JPH04256847A - High-energy-resolution detecting method for vacuum ultraviolet ray and inverse photoelectron spectroscopic device using this detecting method - Google Patents

Abstract

PURPOSE:To obtain a detecting method for detecting vacuum ultraviolet rays at high energy resolution and to obtain an inverse photoelectron spectroscopic device which can perform inverse photoelectron spectroscopy in high accuracy at high energy resolution by utilizing this detecting method. CONSTITUTION:This detecting method is conducted by the following way. Optical filters whose penetrability of vacuum ultraviolet rays is slightly different are provided in front of at least two detectors having the equal photoelectric characteristics. The detectors are directed toward a light emitting source. The pulses of the output signals from both detectors are shaped, and the pulses are counted. The counted values are subtracted to each other. The energy resolution corresponding to the difference between the limit energies of both optical filters is optically detected. The introduction of this detecting method into an inverse photoelectron spectroscopic device is also proposed. Especially, a reflection converging mirror is used, the space in a vacuum container is reduced and the compact configuration is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection method for detecting light in the vacuum ultraviolet region with high energy resolution, and an inverse photoelectron spectroscopy apparatus using this detection method.

0002

2. Description of the Related Art Techniques for spectroscopy of light in the vacuum ultraviolet region are used to evaluate the characteristics of solid surfaces. In this case, the vacuum ultraviolet light detector is installed and used in a vacuum. The detector usually uses a Geiger-Mueller tube or an electron multiplier tube with a photocathode on its detection surface that emits large photoelectrons in the vacuum ultraviolet region. In these detectors, in order to determine the high energy end of the detection energy band, a window material attached to the entrance surface of the detector, usually an ionic crystal, such as lithium fluoride, calcium fluoride, or strontium fluoride, is used. ing. The low energy end is determined by the inherent photoemission properties of the photoelectric material within the detector. That is, in the case of a Geiger-Mueller tube, it is determined by the gas enclosed, such as iodine gas, and in the case of an electron multiplier tube, it is determined by the beryllium copper used for the surface of the photocathode. With these detectors, the energy of light that can be practically detected is around 9 eV, and the bandwidth is 0.5 to 0.6 eV.
It is V.

In recent years, solid materials, especially crystalline materials, are irradiated with a slow electron beam, and the light emitted when the electrons transition to an unoccupied electronic state level in the solid, particularly light in the vacuum ultraviolet region, has been spectrally analyzed, and the light above the Fermi level has been analyzed. The so-called "inverse photoelectron spectroscopy" has been developed, which allows detailed investigation of the unoccupied electronic states located at . , No. 1, 1
990, pp. 2-18). In this spectroscopy,
Various measurement methods have been proposed, but generally a band detector that detects a constant energy band as described above is used, low-velocity incident electrons are applied to the sample, and the energy of the incident electrons is varied within a predetermined range. The intensity of the emitted vacuum ultraviolet light is measured (this measurement method is called the BIS type measurement method). To examine the electron energy bands in more detail,
Still the above detector (resolution 0.5-0.6 eV
) is insufficient, and an energy resolution of around 0.1 eV or lower is desired (for example, see the above-mentioned commentary by Suga, Namatenmoku, Ogawa, and Kinoshita, ``Inverse photoelectron spectroscopy'', Spectroscopy Research, Vol. 39). Volume, No. 1, 1990 No. 2~
(See page 18).

In addition to detectors using Geiger-Mueller tubes or electron multiplier tubes that excite ions or electrons with light in the vacuum ultraviolet region, there are detectors that use diffraction gratings that can perform measurements with even higher energy resolution. Although this resolution can resolve the energy of about 0.15 eV mentioned above, the detection intensity is extremely weak and the S/N ratio of the detection signal is extremely low. In addition, the extremely large space occupied by the device does not avoid the drawbacks of inaccuracy and uneconomical costs, including high equipment and operating costs.

In order to eliminate the above-mentioned difficulties, the present inventor has already proposed a new detector for light in the vacuum ultraviolet region, which consists of a single detector window material that excites the ions or electrons. This is a detection system that exchanges the values and subtracts the measured values of both.

[0006]

[Problems to be Solved by the Invention] An object of the present invention is to eliminate the drawbacks of the conventional detectors described above, and to create a new detection method capable of detecting vacuum ultraviolet light with high energy resolution, especially capable of online measurement. Our goal is to provide the following.

A further object of the present invention is to provide an inverse photoelectron spectroscopy device that spectrally spectra vacuum ultraviolet light using the above-mentioned detection method, and in particular, a inverse photoelectron spectrometer suitable for BIS type measurement method.

[0008]

[Means for Solving the Problems] According to the present invention, in the detection method mentioned at the beginning, - at least two detectors having the same photoelectric characteristics are directed toward the light emitting source; Each of the detectors is formed by one detection section that converts vacuum ultraviolet light into an electrical signal through photoelectric conversion and electron multiplication, and one optical filter installed in front of this detection section, -
The light transmission ability of the optical filter is sharply attenuated when the energy of the incident light exceeds a certain critical energy, and is sufficiently high below this critical energy, - the critical energy differs slightly for each detector, and - the output from the detection section converts the electrical signal into a pulse signal,
Count the converted pulse signals, subtract the pulse count values of both counters from each other, - consider the difference between the limit energies of the two corresponding detectors as the energy resolution during measurement, and calculate the subtracted pulse count value. This is solved by making the difference between the two amounts equivalent to the amount of vacuum ultraviolet light.

Furthermore, the above-mentioned problem can be solved by the present invention, in which, in the case of a vacuum ultraviolet light spectrometer, a low-velocity electron beam is incident on a sample, and the detection method described in any one of claims 1 to 3 can be carried out. Especially the BIS type measurement method, in which vacuum ultraviolet light is directly detected by arranging two detectors to point directly at the light-emitting region of the sample, the solid angles around the main detection direction being equal to each other, and the detection ranges not overlapping each other. A vacuum ultraviolet light spectrometer based on the method or two detectors capable of injecting a slow electron beam into the sample and performing the detection method described in any one of claims 1 to 3 are used to detect the amount of light emitted from the sample. The light is once reflected by one reflection and focusing mirror attached to each, and the reflected light is focused at a position that does not overlap with each other, and the two detectors are installed near each focusing point, in which case the main detection direction is This problem has been solved by a vacuum ultraviolet light spectrometer based on the BIS type measurement method, which indirectly detects vacuum ultraviolet light by arranging the surrounding solid angles to be equal to each other and whose detection ranges do not overlap with each other.

Further advantageous developments according to the invention are disclosed in the corresponding dependent claims.

[0011]

[Operation] According to the configuration of the detection system described above, the output signals of two photoelectric detectors equipped with filters having similar vacuum ultraviolet light transmission characteristics are constantly subtracted, and high-energy resolution spectroscopic measurements can be performed. It makes it possible. When this detection system is used in an inverse photoelectron spectrometer, online measurement is possible by simply fixing the detection system to a sample tilting table and no special mechanical drive is required for detection.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in more detail below with reference to the drawings illustrating preferred embodiments.

FIG. 1 is a schematic cross-sectional view of a detector used in the present invention. Detector body 10
is a cylindrical tube made of conductive material, with a photocathode inside and a surface mainly covered with Cu-BeO or this C
A first dynode 16 is provided as a conductive member made of u-BeO deposited with a substance that reduces the work function and facilitates photoelectric emission, such as KBr. The incident light hits this first dynode 16, and photoelectrons are emitted from this photocathode. These electrons are multiplied by the next-stage electron multiplier 18, in this example an electron multiplier electrode, and finally sent to the collector 2.
Reach 0. The electrons collected in the collector are amplified by the first-stage amplifier PA, waveform-shaped, and introduced into a next-stage counter (not shown). Electrodes for electron multiplication include
During operation, a negative high voltage (normally, the maximum value is several kV) whose resistance is divided sequentially and whose value is not small is applied by the high voltage power supply HT.

As shown in the figure, the light to be detected enters from the electrostatic shield mesh 12 corresponding to the window portion, passes through the optical filter 14 and reaches the photocathode 16. The electrostatic shield mesh 12 is provided to prevent external disturbance electric fields or stray electrons from entering, and to enhance light transmission.
Use the thinnest wire material possible, such as W wire. Filter 14 is typically an ionic crystal, such as LiF, CaF2
, SrF2 are used. This filter 14 has a transmittance that rapidly decreases in the high energy region of the vacuum ultraviolet light spectral range. This energy limit is determined by the exciton energy absorption edge in the optical filter crystal used. The decrease in the sensitivity of the detector in the low energy region is due to the decrease in the photoelectron emission ability of the photocathode, and the overall detection intensity exhibits sensitivity characteristics as shown in FIG. For example, for detector D1, the relative detection intensity increases gradually from low energy and drops sharply at a certain energy limit E1.

According to the present invention, two detectors shown in FIG. 1 are used, and in this case, filters 14 having optical transmission characteristics slightly different from each other are used for both detectors. That is, Figure 2
Using two detectors equipped with filters 14 with detection intensity characteristics as shown in FIG. After a predetermined period of time (details will be explained later) in each corresponding counter, the two output signals are subtracted from each other, and the difference is used to calculate the amount of light that is substantially between energies E1 and E2. Detecting intensity. The slight difference in relative intensities between the intensity characteristic curves CH1 and CH2 (exaggerated in FIG. 2 for convenience of explanation) is due to the relatively similar shape of the curves, and therefore the energy In many cases, a limited amount of light between bands E1 and E2 can usually be measured with sufficient accuracy. However, if necessary, the above differences can be further corrected by electronic processing. Further explanation regarding this will be provided later.

When the above-mentioned detection method is used in actual inverse photoelectron spectroscopy, in order to define the direction of the sample S and the incident electrons and the main detection direction nD, the direction of the incident electrons is taken as the z-axis, and the sample is The xyz orthogonal coordinate system as shown in Fig. 3, with the x axis parallel to the tilt axis of
It is convenient to introduce a φ-spherical coordinate system. In this case, the inclination angle of the sample S is designated by θ0.

As shown in FIG. 4, the vacuum ultraviolet light detection system of the first embodiment of the present invention detects the vacuum ultraviolet light generated by low-velocity electrons E entering the irradiation area O of the sample S using two detectors D.
1 and D2 in which detection is performed simultaneously in different main detection directions nD1 and nD2, respectively, and the optical transmission characteristics of the two filters are different. Detector D1
and D2 directly detect the vacuum ultraviolet light emitted from the irradiation area O, and the main detection directions of the detectors are both directed toward the irradiation area O.

Furthermore, in order to collect as much vacuum ultraviolet light as possible to be detected, detectors D1 and D2 are used that have as large a solid angle as possible around the main detection directions nD1 and nD2, that is, the detection windows are effectively wide. , it is desirable to make the spacing between the sample S and each of the detectors D1 and D2 as narrow as possible.

Furthermore, it is advantageous to arrange the detectors D1 and D2 symmetrically with respect to the electron beam E and the sample S in order to make the amounts of light incident on both the detectors D1 and D2 approximately equal. That is, the main detection directions nD1, n of both detectors D1, D2
It is particularly advantageous if D2 and the azimuthal angles φ1, φ2 are equal to each other and their detection solid angles are respectively equal in the φ and θ directions.

FIG. 5 shows a schematic diagram of a detection system of a reverse photoelectron spectroscopy apparatus according to a second embodiment of the present invention. In this case, only one of the two detectors is shown to avoid complexity. 5A shows the detection system viewed from the direction in which the electron beam is incident, and FIG. 5B shows a side view of FIG. 3 viewed from the x-axis direction. As can be seen from both figures, in this embodiment, the light emitted in the main detection direction nD is once received by a mirror M having a condensing function, and then reflected in the direction of the detector D and condensed. The surface material of the mirror M is usually a pure metal such as gold or aluminum for vacuum ultraviolet light. In some cases, ionic crystals with high light transmittance may be attached to the metal surface to make it chemically and optically stable.

The advantage of the detection system of the method shown in FIG. 5 is that the focal length of the reflecting mirror made of a spherical, ellipsoidal or other curved surface is appropriately selected so that the reflected light can be detected at a desired location away from the sample surface. The point is that the light can be focused on vessel D. Therefore, the working space above the sample surface is large and requires other surface evaluation analyses, such as RHEED, LEED, A
This is particularly advantageous when performing composite measurements that combine analyzes such as UGER, ESCA, XPS, etc. In addition, in the optical system of this analysis method, a diaphragm plate Ap having a predetermined aperture angle is provided in front of the mirror M in order to regulate and measure the direction of light emission. That is, the opening angle 2Δφ in the φ direction (FIG. 5A) and the opening angle 2Δθ in the θ direction (FIG. 5B) are determined by the size of the aperture of the aperture plate Ap and the distance to the sample S.
Its solid angle is given by 4ΔφΔθ. Furthermore, as in the case of the first embodiment shown in FIG. 4, the main detection directions of the two detectors in FIG. 5 are arranged at symmetrical positions with respect to the yz plane,
It is advantageous if the detection opening angles in the θ and φ directions are the same.

Next, processing of the detection signal obtained by the detection system according to the present invention will be explained based on FIG. 6.

As already explained above, the detection system DSY according to the present invention shapes the multiplication currents of the two detectors D1 and D2 into counting pulses by the attached first-stage amplifiers PA1 and PA2, respectively, and performs counting. CT1, CT
2 will be introduced. Each counter CT1, CT2 counts the input pulses and converts both counts into digital signals and introduces them into the difference former DF. The difference former DF outputs the difference between both count values or the difference between the count values after predetermined correction (details will be explained later) to the main processing unit MP as a digital output signal corresponding to a detection signal with high energy resolution. Hand over. During the counting period, the main processing unit MP sends a set signal to start counting and a reset signal to stop counting after a predetermined time according to a program stored in the main processing unit MP in advance.
is supplied to each counter CT1, CT2 via a bus connection (only implicitly shown in the figure).

The main processing unit MP includes an interface for transmitting and receiving input/output signals, a storage unit consisting of ROM, RAM, etc., a microprocessor, a data bus connection for transmitting and receiving data between each unit, required power supply, etc. (not shown). In addition to counting the above-mentioned detection output signals, other parameters representing the detected measurement conditions, such as the sample inclination angle θ0, the incident electron energy VE, and the sample temperature Tp, are introduced into the arithmetic unit MP. In addition, the keyboard KB is equipped to specify the input signal of the auxiliary parameter AUX1 and the program for data processing.
An input signal from is also introduced. The vacuum ultraviolet light detection signal is data-processed in this main processing unit MP according to a predetermined program, and the results are output to an image display unit CRT and/or a data plotter or printer. The main processing unit MP also supplies output signals specifying experimental conditions, such as incident electron energy, irradiation current, sample heating, and sample tilt, to a predetermined drive circuit (not shown) via output terminals EM, AUX2, etc. be done.

[0025] Here, a supplementary explanation will be given of the case where the count values of both counters CT1 and CT2 are corrected by the arithmetic processing of the difference former D described above. That is, it has been explained that there is a slight difference in the detection strength of the two types of filters 14 shown in FIG. In addition, errors in the mechanical installation conditions or electrical setting conditions of the detector are expected to occur as errors in the pulse count value as the final detection intensity. If the error in relative detection intensity due to these causes is so small that it can be ignored, it is sufficient to directly subtract both pulse count values. However, if these errors cannot be ignored, it is necessary to correct the count value of the output count pulse. In that case, it is necessary to provide a digital multiplication circuit (not shown) for multiplying by a constant coefficient between one or both of the counters CT1 and CT2 and the difference generator DF. The constant count is
For example, it can be determined experimentally by equipping an actual spectrometer with a reference sample that emits vacuum ultraviolet light of known energy.

In the detection method according to the present invention, since the solid angle of the vacuum ultraviolet light taken in by each detector is large, both counters CT
The counting period of 1,CT2 is generally quite short and counting and difference formation can be performed on-line. However, when increasing the energy resolution or when the emitted light intensity is weak, it is necessary to lengthen the counting period and integrate the number of pulses until a specific count value is reached in order to avoid statistical fluctuations. In this case, it is advantageous to temporarily store the counted value in a storage unit in the main processing unit MP, and take out the counted value from this unit and process it as necessary.

Finally, in the figures described above, in order to avoid confusion, many elements that are actually necessary have been omitted from the drawings. For example, in the structure of the detector shown in FIG. 1, the support members for the filter 14, the first dynode 16 which is the photocathode, the support members for the electron multiplier electrode 18, etc. are omitted from the drawing. These are known per se and can be easily conceived by those skilled in the art.

However, various modifications other than the configuration shown can be considered. For example, the filter 14 could be placed in front of the electrostatic shielding mesh 12 in the detector of FIG. It is necessary to provide shielding means. Furthermore, it is important to use a conductive material for the detector body 10 and to select a material that releases less gas in a vacuum. Others, electron multiplier electrode 18
It is particularly advantageous if the body 10 is made of magnetically annealed permalloy or the like in order to prevent stray magnetic fields from acting on the body. The electron multiplier 18 can also be formed using a channel plate or the like made of a ceramic material with a high secondary electron emission ability, instead of a multi-stage electrode. Further, depending on the case, the photoelectric conversion section, that is, the photocathode 16 and the electron multiplier section 18 may be formed by a Geiger-Mueller tube.

In any case, it goes without saying that all of these possible modifications fall within the scope of the present invention as long as they satisfy the configurations defined in the claims. Although the description has mainly been made regarding an inverse photoelectron spectrometer, the detection method according to the present invention can be applied to, for example, a polarization analysis type inverse photoelectron spectrometer, an inverse photoelectron spectrometer using a polarized electron beam, or an object where the sample is not a solid but a liquid or a gas. Needless to say, it can be applied extremely effectively to spectroscopy of vacuum ultraviolet light from objects.

[0030]

ADVANTAGEOUS EFFECTS OF THE INVENTION The vacuum ultraviolet light detection system according to the present invention ensures spectroscopic measurements with high energy resolution (approximately 0.1 to 0.2 eV). Moreover, since the structure is simple, no mechanical movable adjustment part is required, and the light receiving intensity is strong, the detection output signal can be processed online at all times if necessary. Therefore, by equipping an inverse photoelectron spectrometer with the detection system proposed here, it will significantly simplify the attached mechanical mechanism and simplify electrical processing, making it possible to perform spectroscopic measurements with high precision and high reproducibility. .

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a detector used in the present invention.

FIG. 2 is a characteristic curve diagram showing extremely exaggerated relative detection intensities of two types of detectors used.

FIG. 3 is a layout diagram that defines geometric parameters for specifying the interrelationship of the sample, incident electrons, and detection direction.

FIG. 4 is a schematic perspective view of a first embodiment of the inverse photoelectron spectroscopy apparatus according to the present invention, in which excitation light is directly captured by a detector.

FIG. 5 is a schematic plan view (A) and side view (B) of a second embodiment of the inverse photoelectron spectroscopy apparatus according to the present invention, in which excitation light is captured using a reflective focusing optical system. However, to avoid complexity, only one detector is shown.

FIG. 6 is a block circuit diagram showing arithmetic processing of a detection optical signal and other data processing according to the present invention.

[Explanation of symbols]

10 Detector body 12 Electrostatic shield mesh 14
Filter 16 First dynode 18 Electron multiplication stage 20 Collector HT Negative high voltage power supply PA, PA1, PA2 First stage amplifier E1, E2
Absorption energy edge S Sample E Incident electron beam θ0 Sample inclination angle D, D1, D2 Detector M Reflection focusing mirror Ap Aperture DF Difference former DSY Detection system MP Main processing unit

Claims (6)

[Claims] 1. A detection method capable of detecting vacuum ultraviolet light with high energy resolution by receiving vacuum ultraviolet light emitted from a light emitting source and converting the amount of received light into an electrical output signal, comprising: at least two detectors having the same characteristics are directed, - each of said detectors has one detection section for converting vacuum ultraviolet light into an electrical signal by photoelectric conversion and electron multiplication, and is installed in front of this detection section; Formed with one optical filter, -
The light transmission ability of the optical filter is sharply attenuated when the energy of the incident light exceeds a certain critical energy, and is sufficiently high below this critical energy, - the critical energy differs slightly for each detector, and - the output from the detection section converts the electrical signal into a pulse signal,
Count the converted pulse signals, subtract the pulse count values of both counters from each other, - consider the difference between the limit energies of the two corresponding detectors as the energy resolution during measurement, and calculate the subtracted pulse count value. A detection method characterized in that the difference between the two is determined to be an amount equivalent to the amount of vacuum ultraviolet light. [Claim 2] The difference between the two limit energies is 0.
．． 2. The detection method according to claim 1, wherein the voltage is 2 eV or less. [Claim 3] In order to compensate for the difference in detection characteristics of the two detectors, a count value obtained by counting the number of pulses by one detector is multiplied by a predetermined coefficient, and then both count values are subtracted from each other. Detection method in item 1 or 2. 4. A low-velocity electron beam is made incident on the sample, and two detectors capable of performing the detection method according to any one of claims 1 to 3 are directed directly to the light emitting region of the sample, and the main detection direction is In particular, an inverse photoelectron spectrometer based on a BIS type measurement method is characterized in that it directly detects vacuum ultraviolet light by arranging the solid angles around the two to be equal and the detection ranges not overlapping each other. 5. A low-velocity electron beam is incident on the sample, and two detectors capable of carrying out the detection method according to any one of claims 1 to 3 are used to detect the light emitted from the sample. The two detectors are installed near each focusing point, and the solid angles around the main detection direction are adjusted to each other. A reverse photoelectron spectroscopy device based on a BIS type measurement method, characterized in that the detection ranges are arranged equally and do not overlap each other, and vacuum ultraviolet light is indirectly detected. 6. The inverse photoelectron spectroscopy apparatus according to claim 4, wherein the two detectors are arranged symmetrically with respect to a plane including the sample normal and the incident direction of the electron beam.