JP2947440B2 - Simultaneous measurement of electron energy loss - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simultaneous electron energy loss measuring apparatus, and more particularly, to an orbit separation of an electron beam transmitted through a sample in accordance with its energy, so that the spectrum of each energy can be measured simultaneously and in parallel. The present invention relates to an electronic energy loss simultaneous measurement device as described above.

[0002]

2. Description of the Related Art An electron beam whose energy has been partially lost due to inelastic collision with its atoms and molecules when passing through a sample is deflected by a fan-shaped magnetic field to separate orbits, and is obtained based on the amount of deflection. The method of identifying atoms and molecules from the spectrum is generally based on electron energy loss analysis (EELS: ELECTRON ENERG).
Y LOSS SPECTROMETER).

In the conventional EELS, the intensity of a sector magnetic field is continuously changed (scanned), and an electron beam passing through a slit provided at a subsequent stage is detected by an electron multiplier to obtain a spectrum. However, this method has a problem that the analysis efficiency is low because only electrons in a specific energy band passing through a narrow slit can be detected.

In order to solve such a problem, for example, in US Pat. No. 4,174,479, electrons having different energies are maintained by using a rectangular flat detector (microchannel plate array) while keeping the intensity of a sector magnetic field constant. A so-called electron energy loss simultaneous measurement device (PEELS: PARALLE) that measures the spectrum of a line simultaneously and in parallel.
L-DETECTION EELS) has been proposed.

FIG. 8 schematically shows the structure of the main part of the conventional PEELS. FIG. 8A shows the trajectory of an electron having a specific energy, and FIG. () Is a diagram showing the trajectory of an electron beam orbitally separated according to its own energy by a fan-shaped magnetic field, and (c) is a diagram showing the trajectory of the electron beam when viewed from the electron gun 13 side.

As shown, in the conventional PEELS,
Three magnetic quadrupole lenses Q1, Q2, Q3 are arranged between the sector magnetic field 15 and the flat panel detector 50. Q1 Lens 2
1 is set at a convergence point 31 in the y direction (magnetic field direction of the sector magnetic field) by the sector magnetic field 15 as shown in FIG.
As shown in (a), it functions to focus the electron beam on the flat panel detector 50. Q3 lens 23
As shown in (b), the energy spectrum distributed in the x-direction by the sector magnetic field 15 functions to increase the dispersion distance on the plane detector 50.

On the other hand, the Q2 lens 22 is provided between the Q1 lens 21 and the Q3 lens 23, and the width (y direction) of the energy spectrum is not diffused even when the energy spectrum dispersion distance is expanded by the Q3 lens 23. In order to achieve this, as shown in FIG. 3C, a function is formed to form a convergent point 32 of the electron beam in the y direction at the center position of the Q3 lens 23. That is, as a general characteristic of the Q lens, the magnetic field cancels out near the central axis (z) and has no lens action. Therefore, if the center position of the lens Q3 is made to coincide with the y-directional convergence point 32 of the electron beam, The width of the energy spectrum can be kept constant even if the dispersion distance of the energy spectrum on the plane detector 50 is increased by changing the lens strength of the lens Q3.

As described above, in order to make the dispersion distance variable while keeping the width of the energy spectrum constant, in the conventional PEELS, at least three four magnetic fields are provided between the sector magnetic field 15 and the plane detector 50. Heavy pole lens Q1, Q
2, Q3 needs to be provided. If a lens 24 (Q4) is provided between the Q3 lens 23 and the plane detector 50 as shown by a dotted line in FIG. 9C, the width of the spectrum and the dispersion distance can be controlled independently. Become like

[0009]

The above-mentioned prior art has the following problems. (1) In order to be able to perform partial enlarged projection of the energy spectrum over a wide range, it is necessary to reduce the dispersion distance so that a wide range of spectrum can be measured simultaneously. It is necessary to increase the distance to the magnetic field to reduce the size. In order to increase the distance from the sample to the sector magnetic field, it is necessary to reduce the distance from the sector magnetic field to the flat detector. However, in the above-described prior art, at least three Q lenses are required to include the sector magnetic field 15 and the flat detector 50. Therefore, it was difficult to reduce the size of the system. (2) Since at least three lenses are required, the configuration and control are complicated, and accordingly, there is a problem that the size and cost of the apparatus are increased.

An object of the present invention is to provide an electron energy loss simultaneous measurement apparatus which solves the above-mentioned problems of the prior art and can perform partial enlarged projection of a spectrum over a wide range with a simple configuration. .

[0011]

According to the present invention, there is provided a simultaneous electron energy loss measuring apparatus for forming an energy spectrum by orbit-separating an electron beam transmitted through a sample by a fan-shaped magnetic field. Means for generating a sector magnetic field perpendicular to the electron beam, means for detecting an electron beam orbitally separated by the sector magnetic field, first lens means disposed between the sample and the sector magnetic field, It is characterized in that a second lens means is provided between the magnetic field and the detecting means and located at a convergence point of the electron beam in the direction of the magnetic field of the sector magnetic field.

[0012]

In the above construction, the second lens means plays a role of a zoom which largely changes the energy dispersion, and
Lens means serves to focus the electron beam on the flat panel detector. Since the second lens means is located at the convergence point in the y direction, even if the excitation amount of the second lens means is largely changed, the influence of the field is small and the change in the image width in the y direction is small.

[0013]

FIG. 1 is a diagram showing a schematic configuration of a main part of an electron microscope provided with a simultaneous electron energy loss measuring apparatus according to an embodiment of the present invention. FIG. FIG. 2B is a view of FIG. 1A as viewed from the electron gun 11 side. In the figure, the same reference numerals as those described above denote the same or equivalent parts, and this embodiment is characterized in that magnetic quadrupole lenses 21 (Q1) and 22 (Q2) are arranged before and after the sector magnetic field 15, respectively. There is.

FIG. 2 is an enlarged view of the Q2 lens 22. The Q2 lens 22 includes a lens body 22a and a fine movement mechanism 22b.
Are held together by The fine movement mechanism 22b is fixed around the vacuum vessel 27, and the lens body 22a and the vacuum vessel 27 are not fixed. Therefore, by rotating the feed screw 25, the lens body 22a is moved in the traveling direction of the electron beam. Can be finely moved along.

In such a configuration, the electron beam 1 emitted in a divergent state from the electron gun 11 is focused by the focusing lens 3 and irradiated on the sample 12. The electron beam transmitted through the sample 12 is focused by the objective lens 4, and further focused by the imaging lens 5 to the point light source 13. After a part of the electron beam 1 has its beam spread restricted by the aperture 14,
1 The lens 21 passes through a fan-shaped magnetic field 15 forming a magnetic field space perpendicular to the plane of the drawing, and a Q2 lens 22. In the sector magnetic field 15, the electron beam 1 is orbitally separated according to its energy, reaches the flat detector 50, and forms an energy spectrum. The Q1 lens 21 and the Q2 lens 22 are excited by a power supply 26.

The Q1 lens 21 transmits the electron beam to the flat detector 5
It works to focus on zero and the Q2 lens 22
Expands the energy spectrum to produce a flat detector 50
Functions to project on. The Q2 lens 22 is
It is arranged at the convergence point 31 in the y direction by the lens 21 and the fan-shaped magnetic field 15 obliquely entering and exiting. For this reason, the excitation spectrum of the Q2 lens 22 is greatly changed to reduce the energy spectrum by x.
Even if the image is enlarged in the direction, the influence of the field is small and the change of the image width of the energy spectrum in the y direction can be suppressed to a small value. If it is desired to measure the spectrum of the energy loss over a wide range, the field of the Q2 lens may be weakened to focus only on the Q1 lens.

FIG. 5 shows simulation results of the energy dispersion zoom effect of the conventional PEELS having the configuration shown in FIG. 3 and the PEELS having the configuration shown in FIG. 4 to which the present invention is applied. FIG. The simulation used here used a program "TRIO" for orbit analysis of an ion optical system of a mass spectrometer, which was developed at Matsuo Laboratory of Osaka University.

The horizontal axis QKM in FIG. 5 is a field constant of a Qz lens which plays a role of varying the zoom of dispersion, and corresponds to a Q3 lens in the prior art and a Q2 lens in the present embodiment. The vertical axis represents the velocity dispersion coefficient D, which corresponds to 0.5 times the energy dispersion coefficient. It can be said that the larger the change in this value, the higher the dispersion zoom effect. The focus on the flat panel detector 50 is shared by a Q1 lens (hereinafter, sometimes referred to as a Qf lens), and its value is determined by the zoom Q
z Proportional to lens value.

The constant QKM of the field of the Q lens is the above-mentioned “TRI”
O ”is represented by the following equation. Here, e is the charge of the electron, B is the magnetic flux density of the quadrupole lens, QRM is the radius of the inscribed circle between the quadrupoles, m is the mass of the electron, and U is the acceleration voltage of the electron.

QKM = ± (eB / QRM) ^1/2 × (2 mU) ^1/4 (1) In the case of the present invention, the velocity dispersion coefficient D changes from 0.22 to 245, and the zoom magnification of 1114 times Is obtained. On the other hand, in the case of the prior art in the same scale arrangement, the speed dispersion coefficient D changes from 3.0 to 130, and it can be seen that the zoom magnification is only 43 times.

FIG. 6 shows the field constant Q of the zoom Qz lens.
FIG. 5 is a diagram showing a relationship between KM and a y-direction aberration coefficient B. In the present embodiment, the range (-1) which is almost the same as that of the prior art is used.
<B <1). However, the y-direction aberration coefficient B
Since the position of the Q2 lens has a delicate effect to keep the distance within this range, as described with reference to FIG. Is desirable.

FIG. 7 is a diagram showing the correlation between the QKM of the zoom lens Qz and the focusing lens Qf according to the present embodiment and the prior art. , A proportional relationship is established, and it is understood that the strength of the spot can be reduced by about 1/4 as compared with the prior art. Therefore, if one of the zoom lens Qz and the focus lens Qf is manually controlled by storing the correlation in an appropriate storage means such as a memory,
In response to this, the other excitation amount can be automatically controlled.

[0023]

As described above, according to the present invention, the following effects are achieved. (1) Since the number of Q lenses for forming the energy spectrum can be reduced to two, the configuration and control are simplified. In addition, since the distance between the sector magnetic field and the flat detector can be shortened, the distance from the sample to the sector magnetic field can be increased by that much to make it a reduced system, and the partial enlarged projection of the spectrum can be performed over a wide range. Can be performed over (2) Since the maximum value of the variance is improved about twice and the minimum value is reduced to 7%, the zoom magnification can be improved 26 times as compared with the related art. (3) Even though the zoom magnification is greatly improved, the change in the image width of the spectrum can be suppressed to the same level as before, so that the detection sensitivity does not decrease.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical system of an electron energy loss simultaneous measurement apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a magnetic quadrupole lens provided with a fine movement mechanism.

FIG. 3 is a diagram showing a specific configuration of an optical system of a conventional simultaneous measurement system for electron energy loss.

FIG. 4 is a diagram showing a specific configuration of an optical system of the simultaneous electron energy loss measuring device to which the present invention is applied.

FIG. 5 is a diagram showing a simulation result of a distributed zoom effect.

FIG. 6 is a diagram comparing changes in the y-direction aberration coefficient B between the present invention and the prior art.

FIG. 7 is a diagram showing a correlation between excitation amounts of a zoom Qz lens and a focusing Qf lens.

FIG. 8 is a diagram for explaining a basic configuration of a conventional technique.

[Explanation of symbols]

Reference Signs List 11: electron gun, 12: sample, 14: stop, 15: oblique input / output sector magnetic field, 21: magnetic field quadrupole (Q1) lens, 22
... Q2 lens, 23 ... Q3 lens, 24 ... Q4 lens,
25: Lead screw, 26: Q lens control power supply, 27: Vacuum container, 31, 32: Convergent point in y direction, 50: Flat detector

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-229749 (JP, A) JP-A-56-91365 (JP, A) JP-A-60-189857 (JP, A) JP-A 55-91 72900 (JP, A) JP-A-3-250545 (JP, A) JP-A-6-310063 (JP, A) JP-A-62-113350 (JP, A) Patent 2872001 (JP, B2) F. Egerton, "The use of electrons between a TEM specimen and an electronon spectrometer", Optik, 1980, Vol. 56, No. 4, p. 363-376 (58) Field surveyed (Int.Cl. ⁶ , DB name) H01J 49/00-49/48 H01J 37/00-37/295

Claims (4)

(57) [Claims] An electron energy loss simultaneous measurement apparatus for forming an energy spectrum by orbit-separating an electron beam transmitted through a sample with a sector magnetic field to generate a sector magnetic field perpendicular to the electron beam transmitted through the sample. Means for detecting an electron beam orbitally separated by the sector magnetic field; first lens means arranged between the sample and the sector magnetic field; and means for detecting a sector magnetic field between the sector magnetic field and the detection means. A second lens means arranged at a convergence point of the electron beam in the direction of the magnetic field. 2. The apparatus according to claim 1, wherein said first lens means focuses an electron beam on said detecting means, and said second lens means enlarges a dispersion distance of an energy spectrum on said detecting means. 2. A simultaneous electron energy loss measuring device according to claim 1. 3. The apparatus according to claim 1, wherein the second lens means is finely movable along a traveling direction of the electron beam.
Or the simultaneous electron energy loss measurement device according to 2. 4. The method according to claim 1, wherein the magnetic flux density of one of the first and second lens means is automatically changed as a function of the other magnetic flux density. Simultaneous measurement of electron energy loss.