CN112577985A

CN112577985A - Method, electron microscope system and computer program product for reducing topology artifacts

Info

Publication number: CN112577985A
Application number: CN202010931769.0A
Authority: CN
Inventors: R.阿诺德; W.伯格; M.博塞; S.迪默; H.多默; M.埃德尔曼; 韩露阳; M.希特尔; A.詹森; S.迈耶; K.舒伯特
Original assignee: Carl Zeiss Microscopy GmbH
Current assignee: Carl Zeiss Microscopy GmbH
Priority date: 2019-09-27
Filing date: 2020-09-07
Publication date: 2021-03-30
Also published as: DE102019214879A1

Abstract

The invention comprises a method for reducing topology artifacts in EDS analysis of a microscopic sample, as well as an electron microscope system and a computer program product. The method is performed with an electron microscope system, comprising: an electron column generating an electron beam; a scanning system; an EDS detector that detects X-ray signals; a movable stage holding the specimen, the stage configured to move at least along axes x and y and rotate about an axis of rotation, the stage configured to perform a computational center rotation and/or a concentric rotation. The method comprises the following steps: a) selecting a region of interest (ROI) on the sample while maintaining the ROI in a first orientation relative to the EDS detector; b) performing a first EDS analysis to obtain a result a; c) rotating the specimen stage by an angle α about the rotation axis such that the ROI is maintained in a second orientation relative to the EDS detector; d) compensating for sample table rotation; e) performing a second EDS analysis to obtain a result B; f) and combining the result A and the result B.

Description

Method, electron microscope system and computer program product for reducing topology artifacts

Technical Field

The invention relates to a method and a device for preventing or at least reducing topology artifacts that can occur in EDS analysis of three-dimensional microscopic samples.

Background

EDS (energy dispersive spectroscopy) is a method for analyzing material characteristics.

An electron beam (also called a primary electron beam) is scanned over the surface of the sample to be examined. X-ray photons are released due to the interaction between the impinging primary electrons and the atoms of the sample material.

The spectrometer is used to analyze the emitted X-rays by energy. Since the emitted X-rays have energies that are characteristic of the excited chemical elements, the detected X-ray signals provide information about the chemical composition of the sample material. A typical mode of operation of EDS systems is "line scanning" or "element mapping.

Not only X-ray photons, but also other interaction products of the interaction of the primary electrons with the sample material may be detected for imaging and/or analysis of the sample.

Common interaction products are backscattered electrons (BSE) and Secondary Electrons (SE), which can be detected by a suitable detector. Typically, the detected electrons are used to generate an image of the sample.

A typical system for performing a combined analysis of the interaction products is an SEM (scanning electron microscope) system with EDS functionality.

The SEM includes an electron beam column for generating and focusing a primary electron beam. The sample is positioned in a sample chamber (also referred to as a vacuum chamber) in which vacuum conditions are maintained during operation. Furthermore, SEM systems typically include suitable electronic detectors, such as BSE detectors and/or SE detectors for imaging, and EDS detection systems for detecting X-ray signals.

Further, the combination of the element analysis data with the imaging method allows generating an element distribution image (element mapping). To this end, a complete spectrum of elements may be collected to obtain each pixel of the digital high resolution image.

Typically, the EDS detector is located on one side of the sample chamber. This lateral arrangement of the EDS detector causes one side of the EDS detector to be illuminated, thereby causing strong topographical effects in the EDS analysis. This can cause artifacts, especially when examining three-dimensional samples or samples with different surface profiles. X-ray photons emitted in regions not within the line of sight of the EDS detector cannot be detected because, unlike electrons, X-rays travel along a straight line from the origin to the detector.

One way to address this problem is to provide a plurality of EDS detectors positioned in a plurality of orientations relative to the specimen. A typical solution is to provide two EDS detectors arranged in opposite directions.

Such a detector configuration may reduce adverse terrain effects, but significantly increase the cost of the EDS system. Moreover, two EDS detectors require a large space within the sample chamber.

Disclosure of Invention

It is an object of the present invention to provide a method of performing EDS analysis with a single EDS detector in which topology artifacts can be minimized.

Another object is to provide an EDS analysis method in which residual errors can be eliminated, thereby enabling to obtain EDS data with improved quality.

Furthermore, it is an object to propose an electron microscope system for performing the method of the invention and a computer program product configured to control the electron microscope system when performing the method of the invention.

To obtain valid EDS data, it is necessary to record X-ray signals at different viewing angles. For this reason, the EDS detector and the sample should be arranged in different orientations from each other. After images are taken from different perspectives, the images can be combined to receive a representation of the complete specimen.

The invention is based on the finding that the required relative orientation of the sample and the EDS detector can be easily obtained by rotating the sample by an angle α with the aid of the sample table of the SEM system. By doing so, the EDS detector, although stationary, can record different angles of the specimen so that images of different viewpoints can be obtained. This will minimize topology artifacts. Also, another advantage is that the combination of different images results in less noise contribution of the complete image.

The proposed solution is advantageous because only one EDS detector is required, thereby saving space and cost of the sample chamber.

The orientation of the sample can be changed by rotating the sample stage by an angle θ about the rotation axis R (i.e., in this case, the angle α is the angle θ). The rotation axis R is aligned parallel to the optical axis of the electron column of the SEM system.

However, after rotating the specimen, the specimen image shows a different orientation compared to the image of the non-rotated specimen. This may cause a problem that images taken at different angles cannot be easily merged.

According to the present invention, obstacles can be overcome by compensating for physical rotation of the object (i.e., the specimen) during image acquisition by digitally rotating the recorded image or by rotating the scan direction.

In order to analyze a sample in an SEM system, an electron beam is moved over the sample surface within a scan area. In doing so, the electron beam is directed along a scan path in a direction, which is referred to as the scan direction. The SEM system is configured to provide the possibility of scanning in different scanning directions. For this purpose, the scanning direction may be about an axis R located at the center of the scanning area_SAnd (4) rotating. Axis R_SIs in axial parallel with the optical axis of the electron column.

In an alternative embodiment, the specimen table is rotated about the tilt axis T through an angle

Causing the specimen to tilt (i.e., in this case, the angle α becomes the angle ═ angle-

). This means that the sample surface is held in a different orientation with respect to the optical axis and the EDS detector.

In this case, the physical rotation of the sample can be compensated for by applying tilt compensation (sometimes also referred to as tilt correction). Tilt compensation is a function of the SEM system. The aspect ratio of the scan area is changed such that the image height is reduced to compensate for the effect of projecting the inclined surface. The number of scan lines in the image height remains constant.

Moreover, the present invention allows for correction of residual errors that may occur due to inaccuracies in the specimen stage motion, scan rotation function, and/or image offset function.

To compensate for these residual errors, at least first and second SEM images are recorded with an electron detector that does not show any major orientation. By comparing the first image with the second image, a residual error may be determined. The first, second and third SEM images may also be recorded in order to perform the correction process twice.

Alternatively, the residual offset and rotation of the ROI may be iteratively corrected to further minimize the error. Examples of processing methods are cross-correlation, feature detection, fiducial marks, etc.

With knowledge of the residual error, the error of the recorded EDS data can be compensated. This may be done before or after performing the EDS analysis. There are several ways of performing error correction, for example by adjusting beam offset, by adjusting image offset or by correcting errors digitally.

Drawings

Exemplary embodiments are explained below with the aid of figures.

Fig. 1 schematically shows a SEM system with a lateral EDS detector arrangement.

Fig. 2a shows the effect of a side detector arrangement for line scanning (fig. 2a), and fig. 2b shows the effect of a side detector arrangement for element mapping.

Fig. 3 depicts the principle of a method that can be implemented in different forms of embodiment.

Fig. 4 is a flow chart of a first embodiment of the present invention, showing a basic variation of the scan direction rotation.

Fig. 5 is a flow chart of a second embodiment of the present invention, which is similar to the first embodiment, but with a numerical rotation of the EDS results.

Fig. 6 shows a flow chart of a third embodiment, in which the scanning direction is rotated and the residual error is corrected before the EDS analysis.

Fig. 7 shows a flow chart of the fourth embodiment. Here, the scanning direction is rotated and the residual error is corrected after EDS analysis.

Fig. 8 shows a flow chart of a fifth embodiment, similar to the embodiments of fig. 6 and 7, in which residual errors are corrected before and after EDS analysis.

Fig. 9 shows a flow chart of a sixth embodiment, in which the analysis data is digitally rotated and the residual error is digitally corrected after EDS analysis.

Fig. 10 shows a seventh embodiment in which EDS data is collected while holding the sample at multiple tilt angles.

Fig. 11 shows an eighth embodiment in which EDS data is collected while holding the sample at multiple tilt angles and the residual error is corrected before performing the second EDS analysis.

Fig. 12 shows a ninth embodiment in which EDS data is collected while holding a sample at a plurality of inclination angles, and residual errors are digitally corrected.

Fig. 13 shows a tenth embodiment in which EDS data is collected while holding a specimen at a plurality of inclination angles, and residual errors are corrected before and after performing EDS analysis.

Fig. 14 shows an SEM system with EDS functionality, configured to perform the method of the invention.

Detailed Description

Fig. 1 shows a side view of a typical configuration of an SEM system 1 with EDS analysis functionality: the EDS detector 4 is installed at one side of the sample chamber 3. A primary electron beam 7 is generated in the electron beam column 2 and directed to the sample 6. X-ray photons 5 emitted from the sample 6 are detected by the EDS detector 4.

However, due to its lateral arrangement, the EDS detector 4 only faces one side of the sample, which generally causes strong topographical effects in the EDS analysis. Side illumination can produce variations in the detected X-ray signal, particularly when performing line scans or elemental mapping.

Fig. 2 shows the effect of the side detector arrangement when detecting X-ray signals.

Fig. 2a schematically shows the effect of the EDS detector arrangement of fig. 1 when the SEM system is operated in a line scan mode. The line scan mode refers to scanning the primary electron beam along a line across the surface of the sample while recording the X-ray signal. The upper graph 7 shows the topography of the sample (in side view) and the lower graph 8 shows the X-ray signal detected by the side EDS detector 4.

Fig. 2b depicts the situation when the SEM system is operating in element mapping mode.

The element mapping mode refers to performing several line scans at adjacent locations so that two-dimensional images (also called EDS maps) can be put together.

The left side of fig. 2b shows an SEM image 10 of a sample 11 in a top view. For example, the SEM image may be a BSE image or an SE image. The sample particle 11 has a circular shape.

On the right side of fig. 2b, the corresponding EDS map of the same sample particle 11 is shown. As a result of the lateral EDS detector arrangement, some information is lost due to shadowing effects.

In summary, the lateral arrangement of the EDS detector as shown in fig. 1 may lead to falsification of the detected EDS signal. The process of the present invention overcomes this disadvantage.

Fig. 3 depicts the principle of the method according to the invention. The method can be implemented in several different forms of preferred embodiments, which are shown and described in fig. 4 to 13.

To perform the method, the microscopic sample is held on a movable sample stage in a sample chamber of an electron microscope (e.g., SEM system).

Since some steps of the method are performed in real space and other steps are performed in image space, fig. 3 shows real space steps on the left side and image space steps on the right side.

The object in real space, i.e. the specimen to be examined, is represented as an image in image space. Typically, an image is a two-dimensional representation of the collected signals, where the signals are spatially resolved.

When working with SEM systems, the signals that can be obtained may be several interaction products of the primary electron beam interacting with the sample material, such as backscattered electrons (BSE) or Secondary Electrons (SE), resulting in BSE images and SE images, respectively. The detectable signal may also be an X-ray photon, so that a spatially resolved energy spectrum or elemental map may be obtained.

In the present invention, the term "image" is used in a broad sense to describe any kind of signal representation in image space, such as a BSE image, an SE image, an elemental line scan or a line profile or an elemental map. The term "SEM image" is understood to mean an electron optical image, such as a BSE image or an SE image.

Part a) of fig. 3 shows a sample 34 (top view) which is arranged on a sample table 31 in a sample chamber of an SEM system having EDS functionality. The sample includes a first side 37 and a second side 38.

The primary electron beam may be focused onto the specimen 34 and scanned within the scan area 33 along a scan path over the specimen 31. The electron beam propagates along an optical axis of the electron column, which is oriented perpendicular to the projection plane. The electrons are scanned once in a first scanning direction (indicated by arrow 35).

The EDS detector 32 is disposed at a lateral position of the sample chamber. The EDS detector 32 detects X-ray signals emitted from the specimen 34.

The captured signals may be used to generate an image 36 (portion b) of the sample, referred to as result a. Due to the lateral arrangement of the EDS detector 32, only signals emitted from the first side 37 of the specimen can be detected. They are indicated in the image 36 as side 37' (part b). However, the second side 38, which is the distal side with respect to the EDS detector, cannot be displayed in result a.

The sample table 31 is then rotated about the rotation axis R by an angle θ, for example, 180 °. The axis R is parallel to the optical axis of the electron column. Thus, the sample 34 changes its orientation with respect to the EDS detector 32, as shown in section c). The second side 38 of the sample now faces the EDS detector and can be recorded by generating a second image (referred to as result B).

The table rotation motion is performed with a computing center (compu-centric). The centre of the rotation axis R is located at a particular point on the xy-plane. The ROI will be located at a distance from the center of rotation. Thus, mechanical rotation along axis R typically causes the ROI to move away from the imaged region. To keep the ROI within the imaged region, the table is moved centrally by the calculation. This means that depending on the relative position of the ROI with respect to the center of rotation, the motion of the table rotation in the x/y direction can be compensated.

However, the second image collected by the EDS detector after the stage rotation has a different orientation (portion d2) than the previous image. This would make it difficult to accurately combine the information of the second image (altered orientation) with the information of result a (original orientation) to obtain a whole picture of the specimen.

Therefore, the physical rotation of the sample should be compensated so that different results can be easily combined.

One way is to change the scanning direction 35 when performing EDS analysis on the second image (result B), as shown by section d 1). The scanning direction 35 is rotated about the rotation axis Rs by the same angle theta but in the opposite direction, resulting in a second scanning direction 39. The rotation axis Rs is located at the center of the scanning area. Rs is axially parallel to the axis of rotation R.

Thus, the physically changed orientation of the sample with respect to the EDS detector can be compensated for when capturing the X-ray signal, as shown in section e 1). Thus, side 38 can be imaged as side 38', but the orientation of the recorded second image 311 (result B) is the same as that of result a.

Finally, result B may be merged with result a, so that a complete data set of the sample is generated (part f 1)).

Another way of compensating for the changed orientation of the object to be examined is to capture an image and then digitally rotate the image. As shown in section d2), EDS data is collected at the actual orientation. The result is referred to as result B. The image 310 is then digitally rotated by an angle θ (portion e2)) to obtain a rotated result B referred to as B.

Result B has the same orientation as result a. Finally, result B may be merged with result a to obtain the complete EDS data set (part f 2)).

This is a basic principle of the first to sixth embodiments described below.

However, the rotation of the sample stage (including the sample) is not limited to the rotation about the axis R. The sample stage may also be rotated about the tilt axis T to tilt the sample with respect to the optical axis of the electron column and the EDS detector.

To this end, the specimen table includes a tilt axis T that is disposed in a plane spanned by axes x and y. For example, the tilt axis T may be parallel to the axis x. The sample stage is rotatable about a tilt axis T so that the orientation of the sample with respect to the optical axis of the EDS detector and the electron beam can be changed.

To compensate for motion about the tilt axis T, tilt compensation may be applied. Tilt compensation is a function of the SEM system. The aspect ratio of the scan area is changed such that the image height is reduced to compensate for the effect of projecting the inclined surface. The number of scan lines in the image height remains constant.

The principle of rotating the sample about the tilt axis T to obtain different orientations between the sample and the EDS detector is the basis of the seventh to tenth embodiments of the invention (fig. 10 to 13).

Fig. 4 shows a flow chart of a first embodiment of the invention, which is a basic variant in which the scanning direction is rotated.

In a first step S4-1, a region of interest (ROI) on the sample is selected. A first EDS analysis is performed, i.e., a first set of EDS data is collected, for example, by performing a line scan or EDS mapping analysis (step S4-2). This first set of EDS data is referred to as result A. Then (step S4-3), the sample stage is rotated by a certain angle θ (theta). Since the calculation centrally rotates the specimen table, the ROI remains in the field of view.

In step S4-4, the scanning direction is rotated in the opposite direction by the same angle θ.

Subsequently, another EDS analysis is performed (S4-5), resulting in the collection of a second set of EDS data referred to as result B. Likewise, the set of EDS data may include EDS mapping or line scan data.

In step S4-6, result B is added to result A. This means that the element information obtained in result B is integrated into the element information of result a obtained previously.

Finally (step S4-7), steps S4-3 through S4-6 are repeated at a plurality of angles θ such that a combined data set is obtained from different angles of the specimen (step S4-6). After repeating the process several times, the sample has been completely recorded so that the combined result comprises a complete data set.

Fig. 5 shows a flow chart of a second embodiment of the invention, which is similar to the one described as a basic variant of the first embodiment. However, in the second embodiment, digital rotation is performed instead of rotation in the scanning direction.

The first steps 4-1 to 4-3 are the same as the first embodiment. As described for the first embodiment, an ROI is selected and a first set of EDS data is collected (result a). Then (step S4-3), the table is rotated by a certain angle theta (theta) with the center of the calculation.

Starting with the next step S5-4, the process differs from the previous embodiment.

In step S5-4, a second EDS analysis is performed in order to obtain a so-called result B.

Then (S5-5), the result B is digitally rotated. For this purpose, image rotation is performed by transforming the coordinates of each pixel in accordance with a rotation matrix around the center of the image.

In step S5-6, the rotation result B is added to the result a so that the element information obtained in the result B is integrated into the element information of the result a obtained previously.

Finally (step S5-7), steps 4-3 through S5-6 are repeated at a plurality of angles θ such that the combined data set obtained in step S5-6 includes different perspectives. After repeating the process several times, the sample has been completely recorded so that the combined result comprises a complete data set.

Fig. 6, 7 and 8 show further embodiments of the invention. These embodiments are characterized by performing rotation of the scanning direction and error correction. These embodiments distinguish one from another in the order in which the correction steps are performed, i.e., before or after the second EDS data set is recorded (result B).

A calibration step may be required because computing the center rotation may not bring the ROI at different angles to exactly the same position and orientation due to the limited accuracy of the specimen table.

Fig. 6 shows a flow chart of the third embodiment. Here, before recording EDS data, rotation of the scanning direction is performed and a residual error is corrected.

In a first step S6-1, an ROI is selected. After the ROI was selected, SEM image I was recorded₁(step S6-2). For example, the SEM image may be a BSE image or an SE image.

Ideally, SEM images should be taken using detectors that do not show specific orientation information (e.g., a ring-shaped BSE detector located above the specimen). The detector may also be an axially symmetric SE detector (so-called in-lens detector) integrated in the electron beam column.

Then, EDS analysis is performed (S6-3). By collecting X-ray signals emitted from a sample, line scan analysis or EDS mapping can be performed as EDS analysis.

The result of the EDS analysis is referred to as result A. Steps S6-2 and S6-3 may also be performed in the reverse order.

Then (step S6-4), the sample stage is rotated by the angle θ at the center of the calculation. In step S6-5, the scanning direction is rotated in the opposite direction by the same angle θ.

Subsequently (step S6-6), a second SEM image I is recorded₂. This means that in the example given, the second BSE image I is recorded₂。

Then (step S6-7), by comparing the images I₁And image I₂To determine residual errors of specimen table motion and scan rotation.

By knowing the residual errors, these errors can be corrected in the next step S6-8. This can be done by adjusting the rotation of the scan direction rotation and/or by adjusting the beam offset.

The beam shifting function of the SEM system allows changing the point of influence of the primary beam on the sample.

In step S6-9, a second EDS analysis is performed, resulting in result B. Finally, as described above, the result B is added to the result a (step S6-10). As described previously, in step S6-11, the process of the third embodiment may be repeated at a plurality of angles θ.

FIG. 7 shows a flow chart of a fourth embodiment of the present invention in which error correction is performed after the EDS data is collected.

The first steps S6-1 to S6-6 are the same as described for the third embodiment (fig. 6).

Unlike the process of fig. 6, in step S7-7 of the fourth embodiment, a second EDS analysis is performed to obtain a result B. Then (step S7-8), by comparing SEM image I₁And SEM image I2 to determine residual error. Subsequently (step S7-9), the residual error is digitally corrected for the result B.

Finally, the process of adding the corrected result B to the result A (S7-10) and steps S6-4 to S7-10 is repeated at a plurality of angles θ (step S711).

Fig. 8 shows a flow chart of a fifth embodiment of the present invention. Here, the correction of the residual error is performed twice: before and after the collection of EDS data.

Steps S6-1 to S6-8 of the third and fifth embodiments are the same. As shown in FIG. 6, the process of steps S6-1 to S6-8 results in the recording of SEM image I₁And result a, while the sample stage has rotated by the angle θ, the scan direction has rotated by the same angle θ, but in the opposite direction. Furthermore, a second SEM-image I has been recorded₂. In the first error correction process, by comparing SEM image I₁And I₂The residual error is corrected.

Fig. 8 focuses on the different steps of the fourth embodiment starting from S8-9, which immediately follows step S6-8 (first error correction).

In step S8-9, a second EDS analysis is performed while additionally recording a third SEM image I₃。

By comparing SEM images I₃And I₁The residual error is determined again (S8-10).

Then, the residual error of the result B is digitally corrected (S8-11, second error correction).

In step S8-12, the correction result B is added to the result a as described previously.

As described for the other embodiments, the steps of the process may be repeated at a plurality of angles θ from the rotation of the specimen stage (steps S8-13).

Fig. 9 shows a flowchart of a sixth embodiment, in which the SEM image is digitally rotated and residual errors corrected after EDS analysis.

Steps S6-1 to S6-4 of the third and sixth embodiments are the same. As shown in FIG. 6, in steps S6-1 to S6-4, SEM image I is recorded₁And result A. The sample table is rotated by an angle θ.

Fig. 9 shows the different steps of the sixth embodiment starting from S9-5, which immediately follows step S6-4 (table rotation).

In step S9-5, SEM image I is recorded₂. EDS analysis is then performed (S9-6) to obtain result B.

In step S9-7, SEM image I₂And result B is along withThe sample rotation (i.e., sample stage rotation) is numerically rotated by an angle θ in the opposite direction. This produces a digitally rotated image I₂And the result B after digital rotation.

Then (S9-8), by comparing I₂Sum of original images I₁Residual errors of image offset and image rotation are determined. One example method of determining the image offset is phase correlation. On the other hand, image rotation can typically be determined by tracking corresponding features between two images.

With knowledge of the residual error, the error of result B is digitally corrected, thereby producing result B (step S9-9).

Finally (S9-10), the corrected result B is added to a. In step S9-11, steps S6-4 through S9-10 are repeated at a plurality of angles θ.

Fig. 10 to 13 show an embodiment in which the specimen stage (together with the specimen) is tilted with respect to the optical axis of the electron column. To this end, the specimen table includes an inclined axis T. Also, the specimen stage is configured to perform a calculation center (comput-centric) tilt or an concentricity (eutrical) tilt of the specimen. When the sample is tilted centrally or concentrically in the calculation, the ROI remains in the field of view of the SEM's optical system.

Fig. 10 shows a seventh embodiment of the present invention. In the present embodiment, EDS data is recorded while holding the specimen at a plurality of inclination angles with respect to the optical axis.

In step S10-1, an ROI is selected. Then (step S10-2) EDS analysis is performed to obtain result a.

In step S10-3, the sample stage is tilted at a certain angle with the center of the calculation

Inclination angle

Is the angle between the tilted sample surface and the optical axis of the electron beam.

Alternatively, the specimen table may be concentrically tilted at an angle

In any case, the ROI of the tilted specimen is always located within the field of view.

Then (step S10-4), at the same angle

Tilt compensation is performed as described in fig. 3.

In step S10-5, another EDS analysis is performed, resulting in result B. Finally (step S10-6), result B is added to result A.

Finally (step S10-7), at a plurality of angles

Steps 10-3 through S10-6 are repeated so that the combined data set obtained in step S10-6 includes different perspectives between the specimen and the EDS detector. After repeating the process several times, the sample has been completely recorded so that the combined result comprises a complete data set.

FIGS. 11-13 illustrate embodiments in which the sample is held at different tilt angles with respect to the optical axis

While EDS data is collected and residual errors of image offsets are corrected. Error correction may be performed before EDS analysis (fig. 11, eighth embodiment), after EDS analysis (fig. 12, ninth embodiment), or both before and after EDS analysis (fig. 13, tenth embodiment).

Fig. 11 shows a flowchart of the eighth embodiment. In this embodiment, the sample is held at a plurality of tilt angles

While error correction is performed prior to EDS.

In a first step S11-1, an ROI is selected. Then (S11-2), SEM image I was recorded₁. For example, the SEM image may be a BSE image or an SE image. And, by collecting hair from the sampleThe emitted X-ray signals to perform EDS analysis (S11-3). The result of the EDS analysis is referred to as result A. Steps S11-2 and S11-3 may also be performed in the reverse order.

In the subsequent step (S11-4), the rotation angle of the sample stage about the inclination axis T is calculated to be central

Alternatively, the sample stage is rotated concentrically about the tilt axis T by an angle

In any case, the ROI remains in the field of view.

In step S11-5, the same angle is used

Tilt compensation is applied as described with respect to fig. 3.

Subsequently (S11-6), a second SEM image I was recorded₂。

Then (S11-7), by comparing the images I₁And image I₂To determine the residual error of the image offset.

Image offset is the difference between two images.

By knowing the residual error, the error can be corrected in the next step S118. This can be done by adjusting the beam offset. Beam offset is a parameter applied to SEM scanning systems. The value of the image shift is then applied in the opposite direction to the beam shift on the SEM.

In step S11-9, a second EDS analysis is performed, resulting in result B. Finally, result B is added to result a (S11-10).

As previously described for the embodiments, at multiple angles

The process described in steps S11-4 to S11-10 is then repeated (step S10-7).

Fig. 12 shows a flow chart of a ninth embodiment, wherein the process comprises steps for digitally correcting residual errors after EDS analysis.

Steps S11-1 to S11-4 of the eighth and ninth embodiments are the same. As described with respect to FIG. 11, in steps S11-1 through S11-4, a first SEM image I is recorded₁And first EDS data (result a). Further, the sample is tilted at an angle

FIG. 12 explicitly shows the different steps of the ninth embodiment starting from S12-5, which follows step S11-4 (rotation about the tilt axis).

In step S12-5, a second SEM image I of the ROI is recorded₂. Also (step S12-6), a second EDS analysis is performed to obtain result B.

Then (step S12-7), by converting the image I₂And image I₁A comparison is made to determine the residual error of the image offset.

Subsequently (step 12-8) the residual error is corrected by digitally processing the result B.

This is done by calculating the image offset and rotation difference according to the methods described previously. The coordinates of each pixel in result B are then shifted and rotated in the opposite direction according to the result of the last step.

In step 12-9, the corrected result B is added to the result a.

At a plurality of inclination angles

The process of steps S11-4 to S12-9 is repeated (step S12-10).

Fig. 13 shows a flowchart of the tenth embodiment. The tenth embodiment is similar to the eighth embodiment except that here the correction of residual errors is performed twice, i.e. before and after the second EDS analysis.

Steps S11-1 to S11-8 of the eighth embodiment and the tenth embodiment are the same.

After performing step S11-8 (first error correction), the process of the tenth embodiment continues with step S13-9, in which a third SEM image I is recorded₃。

Then (step S13-10), a second EDS analysis is performed, resulting in result B.

In a next step S13-11, by comparing the images I₃And image I₁To determine the residual error. Then (step S13-12) the residual error of the result B is digitally corrected. Finally, the corrected result B is added to the result a (step S13-13).

In step S13-14, a plurality of inclination angles are set

Steps S11-4 through S13-13 are repeated.

Fig. 14 shows an SEM system configured to perform the method of the invention.

SEM system 14-1 includes a specimen mount 14-11 for holding a specimen 14-10. The sample stage 14-11 is located within a sample chamber 14-17, which is maintained under vacuum during operation.

SEM system 14-1 includes an electron beam column 14-2. In the electron source 14-3 of the electron beam column 14-2, electrons can be generated. Along the optical axis 14-5 of the electron beam 14-2, electrons (primary electrons) are accelerated, focused by means of the first and second lens systems 14-4, 14-6 and cut by the aperture 14-15.

Furthermore, the electron beam column 14-2 includes a scanning system 14-13 that directs a primary beam along a scanning path over the specimen surface. The scanning system 14-13 is configured to provide the possibility of rotating the scanning direction. Furthermore, the scanning system is configured to perform a beam shift, which allows shifting the scanning area.

Further, SEM system 14-1 includes an EDS detection system configured to detect X-ray signals emitted from the specimen. The EDS detection system includes an actual EDS detector 14-8 for collecting X-ray photons, and a spectrometer 14-7 for analyzing the emitted X-ray photons in terms of energy.

Advantageously, SEM system 14-1 also includes additional detectors for detecting interaction products, such as BSE detector 14-12 for detecting BSE and/or SE detector 14-14 for detecting SE.

Preferably, the recorded results may be displayed on a display 14-16, such as an SEM image of the sample. Comparing a pair of images allows the determination and execution of an image offset, which may be required to perform one of the above processes.

The operation of the SEM system 14-1 is controlled by the controller unit 14-9.

The specimen table is configured to move at least along axes x and y and rotate about an axis of rotation R. It is also possible that the specimen table is also rotated about the inclination axis T.

Preferably, specimen tables 14-11 are configured to move concentrically. This means that all the axes of rotation are arranged in such a way that they intersect at the same point. This concentric type of specimen table allows the ROI to remain stationary while in the field of view even if the specimen table is rotated.

The specimen table 14-11 includes at least an axis of rotation R. The specimen table is configured to rotate about an axis R by a variable angle θ.

Preferably, the specimen table 14-11 further includes a tilt axis T. The specimen table 14-11 is rotatable about an inclined axis T through variable angles

Also, the specimen table 14-11 is preferably configured to perform rotation in a manner that calculates the center. This means that the ROI on the specimen remains within the field of view at all times, regardless of which rotational movement is performed. Any shift in the ROI that may occur when rotating the specimen table can be eliminated by a computational correction of the table motion along the relevant axis.

Preferably, the operation of SEM system 14-1, including the detection process and movement of specimen stage 14-11, is controlled by controller unit 14-9.

A computer program product comprising a sequence of commands may be loaded into the controller unit 14-9. When the command sequence is executed, SEM system 14-1 performs the method of the present invention.

Reference numerals

1 SEM System with EDS analysis function

2 electron light column

3 sample chamber

4 EDS detector

5X-ray photons

6 sample table

7 test specimen

8 Electron Beam

9 graph: shape of test sample

10, graph: x-ray signal

11 views of EDS Detector

12 test specimens

12' specimen image

13 display

R axis of rotation

T inclined axis

31 specimen table

32 EDS detector

33 scan area

34 sample (object)

35 first scanning direction

First image of 36 sample (result A)

37 first side of

37' first side image

38 second side surface

39 second scanning direction

310 sample image

311 sample image

312 merged image of specimen

A results A

B results B

B rotating result B

S4-1 ROI selection

S4-2 performs a first EDS analysis (results A)

S4-3 rotating the table by an angle theta

S4-4 rotational scan direction

S4-5 performing a second EDS analysis (result B)

S4-6 adding result B to result A

S4-7 repeats at multiple angles θ

S5-4 performing a second EDS analysis (result B)

S5-5 digitally rotating result B

S5-6 adds the rotation result B to the result A

S5-7 repeats at multiple angles θ

S6-1 ROI selection

S6-2 records a first SEM image I₁

S6-3 performs a first EDS analysis (results A)

S6-4 rotating the table by an angle theta

S6-5 rotational scan direction

S6-6 recording a second SEM image I₂

S6-7 by comparison I₁+I₂Determining residual error

S6-8 correcting residual errors

S6-9 performing a second EDS analysis (result B)

S6-10 adds result B to result A

S6-11 repeating at multiple angles θ

S7-7 performs a second EDS analysis (result B)

S7-8 by comparison I₁+I₂Determining residual error

S7-9 digitally corrects the residual error for result B

S7-10 adding the corrected result B to the result A

S7-11 repeating at multiple angles θ

S8-9 performing a second EDS analysis (result B) + accompanying SEM image I₃

S8-10 by comparison I₁+I₃Determining residual error

S8-11 digitally corrects the error of result B

S8-12 adds the corrected result B to the result A

S8-13 repeats at multiple angles θ

S9-5 recording a second SEM image I₂

S9-6 performing a second EDS analysis (result B)

S9-7 digitally rotating image I₂+ result B obtains I₂*+B*

S9-8 by comparison I₂*+I₁Determining residual error

S9-9 digitally correcting B to obtain B

S9-10 adds result B to result A

S9-11 repeating at multiple angles θ

S10-1 ROI selection

S10-2 performs a first EDS analysis (results A)

S10-3 inclination angle

S10-4 at an angle

Using tilt compensation

S10-5 performing a second EDS analysis (result B)

S10-6 adding result B to result A

S10-7 at multiple angles

Repetition of

S11-1 ROI selection

S11-2 records a first SEM image I₁

S11-3 performs a first EDS analysis (results A)

S11-4 inclined angle

S11-5 at an angle

Using tilt compensation

S11-6 recording a second SEM image I₂

S11-7 by comparing image I₂And I₁Determining residual error of image offset

S11-8 correcting residual errors by beam offset

S11-9 performing a second EDS analysis (result B)

S11-10 adds result B to result A

S11-11 at multiple angles

Repetition of

S12-5 recording a second SEM image I₂

S12-6 performing a second EDS analysis (result B)

S12-7 by comparing image I₂And I₁Determining residual error of image offset

S12-8 digitally corrects the residual error for result B

S12-9 adding the corrected result B to the result A

S12-10 at multiple angles

Repetition of

S13-9 records a third SEM image I₃

S13-10 performs a second EDS analysis (result B)

S13-11 by comparing image I₃And I₁Determining residual error

S13-12 digitally corrects the residual error for result B

S13-13 adding the corrected result B to the result A

S13-14 at multiple angles

Repetition of

14-1 SEM system

14-2 electron light column

14-3 electron source

14-4 first lens system

14-5 optical axis

14-6 second lens system

Spectrometer of 14-7 EDS system

14-8 EDS detector

14-9 controller unit

14-10 test specimens

14-11 sample table

14-12 BSE detector

14-13 scanning system

14-14 SE detector

14-15 aperture

14-16 display

R axis of rotation

T rotation axis (Tilt)

Claims

1. A method implemented with an electron microscope system for reducing topology artifacts in EDS analysis of a microscopic sample, the electron microscope system comprising

-an electron column for generating an electron beam, wherein the electron column comprises an optical axis;

a scanning system for scanning the electron beam over the specimen in a scanning area,

an EDS detector for detecting X-ray signals,

-a movable stage for holding the sample,

the stage is configured to move at least along axes x and y and to rotate around a rotation axis, wherein the stage is configured to perform a calculation-centric rotation and/or a concentric rotation,

the method comprises the following steps:

a) selecting a region of interest (ROI) on the sample while maintaining the ROI in a first orientation relative to the EDS detector;

b) performing a first EDS analysis to obtain a result a;

c) rotating the specimen stage by an angle α about the rotation axis such that the ROI is maintained in a second orientation relative to the EDS detector;

d) compensating for the specimen stage rotation by performing one of the following actions:

-rotating the scanning direction by an angle α in the opposite direction;

-digitally rotating the result a in the opposite direction by an angle α;

-applying a tilt compensation of the angle α;

e) performing a second EDS analysis to obtain a result B;

f) and combining the result A and the result B.

2. The method according to claim 1, wherein the method comprises the further step of:

g) repeating steps c) to f).

3. The method of claim 1 or 2, wherein the specimen stage rotates about a rotation axis R arranged parallel to the optical axis of the electron optical column.

4. The method according to one of claims 1 to 3, wherein the method further comprises the step of:

-recording a first SEM image I before rotating the specimen table₁；

-recording a second SEM image I after the specimen table has been rotated₂；

By comparing the first image I₁And the second image I₂Determining the residual error;

-correcting the residual error.

5. The method according to claim 4, wherein the correction of the residual error is performed by digitally correcting the error of the result B.

6. The method according to claim 4 or 5, wherein the method comprises the further step of:

-andthis second EDS analysis together records the accompanying third SEM image I₃；

-by comparing the first SEM image I₁And the third image I₃Determining the residual error:

-digitally correcting the residual error of the result B.

7. The method according to claim 4, wherein the method comprises the further step of:

-digitally rotating the second SEM image I₂And a result B;

by comparing the rotated second SEM image I₂And a first SEM image I₁Determining a residual error;

-digitally correcting the residual error of the rotation result B.

8. The method of claim 1 or 2, wherein the specimen stage rotates about a tilt axis T, the tilt axis being disposed in a plane spanned by axes x and y.

9. The method according to claim 7, wherein the method comprises the further step of:

-recording a first SEM image I before rotating the specimen table₁；

-recording a second SEM image I after the specimen table has been rotated₂；

By comparing the first image I₁And the second image I₂Determining a residual error of the image offset;

-correcting the residual error by varying the beam offset.

10. The method according to claim 7, wherein the method comprises the further step of:

-recording a first SEM image I before rotating the specimen table₁；

-recording a second SEM image I after the specimen table has been rotated₂；

-by comparing the first SEM image I₁And the second SEM image I₂Determining the residual error;

digitally correcting the residual error of result B.

11. The method according to claim 8, wherein the method comprises the further step of:

-recording a third SEM image I after the residual error has been corrected by changing the beam offset₃；

-by comparing the first SEM image I₁And the third SEM image I₃Determining the residual error;

-digitally correcting the residual error of the result B.

12. An electron microscope system comprises

-a scanning system for scanning the electron beam over the specimen in a scanning area;

-an EDS detector for detecting X-ray signals;

-a movable stage for holding the sample;

the stage is configured to move at least along axes x and y and to rotate around a rotation axis, wherein the stage is configured to perform a computational center rotation and/or a concentric rotation,

-a controller unit for controlling the operation of the electron microscope system;

the electron microscope system is configured to perform the method according to claims 1 to 10.

13. A computer program product comprising a command sequence, the computer program product being loadable into a controller unit of an electron microscope system and configured to cause the electron microscope system to perform the method according to claims 1 to 10 when the command sequence is executed.