JP2006331997A - Electron source and electron beam application device equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a conventional device is specialized for keeping a vacuum chamber to an ultrahigh vacuum, needs a complicated and expensive differential exhaust system, is high in manufacturing cost, and complicated in handling operation. <P>SOLUTION: An electron source is provided with a cathode 31 for electron discharge, a control electrode 32 which controls an intake of electron from the cathode 31 according to a control voltage and an anode 33 which accelerates the speed of an electron by impressing a high voltage between the cathode 31 and the anode, and the cathode 31 is made a low vacuum type by forming an orienting carbon nano-wall film 31b of which the electron discharge surface is oriented on the surface of a conductor 31a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electron source used in an electron beam application apparatus such as a scanning electron microscope (SEM) and the electron beam application apparatus. In addition to the scanning electron microscope, for example, transmission electron microscopes (TEM), Auger electron spectroscopy analyzers (AES), reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), etc. There is a device.

Many such electron beam application apparatuses have been proposed in Patent Document 1 and the like. In such an electron beam application apparatus, for example, in an environmental control type scanning electron microscope, a vacuum chamber in which an electron source for generating an electron beam is housed and a sample chamber in which a sample is placed are in contact with each other through a pressure limiting opening. ing. In such a scanning electron microscope, the pressure in the sample chamber is maintained at, for example, quasi-atmospheric pressure (10 ³ to 10 ⁴ Pa) by a vacuum pump in order to enable observation of the sample from the observation window. For example, an ultrahigh vacuum of 10 ⁻⁸ Pa or higher is set. Thus, the vacuum chamber is divided into a plurality of chambers by the orifice, and each chamber is evacuated by a separate vacuum pump, so-called differential evacuation. That is, the uppermost electron source installation space in the vacuum chamber is an ultra-high vacuum space. However, in order to keep the vacuum chamber in an ultra-high vacuum, it is necessary to specialize the structure of the apparatus, and since a complicated and expensive differential pumping system is required, the manufacturing cost of the scanning electron microscope is expensive. In addition, the handling operation is complicated due to the ultra-high vacuum, which is inconvenient.
JP 2002-350731 A

  Therefore, the problem to be solved by the present invention is that the electrons required for analysis, analysis, measurement, observation, etc. of the sample in the sub-atmospheric pressure sample chamber even if the electron source is of a low vacuum type and the vacuum chamber is low vacuum. It is to provide an electron source capable of irradiating a line. Moreover, the problem which should be solved by this invention is providing the electron beam application apparatus provided with such an electron source.

  An electron source according to the present invention is an electron source that is arranged in a vacuum chamber of an electron beam application apparatus and emits electrons into a sample chamber for elemental analysis, analysis, measurement, observation, etc., and is a cathode for electron emission And a control electrode that controls extraction of electrons from the cathode according to the control voltage, and an anode that accelerates the electrons by applying a high voltage between the cathode and the cathode on the surface of the conductor. This is characterized in that an oriented carbon nanowall film having an oriented electron emission surface is formed into a low vacuum type.

  This carbon nanowall film is a form in which a large number of nano-order wall-like carbon flakes (wall-like portions) are highly oriented in the predetermined electron emission direction and are aggregated and coupled, and has a crystal structure close to that of graphite with high electrical conductivity. It consists of several dozen layers of graphene sheets, and when a voltage is applied, a high electric field concentration occurs on the wall-shaped upper surface which is an end, and electrons are emitted.

The electron source of the present invention has, for example, an electric field strength between the cathode and the anode of 2.5 to 3.0 (MV / m) even when the vacuum chamber has a low vacuum of 10 ⁻¹ to 10 ⁻² Pa. In the case of m), for example, 1E-4 to 1E-3 (A) can be obtained as the field emission current, and sufficient electron emission can be obtained. In addition, a constant anode current can be obtained in the saturation region where the anode voltage is 3.0 kV or more, and this anode current can be controlled by the control voltage, so that stable electron emission excellent in controllability can be obtained. it can.

That is, in the present invention, since a cathode is an electron-emitting device the electron emission surface in the anode direction to the conductor surface is composed of a field-emission cold cathode forming an oriented carbon nano wall film oriented, 10 ^{- Even} if it is installed in a vacuum chamber of low vacuum of ¹ to 10 ^-2 Pa, it is necessary for elemental analysis, analysis, measurement, observation, etc. of the sample inside the sample chamber of sub-atmospheric pressure of 10 ³ to 10 ⁴ Pa Can be irradiated with a sufficient amount and intensity. Therefore, in the present invention, the vacuum chamber should be kept at a low vacuum instead of an ultra-high vacuum, so there is no need to make the vacuum chamber an ultra-high vacuum as in the prior art, and the device structure can be simplified rather than specially. In addition, since the differential pumping system can be simple, the manufacturing cost of the electron beam application device can be greatly reduced, and the handling operation is simplified because it is low vacuum unlike ultra high vacuum.

  According to the present invention, the manufacturing cost of the electron beam application apparatus can be reduced, and the handling operation is simplified.

  Hereinafter, an electron beam application apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the embodiment, the present invention is applied to an environment-controlled scanning electron microscope as an example of an electron beam application apparatus, but the present invention is not limited to this scanning electron microscope. The present invention can be applied to any electron beam application apparatus that performs analysis, measurement, observation, and the like.

  1 is a diagram showing a simplified scanning electron microscope of an environmental control type, FIG. 2 is a diagram showing a conceptual configuration of the electron source of FIG. 1, and FIG. 3 is a portion A and a portion B in the cathode of FIG. FIG. 4 is a diagram showing the operating characteristics of the electron source, and FIG. 5 is a diagram showing a method for forming an oriented carbon nanowall film on the cathode surface.

Referring to FIG. 1, a scanning electron microscope 1 according to the present embodiment has an electron source 3 disposed in an upper stage portion of a vacuum chamber 2 and a condenser lens 4 disposed outside a middle stage portion of the vacuum chamber 2 so that a vacuum can be obtained. A scan coil 5 is disposed outside the lower part of the chamber 2. The vacuum chamber 2 is conceptually shown as one room. The vacuum chamber 2 and the sample chamber 6 are in contact with each other via a differential exhaust unit 7. A gas (for example, water vapor) for performing gas amplification is supplied to the sample chamber 6 from a gas supply source (not shown), and the pressure of the gas in the sample chamber 6 is maintained at a quasi-atmospheric pressure by a vacuum pump (not shown). The vacuum chamber 2 is maintained at a low vacuum (10 ⁻¹ to 10 ⁻² Pa) by a vacuum pump (not shown). In addition to the above, the scanning electron microscope 1 has a secondary electron detector, an amplifier, and the like, but the illustration and description thereof are omitted for simplification of description.

  The electrons emitted from the electron source 3 are focused by the condenser lens 4 and irradiated onto the sample 8 inside the sample chamber 6. The electrons are scanned on the sample 8 by the scan coil 5 and are focused on the sample 8 by the objective lens 9. Secondary electrons are generated from the sample 8 by the electron irradiation, and processing for elemental analysis, analysis, measurement, observation, and the like of the sample 8 is performed in the scanning electron microscope 1 using the secondary electrons.

  The scanning electron microscope 1 having the above configuration is characterized in that the electron source 3 has the following configuration.

  The electron source 3 is applied with a high voltage between the cathode 31 for electron emission, the control electrode 32 for controlling extraction of electrons from the cathode 31 according to the control voltage, and the cathode 31, and directs electrons to the sample chamber 6. And an anode 33 to be accelerated. The cathode 31 is formed by forming an oriented carbon nanowall film 31b having an electron emission surface 31c oriented in the direction of the anode 33 on the surface of the conductor 31a. The conductor 31a includes a tip 31a1 having a conical shape or a truncated cone shape. The oriented carbon nanowall film 31b is formed in the shape of a wall in the direction of the cone axis on the surface of the tip 31a1 of the conductor 31a, and is oriented so that the electrons 34 converge and emit in the direction of the cone axis. Specifically, the portion surrounded by circle A in FIG. 2 is the top of the electron emission surface 31c, and this top is relatively flat. As shown in FIG. 3, the wall portion 31b1 of the oriented carbon nanowall film 31b is formed in this portion so as to be substantially perpendicular to the top flat surface and oriented. A portion surrounded by a circle B in FIG. 2 is a slope portion of the electron emission surface 31c. As shown in FIG. 3, the slope portion is oriented with the wall portion 31b1 of the orientational carbon nanowall film 31b formed obliquely to the slope portion but substantially parallel to the cone axis direction. Therefore, the whole can emit electrons from the oriented carbon nanowall film 31b of the cathode 31 of the electron source 3 toward the direction of the cone axis.

  In the electron source 3 described above, the anode voltage Va is applied between the cathode 31 and the anode 33, and the control voltage Vg is applied between the cathode 31 and the control electrode 32. As shown in FIG. 4, the horizontal axis represents the anode voltage Va (kV) and the vertical axis represents the anode current Ip (μA). When the anode voltage Va is 4 kV or more, the anode current Ip is saturated. The anode current Ip can be controlled by the control voltage Vg. Therefore, the electron source 3 of the embodiment is an electron source excellent in controllability of electron emission.

  The oriented carbon nanowall film 31b described above can be formed on the surface of the conductor 31a by a direct current plasma CVD method or the like, as shown in FIG. That is, the oriented carbon nanowall film 31b introduces a source gas of CH4 / H2 and applies a DC voltage between the anode 40 and the cathode 50 in this gas atmosphere to generate plasma 60 on the anode 40. An oriented carbon nanowall film 31b can be formed on the placed conductor 31a.

In the electron source 3 of the present embodiment described above, the required vacuum is a low vacuum of 10 ⁻¹ to 10 ⁻² Pa, and can be reached by a single rotary pump. This degree of vacuum is relaxed about 1 million times as compared with a conventional cold cathode operated at room temperature, and about 100 times as compared with a tungsten hot filament. In the embodiment, since the electron source 3 is provided, the vacuum chamber 2 in which the electron source 3 is installed can be set to a low vacuum, so that an expensive differential exhaust system as in the prior art is not necessary. The scanning electron microscope can be manufactured at a low cost, and the handling operation is easy.

  The present invention is not limited to the above-described embodiment, and includes various changes or modifications within the scope described in the claims.

It is a figure which shows the structure of the scanning electron microscope of an environment control type | mold which concerns on embodiment of this invention. It is a figure which shows the structure of the electron source of FIG. It is a figure which expands and shows the cold cathode of an electron source. It is a figure which shows the operating characteristic of an electron source. It is a figure which shows the direct-current plasma film-forming method which forms a CNW film into a conductive substrate surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scanning electron microscope 2 Vacuum chamber 3 Electron source 31 Cathode (conductor 31a, oriented carbon nanowall film 31b)
32 Control electrode 33 Anode 4 Condenser lens 5 Scan coil 6 Sample chamber 7 Objective lens 8 Sample

Claims (6)

  An electron source that is arranged in the vacuum chamber of an electron beam application device and emits electrons into the sample chamber for elemental analysis, analysis, measurement, observation, etc., according to the cathode for electron emission and the control voltage A control electrode for controlling extraction of electrons from the cathode; and an anode for accelerating the electrons by applying a high voltage between the cathode, and the electron emission surface is oriented on the surface of the conductor. An electron source characterized in that an oriented carbon nanowall film is formed into a low vacuum type. The cathode conductor has a conical or frustoconical tip,
An electron source characterized in that the oriented carbon nanowall film is formed in a wall shape in the direction of the conical axis on the surface of the tip, and is oriented so that electrons are converged and emitted in the direction of the conical axis. The electron source according to claim 1 or 2, wherein the low vacuum is 10 ^-1 to 10 ^-2 Pa.   In an electron beam application apparatus that arranges an electron source in a vacuum chamber and irradiates electrons from this electron source into the sample chamber for elemental analysis, analysis, measurement, observation, etc., the vacuum chamber is kept at a low vacuum, A high voltage is applied between the electron source, a cathode for electron emission, a control electrode for controlling extraction of electrons from the cathode according to a control voltage, and the cathode to direct the electrons to the sample chamber. An electron beam comprising: an anode for acceleration, wherein the cathode is a low vacuum type in which an oriented carbon nanowall film having an electron emission surface oriented in the anode direction is formed on the surface of a conductor. Applied equipment. The cathode conductor has a conical or frustoconical tip,
5. The oriented carbon nanowall film is formed in a wall shape in the direction of a conical axis on the surface of the tip, and is oriented so that electrons converge and emit in the direction of the conical axis. The electron beam application apparatus described in 1. 6. The electron beam application apparatus according to claim 4, wherein the vacuum chamber is maintained at a low vacuum of 10 ⁻¹ to 10 ⁻² Pa.

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