JPH07270348A - X-ray photoelectron spectroscope - Google Patents

Abstract

PURPOSE:To track with a high time resolution a transient change of a composition or a chemical coupling state of a substance with a simple X-ray photoelectron spectroscope using a commercially available X-ray tube. CONSTITUTION:The apparatus is based on a photoelectron spectroscope using a soft X-ray generator 13. A deflection plate 9 is set between a sample 1 as a source of photoelectrons and an energy analyzer 11. A detection gate for photoelectrons which consists of the deflection plate 9 and a diaphragm 8 is opened/closed in synchronization with the impression of a pulse voltage or a pulse light as outer disturbances to the sample 1. Photoelectrons 10 are taken into the energy analyzer 11 for a minute time DELTAtau after a predetermined delay time tau from an outer disturbance pulse 12, thereby to detect an energy spectrum. Because of the sweeping of the delay time tau, transient change of a surface state of the sample 1 can be tracked with a high time resolution. When a secondary electron multiplier tube which can detect a reaching position of photoelectrons of diffused energy is used in a detector 14 of the energy analyzer 11, a measuring time is furthermore shortened.

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 spectroscope, and more particularly to a time-resolved X-ray photoelectron for tracking transient changes in the composition or chemical bonding state of substances with respect to disturbances such as electric field, magnetic field or light. The present invention relates to a spectroscopic device.

[0002]

2. Description of the Related Art An electron beam exposure technique in which an electron beam emitted from an electron gun is blanked at high speed by an electrostatic deflection plate or a deflection coil to draw a circuit pattern directly on a silicon substrate or the like is well known. Further, a scanning electron microscope capable of visualizing the dynamic characteristics of an integrated circuit has also been developed by applying the above electron beam exposure technique. This is edited by Katsumi Ura and Hiroshi Fujioka, "The World of LSI Seen with an Electron Microscope,"
As described in Nikkan Kogyo Shimbun (1990), pages 70 to 71, an electron beam from an electron microscope is used.
It is a device that irradiates in a pulse shape in synchronization with the periodic voltage applied to the observation site, and the obtained secondary electron image is a stroboscopic photograph of the potential distribution of the integrated circuit. Now
It is assumed that the integrated circuit is supplied with a signal from a signal generator and the voltage on the electrode under test changes periodically. At this time, paying attention to 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 radiated onto the electrode to be measured in a pulsed manner only at the moment of 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 can be observed at that phase. 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 an ultra-high-speed phenomenon of nanosecond or even picosecond order. Even so, an ordinary video band detector for a scanning electron microscope can be used as it is for observing a potential contrast image. When the electron beam as a probe in the above-described stroboscopic scanning electron microscope observation is replaced with a pulse laser, time-resolved measurement of absorption and fluorescence can be performed. As described above, the stroboscopic observation method in which the time-resolved measurement is performed using the pulsed probe is a very effective method as a method for tracking the transient phenomenon of the state change of the substance.

A similar concept is also adopted in photoelectron spectroscopy, and as an example, Physical Review Letters (Physical Review Letter).
s), Vol. 67, p. 1553, 1991, a spectroscopic method using a pulse laser is mentioned.
FIG. 2 is a schematic configuration diagram of an apparatus used therein.
Referring to the figure, here, germanium is used as the sample 1, and the germanium is irradiated with a picosecond dye laser 2 of 1.76 ev as a disturbance in a pulsed manner as shown in the figure, so that the germanium (sample 1) Excite the valence electrons to the unoccupied state. Then, after a certain delay time τ from the application of the disturbance, the excited electrons are taken out of the sample as a photoelectron pulse 4 in synchronization with the application of the disturbance by the higher harmonic 3 of the dye laser of 10.56 ev. Since the extracted photoelectrons 4 are detected by the secondary electron multiplier 5 after a certain flight time, the measured flight time is converted to obtain the photoelectron energy. The delay time τ is swept by this method, 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, one using synchrotron radiation is introduced in Vol. 68, page 1014, 1992.
Here, instead of the above-mentioned pulsed dye laser, a pulse of synchrotron radiation is used for time-resolved measurement of the inner nuclear level spectrum of gallium arsenide.

In connection with the present invention, some of the stroboscopic observation methods / devices described so far are characterized in that they all use a pulsed probe to enable high-speed tracking of transient phenomena. That is.

[0006]

However, although the conventional X-ray photoelectron spectrometer using a pulse laser has a high time resolution, the core levels of the constituent elements of the sample, which are indicators for knowing the composition and chemical bond state of the substance, are obtained. Needed to excite
It is difficult to realize energy of several hundreds eV with a pulse laser.

On the other hand, the apparatus using synchrotron radiation can use X-rays for the incident probe, and therefore can give sufficiently high energy necessary for analysis to the substance. However, since the synchrotron radiation facility itself belongs to the field of high energy physics research and many are shared use facilities,
Its use is very time-constrained and impractical. For example, in the example of the synchrotron radiation facility of Brookhaven National Laboratory in the United States, the operation mode (single bunch
Mode), and the time available for time-resolved X-ray photoelectron spectroscopy is very limited. In Japan, for example, Photon Factory (Photon Factory) of the Institute for High Energy Physics can be used. However, due to the same situation as described above, it can be used for time-resolved measurement, for example, in a year. It's only about a week. Therefore, it can be said that time-resolved measurement using synchrotron radiation is a special analysis technique that is difficult to spread.

Therefore, it is an object of the present invention to provide a practical device capable of tracking a rapid change in the composition of a substance or the state of chemical bonding to the nanosecond order.

[0009]

The X-ray photoelectron spectroscopy apparatus of the present invention includes an X-ray source for generating X-rays for continuously irradiating a sample, and an electric field, a magnetic field, light, or the like on the sample. Means for giving a disturbance, an electron optical system for forming a reduced image of the X-ray irradiation surface from the photoelectrons emitted from the X-ray irradiation surface of the sample by irradiation of X-rays, and formation of the above-mentioned reduced image A small aperture located on the surface, a deflection system arranged between the electron optical system and the aperture for deflecting the photoelectrons that have passed through the electron optical system, and a photoelectron that has passed through the aperture and that An energy analyzer for measuring a kinetic energy distribution is included, and the sample is continuously irradiated with X-rays in order to measure the time response characteristic of the state of the material surface to the applied disturbance. The above disturbance is marked as a periodic pulse in In addition, the pulsed disturbance is used as a trigger to deflect the photoelectrons passing through the deflection system, and a gate that opens and closes in synchronism with the disturbance is provided when the photoelectrons are taken into the energy analyzer through the diaphragm. It is characterized by that.

The X-ray photoelectron spectroscope of the present invention is the X-ray photoelectron spectroscope having the above-mentioned structure, and the photoelectron detector of the energy analyzer can detect the arrival position of the photoelectrons dispersed in energy. It is characterized by using a secondary electron multiplier.

[0011]

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

The present invention focuses on the high-speed operation of the strobe measuring method described above, but applies this principle to the photoelectrons emitted from the sample, not to the measuring probe (irradiated X-ray). Thus, electron spectroscopy with high time resolution is performed with a practical device using a normal X-ray tube. That is, in the photoelectron X-ray spectroscopic apparatus of the present invention, instead of changing the measuring probe from the pulse X-ray to the continuous X-ray, blanking synchronized with the disturbance is applied to the intake of the emitted photoelectrons into the energy analyzer. This ensures the high time resolution of stroboscopic spectroscopy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. With reference to FIG. 1A schematically showing the configuration of an embodiment of the present invention, it is characteristic of the present invention that the X-ray 6 as a probe is not a pulse but a continuous X-ray, and an electron lens. Deflection plate 9 between 7 and diaphragm 8
Is provided, and the photoelectrons 10 are deflected before being taken into the energy analyzer 11. In the present embodiment, in the state where the sample 1 is continuously irradiated with the X-ray 6 as a probe, as shown in FIG. 1B, the sample 1 is periodically subjected to disturbance such as an electric field, a magnetic field, or light. Pulse 12
Add as. Using this pulse input as a trigger, after the delay time τ has elapsed from the application of the disturbance, the voltage applied to the deflection plate 9 is cut for a minute time Δτ to stop the blanking so that the photoelectrons 10 pass through the diaphragm 8. And take it into the energy analyzer 11. By changing this delay time τ variously, that is, by sweeping, a time-resolved spectrum can be obtained. The time Δτ is the time required for energy spectroscopy per disturbance pulse, and this is the time resolution. The configuration of this embodiment will be described more specifically below.

The X-ray generator 13 is a commercially available 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 focusing the photoelectrons 10 from the X-ray irradiation surface of the sample 1 on the diaphragm 8. The diaphragm 8 is a metal plate provided with small holes. Since it is necessary to collect photoelectrons from a wide range of the sample 1 in order to obtain a higher photoelectron intensity, the electron lens 7 forms a reduced image of the object plane (photoelectron emission surface of the sample 1) on the diaphragm 8. It is set.

The deflector 9 blanks the photoelectrons by deflecting the photoelectrons that have passed through the electron lens 7. That is, normally, the voltage applied to the deflecting plate 9 deflects the photoelectrons in flight between the deflecting plates 9 so that they cannot pass through the aperture 8 of the small hole, but the time Δτ in FIG. The deflection voltage is cut only during the period to cancel the deflection so that the photoelectrons pass through the diaphragm 8 and enter the energy analyzer 11.

The energy analyzer 11 is of the electrostatic hemisphere type. The detector 14 is composed of a secondary electron multiplier capable of detecting the arrival position of energy-dispersed photoelectrons in two dimensions. The detector 14 has a structure in which secondary electron multipliers are two-dimensionally arranged in a matrix, and a detector already in practical use can be used. For example, Journal of Electron Spectroscopy and
Related Phenomena (Journal of E
electron SpectroscopyandRe
later Phenomena), Volume 52, 74
The photoelectron spectrometer reported in page 7, 1990 uses a multi-channel plate, which is a secondary electron multiplier tube densely arranged in the two-dimensional direction.
A spatial resolution of μm is achieved.

The position of the deflecting plate (or the deflecting coil) may be arranged in the energy analyzer, but in this embodiment, the deflecting plate 9 is arranged on the electron lens 7 side. In order to obtain an electron spectrum with high energy resolution, it is necessary to make the velocity of the electrons flying in the energy analyzer as slow as possible, and usually the photoelectrons slow down before entering the energy analyzer. When the speed of the photoelectrons becomes slow, the flight time becomes long and the time resolution decreases, so in this embodiment,
The deflecting plate 9 is arranged on the side of the electron lens 7 before the photoelectrons 10 are completely decelerated.

In FIG. 1A, a disturbance pulse 12 such as an electric field or light is applied to the sample 1 while the sample 1 is continuously irradiated with the X-ray 6. From this, the delay time τ
After that, the deflection plate 9 is turned off, the photoelectrons 10 imaged on the diaphragm 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 trajectories dispersed in energy, and
It reaches different positions on the detector 14 (in FIG. 1A, different positions on the horizontal axis of the paper). Therefore, by using a detector capable of detecting the arrival position of photoelectrons, photoelectrons of different energies can be detected at a time without sweeping the applied voltage of the energy analyzer. That is, in principle, the total 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 position where the photoelectrons arrive, only one energy spectrum can be detected for one disturbance pulse. The applied voltage must be swept. That is, in order to detect the total energy spectrum at a certain delay time τ, the applied voltage to the energy analyzer and the delay time τ are determined, a disturbance pulse is applied, and photoelectrons with energy corresponding to the applied voltage are detected. Then, the delay time is fixed to τ, the applied voltage to the energy analyzer is changed, and the photoelectrons having the energy corresponding to the applied voltage are detected repeatedly. Will be obtained. Therefore, to get the same energy spectrum,
The measurement time is extremely long as compared with the present embodiment. In this embodiment, since the detector 14 is a secondary electron multiplier capable of detecting the arrival position of photoelectrons, the applied voltage sweep of the energy analyzer 11 as described above is not necessary. Thereby, when observing the core level spectrum of an atom whose energy spread is as small as a few eV, it is possible to trace the necessary time change of the total energy spectrum in a short time only by the blanking operation. In the present embodiment, the detector 14 is
Although the arrival position of the photoelectron can be detected in two dimensions, the position of the arrival photoelectron may be detected in only one dimension (left-right direction on the paper surface), as is clear from the above description. If the detector is capable of two-dimensional detection, it is possible to detect photoelectrons having a spread in the direction perpendicular to the paper surface in FIG. The ratio is improved.

The time-resolved X-ray photoelectron spectroscopic apparatus of this embodiment has the above-described structure and enables tracking of the time response phenomenon which was difficult with the conventional practical apparatus.

It should be noted that, as in the present embodiment, a device configured to perform blanking in synchronization with the disturbance not on the probe X-rays but on the emitted photoelectrons, and the energy for the phenomenon slower than microseconds The method of gating the current pulse by the photoelectrons detected after being spectrally separated by the electronic circuit is simpler and more practical because it does not reduce the intensity by blanking as described above. However, in order to follow a faster time change with this method, it is necessary to speed up the flight time of photoelectrons in the energy analyzer, which causes a decrease in energy resolution. That is, in the method of applying a gate after the detector, since the time resolution and the energy resolution have a contradictory relationship, it is necessary to follow the time change faster than microsecond while keeping the practical energy resolution of 1 ev or less. It is preferable to configure as in the embodiment.

Further, generally, in an apparatus using an X-ray tube of several hundred watt class, which is relatively easy to obtain, the X-ray intensity is small, so that it takes several minutes to obtain a practical S / N ratio spectrum. Sometimes it takes several hours of measurement time. Even in the X-ray photoelectron spectrometer 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. Good.

[0024]

As described above, the X-ray photoelectron spectroscopic apparatus of the present invention is simple and practical because the commercially available X-ray tube can be used by changing the measuring probe from the pulse X-ray to the continuous X-ray. The high temporal resolution of stroboscopic spectroscopy is achieved by performing a blanking synchronized with the disturbance on the intake of emitted photoelectrons into the energy analyzer, instead of changing the measurement probe to continuous X-rays. Has been secured.

As a result, according to the present invention, an X-ray photoelectron spectrometer having a nanosecond-order time resolution and high practicality can be realized, and transient changes in the composition or chemical bond state of a substance can be easily performed for a long time. It becomes possible to track with resolution.

[Brief description of drawings]

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

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

[Explanation of symbols]

 1 Sample 2 Excitation dye pulse laser 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)

[Claims] 1. An X-ray photoelectron spectrometer for irradiating a sample with excited X-rays and measuring the kinetic energy distribution of emitted photoelectrons, comprising: a unit for continuously irradiating the sample with the excited X-rays; A means for giving a disturbance such as an electric field, a magnetic field, or light as a periodic pulse, an energy spectroscopic means for taking in the emitted photoelectrons to perform energy spectroscopy, and an application of the disturbance for taking in the emitted photoelectrons to the energy spectroscopic means. An X-ray photoelectron spectroscopic apparatus comprising: one of a means for synchronizing with the application of the disturbance and a means for synchronizing detection of a current pulse by photoelectrons after energy spectroscopy. 2. An X-ray source for generating X-rays for continuously irradiating a sample, means for giving a disturbance such as an electric field, a magnetic field or light to the sample, and irradiation of the X-rays. 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 of a small hole located on the image formation surface of the reduced image, and the electron A deflection system arranged between the optical system and the diaphragm for deflecting photoelectrons that have passed through the electron optical system, and an energy analyzer that takes in the photoelectrons that have passed through the diaphragm and measures the kinetic energy distribution thereof. In order to measure the time response characteristic of the state of the material surface to the applied disturbance, the disturbance is periodically applied to the sample while the X-ray is continuously irradiated to the sample. While applying as a pulse, A gate that opens and closes in synchronism with the disturbance is provided when the photoelectrons passing through the deflection system are deflected by using a pulsed disturbance as a trigger to take in the photoelectrons into the energy analyzer. An X-ray photoelectron spectroscopy apparatus characterized by the above. 3. The X-ray photoelectron spectrometer according to claim 2, wherein the photoelectron detector of the energy analyzer is a secondary electron multiplier capable of detecting the arrival position of the photoelectrons having energy dispersion. An X-ray photoelectron spectroscopy apparatus characterized by: