JPS63190239A - Method for measuring reflection electron energy loss fine structure - Google Patents

Abstract

PURPOSE:To obtain a small-sized device easy to utilize by slantly radiating an incident electron beam on the sample surface at a small angle and measuring the energy loss spectrum of nonelastic scattered electrons reflected from the sample surface to measure the fine structure. CONSTITUTION:High-speed electrons are radiated to the surface of a sample to be measured 8 at a low incident angle with a device as shown by the figure, the energy loss spectrum of the nonelastic scattered electrons reflected from the surface of the sample to be measured 8 is measured by an energy analyzer 9, and the spectrum equivalent to the inner shell-excited X-ray absorption spectrum is determined. The vibration component (EXAFS) indicated in the spectrum and the X-ray absorption near edge structure (XANES) are analyzed to obtain the information on the surface arrangement and electronic state. Accordingly, measurement is performed by incident electrons, thus a large-scale facility such as the synchrotron orbital radiation light is not required and a small-sized electron source is sufficient, and the difficult problem of the spectroscopy is eliminated and the device is made easy to handle.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reflected electron energy loss fine structure measurement method for obtaining surface structure information by irradiating a sample with an electron beam.

[Conventional technology]

Surface analysis has been considered to be a particularly difficult field, but in recent years, the need for surface analysis equipment has increased. The reason for this is that the influence of surfaces has increased with the miniaturization of electronic devices, and that functional surfaces, such as catalysts,
It is useful for analyzing the operating characteristics of gas detection sensors and the like based on surface reactions, and for improving surface protective films.

In surface evaluation, the three elements of evaluation are atomic arrangement (regular arrangement of atoms and interatomic distance), atomic composition (atomic composition ratio of surface layer), and electronic state (interatomic bonding state, interatomic electron distribution, and surface polarization). However, the most basic information about surfaces is the structural knowledge of atomic arrangement and interatomic distance.

Conventional structural analyzes of atomic arrangement include a method of analyzing using a microscope, a method of analyzing using a diffraction image, and the like. The latter analysis using diffraction images includes analysis using elastic scattered waves using X-rays, neutron beams, and electron beams, and analysis using inelastic scattered waves. Particularly in recent years, a method has been used to determine the interatomic distance by observing the vibrational structure that appears near the absorption of X-rays and applying numerical processing to it. In this method, the range from the absorption edge to around 30 eV reflects the multiple scattering effect, so for convenience of theoretical treatment, it is distinguished from the vibrational structure that follows, and the latter is EXA F S (
Extended X-ray Absorpt
ion Fine 5structure, wide area X-ray absorption fine structure), whereas the former is called
S (X-ray Absorption Nea
It is called Edge 5structure (X-ray absorption adjacent fine structure). Therefore, the inner shell XwA absorption spectrum contains a large structure XAN near the rise of the absorption edge.
ES and a small, slowly vibrating structure EXAFS further away can be seen simultaneously. The difference between the two is due to the difference in the kinetic energy of the photoelectrons emitted from the inner shell by X-rays, but the means to analyze them and the information obtained are also very different. XvA from EXAFS
Information can be obtained about the distance between the atom that absorbs and its surroundings, mainly the atom with the -th coordination number, and its coordination number.
XANES provides information about the three-dimensional structure and electronic state of the cluster to the extent that it reflects the spectrum.

The probability of inelastic scattering decreases as the loss energy ΔE increases, so the probability of inelastic scattering decreases as the loss energy ΔE increases.
) and the shallower inner shell (L of Al.

Excitation light from an excitation synchrotron (shell, etc.) is 200
~300eV is the area of greatest strength. This region is also the most difficult region to perform spectroscopy using synchrotron radiation.

Inelastic scattering of high-speed electrons was previously described by Bethe as 1
It was theoretically treated in the 1930s, and it was predicted that the cross section of inelastic scattering in the forward direction would reproduce the optical absorption cross section. However, it is only recently that such precise experiments have been carried out.

In particular, Brion et al. have compiled more than 60 papers on the optical absorption cross section of molecules using electron loss spectroscopy.

Since the electron loss differential cross section in the forward direction of high-speed electrons reproduces the optical absorption cross section, when an energy loss equivalent to ionization from the inner shell is observed, EXAFS and XANES can of course measure it using this method. become able to do.

In fact, using this method, gas-phase molecules and transition metals can be
The XANES of thin films of T i Oz has been measured. This measurement method does not use synchrotron radiation and is much cheaper than EXAFS or XANE.
It has the advantage that S can be measured.

[Problem that the invention seeks to solve]

Conventional EXAFS using synchrotron radiation has various problems. For example, (1) the signal in the fluctuating portion is weak, so an extremely powerful light source is required. ■It is necessary to irradiate with monochromatic light, so a precise monochromating device is essential. ■Measurement is possible even in the atmosphere, but atmospheric absorption correction must be taken into account. ■As a result, the light source requires a large facility and a very large magnetic field is placed to accelerate the electrons, resulting in large and expensive equipment that cannot be easily used in places such as laboratories.

Large-scale synchrotron radiation facilities require many people to operate, and strict restrictions on location and time make it difficult to conduct sufficient research. Furthermore, the method of observing EXAFS in the loss spectrum using a high-speed electron microscope requires cutting the sample into thin sections, which requires advanced processing techniques.

The present invention solves the above-mentioned problems, and aims to provide a method for measuring the fine structure of reflected electron energy loss that is small and easy to use.

[Means for solving problems]

To this end, the method for measuring the backscattered electron energy loss fine structure of the present invention places an electron gun, a solid sample on a holder, and an energy analyzer in an ultra-high vacuum, and injects an electron beam into the sample. In a backscattered electron energy loss microstructure measuring device that measures structures, inelastic scattering is used in which the energy of incident electrons is set to about 1 KeV or more, and the incident electron beam is obliquely incident on the sample surface at a small angle and reflected from the sample surface. It is characterized by measuring the fine structure by measuring the energy loss spectrum of electrons.

[Effect]

In the backscattered electron energy loss fine structure measurement method of the present invention, high-speed electrons are made incident on the sample surface at a low incident angle, and the energy loss of the backscattered electrons is measured (only electrons with small scattering angles are collected). A spectrum equivalent to an X-ray absorption spectrum can be obtained. Therefore, information about the surface arrangement, electronic state, etc. can be obtained by analyzing the vibrational components (EXAFS) and X-ray absorption edge near fine structure (XANES) appearing in the spectrum. In this case, since it is obliquely incident, it is sensitive to surface information, and equivalent information can be obtained without using a strong short wavelength light source. Furthermore, since it is extremely easy to change the energy of incident electrons and keep the incident intensity constant, changes in the depth direction can also be detected.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of one embodiment of the apparatus applied to the reflected electron energy loss microstructure measuring method of the present invention, FIG. 2 is a diagram for explaining the action on the microstructure due to external stimulation, and FIG. The figure shows an example of the geometry of incident electrons, Figure 4 is a diagram to explain the relationship between the scattering angle and reflected electron energy loss, and Figure 5 is a diagram to explain the magnitude of momentum transfer of high-speed electrons. This is a diagram.

In FIG. 1, 1 is an electron gun, 2 is a focusing coil, 3 is a deflection coil, 4 and 5 are observation windows, 6 is a work function measuring device, 7 is a standard sample, 8 is a measurement sample, 9 is an energy analyzer, 10
1 is a manipulator, 11 is a fluorescent plate, 12 is an energy analyzer operating section, and 13 is an ultra-high vacuum pump.

For example, an FE GUN is used as the electron gun 1 in order to provide high brightness and fine focus to increase sensitivity. The manipulator 10 is capable of rotation around an axis, tilting, and three-dimensional movement up and down, left and right, and controls the center position and angle of the measurement sample 8, thereby controlling the electron beam irradiated from the electron gun l. The irradiation angle for the measurement sample 8 is adjusted. The energy analyzer operation unit 12 skewers the energy analyzer 9 for 7 minutes in the measurement state, thereby adjusting the take-out angle of the energy analyzer 9. The fluorescent plate 11 is placed behind the measurement sample 8 , and the energy analyzer 9 rotates around the measurement sample 8 according to the operation of the energy analyzer operating section 12 and is moved away from the straight line connecting the measurement sample 8 and the fluorescent plate 11 . When this happens, the diffraction pattern of the measurement sample 8 is copied onto the fluorescent surface, thereby making RHEED observation possible at the same time. The ultra-high vacuum pump 13 uses, for example, a spatium ion pump or a cryopump as the main pump, and a sublimation pump in combination with the 10-? pa
Or preferably achieve an even higher ultra-high vacuum.

In the backscattered electron energy loss fine structure measurement method of the present invention, high-speed electrons are measured on a measurement sample 8 using an apparatus as shown in FIG.
The energy loss spectrum of the inelastically scattered electrons reflected from the surface of the measurement sample 8 is measured by the energy analyzer 9 (only the electrons with small scattering angles are collected), and the energy loss spectrum of the inelastically scattered electrons is measured by the energy analyzer 9. Obtain a spectrum equivalent to the Xi absorption spectrum. The vibrational components (EXAFS) that appear in the spectrum and the fine structure near the X-ray absorption edge (XANE)
S) is analyzed to obtain information about surface arrangement, electronic state, etc.

First, EXAFS measurement will be explained. When light passes through an object, it absorbs light of a certain wavelength, causing a color change in the emitted light. This is because atoms only absorb light that can cause them to resonate. A similar phenomenon occurs when X-rays (light with a short wavelength) are incident, but if you look closely, you will find that when absorption occurs, if you change the wavelength of the X-rays, the amount of absorption becomes thicker (or smaller). This fluctuation is called the absorption fine structure.Now, as shown in Figure 2, when one atom A receives external stimulation (in this case, X & JI), the electrons it has When one is thrown out, it will hit the neighboring atom B and bounce back.An electron has the characteristics of a wave,
Therefore, due to the interference effect between the electrons emitted from A and the electron waves that are scattered once by B and returned, a fine structure is created in the absorption structure unique to atoms. The interval of this structural variation and the interval between atoms are connected by a relatively simple theoretical formula, and the interatomic distance is calculated from the experimental data of EXAFS.

In this case, of course, this method can be applied if the atoms are regularly arranged and the entire sample is a single crystal. In addition, in a small area, the atomic arrangement is fixed, but if the entire sample is not aligned, for example, small dice of the same shape are not lined up neatly, but are scattered with their orientations not aligned. , we can find the distance between the particles that make up the dice.

As mentioned earlier, EXAFS has a fine structure over a wide range of several hundred eV from the absorption edge, whereas
The fine structure in the V range is caused by different causes than in EXAFS. Whereas EXAFS is caused by a single scattering of electrons that fly out in response to an external stimulus,
With XANES, since the energy of electrons is small, they are bounced off many times by surrounding atoms, and this occurs due to the interference of multiple scatterings, so it is difficult to detect the positions of light elements (C, N, 0, etc.) that are difficult to detect with EXAFS. It will be useful to know. The same is true when using electrons instead of light, and E
Along with XAFS, XANES can also measure light elements, and is effective in analyzing materials and phenomena that are difficult to use with other methods, such as organic matter and gas adsorption/desorption phenomena on surfaces.

The conditions for reproducing the light absorption cross section by inelastic scattering of electrons are, firstly, that the kinetic energies of the incident and scattered electrons are sufficiently large (the Born approximation can be used). Momentum is Pt sIf the momentum of the incident electron is P, then the momentum transfer of the high-speed electron ΔP=Pr The product of the magnitude of Pt and the magnitude of the excited inner orbit is smaller than 1.

As can be seen from FIG. 5, the magnitude of ΔP is the smallest in forward scattering. Figure 3 shows three typical geometric arrangements, among which +8) and (bl are the arrangements that reproduce the light absorption cross section. To the best of the inventors' knowledge, no measurement example has been found; even in the arrangement (C), /y" in Italy ++, -
'f 礒（Tuna・Jun 1; Kaya Boo% 1 k A I-CV
A f"C' JJL 77% a'lt key is observed in the loss spectrum. Of course, in this case EXAFS
Although the formula for analyzing cannot be applied directly, it contains local geometric information.

When an incident electron loses part of its energy and is scattered, the method of detecting the energy loss is called the electron energy loss spectrum method. However, even though it is simply an energy loss spectrum, the information it seeks to obtain for material evaluation is completely different depending on the implementation conditions. Energy loss of reflected electrons has characteristics as shown in FIG. 4 depending on the scattering angle, and in order to obtain EXAFS, the scattering of electrons incident at relatively high energy must be within the small-angle scattering range.

The electron energy loss spectrum is based on the incident energy E0
It can be divided into the following three areas depending on the information obtained.

■, low energy region (E6≦10eV) surface elementary excitation (
It is used to investigate the dispersion of surface phonon excitation (surface phonon excitation, surface electron excitation), vibration of surface adsorbed species, etc. Since these elementary excitations are on the order of 10 meV (fmeV=8 cm-'), that much resolution is required. For example, when Co is adsorbed on a metal surface, it can be determined whether the CO is dissociatively adsorbed or not based on the presence or absence of Co stretching vibration. (Dissociation adsorption if there is no Co stretching vibration) ■, intermediate energy region (E, ~100 eV, LE E
D Sff region) Suitable for investigating electronic excitation and surface plasmon excitation on the surface. Since these excitation energies are on the order of 1 to 10 eV, no resolution is required.Since the moment of excitation is not based on the dipole selection rule, optically prohibited pans and dos are also observed.

■High energy region (Eo>1keV) It has long been used for research on bulk plasmons.

This revealed the dispersion of plasmons and the regularity of the intensity of energy loss due to plasmons.

Finally, in the high energy region, the Horn approximation, which treats the electron wave function as a plane wave, holds true, making it much easier to handle. However, even using this approximation, it is difficult to interpret inelastic scattering at a general scattering angle, but if the scattering angle is sufficiently small, the inelastic scattering intensity exactly reproduces the optical absorption intensity. That is, it follows the electric dipole approximation law. In particular, if excitation from the inner shell is observed, EXAFS and XANES can be measured without using synchrotron radiation.

By analyzing these data, it becomes possible to obtain information about the local geometric structure and electronic structure around the excited atoms. When the scattering angle is large, the scattering intensity is small and the electric dipole approximation is broken.

FIG. 6 is a diagram showing an example of the configuration of a system for measuring a work function. The standard sample is brought close to the measurement sample and the distance between the two is changed periodically. When the two potentials are different, an alternating current flows, and this signal is sent from the preamplifier 21 to the phase detector 2.
2 to the DC amplifier 27 and integrated by the integrator 28. Therefore, the amount of feedback when the detection signal becomes 0 due to this feedback, that is, the output value of the integrator 28, is recorded in the recorder 29 as a potential difference between the two. in this way,
Once the work function can be measured, the state of surface polarization can be determined.

As described above, the backscattered electron energy loss fine structure measurement method according to the present invention enables highly accurate surface analysis, determines the distance between surface atoms of catalyst materials, surface adsorbed substances, etc., and determines the distance between surface atoms in amorphous silicon and ceramics. This can contribute to the determination of atomic spacing, research on the surface state of multi-Ji thin films, surface-modified layers, and other fields.

Note that the present invention can be modified in various ways, and is not limited to the above-mentioned embodiments. It may also be used to apply vibration to the sample and enable signal detection with high sensitivity.

When incident electrons are scattered while the sample is vibrating, the scattering intensity changes significantly depending on the scattering angle as shown in Figure 4. Therefore, a phase detection amplifier is used to detect signal fluctuations synchronized with the excitation vibrations. By using this, signals can be extracted with high sensitivity. This detection method, which can be appropriately called the angle modulation method, is extremely effective for low-angle scattering experiments.

Even when measuring the angular dispersion near the diffraction point of RHEED, it is easy to measure using this method,
It is also a powerful means of creating new ideas that have not been done before, as it can be widely applied to angle-resolved experiments in electron energy loss spectroscopy.

Furthermore, excitation of the sample can of course be useful in measuring the surface potential using the Kelvin method as shown in FIG. Since the reference electrode used to measure the surface potential difference can be stably vibrated at a position extremely close to the sample surface, in this case as well, the amplitude is significantly improved and accuracy is increased.

Furthermore, by installing a charged particle generator that integrates an electron source and an ion source in place of the electron gun, it becomes possible to determine the surface defect structure by ion scattering spectroscopy.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, compared to transmission electron energy loss spectroscopy, this method uses oblique incidence to obtain surface information, unlike the method that only obtains average information of the bulk. Data can be obtained and observation near the surface becomes possible. Compared to back reflection energy loss spectroscopy, accurate EXAFS and XANES vibrational components can be provided. Compared to methods using synchrotron radiation, which require large-scale equipment and manpower, experiments can be easily performed on a laboratory scale.

In addition, since measurement is performed by electron injection, large-scale facilities such as synchrotron synchrotron radiation are not required, and a small electron source can be used, eliminating difficult problems with spectroscopic technology and making it easier to handle.■ Irradiation energy can be changed freely, and the electron energy loss spectrum can provide different information in the depth direction depending on the energy level of the incident electrons. ■It is relatively inexpensive. Although measurement in vacuum is required, this is not a problem since vacuum is essential for surface research.

In the method using light incidence, the intensity of transmitted light is measured or photoelectrons are detected, whereas in the case of electron incidence, EXAFS can be obtained by analyzing the energy of scattered electrons. Furthermore, since reflected electrons are observed instead of transmitted electrons, there is no need to finish the sample uniformly thin, any sample surface can be targeted, and there is no need to prepare a single sample that requires skill. Therefore, sample preparation becomes easy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of one embodiment of the apparatus applicable to the reflected electron energy loss microstructure measurement method of the present invention, FIG. 2 is a diagram for explaining the action on the microstructure due to external stimulation, and FIG. The figure shows an example of the geometry of incident electrons, Figure 4 is a diagram to explain the relationship between the scattering angle and reflected electron energy loss, and Figure 5 is a diagram to explain the magnitude of momentum transfer of high-speed electrons. FIG. 6 is a diagram showing an example of the configuration of a system for measuring a work function. In Figure 1, 1 is an electron gun, 2 is a focusing coil, 3 is a deflection coil, 4 and 5 are observation windows, 6 is a work function side regulator, 7 is a standard sample, 8 is a measurement sample, and 9 is an energy analyzer. , 10
1 is a manipulator, 11 is a fluorescent plate, 12 is an energy analyzer operating section, and 13 is an ultra-high vacuum pump. Applicant New Technology Development Corporation Agent Patent Attorney Ryukichi Abe Figure 1 Figure 2 Figure 3 (4) (C) 0'5'TO"Is'20'
2! 5"37' 袈女l!l Izumi 5th figure 6th figure

Claims (5)

[Claims] (1) A backscattered electron energy loss microstructure measuring device that measures the microstructure of the sample by arranging an electron gun, a solid sample on a holder, and an energy analyzer in an ultra-high vacuum, and injecting an electron beam into the sample. In this case, the energy of the incident electron is 1K
eV or more, and the fine structure is measured by making the incident electron beam obliquely incident on the sample surface at a small angle and measuring the energy loss spectrum of inelastically scattered electrons reflected from the sample surface. Backscattered electron energy loss fine structure measurement method. (2) The structure change in the depth direction from the surface of the sample to the inside is measured by changing the energy value and angle of incidence of the incident electron beam and the detection angle of the energy analyzer. The method for measuring the backscattered electron energy loss fine structure described in Section 1. (3) Backscattered electron energy loss fine structure measurement according to claim 1, characterized in that the incident angle of the electron beam and the measurement position of the sample are changed by operating the sample holder from outside the vacuum container. Method. (4) The method for measuring the fine structure of reflected electron energy loss according to claim 1, characterized in that the detection angle of the energy analyzer is changed by operating from outside the vacuum container. (5) A method for measuring reflected electron energy loss microstructure according to claim 1, characterized in that a fluorescent plate is installed in front of the electron gun to also measure reflected high-speed electron diffraction.