JPS63231852A - Charged particle beam application device - Google Patents

Abstract

PURPOSE:To select the accelerating voltage without adjusting the electric field and magnetic field every time by controlling a specific energy filter based on the predetermined relationship between the strength of the electric field and magnetic field and the accelerating voltage of a charged particle beam. CONSTITUTION:A deflection type Wien filter 10 constituted so that the electric field and the magnetic field cross at a right angle is provided to reduce the energy width of an electron beam 8. The relationship between the electric field E, magnetic field B, and charged particle beam accelerating voltage is determined in advance and calculated by an arithmetic unit 50 and outputted to amplifiers 56, 57 amplifying the inputs to a high-voltage power supply 40 and the filter 10. Accordingly, the optional voltage V can be selected without adjusting the electric field E and magnetic field B every time the voltage is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a charged particle beam application device, and particularly to an automatic control device suitable for an energy filter or a mass separator.

[Conventional technology]

Conventionally, in order to improve the resolution of a scanning electron microscope, a third lens was used in which the sample was placed inside the objective lens to reduce aberrations.
The electron optical system shown in the figure is used. (Japan Society for Electron Microscopy, Proceedings of the 40th Academic Conference, p. 211) Even when such an optical system is used, there is a drawback that the resolution is reduced due to chromatic aberration, especially at low acceleration voltages.

In order to solve this problem, it is necessary to reduce the energy width of the electron beam to reduce chromatic aberration. Therefore, we have already devised an electron optical system using an energy filter. This electron optical system is shown in FIG. Here, filter 1
A so-called Wien filter in which the electric field and the magnetic field are orthogonal to each other is suitable as the zero. However, this conventional example does not disclose anything about adjusting the filter when changing the accelerating voltage.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional technology, in a Wien filter-type energy filter or mass separator in which electric and magnetic fields are perpendicular to each other, there is a problem in that it is necessary to adjust the strength of the electric and magnetic fields each time the accelerating voltage is changed. was there.

[Means for solving problems]

In order to solve the above problem, the relationship between the accelerating voltage and the strength of the electric field or magnetic field should be clarified and incorporated into the device configuration.In this way, even if the accelerating voltage is changed,
There is no need to adjust the strength of the electric and magnetic fields each time, and the strength of the electric and magnetic fields can be adjusted automatically.

[Effect]

A Wien filter is a device in which a charged particle beam with a desired energy (V) is allowed to travel straight, and a charged particle beam with a different energy is deflected and bent.

The relationship between the strength of the electric field E and the magnetic field B at this time can be expressed as E=1HB (1). Here, k = r-7m (e: charge.

m: mass of charged particle) is a constant. If the charged particle beam 81, which differs by V from the desired energy, is placed at the edge of the aperture 11, the charged particle beam can be completely cut off. If the radius of this diaphragm 11 is r, then the electric field E may satisfy the following equation.

E = k2V2/ A V
-(2) Here, kz = r/QL is a constant, Q is the half width of the action length of the electric field E, and L is the distance between the deflection fulcrum 20 of the filter 10 and the aperture 11. At this time, the magnetic field B is (1
), from equation (2), B = k s VT/AV
−(3) where k8 is a constant.

On the other hand, the electric field E is proportional to the applied voltage U of the electrostatic deflector, and the magnetic field B is proportional to the coil current of the magnetic field deflector. That is, U=4V”/ΔV
−(4) I = k F, VT/AV
- Equivalent to (5). Here, k4t
k5 is a constant.

Therefore, if such a relationship is incorporated into the device configuration, the above problems can be solved.

〔Example〕

An embodiment in which the present invention is applied to a scanning electron microscope will be described below with reference to FIG.

An electron beam 8 emitted from the FE electron gun 1 is accelerated to a desired voltage by an accelerating lens 2. After the electron beam 8 passes through the condenser lens 3, the energy of the electron beam is separated by the Wien filter 10, and only the electron beam with a desired energy width passes through the aperture 11. This electron beam is imaged onto the surface of the sample 7 by the objective lens 6. Secondary electrons 9 generated on the surface of the sample 7 are detected by the detector 5 and become a video signal.

Here, the output of the high voltage power supply 40 that determines the acceleration voltage of the electron beam 8 is the electron gun 1. is applied to. At the same time, a signal from a voltage determining part (for example, a detection resistor) inside the power supply is input to a ΔV determiner 51, a squarer 52, and a square rooter 53.

The outputs of the ΔV determiner 51 and the squarer 52 are input to the first arithmetic unit 54, and an arithmetic operation corresponding to equation (4) is performed. This output becomes an applied voltage U that creates a desired electric field E through an amplifier 56. Furthermore, the first arithmetic unit 54 and the square root unit 5
The output of 3 is input to the second arithmetic unit 55, and an arithmetic operation corresponding to equation (1) is performed. This output becomes a coil current I that creates a desired magnetic field B through an amplifier 57.

4. Configure as below to form equations (4) and (1). k
The amplification factors of the first arithmetic unit 54, the second arithmetic unit 55, and the amplifier 56 and the amplifier 57 corresponding to z are adjusted in advance at a specific acceleration voltage. At this time, even if the accelerating voltage is changed, the desired applied voltage U can be maintained as explained in [Operation].
and coil current I are automatically given, eliminating the need to adjust the numbers. In addition, the Δ■ determiner 51- is configured to change in conjunction with the acceleration voltage, but if the acceleration voltage is constant regardless of the acceleration voltage, it is sufficient to output a constant signal, and the V determiner 51 is omitted. You can also.

In the present invention, the desired applied voltage U and coil current I are configured by various calculation units 51 to 55, but it is configured by a calculation unit 50 that combines these, and the applied voltage TJ and coil current I are calculated by a plurality of accelerating voltages. It is also possible to calculate this in advance and interpolate U and ■ for the acceleration voltage to be used. Furthermore, although an electromagnet was used for the magnetic field B in this example,
This can also be done using a permanent magnet. At this time, since B is fixed, the electric field E, that is, the applied voltage U
The configuration should be such that it determines the

The point is that even if the accelerating voltage changes, as long as the electric field E and the magnetic field B can be changed in conjunction with the accelerating voltage so that equation (j) is always satisfied, the present invention can be applied in any configuration. objective can be achieved.

In the present invention, automatic adjustment of the lenses 3 and 6 when the accelerating voltage changes is omitted, but these can also be performed at the same time. Furthermore, although the sample 7 was placed inside the objective lens 6 and the secondary electron detector 5 was placed on the electron gun side of the objective lens 6, this arrangement is not limited to the embodiment shown in FIG. Needless to say. Further, the type (magnetic field type, electrostatic type) and number of lenses and the type of electron gun are not limited to those in this embodiment, and the present invention can be used.

The present invention has been described with respect to an energy filter for electron beams. However, this application is not limited to this, and can also be applied similarly when a Wien filter is used as a mass separation filter for ion beams in a device in which the electron gun is replaced with an ion gun, for example. That is, it can be used in general charged particle beam application devices.

〔Effect of the invention〕

As described above, according to the present invention, there is no need to adjust the electric field or magnetic field each time the accelerating pressure is changed, so that the charged particle beam application device can arbitrarily select the accelerating voltage. It becomes possible to provide

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of a scanning electron microscope showing an embodiment of the present invention, Fig. 2 is a basic configuration diagram of a scanning electron microscope already devised, and Fig. 3 is a diagram of a scanning electron microscope with high resolution. Basic configuration diagram of a conventional scanning electron microscope. 1... Field emission type electron gun, 2... Accelerating lens, 3...
... Condenser lens, 4... Deflector, 5... Secondary electron detector, 6... Objective lens, 7... Sample, 8...
...Electron beam, 9...Secondary electron, ]-o...Wien filter, 11...Aperture, 20...Deflection fulcrum, 4o
. . . High voltage power supply, 50 .
. . .]-operation unit, 55 . . . 2nd operation unit, 56.57
...Amplifier, 8o...Electron beam with desired energy, 81.82...Electron beam with energy other than desired.

Claims (1)

[Claims] 1. A charged particle source, a lens means for narrowing the charged particle beam emitted from the charged particle source, a scanning means for two-dimensionally scanning the particle beam on a sample surface, and an electric field and a magnetic field. In a charged particle beam application device equipped with deflection type energy filter means configured to be orthogonal to each other, the strength of the electric field or the magnetic field, or both, is changed in conjunction with a change in the accelerating voltage of the charged particle beam. Features of charged particle beam application equipment. 2. The charged particle beam application device according to item 1, wherein the ratio between the electric field strength and the magnetic field strength is changed in proportion to the square root of the accelerating voltage. 3. The charged particle beam application device according to item 1 or 2, characterized in that the strength of the electric field is changed in proportion to the square of the accelerating voltage. 4. The charged particle beam application device according to items 1 to 3, characterized in that the strength of the magnetic field is changed in proportion to the 1.5th power of the accelerating voltage. 5. The charged particle beam application device according to any one of items 1 to 4, characterized in that the filter sensitivity of the energy filter is changed in conjunction with changes in the accelerating voltage. 6. The electric field and magnetic field strengths are determined in advance for a plurality of accelerating voltages, and the electric field and magnetic field strengths for the desired accelerating voltage are determined by interpolation from the values determined above. The charged particle beam application device according to item 1.