JP2000299079A - Energy filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an energy filter image selecting the prescribed energy range by providing a means periodically changing the blocking potential of a blocking potential filter, holding a first blocking potential for a first period, holding a second blocking potential for a second period, and repeating the process at the cycle of the sum of the first period and the second period. SOLUTION: An ultraviolet radiating device 12 radiates ultraviolet rays to a sample 10 through a quartz port 13. The energy of ultraviolet rays emits photoelectrons from a region exceeding the work function on the surface of the sample 10. The space intensity distribution of photoelectrons is energy- selected by a blocking potential energy filter 7 via an objective lens and a deceleration lens 6. The pulse generator 16 of a computer system 15 applies periodic blocking potentials to the energy filter 7. A blocking potential E1 is held for a period τ1, then a blocking potential E2 is held for a period τ2, and the process is repeated at the cycle of the period of τ1+τ2, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron energy filter, and more particularly to an analysis or observation device provided with an energy filter.

[0002]

2. Description of the Related Art Methods based on various principles have been developed for energy filters for electrons. One of the methods using an electric field is a filtering potential type filter, and the other is a method using a magnetic field. An Ω filter and a Wien-filter, which is one of methods using both electric and magnetic fields, are known (“Electron Ene
rgy-Loss Spectroscopy in the Electron Microscope ”
by RFEgerton: PLENUMPRESS 1989). Among these, the blocking potential type filter has a simple structure and a low manufacturing cost, and is therefore used as a simple energy filter in a low-speed electron diffraction device, a reflection high-speed electron diffraction device, a photoelectron microscope, or the like.

The operation of a conventionally used blocking potential type filter will be described by taking as an example a case where the filter is mounted on a photoelectron microscope. Consider a solid surface in which two types of work functions, φ1 and φ2, are mixed. When this surface is irradiated with monochromatic (energy hν>φ2> φ1), E1 is emitted from the region φ1.
Photoelectrons having a kinetic energy of not more than = hν−φ1 are emitted, and photoelectrons having a kinetic energy of not more than E2 = hν−φ2 are emitted from the region φ2. Assuming that E is a set value of the blocking potential type filter (electrons whose initial kinetic energy is less than Er are blocked), if E <E2, a part of both photoelectrons from φ1 and φ2 pass through the energy filter. So both regions are observed with some contrast. If E2 <E <E1, the photoelectrons emitted from the region φ2 cannot pass through the energy filter at all, so that only the region φ1 is observed as an image. If E1 <E, it is blocked by all optoelectronic filters. By changing the blocking potential E in this way, it is possible to measure the work function of the surface or to identify regions having different work functions.

[0004]

The blocking potential type energy filter is a high-pass type energy filter that allows electrons exceeding a specific energy to pass therethrough. It is not possible to select a specific range of energy like a band-pass type energy filter. Can not. Due to this limitation, for example, when a blocking potential type filter is applied to a photoelectron microscope, it is generally not possible to separate and display a region having a specific work function in one energy filter image (the photoelectron only in the region φ2 described above). This corresponds to the lack of a microscope image).

A first object of the present invention is to eliminate this restriction in the blocking potential type filter and to provide a means for forming an energy filter image for selecting a specific energy range. Still another object of the present invention is to provide a means for separating energy filters not only in a single energy range but also in a plurality of energy ranges and forming them quasi-simultaneously.

[0006]

According to the present invention, the above object is achieved by taking the following measures.

(1) The energy filter of the present invention includes means for periodically changing the stop potential E of the stop potential filter. For example, an energy filter that holds the blocking potential E1 for a time τ1 and subsequently holds the blocking potential E2 for a time τ2, and repeats this with a period of time τ1 + τ2.

(2) The present invention has a plurality of storage areas for storing a plurality of energy filter images, selects a plurality of energy filter images picked up by the image pickup means, and distributes the selected energy filter images to the plurality of storage areas. It has means for storing. For example, the energy filter image captured at the capture time of τ1 under the condition of the blocking potential E1 is stored in the storage area 1, and the energy filter image captured at the capture time of τ2 under the condition of the blocking potential E2 is stored in the storage area 2. You. The energy filter images stored in these storage areas are repeatedly updated at a period τ1 + τ2.

(3) The present invention performs an operation between images from a plurality of energy filter images stored in the storage area,
Means for sequentially and periodically executing a process of displaying or storing the resulting image is provided. For example, the blocking potential E1
From the energy filter image I1 stored in the storage area 1 at the capture time of τ1,
, The energy filter image I2 stored in the storage area 2 is subtracted for each pixel, and the result is stored in the storage area or displayed on a monitor.

According to the present invention, the state of a sample to be observed often changes every moment. In the above example, the area φ1 and the area φ2 change with time. If the present invention is used, it is possible to identify the area φ1 and the area φ2 and observe and record how these areas change in real time.

[0011]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram of a photoelectron microscope equipped with an energy filter according to a first embodiment of the present invention. The barrel 2 of the photoelectron microscope mounted on the vacuum vessel 1
Is a three-stage electrostatic lens and deceleration lens unit 6 including an objective lens 3, an intermediate lens 4, a projection lens 5, an energy filter 7, a micro channel plate 8,
And a fluorescent screen 9. Sample 10 to be observed
Is set on the sample stage 11 and the ultraviolet light generator 12
UV light is applied to the sample through the quartz port 13 from above. Photoelectrons are emitted from the region where the energy of the ultraviolet light exceeds the work function of the sample surface. The spatial intensity distribution of the photoelectrons is expanded by passing through the three-stage electrostatic lens, and after being appropriately decelerated by the deceleration lens section 6, the energy is sorted by the blocking potential type energy filter 7. That is, only electrons having kinetic energy equal to or greater than the set value pass through the energy filter 7. The signal intensity of the electrons that have passed through the energy filter 7 is amplified by the microchannel plate 8, and a photoelectron energy filter image is formed on the fluorescent screen 9. The photoelectron image formed on the fluorescent plate 9 can be observed from the atmosphere side using the imaging device 14.

The computer control and processing system 15 comprises:
This is for controlling a blocking potential applied to the energy filter, and for taking in a photoelectron image picked up by the image pickup device 14 and executing image processing. The pulse generator 16 applies a periodic blocking potential to the energy filter 8 according to a command transmitted from the computer. For example, assume that the blocking potential E1 is held for a time τ1, and then the blocking potential E2 is held for a time τ2, and the time τ1 +
This is repeated with τ2 as a cycle. The image captured by the imaging device 14 is allocated to a plurality of areas of the frame memory 18 by the frame memory selector 17 and recorded in synchronization with the fluctuation of the blocking potential applied to the energy filter 8. The image stored in the frame memory is subjected to arithmetic processing between the images by the image processor 19, and the result is displayed on the monitor 20. The operation between the images may be any operation depending on the purpose. For example, a simple subtraction process, or a subtraction after multiplying by a coefficient according to the luminance level or the value of τ1, τ2, or Suitable 2
Subtraction after performing the value conversion processing is considered. It is desirable that the time required for processing such as image capture and calculation be within the fluctuation period τ of the blocking potential τ = τ1 + τ2. The calculation result is displayed in real time. If the processing time exceeds τ1 + τ2, it is possible to set an appropriate dead time and set the period τ to τ> τ1 + τ2.

FIG. 2 shows a reflection high-speed electron diffractometer (RHEE) equipped with an energy filter according to a second embodiment of the present invention.
It is a block diagram about D). The reflection high-speed electron diffraction device equipped with an energy filter is integrated with a vacuum vessel 21, a field emission type electron gun 22, an electron lens system 23, a sample 24 and a sample stage 25 in the vacuum vessel, and a fluorescent plate. An energy filter 26 is provided. The energy filter 26 includes two metal meshes 27 and 28,
It is composed of a fluorescent plate 29.

Electrons emitted from the electron gun 22 are focused and scanned on a sample 24 by a focusing lens and a deflection lens provided in an electron lens system 23. While the fluorescent plate 29 and the metal mesh 27 on the sample side are kept at substantially the ground potential, a blocking potential that varies with time is applied to the metal mesh 28 on the fluorescent plate side by the function generator 30. The common potential of the function generator 30 is set to the same high potential as that of the electron gun 22, and a fluctuating voltage is applied with the common potential as the origin.

The electron beam accelerated to the kinetic energy E by the acceleration voltage of the electron gun 22 is elastically or inelastically scattered on the sample surface. Among them, the energy filter image is formed by the blocking potential applied to the metal mesh 28.
Only electrons with energies above E '. That is, the electrons passing through the metal mesh 27 are decelerated by the electric field between the metal meshes 27-28, and only the electrons having the energy exceeding the stop potential E 'pass through the metal mesh 28. The electrons that have passed through the metal mesh 28 are again accelerated by the electric field between the metal mesh 28 and the fluorescent screen 29 to form an energy filter image on the fluorescent screen. This energy filter image is directly observed with the naked eye from the atmosphere side or photographed by the imaging device 31.

The computer system 32 controls the function generator 30 and, at the same time, controls electron beam scanning, captures images captured by the imaging device 31, and performs image processing. The image captured by the imaging device 31 is synchronized with the function generator 30 so that the frame memory selector 33
An energy filter image corresponding to a periodically fluctuating blocking voltage can be separated and assigned to a plurality of regions of the frame memory 34. The image stored in each frame memory is processed by the image processor 35, and then displayed on one or a plurality of monitors 36, recorded, or stored in another frame memory.

As an example, a case where a scanning RHEED image is photographed from a luminance signal in an appropriate area in an energy filter image will be considered. If the electron scanning time (or staying time) per pixel is τ, the time τ1 becomes the blocking potential E1, τ2 =
τ−τ1 is set to the blocking potential E2, and this is periodically repeated. The energy filter signals E1 and E2 are distributed to the frame memories 1 and 2 for each pixel in synchronization with the scanning of the electron beam. In order to obtain an energy filter image of electrons having energies between E2 and E1, the frame memory 1 may be subtracted from the frame memory 2 for each pixel, and the result may be stored in the frame memory 3. As described above, the high-pass type energy filter is used as if it has the function of a band-pass type energy filter by periodically changing the stop potential and capturing and processing the energy filter image in synchronization with the fluctuation. It becomes possible.

[0019]

According to the present invention, in an observation device such as a photoelectron microscope, a reflection high-speed electron diffraction device, or a low-speed electron diffraction device, an energy filter image formed by electrons having a specific range of energy can be obtained almost in real time. This has the effect of becoming

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a photoelectron microscope equipped with an energy filter according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a reflection high-speed electron diffraction apparatus equipped with an energy filter according to a second embodiment of the present invention.

[Explanation of symbols]

 1, 21 Vacuum container 2 Lens barrel 3 Objective lens 4 Intermediate lens 5 Projection lens 6 Reduction lens 7, 26 Energy filter 8 Microchannel plate 9, 29 Fluorescent plate 10, 24 Sample 11, 25 Sample stage 12 Ultraviolet irradiation device 13 Quartz port , 31 imaging device 15, 32 computer system 16 pulse generator 17, 33 frame memory selector 18, 34 frame memory 19, 35 image processor 20, 36 monitor 22 electron gun 23 electron lens system 27, 28 metal mesh 30 function generator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G001 AA03 BA08 BA14 BA18 CA03 DA09 EA06 FA06 GA01 GA06 GA09 HA01 HA07 HA12 HA13 JA02 JA11 JA13 JA14 KA01 SA02 SA03 SA11 5C033 NN02 NP04 5C038 KK15 KK17 KK18

Claims (6)

[Claims] 1. A blocking potential type energy filter for selectively passing only electrons having a kinetic energy exceeding a certain set value, comprising: means for periodically changing different set blocking potentials. filter. 2. The energy filter according to claim 1, further comprising means for separately storing energy filter images formed by different blocking potentials. 3. The image processing apparatus according to claim 1, further comprising means for performing an operation between the images on the energy filter images formed by different blocking potentials, and displaying or storing the operation result.
An energy filter according to claim 1. 4. An emission electron microscope having the energy filter according to claim 3. 5. A low-speed electron diffraction apparatus having the energy filter according to claim 3. 6. A reflection high-speed electron diffraction device having the energy filter according to claim 3.