 6 , eight calibration peaks 60a-60h are depicted. In the depicted example, the first calibration peak 60a corresponds to the Kα (K-alpha) X-ray emission line of oxygen; the second calibration peak 60b corresponds to the Kα X-ray emission line of sodium; the third calibration peak 60c corresponds to the Kα X-ray emission line of magnesium, and the fourth emission line 60e corresponds to the Kα X-ray emission line of aluminum. The fifth to eighth calibration peaks 60f, 60g and 60h similarly correspond to specific X-ray emission lines of the elements.

[0271] Using consecutive pairs of calibration peaks 60, a piecewise transformation can be determined. Two calibration peaks 60 are consecutive if none of the other calibration peaks 60 includes an energy between the energies of the two consecutive calibration peaks. Figure 6 In the example of FIG. 1 , the first calibration peak 60a and the second calibration peak 60b form a first pair of continuous calibration peaks 60a-60b. Similarly, the second calibration peak 60b and the third calibration peak 60c form a second pair of continuous calibration peaks 60b-60c. The third to seventh pairs of continuous calibration peaks are similarly formed by calibration peaks 60c-60d, 60d-60e, 60e-60f, 60f-60g, and 60g-60h.

[0272] It should be understood that the spectrum may also include other peaks. For example, the spectrum may include peak 61, which is not calibration peak 60. As shown, other peaks 61 that are not calibration peak 60 may exist between consecutive calibration peaks 60. For example, peak 61 exists between consecutive calibration peaks 60e and 60f.

[0273] Each of the successive calibration peaks 60 (and in particular their respective energies) defines a respective piecewise energy region within which a respective piecewise transform may be applied.

[0274] Figure 7 Shown in Figure 6 The segmented energy region 70 is marked on the spectrum of Figure 6For each pair of continuous calibration peaks 60, there may be a corresponding segmented energy region 70. Specifically, the first pair of continuous calibration peaks 60a-60b may define a first segmented energy region 70a. The second pair of continuous calibration peaks 60b-60c may define a second segmented energy region 70b. Similarly, the third to seventh pairs of continuous calibration peaks 60c-60d, 60d-60e, 60e-60f, 60f-60g, and 60g-60h define third to seventh segmented energy regions 70c, 70d, 70e, 70f, and 70g, respectively.

[0275] For each segmented energy region 70, a corresponding segmented transform may be applied.

[0276] Figure 8 Shown in Figure 6 In the depicted example, each piecewise transformation 80 is a linear transformation, as indicated by the corresponding straight line describing the corresponding piecewise transformation 80. Figure 8 , straight lines 80a-80g may indicate parameters of respective piecewise transformations 80 (which in this example are of linear type), and solid circles depict boundaries of respective piecewise energy regions 70 in which each piecewise transformation 80 may be applied. Figure 6 The energy of the calibration peak 60 in FIG.

[0277] Therefore, the first segmented transformation 80a can be applied to the first segmented energy region 70a. That is, the first segmented transformation 80a can be used to transform all reference numbers of energy in the first segmented energy region 70 [TP386530EPPRI1]

[0278] Similarly, the second segment transformation 80b can be applied to the second segment energy region 70b. That is, the second segment transformation 80a can be used to transform all reference data of energy in the second segment energy region 70. Similarly, the third segment transformation to the seventh segment transformation 80c, 80d, 80e, 80f and 80g can be applied to the third segment energy region to the seventh segment energy region 70c, 70d, 70e, 70f and 70g, respectively.

[0279] The piecewise transform 80 may be defined by a piecewise defined function (also referred to as a piecewise function).

[0280] Fig. 9 The measured spectrum 96 (dashed line), the corresponding reference spectrum 92 (dotted line), and the calibrated reference spectrum 94 (bold line) are shown. That is, for the measured spectrum 96, Fig. 9Corresponding reference spectra before (spectrum 92) and after (spectrum 96) calibration are depicted. The calibrated reference spectrum 94 may be obtained by applying at least the peak width transform 50 and / or the piecewise transform 80. As may be noted, the calibrated reference spectrum 94 is more similar to the measured spectrum 96 than the reference spectrum 92 before calibration. In this example, a 97.65% correlation is observed between the measured spectrum 96 and the reference spectrum 92 before calibration, while a 99.62% correlation is observed between the measured spectrum 96 and the calibrated reference spectrum 94.

[0281] Fig.10 is a diagram showing calibration reference data calibrated using the techniques of the present disclosure. Figure 2 Phase identification diagram in a mineral sample of FIG. As can be noticed, in the boundary between chalcopyrite 22 and chalcocite 24, the presence of bornite 26 (which is an artifact) is significantly reduced.

[0282] Fig.11 Shown are the peak energy differences between 3 different measurement data and corresponding reference data for scenarios where the reference data is not calibrated, the reference data is calibrated using the prior art, and the reference data is calibrated using the teachings of the present disclosure.

[0283] Specifically, the horizontal axis depicts energy levels in keV and the vertical axis depicts peak energy increments in eV. The peak energy increment (or peak energy difference) is defined as the difference between a peak of the measured data and a corresponding peak of the (calibrated) reference data. The peak energy increment is therefore a measure of the difference that exists between the measured data and the corresponding (calibrated) reference data. It should be understood that the peak energy increment should be as small as possible and ideally zero.

[0284] In the top graph, the reference data is not calibrated. In the middle graph, the reference data is calibrated using the prior art. In the bottom graph, the reference data is calibrated using the techniques of the present disclosure. Dotted lines 102, 112, and 122 depict the peak energy increments of the spectrum obtained from the first sample. Dashed lines 106, 116, and 126 depict the peak energy increments of the spectrum of the second sample. Solid lines 104, 114, and 124 depict the peak energy increments of the spectrum of the third sample.

[0285] [TP386530EPPRI1]

[0286] For calibration Fig.11 The prior art for reference data for the scenario shown in the middle graph of involves using a single linear transformation over the entire range of the reference data, generated using the minimum and highest unobstructed peaks on the measured data.

[0287] As depicted, the peak increments for all three samples are smaller on the middle graph than on the top graph. That is, the prior art calibration technique provides some improvement. On the other hand, the disclosed technique provides a greater improvement, as shown by the scale of the vertical axis. That is, it has been observed that the disclosed technique provides a peak increment that is about 1000 times smaller than the prior art.

[0288] Fig.12 A flow chart of the method is depicted. The method can be used to generate reference data for calibration. For example, the method can be used to calibrate an EDS instrument.

[0289] The method includes S1 providing reference data and measurement data. The method may also include S2 determining a peak width transformation. S2 may be as described in reference Figures 3 to 5 The method may further comprise S3 determining at least one segment transformation. S3 may be as described in reference Figures 6 to 8 Optionally, the method may include S4 determining a single end-to-end transformation. S4 may be based on the reference Fig.11 (middle curve) is performed by the prior art discussed in detail. The method may also include S5 applying a peak width transform and / or at least one segment transform. Preferably, both the peak width transform and at least one segment transform are determined and applied. More preferably, the peak width transform is applied before at least one segment transform. Optionally, the method may include S6 applying an end-to-end transform. Preferably, the end-to-end transform is applied on an energy region outside the energy region where at least one segment transform is applied. The method includes S7 generating reference data for calibration.

[0290] Although not shown, the method may also include determining the elemental composition of the sample by elemental decomposition based on comparison of the measured data with calibrated reference data.

[0291] Fig.13 An example of a system 300 having an X-ray detector 340 suitable for analyzing a sample is shown. A beam source 341 and a power supply and control unit 345 are provided with the system 300. The beam source 341 may be used to emit a beam 332. The beam 332 may be an electron beam, an ion beam, or an X-ray beam.

[0292] System controller 333 may control the operation of various portions of system 300. Vacuum chamber 310 may be evacuated using ion pump 368 and mechanical pumping system 369 under the control of vacuum controller 334.

[0293] The electron beam 332 can be focused onto a sample 302, which can be set on a sample stage 304. The sample stage 304 can be a movable XY stage 304 within the lower vacuum chamber 310. When the beam hits the sample 302, the sample 302 emits X-rays, the energy of which is related to the elements in the sample 302. X-rays with an energy inherent to the elemental composition of the sample are generated near the beam incidence area. The emitted X-rays are collected by an X-ray detector 340, which is preferably a silicon drift detector [TP386530EPPRI1]

[0294] An energy dispersive detector of the X-ray detector type is used, but other types of detectors may also be used which generate a signal having an amplitude proportional to the energy of the detected X-rays.

[0295] The output from the detector 340 may be amplified and classified by a processor 320, which may count and classify the total number of X-rays detected during a specified time period at a selected energy and energy resolution and a channel width typically between 2.5 eV and 20 eV per channel. The processor 320 may include a computer processor; an operator interface device (such as a keyboard or computer mouse); a program memory 322 for storing data and executable instructions; an interface device for data input and output, executable software instructions contained in an executable computer program code; and a display 344 for displaying the results of the multivariate spectral analysis via a video circuit 342.

[0296] Processor 320 can be part of a standard laboratory personal computer and is typically coupled to at least some form of computer-readable media. Computer-readable media including both volatile and non-volatile media, removable and non-removable media can be any available media that can be accessed by processor 320. As an example and not limitation, computer-readable media include computer storage media and communication media. Computer storage media include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules or other data. For example, computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical disk storage, cassette, magnetic tape, disk storage or other magnetic storage device, or any other medium that can be used to store the desired information and can be accessed by processor 320.

[0297] Program memory 322 may include computer storage media in the form of removable and / or non-removable, volatile and / or non-volatile memory, and may provide storage of computer-readable instructions, data structures, program modules, and other data. Typically, processor 320 is programmed using instructions stored in various computer-readable storage media of the computer at different times. Programs and operating systems are typically distributed on, for example, floppy disks or CD-ROMs. They are installed or loaded into the auxiliary memory of the computer from the floppy disk or CD-ROM. When executed, they are at least partially loaded into the main electronic memory of the computer. When such media contain instructions or programs for implementing the following steps together with a microprocessor or other data processor, the present invention described herein includes these and other various types of computer-readable storage media. When programmed according to the methods and techniques described herein, the present invention also includes the computer itself.

[0298] The X-ray spectrum obtained as described above may be stored in a portion of the memory 322, such as the measured spectrum memory portion 323. Reference data is also stored in the measured spectrum memory 323.

[0299] [TP386530EPPRI1]

[0300] Although the illustrated embodiment includes a scanning electron microscope, related embodiments may use a transmission electron microscope or a scanning transmission electron microscope to generate X-rays from a sample. An X-ray fluorescence system may also be used to generate X-rays from a sample. Other embodiments may detect other characteristic radiation from a sample, such as gamma rays.

[0301] The preferred method or apparatus of the present invention has many novel aspects, and because the present invention can be implemented in different methods or equipment for different purposes, not every aspect needs to be present in each embodiment. In addition, many aspects of the described embodiments may be able to obtain patents separately. The present invention has a wide range of applicability and can provide many benefits as described and shown in the above embodiments. The embodiment will vary greatly according to the specific application, and not every embodiment will provide all benefits and meet all goals that can be achieved by the present invention.

[0302] It should be appreciated that embodiments of the present invention can be implemented via a combination of computer hardware, hardware and software or by a computer instruction stored in a non-transient computer-readable memory. These methods can be implemented in a computer program using standard programming techniques (including a non-transient computer-readable storage medium configured with a computer program), wherein according to the method and accompanying drawings described in this specification, the storage medium so configured enables the computer to operate in a specific and predefined manner. Each program can be implemented with a high-level programming or object-oriented programming language to communicate with a computer system. However, if necessary, the program can be implemented with assembly language or machine language. In any case, the language can be a compiled language or an interpreted language. Moreover, the program can be run on a dedicated integrated circuit programmed for this purpose.

[0303] In addition, the method can be implemented in any type of computing platform, including but not limited to personal computers, microcomputers, mainframes, workstations, networked or distributed computing environments, computer platforms separated, integrated or communicating with charged particle tools or other imaging devices, etc. Various aspects of the present invention can be implemented in machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated with a computing platform, such as a hard disk, an optical read and / or write storage medium, a RAM, a ROM, etc., so that the storage medium or device can be read by a programmable computer to construct and operate the computer to perform the process described herein when the computer reads the storage medium or device. Moreover, the machine-readable code or part thereof can be transmitted via a wired or wireless network. When such a medium contains instructions or programs for implementing the above steps together with a microprocessor or other data processor, the present invention described herein includes these and other various types of non-transitory computer-readable storage media. When programmed according to the methods and techniques described herein, the present invention also includes the computer itself.

[0304] The computer program can be applied to input data to perform the functions described herein, thereby transforming the input data to generate output data. The output information is applied to one or more output devices, such as a display monitor [TP386530EPPRI1]

[0305] In a preferred embodiment of the present invention, the transformed data represents a physical tangible object, including generating a specific visual depiction of the physical tangible object on a display.

[0306] In the following discussion and claims, the terms "including" and "comprising" are used in an open-ended manner and should therefore be interpreted to mean "including but not limited to". If any term is not particularly defined in this specification, it is intended to be given its ordinary meaning. The accompanying drawings are intended to aid in understanding the present invention and are not drawn to scale unless otherwise indicated. Particle beam systems suitable for practicing the present invention are commercially available from, for example, FEI Company (the assignee of the present application).

[0307] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and modifications may be made to the embodiments described herein without departing from the essence and scope of the present invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the specific embodiments of the processes, machines, manufactures, material compositions, modes, methods and steps described in the specification. It will be readily understood by those of ordinary skill in the art from the disclosure of the present invention that processes, machines, manufactures, material compositions, modes, methods or steps that currently exist or will be developed later to perform functions substantially the same as the corresponding embodiments described herein or to achieve substantially the same results may be utilized according to the present invention. Therefore, the appended claims are intended to include such processes, machines, manufactures, material compositions, modes, methods or steps within their scope.

Claims

1. A method, comprising: providing reference data indicative of at least one reference energy dispersive X-ray spectrum; providing measurement data indicative of at least one measured energy dispersive X-ray spectrum obtained from the sample; determining a transformation based on a comparison of the measured data with the reference data; The method further comprises detecting a calibration peak on the measurement data, and Wherein determining a transformation comprises determining at least one piecewise transformation based on the calibration peaks and the reference data.

2. The method according to the preceding claim, wherein the measurement data includes measurement spectrum peaks; wherein the calibration peaks are a subset of the measured spectrum peaks; Wherein detecting calibration peaks on the measurement data comprises classifying at least some of the measurement spectrum peaks as calibration peaks.

3. The method according to the preceding claim, wherein the classification of at least some of the measured spectral peaks as calibration peaks is based on the intensity of the measured spectral peaks relative to the intensity of background radiation.

4. A method according to any one of the preceding two claims, wherein if a specific measurement spectral peak is unobstructed, so that the energy difference between any other measurement spectral peak in the measurement data present in the same measurement spectrum as the specific measurement spectral peak and the specific measurement spectral peak exceeds a blocking threshold, then the specific measurement spectral peak is classified as a calibration peak.

5. The method of any one of the preceding claims, wherein detecting a calibration peak on the measurement data comprises (a) For each measured spectrum in the measurement data: (a1) detecting all measurement peaks in the measurement spectrum; (a2) rejecting a measured spectrum peak in the measured spectrum that includes a peak-to-background ratio that is less than an intensity ratio threshold, wherein the peak-to-background ratio is a ratio of the intensity of the measured spectrum peak to the intensity of background radiation; [TP386530EPPRI1] (a3) rejecting measured peaks in the measured spectrum that overlap with other measured peaks in the measured spectrum, wherein two peaks in the measured spectrum overlap if they comprise an energy difference that is less than a blockade threshold; (b) grouping all non-rejected measured peaks from (a) according to the X-ray emission lines they indicate; (c) In each of the groups, the non-rejected measured spectrum peak having the highest peak-to-background ratio is determined as the calibration peak.

6. A method according to any one of the preceding claims, wherein each of the at least one piecewise transformation is determined based on a corresponding pair of consecutive calibration peaks, Wherein two calibration peaks are consecutive, the proviso is that no other calibration peak of the measurement data includes an energy between the energies of the two consecutive calibration peaks.

7. A method according to the preceding claim, wherein each of the at least one segmented transformation is selectively applied to a corresponding segmented energy region of the reference data, the corresponding segmented energy region containing energies that are between or equal to the corresponding energies of the corresponding pair of calibration peaks.

8. A method according to any one of the preceding claims, wherein each of the at least one piecewise transform is a linear transform.

9. A method according to any one of the preceding claims, wherein the method comprises respectively calculating reference peak width parameters of a plurality of reference spectrum peaks, wherein each reference peak width parameter indicates an energy range contained by a corresponding reference spectrum peak; respectively calculating measurement peak width parameters for a plurality of measurement spectrum peaks, wherein each measurement peak width parameter indicates an energy range encompassed by a corresponding measurement spectrum peak; Wherein determining the transformation comprises determining a peak width transformation based on the reference peak width parameters and the measured peak width parameters.

10. The method according to any one of the preceding claims, wherein determining the transformation comprises determining an end-to-end transformation based on the first measured spectrum peak, the second measured spectrum peak, and the reference data; wherein the first measured spectrum peak is the first unobstructed measured spectrum peak having the lowest energy in the measured data, and The second measured spectrum peak is a second unobstructed measured spectrum peak having the highest energy in the measured data, [TP386530EPPRI1] If the energy difference between any other spectral peak in the measurement data present in the same measurement spectrum as the specific measurement spectral peak and the specific measurement spectral peak exceeds a blocking threshold, the specific measurement spectral peak is unblocked.

11. A method according to any preceding claim, further comprising applying the transformation to the reference data to generate calibrated reference data.

12. The method of claim 2, wherein applying the transformation comprises: applying the at least one piecewise transformation over an energy region containing energies between a minimum energy and a maximum energy of the calibration peak, the energy region including the minimum energy and the maximum energy of the calibration peak, and The end-to-end transformation is applied over an energy region that includes energies less than the minimum energy of the calibration peak and energies greater than the maximum energy of the calibration peak.

13. The method according to any one of the two preceding claims and having the features of claim 9, wherein applying the peak width transformation comprises using the peak width transformation to adjust the reference peak width parameter of at least one reference spectral peak.

14. The method according to any one of the preceding claims, further comprising determining the elements contained in the sample by comparing the measurement data with the calibrated reference data.

15. A system, comprising: a beam source for emitting a beam onto a sample; an X-ray detector for detecting X-rays emitted from the sample upon impact of the beam; A computer readable memory storing reference data indicative of at least one reference energy dispersive X-ray spectrum and computer instructions for: obtaining measurement data indicative of at least one measured energy dispersive X-ray spectrum obtained from the sample; determining a transformation based on a comparison of the measured data with the reference data; Wherein the system is configured to perform a method according to any one of the preceding claims.

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