JP3496722B2 - electronic microscope - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope and, more particularly, to prevent damage of a sample by preventing negative ions emitted from an electron source together with an electron beam from reaching a sample when an accelerating voltage is increased. The electron microscope.

[0002]

2. Description of the Related Art In an electron microscope having an extremely high acceleration voltage (for example, 1 MV or more), lanthanum hexaboride having a large electron flow is often used as a cathode material. However, when lanthanum hexaboride is used as the cathode material, there is a problem that the sample is damaged because the high-density negative ions generated in the cathode portion are accelerated together with the electron beam and are irradiated to the sample.

In order to solve such problems, various attempts have been made to trap the negative ions by the electrostatic lens action in order to avoid irradiation of the negative ions reaching the sample.

For example, in the abstract of the spring meeting of the Japan Institute of Metals (1992.4), entitled "Gun-Damage-Free" Transmission Electron Microscope Prototype and Test ", a method of sliding an electron source or a three-stage A deflector is used to temporarily deflect only the electron beam out of the optical axis by using the mass difference between the electron beam and the negative ion, and only the negative ion is trapped on the optical axis. A method of returning the sample to the shaft and irradiating the sample has been reported.

[0005]

In the above structure, the deflected electron beam must be returned to the original optical axis in order to trap the negative ions, but it is extremely difficult to adjust the electron beam, and the optical axis is therefore difficult to adjust. There was a problem that astigmatism was generated due to the shift.

Further, in the above-mentioned structure, since the deflector has a three-stage structure, there is a problem that the device becomes complicated and large-sized.

The object of the present invention is to solve the above-mentioned problems of the prior art, to reliably trap negative ions to prevent sample damage, and to perform axis alignment easily and reliably.
It is to provide an electron microscope having a simple configuration.

[0008]

In order to achieve the above object, the present invention provides an electron microscope which obtains an observation image by irradiating a sample with an electron beam emitted from an electron source and accelerated and converged. The electron source and the acceleration system arranged on the first optical axis, the lens system and the sample arranged on the second optical axis parallel to the first optical axis, and the electron beam on the first optical axis. It is characterized in that it is provided with a deflecting means for deflecting up to the second optical axis.

[0009]

According to the above-mentioned structure, the electron beam emitted from the electron source on the first optical axis is deflected on the second optical axis by the deflecting means and is arranged on the second optical axis. The sample is irradiated. On the other hand, the negative ions emitted from the electron source on the first optical axis go straight without being deflected by the deflecting means and remain on the first optical axis, so that the electron beam and the negative ions are completely separated. The negative ions are not irradiated on the sample.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing the configuration of an ultrahigh voltage transmission electron microscope which is an embodiment of the present invention.

In FIG. 1, an electron source 1, an accelerating tube 2, an upper deflector 3 and a Faraday cup 9 are coaxially arranged on a first optical axis Y1. Also, the second optical axis Y
2, a lower deflector 4, a converging lens 12, a sample 13,
The objective lens 14, the intermediate lens 15, the projection lens 16, and the transmission image fluorescent plate 17 are coaxially arranged. A widening device 10 and an ammeter 11 are connected to the Faraday cup 9.

Below the lower deflector 4, the respective optical axes Y1 and Y are provided.
The transmissive fluorescent plate 5 and the mirror 6 are arranged so as to straddle the two. As shown in FIG. 3, optical axis marks 24 and 25 are respectively written at the intersections with the first optical axis Y1 and the second optical axis Y2 on the transmissive fluorescent screen 5. The image formed on the fluorescent plate 5 is transmitted to the TV via the mirror 6.
The image is taken by the camera 7 and displayed on the CRT 8.

Since the fluorescent plate 5 and the mirror 6 are arranged on the axis of the electron beam, it is necessary to be able to displace them outside the optical axis after the adjustment of the deflectors 3 and 4 for optical axis alignment is completed. It is desirable to have a mechanism that can be put in and taken out under vacuum in a direction orthogonal to the optical axis.

In the transmission electron microscope having such a structure, the negative ions 19 and the electron beam 20 emitted from the electron source 1 are both accelerated by the accelerating tube 2. Here, when the deflectors 3 and 4 are not energized, the negative ions 19 and the electron beam 20 go straight and reach the Faraday cup 9, so the negative ion 19 and the electron beam 2 are detected by the ammeter 11.
A current value of 0 can be detected.

On the other hand, when the deflectors 3 and 4 are energized,
Negative ions 19 and electron beam 20 emitted from the accelerating tube 2
Enters the deflection magnetic field generated by the upper deflector 3, but the negative ions 19 have a larger mass than the electron beam 20, so they are not deflected by the deflector magnetic field for the electron beam, and go straight on as they are and the Faraday cup 9 To reach. At this time, ammeter 1
In 1, the current value of only the negative ions 19 can be detected.

On the other hand, the electron beam 2 deflected by the upper deflector 3
0 is deflected by the lower deflector 4 in the direction opposite to the deflection direction of the upper deflector 3 by an equivalent amount, and is aligned with the optical axis Y2 of the electron optical lens system parallel to the optical axis Y1.

Due to the two-stage deflection operation, the electron beam 20 incident on the converging lens 12 does not contain the negative ions 19.

The electron beam 20 converged by the converging lens 12 is applied to the sample 13, and the electron beam transmitted through the sample 13 is subjected to the lens action by the objective lens 14, the intermediate lens 15 and the projection lens 16 and is then projected onto the fluorescent plate 17. Connect the transmission images.

By the way, in the above-mentioned two-axis electron microscope, the electron beam 20 deflected to the outside of the first optical axis Y1 by the upper deflector 3 is accurately aligned with the second optical axis Y2 by the lower deflector 4. Need to match.

Therefore, in this embodiment, as follows,
The optical axis can be easily adjusted while observing the TV image on the CRT 8.

The axis alignment method according to this embodiment will be described below.

Whether or not the electron source 1 and the accelerating tube 2 are accurately arranged on the first optical axis Y1 depends on whether or not the electrons on the transmissive fluorescent plate 5 when the deflectors 3 and 4 are not energized. It can be determined whether or not the line spot position matches the optical axis mark 24.

Whether or not the electron beam 20 deflected by the deflectors 3 and 4 is located on the second optical axis depends on whether the deflector 3 or 4 is energized. It can be determined whether or not the electron beam spot position above coincides with the optical axis mark 25.

When aligning the optical axes, the deflectors 3, 4 are
By displaying the TV camera image in synchronism with the ON / OFF cycle of, the beams of both axes can be observed simultaneously on the CRT 8 in a stationary state.

FIG. 2 is a block diagram of a system for displaying a TV camera image in synchronism with the switching periods of the deflectors 3 and 4, and the same symbols as those used above represent the same or equivalent portions.

In the figure, the deflector control device 23 controls the supply current to the deflectors 3 and 4 so that the deflecting amounts by the deflectors 3 and 4 are in the opposite directions and are equal to each other. The control CPU 22 controls the deflectors 3, 4 by the deflector controller 23.
The ON / OFF timing of the deflector control device 23 is controlled based on the control signal from the TV camera controller 21 so that the ON / OFF cycle of 1 is synchronized with the one frame cycle of the TV.

According to this structure, the beams on the first and second optical axes can be simultaneously observed in a stationary state by the afterimage effect, so that the optical axes can be aligned accurately and easily.

According to the present embodiment, the electron beam and the negative ions emitted from the electron source are completely separated, and the sample is irradiated with only the electron beam, so that observation without sample damage is possible. Become.

Further, in this embodiment, since the deflector has a two-stage structure, the structure is simplified as compared with the conventional three-stage structure.
It is possible to prevent the device from becoming large and complicated.

Further, in this embodiment, the respective optical axes Y1 and Y2 are
Since the transmissive fluorescent plate is arranged so as to straddle the optical axis and optical axis marks are provided at the intersections with the optical axes Y1 and Y2 on the transmissive fluorescent plate, the optical axis alignment can be performed easily and surely. Become.

Although the present invention is applied to the transmission electron microscope (TEM) in the above embodiment, the present invention is not limited to this, and the scanning electron microscope (SEM) is used.
It can also be applied to a scanning transmission electron microscope (STEM) and the like.

[0032]

As described above, according to the present invention, the following effects can be achieved. (1) Of the electron beam and negative ions emitted from the electron source, the electron beam is deflected and irradiates the sample, but the negative ion travels straight without being deflected, so that the negative ion irradiates the sample. Therefore, sample damage due to negative ions is prevented. (2) Since the optical axis of the electron source and the accelerating system and the optical axis of the lens system and the sample are provided separately, the deflector can be configured in two stages, and the device can be prevented from becoming large and complicated. (3) Since the optical axis mark indicating each optical axis position is provided on the fluorescent plate orthogonal to the first and second optical axes, the optical axis can be easily aligned simply by aligning the electron beam spot with the optical axis mark. become able to.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a transmission electron microscope that is an embodiment of the present invention.

FIG. 2 is a block diagram of a system for controlling a biasing cycle of a deflector.

FIG. 3 is a plan view of a fluorescent plate having an optical axis mark.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron source, 2 ... Accelerator, 3 ... Upper deflector, 4 ... Lower deflector, 5 ... Transmissive fluorescent plate, 6 ... Mirror, 7 ... TV camera, 8 ... CRT, 9 ... Faraday cup, 10 ... Image width Vessel, 11 ... ammeter, 12 ... converging lens, 13 ... sample, 1
4 ... Objective lens, 15 ... Intermediate lens, 16 ... Projection lens, 17 ... Electron microscope observation fluorescent plate, 19 ... Negative ions, 2
0 ... electron beam

Front Page Continuation (72) Inventor Shuji Kokubun 882 Imo, Katsuta-shi, Ibaraki Hitachi Ltd. Measuring Instruments Division (72) Inventor Katsumi Ura 1-14-9 Takakura-cho, Miyakojima-ku, Osaka-shi, Osaka (56) ) Reference JP-A-63-213247 (JP, A) JP-B-49-22351 (JP, B1) JP-B-47-21347 (JP, B1) JP-B-44-31292 (JP, B1) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01J 37/04 H01J 37/26 H01J 37/22 H01J 37/147

Claims (4)

(57) [Claims] 1. An electron microscope, which is arranged on a first optical axis and emits an electron beam and negative ions, in an electron microscope which obtains an observation image by irradiating a sample with an electron beam emitted from an electron source and accelerated / focused.
An electron source and an acceleration system, a lens system and a sample arranged on a second optical axis parallel to the first optical axis, and an electron beam on the first optical axis deflected to the second optical axis. And a Faraday cup arranged below the deflecting means on the first optical axis. 2. A fluorescent plate mounted so as to be orthogonal to the first and second optical axes, wherein marks are provided at intersections with the first optical axis and intersections with the second optical axis on the fluorescent plate. The electron microscope according to claim 1, wherein: 3. An electron microscope, which is arranged on a first optical axis and emits an electron beam and negative ions, in an electron microscope which obtains an observation image by irradiating a sample with an electron beam emitted from an electron source and accelerated / focused.
An electron source and an accelerating system, a lens system arranged on a second optical axis parallel to the first optical axis and converging an electron beam with which the sample is irradiated, and an electron beam on the first optical axis. A first deflecting means for deflecting the light beam off the optical axis; a second deflecting means for deflecting the electron beam deflected off the optical axis on the second optical axis; and a first deflecting means straddling the first and second optical axes. An electron microscope comprising: a transmissive fluorescent plate arranged; and a current detecting means disposed on the first optical axis below the transmissive fluorescent plate. 4. An electron microscope which obtains an observation image by irradiating a sample with an electron beam emitted from an electron source and accelerated / focused, and is arranged on a first optical axis to emit an electron beam and negative ions.
An electron source and an accelerating system, a lens system and a sample arranged on a second optical axis parallel to the first optical axis, and an electron beam among the electron beam and the negative ions on the first optical axis. An electron microscope, comprising: selective deflecting means for selectively deflecting light onto a second optical axis.