JP2629594B2 - X-ray photoelectron spectroscopy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray photoelectron spectrometer, and more particularly to a time-resolved X-ray photoelectron spectrometer for tracking a transient change in a composition or a chemical bond state of a substance to a disturbance such as an electric field, a magnetic field or light. The present invention relates to a spectroscopic device.

[0002]

2. Description of the Related Art An electron beam exposure technique of blanking an electron beam emitted from an electron gun at a high speed with an electrostatic deflecting plate or a deflecting coil and directly drawing a circuit pattern on a silicon substrate or the like is well known. In addition, a scanning electron microscope capable of visualizing dynamic characteristics of an integrated circuit by applying the above-described electron beam exposure technology has been developed. This is based on Katsumi Ura and Hiroshi Fujioka, “The World of LSIs Seen with an Electron Microscope,”
As described in pages 70 to 71, Nikkan Kogyo Shimbun (1990), an electron beam from an electron microscope was
This device irradiates pulses in synchronization with the periodic voltage applied to the observation site, and the obtained secondary electron image is a strobe photograph of the potential distribution of the integrated circuit. Now
Assume that an integrated circuit is supplied with a signal from a signal generator and the voltage on an electrode to be measured changes periodically. At this time, focusing on a certain phase of the voltage waveform, the same voltage appears repeatedly. Therefore, when the electron beam from the electron microscope is synchronized with the cycle of the circuit voltage and is repeatedly irradiated on the electrode to be measured in a pulse only at a certain phase, the pulsed electron beam always has the same phase, that is, the same. The sample is irradiated at the voltage of. That is, a "frozen" potential contrast image at that phase can be observed. This potential contrast image corresponds only to the voltage at that phase, and the detection signal contains only information at that phase, so even if the voltage change is a nanosecond or even a picosecond order ultrafast phenomenon Even if it is, a video band detector for an ordinary scanning electron microscope can be used as it is for observation of the potential contrast image. The electron beam as a probe in the above-mentioned observation with a stroboscopic scanning electron microscope can be subjected to time-resolved measurement of absorption and fluorescence by replacing this with a pulse laser. As described above, the stroboscopic observation method of performing time-resolved measurement using a pulse-like probe is a very effective method as a method of tracking a transient phenomenon of a state change of a substance.

[0003] A similar concept has been adopted also in the photoelectron spectroscopy, as an example, Physical Review Letters (Ph v sical Review Letter
s), Vol. 67, No. 1 1 53 pages, and a spectroscopic method using a pulsed laser that is reported in 1991.
FIG. 2 is a schematic configuration diagram of the device used therein.
Referring to the figure, here, germanium is used as a sample 1, and a 1.76 ev picosecond dye laser 2 is radiated as a disturbance to the germanium in a pulse shape as shown in FIG. The valence electrons are excited to an unoccupied state. After a certain delay time τ from the application of the disturbance, the excitation electrons are taken out of the sample as photoelectron pulses 4 in synchronization with the application of the disturbance by the higher harmonics 3 of the dye laser of 10.56 ev. The photoelectrons 4 taken out are detected by the secondary electron multiplier 5 after a certain flight time, and the energy of the photoelectrons is obtained by converting the measured flight time. With this method, the delay time τ is swept, the photoelectron intensity at each delay time is measured, and the time until the excited electrons return to the ground state is measured.

As another example of photoelectron spectroscopy using pulsed light, a method using synchrotron radiation is introduced in Vol. 68, p. 1014, 1992 of the same magazine.
Here, a pulse of synchrotron radiation is used for time-resolved measurement of the core level spectrum of gallium arsenide instead of the above-described pulse dye laser.

[0005] In the context of the present invention, it is characteristic of some of the strobe observation techniques and devices described so far that they all enable fast transient tracing using pulsed probes. That is.

[0006]

However, although a conventional X-ray photoelectron spectrometer using a pulsed laser has a high time resolution, the core level of a constituent element of a sample, which is an index for knowing the composition and chemical bonding state of a substance. Required to excite the
It is difficult to achieve energy of several hundred eV with a pulse laser.

On the other hand, an apparatus using synchrotron radiation can use X-rays as an incident probe, and can provide a substance with sufficiently high energy required for analysis. However, the synchrotron radiation facility itself belongs to the field of high-energy physics research, and many are shared facilities,
Its use is very time-sensitive and practicable. For example, in the example of the synchrotron radiation facility at the Brookhaven National Laboratory in the United States, the synchrotron radiation itself is operated in a time-resolved operation mode (single bunch and single bunch).
Mode), and the time available for time-resolved X-ray photoelectron spectroscopy is very limited. In Japan, for example, the Photon Factory of the High Energy Physics Laboratory is available, but here too, due to the same circumstances as described above, time-resolved measurements can be used, for example, annually. It only lasts about a week. Thus, it can be said that time-resolved measurement using synchrotron radiation is a special analysis technique that is difficult to spread.

Accordingly, an object of the present invention is to provide a practical apparatus capable of tracking a time-dependent change of a composition or a chemical bonding state of a substance at a high speed up to the order of nanoseconds.

[0009]

An X-ray photoelectron spectroscopy apparatus according to the present invention comprises an X-ray source for generating X-rays for continuously irradiating a sample, and an X-ray photoelectron spectrometer. Means for giving a disturbance, an electron optical system for forming a reduced image of the X-ray irradiation surface from photoelectrons emitted from the X-ray irradiation surface of the sample by X-ray irradiation, and imaging of the reduced image described above. The aperture of the small hole located on the surface, a deflection system disposed between the electron optical system and the aperture to deflect the photoelectrons that have passed through the electron optical system, and the photoelectrons that have passed through the aperture and An energy analyzer for measuring a kinetic energy distribution, wherein the sample is continuously irradiated with X-rays in order to measure a temporal response characteristic of a state of a material surface to an applied disturbance. Mark the above-mentioned disturbance as a periodic pulse In addition, a gate that opens and closes in synchronism with the disturbance is provided when taking in the photoelectron into the energy analyzer through the aperture by configuring the photoelectron passing through the deflection system to be deflected by using the pulse-like disturbance as a trigger. It is characterized by having.

In the X-ray photoelectron spectrometer of the present invention, the X-ray photoelectron spectrometer of the present invention is capable of detecting the arrival position of energy-dispersed photoelectrons in the photoelectron detector of the energy analyzer. A secondary electron multiplier is used.

[0011]

Since the X-ray photoelectron spectrometer of the present invention uses X-rays as a measurement probe, unlike the spectrometer using pulsed laser light as a probe, high energy required for analysis can be obtained. In addition, since continuous X-rays are used instead of pulsed X-rays as irradiation X-rays as the measurement probe, a commercially available continuous X-ray source can be used. Therefore, the spectrometer of the present invention is much more practical than a spectrometer using synchrotron radiation.

The present invention focuses on the high-speed operation of the above-described strobe measurement method. However, this principle is not applied to a measurement probe (irradiation X-ray) but to photoelectrons emitted from a sample. With this, electron spectroscopy with high time resolution is performed by a practical device using a normal X-ray tube. That is, in the photoelectron X-ray spectrometer of the present invention, instead of changing the measurement probe from pulsed X-rays to continuous X-rays, blanking synchronized with disturbance is performed in the direction of taking in the emitted photoelectrons into the energy analyzer. This ensures the high temporal resolution of strobe light spectroscopy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 1A schematically showing the configuration of an embodiment of the present invention, the present invention is characterized in that the X-ray 6 as a probe is not a pulse but a continuous X-ray, and that an electron lens Between the diaphragm 7 and the diaphragm 8
And the photoelectrons 10 are deflected before being taken into the energy analyzer 11. In this embodiment, while the sample 1 is continuously irradiated with the X-rays 6 as a probe, as shown in FIG. 1B, the sample 1 is subjected to a periodic disturbance such as an electric field, a magnetic field or light. The perfect pulse 12
Add as With this pulse input as a trigger, after a delay time τ has elapsed from the application of the disturbance, the voltage applied to the deflection plate 9 is cut off for a short time Δτ to stop blanking, and the photoelectrons 10 pass through the aperture 8. And taken into the energy analyzer 11. By changing this delay time τ in various ways, that is, by sweeping, a time-resolved spectrum can be obtained. The time Δτ is the time required for energy spectroscopy per disturbance pulse, which is the time resolution. Hereinafter, the configuration of the present embodiment will be described more specifically.

The X-ray generator 13 is a commercial soft X-ray tube of the twin anode type of Al and Mg, and has an output of 500 watts.

The electron lens 7 is for imaging the photoelectrons 10 from the X-ray irradiation surface of the sample 1 on the stop 8. The aperture 8 is provided with a small hole in a metal plate. In order to obtain a higher photoelectron intensity, it is necessary to collect photoelectrons from a wide range of the sample 1. Therefore, the electron lens 7 forms a reduced image of the object surface (photoelectron emission surface of the sample 1) on the diaphragm 8. You have set.

The deflecting plate 9 blanks the photoelectrons by deflecting the photoelectrons passing through the electron lens 7. That is, the photoelectrons in flight between the deflecting plates 9 are normally deflected by the voltage applied to the deflecting plates 9 so as not to pass through the aperture 8 of the small hole, but the time Δτ in FIG. During this time, the deflection voltage is turned off to cancel the deflection, so that the photoelectrons pass through the aperture 8 and enter the energy analyzer 11.

The energy analyzer 11 is of an electrostatic hemisphere type. The detector 14 is composed of a secondary electron multiplier capable of two-dimensionally detecting the arrival position of energy-dispersed photoelectrons. The detector 14 has a structure in which secondary electron multipliers are two-dimensionally arranged in a matrix, and a detector which has already been put to practical use can be used. For example, the Journal of Electron Spectroscopy and
Related Phenomena (Journal of E
electron SpectroscopyandRe
laten Phenomena), Vol. 52, No. 74
The photoelectron spectroscopy apparatus reported on page 7, 1990, uses secondary electron multipliers densely arranged in a two-dimensional direction with the name of a multi-channel plate.
A spatial resolution of μm has been achieved.

The position of the deflecting plate (or deflecting coil) can be arranged in the energy analyzer. In this embodiment, the deflecting plate 9 is arranged on the electron lens 7 side. To obtain an electron spectrum with high energy resolution, the speed of electrons flying through the energy analyzer must be reduced as much as possible, and usually the photoelectrons decelerate before entering the energy analyzer. When the speed of the photoelectrons decreases, the flight time increases and the time resolution decreases.
The deflecting plate 9 is arranged on the side of the electron lens 7 before the photoelectrons 10 are decelerated and completely stopped.

In FIG. 1A, a disturbance pulse 12 such as an electric field or light is applied to the sample 1 while the X-ray 6 is continuously irradiated on the sample 1. And the delay time τ
After that, the deflecting plate 9 is turned off, the photoelectrons 10 formed on the stop 8 are taken into the energy analyzer 11 for a time Δτ, and the energy is dispersed, and then the arrival position of the photoelectrons is detected by the detector 14. .

The photoelectrons having different energies in the energy analyzer 11 have their orbits dispersed after energy dispersion.
It reaches a different position on the detector 14 (a different position on the left-right axis in FIG. 1A). Therefore, if a detector capable of detecting the arrival position of photoelectrons is used, photoelectrons of different energies can be detected at once without sweeping the applied voltage of the energy analyzer. That is, in principle, the entire energy spectrum at the delay time τ can be obtained with one disturbance pulse 12. On the other hand, if the detector does not have the function of detecting the arrival position of the photoelectrons, only one energy spectrum can be detected for one disturbance pulse. The applied voltage must be swept. That is, in order to detect the entire energy spectrum at a certain delay time τ, a disturbance pulse is applied after determining the voltage applied to the energy analyzer and the delay time τ, and photoelectrons having energy corresponding to the applied voltage are detected. Then, with the delay time fixed at τ, the operation of changing the applied voltage to the energy analyzer and detecting photoelectrons having energy corresponding to the applied voltage is repeated, and the entire energy spectrum is started. Is obtained. Therefore, to obtain the same energy spectrum,
The measurement time is much longer than in this embodiment. In this embodiment, since the secondary electron multiplier capable of detecting the arrival position of the photoelectrons is used as the detector 14, it is not necessary to sweep the applied voltage of the energy analyzer 11 as described above. As a result, when observing the core level spectrum of an atom whose energy spread is as small as several eV, it is possible to track a required time change of the entire energy spectrum in a short time only by the blanking operation. In this embodiment, the detector 14 is
Although the arrival position of the photoelectrons can be detected two-dimensionally, as is clear from the above description, the position detection of the arrival photoelectrons may be performed only one-dimensionally (in the horizontal direction on the paper). A detector capable of two-dimensional detection can also detect photoelectrons having a spread in the direction perpendicular to the paper surface of FIG. 1A, so that a higher photoelectron intensity can be obtained, and the S / N is correspondingly increased. The ratio improves.

The time-resolved X-ray photoelectron spectrometer of the present embodiment has the above-described configuration, and enables tracking of a time-response phenomenon, which was difficult with a conventional practical device.

As in this embodiment, an apparatus configured to apply blanking in synchronism with disturbance to emitted photoelectrons instead of probe X-rays. A method of applying a gate to a current pulse due to photoelectrons detected after spectroscopy by an electronic circuit is simple and more practical because the intensity is not reduced by blanking as described above. However, in order to follow a faster time change with this method, it is necessary to increase the time of flight of the photoelectrons in the energy analyzer, which leads to a decrease in energy resolution. In other words, in the method of applying a gate after the detector, since the time resolution and the energy resolution are in an opposite relationship, it is necessary to follow the time change faster than microsecond while maintaining the practical energy resolution of 1 ev or less. It is preferable to configure as in the embodiment.

In general, an apparatus using an X-ray tube of several hundred watts, which is relatively easily available, has a low X-ray intensity, so that it takes several minutes to obtain a practical S / N ratio spectrum. Sometimes it takes several hours of measurement time. In the X-ray photoelectron spectroscopy apparatus of the present invention, such an increase in measurement time is unavoidable, but in that case, a cycle of high-speed time-resolved measurement is repeated many times, and finally, data of the same delay time is integrated. I just need.

[0024]

As described above, the X-ray photoelectron spectroscopy apparatus of the present invention can be changed from a pulsed X-ray to a continuous X-ray as a measuring probe so that a commercially available X-ray tube can be used. In addition to increasing the measurement time, instead of changing the measurement probe to continuous X-rays, the acquisition of the emitted photoelectrons into the energy analyzer is subjected to blanking synchronized with the disturbance, so that the high time resolution of strobe spectroscopy Is secured.

As a result, according to the present invention, a highly practical X-ray photoelectron spectrometer having a time resolution on the order of nanoseconds and high practicality can be realized, and a transient change in the composition of a substance or a chemical bond state can be easily performed in a high time. It is possible to track with a resolution.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration diagram of an embodiment of the present invention and a time chart of an applied voltage.

FIG. 2 is a schematic configuration diagram of a conventional X-ray photoelectron spectroscopy device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sample 2 Dye pulse laser for excitation 3 Dye pulse laser for photoemission 4 Photoelectron pulse 5 Secondary electron multiplier 6 X-ray 7 Electron lens 8 Aperture 9 Deflection plate 10 Photoelectron 11 Energy analyzer 12 Disturbance pulse 13 X-ray generator 14 Detector

Claims (3)

(57) [Claims] 1. An X-ray photoelectron spectrometer for irradiating a sample with excitation X-rays and measuring a kinetic energy distribution of emitted photoelectrons, a means for continuously irradiating the sample with the excitation X-rays, Means for applying a disturbance such as an electric field, a magnetic field or light as a periodic pulse; energy spectroscopy means for taking in the emitted photoelectrons for energy spectroscopy; and applying the disturbance for taking in the emitted photoelectrons into the energy spectroscopy means. X-ray photoelectron spectrometer, characterized in that it comprises a means for synchronizing the. 2. An X-ray source for generating X-rays for continuously irradiating a sample, a unit for applying a disturbance such as an electric field, a magnetic field, or light to the sample, and the X-ray irradiation An electron optical system for forming a reduced image of the X-ray irradiation surface from photoelectrons emitted from the X-ray irradiation surface of the sample, an aperture for a small hole located on an image forming surface of the reduced image, A deflection system disposed between an optical system and the aperture for deflecting photoelectrons that have passed through the electron optical system; and an energy analyzer that captures the photoelectrons that have passed through the aperture and measures the kinetic energy distribution. In order to measure the temporal response characteristic of the state of the material surface to the applied disturbance, the disturbance is periodically applied to the sample while the sample is continuously irradiated with the X-rays. Applied as a simple pulse By providing a configuration in which a pulsed disturbance is used as a trigger to apply a deflection to photoelectrons passing through the deflection system, a gate that opens and closes in synchronization with the disturbance is provided for capturing photoelectrons into the energy analyzer through the aperture. An X-ray photoelectron spectroscopy apparatus characterized in that: 3. The X-ray photoelectron spectrometer according to claim 2, wherein a secondary electron multiplier capable of detecting an arrival position of energy-dispersed photoelectrons is used as a photoelectron detector of the energy analyzer. X-ray photoelectron spectroscopy apparatus characterized by the above-mentioned.