JPH11260304A - Secondary electron detector for charged particle beam apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary electron detector for a charged particle beam apparatus having extremely high secondary electron detection efficiency by making the shape of a collecting electrode optimum. SOLUTION: A collecting electrode 30 is made of a metallic plate, and a large number of apertures 31 are punched in the metallic plate. The apertures 31 are hexagonal in shape and are so arranged as to keep respective sides of the hexagons of the neighboring hexagonal apertures 31 face to face at short width gaps in the metallic plate and as to give the densest filling ratio. When a circle encircling the hexagon or each aperture 31 is defined as R, the width of the metallic plate parting the neighboring apertures 31 as d, the gap between the center of neighboring hexagonal apertures as T, d is necessarily about 0.1 mm if the thickness t of the metallic electrode plate 30 is about 0.1 mm in order to keep the electrode structure. Also, in that case, if R is 0.4 mm, T is necessarily becomes 0.79 mm and transmittance 76.3%. Furthermore, if the R is 1.3 mm, the transmittance reaches 91.7%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary electron detector for a charged particle beam apparatus capable of efficiently detecting secondary electrons obtained from a sample as a result of irradiating the sample with an electron beam or an ion beam.

[0002]

2. Description of the Related Art A scanning electron microscope or a scanning ion microscope (also referred to as a focused ion beam device) focuses an excited particle beam (an electron beam or an ion beam) finely on a sample surface and further focuses the beam two-dimensionally on the sample. Scanning.
Then, secondary electrons generated by irradiating the sample with the beam are detected, and a scanned image of the sample is obtained based on the detection signal.

FIG. 1 shows such a scanning ion microscope. In the figure, reference numeral 1 denotes an ion source also serving as a converging lens,
The ion beam IB generated from the ion source 1 and accelerated is
The light is focused finely by the electrostatic objective lens 2 and is irradiated onto the sample 3 as a spot beam. Sample 3 is XY
It is placed on the moving stage 4.

As the ion source 1, for example, a field emission type liquid gallium (Ga) ion source is used, and a strong electric field is applied to the tip of a thin and sharp emitter 5 to extract Ga ions. Further, the ion source 1 is connected to a control system 6, and a high accelerating voltage and a converging lens voltage are applied to the ion source 1 from the control system 6.

The electrostatic objective lens 2 includes a center electrode and an outer electrode outside the center electrode. A high voltage is applied to the center electrode from a control system 6. The outer electrode is grounded.

A beam limiting aperture (not shown) and an electrostatic deflector 7 are arranged along the optical path of the ion beam IB. The electrostatic deflector 7 is configured to be supplied with a scanning signal from a beam scanning device 8.

By irradiating the sample 3 with the ion beam,
Secondary electrons are generated, and the secondary electrons e are detected by the secondary electron detector 9. The detection signal of the detector 9 is transmitted to the secondary electron detection system 1 including an amplifier and a contrast adjustment circuit.
0, and is supplied to a display device 11 such as a cathode ray tube. The operation of such a configuration will now be described.

In the above configuration, a high voltage of, for example, 30 kV is applied to the ion source 1 from the control system 6, and the ion beam IB emitted from the ion source 1 is accelerated to 30 keV. This ion beam is focused on the surface of the sample 3 by the objective lens 2.

Further, an electrostatic deflector 7 is provided on the optical path of the ion beam, and a scanning signal is supplied to the deflector 7 from a beam scanning device 8. As a result, the ion beam focused on the surface of the sample 3 is scanned in a raster shape,
The irradiation area of the ion beam for processing is controlled,
A scanned image based on the ion beam scanning is obtained.

A scanned image of the ion beam is scanned with the ion beam on the sample surface using the deflector 7, and secondary electrons generated from the sample are detected by the detector 9 based on the scanning. The detection signal of the detector 9 is supplied to the display device 11 via the secondary electron detection system 10. The cathode ray tube 11 is supplied with a scanning signal from the beam scanning device 8, so that a scanned image of the sample 3 by the ion beam is displayed on the cathode ray tube 11.

With the above-described configuration, a thinner beam can be obtained as the beam current is smaller, due to the nature of the charged particle beam optical system. That is, a high-resolution image can be obtained as a result. On the other hand, the amount of the secondary electron signal from the sample decreases as the beam current decreases, and the image quality deteriorates. Therefore, in order to obtain a high-resolution and high-quality image,
It is desired that the detection efficiency of the secondary electron signal is high.

There are several methods for detecting secondary electrons.
FIG. 2 shows a configuration of a secondary electron detector often used. In the figure, reference numeral 15 denotes a scintillator which generates light by incidence of secondary electrons, and a portion around the scintillator 15 includes:
An accelerating electrode 16 for accelerating secondary electrons to collide with the scintillator is arranged. Several kV on the accelerating electrode 16
Is applied.

The scintillator 15 is attached to a light guide 17, and light from the scintillator 15 is guided to the outside of the sample chamber wall 18 through the light guide 17. A photomultiplier 19 is arranged outside the sample chamber wall 18 at the end of the light guide 17, and light passing through the light guide 17 is converted into electrons by the photomultiplier 19, and the electrons are further multiplied. . The output signal of the photomultiplier 19 is used as a secondary electron detection signal output.

A collection electrode 20 is disposed in front of the scintillator 15 in order to efficiently direct secondary electrons from the sample to the scintillator 15. A positive voltage of several tens of volts is applied to the collection electrode 20. As the collection electrode 20, as shown in FIG. 3A, an electrode 23 in which a number of openings 22 are formed in a metal plate 21, or as shown in FIG. The electrode 25 is used.

In such a detector, secondary electrons are efficiently collected by the collecting electrode 20 toward the scintillator 15. The secondary electrons collected by the collection electrode 20 are accelerated by a relatively high voltage applied to the acceleration electrode 16 and collide with the scintillator 15.

The scintillator 15 emits light due to the collision of secondary electrons, and this light emission enters a photomultiplier 19 disposed outside the sample chamber via a light guide 17. The light incident on the photomultiplier 19 is converted into electrons, and the electrons are further multiplied. The multiplied electrons are finally converted into electric signals and output as detectors.

[0017]

Problems to be Solved by the Invention 2 as shown in FIG.
The secondary electron detector is placed at a position that does not interfere with the objective lens 2, the sample 3, and the like, as shown in FIG. The detection efficiency of the secondary electron signal of this detector depends on the shape of the collection electrode 20, the transmittance (opening ratio), the voltage applied to the electrode 20, and the like. The applied voltage is optimized according to the circumstances of the device, but the shape of the collection electrode has a considerable effect on the detection efficiency. FIG.
In (a), it is about 60%, and in (b), it is less. The present invention has been made in view of such a point, and an object thereof is to optimize a shape of a collection electrode and realize a secondary electron detector for a charged particle beam device having extremely high secondary electron detection efficiency. To be.

[0018]

A secondary electron detector for a charged particle beam apparatus according to the first invention is a detector for detecting secondary electrons generated from a sample by irradiating the sample with a charged particle beam. A scintillator that emits light by collision of secondary electrons, a light guide that guides the light of the scintillator, a photomultiplier that converts light from the light guide into electrons and multiplies them, In a secondary electron detector including a collection electrode to which a voltage is applied, a number of regular hexagonal openings are formed in the collection electrode, and each hexagonal opening is adjacent to a side of a regular hexagon. It is characterized in that comrades are arranged in opposing close packing.

According to the first aspect of the present invention, an electrode having a large number of regular hexagonal openings is used as a collection electrode to which a positive voltage is applied, which is arranged in front of the scintillator, and each hexagonal opening is adjacent to each other. Hexagonal sides are arranged in close-packed opposition.

According to a second aspect of the present invention, in the first aspect, the radius of the circle contacting the regular hexagon is R, the width of the electrode plate portion separating the adjacent hexagonal openings is d, and the distance between the centers of the hexagons ( When the period is T, R is set in a range of 0.4 to 1.3 mm, and d and T are d = 0.1 (1 ± 0.1 R) mm T = 2 (Rcos30 ° + d / 2) mm did.

According to a third aspect, in the second aspect, when the thickness of the collecting electrode is t, t is 0.1 (1 ± 0.1 R) mm.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 shows a second embodiment according to the present invention.
The shape of the collection electrode 30 of the secondary electron detector is shown. This collecting electrode is the collecting electrode 20 of the secondary electron detector shown in FIG.
Is used instead of

The collection electrode 30 is formed of a metal plate, and a plurality of openings 31 are formed in the metal plate. The hexagonal opening 31 is a close-packed structure that is arranged to face the side of the hexagonal opening where the sides are adjacent to each other with a short width metal plate therebetween.

Now, in the electrode structure of FIG.
Let R be the radius of a circle contacted by one hexagon, d be the width of the metal plate separating the hexagons, and T be the distance between centers of adjacent hexagonal openings. Now, the thickness t of the metallic electrode plate 30 is set to 0.1 m.
If it is about m, d needs to be about 0.1 mm in order to maintain the electrode structure.

At this time, if R is 0.4 mm, T is 0.79 mm, and the transmittance is 76.3%. FIG.
Is R = 0.4 to 1.3 mm when d = 0.1 mm
The transmittance (aperture ratio...%) When changed is shown.
FIG. 7 shows the relationship between the intervals (periods) T and T / 2 between the centers of the hexagons and the radius R of the circle.

As shown in FIG. 6, the radius R is 1.3 mm.
, The transmittance reaches 91.7%. If R is too large, a large aperture is formed, which is not preferable because the influence of the electric field protrudes. If d is not made large to some extent, the electrode structure cannot be maintained. Conversely, if d is increased, the transmittance is reduced, and the detection efficiency of secondary electrons is reduced.

Based on these considerations, the optimum shape as a collection electrode is to form a large number of regular hexagonal openings in the electrode and arrange the hexagons in a close-packed state.
The size of each hexagon has the following condition. In addition, as a precondition of the following conditions, R is 0.1-1.3 mm.
Range.

D = 0.1 (1 ± 0.1R) mm T = 2 (Rcos30 ° + d / 2) mm t = 0.1 (1 ± 0.1R) mm The collecting electrode under the above conditions 60-90%
The above transmittance is possible, and as a result, the detection efficiency of the secondary electrons can be improved by several tens of% compared with the related art.

[0029]

As described above, in the secondary electron detector for a charged particle beam apparatus according to the first invention, a regular hexagonal-shaped collection electrode disposed in front of the scintillator and to which a positive voltage is applied is used. Since the hexagonal openings are arranged in a close-packed manner in which adjacent regular hexagonal sides are opposed to each other, 60 to 9
High transmittance of secondary electrons of 0% or more can be achieved, and secondary electron detection efficiency can be greatly improved.

According to a second aspect, in the first aspect, the radius of the circle contacting the regular hexagon is R, the width of the electrode plate portion separating adjacent hexagonal openings is d, and the distance between the centers of the hexagons ( When the period is T, R is set in a range of 0.4 to 1.3 mm, and d and T are d = 0.1 (1 ± 0.1 R) mm T = 2 (Rcos30 ° + d / 2) mm Therefore, a high transmittance of 60 to 90% or more of secondary electrons can be obtained in the collection electrode, and the detection efficiency of secondary electrons can be significantly improved.

In the third invention, in the second invention, when the thickness of the collection electrode is t, t is set to t = 0.1 (1 ± 0.1R) mm. High transmittance of secondary electrons of 60 to 90% or more is possible, and the detection efficiency of secondary electrons can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a general scanning ion microscope.

FIG. 2 is a diagram showing a secondary electron detector using a photomultiplier.

FIG. 3 is a diagram showing an example of the shape of a conventionally used collecting electrode.

FIG. 4 is a diagram illustrating an arrangement state of the detector illustrated in FIG. 2;

FIG. 5 is a view showing the shape of a collecting electrode used in the present invention.

FIG. 6 is a graph showing a relationship between a radius R of a circle in contact with a regular hexagon and transmittance.

FIG. 7 is a graph showing a relationship between a radius R of a circle contacting a regular hexagon and an interval T between centers of the hexagon.

[Explanation of symbols]

 Reference Signs List 15 scintillator 17 light guide 19 photomultiplier 20, 30 collection electrode 31 opening

Claims (3)

[Claims] 1. A detector for detecting secondary electrons generated from a sample by irradiating the sample with a charged particle beam, comprising: a scintillator emitting light by collision of the secondary electrons; and a light guide for guiding light of the scintillator. A secondary electron detector including a photomultiplier that converts light from the light guide into electrons and multiplies the electrons, and a collection electrode that is disposed on the front of the scintillator and to which a positive voltage is applied.
The collection electrode is provided with a large number of regular hexagonal openings, and each hexagonal opening is arranged in a close-packed manner in which adjacent regular hexagonal sides face each other. Secondary electron detector for beam device. 2. When the radius of a circle contacted by a regular hexagon is R, the width of an electrode plate portion separating adjacent hexagonal openings is d, and the interval (period) between centers of hexagons is T, R is 0. .4 ~
2. A range of 1.3 mm, wherein d and T are such that d = 0.1 (1 ± 0.1 R) mm and T = 2 (Rcos 30 ° + d / 2) mm. Secondary electron detector for charged particle beam devices. 3. The charged particle beam apparatus according to claim 2, wherein t is 0.1 (1 ± 0.1 R) mm, where t is the thickness of the collection electrode. Secondary electron detector.