JP2008256526A - Nanowire crosslinking device utilizable for shape measurement of electron beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nanowire crosslinking device capable of measuring the shape of a fine electron beam by a simple method, its forming method, and an electron beam shape measuring method applying the device. <P>SOLUTION: In the forming method of the nanowire crosslinking device, a nanowire, for example, a carbon nanotube, is arranged so as to cross a metal plate, and both end parts of the nanowire are fixed to the metal plate. The nanowire crosslinking device has the nanowire installed so as to cross the metal plate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is applied to an electron beam application apparatus such as an electron microscope for drawing a desired pattern on a wafer by an electron beam in a manufacturing process of a semiconductor device or drawing a mask pattern when manufacturing a mask for a stepper. The present invention relates to a technique for measuring the shape of an electron beam, and more particularly to a nanowire cross-linking device using nanowires such as carbon nanotubes applied to the measurement.

The most rudimentary method for measuring the shape of an electron beam is the “two-aperture method” (see, for example, Non-Patent Document 1). This is used for large light sources such as LaB ₆ or tungsten filaments. Two holes (apertures) are arranged at a distance from each other on the optical axis of the electron optical system, and the current passing through the two apertures is measured with a Faraday gauge or the like. Then, “brightness”, which is a current amount per unit area and unit solid angle, is obtained from the measured current, the aperture diameter, and the distance between the apertures.

There are some anomalous methods that do not use two-apertures. “Knife-edge method” that obtains a beam profile by scanning a focused beam on a knife-edge specimen with a point filament or sharp edge (for example, non-patented) Document 2 and Patent Document 1), or “shadow image method” (for example, see Non-Patent Document 3) that measures the beam diameter without focusing the beam on the sample.
These methods are characterized in that they can be easily realized because the measurement system can be easily configured inside the scanning electron microscope. However, these two methods cannot in principle measure an electron beam that is thinner than the diameter of the diaphragm or the mesh interval.

On the other hand, in the field of electron beam application, in recent years, a thinner electron beam has been demanded, and many fine electron emission materials such as carbon nanotubes and single atom emitters have been studied. However, there is a problem that it is not possible to easily measure the shape of the fine beam.
The method of measuring a minute electron beam uses a transmission electron microscope (TEM), enlarges the light source at a high magnification, directly measures the beam diameter, calculates the brightness, Fresnel fringe, biprism A measurement method using interference of electron waves such as interference fringes (see Non-Patent Document 4, for example) is used. Since this interference fringe has a relationship with the wavelength of the electron wave assured by quantum mechanics, it is theoretically possible to perform precise measurement in the order of the wavelength of the electron wave. However, the method of measuring TEM or electron beam interference is technically difficult and is not a method that can be measured in a general environment.

Alec N. Broers Kohler, illumination and brightness measurement with lanthanum hexaboride cathodes, J. Vac. Sci. Technol. 16 (6), Nov / Dec. 1979 S A Rishton, S P Beamout and C C Wilkinson, Measurement of the profileof finely focused electron beams inscanning electron microscope, J. Phys. E Sci. Instrument, Vol. 17, 1984 Oliver C. Wells, EXPERIMENTALMETHOD FOR MEASUREING THE ELECTRON-OPTICAL PARAMETERS OF THE CCANNING ELECTRONMICROSCOPE (SEM) SCANNING ELECTRON MICOSCOPY / 1977 VOL. 1 N. d. Jonge, Y. Lamy, K. Schoots, T. H. Oosterkamp, High brightness electron beam from a multi-walled carbonnanotube, NATURE 420,393 (2002) Japanese Patent Laid-Open No. 5-80158

In the application of an electron beam, information on the electron beam shape such as the electron beam diameter is important.
In application of electron beam, a thinner electron beam is required. However, in the conventional technique, a fine electron beam is measured unless a technically difficult method using interference of electron waves is used. I can't. Considering the future development of electron beam application, it is important to establish a technology that can easily measure a small-diameter electron beam without using electron wave interference.
The present invention provides a nanowire cross-linking device capable of measuring the shape of a fine electron beam (including the diameter of the electron beam) by a simple method and a method for producing the nanowire cross-linking device. The purpose is to realize a measurement method.

As a result of intensive studies in view of the above problems, the present inventors have found that it is preferable to use carbon nanotubes or the like that are stably present nanomaterials having a diameter of about nanometers, and based on these findings, the present invention It came to make.
That is, the present invention
(1) a nanowire cross-linking device having nanowires laid across a metal plate,
(2) The nanowire cross-linking device according to (1), which is applied to shape measurement of an electron beam,
(3) A method for producing a nanowire cross-linking device in which nanowires are arranged so as to cross a metal plate, and both end portions of the nanowire are fixed to the metal plate,
(4) The method for producing a nanowire-crosslinking device according to (3), wherein the arranged nanowire is a carbon nanotube, a metal-coated carbon nanotube, a metal nanowire, or a semiconductor nanowire,
(5) The method for producing a nanowire cross-linking device according to (3), wherein the nanowire to be arranged is a carbon nanotube, and fixing to the metal plate is performed by heating, and (6) the method according to (1) The nanowire cross-linking device is placed on the electron optical axis, the nanowire is scanned with an electron beam, and either the amount of electrons absorbed, the amount of electrons reflected, or the amount of secondary electrons generated is absorbed in the area of the nanowire with which the electron beam conflicts Or a method of measuring the shape of an electron beam based on one or more
Is to provide.

By using the nanowire cross-linking device of the present invention, it is possible to measure the shape of a fine electron beam having a diameter of several nanometers, which could not be measured by a practical method. And since the measurement method does not use electron wave interference, it is possible to easily measure a fine electron beam shape, and also to measure not only the diameter of the electron beam but also the shape of the electron beam such as emittance. .
In addition, the measurement using the nanowire cross-linking device of the present invention can be used as a standard data for examining performance with subjectivity such as resolution in a scanning electron microscope.

A method for producing the nanowire cross-linking device of the present invention will be described.
As the nanowire, for example, a carbon nanotube, a metal-coated carbon nanotube, a metal nanowire, a semiconductor nanowire, or the like can be used, and a carbon nanotube is preferable.
As a preferred embodiment of the present invention, a case where carbon nanotubes (hereinafter sometimes abbreviated as CNT) are used will be described.
A carbon nanotube is a huge carbon molecule having a cylindrical crystal structure that exists stably and has a diameter of several nanometers to several tens of nanometers, and is called a nanomaterial.
Therefore, a hole having a diameter of 1 to 20 μm, preferably about 20 μm, is provided in a metal substrate having a size of about 30 mm × 30 mm × 200 μm, for example, a substrate in which metal is deposited on gold, stainless steel, or a silicon oxide film. In order to measure a large electron beam, the larger the hole diameter, the better. However, the present nanotubes having a length of about 20 μm can be used. One carbon nanotube is erected so as to pass through the center of the hole, and both ends of the CNT are fixed to a metal substrate to form a “nanowire crosslinking device”.
Alternatively, a “nanowire cross-linking device” can be created by installing CNTs between two metal plate electrodes and fixing both ends of the CNTs to the plate electrodes by heating.

Good electrical and mechanical joint strength is required at the joint between CNT and metal. If the joint has a large resistance, it is impossible to detect a minute current, and if the strength of the mechanical joint is insufficient, it can be predicted that the structure will collapse due to exposure to the electron beam.
A general method for joining carbon nanotubes and metals, such as APPL. Phys. Lett. 74 (1999) 4061 (hydrocarbon (CxHy), which is a gas component in a vacuum, is decomposed with an electron beam and the components are used to CNT and a substrate (for example, a probe for a probe for a scanning probe microscope). Although it may be a method of joining the needle) by joining), it has been found that the joining is insufficient. We have established a better method for coating and fixing the vicinity of the carbon nanotube junction with metal by utilizing the phenomenon of metal atoms moving to the carbon nanotube surface.

  In this fixing method, when carbon nanotubes are installed on a metal electrode and heated to about 450 to 550 ° C. in a vacuum atmosphere or an oxygen-free gas replacement atmosphere by an electric furnace or the like, the metal atoms of the electrode move on the CNT surface. Thus, it was confirmed that the metal covered the CNT and made an ideal contact state. FIG. 1 is an SEM photograph of a CNT and a gold electrode, and shows a state where the CNT is installed on the metal plate electrodes on both sides. FIG. 2 is a result of X-ray analysis (Energy Dispersive X-ray Spectrometer; hereinafter referred to as EDX) in the AA ′ axis and the BB ′ axis in FIG. A characteristic X-ray is detected. In the BB ′ axis, since the peak position of the gold atom overlapped the carbon atom peak position, it can be confirmed that the gold atom is thermally transported on the CNT. Since no gold atom peak was detected on the carbon atom peak in the AA ′ axis, gold atoms were not transported to the position of the AA ′ axis, and the CNT was exposed. This result indicates that the metal atoms have moved on the surface of the CNT to the position of the BB ′ axis by heating, which means that the CNT can be firmly bonded and fixed to the metal plate electrode.

FIG. 3 is an SEM photograph of another example of the CNT and the metal plate electrode, and shows a state in which the CNT is cross-linked to the metal plate electrodes on both sides. When CNTs are installed between the electrodes and heated to about 500 ° C. in an electric furnace or the like in a vacuum atmosphere or a gas replacement atmosphere without oxygen, the metal atoms of the electrodes move on the CNT surface as described above. Make a good contact.
FIG. 4 is a graph showing changes in current-voltage characteristics depending on the heating temperature and heating time applied to the bonding of the substrate shown in FIG. 3 using an electric furnace. It was shown that the electrical resistance was close to a metallic behavior at each heating time, and it was confirmed that the electrical characteristics were good.
That is, it can be assumed that the mechanical strength is sufficient by fixing by heating, and that the electrons absorbed from the electron beam to the nanowire can be accurately measured by improving the electrical characteristics of the junction.
Explaining the fixing method of the nanowires other than the carbon nanotubes, the metal-coated carbon nanotubes, metal nanowires, and semiconductor nanowires are installed and fixed between the two metal electrodes by the EBID method described above. As for the semiconductor nanowire, the electrical characteristics and mechanical characteristics of the fixed portion can be improved by the above-described heating method as in the case of the carbon nanotube.

  The present invention is a nanowire bridging device having a nanowire, for example, a carbon nanotube, which is constructed so as to cross a metal plate, produced by the method as described above. Another example is shown in FIG. 5 as an SEM photograph. The SEM image is a nanowire cross-linking device in which one CNT is installed in a hole having a diameter of 5 μm on a stainless steel thin plate.

Next, a preferred example of a method for measuring the shape of a fine electron beam using the nanowire crosslinking device of the present invention will be described in detail.
When this nanowire cross-linking device is placed on the electron optical axis and scanned with an electron beam to be measured on the nanowire using a deflection coil, the following phenomenon occurs in the minute area of the nanowire that the electron beam conflicts with. .
a) An electron beam is absorbed by the nanowire, and a current flows between the electrodes at both ends of the nanowire and the ground of the device.
b) A part of the electron beam is reflected to generate reflected electrons, generating reflected electrons proportional to the area hit by the electron beam.
c) Further, secondary electrons are generated only from the surface region of the nanowire hit by the electron beam.

  These absorbed electrons, reflected electrons, and secondary electrons generated by the electron beam hitting the nanowire are all correlated with the contact area between the nanowire and the electron beam. Therefore, it is possible to measure the electron beam diameter and electron beam shape by measuring their intensities using “Ammeter”, “Backscattered electron detector” and “Secondary electron detector”. .

FIG. 6 is an explanatory view showing one embodiment of the electron beam beam diameter measuring method of the present invention.
A through-hole 2 is provided in a silicon wafer 1 of about 50 μm using an etching process, and a metal thin film (for example, an Au thin film) 3 is formed on the upper surface in the vicinity of the through-hole 2 by a vapor deposition process or the like. The nanowire device is formed by cross-linking the carbon nanotube 4 to the penetrating portion with the metal thin film 3 portion as a supporting / fixing point. When the electron beam 5 crosses the nanotube constructed from the direction of the arrow in FIG. 6, secondary electrons, reflected electrons, and absorbed charges are generated in an amount proportional to the surface area of the CNT hit by the electron beam. The electron beam diameter can be estimated from the scanning distance by detecting a minute current that flows from the secondary electron detector, the backscattered electron detector, or the electrode of the CNT fixing portion to the device ground.
FIG. 6 shows a state in which the reflected electrons are detected by the reflected electron detector 6. Either detection method can be detected by an independent path, and a detector having a strong signal strength is used depending on the case.

FIG. 7 shows an electron beam reflected electron detector (if the electron beam energy is large, the electron beam passes through the CNT and the reflected electron detection intensity becomes weak. In this case, an absorption current and a secondary electron detector are used.) An example of detection is shown below. As shown in FIG. 7, when the electron beam traverses the installed carbon nanotube, reflected electrons are generated from the electron beam hitting the CNT surface, and the reflected electrons are detected according to the area of the CNT hitting the electron beam. . That is, the electron beam is cut by a rectangle formed by the diameter of the CNT and the length of the electron beam perpendicular to the CNT, and a signal intensity corresponding to the area is obtained.
When the electron beam is scanned, (a) when the CNT is not touched, the signal intensity of the detector cannot be obtained. (b) The signal intensity is obtained when scanning starts and the electron beam starts to contact. Also, (c) when the maximum diameter of the electron beam is CNT, the signal intensity of the detector is maximized. Here, the scanning distance of (c) → (b) is the radius of the electron beam (when the electron beam is circular). In the case of an elliptical shape, the major axis radius and the minor axis radius are obtained by changing the scanning direction by 90 degrees. When the beam shape is circular or elliptical, the beam shape can be specified by the above operation.

Furthermore, the detector signal intensity per unit area is determined based on the signal intensity of the detector corresponding to the rectangular area formed by the electron beam diameter (long and short axis radius) measured by the above measurement method and the CNT diameter (known). I want. Since the diameter of the CNT is constant, the length of an arbitrary part of the electron beam can be obtained. Therefore, the total area and shape can be measured even with an electron beam having asymmetric distortion.
When secondary electrons are used instead of reflected electrons, the principle is completely the same except that a secondary electron detector is used as a detector. Also, when using the absorbed charge, a very small current (proportional to the area where the CNT and electron beam overlap) is detected from the electrode at the CNT support point to the device ground, and the electron beam scanning method is the same. Use the principle.
Secondary electrons, reflected electrons, and absorbed charges can be detected by independent paths, and can be used in the form of so-called compensation to improve measurement accuracy.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

[Creation of nanowire cross-linking device]
A carbon nanotube with a diameter of 2 nm is mounted on a gold vapor deposition substrate having a gap of 2 μm on a silicon oxide film on a silicon substrate of 20 mm × 20 mm × 500 μm, and a carbon nanotube having a diameter of 20 nm is installed between the gold vapor deposition electrodes. For 1 hour, 6 hours, and 21 hours to fabricate a nanowire device. On the other hand, a carbon nanotube with a diameter of 20 nm was erected on the upper part of a stainless steel substrate having a through hole with a diameter of 5 μm of 30 mm × 30 mm × 100 μm, thereby producing a nanowire device.

2 is an SEM photograph in which carbon nanotubes are installed between gold electrodes. 2 is a graph showing a result of detecting a gold peak on a CNT by EDX in a cross section taken along lines AA ′ and BB ′ in FIG. It is a SEM photograph of another example in which the carbon nanotube was constructed between gold electrodes. It is a graph which shows the current voltage characteristic by the heating temperature at the time of joining, and a heating time. It is a SEM photograph of an example of the nanowire bridge | crosslinking device of this invention. It is explanatory drawing which shows one embodiment of the shape measuring method of the electron beam of this invention. It is a graph which shows the relationship between an electron beam and a carbon nanotube position, and the signal strength from the scanning position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon wafer 2 Through-hole 3 Metal thin film 4 Carbon nanotube 5 Electron beam 6 Backscattered electron detector

Claims (6)

  A nanowire cross-linking device having nanowires laid across a metal plate.   The nanowire cross-linking device according to claim 1, which is used for measuring the shape of an electron beam.   A method for producing a nanowire cross-linking device in which nanowires are arranged across a metal plate and both end portions of the nanowire are fixed to the metal plate.   The method for producing a nanowire cross-linking device according to claim 3, wherein the arranged nanowire is a carbon nanotube, a metal-coated carbon nanotube, a metal nanowire, or a semiconductor nanowire.   4. The method for producing a nanowire cross-linking device according to claim 3, wherein the nanowire to be arranged is a carbon nanotube, and fixing to the metal plate is performed by heating.   The nanowire cross-linking device according to claim 1 is arranged on an electron optical axis, and the nanowire is scanned with an electron beam, and the amount of electrons absorbed, the amount of electrons reflected and the amount of electrons generated are A method of measuring the shape of an electron beam based on any one or more of secondary electron quantities.