JPH06235707A - Surface/interface structure analyzing method - Google Patents

Abstract

PURPOSE:To provide a surface/interface analyzing method in which atomic sequence can be analyzed even for a different chemical bonding state of atoms constituting the surface of the interface. CONSTITUTION:(111)B face sample of oxidized gallium arsenide subjected to sulfur surface treatment is irradiated with monochromatic soft X-rays of 2472eV representative of the energy for observing the structure close to the X-ray absorbing end of a nonoxidizing sulfur atom. The incident angle is varied around a Bragg diffraction angle, i.e., 50.201 deg., thus measuring the intensity of sulfur Kalphafluorescent X-rays emitted from sulfur atoms excited by an X-ray standing wave. Similarly, the sample is irradiated with monochromatic soft X-rays of 2482 eV representative of the energy for observing the structure close to the X-ray absorbing end of a sulfur oxide atom at an incident angle of Bragg diffraction angle, i.e., 49.925 deg., or thereabout thus measuring the intensity of fluorescent X-rays. Positional analysis is conducted individually for nonoxidizing sulfur atom and oxidized sulfur atom based on the intensity profiles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface / interface structure analysis method for analyzing the atomic arrangement on the surface and interface of a semiconductor or a metal material by using an X-ray standing wave. The present invention relates to a surface / interface structure analysis method for identifying and analyzing a chemical bond state.

[0002]

2. Description of the Related Art When a substrate crystal is highly perfect and Bragg conditions are satisfied for monochromatic parallel X-rays, an incident X-ray and its diffracted X-ray interfere with each other due to a dynamic diffraction effect of the X-ray. Occurs, and a standing wave having the same period as the distance between the reflecting surfaces of the crystal is generated near the surface of the crystal where the incident X-rays and the diffracted X-rays overlap. Then, in 1964, BWBatterman reported that the positions of the antinodes and nodes of the X-ray standing wave changed in the vicinity where the Bragg condition was satisfied. Since the 1980s, this phenomenon has been applied to the structural analysis of the arrangement of atoms constituting the surface layer of the sample or the interface layer of the sample having a multi-layered structure having different compositions.

In such a surface / interface structure analysis method,
First, the incident angle of a monochromatic X-ray having a single energy to the sample is continuously changed in the vicinity of the Bragg condition being satisfied by a highly accurate goniometer that can freely adjust the orientation of the sample crystal, and the incident X-ray and diffraction The intensity of the secondary radiation from the atom to be analyzed excited by the X-ray standing wave in which the X-rays overlap is measured. The secondary radiation includes, for example, fluorescent X-rays, which are characteristic X-rays emitted from a substance by being excited by X-ray irradiation and having energy peculiar to the substance.
Since the intensity of the secondary radiation shows an intensity profile that is an intensity characteristic peculiar to the atomic position, the position of the atom on the crystal surface or the atom adsorbed on the crystal surface can be determined. Further, by measuring the intensity profile of fluorescent X-rays having a high transmissivity as the secondary radiation, the positions of the impurity atoms contained in the crystal and the atoms existing near the interface layer in which the impurities are embedded can be analyzed.

By the way, the K-absorption edge or L corresponding to the energy capable of driving out an electron from the K-shell or L-shell of an atom.
In the high energy region up to about 50 eV from the absorption edge, an X-ray absorption near edge structure (XANES) in which the absorption coefficient oscillates in a short cycle and is complicated, and secondary radiation is observed in this region. The excitation efficiency of a is drastically changed by the energy of the incident X-ray. Therefore, since the structure near the X-ray absorption edge emits unnecessary secondary radiation that hinders measurement, in the conventional structure analysis using the X-ray standing wave, the atoms to be analyzed are excited by the secondary radiation. The energy of incident X-rays for emitting secondary radiation has been higher than the K-absorption edge and the L-absorption edge, whose energy dependence of the excitation efficiency of secondary radiation is small, by several hundreds eV or more.

The atomic arrangement on the surface or interface depends on the chemical bonding state of those atoms. The chemical bond state of atoms forming the surface or interface is not limited to one kind, and several kinds of chemical bond states may coexist in an island shape. Further, even if the same kind of atoms have different chemical bond states on the surface first layer and the second layer, the chemical bond state may differ and the bond distance between atoms may differ also in the depth direction of the surface or interface. Conceivable. Therefore, since the surface / interface structure analysis method using the X-ray standing wave as described above does not distinguish between the chemical bond states of the atoms to be analyzed, it is possible to analyze all the atoms to be analyzed existing on the surface or interface. We can say that we are getting information about the average sequence.

[0006] Regarding these, reference [BWBatt
erman; `` Effect of Dynamical Diffraction in X-Ray Fl
uorescence Scattering '', Phys. Rev., Vol.133A, p.759-76
4, 1964 (Bataman; "Effect of dynamical diffraction on X-ray fluorescence scattering", Physical Review, Volume A133, 7).
59-764, 1964)] and the literature [PLCowan
et al.,; "X-Ray Standing Waves at Crystal Surface
S., Phys. Rev. Lett., Vol.44, p. 1680-1683, 1980 (Kauan et al .; "X-ray standing wave on the crystal surface", Physical Review Letter, Vol. 44, pp. 1680-1683, 1980.
Year)]].

[0007]

As described above, the conventional X
Since the surface / interface structure analysis method using line standing waves cannot distinguish the chemical bond state of the analysis target atoms, only information on the average sequence of all the analysis target atoms existing on the surface or interface can be obtained. There was a problem that it did not exist.
In order to solve the above-mentioned problems, it is an object of the present invention to provide a surface / interface structure analysis method capable of analyzing the atomic arrangement even if the chemical bonding states of the atoms constituting the surface or interface are different. .

[0008]

According to the present invention, the energy of the X-ray absorption edge of an atom or the X-ray absorption of the atom constituting the interface layer of a sample having a multilayer structure composed of a surface layer of the sample or layers having different compositions is used. A monochromatic X-ray having energy that allows the structure near the X-ray absorption edge to be observed in an energy region higher than the edge is incident on the sample.

[0009]

According to the present invention, a monochromatic X-ray having energy at the X-ray absorption edge of an atom constituting the surface layer or interface layer of the sample, or energy at which the structure near the X-ray absorption edge of the atom is observed, From the atoms excited by the X-ray standing wave generated by the interference effect of the incident monochromatic X-rays and the diffracted X-rays, the sample is irradiated while the incident angle is continuously changed in the vicinity of the incident angle causing the Bragg diffraction. Secondary radiation is measured.

[0010]

EXAMPLE FIG. 1 is a diagram for explaining a surface / interface structure analysis method according to an example of the present invention, in which sulfur Kα fluorescence is applied to an oxidized sulfur surface-treated gallium arsenide (111) B-plane sample. It is a figure which shows the result of having measured the intensity | strength of X-ray. In this measurement, first, a gallium arsenide (111) B-plane wafer whose crystal plane is the (111) B plane was immersed in an ammonium sulfide solution for about 1 hour, heated in vacuum at 300 ° C. for 15 minutes, and then left in the atmosphere. The sulfur surface-treated gallium arsenide (111) B-face sample is oxidized.

Next, monochromatic soft X obtained by dispersing radiation from a synchrotron, which is a continuous X-ray source, with an InSb crystal.
Wires are used for this oxidized sulfur surface treated gallium arsenide (11
1) Irradiate a B-plane sample as incident X-rays, and continuously change the energy of the monochromatic soft X-rays in the sulfur K absorption edge region near 2470 eV of sulfur atoms. And FIG.
Irradiates such a monochromatic soft X-ray to excite the sulfur atom, and the intensity of the sulfur Kα fluorescent X-ray emitted when the electron moves to the K shell, which is the most inner shell level of the sulfur atom, is X. It is a result measured using a line semiconductor detector.

In FIG. 1, an absorption edge peaking at the energy of a monochromatic soft X-ray of 2472 eV, an absorption edge peaking at 2482 eV, and 2520 e from each of these absorption edges.
In the region up to V, a structure near the X-ray absorption edge is observed. Based on this structure near the X-ray absorption edge, the intensity of the sulfur Kα fluorescent X-ray rapidly increases from around 2470 eV to 2472 e.
The absorption edge of V is the K absorption edge of unoxidized sulfur. Similarly, the huge absorption edge of 2482 eV is the K absorption edge of oxidized sulfur, and this K absorption edge has moved to the energy side about 10 eV higher than the K absorption edge of unoxidized sulfur. .

That is, in FIG. 1, the structures near the X-ray absorption edge of the unoxidized sulfur atoms and the oxidized sulfur atoms are superposed, and unoxidized sulfur atoms and sulfur oxide atoms are mixed on the gallium arsenide (111) B surface. It means that you are doing. Therefore, although the specific surface structure is not known from these results, the chemical bond states could be distinguished. And since the absorption edge shows the energy with the highest excitation efficiency of the substance,
It can be seen that unoxidized sulfur atoms can be selectively excited by using monochromatic soft X-rays having an energy of 72 eV, and mainly sulfur oxide atoms can be selectively excited by using monochromatic soft X-rays of 2482 eV.

Next, from the above results, the intensity of the sulfur Kα fluorescent X-ray which is the secondary radiation is measured using the X-ray standing wave.
FIG. 2 is a diagram showing the results of measuring the intensity of sulfur Kα fluorescent X-rays by changing the incident angle of monochromatic soft X-rays. The horizontal axis is the displacement angle from the Bragg diffraction angle when the Bragg diffraction angle, which is the X-ray incident angle satisfying the Bragg condition, is set to 0, and the vertical axis shows the intensity of the sulfur Kα fluorescent X-rays where Bragg reflection does not occur. The strength is standardized with the strength at that time being 1.0. Also,
White circles indicate the intensity of sulfur Kα fluorescent X-rays when irradiated with monochromatic soft X-rays with energy of 2472 eV, and black circles indicate 2482.
The intensity of the sulfur Kα fluorescent X-ray at eV, the curve is the theoretically calculated theoretical profile that best fits these experimental data.

In the measurement of FIG. 2, 2472 eV of monochromatic soft X
The incident angle of the ray was changed centering on the Bragg diffraction angle of 50.201 degrees, and the oxidized sulfur surface-treated gallium arsenide (111) B-plane sample was irradiated, and the sulfur excited by the X-ray standing wave was irradiated. The intensity of sulfur Kα fluorescent X-rays from the atoms is measured by an X-ray semiconductor detector. Then, this incident angle is changed from -132 seconds to +263 seconds. Similarly, the intensity of the sulfur Kα fluorescent X-ray is measured while changing the monochromatic soft X-ray of 2482 eV around the Bragg diffraction angle of 49.925 degrees.

Since the energy of the incident monochromatic soft X-rays and the energy of the X-ray standing waves are the same, when the monochromatic soft X-rays of 2472 eV are used, the sulfur Kα fluorescent X-rays emitted from the unoxidized sulfur atoms are Measured, 2482 eV monochromatic soft X
When the line is used, the amount emitted from the unoxidized sulfur atom is also included to some extent, but the sulfur Kα fluorescent X-ray emitted mainly from the sulfur oxide atom is measured.

The two profiles in FIG. 2 are different, which means that the sulfur oxide atoms and the unoxidized sulfur atoms on the surface of gallium arsenide have different atomic arrangements. That is, the intensity profile (2482 eV) of the sulfur Kα fluorescent X-ray emitted from the sulfur oxide atom is close to a left-right symmetry with 0 as the center, which means that the oxidized sulfur atoms do not line up regularly but at random positions. It means occupying.
On the other hand, the intensity profile (2472 eV) of the sulfur Kα fluorescent X-ray emitted from the unoxidized sulfur atom is clearly asymmetric, and it is assumed that the sulfur atoms are regularly arranged at the position of arsenic on the surface of gallium arsenide. It matches the theoretical profile calculated on the assumption. Therefore, the surface atomic arrangement of the oxidized sulfur surface-treated gallium arsenide (111) B plane can be determined based on these results.

FIG. 3 is a diagram showing a structural model of the surface atomic arrangement of the oxidized sulfur surface-treated gallium arsenide (111) B plane obtained in this example. S (black circle) is a sulfur atom, As (white large circle) is an arsenic atom, Ga (shaded circle) is a gallium atom, O (white small circle) is an oxygen atom, SOx is an oxidized sulfur atom, and a broken line is gallium arsenide. Represents the surface of. FIG. 3 is produced based on the theoretical profile that best matches the measured data in FIG.
As shown in FIG. 3, the unoxidized sulfur atom S occupies a fixed position on the surface of gallium arsenide GaAs, but the oxidized sulfur atom SOx does not occupy a fixed position.

As described above, since the monochromatic soft X-ray having the energy of the sulfur K absorption edge which changes depending on the chemical bonding state of the sulfur atom is used to generate the X-ray standing wave, the position of the oxidized sulfur atom is It became possible to distinguish and analyze the position of unoxidized sulfur atom. As is clear from this result, it is possible to identify the chemical bond state of the sulfur atom existing on the surface, which could not be done conventionally, and analyze the position of the atom in each chemical bond state, and to determine the exact structure of the atomic arrangement on the surface. .

Although the present embodiment is applied to the structural analysis of the atomic arrangement on the crystal surface, it can also be applied to the structural analysis of the atomic arrangement on the interface. Further, in this embodiment, fluorescent X-rays are used as the secondary radiation, but it is also possible to use other secondary radiation such as photoelectrons and Auger electrons.

[0021]

According to the present invention, the phenomenon that the energy at the absorption edge changes depending on the chemical bond state of atoms, and the chemical bond state in the structure near the X-ray absorption edge in the high energy region up to about 50 eV from the X-ray absorption edge. Based on the phenomenon that a peak peculiar to is observed, the monochromatic X-rays having the energy at the X-ray absorption edge of atoms constituting the surface or the interface or the energy at which the structure near the X-ray absorption edge is observed are X-ray stationary. Since it is used to generate a wave, by measuring the secondary radiation from the atoms excited by this X-ray standing wave, the atomic arrangement structure of the same atomic species having different chemical bond states on the surface or interface is demarcated. It can be analyzed separately.

[Brief description of drawings]

FIG. 1: Oxidized sulfur surface treated gallium arsenide (11
1) A diagram showing the results of measuring the intensity of sulfur Kα fluorescent X-rays on a B-side sample.

FIG. 2 is a diagram showing the results of measuring the intensity of sulfur Kα fluorescent X-rays while changing the incident angle of monochromatic soft X-rays.

FIG. 3 is a diagram showing a structural model of a surface atomic arrangement of an oxidized sulfur surface-treated gallium arsenide (111) B plane obtained in this example.

Claims (1)

[Claims] 1. An X-ray standing wave is generated from an interference effect of an incident X-ray and a diffracted X-ray by injecting an X-ray at a specific incident angle that causes Bragg diffraction due to a crystal structure of a sample. In the surface and interface structure analysis method for measuring secondary radiation from atoms excited by a standing wave, the X-ray absorption of atoms constituting the interface layer of a sample surface layer or a multilayer structure composed of layers with different compositions Surface / interface structure analysis, characterized in that the sample is irradiated with monochromatic X-rays having energy at the edge or energy at which a structure near the X-ray absorption edge is observed in an energy region higher than the X-ray absorption edge of the atom. Method.