JP2010251041A - Scanning transmission electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in detection of images by an annular dark-field scanning transmission electron microscope (ADF-STEM) that, in conventional cases, a low-angle ADF-STEM image and a high-angle ADF-STEM image can not be detected at the same time, so that such an image-processing work as a positioning processing for contrast comparison is necessary. <P>SOLUTION: By concentrically dividing an annular detector 6 of the ADF-STEM, an image without displacement can be detected as scattered electrons at high angles and low angles are detected at the same time, and precise distortion contrast can be simply detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a scanning transmission electron microscope, and more particularly to a technique effective when applied to an annular dark field scanning transmission electron microscope used to detect distortion of a sample having a crystal structure.

  An annular dark field scanning transmission electron microscope (ADF-STEM) irradiates a sample while scanning a focused electron beam, and scatters electrons due to the vibration of atoms in a ring below the sample. It is an electron microscope formed as an image using a detector. When distortion occurs in a sample crystal, the magnitude of atomic vibration changes. Since ADF-STEM can change the detection angle by changing the position of the detector, it is possible to detect the change in the magnitude of atomic vibration due to crystal distortion by setting the detection angle to the low angle side, It has been reported that contrast corresponding to distortion can be obtained. Since this contrast changes monotonously with respect to the magnitude of strain, it is considered effective for visualization of crystal strain (strain mapping).

  In Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-146781), a target portion of a thin piece sample can be analyzed with a TEM or STEM from a plane direction and a cross-sectional direction, and also analyzed with a TEM or STEM from a plane direction and a cross-sectional direction. A sample preparation apparatus capable of preparing a sample for performing the above is disclosed.

  Further, Non-Patent Document 1 uses a dark-field scanning transmission electron microscope to detect distortion in a silicon substrate by detecting an electron beam scattered on a sample with a high-angle and low-angle detector. A technique is disclosed that can detect the amount of distortion contrast when the thickness of the sample is known.

  Further, in Non-Patent Document 2, changing the radius of the inner diameter of the annular detector of the dark field scanning transmission electron microscope does not greatly affect the detected image. A technology has been disclosed that it is appropriate to detect at a special detection angle in a low-temperature environment.

  In Non-Patent Document 3, when a dark field scanning transmission electron microscope is used and a scattered electron beam is detected at a high angle, the accumulated defects are close to the surface of the sample and the diameter is small. A technique for detecting strong distortion contrast has been disclosed.

  Non-Patent Document 4 discloses a technique in which the strain contrast of a semiconductor layer into which impurities are implanted is related to the difference in atomic scattering between impurities and matrix atoms.

JP 2000-146781 A

Study of strain fields at a-Si / c-Si interface, Z. Yu, D.A.Muller and J. Silcox, Journal of Applied Physics, Vol.95 (2004) pp.3362. Detector geometry, thermal diffuse scattering and strain effects in ADF STEM imaging, Ultramicroscopy, vol.58 (1995) pp.6 Imaging elastic strains in high angle annular dark field scanning transmission electron microscopy, Ultramicroscopy, vol.52 (1993) pp353. On the electron microscope contrast of doped semiconductor layers, D.D.Perovic at al, Philosophical Magazine A, 1991, vol.63 (1991) pp.757

  As shown in FIG. 1, the ADF-STEM irradiates the sample 2 while scanning the focused electron beam 1, and detects the scattered electrons 3 by vibration of atoms using an annular detector 4 below the sample. The electron microscope forms a detected image and monitors it on the PC 5.

  As shown in FIG. 2B, when the electron beam 1 is irradiated onto the sample 2 with an ADF-STEM and the scattered electrons 3 are detected on the low angle side with the detection angle X, the contrast corresponding to the distortion is obtained. Obtainable. However, since the contrast of this low angle ADF-STEM (LAADF-STEM) changes not only due to distortion but also due to the difference in the composition of the sample 2, whether the contrast change is due to composition or distortion. Carving is necessary. This separation is possible by comparison with a high angle ADF-STEM (HAADF-STEM) that detects scattered electrons 3 on the high angle side, but in the device described in Non-Patent Document 1, the low angle side is used. In this case, it is necessary to perform complicated processing to compare the HAADF-STEM image and the LAADF-STEM image.

  In addition, when detecting the scattered electrons 3 at a low angle and a high angle with a conventional ADF-STEM, as shown in FIG. 2A, the sample 2 is irradiated with the electron beam 1 to detect the ADF-STEM detector 4. Are moved up and down, and the scattered electrons 3 are detected by changing the distance (camera length) between the detector 4 and the sample 2. For this reason, the LAADF-STEM image and the HAADF-STEM image cannot be detected simultaneously. If simultaneous detection is not possible, the detection positions of LAADF-STEM and HAADF-STEM are not exactly the same, and image processing operations such as alignment processing for contrast comparison are required.

  In addition, since the strain of the crystal changes depending on how the stress is applied in the sample 2, the magnitude of the strain generally differs depending on the crystal orientation. Since the detector of the conventional ADF-STEM is annular, the obtained distortion contrast is the average of each orientation of the crystal, and there is a problem that it is difficult to resolve the distortion component.

  Furthermore, when there are impurity atoms in the mother crystal, the mother crystal is distorted due to the influence of the impurity atoms, so that the influence of the distortion may become significant due to scattering of a specific crystal orientation depending on the type and situation of the impurity atoms. However, when the change is detected by the conventional annular detector, the scattered electrons are detected in all directions, so that there is a problem that the change in distortion cannot be detected efficiently.

  A first object of the present invention is to provide an ADF-STEM that can detect scattered electrons simultaneously at a high angle and a low angle and easily detect an accurate distortion contrast.

  A second object of the present invention is to provide an ADF-STEM capable of resolving and detecting a strain component of a crystal depending on its orientation.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in this application, the outline of one embodiment of a representative one will be briefly described as follows.

A scanning transmission electron microscope according to an embodiment of the present invention includes:
Irradiate the sample with a focused electron beam,
Scanning the electron beam;
Detecting electrons scattered by being irradiated on the sample with a detector below the sample,
In a scanning transmission electron microscope that forms a detected image and monitors it on a PC,
The detection surface of the detector is divided into a plurality of parts.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  According to an embodiment of the present invention, the ADF-STEM annular detector is divided into concentric circles, for example, to simultaneously detect scattered electrons at a high angle and a low angle, thereby easily detecting an accurate distortion contrast. can do.

  In addition, according to an embodiment of the present invention, by dividing the ADF-STEM annular detector, for example, radially, the distortion component of the crystal can be decomposed and detected by the orientation.

It is a schematic diagram which shows the detection method of ADF-STEM which concerns on this invention. (A) is sectional drawing which shows the detection method of the conventional ADF-STEM typically. (B) is sectional drawing which shows the detection method of the conventional ADF-STEM typically. It is typical sectional drawing of the detector of ADF-STEM in this invention. 4 is an upper plan view of the detector of the ADF-STEM in Embodiment 1. FIG. It is an upper part top view of the detector of the conventional ADF-STEM. 4 is an upper plan view of the detector of the ADF-STEM in Embodiment 1. FIG. (A) is an upper top view of the detector of ADF-STEM in Embodiment 2. FIG. FIG. 6B is an upper plan view of the ADF-STEM detector according to the second embodiment. 6 is an upper plan view of a detector of an ADF-STEM in Embodiment 3. FIG. It is an upper part top view of one Example of the detector of ADF-STEM in the present invention.

  In the following embodiments, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other. There are some or all of the modifications, details, supplementary explanations, and the like.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.

  Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. In addition, in the embodiment, etc., when “consisting of A” or “consisting of A” is used to exclude other elements, unless specifically stated that only those elements are stated. It goes without saying that it is not.

  Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  In addition, when referring to materials, etc., unless specified otherwise, or in principle or not in principle, the specified material is the main material, and includes secondary elements, additives It does not exclude additional elements. For example, unless otherwise specified, the silicon member includes not only pure silicon but also an additive impurity, a binary or ternary alloy (for example, SiGe) having silicon as a main element.

  Also, components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof is omitted.

  In the drawings used in the following embodiments, even a plan view may be partially hatched to make the drawings easy to see.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
The present embodiment is applied to an annular dark field scanning transmission electron microscope (ADF-STEM), and FIG. 3 shows an overall view of the ADF-STEM. An ADF-STEM 21 shown in FIG. 3 includes an electron gun 22, a condenser lens 23, a scanning coil 24, an objective lens 25, a contrast diaphragm 26, a detector 6, a spectrometer 27, a spectral spectrum detector 28, and an energy dispersive X-ray analysis. An apparatus 29 is provided, and the installed sample 2 is irradiated with the electron beam 1 from the electron gun 22, the electron beam 1 is scanned by the scanning coil 24, and the scattered electrons 3 are detected by the detector 6 and the spectral spectrum detector 28. It is a device to detect.

  Next, FIG. 4 shows an upper plan view of the detector of the ADF-STEM in the present embodiment.

  In the ADF-STEM shown in FIG. 4, the detection surface of the detector 6 is divided into two on the inner side and the outer side, the LAADF-STEM detector 7 on the inner side, and the HAADF-STEM detector 8 on the outer side.

  Here, as shown in FIG. 5, since the width of the conventional detector 4 is constant, an arbitrary detection angle X (FIG. 2B) cannot be selected. In order to detect the LAADF-STEM image and the HAADF-STEM image, it is necessary to set the detection angle X to the inner and outer angles. However, as shown in FIGS. In the ADF-STEM, the detection angle X is changed by moving the detector 4 up and down in order to detect the LAADF-STEM image and the HAADF-STEM image.

  However, since the conventional method of moving the detector 4 up and down cannot detect the LAADF-STEM image and the HAADF-STEM image at the same time, the detection positions of the images are not exactly the same, and alignment processing for contrast comparison is performed. Image processing work such as was necessary.

  Therefore, in the ADF-STEM of the present embodiment shown in FIG. 4, the LAADF-STEM image and the HAADF-STEM image can be obtained at the same time by concentrating the detector 6 inward and outward. Since the LAADF-STEM image and the HAADF-STEM image obtained at the same time have no misalignment, it is possible to acquire atomic number information from the HAADF-STEM image and easily extract only the contrast due to distortion from the LAADF-STEM image. Is possible. For this reason, the distortion of the mother crystal due to impurities can be detected efficiently, and the distribution of light elements and low-concentration impurities that were difficult to detect with a normal electron microscope can be visualized.

  Although FIG. 4 shows an example in which the detector 6 is divided into two on the inner side and the outer side, as shown in FIG. 6, the number of the detectors 6 may be further increased. In this case, by selecting an arbitrary detector, it is possible to arbitrarily set the inner and outer detection angles X (FIG. 2 (b)), so that a distortion component having a desired magnitude has been revealed. An image can be obtained.

(Embodiment 2)
As an example of the ADF-STEM according to the present invention, in the second embodiment, an ADF-STEM having a detector in which a detection surface is radially divided will be described.

  FIG. 7 shows the detector 6 as an ADF-STEM according to the second embodiment.

  As shown in FIG. 7A, the detectors 6 of the ADF-STEM according to the present embodiment are radially divided into even numbers, and each of the divided detectors is paired with an opposing detector. Detecting the strain direction dependency of the sample. That is, in the detector 6, the detector A is at a position facing the detector A ', and the detector B is at a position facing the detector B'.

  When the sample is stressed, it is considered that the intensity of scattered electrons varies depending on the scattering direction. Distortion can be resolved by detecting the electrons in the specific direction and displaying them by direction.

  As shown in FIG. 5, the conventional ADF-STEM detector detects an image with only one surface of the annular detector 4, so that the obtained distortion contrast is the average of each orientation of the crystal, and the distortion component of the sample. It was impossible to read the direction dependency of

  Therefore, in the detector 6 in the present embodiment shown in FIG. 7A, the detector 6 is radially divided so that the direction to be detected can be arbitrarily selected, and the direction dependency of the distortion component is detected. It was possible. Further, by detecting scattered electrons in the channeling direction from impurities having a strain field, the distribution of impurities can be obtained.

  Note that when reading the dependence on directionality, the same image is detected by a detector (for example, detector A ′) facing an arbitrary detector (for example, detector A), so two pairs of detectors facing each other are used. To detect direction dependency.

  Further, in the present embodiment, as shown in FIG. 7B, a larger number may be used as long as the number to be divided is an even number. In this case, since a detection image can be obtained with a finer direction than the detector 6 in FIG. 7A, it is possible to detect more detailed direction-dependent distortion.

(Embodiment 3)
As an example of the ADF-STEM according to the present invention, in the third embodiment, an ADF-STEM using a CCD (Charge Coupled Device) as a detector will be described.

  As an ADF-STEM according to the third embodiment, FIG. 8 shows a CCD 9 as a detector. In the CCD 9 shown in FIG. 8, an area indicated by hatching indicates an annular area corresponding to a conventional ADF-STEM detector.

  An image detected by each CCD element 10 by the ADF-STEM is stored in the PC, and a selected region of an arbitrary shape of the image is integrated to form a pseudo STEM image.

  Since the image data is stored in the PC, it can be analyzed after the measurement according to the analysis purpose of the measurer. Also, the image integration shape can be arbitrarily changed, and various analyzes are possible, which is highly convenient.

  Since the CCD 9 is used as the detector, the contrast of only the distortion distribution can be obtained by selecting the area of the CCD 9 corresponding to the LAADF-STEM or HAADF-STEM detector when detecting the ADF-STEM image. it can. Further, the distortion component of the crystal, which varies depending on the orientation, can be detected by decomposing the directionality dependency of the strain by selecting the region of the CCD 9 having a desired orientation.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  For example, as shown in FIG. 9, the detector 6 can be applied as a detector having the features of the first and second embodiments by dividing the detector 6 into concentric circles and further dividing the detector 6 into radial shapes. .

  It is also possible to obtain a three-dimensional image by reconstructing electron tomography by acquiring a continuous tilt image of only the distortion component by any one of the first to third embodiments. In this case, a three-dimensional image such as a distortion component or a crystal defect caused by the distortion can be acquired with high accuracy without causing a positional shift even when the distortion component is extracted.

  The present invention is widely used for scanning transmission electron microscopes.

1 Electron beam 2 Sample 3 Scattered electrons 4 Detector 5 PC
6 detector 7 LAADF-STEM detector 8 HAADF-STEM detector 9 CCD
10 CCD elements 21 ADF-STEM
DESCRIPTION OF SYMBOLS 22 Electron gun 23 Condenser lens 24 Scan coil 25 Objective lens 26 Contrast stop 27 Spectrometer 28 Spectral spectrum detector 29 Energy dispersive X-ray analyzer A Detector A 'Detector B Detector B' Detector X Detection angle

Claims (1)

Irradiate the sample with a focused electron beam,
Scanning the electron beam;
Detecting electrons scattered by being irradiated on the sample with a detector below the sample,
In a scanning transmission electron microscope that forms a detected image and monitors it on a PC,
A scanning transmission electron microscope characterized in that a detection surface of the detector is divided into a plurality of parts.

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