JP2003203595A - Electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron microscope such as a scanning electron microscope and a transmission type electron microscope capable of effectively neutralizing charge-up on a sample surface such as an insulator. <P>SOLUTION: A thermoelectron generated from a filament 9 enters a chamber 7 by passing through an opening 8. In this case, the electron ionizes gas by colliding with a gas molecule in the chamber 7. Among generated ions, an ion having an upward directional velocity vector is changed in the downward direction on the direction by an electric field formed by an ion shielding electrode 13. This ion current moves along a line of magnetic force made by an objective lens 3, and finally reaches a sample surface. Thus, the charge-up can be efficiently neutralized. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope such as a transmission electron microscope or a scanning electron microscope, which neutralizes charge-up of a sample.

[0002]

2. Description of the Related Art In a scanning electron microscope, an electron beam generated from an electron gun is focused on a sample finely, and the irradiation position of the electron beam on the sample is two-dimensionally scanned. Secondary electrons generated by irradiating the sample with the electron beam are detected, and the detection signal is supplied as a brightness modulation signal to the cathode ray tube synchronized with the scanning of the electron beam. The secondary electron image is displayed.

Further, in the transmission electron microscope, the sample is irradiated with an electron beam, and the electron transmitted through the sample is imaged and projected on the fluorescent screen. In such a scanning electron microscope or transmission electron microscope, when the sample is an insulator or a semiconductor, electric charges are accumulated on the sample surface, and a so-called charge-up phenomenon occurs. When the charge-up occurs, the image becomes whitish as a whole and becomes unclear and difficult to observe.

Therefore, the charge accumulated in the sample is neutralized (charge-up is alleviated). As one of the neutralization methods, an ion source is installed in the vicinity of the sample, and positive ions generated from the ion source are irradiated on the surface of the charged sample.

[0005]

When the above-mentioned method of irradiating a sample with ions is applied to an in-lens type scanning electron microscope or a transmission electron microscope in which the sample is placed in the magnetic field of the objective lens, the sample surface is strongly affected. Since there is a magnetic field, in the above method, the ions from the ion source are wrapped around the magnetic field lines of the magnetic field and cannot reach the sample surface.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a scanning electron microscope and a transmission electron microscope capable of effectively neutralizing charge-up on the surface of a sample such as an insulator. Etc. to realize an electron microscope.

[0007]

An electron microscope according to the present invention comprises an ionization chamber arranged above a sample and having an electron beam passage opening, and a chamber for supplying electrons for ionization into the chamber. The ionization chamber is provided with an electron source provided on a side part and an ion shield electrode for inverting the ions generated in the ionization chamber and upwardly generated by applying a potential higher than the potential of the ionization chamber to the upper part of the ionization chamber. The potential of was set to a positive potential slightly higher than the ground potential, so that the ions generated in the ionization chamber were efficiently guided to the sample surface and the charge-up on the sample surface was neutralized.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of a scanning electron microscope according to the present invention, in which an electron beam EB generated and accelerated by an electron gun 1 is finely focused on a sample 4 by a condenser lens 2 and an objective lens 3.

The electron beam EB is two-dimensionally scanned by the scanning coil 5 on a desired region of the sample 4. Sample 4
Secondary electrons generated by the irradiation of the electron beam on the secondary electron detector 6 are detected by the secondary electron detector 6 provided at a position apart from the optical axis above the objective lens 4.

The secondary electron detector 6 includes a corona ring to which a positive high voltage is applied to collect secondary electrons, a scintillator which collides with the secondary electrons to generate light, an optical fiber which guides the light of the scintillator, and a scintillator. It is composed of a secondary electron multiplier tube that generates electrons by the light of and emits electrons.

Although not shown, the detection signal of the secondary electron detector 6 is supplied to the cathode ray tube as a brightness modulation signal via an amplifier and a signal processing circuit for adjusting the brightness and contrast of the image. As a result, the secondary electron image of the desired region of the sample is displayed on the cathode ray tube.

The secondary electron image of the sample 4 can be observed by the above-mentioned operation. When the sample 4 is an insulator or a semiconductor, the surface of the sample 4 is irradiated with the electron beam EB on the sample. Charges are accumulated, and so-called charge-up occurs. When this charge-up occurs, the image becomes whitish as described above, and the image becomes unclear, which hinders image observation.

Therefore, in the embodiment shown in FIG. 1, an ionization chamber 7 having an opening for passing the electron beam EB is provided above the objective lens 3. An electron passage opening 8 is provided on one side of the ionization chamber 7, and a filament 9 is provided close to the opening 8.

In the ionization chamber 7, a potential difference of + several tens to + several hundreds V is applied to the filament 9 by the power source 10, and a potential of + Vg (V) is applied to the ground by the power source 11. Further, the filament 9 is configured to be heated by the heating power supply 12.

An ion shield electrode 13 having an electron beam EB passage opening is provided above the ionization chamber 7, and a voltage of about Vg + 10 (V) is applied to the ion shield electrode 13 by a power supply 14. Has been done.

A ground electrode 15 is provided between the ionization chamber 7 and the objective lens 3, and a ground electrode 16 is provided between the condenser lens 2 and the ion shield electrode 13. The ionization chamber 7, the ion shield electrode 13, and the ground electrodes 15 and 16 are each structured to be axisymmetric with respect to the optical axis of the electron beam EB, so as to prevent improper deflection of the electron beam EB. Has been

With the above structure, the electron beam EB generated and accelerated by the electron gun 1 is finely focused on the surface of the sample 4 by the condenser lens 2 and the objective lens 3. Also,
The electron beam EB is two-dimensionally scanned on the desired region of the sample 4 by the scanning coil 5. For example, secondary electrons generated by irradiating the sample 4 with the electron beam are secondary electron detectors 6 provided at positions above the objective lens 4 away from the optical axis.
Detected by. Although not shown, the detection signal of the secondary electron detector 6 is supplied to the cathode ray tube as a brightness modulation signal via an amplifier and a signal processing circuit for adjusting the brightness and contrast of the image. As a result, the cathode ray tube has
A secondary electron image of the desired area of the sample will be displayed.

When the sample 4 is an insulator or semiconductor,
By irradiating the sample with the electron beam EB, charges are accumulated on the surface of the sample 4, so-called charge-up occurs. When this charge-up occurs, the image becomes whitish as described above, and the image becomes unclear, which hinders image observation.

When this charge-up occurs, the filament 9 is heated and thermoelectrons are generated. Thermoelectrons
The filament 9 is drawn toward the ionization chamber 7 having a potential difference of + several tens to + several hundreds of V, and enters the chamber 7 through the opening 8. At this time, the electrons collide with gas molecules in the chamber 7 and ionize the gas.

Among the generated ions, those having a downward velocity vector are drawn into the ground electrode 15 as they are, and move further downward. On the other hand, the direction of the ions having the upward velocity vector can be changed to the downward direction by the electric field formed by the ion shield electrode 13 to which a voltage of about Vg + 10 (V) is applied.

In this way, a downward ion flow is created. This ion flow is Vg (e
V). This ion flow moves along the magnetic field lines created by the objective lens 3 and finally reaches the sample surface. FIG. 2 shows the flow of ions generated in the ionization chamber 7.

Since the sample surface is disposed in the vicinity of the maximum magnetic flux density of the magnetic field formed by the objective lens 3, the density of the ion flow reaches the maximum when reaching the sample surface. Therefore, it is possible to efficiently neutralize the charge-up.

In order to realize the optimum neutralization state, the heating power source 12 for the filament 9 is adjusted to control the amount of thermoelectrons generated, and thereby the amount of ions generated in the chamber 7 is adjusted. As a result, the number of positive ions with which the sample 4 is irradiated may be controlled. Further, as another method, the amount of ions toward the sample 4 may be adjusted by adjusting the voltage of the ionization chamber 7 with the variable power source 11.

The embodiment of the present invention has been described above.
The present invention is not limited to this form, and many variations are possible. For example, the case where the present invention is applied to a scanning electron microscope has been described, but the present invention can also be applied to a transmission electron microscope in which a sample is arranged in the magnetic field of the objective lens.

[0025]

As described above, the electron microscope according to the present invention is provided with an ionization chamber having an opening for passing an electron beam, which is arranged above a sample, and for supplying electrons for ionization into the chamber. An electron source provided on the side of the chamber and an ion shield electrode for reversing ions generated in the ionization chamber and directed upward are applied with a potential higher than the potential of the ionization chamber at the upper part of the ionization chamber, The potential of the ionization chamber was a positive potential slightly higher than the ground potential. As a result, the ions generated in the ionization chamber can be efficiently guided to the sample surface, and the charge-up on the sample surface can be neutralized.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a scanning electron microscope according to the present invention.

FIG. 2 is a diagram showing a flow of ions generated in an ionization chamber.

[Explanation of symbols]

1 electron gun 2 condenser lens 3 Objective lens 4 samples 5 scanning coils 6 Secondary electron detector 7 Ionization chamber 8 openings 9 filament 10, 11, 12, 14 Power supply 13 Ion shielding electrode 15,16 Earth electrode

Claims (5)

[Claims] 1. An electron microscope in which a sample is arranged in a magnetic field of an objective lens, for supplying an ionization chamber having an opening for passing an electron beam, which is arranged above the sample, and electrons for ionization into the chamber. In addition, an electron source provided on the side of the chamber and an ion shield electrode for reversing the ions generated in the ionization chamber and directed upward when a potential higher than the potential of the ionization chamber is applied to the upper part of the ionization chamber. An electron microscope equipped with the positive potential of the ionization chamber that is slightly higher than the ground potential. 2. The electron microscope according to claim 1, wherein ground electrodes are provided below the ionization chamber and above the ion shield electrode. 3. An ionization chamber, an ion shield electrode,
The electron microscope according to claim 2, wherein the ground electrode is formed symmetrically with respect to the optical axis of the electron beam. 4. A scanning electron microscope in which a sample is placed in a magnetic field formed by an objective lens and a desired region of the sample is two-dimensionally scanned by a focused electron beam.
The electron microscope according to 3 above. 5. The electron microscope according to claim 1, wherein the sample is a transmission electron microscope arranged in a magnetic field formed by an objective lens, and an electron transmitted through the sample is imaged.