RU2370758C2 - Device for analysing perfection of structure of crystalline layers - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: device for analysing perfection of the structure of crystalline layers has series-arranged X-ray source, apparatus for monochromatisation and collimation of X-rays, the analysed object with turning apparatus, first energy analyser, first electron detector and X-ray detector. The analysed object, first energy analyser and first electron detector are kinematically linked to each other and are placed in a vacuum chamber. The axis of the first analyser is aligned with the surface of the analysed object and the focal point of the energy analyser is aligned with the X-ray diffraction reflection region. The device also has a second electron detector, second energy analyser, placed in a vacuum chamber in line with the first energy analyser and kinematically linked to the analysed object and the second electron detector. The energy analysers used are spherical mirror type analysers, whose focal points are aligned. The electron detectors are placed on the surface of inner spherical electrodes of the first and second energy analysers at points which are opposite the focal point.

EFFECT: more accurate and faster analysis.

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Description

The invention relates to apparatus for analyzing the surface structure, surface layers and crystal interfaces by a method based on energy dispersive measurements of secondary emission (photo and Auger electrons, X-ray fluorescence radiation) excited in a crystal by a standing X-ray wave, and called the standing X-ray wave method .

For example, in the case of photoelectron emission, recording the angular dependences of the yield of photoelectrons with different energy losses under conditions of dynamic x-ray diffraction will provide information on the structure of layers located at different depths, and if a line of zero electron losses is highlighted, data on the crystal surface structure / 1 /.

Several devices are known for studying the perfection of the structure of crystalline layers by the method of standing x-ray waves.

One of them is a two-crystal vacuum diffractometer / 2 /, designed for research under high vacuum conditions of electron emission accompanying dynamic x-ray diffraction.

The device contains an x-ray source, an x-ray detector, a vacuum chamber with windows for x-ray radiation, in which a crystal monochromator, a test crystal with rotation and linear displacement means, an energy analyzer with an electron detector are placed.

The main disadvantages of this device are its structural complexity, excessive saturation of the vacuum volume with precision goniometric and analytical devices, which complicates the operation of the device and its manufacturing technology.

These disadvantages are eliminated in the diffraction x-ray photoelectron spectrometer / 3, 4 /. The device implements a three-crystal X-ray diffraction scheme.

The first and second monochromator crystals, the radiation source are mounted on parallel guides and placed outside the vacuum volume of the working chamber, where the crystal under study, the electron energy analyzer and the X-ray detector are kinematically rigidly connected to each other, and the crystal under study is equipped with rotation means. A 127-degree cylindrical deflector is used as an electron energy analyzer, with the axis of the energy analyzer aligned with the normal to the surface of the object under study, and the focus of the energy analyzer aligned with the X-ray diffraction reflection region.

A disadvantage of the known device is the limited research range due to the screening of the incident and diffracted X-ray beams by the energy analyzer at large diffraction angles.

This disadvantage is eliminated in the installation for studying the external photoelectric effect during x-ray diffraction / 5 /, which is the closest in its essential features to the claimed object.

The apparatus comprises sequentially located X-ray source, means of monochromatization and collimation of X-ray radiation, a test crystal with rotation means, an energy analyzer of electrons and an electron detector, moreover, the energy analyzer, electron detector and the studied object are kinematically rigidly connected to each other and are located in a vacuum chamber, while the axis the energy analyzer is aligned with the surface of the object under study, and the focus of the energy analyzer is aligned with the diffraction reflection region X-rays from the investigated crystal. An electrostatic analyzer such as a cylindrical mirror is used here as an energy analyzer.

In the work / 6 / using examples of studying the surface of silicon crystals coated with SiO ₂ oxide films _of various thicknesses using the device / 5 /, it was shown that to analyze the structure of the thinnest surface layers, it is necessary to obtain the yield curve K from the angular dependence of the KLL yield of Auger electrons photoelectrons with the corresponding weight, determined by the energy spectrum of electrons, the angular dependence of the output of the actual KLL Auger electrons. Obviously, with the simultaneous registration of these two angular dependences of the output of photo- and Auger electrons of different energy groups under the conditions of one experiment, the accuracy and expressness of the analysis will be significantly higher than with sequential registration in time.

However, this device / 5 / does not allow simultaneous registration of two or more angular dependences of the output of photoelectrons with different energies.

In addition, the design of the energy analyzer and its location determine the low efficiency of registration of the emitted electrons of various energy groups and, as a consequence of this, a long accumulation of experimental data.

Thus, significant disadvantages of the known device are low accuracy and rapidity of analysis.

The aim of the invention is to improve the accuracy and rapidity of analysis.

This goal is achieved by the fact that the known device for studying the perfection of the structure of crystalline layers, containing sequentially located x-ray source, means of monochromatization and collimation of X-ray radiation, an object under investigation with rotation means, a first electron energy analyzer, a first electron detector and an X-ray detector, the first energy analyzer , the first electron detector and the object under study are kinematically connected with each other and located s in the vacuum chamber, while the axis of the energy analyzer is aligned with the surface of the object under study, and the focus of the energy analyzer is aligned with the X-ray diffraction reflection region, it is additionally equipped with a second energy analyzer and a second electron detector, the second energy analyzer being placed axially with the first energy analyzer and kinematically connected with the object being studied, at For this purpose, spherical mirror energy analyzers are used as energy analyzers, the foci of which are combined, and the electric detectors The novae are placed on the surfaces of the internal spherical electrodes of the first and second energy analyzers at points diametrically opposite to the focal points.

Comparative analysis with the prototype allows us to conclude that the inventive device is characterized in that it is equipped with a second electron detector, a second energy analyzer placed axially with the first energy analyzer in the vacuum chamber and kinematically connected with the test object and the second electron detector, while spherical ones are used as energy analyzers mirror energy analyzers, the foci of which are aligned, and electron detectors are placed on the surfaces of the internal spherical electrodes first and second energy analyzers at points diametrically opposed to focal points.

Thus, the claimed technical solution meets the criteria of the invention of "novelty."

Analysis of the criterion of "significant differences" indicates the following. Known use as energy analyzers of the type "spherical mirror" / 7 /. It is also known to place the detector on the surface of the inner electrode of the analyzer "spherical mirror" at a point diametrically opposite the focal point / 7 /. However, it should be noted that such features of the claimed device as supplying it with a second energy analyzer located axially with the first analyzer and the second detector (i.e., in fact the device is supplemented with a second identical energy analysis channel) kinematically connected with the object under study, and the focal points are combined both analyzers in the region on the surface of the sample are new and are not found in similar solutions.

Thus, the set of distinctive features of the device is not obvious, ensures the achievement of a positive effect, as a result, the inventive device meets the criterion of "significant differences".

The invention is illustrated in the drawing, where figure 1 schematically shows a General view of the proposed device; figure 2 schematically shows a node of energy analyzers.

The composition of the device for studying the perfection of the structure of crystalline layers includes an X-ray beam forming device 1 and a measuring device 2.

The X-ray beam forming device 1 comprises an X-ray source 3, collimator slots 4, a monochromator crystal 5 mounted on a crystal holder 6 of a goniometric device 7, the main axis of which is O _1, is perpendicular to the equatorial plane. In addition, the device 1 of the formation of the x-ray beam is equipped with a device 8 for joint angular rotation of the source 3 with the first collimator slit 4 around the axis О ₁ , a device 9 for joint linear displacements of the source 3, collimator slots 4, goniometric device 7 in the direction perpendicular to the x-ray axis of the device K ₁ - K ₂ .

The measuring device 2 is a vacuum chamber 10, in the center of which a test object 12 is mounted on the crystal holder 11.

Along the vertical axis of the chamber 10, two energy analyzers 13, 14 of the type of electrostatic spherical mirror are axially mounted on the upper and lower end surfaces of the crystal holder 11 (one on each of the end surfaces of the crystal holder 11). Each energy analyzer 13, 14 contains inner 15, 16 and outer 17, 18 spherical electrodes of radius r ₁ and r ₂ .

In the places of passage of electron beams, each inner electrode 15, 16 has windows 19, 20 tightened by a transparent metal mesh, and a diaphragm 21, 22 made in the form of a small round or rectangular shape of the hole. The centers of the holes are placed at points P ₁ P ₂ diametrically opposite to the point S at which the photoelectron source is located, and are located on the geometric extension of the spherical surface of the internal electrodes. Behind the diaphragms 21, 22, electron detectors 23, 24, respectively, are installed.

The axis H ₁ -H _{2 of the} energy analyzers 13, 14 is aligned with the surface of the investigated object 12, and the foci of these energy analyzers are aligned at point S, which is located in the vicinity of the region of diffraction reflection of X-rays from the crystal 12 under study. The dotted line in the projection onto a plane perpendicular to the crystal surface 12 , Fig.2 outlines the contour of the incident on the crystal 12 and the reflected x-ray beams.

In places where the x-ray beam passes, the chamber 10 has windows 25 made of vacuum-tight beryllium foil. A vacuum shutter 26 is installed on the side surface of the chamber 10, and a magnetic discharge pump is installed on the upper flange-cover of the chamber 10.

The camera 10 is installed on the device 27 movements, which is designed to conduct quotation of angular and linear movements around and along, respectively, the axes O ₃ -O ₄ , O ₅ -O ₆ .

In turn, the movement device 27 is mounted on the upper platform 28 of the main goniometer 29. An X-ray detector 31 is installed on the second, lower platform 30 of this goniometer. The upper 28 and lower 30 platforms are axially mounted and can rotate roughly or smoothly around the main axis of the 29-O ₂ goniometer. The device operates as follows.

The x-ray beam from source 3 is limited by the divergence of the first collimator gap 4 and falls at a diffraction angle θ _M1 for the selected system of crystallographic planes onto a crystal-monochromator 5.

The X-ray beam diffracted by the monochromator crystal 5, in turn, is limited by the divergence of the second collimator slit 4 and falls at the diffraction angle θ ₂ onto the studied crystal 12. Both the monochromator crystal 5 and the studied object 12 are located in the Bragg diffraction geometry. The X-ray beam diffracted by the crystal 12 is detected by the detector 31.

As a result of the interaction of x-ray radiation with the substance of the studied object 12, photoelectrons are formed in it, which are emitted from the irradiated surface of the crystal 12 into vacuum at various angles α to the axis of symmetry H ₁ -H _{2 of the} energy analyzers 13, 14. Satisfying the conditions:

where e is the electron charge;

r ₁ and r ₂ are the radii of the inner 15, 16 and outer 17, 18 of the spherical electrodes of the energy analyzers 13, 14, respectively;

U ₁ - holding potential between the electrodes 15, 17 of the energy analyzer 13;

U ₂ - holding potential between the electrodes 16, 18 of the energy analyzer 14;

E - photoelectron energy leads to the fact that all the photoelectrons emerging from the source S, regardless of angle α, are collected at the centers of the holes of the diaphragms 21, 22 after reflection, after which they are detected by detectors 23,24.

Thus, for a given value of the holding potential U ₁ = U _11, particles of a certain kinetic energy E = E ₁ that satisfy the relation with (1) are focused on the opening of the receiving diaphragm 21. Accordingly, when U ₂ = U _22, particles of a certain kinetic energy E = E ₂ that satisfy relation (2) are focused on the opening of the receiving diaphragm 22. Due to the dispersion in energy, particles of other energies are scattered and fall into the holes 21, 22 in a small amount.

The device operates in energy and angular sweep modes.

In the energy sweep mode, at a fixed angular position of the crystal 12, at the same time, the holding potentials U ₁ and U _{2 of the} energy analyzers 13, 14 are changed to the same extent. As a result, the electronic output signals are recorded sequentially from the energy sections using detectors 23, 24 and the total the signal from these detectors receive the energy spectrum of electrons. Then, from the obtained energy spectrum of electrons, the electron energies E ₁ and E ₂ are determined, for which, in the angular sweep mode, it is necessary to determine the angular dependences of the electron yield intensities under X-ray diffraction conditions.

In the angular sweep mode, the potentials U ₁ and U ₂ are established at the electrodes of the energy analyzers 13, 14, at which only electrons with energies E ₁ and E ₂ , respectively, will get on the detectors 23, 24. Then, at fixed holding potentials U ₁ and U ₂ , goniometer 29 smoothly rotates the studied crystal 12 around the main axis of the goniometer O ₂ in a small angular interval near the exact reflection angle θ _{2 of the} studied crystal 12, while the detector 23 records the output intensity electrons with kinetic energy E ₁ , the detector 24 is the intensity of the output of electrons with kinetic energy E ₂ , and the detector 31 is the intensity of x-ray diffraction reflection from the surface of the crystal 12.

Thus, in the angular scan mode, simultaneously under the conditions of one experiment, the angular dependences of the X-ray reflection intensities — I (θ) and electron yield æ ₁ (θ) and æ ₂ (θ) with kinetic energies E ₁ are recorded by the detectors 31, 23, 24 and E ₂ , respectively.

As you know, the most surface-sensitive, when diagnosing the structure of crystals by the method of standing x-ray waves are Auger electrons, leaving with zero energy loss. Therefore, to obtain information about the surface structure from the position of the peak peak of Auger electrons in the electronic spectrum, the kinetic energy of these electrons is determined - E ₁ .

However, the number of electrons with an energy of E _1, in addition to Auger electrons leaving the surface of the crystal with zero energy loss, also includes electrons leaving the deep layers of the studied crystal 12 and having lost a significant part of their energy in the process of reaching the surface. These electrons create a spurious signal when registering the angular dependence of the yield of Auger electrons. A useful signal — the angular dependence of the yield of Auger electrons proper — is obtained by subtracting from the angular dependence of the yield of electrons with energy E ₁ (holding potential U ₁ ) the yield curve of photoelectrons with energy E2 (holding potential U ₂ ) with the corresponding weight P ₁ determined from the energy spectrum electrons obtained in the energy sweep mode.

Thus, by setting the potentials U ₁ and U ₂ in the angular sweep mode on the electrodes of the energy analyzers 13, 14, the angular dependence of the output intensity of the Auger electrons proper is obtained under the conditions of one experiment using the difference signal of the electronic output detected by the detectors 23, 24 according to which it is subsequently judged on the surface structure of the crystal 12, which significantly increases the accuracy and expressness of the analysis in comparison with the known devices.

Measurements are always preceded by an adjustment. The adjustment of the device is as follows. On the optical axis of the device K ₁ -K ₂ passing through the axis O _{2 of the} main goniometer 29, the axis of rotation O _{1 of the} goniometric device 7, the radiation source 3, collimator slots 4 and the X-ray detector 31 are set, the optical axes O ₁ and O ₂ connected to the working surface of the monochromator crystal 5 mounted on the crystal holder 6, and with the surface of the test crystal 12 mounted on the crystal holder 11, respectively. To do this, use the corresponding devices 8, 9, 27 and goniometers 7, 29. With the joint rotation device 8, the radiation source 3, the first collimator slit 4 are rotated around the axis O ₁ by an angle

2θ _M1 relative to the optical axis of the proposed device K ₁ -K ₂ .

Then, the lower platform 30 of the goniometer 29 and the kinematically rigidly connected detector 31 with respect to the axis K ₁ -K _{2 are} deployed at an angle of 2θ ₂ . The upper platform 28 and, together with it, the device 27, the vacuum chamber 10 with energy analyzers 13, 14 and the test crystal 12 are also rotated by an angle θ ₂ relative to the axis K ₁ -K ₂ . After that, smoothly moving the crystal 12 using the goniometer 29 around the axis O ₂ and using the device 27 around the axes O ₃ -O ₄ , O ₅ -O ₆ , set it in a reflective position in which the x-ray diffracted by the crystal 12 is detected by the detector 31 .

Energy dispersive measurements of electron photoemission are carried out at a residual pressure in the vacuum chamber of 10 not higher than 10 ^-6 Pa (pumping means are not shown in the drawings).

Thus, due to the fact that the inventive device for studying the perfection of the structure of crystalline layers is additionally equipped with a second electron detector, a second energy analyzer placed axially in the vacuum chamber with the first energy analyzer and kinematically connected with the crystal under study and the second electron detector, and also due to the fact that as energy analyzers, spherical mirror energy analyzers were used, the foci of which are aligned, and electron detectors are placed on the surfaces The internal spherical electrodes of the first and second analyzers at points diametrically opposite to the focal points significantly increased the accuracy and expressness of the analysis in comparison with the known instruments.

Literature

1. Kovalchuk M.V., Kon V.G. X-ray standing waves - a new method for studying the structure of crystals, Physics-Uspekhi, 1988, v.148, issue 5, pp. 5-46.

2. Kikuta S., Takahashi, Tuzi Y., Fukudome R. Double crystal vacuum X-ray diffractometer // Rev. Sci. Instrum. - 1977. - Vol. 48, No. 12, p. 1576-1580.

3. Kovalchuk M.B., Shilin Yu.N., Denisov A.G., Gravshin Yu.M., Zeltser I.A., Lyapin V.M., Senichkina R.S. Diffraction vacuum X-ray photoelectron spectrometer. / PTE, 1987, No. 3, pp. 191-195.

4. Gravshin Yu.M., Zeltser I.A., Kovalchuk M.V., Senichkina R.S., Shilin Yu.N. X-ray diffraction photoelectron spectrometer. / Electronic Industry, 1989, No. 4, p.23-24.

5. Aleksandrov P.A., Bresler E.E., Bugrov D.A., Zashkvara V.V., Imamov P.M., Pashaev E.M., Redkim B.C. Installation for studying the external photoelectric effect during x-ray diffraction. / LTGE, 1986, No. 1, p.198-201.

6. Pashaev E.M., Abdulaev M.I. The output of Auger electrons in the conditions of x-ray diffraction. / Crystallography, 1989, T.34, issue 1, s.263-265.

7. Zashkvara V.V., Yurchak L.S., Bylinkin A.F. Electron-optical properties of an electrostatic spherical mirror and systems based on it (1), ZhTF, 1988, vol. 58, issue 10, pp. 2010-2020.

Claims (1)

A device for studying the perfection of the structure of crystalline layers, containing a sequentially located x-ray source, means of monochromatization and collimation of X-ray radiation, a test object with rotation means, a first energy analyzer, a first electron detector and an X-ray detector, the object being studied, the first energy analyzer and the first electron detector kinematically connected to each other and located in a vacuum chamber, the axis of the first analyzer is aligned with the surface of the investigated object, and the focus of the energy analyzer is combined with the X-ray diffraction reflection region, characterized in that, in order to increase the accuracy and expressness of the analysis, the device is additionally equipped with a second electron detector, a second energy analyzer placed axially in the vacuum chamber with the first energy analyzer and kinematically connected with the studied object and a second electron detector, while spherical mirror energy analyzers, f Coosa which are aligned, and the electron detectors are arranged on the surfaces of spherical internal electrodes of the first and second energy analyzers at points which are opposite the focal point.

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