JP2008066057A - Scanning transmission electron microscope - Google Patents

Abstract

A scanning transmission electron microscope for improving the resolution of an electron diffraction image is provided.
An electron beam passage hole in a sample holder 30 mounted on a sample stage 9 is connected to a hole 31 in a direction along the electron beam optical axis O and a direction perpendicular to the direction of the hole. The scattering angle limiting stop 11 is inserted at the boundary between the hole 31 and the hole 33, and the scintillator 13 is provided in the hole 33 so as to be inclined with respect to the electron beam optical axis O. A photoelectron image multiplier 14 is provided at the outlet.
[Selection] Figure 3

Description

  The present invention relates to a scanning transmission electron microscope provided with a sample holder.

  A scanning transmission electron microscope (commonly known as STEM) is an electron microscope having the characteristics of both a transmission electron microscope and a scanning electron microscope. In particular, a scanning transmission electron microscope using a field emission electron gun as an electron gun can obtain a high-resolution transmission electron image with extremely high contrast even at a relatively low acceleration voltage of 5 kV to several tens of kV. It has been attracting attention and is also used as a means for evaluating and measuring the cross-sectional microstructure of semiconductors, which have recently been remarkably miniaturized and multilayered.

  FIG. 1 shows a schematic diagram of a scanning transmission electron microscope apparatus.

  In the figure, 1 is an electron gun, and 2 is a primary electron beam emitted from the electron gun 1. 3 is a focusing lens for focusing the electron beam 2 from the electron gun 1 on, for example, a thin film sample 5, and 4X and 4Y are scanning the sample 5 in the X and Y directions with the electron beam 2. An X-direction scanning coil and a Y-direction scanning coil.

  Reference numeral 6 denotes a sample holder for fixing the sample 5, and a hole 8 through which an electron 7 transmitted through the sample 5 (referred to as a transmitted electron) passes is formed along the electron beam optical axis O in the center.

  Reference numeral 9 denotes a sample stage on which the sample holder 6 is mounted. A hole 10 is formed in the center along the electron beam optical axis O so as to continue to the hole 8.

  Reference numeral 11 denotes a scattering angle limiting stop for limiting the passage of the transmitted electron 7, and reference numeral 12 denotes a transmitted electron that has passed through the scattering angle limiting stop 11.

  Reference numeral 13 denotes a scintillator that converts the transmitted electron 12 into light, and reference numeral 14 denotes a photomultiplier tube that converts the converted light into an electronic signal. The scintillator 13 constitutes transmitted electron detection means.

  The sample stage 9, the scattering angle limiting aperture 11, the scintillator 13, and the photomultiplier tube 14 are arranged in a sample chamber (not shown) of the scanning transmission electron microscope apparatus main body 100, and the sample holder 6 is the sample stage. 9 is detachable.

  The scanning transmission electron microscope apparatus having the above configuration operates as follows.

  First, the operator mounts the sample holder 6 on which the thin film sample 5 is fixed on the sample stage 9.

  The electron beam 2 emitted from the electron gun 1 is accelerated by an accelerating means (not shown), focused by a focusing lens 3, and scanned on the sample 5 by X and Y direction scanning coils 4X and 4Y.

  By scanning on the sample 5 with such an electron beam 2, the electrons 7 scattered in the sample 5 or transmitted through the sample without scattering are emitted from the lower surface of the sample 5.

  The transmitted electrons 7 have different intensities and scattering angles depending on the state inside the sample 5, the thickness of the sample, and the kind of atoms constituting the sample. The scattering angle of the transmitted electrons also changes depending on the acceleration voltage of the electron beam 2. For example, when the acceleration voltage decreases, the ratio of scattering by the sample increases, and the electron beam light of the transmitted electrons emitted from the lower surface of the sample. The emission angle (scattering angle) from the axis O increases.

  The transmitted electrons 7 emitted from the lower surface of the sample 5 pass through the holes 8 and 10 of the sample holder 6 and the sample stage 9 and then reach the scattering angle limiting stop 11. The aperture is limited in the diameter of the hole formed in the center so that only transmitted electrons having a specific scattering angle can pass therethrough.

  As a scattering angle limiting stop for limiting the passage of such transmitted electrons, in addition to those having a hole in the center as in the structure shown above, and restricting the passage of transmitted electrons by the diameter of the hole, As shown in FIG. 2, there is one (16) in which a shielding plate 17 is arranged at the center to restrict the passage of transmitted electrons.

  In general, when the former diaphragm 11 is used, the electron diffraction image forms a bright field image, and when the latter diaphragm 16 is used, a dark field image is formed.

  The transmitted electrons 12 that have passed through the scattering angle limiting aperture 11 collide with the scintillator 13 and are converted into light, and further converted into an electrical signal by the photomultiplier tube 14. Then, it is amplified by an amplifying means (not shown) and sent to a display means (not shown) via an A / D converter (not shown).

  The display means (not shown) modulates the intensity of the transmitted signal and displays an electron diffraction pattern reflecting the internal structure of the sample 5.

No. 59-150159

  The scanning transmission electron microscope having the above structure has the following problems.

  When the vicinity of the hole including the hole portion of the scattering angle limiting stop 11 is contaminated by the collision of the electron beam, the scattering angle limiting stop 11 needs to be replaced.

  When the scattering angle limiting diaphragm 11 is replaced, the scattering angle limiting diaphragm in use is fixed in the sample chamber. Therefore, the entire apparatus is completely stopped and the replacement operation is performed after the sample chamber is opened. Therefore, a remarkably long working time is generated.

  Further, the electrons transmitted through the sample 5 must pass through the hole 8 of the sample holder 6 and the hole 10 of the sample stage 9 before reaching the scintillator 13. That is, since the distance from the sample 5 to the transmission electron detection means is long, transmission electrons having a large scattering angle (transmission electrons indicated by 18 in FIG. 1) collide with the inner wall of the sample holder 6 or the sample stage 9. . Then, secondary electrons are generated from the colliding portion, and when the secondary electrons enter the transmission electron detection means, the result is noise of an electron beam diffraction image displayed on the display means (not shown). This leads to a decrease in resolution.

The present invention has been made for the purpose of solving such problems, and provides a novel scanning transmission electron microscope.

  The scanning transmission electron microscope of the present invention focuses an electron beam from an electron gun on a sample set in a sample holder mounted on a stage, and scans the sample with the electron beam. The transmitted electrons that pass through the electron beam passage hole in the sample holder and further pass through the aperture are converted into light by a scintillator, and the light is converted into an electric signal by a photoelectric detection means. Based on the electric signal A scanning transmission electron microscope configured to obtain an electron beam diffraction image of the sample is characterized in that the diaphragm and the scintillator are provided in an electron beam passage hole in the sample holder.

  According to the present invention, the scattering angle limiting diaphragm can be easily replaced and can be replaced in a short time.

  Further, according to the present invention, it is possible to easily observe a bright field image and a dark field image only by exchanging the scattering angle limiting diaphragms for the bright field image and the dark field, and the observation efficiency is improved.

  In addition, according to the present invention, since the distance between the sample and the transmitted electron detecting means can be shortened, the transmitted electrons that have passed through the sample can reach the inner wall of the passage before reaching the transmitted electron detecting means. Collisions are reduced, noise on the electron beam diffraction image is reduced, and an electron beam diffraction image with high contrast and high resolution can be obtained.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 3 is a schematic diagram of a scanning transmission electron microscope apparatus shown as an example of the present invention. In the figure, the same reference numerals as those used in FIG. 1 denote the same components.

  The structural difference between the scanning transmission electron microscope of the present invention shown in FIG. 3 and the conventional scanning transmission electron microscope shown in FIG. 1 is mainly in the structure of the sample holder.

  That is, the conventional sample holder has a hole through which an electron beam passes at the center and has a structure in which only the sample is placed. The sample holder 30 of the scanning transmission electron microscope shown in FIG. 3 has the following structure. Have

  That is, the sample holder shown in FIG. 3 mounts the sample 5 and has a first cylinder 32 having an electron beam passage hole 31 along the electron beam optical axis direction (vertical direction) at the center, and the electron beam passage The second cylinder 34 has an electron beam passage hole 33 in a horizontal direction (a direction perpendicular to the electron beam optical axis O) connected to the hole 31.

  And the clearance gap is opened in the boundary part with the 2nd cylinder 34 of the said 1st cylinder 32, and the scattering angle limiting aperture_diaphragm | restriction 11 can be inserted here. Further, when the scattering angle limiting aperture 11 is inserted, screws 35A and 35B are provided around the first cylindrical body 32 for adjusting the level of the scattering angle limiting aperture 11 and fixing it in the gap. ing.

  In the electron beam passage hole 33 of the second cylindrical body 34, the transmitted electrons passing through the first electron beam passage hole 31 are converted into light, and the electron beam passage hole 33 in the horizontal direction is converted into light. A scintillator 13 that is directed toward the exit of the hole is disposed so as to be inclined (for example, 45 degrees) with respect to the electron beam optical axis direction (vertical direction).

  Note that the exit of the electron beam passage hole 33 of the second cylindrical body 34 is mounted on the sample stage 9 so that the incident surface of the photoelectron image multiplier tube 14 is in contact therewith.

  In the scanning transmission electron microscope apparatus having such a configuration, the operator creates a thin film sample to be observed and mounts it on the first cylinder 32 of the sample holder 30. Then, the scattering angle limiting diaphragm 11 is inserted into a gap provided at the boundary between the first cylinder 32 and the second cylinder 34, and the pressing of the screws 35A and 35B is adjusted to adjust the level of the diaphragm. Adjust to fix the aperture in the gap.

  The sample holder 30 to which the sample 5 is attached and the scattering angle limiting aperture 11 is attached is once loaded into the sample exchange chamber 51 attached to the sample chamber 50 and then loaded into the sample chamber 50.

  FIG. 4 shows a schematic diagram of a scanning transmission electron microscope apparatus. In the figure, reference numeral 50 denotes a sample chamber, 55 denotes an electron microscope barrel mounted in the sample chamber 50, 51 denotes a sample exchange chamber, 54 denotes a holder mounting table on which the sample holder 30 is placed, and 52 denotes the sample exchange chamber 51. A first gate valve 53 between the sample exchange chamber 51 and the sample chamber 50, and a sample holder 30 from the atmosphere to the sample exchange chamber 51 in the atmosphere. A first carry-in mechanism (not shown) for carrying a sample holder 30 into the sample chamber 50 from the sample exchange chamber 51 into the sample exchange chamber 51 is not shown. Are provided.

  When the sample holder 30 is put into the sample exchange chamber 51 from the atmosphere, the first gate valve 52 is opened with the second gate valve 53 closed, and the sample holder 30 is placed in the sample exchange chamber by a first carry-in mechanism (not shown). 51 is placed on a holder mounting table 54 provided in 51. Then, the first gate valve 52 is closed and the sample exchange chamber 51 is evacuated until a predetermined pressure is reached, then the second gate valve 53 is opened, and the sample holder 30 is opened by a second carry-in mechanism (not shown). Is mounted on the sample stage 9, and the second gate valve 53 is closed.

  Then, after the inside of the sample chamber 50 reaches a predetermined pressure, the sample 5 is scanned with the electron beam from the electron gun 1 in the electron microscope barrel 55. Through this scanning, the transmitted electrons 7 emitted from the lower surface of the sample 5 pass through the electron beam passage hole 31 of the first cylinder 32 and the hole of the scattering angle limiting aperture 11 constituting the sample holder 30, and the second cylinder 34. It collides with the scintillator 13 provided inside. The transmitted electrons that have collided with the scintillator 13 are converted into light here, and enter the photomultiplier tube 14 disposed opposite to the exit of the hole through the electron beam passage hole 33 formed in the horizontal direction. The incident light is converted into an electrical signal here, amplified by an amplifier (not shown), A / D converted by an A / D converter (not shown), and then displayed on the display means (see FIG. (Not shown). The display means modulates the intensity of the transmitted signal and displays a bright-field electron diffraction image reflected on the internal structure of the sample 5.

  Next, when observing a dark-field electron diffraction image, the second gate valve 53 is opened, and the sample holder 30 is placed on the holder mounting table in the sample exchange chamber 51 by a second carry-in mechanism (not shown). 54, the second gate valve 53 is closed. Then, the first gate valve 52 is opened, and the sample holder 30 is transported to the atmosphere by a first carry-in mechanism (not shown). Then, the scattering angle limiting diaphragm 11 is removed from the sample holder 30, and instead, a dark field scattering angle limiting diaphragm 16 having a shielding plate 17 at the center is mounted as shown in FIG. Then, the sample holder 30 is mounted on the sample holder 9 by performing the same series of operations as described above. In this way, using the same sample holder, it is easy to observe the bright-field and dark-field images of the electron diffraction pattern, and it is also possible to exchange the scattering angle limiting diaphragms for bright and dark fields in a short time. Work becomes possible, and the work can be greatly improved.

  Instead of placing the scintillator 13 in the second cylinder 34 by tilting (for example, 45 degrees) as in the above example, the scintillator 13 is placed horizontally and tilted rearward as shown in FIG. A reflection mirror 36 (for example, 45 degrees) may be disposed so that the light emitted from the scintillator 13 is directed toward the electron beam passage hole 33 and is incident on the photoelectron image multiplier tube 14.

  Further, the magnification of the electron diffraction image may be made variable by making the distance between the sample 5 and the scintillator 13 (that is, the camera length) variable.

  In the above example, the light from the scintillator 13 is guided to the photoelectron image multiplier 14 through the electron beam passage hole 33. However, a light transmission medium (for example, a light guide or an optical fiber) is disposed on the rear surface of the scintillator 13. Then, the light from the scintillator 13 may be guided to the photoelectron image multiplier tube 14.

It is the schematic which showed an example of the conventional scanning transmission electron microscope apparatus. An example of a scattering angle limiting stop for limiting the dark field is shown. 1 shows a schematic example of a sample holder portion of a scanning transmission electron microscope apparatus of the present invention. 1 is a schematic view of a scanning transmission electron microscope apparatus of the present invention. The other schematic example of the sample holder part of the scanning transmission electron microscope apparatus of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron gun 2 ... Primary electron beam 3 ... Condensing lens 4X ... X direction scanning coil 4Y ... Y direction scanning coil 5 ... Sample 6 ... Sample holder 7, 12, 15 ... Transmission electron 8, 10 ... Electron beam passage hole 9 ... Sample stage 11, 16 ... Scattering angle limiting aperture 13 ... Scintillator 14 ... Photomultiplier tube 17 ... Shield plate 30 ... Sample holder 31 ... Electron beam passage hole 32 ... First cylinder 33 ... Electron beam passage hole 34 ... Second cylinder Body 35A, 35B ... Screw 36 ... Reflection mirror 50 ... Sample chamber 51 ... Sample exchange chamber 52 ... First gate valve 53 ... Second gate valve 54 ... Holder mounting table 55 ... Electron microscope column

Claims (7)

  An electron beam from an electron gun is focused on a sample set in a sample holder mounted on a stage, and the sample is scanned with the electron beam, transmitted through the sample, and electrons in the sample holder The transmitted electrons that have passed through the line passing hole and further passed through the aperture are converted into light by a scintillator, the light is converted into an electric signal by a photoelectric detection means, and an electron beam diffraction image of the sample based on the electric signal is obtained. The scanning transmission electron microscope according to claim 1, wherein the diaphragm and the scintillator are provided in an electron beam passage hole in the sample holder.   The electron beam passage hole in the sample holder is composed of a hole in a direction along the electron beam optical axis and a hole in a direction perpendicular to the direction of the hole. 2. A scanning transmission electron microscope according to claim 1, further comprising means.   The scanning transmission electron microscope according to claim 1, wherein the scintillator is provided so as to be inclined with respect to the electron beam optical axis so that the converted light is directed to the photoelectric conversion means.   The scintillator is provided in a direction perpendicular to the electron beam optical axis, and a reflection mirror is provided at the rear thereof so that the converted light travels toward the photoelectric conversion means. Scanning transmission electron microscope.   The scanning transmission electron microscope according to claim 1, wherein a distance between the sample and the scintillator is variable.   2. The scanning transmission electron microscope according to claim 1, wherein a gap is formed in the sample holder so that the diaphragm can be inserted and extracted in a direction perpendicular to the electron beam optical axis.   7. The scanning transmission electron microscope according to claim 6, wherein when the diaphragm is inserted into the gap, pressing means for adjusting the level of the diaphragm is provided on the sample holder.

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