JPH06162977A - Omega filter - Google Patents

Abstract

PURPOSE:To realize image-formation with a simple construction without any astigmatism. CONSTITUTION:A sector 11 consists of a pair of magnetic pole pieces 13 and 13', a yoke 14 for connecting them to each other and coils 15 and 15'. A sector 12 is manufactured in the same manner. The sector 11 and the sector 12 are disposed close to each other and excited so as to have magnetic field distributions of opposite polarities. Assuming that electron rays are incident on the sector 12, the incident electron ray are deflected by the sector 12 at first temporarily enter into the sector 11, are deflected to progress along substantially semi-circle trajectory, again enter into the sector 12 to be deflected and get out of the sector 12 along omega letter-shaped trajectory as a whole. Since the coils for correcting the magnetic field distributions are arranged in a loop shape on both of an optical axis along the optical axis on the mutually opposite surfaces of the magnetic pole pieces, of the sector 11 and 12, the electron rays can form an image without producing astigmatism by allowing appropriate current to flow through the coils.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an omega filter.

[0002]

2. Description of the Related Art An Omega filter is known as one of the energy analyzers for analyzing the energy of a charged particle beam such as an electron beam. An example of the configuration is shown in FIG. FIG. 7 is a diagram showing an example of the configuration of a conventionally proposed omega filter, which includes four sector-type electromagnets (hereinafter, simply referred to as “sectors”) 1, 2, 3, 4. Then, the sectors 1 and 4 are excited so that the magnetic fields have the same polarity, and the sectors 2 and 3 are excited so that the magnetic fields have the opposite polarities to the sectors 1 and 4. For example, when the charged particle beam is an electron beam, each sector 1 to 4 is excited so that the magnetic field B becomes as shown in the figure. As a result, the charged particle beam, for example, the electron beam that has entered the sector 1 travels along the optical axis O having a substantially Ω shape and is emitted from the sector 4. The charged particle beam emitted from the sector 4 is in the same straight line as the charged particle beam incident on the sector 1. In FIG. 7, reference numeral 5 denotes a hexapole lens for correcting the secondary aberration.

As described above, in the Omega filter, the incident charged particle beam and the emitted charged particle beam are on the same straight line, so that they are used when performing energy analysis of an electron beam transmitted through a sample in a transmission electron microscope or the like. Has been.

[0004]

However, in the conventional omega filter, in addition to the problem that the structure is complicated because four sectors are used, the shape of the pole pieces forming each sector is There has been a problem that design and adjustment of mutual arrangement of sectors are very troublesome.

For example, astigmatism-free imaging is required not only in the omega filter but also in an apparatus that handles a charged particle beam. Therefore, as shown in FIG. 7, the end face of the entrance of each sector is not perpendicular to the optical axis O but is inclined by a predetermined angle θ. The same applies to the end face of the exit port of each sector. Then, by setting the inclination angle of this end face with respect to the optical axis O to an optimum value, a converging action is generated in the magnetic field direction with respect to the charged particle beam near the end face of each sector (hereinafter referred to as a fringe). Therefore, astigmatism-free imaging can be realized.
It is not easy to find the optimum tilt angle, and this tilt angle is different between the entrance and the exit and is different for each sector, so the design is very troublesome.

Further, it is generally required that the energy filter has no second-order aberration. In order to prevent the second-order aberration from occurring, the magnetic field distribution in each sector should be uniform, and a uniform field is formed at the time of design. Is very difficult to obtain and the magnetic field distribution will be more or less non-uniform, thus
In reality, it is inevitable that secondary aberration will occur.

Therefore, as one of the methods for correcting the secondary aberration, it is widely practiced that the end surface of each sector is not a straight line as shown in FIG. 7 but a quadric surface. Astigmatism-free imaging can be realized and the secondary aberration can be corrected by making the end surface of each sector a quadric surface, but this design is also not easy. Further, as shown in FIG. 7, the hexapole lens 5 is arranged at an appropriate position to correct the secondary aberration, but the configuration becomes more complicated.

As described above, in the Omega filter, not only the end faces of the four sectors are very important, but also the positional relationship between the sectors and the accuracy of each sector have a very important influence. If there is an error in the arrangement or adjustment of each sector, even a slight error will eventually cause a large aberration.

The present invention solves the above problems and provides an omega filter which can realize astigmatic imaging with a simple structure and can obtain a substantially uniform magnetic field distribution. It is intended.

[0010]

In order to achieve the above object, an omega filter according to a first aspect of the present invention comprises a first sector type electromagnet having a pair of flat plate-shaped magnetic pole pieces arranged to face each other, and a pair of first sector type electromagnets. Plate-shaped magnetic pole pieces are arranged to face each other, and the second sector type electromagnet is excited to have a polarity opposite to that of the first sector type electromagnet, and the first sector type electromagnet and the An omega filter in which a second sector-type electromagnet is arranged in close proximity to the first sector-type electromagnet and the second sector-type electromagnet on opposite surfaces of each pole piece along the optical axis. It is characterized by being given a predetermined inclination.

The Omega filter according to claim 2 is
A first sector-type electromagnet having a pair of flat-plate magnetic pole pieces arranged to face each other, and a pair of flat-plate-shaped magnetic pole pieces arranged to face each other, and having a polarity opposite to that of the first sector-type electromagnet. An omega filter comprising: a second sector-type electromagnet to be excited, wherein the first sector-type electromagnet and the second sector-type electromagnet are arranged in proximity to each other.
Of the sector type electromagnet and the second sector type electromagnet, the coils for correcting the magnetic field distribution are arranged on both sides of the optical axis along the optical axis on the surfaces facing each other. .

[0012]

The operation of the omega filter according to claim 1 is as follows. This omega filter includes a first sector electromagnet and a second sector electromagnet. And
These two sector type electromagnets are arranged close to each other. Further, both of these two sector type electromagnets have a configuration in which a pair of flat plate-shaped magnetic pole pieces are arranged so as to face each other, but they are excited so that the magnetic field distributions have opposite polarities.

Therefore, for example, if a charged particle beam is incident on the first sector-type electromagnet, the incident charged particle beam is first deflected by the first sector-type electromagnet, and then the first sector-type electromagnet is deflected.
Once exiting the sector type electromagnet and entering the second sector type electromagnet, where it is deflected by the second sector type electromagnet and travels in a substantially semi-circular orbit, and then enters the first sector type electromagnet again for deflection. First, following the trajectory of the Ω shape
From the sector type electromagnet, but at this time, since the facing surfaces of the magnetic pole pieces of the first and second sector type electromagnets are provided with a predetermined inclination along the optical axis, the charged particle beam is not emitted. It is imaged without producing points.

Next, the operation of the Omega filter according to claim 2 is as follows. This omega filter includes a first sector electromagnet and a second sector electromagnet. Then, these two sector type electromagnets are arranged close to each other. Further, both of these two sector type electromagnets have a configuration in which a pair of flat plate-shaped magnetic pole pieces are arranged so as to face each other, but they are excited so that the magnetic field distributions have opposite polarities.

Therefore, for example, assuming that a charged particle beam is incident on the first sector type electromagnet, the incident charged particle beam is first deflected by the first sector type electromagnet, and then the first sector type electromagnet is deflected.
Once exiting the sector type electromagnet and entering the second sector type electromagnet, where it is deflected by the second sector type electromagnet and travels in a substantially semi-circular orbit, and then enters the first sector type electromagnet again for deflection. First, following the trajectory of the Ω shape
It is emitted from the sector type electromagnet.

Since coils for correcting the magnetic field distribution are arranged on both sides of the optical axis along the optical axis on the opposing surfaces of the magnetic pole pieces of the first and second sector type electromagnets,
By passing an appropriate current through this coil, a converging action on the charged particle beam can be produced, and astigmatism-free imaging can be realized.

[0017]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view showing the configuration of an embodiment of the omega filter according to the present invention, and FIG. 2 is a plan view thereof.
2 is a sector, 13 and 13 'are pole pieces, 14 is a yoke, 1
Reference numerals 5 and 15 'are coils, 16 and 16' are magnetic pole pieces, 17 is a yoke, 18 and 18 'are coils, and O is an optical axis. In addition,
In FIG. 2, the yokes 14, 17 and the coils 15, 1
5 ', 18, and 18' are omitted. For convenience of explanation, the x-axis and the y-axis orthogonal to each other are taken as shown in the figure, and the axis orthogonal to both the x-axis and the y-axis is the z-axis.

In FIG. 1, a pair of magnetic pole pieces 13 and 13 ′ arranged to face each other are magnetically connected by a yoke 14. The coils 14 and 15 'are provided on the yoke 14.
Is wound. This is sector 11. Sector 1
2 is also the same, and a pair of magnetic pole pieces 16 and 16 'arranged so as to face each other are magnetically connected by a yoke 17, and coils 18 and 18' are wound around the yoke 17. The sector 11 and the sector 12 are arranged close to each other, but it is preferable that the gap between them is 1/2 or less of the gap between the two magnetic pole pieces of each sector 11, 12.

These sectors 11 and 12 are excited so that their magnetic fields have opposite polarities. For example, as shown in the figure, if a downward magnetic field is generated in the sector 11, the sector 12 is made to generate an upward magnetic field. The magnetic fields of the sectors 11 and 12 are of course the same.

Now, assuming that a charged particle beam, for example, an electron beam is incident on the sector 12, the sectors 11, 1
When 2 is excited as described above, the electron beam travels along the optical axis O having a substantially Ω shape as shown in FIG. At this time, it is natural that the electron beam incident on the sector 12 and the electron beam emitted from the sector 12 are on the same straight line.

Here, the pole pieces 16, 16 'of the sector 12 are
The surfaces facing each other have a predetermined inclination along the optical axis O. For example, the cross section at AA 'in FIG. 2, that is, the cross section orthogonal to the optical axis O is as shown in FIG.
The portions along the optical axis O of 6, 16 'are inclined. The same applies to the sector 11.

According to the above construction, by appropriately selecting the degree of this inclination, a converging action in the magnetic field direction (y direction) can be generated with respect to the charged particle beam. Can be realized. Therefore,
It is not necessary to incline the end surface of the entrance of the charged particle beam and the end surface of the exit of the charged particle beam with respect to the optical axis O or form a quadratic surface as in the conventional case. As shown in FIG. The light can be made to enter vertically and can be emitted vertically from the sector 12.

Further, in this omega filter, the area of each pole piece can be made sufficiently large, and therefore the magnetic field distribution can be made to be a substantially uniform field in the vicinity of the optical axis O. Aberrations are of little concern.

Further, since the sector 11 and the sector 12 are arranged close to each other, the magnetic field distribution in the gap between the sector 11 and the sector 12 becomes steep as shown in FIG. 4, and so-called SCOFF (Sharp Cut Off Fringing Field) It can be easily realized. Therefore, it is possible to solve the problem of the fringe field between the sectors, which has been a problem in the conventional omega filter using four sectors, and it is also possible to solve the problem of mutual arrangement between the sectors.
Therefore, the design of the Omega filter can be greatly simplified compared to the conventional one. That is, making the fringe field steep is a very important item in an electron optical system using a plurality of sectors, not limited to the omega filter. By thus making the fringe field steep, each sector is Although it can be considered as independent, not as mutually related, it is very difficult to make the fringe field steep in the past, and therefore in the conventional omega filter, each sector is regarded as independent. It was difficult to handle and it was necessary to design the fringe field in consideration of the positional relationship between each sector, which was very difficult.

Although one embodiment of the present invention has been described above, another embodiment will be described with reference to FIGS. 5 and 6. The same parts as those in the above embodiment are designated by the same reference numerals as those in FIG.

This embodiment differs from the above-mentioned embodiments only in the means for realizing astigmatic imaging. That is, the overall configuration is similar to that shown in FIG. 1, and two sectors are arranged close to each other, and the charged particle beam travels along the optical axis O shown in FIG. But the pole pieces 13, 13 'and 16, 16' of the two sectors 11, 12 are all flat plates, with coils on either side of the optical axis O along the optical axis O of their opposite faces. It is different from the above embodiment in that it is provided.

That is, the pole piece 1 of the pole piece 13 of the sector 11
Loop-shaped coils 21, 22 and 23, 24 are provided on both sides of the optical axis O along the optical axis O on the surface facing 3 '. The same applies to the pole piece 13 '. Similarly, loop-shaped coils 25, 26 and 27, 28 are provided on both sides of the optical axis O along the optical axis O on the surface of the magnetic pole piece 16 of the sector 12 facing the magnetic pole piece 16 '. The same applies to the pole piece 16 '. Then, these coils are excited so that a converging action occurs in the y direction with respect to the charged particle beam. For example, the cross section corresponding to AA 'in FIG. 2 and the magnetic field distribution by the coil are as shown in FIG.
In FIG. 6, reference numerals 25 'and 26' denote coils provided on the magnetic pole piece 16 'so as to face the coils 25 and 26 provided on the magnetic pole piece 16, respectively.

According to the above construction, by adjusting the value of the current supplied to the coils provided on these magnetic pole pieces, it is possible to produce a converging action in the y direction on the charged particle beam. No imaging can be realized. Therefore, as in the above-described embodiment, it is possible to vertically enter the sector 12 and emit vertically from the sector 12. In addition, the fact that the second-order aberration hardly poses a problem and SCOFF can be easily realized, and thus the design is easy, are the same as in the above-described embodiments.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to the above embodiments and various modifications can be made.

[0030]

As is apparent from the above description, according to the present invention, not only astigmatism-free imaging can be realized with a simpler structure, but also the problem of secondary aberration does not occur. Moreover, since SCOFF can be easily realized,
The design burden is greatly eased.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a plan view of the configuration shown in FIG.

3 is a cross-sectional view taken along the line AA ′ in FIG.

FIG. 4 is a diagram showing an example of a magnetic field distribution in a gap between two sector type electromagnets.

FIG. 5 is a diagram showing another embodiment of the present invention.

FIG. 6 is a diagram showing the embodiment shown in FIG.
It is a figure which shows the example of the magnetic field distribution by the cross section and coil corresponding to.

FIG. 7 is a diagram showing a configuration example of a conventional omega filter.

[Explanation of symbols]

11, 12 ... Sector, 13, 13 '... Pole piece, 14 ... Yoke, 15, 15' ... Coil, 16, 16 '... Pole piece,
17 ... Yoke, 18, 18 '... Coil, O ... Optical axis.

Claims (2)

[Claims] 1. A first sector-type electromagnet having a pair of flat plate-shaped magnetic pole pieces arranged to face each other, and a first sector-type electromagnet having a pair of flat-plate magnetic pole pieces arranged to face each other. Is an omega filter comprising a second sector-type electromagnet that is excited to have opposite polarities, and wherein the first sector-type electromagnet and the second sector-type electromagnet are arranged close to each other. An omega filter characterized in that the magnetic pole pieces of one sector type electromagnet and the second sector type electromagnet are provided with facing surfaces facing each other with a predetermined inclination along the optical axis. 2. A first sector type electromagnet having a pair of flat plate-shaped magnetic pole pieces arranged to face each other, and a first sector type electromagnet having a pair of flat plate-shaped magnetic pole pieces arranged to face each other. Is an omega filter comprising a second sector-type electromagnet that is excited to have opposite polarities, and wherein the first sector-type electromagnet and the second sector-type electromagnet are arranged close to each other. Coils for correcting the magnetic field distribution are arranged on both sides of the optical axis along the optical axis on the opposing surfaces of the magnetic pole pieces of the first sector electromagnet and the second sector electromagnet. Omega filter to do.