JP2004079343A - Magnetic field type energy filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easily manufacturable energy filter of S-type. <P>SOLUTION: The energy filter has the first to fourth magnetic field regions F1-F4 in such an arrangement that the distribution of the magnetic field and the locus of an electron beam are counter-symmetrical about the middle point M between the second F2 and third magnetic field regions F3, wherein the first M1 and third magnetic poles M3 to produce the first F1 and third magnetic field regions F3 have a common ampere turn C1 while the second M2 and fourth magnetic poles M4 to produce the second F2 and fourth magnetic field regions F4 have a common ampere turn C2. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic field type energy filter having a plurality of magnetic field regions and transmitting an electron beam having a predetermined energy.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electron beam energy loss spectrometer (EELS) that connects to an electron microscope and performs energy analysis of a minute portion has been used. At present, the energy resolution in EELS is determined by the energy width of the electron beam. When a field emission electron gun (FEG) is used, the energy width of the electron beam is about 0.3 to 0.7 eV. Therefore, when it is desired to obtain higher energy resolution, a monochromator for narrowing the energy width is used.
[0003]
Conventionally, many monochromators use a Wien filter. Recently, an electrostatic omega filter has been proposed. In the old days, these monochromators were inserted into a high voltage stage to reduce the energy of the electron beam in order to increase the energy dispersion. For example, an acceleration voltage of 60 kV has been used after being decelerated to about 100 V to 20 V. However, it is possible to use such a large reduction ratio at an acceleration voltage of 100 kV or less, but in an apparatus used at an acceleration voltage that requires multi-stage acceleration of 200 kV or more, it is inevitable that the apparatus be enlarged. It has the disadvantage of reduced practicality and has never been used.
[0004]
Therefore, it has been proposed to install a monochromator before the electron is accelerated. In this technique, a monochromator is set immediately after an electron gun, and electrons transmitted through the monochromator are accelerated.
[0005]
In any case, the monochromator must be installed under high voltage, and therefore, the current and voltage supplied to the monochromator and their control circuits must be installed under high voltage. Can be expensive and huge. If the energy dispersion of the energy filter used in the monochromator is sufficiently large, it can be used above ground potential, and the overall structure of the monochromator is simplified. A mandolin filter is known as a filter having a large energy dispersion. The mandolin filter has an energy dispersion of 6 μm / eV at 200 kV, and is at a level usable as a monochromator for the time being. For example, an electrostatic omega filter can be installed as a monochromator in an electron gun, and a mandolin filter can be used as an energy analyzer.
[0006]
Such a mandolin filter or an omega filter is called an in-column type energy filter because the optical axis of the incident electron beam and the optical axis of the emitted electron beam are in a straight line and are inserted in the middle of the lens barrel.
[0007]
Similarly, as an in-column energy filter, there is an S-type energy filter that deflects an electron beam into an S-shaped orbit by a magnetic field region. The S-type energy filter has an energy dispersion of 6 to 10 μm / eV at 300 kV. This is about twice the energy dispersion of the mandolin filter.
[0008]
FIG. 4 is a diagram illustrating an S-type energy filter.
[0009]
The S-type energy filter has first to fourth magnetic field regions F1 to F4 generated by magnetic poles (not shown). The first to fourth magnetic field regions F1 to F4 are distributed antisymmetrically with respect to an intermediate point M between the second magnetic field region F2 and the third magnetic field region F3. The trajectory of the electron beam is also antisymmetric with respect to the intermediate point M.
[0010]
As an example in the case of using at an acceleration voltage of 300 kV, a yoke for supplying magnetic flux to the magnetic poles for generating the first and fourth magnetic field regions F1 and F4 uses an ampere turn of 385 AT, although the polarity is reversed, respectively. . The yoke that supplies magnetic flux to the magnetic poles that generate the second and third magnetic field regions F2 and F3 uses an ampere-turn of 134 AT each having the opposite polarity. The gaps between the magnetic poles were all 10 mm. With this configuration, an energy dispersion of 10 μm / eV can be obtained at 300 kV. Such a large energy dispersion is also derived from the fact that the radii of the second and third magnetic fields F2 and F3 are larger than the radii of the first and fourth magnetic fields F1 and F4.
[0011]
In the S-type energy filter, the first to fourth magnetic poles for generating the first to fourth magnetic field regions F1 to F4 are arranged on both sides with respect to the optical axis of the electron beam. Are 180 degrees rotationally symmetric. Therefore, compared to a conventional energy filter such as an omega filter having a magnetic pole on only one side of the optical axis, the electron beam can be formed without increasing the distance between the entrance (incident window) and the exit (exit window). Path can be lengthened.
[0012]
In the S-type energy filter, the deflection angle of the electron beam is approximately -110 degrees in the first magnetic field region F1, approximately 250 degrees in the second magnetic field region F2, and approximately -250 degrees in the third magnetic field region F3. , In the fourth magnetic field region F4, the total deflection angle is approximately 720 degrees. Since the total deflection angle of the electron beam in the Omega filter is, for example, 500 degrees, the total deflection angle reaches 1.4 times as compared with this.
[0013]
Further, in the S-type energy filter, the incident optical axis and the output optical axis can be shifted without breaking important symmetry in the energy filter. That is, the input optical axis and the output optical axis can be separated by a predetermined distance. By separating the input optical axis and the output optical axis in this manner, there is an advantage that the degree of freedom in designing the electron microscope is increased.
[0014]
[Problems to be solved by the invention]
By the way, conventionally, it was difficult to actually manufacture an S-type energy filter. In the S-type energy filter, it is difficult to manufacture a configuration such as a yoke and an ampere-turn that realizes the first to fourth magnetic field regions F1 to F4. That is, since the first to fourth magnetic field regions F1 to F4 are close to each other, a space necessary for winding an ampere turn is secured for each yoke that supplies magnetic flux to the magnetic poles that generate the magnetic field regions F1 to F4. It was difficult. Further, since the first to fourth magnetic fields F1 to F4 are alternately opposite in polarity, a yoke that supplies a magnetic flux to the first and fourth magnetic fields F1 and F4 or the second and third magnetic fields F2 and F3. Could not be put together.
[0015]
The present invention has been proposed in view of the above situation, and has as its object to provide an S-type energy filter that is easy to manufacture.
[0016]
[Means for Solving the Problems]
In order to solve the above-described problem, a magnetic field type energy filter according to the present invention has an even numbered magnetic field region of 4 or more, and a magnetic field distribution is antisymmetric with respect to a predetermined point. A common ampere turn is used for magnetic poles of the same polarity among the magnetic poles that generate the region.
[0017]
Preferably, a common ampere-turn is wound around the magnetic poles of the same polarity or the yoke supplying magnetic flux to these magnetic poles.
[0018]
Preferably, the ampere-turn is the product of the number of turns of the coil and the current flowing through the coil.
[0019]
Preferably, each of the magnetic poles has a gap corresponding to the strength of the magnetic field to be generated, that is, a gap.
[0020]
Preferably, the magnetic field region is created in the gap and the trajectory of the electron beam is therein.
[0021]
Preferably, the first and third magnetic field regions have first to fourth magnetic field regions, and the distribution of the magnetic field is antisymmetric with respect to the midpoint between the second and third magnetic field regions. A common ampere turn is used for each of the first and third magnetic poles that generate a region, respectively, and the second and fourth magnetic poles that generate the second and fourth magnetic field regions, respectively.
[0022]
Preferably, a common ampere turn is wound around the first and third magnetic poles, the second and fourth magnetic poles, or the yoke that supplies magnetic flux to these magnetic poles.
[0023]
Preferably, the first and third magnetic poles and the second and fourth magnetic poles have different magnetic pole gaps.
[0024]
Preferably, a magnetic pole for deflecting the electron beam is provided on both left and right sides with respect to the optical axis of the electron beam.
[0025]
Preferably, the sum of the absolute values of the deflection angles of the electron beam is around 720 degrees.
[0026]
Preferably, there are four positions where the tangent of the trajectory of the electron beam is parallel to the incident beam or the output optical axis.
[0027]
Preferably, there are four positions where the tangent of the trajectory of the electron beam is orthogonal to the incident beam or the exit optical axis.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a magnetic field type energy filter according to the present invention will be described in detail with reference to the drawings.
[0029]
The magnetic field type energy filter of the present embodiment has first to fourth magnetic field regions, and the magnetic field region and the trajectory of the electron beam are antisymmetric with respect to the midpoint between the second and third magnetic field regions. It is a type filter.
[0030]
Further, the S-type energy filter of the present embodiment has a configuration in which the optical axis L1 of the incident electron beam and the optical axis L2 of the emitted electron beam are shifted. That is, these optical axes L1 and L2 are separated by a predetermined distance.
[0031]
FIG. 1 is a sectional view showing the configuration of the magnetic pole of the S-type energy filter according to the present embodiment.
[0032]
S-type energy filter includes a pole M1 for generating a first magnetic field region F1, a pole _M2 1 -M2 ₃ for generating a second magnetic field region F2, pole _M3 1 for generating a third magnetic field region F3, M3 and _2, M3 _3, has a magnetic pole M4 to generate a fourth magnetic field region.
[0033]
Electron beam incident on S-type energy filter along the optical axis L1 is deflected -110 degrees substantially by the first magnetic field region F1 to generate the magnetic poles M1, a further generation of the magnetic pole _{M2 1,} M2 2, M2 ₃ Deflected approximately 250 degrees by the second magnetic field region F2. Electron beam passing through the middle point M is deflected substantially -250 degrees by the magnetic poles _{M3 1,} M3 2, M3 ₃ third magnetic field region F3 to generate the further the fourth magnetic field region F4 generated by the magnetic poles M4 110 And is emitted along the optical axis L2.
[0034]
FIG. 2 is a cross-sectional view showing the configuration of the yoke for supplying magnetic flux to the magnetic poles of the S-type energy filter according to the present embodiment and the ampere-turn wound on the yoke.
[0035]
The S-type energy filter according to the present embodiment includes a first yoke Y1 that supplies a magnetic flux to a magnetic pole M1 that generates a first magnetic field region F1, and magnetic poles M2 ₁ , M2 ₂ , that generate a second magnetic field region F2. a second yoke Y2 supplying magnetic flux to the M2 _3, the third yoke Y3 supplying magnetic flux to the magnetic pole _{M3 1,} M3 2, M3 ₃ for generating a third magnetic field region, the fourth magnetic field region F4 And a fourth yoke Y4 for supplying a magnetic flux to the magnetic pole M4 to be generated.
[0036]
The S-type energy filter of the present embodiment has an ampere-turn C1 commonly wound around the first yoke Y1 and the third yoke, and an ampere turn C1 commonly wound around the second yoke Y4 and the fourth yoke Y4. Ampere turn C2.
[0037]
As described above, in the present embodiment, the first and third yokes Y1 and Y3, and the second and fourth yokes Y2 and Y4, which are yokes of the same polarity, respectively wind the ampere turns C1 and C2 in common. This simplifies the configuration.
[0038]
As a result, the space for winding the ampere turns is saved as compared with the case where the ampere turns are wound around the yokes Y1 to Y4. Therefore, according to the present embodiment, the space for winding the ampere-turn can be provided with a margin, thereby facilitating the manufacture.
[0039]
FIG. 3 is a cross-sectional view illustrating the gap between the magnetic poles in the S-type filter according to the present embodiment. This cross-sectional view is obtained by vertically cutting along the cutting line L in the arrangement of the magnetic poles shown in FIG.
[0040]
The figure poles M1 to generate a first magnetic field region F1, pole F2 ₁ for generating a second magnetic field region F2, pole _M3 1 for generating a third magnetic field region F3, M3 ₂ of part respectively shown Have been. Actually, in order to prevent interference between the magnetic poles, the magnetic field regions F1 to F3 are shielded by shields (not shown).
[0041]
Here, a gap d1 = 6 mm poles M1 for generating a first magnetic field region F1, and the third gap d3 = 14 mm pole M3 ₂ for generating a magnetic field region F3, are different. The distance between the magnetic poles was measured at the position where the electron beam passes.
[0042]
Thus, in this embodiment, the magnetic pole M1 and M3 ₂ is supplied to magnetic flux from the first and third yokes Y1, Y3 wound with ampere turns in common, by setting the gap between the magnetic poles properly Thus, the strengths of the first and third magnetic field regions F1 and F3 are respectively set to desired strengths. The same applies to the second and fourth magnetic field regions F2 and F4 to which the magnetic flux is supplied by the second and fourth yokes Y2 and Y4 around which the ampere turn C2 is wound in common.
[0043]
The gap between the magnetic poles is set to be smaller, for example, as the strength of the desired magnetic field region increases. However, the strength of the magnetic field region depends not only on the size of the gap but also on the shape of the magnetic pole.
[0044]
It should be noted that the present invention is not limited to the above-described embodiment, and can be realized in various forms without departing from the scope of the present invention. For example, in the above-described embodiment, the S-type energy filter having the first to fourth four magnetic field regions has been described. However, the present invention is not limited to this. Can be applied to an S-type energy filter having an even number of magnetic field regions.
[0045]
【The invention's effect】
As described above, according to the present invention, an S-type energy filter that is easy to manufacture can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing an arrangement of magnetic poles of an S-type energy filter.
FIG. 2 is a diagram showing an arrangement of a yoke and a coil of an S-type energy filter.
FIG. 3 is a diagram illustrating a gap between magnetic poles.
FIG. 4 is a block diagram illustrating a schematic configuration of an S-type filter.
[Explanation of symbols]
F1~F4 first to fourth magnetic field region L1 electron beam incident optical axis L2 electron beam emission optical axis M midpoints _{M1, M2 1 ~M2 3, M3} 1 ~M3 3, M4 pole Y1~Y4 first to The fourth yoke

Claims (4)

In a magnetic field type energy filter having four or more even magnetic field regions, and the distribution of the magnetic field is antisymmetric with respect to a predetermined point,
A magnetic field type energy filter characterized in that a common ampere turn is used for magnetic poles of the same polarity among magnetic poles generating each magnetic field region. 2. The magnetic field type energy filter according to claim 1, wherein each of the magnetic poles has a gap corresponding to a strength of a generated magnetic field. A magnetic field type energy filter having first to fourth magnetic field regions, wherein the magnetic field distribution is antisymmetric with respect to the midpoint between the second and third magnetic field regions.
The first and third magnetic poles that generate the first and third magnetic field regions, and the second and fourth magnetic poles that generate the second and fourth magnetic field regions, respectively, have a common ampere turn. 2. The magnetic field type energy filter according to claim 1, wherein: 4. The magnetic field type energy filter according to claim 3, wherein the first and third magnetic poles and the second and fourth magnetic poles have different magnetic pole gaps.

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