DE102014103618A1 - Integrated coupling of EDX and BSE acquisition with combined evaluation - Google Patents

Abstract

A detector and combination detector for electron microscopy for characterizing a secondary radiation at a sample portion of a sample under electron microscopy, the detector being alignable with the sample portion, comprising: a first sensor comprising at least a first sensor surface arranged, a secondary radiation comprising a number Detect electrons backscattered from the sample and output them as a BSE-like signal; A second sensor comprising at least one second sensor surface arranged to detect a secondary radiation comprising an energy of an X-ray emanating from the sample and to output it as an EDX signal; wherein - the first sensor and the second sensor are arranged adjacent to each other and substantially radially symmetrical and / or parallel to an axis of symmetry of the detector; - The at least one first sensor surface and / or further first sensor surfaces between the sample portion and a plane in which the at least second sensor surface is located, can be arranged or are when the detector for characterizing the secondary radiation is aligned with the sample portion, wherein the secondary radiation Influence of a focused on the sample portion primary radiation can be generated.

Description

 The invention is in the field of electron microscopy and relates to the recording and evaluation of signals that can be detected by the action of a focused electron beam on a sample. In particular, the invention relates to an EDX detector that takes into account a BSE signal of the same sample section for interpreting an EDX signal of a sample section.

 The analysis of the local chemical composition in the scanning electron microscope (SEM) or in the transmission electron microscope (TEM) is carried out by standard energy-dispersive X-ray analysis (EDX or EDS: energy dispersive spectroscopy). The advantage of the fairly fast analysis is that it has a lower energy resolution than other methods, such as the use of microprobes, which use wavelength-dispersive interpretation. This manifests itself in a difficult unfolding of the signal, especially in the case of the simultaneous presence of numerous elements whose signal is superimposed.

 Against this background, a detector according to claim 1, a combination detector according to claim 6 and a method for BSE-based interpretation of an EDX signal according to claim 7 are proposed. Other embodiments, modifications and improvements will become apparent from the following description and the appended claims.

• – einen ersten Sensor, umfassend zumindest eine erste Sensorfläche, die eingerichtet ist, eine Sekundärstrahlung, umfassend eine Anzahl Elektronen, die von der Probe rückgestreut werden zu erfassen und als ein BSE-ähnliches Signal auszugeben;
• – einen zweiten Sensor, umfassend zumindest eine zweite Sensorfläche, die eingerichtet ist, eine Sekundärstrahlung, umfassend eine Energie einer von der Probe ausgehenden Röntgenstrahlung zu erfassen und als ein EDX-Signal auszugeben;

wobei

• – der erste Sensor und der zweite Sensor zueinander benachbart und im Wesentlichen radialsymmetrisch und/oder parallel zu einer Symmetrieachse des Detektors angeordnet sind, sodass das BSE-Signal und das EDX-Signal im Wesentlichen synchron ausgebbar sind;
• – die zumindest eine erste Sensorfläche und/oder weitere erste Sensorflächen zwischen dem Probenabschnitt und einer Ebene, in der die zumindest zweite Sensorfläche liegt, anordenbar ist bzw. sind, wenn der Detektor zum Charakterisieren der Sekundärstrahlung auf den Probenabschnitt ausgerichtet wird, indem sein vorderer Abschnitt zur Probe weist; und
• – wobei die Sekundärstrahlung unter Einwirkung einer auf den Probenabschnitt fokussierten Primärstrahlung erzeugbar ist.

An electron microscopy detector for characterizing a secondary radiation at a sample portion of an electron microscopically examined sample, having a front and a back portion, wherein the detector is alignable with its front portion on the sample portion, comprising:

• A first sensor comprising at least a first sensor surface arranged to detect a secondary radiation comprising a number of electrons backscattered from the sample and output as a BSE-like signal;
• A second sensor comprising at least one second sensor surface arranged to detect a secondary radiation comprising an energy of an X-ray emanating from the sample and to output it as an EDX signal;

in which

• - The first sensor and the second sensor adjacent to each other and arranged substantially radially symmetrically and / or parallel to an axis of symmetry of the detector, so that the BSE signal and the EDX signal can be output substantially synchronously;
• - The at least one first sensor surface and / or further first sensor surfaces between the sample portion and a plane in which the at least second sensor surface is, can be arranged is or when the detector for characterizing the secondary radiation is aligned with the sample portion by its front portion to the sample; and
• - Wherein the secondary radiation can be generated under the action of a focused on the sample portion primary radiation.

 Advantages of this embodiment include the generation of a BSE-like signal in substantially less time at a substantially improved resolution over that of a BSE image produced by a conventional BSE detector.

 According to a further embodiment, a detector is proposed, in which the features of the first sensor and the second sensor are integrated in a sensor, so that the one sensor is set up, both the number of electrons backscattered by the sample, and the energy of the Sample outgoing X-ray radiation and output as a BSE-like signal and as an EDX signal.

 Significant advantages relate to the reduced space requirement of such a built-in detector in the measuring chamber. This offers advantages for a possible magnification of the sample which can be examined in the measuring chamber, a greater space for movement of the sample on the sample table, the possibility of accommodating other other detectors and probes, the possibility of accommodating special tools, for example in the case of two-beam Microscopes (eg FIB etc.)

 According to a further embodiment, the second sensor of the proposed detector is an EDX detector of known design, comprising at least the components electron trap and / or SDD (Silicon Drift Detector), wherein the electron trap is electrically isolated at least from the SDD and / or other components of the detector and usable as a first sensor.

 Advantages arise for the possibility of an immediate transfer of the proposed detector principle into practice. Already with a common EDX detector can be obtained by minor structural modification (contacting to dissipate the potential) while avoiding additional development effort high quality and practically highly relevant BSE-like images

According to a further embodiment, the proposed detector further comprises a collimator, wherein the first sensor comprises at least one diode, which is arranged adjacent to the collimator, that the EDX signal can be detected without being influenced.

 An advantage of this embodiment is that a detection of the number of incoming electrons is possible even with separate, compared to other components, for example, the housing or the chamber wall running executed, electrical contacting.

 According to a further embodiment, a detector according to the above features is proposed, wherein the at least one first sensor surface and / or further first sensor surfaces are arranged to one another, in particular adjacent to each other, so that the EDX signal can be registered undisturbed.

 Achieved advantages are similar to those of the previously described embodiment.

According to a further embodiment, a combination detector is proposed for a combined and / or synchronous measurement of an EDX signal and a BSE signal comprising a housing, wherein the housing and / or a support structure fulfilling its function comprise a BSE detector and a BSE detector the EDX detector arranged to the BSE detector at least partially supports and / or surrounds.

 This combination of features is intended to express that already a suitably contacted, common EDX detector can deliver the BSE-like signal and can be used for the generation of a BSE-like image of the examined sample section.

 According to a further embodiment, a method for BSE-based interpretation of an EDX signal in the electron microscopic examination of a sample is proposed, wherein a signal and / or a signal pattern using a BSE detector at the same time or in the same spatial direction using a signal or signal pattern detected by an EDX detector is detected and / or both signals or signal patterns are displayed synchronously or alternately on an output unit, such that an element distribution image is superimposed on a BSE image, for example in topographic or Z contrast, and / or a viewer appears as superimposed on an output unit.

 Advantages result from the increased information density of the present microscopy image and relate to virtually all aspects of the use of scanning electron microscopy.

• – Fokussieren eines Primärelektronenstrahls auf eine Probe;
• – Ausrichten eines Detektors einer Bauart die zumindest einer der vorstehend beschriebenen Ausführungsformen gemäß den Ansprüchen 1 bis 5 oder 6 entspricht, sodass ein BSE-Signal und ein EDX-Signal synchron erfasst werden;
• – Erzeugen einer Bildinformation für ein Übersichtsbild zumindest eines Abschnitts der Probe, wobei die Bildinformation umfasst:
• – eine erste Bildinformation, die unter Verwendung eines Signals, das die Zahl einfallender und hauptsächlich schneller Rückstreuelektronen nutzt, um ein BSE-ähnliches Bild zu erstellen, und
• – eine zweite Bildinformation, die unter Verwendung eines Signals des EDX-Detektors erstellt ist,

wobei das Signal des BSE-Detektors und das Signal des EDX-Detektors im Wesentlichen gleichzeitig und – bezogen auf die Probe – in der gleichen Raumrichtung erfasst werden;

• – Darstellen und/oder Speichern der Bildinformation, sodass beim Darstellen der Bildinformation auf einer Ausgabeeinheit einem im Wesentlichen topographische Informationen umfassenden Übersichtsbild elementspezifische Informationen überlagert oder anderweitig eindeutig zugeordnet werden können.

According to a further embodiment, the method proposed above comprises the steps:

• - Focusing a primary electron beam on a sample;
• Aligning a detector of a type corresponding to at least one of the above-described embodiments according to claims 1 to 5 or 6, so that a BSE signal and an EDX signal are detected synchronously;
• Generating image information for an overview image of at least a portion of the sample, wherein the image information comprises:
• A first image information, which uses a signal that uses the number of incident and mainly faster backscattered electrons to create a BSE-like image, and
• A second image information, which is created using a signal of the EDX detector,

wherein the signal of the BSE detector and the signal of the EDX detector are detected substantially simultaneously and in relation to the sample in the same spatial direction;

• Representation and / or storage of the image information, so that when displaying the image information on an output unit, an elementary information comprising substantially topographic information can be superimposed or otherwise unambiguously assigned to element-specific information.

 Advantages of this method result from the above already given and subsequently described in more detail possibilities of providing comprehensive phase information to the examined sample section in a shorter time, with simplified means and at lower costs, than with known detectors.

 The described embodiments can be combined with each other as desired.

 The proposed detector and the method that can be carried out with it increase the reliability of the chemical analysis of a sample by EDX, in addition to the X-ray radiation backscattered electrons (BSE), the number of which depends on the average atomic number of the elements concerned. From the known chemical composition of a sample can thus estimate the expected BSE signal and vice versa.

This is precisely for the critical cases, where the separation of the radiation components of an X-ray radiation of a sample by means of EDX alone An additional source of information is provided that is suitable for the semi-quantitative review of the outcome of the EDX analysis and allows to point out possible errors in an interpretation based solely on EDX.

 A safe phase separation is always difficult and can be faulty if the EDX detector no longer dissolves similar signals of different elements with respect to their energy levels (origin) enough.

 From a pure EDX point of view, this problem can be further limited only by increasing the energy resolution, but this possibility has been largely exhausted by the current detector technology so far. Another possibility for an improved signal separation of the individual beam components is an improvement of the count rate. Here, simply the signal-to-noise ratio is increased to make a signal separation purely mathematically reliable. This path is currently being pursued by the increased use of large-area detectors and is certainly successful in some cases. However, if radiation components produce a relatively significant signal difference (e.g., Pb and O in lead oxides), the problem will of course persist as such, since fluctuations in the much weaker signal then become more apparent. In the prior art, one usually deviates from a microprobe, if more accurate or reliable to be measured. However, the cost of purchasing and operating a suitable microprobe is much higher than that of a SEM itself.

This requires known solutions usually a much higher cost. Indirectly, the use of EDX detectors for evaluating the energy distribution of BSE has already been used in a work by Agemura et al. (2011) (see T Agemura, T Nomaguchi, D Joy: "Digital BSE imaging on SEMs"; Microscopy and Microanalysis, Volume 17, Supplement S2, July 2011, 914-915). , However, the EDX detector was modified in such a way that the detector, which normally only uses X-ray radiation, is used to image the energy distribution of the X-ray radiation AND of the backscattered electrons.

 In contrast, it is suggested here that only the NUMBER of backscattered electrons be considered, not their energy. This has the advantage of a reduced measurement and computational effort, which is reflected in the faster receipt of a result and a simplified design of a new detector.

 For the separation of the X-ray and electron components in the Agemura et al. (2011), as in all known detectors of any manufacturer known to us, an electron trap is used, which usually consists of a strong magnet that deflects the electrons so that they do not hit the X-ray detector.

 The solution proposed here for improved signal evaluation is either to simply pick up the electron signal "discarded" via the electron trap (it is momentarily grounded) or to use an additional detector comprising one or more diodes surrounding the input collimator of the EDS detector are positioned, ie which are integrated into the EDS detector.

 The accompanying drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. The elements of the drawings are relative to one another and not necessarily to scale. Like reference numerals designate corresponding parts accordingly.

1 shows known designs of EDX detectors;

2 and shows the comparison of element-specific grayscale images (right) and BSE images (left).

3 shows the comparison of element-specific greyscale images (right) and BSE images (left).

In particular shows 1 Designs of EDX detectors from Oxford Instruments. Above is the old and below a newer design shown. The reference symbols mean:

LIST OF REFERENCE NUMBERS

1

Collimator arrangement

2

electron trap

3

window

4

crystal

5

FET

6

cooler

7

heat sink

8th

SDD sensor

Both types of construction do not differ, or only insignificantly, in the way in which the EDX detector protects against high-energy electrons (BSE) and both use an electron trap. The annular electron trap 2 deflects the high-energy backscattered electrons with the help of a strong permanent magnet. A grounding ensures the required equipotential bonding, so that the electrons are dissipated unused. All the backscattered electrons that make up the collimator tube 1 could already be used for image generation if the resulting current were tapped. Of course, it would be much more effective to arrange a BSE detector or corresponding diodes around the collimator tube. Such a detector would provide a multiple of the currently unused derived signal.

2 shows greyscale images on the right side, which were recalculated with the aid of an η (eta) value generated by the quantitative element-specific program package (Q-map) in comparison to corresponding BSE images (left). In particular, NbC precipitates in a Ni (Co, Al) matrix are shown in the upper image line. The bottom line of the picture shows a sample of an iron meteorite (Odessa meteorite). The recalculation was carried out from the locally determined chemical composition, or the signal of the EDX detector. From a scientific point of view, this may seem to provide little surprising new information, but the respective BSE image (left) can be recorded in a much shorter time than an EDX image. As can be clearly seen, the image based on the signals of a BSE detector offers significant advantages in terms of its excellent signal-to-noise ratio and local resolution over the EDX signal. The topography visible in the left image results from the tilting of the sample by 70 ° with respect to the primary electron beam in the EBSD measurement mode.

The 3 illustrates on two other material samples the high resolution of the BSE images obtained by picking up the BSE signal (left) compared to EDX grayscale images (right). The greyscale images on the right were recalculated using the η value generated from Q-map. The upper image line shows NbC precipitates in a Ni (Co, Al) matrix. The bottom line of the picture shows a cobalt slag. In the upper image line, the contrast in the left image (BSE, slow scan) and thus the local resolution is significantly better than in the right (EDX) image.

From the bottom line of the image 3 regardless of the measurement artifacts in the picture on the right, there are at least five different phases in the sample. This means that it is already possible to assign the phases on the basis of the BSE image, even if it is not clear what chemistry these phases have in each case. The phase appearing white in the left picture is a Pb oxide. Which stoichiometry it has can also be estimated with the aid of the (EDX) gray values.

 The proposed solution is related to the so-called MLA systems. MLA stands for mineral liberation analysis. The MLA systems use a coupling of EDX and BSE, but with two separate, separate and distinct analytical systems. The aim is to use the BSE acquisition, which is a few orders of magnitude faster, to determine the essential phase components in ores above the backscatter coefficients η (eta) of the individual phases. The backscatter coefficient eta results from the mean ordinal number of the phase. For example, the BSE signals of lead oxide and lead dioxide are significantly different (i.e., the content of lead in the (hypothetical) ore), but the EDX signal of the two oxides is not different. EDX is used on a random basis to calibrate the MLA system or to confirm automatic phase assignments. The manufacturers of BSE detectors and EDX systems are usually not identical. The detectors are both structurally and logically separated from each other, which prevents the proposed here integration of EDX and BSE detection in a detector. This results in easily comprehensible problems for a synchronous detection of corresponding signals from the actual same sample section, which is the focus of the solution proposed here.

• a) Moderne, großflächige Detektoren weisen bauartbedingt mit zunehmender Größe eine abnehmende Energieauflösung auf. Deshalb sind auftretende Signalüberlagerungen zunehmend schlechter zu trennen. Die mit wachsender Größe der Detektorfläche erhöhte Zählstatistik wirkt dem zwar entgegen, ändert aber am eigentlichen Problem wenig.
• b) Die schon erwähnte Mikrosonde ist von der Anschaffung als auch dem Betrieb sehr kostenintensiv und daher nur in Ausnahmefällen eine sinnvolle Ergänzung bekannter Technik. Sie ist jedoch deutlich weniger ortsauflösend und vergleichsweise langsam.
• c) Die µXRF (Röntgenfluoreszensanalyse) ist – eine entsprechende Leistung vorausgesetzt – zwar relativ schnell, dafür aber trotz Verwendung von Mikrofokusröhren bzw. speziellen Optiken, noch schlechter in der Ortsauflösung.

Disadvantages of previously known solutions can be summarized as follows:

• a) Modern, large-area detectors have a decreasing energy resolution with increasing size due to the design. Therefore occurring signal overlays are becoming increasingly difficult to separate. The counting statistics, which are increased with increasing size of the detector surface, counteract this, but do not change much in the actual problem.
• b) The already mentioned microprobe is very expensive from the purchase as well as the operation and therefore only in exceptional cases a meaningful supplement of known technology. However, it is much less spatially resolving and comparatively slow.
• c) The μXRF (X-ray fluorescence analysis) is - assuming a corresponding performance - relatively fast, but in spite of the use of microfocus tubes or special optics, even worse in the spatial resolution.

When measuring the sample both X-rays are emitted as well as electrons backscattered at each point of impact of the electron beam. Both signals are element-specific in principle, the EDX signal consisting essentially of characteristic X-ray radiation of the individual elements, while the number of backscattered electrons is a function of the average atomic number of the respective phase. This means, for example, practically, that in fast measurements by means of EDX between Mo, S and Pb can be distinguished only very difficult or inaccurate, because their radiation components are superimposed, while the different atomic numbers of S, Mo and Pb, even with compounds of these elements a high probability that the number of backscattered electrons varies significantly. As a result, besides the differentiation of the phases, the chemical composition can also be estimated better than with EDX alone. In addition, with high primary electron energies, the information depth and thus the spatial resolution and the backscattered electron signal and the EDX signal are different: As is known, BSE images therefore usually have a better spatial resolution than element distribution maps created from the EDX signal.

 According to the proposed measurement method, the backscattered electrons are additionally registered in addition to the previous detection of the spatially resolved and element-specific X-ray radiation localized by the local electron bombardment. This can be done by using the electron trap of the EDX detector, but also by an additionally mounted on the EDX detector or even in the EDX detector integrated BSE detector.

 Accordingly, a first principal embodiment of the proposed method comprises the use of the already existing, but previously rejected signal of the electron trap of EDX detectors of known design, which intercepts the electrons before hitting the X-ray detector.

 A second principal embodiment involves the provision of a novel combined detector comprising both a measuring arrangement for EDX and a measuring arrangement for BSE. According to the preferred implementation of this new detector concept, the combined detector is adapted to the local conditions in the measuring chamber and comprises a device-specific adapted design. It can be used both on existing detector electronics and the already used signal processing, which is facilitated by the fact that manufacturers for their respective EBSD systems (diffraction backscattered electrons) can usually rely on specially adapted BSE detectors.

 The core of the invention is the coupling of a previously rejected ("waste") signal with a standard signal used to increase its informational value, even with rapid measurements, significantly. Of course, the individual detectors are NOT the subject of the invention, since they already exist. However, there is still no integrated EDX detector, which uses the BSE signal for evaluation, especially for difficult cases.

 Advantages of the proposed new detector or a signal acquisition and evaluation method, the advantages summarized below. For certain compounds where the characteristic radiation components are superimposed, EDX statements are very error prone. Even with the increasingly low-voltage measurements (low-voltage measurements), where virtually all elements in the EDX signal show superpositions, a separation of the individual elementary parts is very ambitious and problematic. In these cases, a combination (phase assignment via gray values, or estimation of the mean ordinal number (Z) via the gray values) is very advantageous. Economically, there are clear advantages from the point of view of the increased reliability of the elemental analyzes. On the other hand, this coupling can lead to a new type of combination detector, which would replace the previous ones in their simple form. As expected, the financial burden of producing the new detectors will be extremely low, so the margin for the manufacturers may be significant, especially compared to the current development effort for better EDX detectors. The advantage should at least be greater than in the transition from small to large detector surfaces, which offers more marketing advantages, rather than an actual improvement in the precision of the measurement signal.

 While specific embodiments have been illustrated and described herein, it is within the scope of the present invention to properly modify the illustrated embodiments without departing from the scope of the present invention. The following claims are a first, non-binding attempt to broadly define the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Agemura et al. (2011) (see T Agemura, T Nomaguchi, D Joy: "Digital BSE imaging on SEMs"; Microscopy and Microanalysis, Volume 17, Supplement S2, July 2011, 914-915) [0025]

Claims (8)

 A detector for electron microscopy for characterizing a secondary radiation at a sample portion of an electron microscopically examined sample, wherein the detector can be aligned with the sample portion, comprising: A first sensor comprising at least a first sensor surface arranged to detect a secondary radiation comprising a number of electrons backscattered from the sample and output as a BSE-like signal; A second sensor comprising at least one second sensor surface arranged to detect a secondary radiation comprising an energy of an X-ray emanating from the sample and to output it as an EDX signal; in which - The first sensor and the second sensor adjacent to each other and arranged substantially radially symmetrically and / or parallel to an axis of symmetry of the detector; - The at least one first sensor surface and / or further first sensor surfaces between the sample portion and a plane in which the at least second sensor surface is located, can be arranged is or when the detector for characterizing the secondary radiation is aligned with the sample portion; - Wherein the secondary radiation can be generated under the action of a focused on the sample portion primary radiation.  The detector of claim 1, wherein the features of the first sensor and the second sensor are integrated in a sensor, such that the one sensor detects both the number of electrons backscattered by the sample and the energy of the X-radiation emanating from the sample, and as BSE similar signal and outputs as EDX signal.  A detector according to claim 1, wherein the second sensor is an EDX detector of known design comprising at least the components electron trap and / or SDD and the electron trap is electrically isolated from at least the SDD and / or other components of the detector and is usable as the first sensor ,  The detector of claim 1 or 2, further comprising a collimator, wherein the first sensor comprises at least one diode disposed adjacent to the collimator so that the EDX signal is detectable unaffected.  A detector according to claim 4, wherein the at least one first sensor surface and / or further first sensor surfaces are arranged to one another, in particular adjacent to each other, so that the EDX signal is undisturbed registerable.  Combination detector for a combined and / or synchronous measurement of an EDX signal and a BSE signal, comprising a housing, wherein the housing and / or a support structure carries a BSE detector and an adjacent to the BSE detector arranged EDX detector at least in sections and / or surrounds.  A method for BSE-based interpretation of an EDX signal in the electron microscopic examination of a sample, wherein a signal and / or a signal pattern is detected using a BSE detector simultaneously to a detected in the same spatial direction using an EDX detector signal or signal pattern and / or both signals or signal patterns are displayed synchronously or alternately on an output unit so that an element distribution image is superimposed on a BSE image, for example in topography or z contrast, and / or superimposed on a viewer.  Method according to claim 7, comprising the steps: - Focusing a primary electron beam on a sample; Aligning a detector of a type corresponding to at least one of claims 1 to 5 or 6 so that a BSE signal and an EDX signal are detected synchronously; Generating image information for an overview image of at least a portion of the sample, wherein the image information comprises: A first image information, which uses a signal that uses the number of incident and mainly faster backscattered electrons to create a BSE-like image, and A second image information, which is created using a signal of the EDX detector, wherein the signal of the BSE detector and the signal of the EDX detector are detected substantially simultaneously and in the same spatial direction with respect to the sample; Representation and / or storage of the image information, so that when presenting the image information on an output unit, an overview image comprising substantially topographic information can be overlaid or otherwise unambiguously assigned element-specific information.

Images