JP3404527B2 - Photoelectron measurement method and photoelectron measurement system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the determination of crystal structures of industrial materials such as miniaturized electronic devices and thin film materials, evaluation of crystallinity, identification of impurity positions, and tracking of structural changes due to temperature changes and chemical changes. The present invention relates to a photoelectron measuring method and a photoelectron measuring system using photoelectron spectroholography, which is effective and detects the intensity distribution pattern of photoelectrons emitted by irradiating a sample with X-rays and acquires an atomic image of the sample by using Fourier transform. .

[0002]

2. Description of the Related Art Photoelectron spectroscopy holography is known as a structure imaging method at the atomic level, which is a combination of photoelectron spectroscopy and holography, which is a technique for recording a three-dimensional structure of a material. For photoelectron spectroholography, see, for example, J. J. Barto
n, "Photoelectron Holograp
hy ", Phys. Rev. Lett. 61, 1356.
(1988). Figure 4 shows the concept of this content.
Will be described with reference to. Among the photoelectrons excited and emitted by irradiating the sample with X-rays, the photoelectron intensity of the photoelectron intensity derived from the predetermined core level of the specific element of this sample is analyzed by the energy analyzer over the entire solid angle extended from the sample. The photoelectron intensity distribution pattern relating to this solid angle can be obtained by detecting using the. This intensity distribution pattern is caused by the interference between the photoelectron-emitted atoms that directly reach the analyzer and those that are scattered after being scattered by the surrounding atoms, so if we regard each as a reference wave and an object wave in holography, Holography at the level is possible. An atomic image can be obtained by Fourier-transforming a hologram image in which the intensity distribution pattern is standardized.

An example of performing photoelectron measurement using photoelectron spectroholography is described in, for example, L.W. T.
Terminello, J .; J. Barton, and
D. A. Lapiano-Smith, "Holog
radical Imaging of Atoms U
Sing Multiple-Wave-Number
Electron Angular Distrib
Motion Patterns ", Phys. Rev.
Lett. 70, 599 (1993). An example of executing this measurement will be described with reference to FIG. In addition, here, FIG. 5 is a schematic diagram showing a measurement system used for performing this measurement. This measurement system uses synchrotron radiation to generate multi-wavelength X-rays.
It has a multi-wavelength X-ray source 11 that radiates rays, and an X-ray spectroscopic system 12 that disperses the X-rays emitted from the X-ray source 11 and extracts predetermined X-rays. The X-ray having a predetermined first wavelength extracted from the X-ray spectroscopic system 12 is applied to the sample 13 to emit photoelectrons excited by the X-ray. By using the energy analyzer 14, scanning for detecting the photoelectrons over a predetermined solid angle extending from the irradiation spot is executed, and the first hologram image in which the photoelectron intensity distribution pattern is standardized is acquired. Similarly,
Second to ninth hologram images corresponding to eight X-rays respectively having different predetermined second to ninth wavelengths are acquired. The first to ninth hologram images are respectively Fourier transformed to obtain the first to ninth atomic images, respectively. These first to ninth atomic images are superposed in consideration of the phase, and an atomic image of the sample is acquired.

Further, photoelectron measurement, which has a relatively large correction effect on the distortion of an atomic image due to scattering anisotropy, is described in B. P. Toner, Z. -L. Han, G .;
R. Harp, and D.H. K. Saldin, Phy
s. Rev. B43, 14423 (1991). This is SWIFT (Scatredred-
A method called Wave-Included FT) is used.

[0005]

Problems to be Solved by the Invention Phys. Rev. L
ett. The measurement system of FIG. 5 described in 70, 599 (1993) requires a large amount of data in order to acquire each of the nine hologram images, so that the measurement time is long. Furthermore, since the measurement time is long, for example, adhesion of stains such as charcoal, water or hydrogen on the clean surface of the sample,
Oxygen loss in the superconductor and the change of calcium fluoride to calcium oxide due to X-ray irradiation greatly deteriorate the sample during measurement, which impairs the reliability of data.

Further, the measuring system of FIG. 5 has a small correction effect on the distortion of the atomic image due to the anisotropy of electron scattering, which is related to forward scattering, so that the error of the atomic position is large. In addition, Phys. Rev. B43, 14423
The photoelectron measurement of (1991) cannot be applied to a sample having an unknown structure when correcting the distortion of an atomic image due to the anisotropy of electron scattering.

Further, since the measurement system of FIG. 5 has a multi-wavelength X-ray source utilizing synchrotron radiation,
The scale of the system is very large, and the development cost of the device related to this system is very high. As a result, in general, the synchrotron radiation facility is often constructed as a public shared-use experimental facility. In this case, the experiment time allowed for each experimenter is limited, and the confidentiality in the industrial material development process is impaired. Further, the measurement system of FIG. 5 requires an X-ray spectroscopic system that disperses the X-rays emitted from the X-ray source and extracts predetermined X-rays.

Therefore, the object of the present invention is to shorten the measurement time and to reduce the error in the atomic position by increasing the correction effect for the distortion of the atomic image due to the anisotropy of electron scattering. It is possible to provide a photoelectron measuring method and a photoelectron measuring system which can be performed and does not need to use a special facility.

[0009]

In order to achieve the above-mentioned object, the photoelectron measuring method according to claim 1 of the present invention is such that two X-rays having different wavelengths are simultaneously irradiated to an irradiation spot of a sample, Two photoelectrons with different energies respectively excited by two X-rays are emitted from this irradiation spot, and a photoelectron spectrum of these two photoelectrons is simultaneously detected over a predetermined solid angle extending from this irradiation spot. , Obtaining a photoelectron spectrum detection value, and calculating two hologram images corresponding to the two photoelectrons based on the photoelectron spectrum detection value,
The difference between these two hologram images is calculated to calculate a difference hologram image, and the difference hologram image is Fourier-transformed to calculate an atomic image.

By simultaneously detecting two photoelectrons having different energies, which are emitted by two X-rays having different wavelengths, which are simultaneously irradiated to the sample, the scanning for simultaneously detecting the photoelectrons is executed only once, and an atomic image is obtained. Can be obtained.
Moreover, the number of data to be processed can be reduced by using only two hologram images. Therefore, the measurement time can be shortened. Furthermore, since the measurement time can be shortened, deterioration of the sample such as aging of the sample can be reduced.

When the difference in energy between the two X-rays is small, the anisotropy of the electron scattering factor is canceled in the step of obtaining the difference hologram image by taking the difference between the two hologram images. The effect of correcting the distortion of the atomic image obtained from the difference hologram image can be increased. Further, by simultaneously detecting the photoelectron spectra of two photoelectrons over a predetermined solid angle extending from this irradiation spot, the difference between the direction in which the energy of one photoelectron is detected and the direction of the other photoelectron is reduced. As a result, the error relating to the difference in this direction of the difference hologram image can be reduced. Therefore, the error in the atomic position can be reduced.

The system scale can be reduced by using only two X-rays having different wavelengths. Therefore, it is not necessary to use a special facility.

According to a second aspect of the present invention, there is provided a photoelectron measuring system, which comprises a sample support for supporting a sample and two samples having different wavelengths at irradiation spots of the sample which are arranged at a predetermined distance from the sample support. Simultaneous irradiation with X-rays
An X-ray source for emitting two photoelectrons having different energies respectively excited by two X-rays from the irradiation spot, and an energy analyzer arranged at a predetermined distance from the sample support, At least one of the sample support and the energy analyzer is rotated to perform scanning for simultaneously detecting the photoelectron spectra of the two photoelectrons over a predetermined solid angle extending from the irradiation spot, so that the photoelectrons are detected. Means for outputting spectrum detection values, hologram image acquisition means for respectively acquiring two hologram images corresponding to the two photoelectrons based on the photoelectron spectrum detection values of the energy analyzer, and these two hologram images Difference hologram image acquisition means for obtaining the difference hologram image as a difference hologram image, and this difference hologram image Is characterized by having the atomic image acquisition means for the Fourier transform value with atomic images, the.

This photoelectron measuring system has substantially the same operation and effect as the photoelectron measuring method according to claim 1 of the present invention.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3 in the accompanying drawings. Here, FIG. 1 is a schematic diagram showing the configuration of the embodiment of the present invention. The sample which is irradiated with X-rays and emits photoelectrons is supported by the sample support 1. An X-ray source 2 capable of simultaneously radiating X-rays X1 and X2 having two different wavelengths relatively close to each other at a predetermined distance in a predetermined direction on the side of the sample which is irradiated with the X-rays and measured in the same direction. Is provided. On the same side of the sample, an energy analyzer 3 is arranged so as to be rotatable about a spherical shell centered on the same side. The energy analyzer 3 is connected to the processing unit 4. The processing unit 4
It comprises a hologram image acquisition means 5 to which the output signal of the energy analyzer 3 is input, a differential hologram image acquisition means 6 following the acquisition means 5, and an atomic image acquisition means 7 further following the acquisition means 6.

The X-ray source 2 will be specifically described below.
The X-ray source 2 has a metal target (anticathode) which accelerated electrons collide with and emit X-rays. This anticathode is formed of a metal composed of one element. When the accelerated electrons strike the anticathode, a plurality of characteristic X-rays of this element are simultaneously emitted. Of these X-rays, X-rays each having two adjacent and relatively close wavelengths (for example, Kα ray and Kβ ray)
However, they are simultaneously radiated as X-rays X1 and X2, respectively. Table 1 (A) shows an example of adjacent characteristic X-rays of the same element.

[0017]

[Table 1]

For example, the energy difference between them is 43 eV.
X-ray X1 of MgKα (1254 eV), which is relatively close to
And an X-ray X2 of MgKβ (1297 eV) at the same time have an anticathode formed of a metal made of Mg.

The first modification of the X-ray source 2 has an anticathode formed by depositing metals composed of two different elements at different positions. The accelerated electrons collide with two metals, respectively, and a plurality of characteristic X-rays are emitted from these two metals, respectively. Table 1 (B) shows an example of adjacent characteristic X-rays of different elements. Among these characteristic X-rays, X-rays each having two adjacent and relatively close wavelengths (for example, M having an energy difference of 233 eV).
gKα (1254eV) and AlKα (1487eV))
However, they are simultaneously emitted as X-rays X1 and X2. Furthermore, the second modification of the X-ray source 2 has an anticathode formed of an alloy composed of two different elements. Even when the X-ray source configured as described above is used, X-rays having two wavelengths relatively close to each other are simultaneously emitted.

As the X-ray source 2, commercially available fixed anticathode type and rotating anticathode type can be used. For example, Rigaku Denki's tabletop rotating anticathode X-ray generator UltraX18, Va
The X-ray source XR3 series for X-ray photoelectron spectroscopy of cum Generators can be used as it is or after improvement.

As the energy analyzer 3, a commercially available electrostatic hemisphere type, toroidal type for simultaneous detection of angular energy or the like can be used. For example, ULVAC-PHI X-ray photoelectron spectroscopy analyzer Quantum series, Shimadzu X-ray photoelectron analyzer ESCA-3400, JEOL photoelectron spectroscopy device JPS-9010 series, or Va.
A high performance X-ray electron spectroscope ESCALAB250 from cum Generators or the like may be used.

A photoelectron measuring method using the system having the above configuration will be described below. The X-rays X1 and X2 simultaneously emitted by the X-ray source 2 are simultaneously applied to the irradiation spots of the sample supported by the sample support 1, respectively. The photoelectron E1 excited by the X-ray X1 is emitted from the irradiation spot.
The photoelectron spectrum of the photoelectron E1 (the intensity of the photoelectron with respect to the energy of the photoelectron) has a plurality of peaks. This is because the X-ray X1 excites and emits a plurality of photoelectrons respectively derived from a plurality of core levels of the sample. Similarly, the photoelectron E2 excited by the X-ray X2 is
It is emitted at the same time as the photoelectron E1. The photoelectrons E1 and E2 emitted from the irradiation spot to the photoelectron entrance opening of the energy analyzer 3 in a solid angle are simultaneously entered into the photoelectron entrance opening of the energy analyzer 3. The energy analyzer 3 simultaneously selects the photoelectrons E1 and E2 that are simultaneously incident for energy, and detects the intensities for the respective energies.
That is, the photoelectron spectra that integrally include the intensities of the photoelectrons E1 and E2 are simultaneously detected. This photoelectron spectrum has a waveform corresponding to photoelectron ES1 derived from a predetermined core level of a specific element of the sample among photoelectrons E1, and photoelectron E2.
Among them, the waveform corresponding to the photoelectron ES2 derived from the same core level as that of the photoelectron E1 is integrally included, and is shown as Y1 and Y2 in the figure, respectively. Photoelectron ES
The difference in energy between 1 and ES2 is equal to the difference in energy between X-rays X1 and X2 and is relatively small. By rotating the energy analyzer 3 around the irradiation spot, the photoelectron spectrum is simultaneously detected once for each part of the entire predetermined solid angle extending from the irradiation spot. Upon this simultaneous detection, the entire predetermined solid angle is scanned once. The energy analyzer 3 outputs a photoelectron spectrum detection value corresponding to the photoelectron spectrum of each solid angle, and this detection value is input to the processing unit 4 for acquiring the atomic image of the sample from the energy analyzer 3.

FIG. 2 is a flow chart showing a processing procedure of the processing unit 4 according to the embodiment of the present invention. Step 1 will be described with reference to FIG. The detection value input to the processing unit 4 is
It is input to the hologram image acquisition means 5 in FIG. The acquisition unit 5 separates the waveform corresponding to the photoelectron ES1 from the photoelectron spectrum of each solid angle of the detected value, and acquires the photoelectron intensity based on this waveform. Further, based on the photoelectron intensity over this solid angle, the photoelectron intensity distribution pattern of the photoelectron ES1 (distribution of photoelectron intensity with respect to the solid angle) is standardized to obtain the hologram image χ1 of the photoelectron ES1. Similarly, the hologram image χ2 of the photoelectron ES2 is acquired.

The holograms χ1 and χ2 are functions of the vector k1 and the vector k2, respectively, where the wave number vectors of the photoelectrons ES1 and ES2, which are almost monochromatic, are set to the vectors k1 and k2, respectively. The direction of the vector k1 is the direction in which the photoelectron ES1 is emitted and detected, which extends from the irradiation spot,
The solid angle of the smallest cone including all the vectors k1 drawn from the irradiation spot (the total solid angle of the vector k1) is equal to the entire predetermined solid angle scanned as described above. Vector k
The same applies to the two directions, and the total solid angle of the vector k1 is equal to the total solid angle of the vector k2. Further, the magnitude of the vector k1 and the magnitude of the vector k2 are constant, and these values are relatively close to each other.

Next, step 2 will be described. The hologram images χ1 and χ2 are input to the difference hologram image acquisition means 6. The acquisition unit 6 calculates the difference hologram image Δχ according to Δχ = χ1-χ2 for hologram images χ1 and χ2 in which the directions of the vector k1 and the vector k2 are substantially the same. This direction,
Also, a wave number vector having a magnitude equal to the average of the magnitudes of the vector k1 and the vector k2 is defined as a vector k. The magnitude of the vector k is constant. Further, Δχ is defined as a function of the vector k. This calculation is performed by calculating all solid angles of the vectors k1 and k2, that is,
Performed over the entire solid angle of vector k (the smallest cone solid angle that includes all vectors k drawn from the illuminated spot).

Since the hologram images χ1 and χ2 have electron scattering anisotropy, the atomic images obtained from the hologram images χ1 and χ2 are distorted due to the scattering anisotropy.
S. Omori, T .; Kozakai and Y.K. N
ihei et al.'s "EPITAXIAL GROWTH O"
F SrF ₂ ON Ge (111) -c (2 × 8) A
S STUDED BY PHOTOELECTRO
N DIFFRACTION AND HOLOGRA
PHY ", Surface Review and Le
As described in Tters, 6, 1085 (1999), by taking the difference between the hologram images χ1 and χ2, a difference hologram image Δχ in which the anisotropy of the electron scattering factor is canceled is obtained. Therefore, in the atomic image obtained from the difference hologram image Δχ, the distortion due to the anisotropy of electron scattering is corrected.

Next, step 3 will be described. The difference hologram image Δχ is input to the atomic image acquisition means 7. The acquisition means 7 is a Fourier integral of the difference hologram image Δχ.

[Equation 1]

In accordance with, the atomic image shown on the left side is acquired. The atomic image has, as an argument, the real space vector of the space that is the symmetry of the measurement of the sample. The atomic image is a value that is proportional to the existence probability of an atom on the real space vector that has it as an argument. This Fourier integration is performed for all solid angles of the vector k that are constant in size.

Referring to FIG. 3, Phys. Rev. Le
tt. 70, 599 (1993) and the atomic image acquired according to the present embodiment are compared. Here, (A) of FIG. 3 is a halftone image displayed on the display of the atomic image of the conventional example, and (B) of FIG.
Is a halftone image displayed on the atomic image display of the present embodiment. Both atomic images are respectively acquired based on two common hologram images acquired by quantum mechanical simulation assuming the measurement. here,
The hologram image is calculated by the spherical wave multiple scattering theory for a germanium crystal sample. The atomic image is Ge (00
1) The second proximity surface of the surface. The first X-ray that irradiates the sample is AlKα (1487 eV) and the second X-ray.
The first and second hologram images are respectively acquired by simulation with the line corresponding to MgKα (1254 eV). FIG. 3A is obtained by superposing two atomic images obtained by Fourier transforming the first and second hologram images, respectively, in consideration of the phase. FIG. 3B is obtained by calculating the difference between the first and second hologram images and performing Fourier transform on the difference. FIG. 3 is a slice of the three-dimensional reproduction image along the second proximity surface of the Ge (001) plane, and the bright portion corresponds to the atomic position. In the image of the atom image of the conventional example of FIG. 3A, noise is extremely large, and a strong ghost peak actually occurs at a position where there are no atoms. On the contrary, no clear peak is seen at the correct position. This is probably due to the anisotropy of electron scattering. On the other hand, in the image of the atomic image of this embodiment in FIG. 3B, four clear peaks forming a square are seen at correct atomic positions. It seems that the correction for the distortion of the atomic image due to the anisotropy of electron scattering worked effectively.

When acquiring an atomic image of a germanium crystal sample according to the present embodiment, the energy difference between two X-rays is about 1 eV to about 250 eV, preferably about 5 eV to about 50 eV.

In the embodiment of the present invention configured as described above in detail, the step 2 for obtaining the difference hologram image and the step 3 for obtaining the atomic image are used by comparing the above-mentioned atomic images. , The effect of correction for the distortion of the atomic image due to the anisotropy of electron scattering can be increased. Therefore, the error of the atomic position of the image of the atomic image can be reduced.

Further, by inputting only the photoelectron spectrum detection value, the processing unit 4 can eliminate the need to acquire information on the structure of the sample to be measured. Therefore, when correcting the distortion of the atomic image due to the anisotropy of electron scattering, it is possible to apply to a sample whose structure is unknown.

An X-ray source 2 which emits only two X-rays
Is a structure having an anticathode, and as the X-ray source 2, for example, a commercially available X-ray tube is used as it is or after improvement, so that the use of synchrotron radiation is unnecessary. Can be Therefore, the scale of the system can be reduced. Also, the cost can be reduced. In addition, since it is possible to measure in a laboratory space, it is possible to relax the limit of the experiment time,
In addition, confidentiality in the process of industrial material development can be increased. Further, the X-ray spectroscopic system necessary for utilizing the synchrotron radiation can be eliminated.

In the present embodiment, the energy analyzer rotates to perform scanning, but the present invention is not limited to this. For example, the sample support 1 rotates to rotate. Good. Further, the sample support 1 and the energy analyzer 3 may be interlocked with each other.

In the present embodiment, scanning is performed once over a predetermined solid angle while performing simultaneous irradiation and simultaneous detection, but the present invention is not limited to this.
It may be executed multiple times.

The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and applications can be made without departing from the spirit of the invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure of a processing unit according to the embodiment of the present invention.

FIG. 3 (A) is a halftone image displayed on a display of an atomic image acquired according to a conventional example, and FIG. 3 (B) is an atomic image acquired according to an embodiment of the present invention. It is a halftone image displayed on the display.

FIG. 4 is a conceptual diagram showing photoelectron spectroholography.

FIG. 5 is a schematic diagram showing a measurement system in a conventional example.

[Explanation of symbols]

1 Sample support 2 X-ray source 3 Energy analyzer 5 Hologram image acquisition means 6 Difference hologram image acquisition means 7 Atomic image acquisition means

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Omori 6-32-10 Miyamoto, Funabashi-shi, Chiba (72) Inventor Masashi Shiraki 1-27-26 Higashiyama, Meguro-ku, Tokyo 102 (72) Inventor Hirohiro Narimatsu 1-35-5 Hakusan, Bunkyo-ku, Tokyo 202 Stoke Heights Hakusan 202 (56) Reference JP-A-7-110311 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 23 / 225-23/227 JISC file (JOIS)

Claims (2)

(57) [Claims] 1. An irradiation spot of a sample is simultaneously irradiated with two X-rays having different wavelengths, and two photoelectrons having different energies excited by these two X-rays are emitted from the irradiation spot, respectively. Scanning for simultaneously detecting the photoelectron spectra of two photoelectrons over a predetermined solid angle extending from this irradiation spot is performed to obtain a photoelectron spectrum detection value. Based on the photoelectron spectrum detection value, the two photoelectron spectra corresponding to the two photoelectrons are obtained. A photoelectron measuring method, characterized in that two hologram images are respectively calculated, a difference hologram image is calculated by taking a difference between these two hologram images, and the difference hologram image is Fourier-transformed to calculate an atomic image. . 2. A sample support for supporting a sample, and a sample support provided at a predetermined interval from the sample support, the irradiation spots of the sample being simultaneously irradiated with two X-rays having different wavelengths, and these two An X-ray source for respectively emitting two photoelectrons having different energies excited by X-rays from the irradiation spot, and an energy analyzer arranged at a predetermined distance from the sample support, At least one of them is rotated in the sample support and the energy analyzer to perform scanning for simultaneously detecting the photoelectron spectra of the two photoelectrons over a predetermined solid angle extending from the irradiation spot to obtain a photoelectron spectrum. Means for outputting a detected value, and two hologra corresponding to the two photoelectrons, based on the detected value of the photoelectron spectrum of the energy analyzer. Hologram image acquiring means for acquiring each of the two hologram images, a difference hologram image acquiring means for taking a value obtained by taking the difference between these two hologram images as a difference hologram image, and a value obtained by Fourier-transforming this difference hologram image as an atomic image. A photoelectron measuring system, comprising: an atomic image acquisition means.