JP2007073307A - Hybrid electron gun - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron gun which generates electron beams by which CL signals with high luminance are obtained from an extremely micro amount of defects and impurities, and which is controllable to a large current. <P>SOLUTION: In the electron gun for a cathode luminescence detection apparatus which is used in an electron beam irradiation system of the cathode luminescence detection apparatus, a plurality of electron guns controlling an electron beam current with a 6-digit dynamic range (6×10<SP>-7</SP>μA-400 μA or more) and controlling an electron beam spot diameter with a 3-digit dynamic range (0.016 μA-100 μA or more) are prepared, and an attaching and detaching mechanism is introduced which makes a hybrid connection for switching each thermoelectron gun. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to cathodoluminescence detection of semiconductors, metals, inorganic materials, organic materials, living bodies, etc., and particularly to determine the quality of trace amounts of impurity atoms, defects and crystals on thin films, surfaces and interfaces of semiconductors and organic materials. The present invention relates to an electron beam irradiation system of a cathodoluminescence detection device suitable for amplification of a weak cathodoluminescence signal reflecting an electronic state indispensable to the device.

Cathodoluminescence (CL) is light emitted from a sample when the material is irradiated with an electron beam from an electron gun. Cathodoluminescence spectroscopy is an electron whose emission process reflects the intrinsic properties of the material. Since it gives a wealth of information about not only the state but also the electronic state created by defects and impurities in the material, it is a powerful means for nondestructive evaluation of materials, and its use has become increasingly popular in recent years.
Specifically, CL spectroscopy is usually from a few kV to a few tens.
Use an electron beam accelerated to kV. For example, if the material is a semiconductor, when an electron beam with an energy sufficiently larger than the band gap of the material is incident, part of the energy is used to excite electrons in the valence band to the conduction band, Excess electron-hole pairs are generated in the crystal. The generation region of electron-hole pairs can be expressed by the range of electrons in the substance.

The CL spectrum is observed as an energy distribution of light emitted when electron-hole pairs excited by an electron beam recombine via electronic states created by defects and impurities. Accordingly, the peak energy of light emission varies depending on the electronic states produced by various defects and impurities, and the intensity thereof is proportional to the concentration of the electronic states. Therefore, the electronic states of the defects and impurities can be evaluated from the analysis of the CL spectrum.
In order to realize the above-described evaluation, the cathodoluminescence detection apparatus includes (1) an electron beam irradiation system, (2) a vacuum vessel, (3) a vacuum exhaust system, (4) a stage for holding a sample, (5) A condensing optical system for condensing the cathodoluminescence emitted from the sample, (6) a light transfer system for transferring the collected light to the spectroscope, and (7) for analyzing the transferred light. A spectrum which is composed of a spectroscopic system, (8) a detection system for detecting the spectroscopic light, and (9) an analysis system for analyzing the detected signal, which is a light intensity distribution with respect to the wavelength of the spectroscopic light. Alternatively, it is possible to visualize and analyze as an image (for example, CL mapping) by acquiring CL while running the electron beam.

In general, an electron beam irradiation system used in a cathodoluminescence detector comprising an electron gun, an electron lens, and a deflection / astigmatism corrector has a depth direction that depends on two-dimensional scanning and acceleration voltage. A commercially available electron microscope apparatus is used because of good controllability of information separation. At this time, a thermoelectron gun having a tungsten (Tungsten: W) hairpin emitter, a thermoelectron gun having a lanthanum hexaboride (LaB ₆ ) emitter, and a ZrO / W emitter having a ZrO-coated ZrO on a W single crystal. By selecting an electron gun structure such as a gun, it is possible to apply a high-definition electron beam that is much higher in definition than a high-brightness CL signal or laser beam. Substance evaluation can be performed with high spatial resolution.
In addition, an electron microscope such as an electron beam excitation current method (EBIC) or an electron probe microanalysis (EPMA) can be incorporated into the electron microscope, and quantitative composite evaluation is also possible.

In addition, as an emitter material in a general electron gun, the prior art relating to an electron emitter and an electron emission array using field electron emission from a sharp point (tips) has long been known, and these emitters are gated arrays ( gated arrays). The first realization of this was announced by CA Spindt, a researcher at the Stanford Research Institute in California (Non-Patent Document 1). Since then, improvements to such emitter arrays have been proposed, including doping the tip volume and surface with electropositive elements (see US Pat.
Further, there is known a method including the step of disposing vanadium or a vanadium compound as an emitter material at each location of a substrate and creating a plurality of emission sites at the location with an average density of ⁻² of at least 10 ² cm (patent) Reference 2).
US Pat. No. 5,772,488 JP 2005-521217 A J. Appl.Phys. 39,7, pp 3504-3505, (1968)

However, in the electron beam irradiation system using the above-mentioned commercially available electron microscope, the electron beam current from the electron gun, the movable range of the spot size, and the acceleration voltage are limited depending on the structure of the electron gun and the performance of the electron microscope apparatus. Will be. Although there are many merits of using an electron microscope, the excitation electron beam current tends to be reduced particularly in order to achieve the original purpose of the electron microscope, which is to obtain a secondary electron image precisely. Therefore, specifically, there is almost no evaluation and research of CL signals by electron beam current excitation at a number &micro; A or more, and so-called blank areas for evaluation and research exist. Table 1 shows the structure and performance of a general electron gun.
In CL spectroscopy, not only electronic states that reflect the intrinsic properties of materials, but also electron states created by defects and impurities in materials are excited with high efficiency (ie, electron-holes at relatively high densities). One of the factors that determine the analytical capability and accuracy of the cathodoluminescence device is how to generate and capture weak light emission. In particular, as the volume of semiconductor materials is currently shrinking and becoming increasingly sophisticated, the importance of trace amounts of defects and impurities has increased, and due to demands in the semiconductor field of quantum wire devices and nanodevices, there is a wide variety of weaker signal strengths. Detecting signals of trace amounts of defects and impurities contained in a monoatomic or submonolayer ultrathin material, or in materials in the nanometer range is essential and indispensable.

FIG. 1 shows a relationship between an electron beam current and a CL signal when a thermal electron gun having a W hairpin emitter of a general electron microscope is used. As shown in the figure, the electron beam current used for excitation is generally proportional to the CL signal intensity.
The present invention has focused on this relationship. That is, in order to obtain a CL signal with high luminance from a very small amount of defects and impurities, it is extremely effective to excite with an electron beam that can be controlled to a larger current. At this time, since the amount of electron-hole pairs generated is determined by the amount of electron beam per unit area, it is necessary to control the beam spot diameter. Furthermore, the residual gas in the vacuum vessel reacts with the electron beam probe and causes sample contamination. Since this is expected to become very remarkable under a large current, an electron beam irradiation system compatible with ultra-high vacuum having a vacuum higher than 10 ⁻¹⁰ Torr is required.

The object of the present invention is to investigate an electron beam irradiation system used in the present cathodoluminescence device, and to develop an electron beam irradiation system of a cathode luminescence device capable of amplifying the CL signal intensity by two orders of magnitude or more than the conventional level. A structure of a hybrid electron gun is provided.

In order to achieve this object, the present invention provides an electron gun used in an electron beam irradiation system of a cathode luminescence detection apparatus comprising an electron gun, an electron lens, and a deflection / astigmatism corrector as shown in Table 1. Introducing a detachable attachment mechanism that enables mixed connection (hybrid type) to simultaneously utilize the performance of thermionic electron gun with LaB ₆ emitter and ZrO / W emitter with different original performance and specifications The electron beam current control with 6-digit dynamic range (6 × 10 ^-7 microamperes to 400 microamperes or more) and 3-digit dynamic range can be achieved by simply replacing the electron gun while maintaining the vacuum in the vacuum chamber. Electron beam spot diameter control (0.016 micrometer to 100
An electron beam irradiation system that enables micrometer or more) will be realized.

That is, the present invention is an electron gun used in an electron beam irradiation system of a cathodoluminescence detection device, and has an electron beam current control (6 × 10 ⁻⁷ microampere to 400 microampere or more) having a dynamic range of 6 digits. And multiple electron guns with electron beam spot diameter control (0.016 micrometers to 100 micrometers or more) with a three-digit dynamic range, and a detachable attachment mechanism capable of hybrid connection for switching and using each electron gun Is an electron gun for a cathodoluminescence detection device.
In the present invention, the cathodoluminescence detection device includes (1) an electron beam irradiation system, (2) a vacuum vessel, (3) a vacuum exhaust system, (4) a stage for holding a sample, and (5) a sample. A condensing optical system for condensing the emitted cathodoluminescence, (6) a light transfer system for transferring the collected light to the spectrometer, and (7) a spectroscopic system for dispersing the transferred light. , (8) a cathode luminescence detection device including a detection system for detecting the dispersed light, and (9) an analysis system for analyzing the detected signal.
Furthermore, the present invention provides a cathodoluminescence detection device comprising ((1) an electron beam irradiation system, (2) a vacuum vessel, (3) a vacuum exhaust system, (4) a stage for holding a sample, and (5) a sample. A condensing optical system for condensing the emitted cathodoluminescence, (6) a light transfer system for transferring the collected light to the spectrometer, and (7) a spectroscopic system for dispersing the transferred light. , (8) a detection system for detecting the dispersed light, and (9) a cathodoluminescence detection device comprising an analysis system for analyzing the detected signal, and (5) a condensing optical system Cassegrain type optical arrangement that can correct chromatic aberration and spherical aberration at the same time on the collecting mirror, and irradiating the sample with the electron beam while acquiring the cathode luminescence from the electron beam irradiation area, Be obtained in-time can be cathodoluminescence detector apparatus according to claim.
In the present invention, the detachable attachment mechanism capable of hybrid connection can replace the electron gun while maintaining the vacuum of the vacuum vessel. At this time, the vacuum can be an ultra-high vacuum higher than 10 ⁻¹⁰ Torr.
Furthermore, in the present invention, the electron gun can be a thermal electron gun having a W hairpin emitter.
Still further, in the present invention, the electron gun can be a thermoelectron gun having a LaB ₆ emitter and a thermoelectron gun having a ZrO / W emitter.

By using this hybrid electron gun, an electron beam current having a 6-digit dynamic range that cannot be reached by a general cathode luminescence electron beam irradiation system without changing any other components of the cathode luminescence detection device. High dynamic range analyzer that enables control (6 × 10 ^-7 microampere to 400 microampere or more) and electron beam spot diameter control (0.016 micrometer to 100 micrometer or more) with a 3-digit dynamic range . This means that the parameter space of research and evaluation that has been limited since the electron microscope has been generally used for CL spectroscopy has been greatly expanded. At the same time, in addition to amplification of the CL signal intensity for this purpose by more than two digits, the hybrid electron gun also serves as a high-density electron beam excitation source for materials. Electron-hole pairs generated in materials are known to cause various phase transitions depending on their density, and form an academic area as a “many-body effect”. Various physical phenomena that are manifested from high-density excited states of matter have many possibilities as phenomena directly connected to new device applications such as light, quantum correlation, illumination, and environmental electronics.
As described above, according to the present invention, information at the atomic and molecular level of a material that surpasses the evaluation limit of the cathodoluminescence method and surpasses other evaluation methods is provided, and is not limited to the field of semiconductor crystal evaluation. It is expected to contribute to expanding the application possibilities of cathodoluminescence in the field. That is, the present invention relates to a cathode luminescence spectrum and time / wavelength from a very small amount of impurities or defects in a semiconductor, metal, organic substance, or other ultra-thin film at a monoatomic layer level or a sub-monolayer level, or a substance typified by a semiconductor. It is extremely effective for steady-state or transient physical property evaluation and electronic state evaluation using the resolved cathodoluminescence image.

The cathodoluminescence (CL) apparatus in which the electron gun of the present invention is used is typically light emitted from the sample when the sample is irradiated with an electron beam from the electron gun, and the cathodoluminescence detection apparatus is mainly ( 1) an electron beam irradiation system, (2) a vacuum vessel, (3) an evacuation system, (4) a stage for holding a sample, (5) condensing optics for condensing cathodoluminescence emitted from the sample A system, (6) a light transfer system for transferring the collected light to the spectroscope, (7) a spectroscopic system for dispersing the transferred light, and (8) detection for detecting the dispersed light. (9) An analysis system for analyzing a detected signal, and an image (by acquiring CL while running a spectrum or an electron beam, which is a light intensity distribution with respect to the wavelength of the dispersed light, As CL mapping) It is a Satoshika and analysis devices.
Furthermore, (5) Cassegrain type optical arrangement that can correct chromatic aberration and spherical aberration at the same time on the condensing mirror constituting the condensing optical system, and obtaining the cathodoluminescence from the electron beam irradiation area while irradiating the sample with the electron beam. At the same time, it is possible to use a cathodoluminescence detection device characterized by acquiring a high-magnification optical microscope image of a sample in real time.
The present invention relates to an electron gun used in an electron beam irradiation system of a cathodoluminescence detection device including an electron gun, an electron lens, and a deflection / astigmatism corrector. Specifically, withdrawal to allow mixing connections to take advantage inherent performance and specifications of different LaB ₆ thermoelectric field emission electron gun having a heat gun and ZrO / W emitter having an emitter, wherein simultaneously (hybrid) The electron beam current control (6 × 10 ^-7 microamperes to 400 microamperes or more) with a dynamic range of 6 digits and 3 digits can be achieved by simply replacing the electron gun while maintaining the vacuum in the vacuum vessel. An electron beam irradiation system capable of controlling the electron beam spot diameter with a dynamic range (0.016 to 100 micrometers or more) will be realized. By using this hybrid electron gun, the cathodoluminescence detection device becomes an analysis device in a high dynamic range that cannot be achieved by a conventional general cathodoluminescence electron beam irradiation system.

FIG. 2 shows a configuration diagram of an electron beam irradiation system. The electron beam irradiation system is mainly composed of an electron gun, an electron lens, and a deflection / astigmatism corrector. As shown in Table 1, electron guns generally have electron gun structures such as a thermal electron gun having a W hairpin emitter, a thermal electron gun having a LaB ₆ emitter, and a thermal field emission electron gun having a ZrO / W emitter. The hybrid electron gun of the present invention adopts a thermal electron gun having a LaB ₆ emitter and a thermal field emission electron gun having a ZrO / W emitter as shown in FIG. Originally, a thermal electron gun having a LaB ₆ emitter and a thermal field emission electron gun having a ZrO / W emitter require a dedicated electron lens and the performance of a deflection / astigmatism corrector, as well as the electron gun and its mechanical connection. However, they are made common and the electron gun part can be exchanged. At this time, the tip of the tip of LaB ₆ emitter adopted a tip with a tip angle of 90 ° and a diameter of 100 micrometers in order to realize a long life with little change in luminance. In particular, in order to obtain a large current, it is necessary to collect electrons emitted from the emitter in the first stage lens at a large incident angle. At this time, since the opening angle of the final stage lens is determined by a value obtained by multiplying the incident angle of the first stage lens by the reduction ratio, the final stage lens has a larger opening angle, and the influence of spherical aberration that increases with the cube of the opening angle is significantly large. It's not a good idea. On the other hand, when the reduction ratio is 1, that is, in an equal magnification system, the influence of spherical aberration can be suppressed. In this electron beam irradiation system, a hybrid electron gun is realized by introducing a detachable mechanism to these electron guns.

Generally, the light source diameter (crossover diameter) of a LaB ₆ emitter is about 10 macro meters. That is, in order to obtain a beam diameter on the order of several tens to several hundreds of micrometers, it is advantageous to reduce the reduction ratio (enlargement system) and suppress spherical aberration. The electron lens system is generally used as a reduction system, but this lens system has a reduction ratio of approximately 30 to 0.2. On the other hand, the thermoelectrolytic emission phenomenon of the ZrO / W emitter appears only in an ultra-high vacuum environment with a vacuum higher than 10 ^-10 Torr. For this reason, the vacuum degree of the electron gun is configured to be an exhaust system that can obtain 10 ^-10 Torr level. Exhaust system an orifice for differential exhaust disposed between the electron gun chamber and the lens system, were respectively the differential exhaust system for exhausting by an ion pump.

FIG. 4 shows the relationship between the beam spot diameter and the electron beam current that can be realized with the present hybrid electron gun. According to the above-described form, the electron gun having the LaB ₆ emitter capable of realizing high brightness, long life and high current stability compared with the electron gun having the W hairpin emitter covers the electron beam current control region of a large current, and By using a ZrO / W emitter, the beam spot diameter control region up to nanometer size, which cannot be reached by an electron gun with a LaB ₆ emitter, is covered. As a result, an electron beam current control with a 6-digit dynamic range (6 × 10 ^-7 microampere to 400 microamperes or more) and an electron beam spot diameter control with a 3-digit dynamic range (0.016 micrometer to 100)
It becomes an electron beam irradiation system with a high dynamic range capable of micrometer or more). Table 1 shows the performance of an electron beam irradiation system using this hybrid electron gun.

On the other hand, since the residual gas in the vacuum vessel reacts with the electron beam probe and causes sample contamination, it is necessary to devise an electron beam irradiation system body. In particular, since it is expected to become very remarkable under a large current, an ultrahigh vacuum compatible electron beam irradiation system having a vacuum higher than 10 ⁻¹⁰ Torr is required. The main gas emission source in the electron beam irradiation system is due to the structure used in the electron lens and the deflection / astigmatism corrector. In this electron beam irradiation system, an electrostatic type is adopted for the electron lens and the deflection / astigmatism corrector which are the gas emission sources. As a result, an environment in which the degree of vacuum in the vacuum vessel is better than 3 × 10 ⁻¹¹ Torr can be realized.

FIG. 5 shows an example in which an electron beam irradiation system using the present hybrid electron source is actually used. Here, the relationship of the CL emission intensity from the AlN thin film and the diamond thin film to the electron beam current is shown, and the thickness of the AlN thin film is about 1 nm. The CL signal from the diamond thin film plotted the emission due to exciton recombination showing an emission peak at 235 nm.

As can be seen from FIG. 5, the AlN thin film can achieve an increase of two orders of magnitude or more compared to the CL signal intensity using a conventional electron microscope. On the other hand, in the case of a diamond thin film, a phenomenon has been discovered in which the electron beam current rapidly increases with a certain electron beam current as a boundary. This phenomenon was first observed with a high-quality diamond film of low-defect density and high-purity device grade using this hybrid electron gun. This non-linear effect is thought to have been caused by the reduction of extrinsic recombination centers due to defects, impurity atoms, etc., and high-density excitons generated in the high excitation electron beam current region acting in the thin film. At the same time as the fundamental physical viewpoint of exciton behavior under high density, the wavelength of this emission is 235 nm, so it is important from the viewpoint of applied physics as a phenomenon directly connected to diamond deep ultraviolet light emitting devices. In particular, this non-linear behavior is a new physical phenomenon discovered in the excitation region that cannot be reached by a conventional cathodoluminescence device using an electron microscope, that is, a blank region in the research. Significance is enormous.

According to the present invention, the weakest cathodoluminescence signal measurable with a conventional high sensitivity cathodoluminescence detector can be further amplified as a CL signal intensity of two or more digits. In the present invention, an analysis apparatus in a high dynamic range that cannot be achieved by a general cathode luminescence electron beam irradiation system is realized by examining an electron beam irradiation system used in the present cathodoluminescence apparatus. The amplification of the weak CL signal intensity by two digits or more is epoch-making because it enables the evaluation of the definite amount of defects and impurities that influence the evaluation result of the material. That is, the present invention relates to a cathode luminescence spectrum, time / wavelength from a very small amount of impurities or defects in a semiconductor, metal, organic substance, or other ultra-thin film at a monoatomic layer level or a sub-monolayer level, or a semiconductor typified by a substance. It is extremely effective for steady-state or transient physical property evaluation and electronic state evaluation using the resolved cathodoluminescence image. At the same time, the electron beam current control with a 6-digit dynamic range and the electron beam spot diameter control with a 3-digit dynamic range constitute a single electron source by only replacing the electron gun while maintaining the vacuum of the vacuum vessel. The structure is not possible, and the hybrid electron gun has a high industrial utility value because it plays a technical role in all fields that require an electron beam as a high-density electron beam excitation source for materials.

The relationship between an electron beam current and a CL signal is shown. Here, the change of the exciton emission intensity from diamond with respect to the electron beam current when using the electron beam irradiation system of a typical electron microscope is plotted. The block diagram of the electron beam irradiation system of this invention is shown. FIG. 3 shows different parts diagrams for a (a) a thermal electron gun having a LaB ₆ emitter and (b) a thermal field emission electron gun having a ZrO / W emitter. The relationship of the beam spot diameter with respect to an electron beam current is shown. Change in CL emission intensity with electron beam current. The black circle shows the change in CL emission intensity from the diamond thin film and the white circle from the AlN thin film.

Claims (7)

An electron gun used in the electron beam irradiation system of the cathodoluminescence detector, with an electron beam current control (6 × 10 ^-7 microamperes to 400 microamperes or more) and a three-digit dynamic range. A plurality of electron guns with electron beam spot diameter control (0.016 micrometer to 100 micrometer or more) have been prepared, and a detachable attachment mechanism capable of hybrid connection for switching and utilizing each electron gun has been introduced. Electron gun for cathodoluminescence detection device. The cathodoluminescence detection device collects (1) an electron beam irradiation system, (2) a vacuum vessel, (3) an evacuation system, (4) a stage for holding the sample, and (5) cathodoluminescence emitted from the sample. A condensing optical system for light; (6) a light transfer system for transferring the collected light to the spectrometer; (7) a spectroscopic system for dispersing the transferred light; 2. An electron gun for use in a cathodoluminescence detection device according to claim 1, which is a cathodoluminescence detection device comprising a detection system for detecting light and (9) an analysis system for analyzing the detected signal. The cathodoluminescence detection device has ((1) an electron beam irradiation system, (2) a vacuum vessel, (3) an evacuation system, (4) a stage for holding a sample, and (5) cathodoluminescence emitted from the sample. A condensing optical system for condensing; (6) a light transfer system for transferring the collected light to the spectrometer; (7) a spectroscopic system for dispersing the transferred light; A detection system for detecting the detected light, and (9) a cathodoluminescence detection device comprising an analysis system for analyzing the detected signal, and (5) chromatic aberration in the condenser mirror constituting the condenser optical system. And a Cassegrain optical arrangement that can correct spherical aberration at the same time. While irradiating the sample with an electron beam, the cathode microscope luminescence from the electron beam irradiation area is acquired at the same time as a high-magnification optical microscope image of the sample is acquired in real time. An electron gun for use in cathode luminescence detecting device according to claim 1 is a cathodoluminescence detector apparatus according to claim Rukoto. 2. The electron gun for use in a cathode luminescence detection device according to claim 1, wherein the detachable attachment mechanism capable of hybrid connection replaces the electron gun while maintaining a vacuum in the vacuum vessel. The electron gun for use in the cathode luminescence detection device according to claim 4, wherein the vacuum is an ultra-high vacuum higher than 10 ^-10 Torr. The thermoelectron gun for use in a cathode luminescence detection device according to claim 1, wherein the electron gun is a thermoelectron gun having a W hairpin emitter. The electron gun for use in a cathode luminescence detection device according to claim 1, wherein the electron gun is a thermal electron gun having a LaB ₆ emitter and a thermal field emission electron gun having a ZrO / W emitter.