JP3152455B2 - Energy distribution measurement device for charged particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the energy distribution of charged particles such as photoelectrons (for example, an electron spectrometer), for example, for analyzing the energy state of molecules and atoms on the surface of a sample or the composition of the surface of the sample. Used for

[0002]

2. Description of the Related Art A sample in a vacuum is irradiated with an electron beam or light.
By measuring the energy distribution of secondary electrons, Auger electrons, photoelectrons, and the like emitted from the sample, the energy and composition of atoms and molecules on the surface of the sample can be known.
There are a stopping electric field type and a deflection electric field type as a method for obtaining the distribution of the released energy.

FIG. 5A is a view for explaining a conventional blocking electric field type electron spectrometer. In a blocking electric field type apparatus, a sample is scanned with an electron beam or the like, and the sample 1 is measured by the voltage and transmitted electrons or secondary electrons transmitted through the sample. First, the sample 1 is irradiated with an electron beam from the electron gun 20. Secondary electrons are generated from the irradiated sample 1, and electrons transmitted through the sample are obtained as transmitted electrons. In the blocking electric field type, all signals generated by irradiation of primary electrons such as reflected electrons, absorbed electrons, Auger electrons, X-rays, and transmitted electrons can be used as image signals in addition to secondary electrons. Secondary electrons and transmitted electrons generated from the sample 1 enter the electron detection devices 21a and 21b, are converted into electronic signals, and are processed by the electronic signal processing circuit 22. By measuring this output with a cathode ray tube or the like, it is possible to not only observe the shape of the sample but also analyze its state and composition. The resolving power of this stopping field type electron spectrometer depends on the diameter of the electron beam.

FIG. 5B is a view for explaining a deflection electric field type electron spectrometer. The sample 1 is irradiated with an electron beam from the electron gun 20. The electron beam generated from the sample 1 passes through the deflection electrode 24 to which a static deflection field is applied. The electron beam that has passed through the deflecting electrode 24 enters the electron detector in the same manner as the stop-field-type electron spectrometer shown in FIG. 5A, and is converted into an electronic signal before being processed by the electronic signal processing circuit 22. By measuring this output with a cathode ray tube 23 or the like, it is possible to not only observe the shape of the sample but also analyze its state and composition.

[0005]

However, in the above conventional apparatus, the resolution of the energy of electrons is limited to several meV. The resolution can be increased by reducing the diameter of the electron beam. However, in general, the current decreases when the diameter is reduced, and there is a limit to improving the resolution.

Accordingly, an object of the present invention is to provide an energy distribution measuring device capable of measuring the energy of discharged particles (eg, photoelectrons) from a sample with high resolution.

[0007]

A charged particle energy distribution measuring apparatus according to the present invention holds a space from a sample held by a sample holding section to an output face plate in a vacuum state, and applies a pulse-like energy to the sample. Irradiating the charged particles emitted from the sample by this irradiation, after drifting, in the energy distribution measuring device of the charged particles deflecting in the direction perpendicular to the traveling direction and leading to the output face plate, the drift and A voltage for acceleration is applied, a limiter aperture electrode having an opening for passing only the charged particles emitted in a substantially vertical direction from the sample, and a deflection electrode to which a sweep voltage for performing the deflection is applied. A focusing means provided between the limiter aperture electrode and the deflection electrode for imaging the beam of charged particles on the output face plate. Characterized in that it comprises and.

[0008]

When the charged particles emitted from the sample travel through the space where drift and acceleration occur, a path difference is generated based on the speed difference in the output direction of the initial speed at the time of ejection. For this reason, in the process of passing through the deflecting electrode to which the sweep voltage for changing the electric field with time is applied, the beam is deflected to a different angle, and thus the path difference generated according to the initial velocity in the drift space is directly applied to the output face plate. Appears disassembled. Further, by providing the limiting aperture electrode and the focusing means, only charged particles emitted from the sample in a substantially vertical direction can be incident on the output face plate with high resolution.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to description of embodiments, the principle of an electron spectrometer will be described as an example of a charged particle energy distribution measuring device according to the present invention. FIG. 1 is a perspective view thereof,
FIG. 2 is a side view. As shown in the figure, an output surface plate 50 on which a drift-producing electrode 2, an electron lens system 3, a deflecting electrode 4, and a fluorescent surface 5 are formed is sequentially arranged in front of the sample 1. Also, a delta function-like excitation pulse such as an ultrashort pulse light is incident on the sample 1, and a voltage V ₁ for drift and acceleration is applied between the sample 1 and the electrode 2. I have. Further, between the pair of deflection electrodes 4, a sweep voltage V _S whose potential difference changes monotonously is applied. Here, the length L from the sample 1 to the electrode 2
This space constitutes a space in which charged particles (for example, photoelectrons) emitted from the sample 1 drift and are accelerated. An opening is formed at the center of the electrode 2 so that only the photoelectrons emitted from the sample 1 in the acceleration direction reach the rearward focusing and deflection space.
Serves as a limiting aperture that cuts off excess photoelectrons. These are all housed in a vacuum container.

Next, the operation and principle of the electron spectrometer according to the present invention will be described.

First, when the sample 1 in the vacuum vessel is irradiated with a pulse light having a negligible time width from a laser pulse light source (not shown), the sample 1
E is released in different directions at approximately the same time. Here, the photoelectrons D and E having a large initial velocity component orthogonal to the acceleration direction strike the electrode 2 which is also an aperture, and are lost. The other photoelectrons A to C pass through the drift space and reach the next focusing and deflection space, and the emission energies of the emitted photoelectrons A to C vary depending on the type and state of the irradiated sample 1. Different. The traveling speed and traveling time of the emitted photoelectrons from the sample 1 also differ due to the difference in the emitted energy. In other words, if the released energy is large, the traveling speed is high and the traveling time is short. Conversely, if the released energy is small, the traveling speed is low and the traveling time is long.

In the case of FIG. 2, a photoelectron A having a large emission energy and a photoelectron B having a small emission energy
Suppose that there is a smaller photoelectron C. Since a voltage is applied between the sample 1 and the electrode 2 also serving as a limit aperture, the three emitted photoelectrons A, B, and C
In this process, the photoelectrons A
Since the emission energy of the photoelectron B is larger than that of the photoelectron B compared to the photoelectron B, the traveling speed becomes faster, and the photoelectron A precedes B and B precedes C. Further, as the traveling time elapses, the traveling distance difference between the photoelectrons A, B, and C increases. That is, A ₂ −B ₂ −C ₂
The distance between them is longer than the distance between A ₁ -B ₁ -C ₁ .

Next, the photoelectrons A to C emitted almost vertically from the sample 1 pass through the closing of the electrode 2 and pass through the deflection electrode 4 to which the oblique voltage that decreases with time is applied. At this time, a larger voltage is applied to the deflection electrode 4 when the preceding emitted photoelectrons pass than when passing the subsequent emitted photoelectrons. For this reason, the preceding emitted photoelectrons pass through the deflection electrode 4 when a larger voltage is applied to the deflection electrode 4, and thus are swept larger than the subsequent emission photoelectrons.

In this case, since the emission energy of the emitted photoelectrons A is greater than that of the emitted photoelectrons B, the emitted photoelectrons A ₂ precede the emitted photoelectrons B ₂ , and
Will be passed. Since the voltage applied to the deflecting electrode 4 decreases with time, the voltage applied to the deflecting electrode 4 is higher when the emitted photoelectrons A ₂ pass than when the emitted photoelectrons B ₂ pass. Thus, the emitted photoelectrons A ₂ are swept more than the emitted photoelectrons B ₂ . As a result, the swept image A ₃ on the phosphor screen 5 corresponding to the emitted photoelectrons A is above the swept image B ₃ on the phosphor screen 5 corresponding to the emitted photoelectrons B.

In the description of the principle of operation, the difference in emission energy of emitted photoelectrons quantitatively indicates how much a transit time difference is generated between the sample 1 and the electrode 2. The distance between the sample 1 and the electrode 2 is L, the applied voltage is V ₁ , and the transit time T from the sample 1 to the electrode 2 when photoelectrons are emitted from the sample almost vertically at V ₀ [eV] is represented by the equation of motion. It is easily determined and is shown in the following equation. T = (2 mL / eE) ^1/2 {(1 + V ₀ / V ₁ ) ^1/2 − (V ₀ / V ₁ ) ^1/2 } where E = V ₁ / L, m: mass of electrons, e: It is an electron charge.

In the above equation, for example, L = 0.1 [m], V ₁
= 100V, emission photoelectrons of 0 eV initial velocity and 1 eV of initial velocity
The transit time difference from the emitted photoelectrons is about 30 ps. On the other hand, how much the transit time difference is detected by the deflection electrode 4 has already been verified by a streak tube,
It is known that a temporal resolution of 1 ps or more can be obtained. Therefore, it can be seen that the time resolution of about 30 ps corresponding to the difference of 1 meV in the above example is sufficient.

However, actually, the photoelectrons emitted from the sample 1 are not always emitted almost vertically, but have various angular distributions. As shown in FIG. 3, the photoelectrons emitted from the sample ₁ within the angle θ ₁ pass through the opening of the electrode 2 as a limit aperture, and are swept by the deflection electrode 4, but emitted at the angle θ ₁ or more. If even the photoelectrons are formed on the phosphor screen 5 as streak images, they cause measurement errors. For example, when the emitted photoelectrons D and the emitted photoelectrons A emitted at the angles θ ₂ and θ ₁ have the same emission energy, the emitted photoelectrons D travel in a detour, and are at least longer than the emitted photoelectrons A. It takes time, and accordingly, the degree of sweep at the deflection electrode 4 becomes low, and the energy is considered to be small. For this reason, the emitted photoelectrons emitted at an angle θ ₁ or more are captured by the electrode 2 as a limit aperture.

By the way, as the size of the opening of the electrode 2 as the limiting aperture is smaller, only the photoelectrons emitted in the vertical direction from the sample 1 are selectively passed, and the measurement error due to the detour of the photoelectrons is reduced. . However, if the aperture is too small, the number of photoelectrons passing therethrough will decrease, and the sensitivity will decrease. Conversely, if the aperture is too large, the resolution when decomposing in space and time with a streak camera will be reduced. Therefore, an electron lens system (not shown) may be provided between the sample 1 and the electrode 2. Specifically, the photoelectron measurement system is composed of an electron lens and an electron direct-type streak camera. Photoelectrons from the sample are converged by the above-described electron lens, and the entrance aperture of the streak tube (corresponding to the opening of the limiting aperture) May be collected. By appropriately selecting the degree of convergence by the electron lens and the size of the aperture, sensitivity and resolution can be set according to measurement conditions. The emitted photoelectrons that are not captured by the limiting aperture electrode 2 spread on the phosphor screen 5 as they are, so that the emitted photoelectrons are collected by the focusing electrode 3 and are collected by the focusing electrode 3 so as not to give an error to the measurement. 5 is not spread.

FIG. 4 is a sectional view showing an embodiment of the electron spectroscopy apparatus according to the present invention. This electron spectroscopy apparatus includes a main body configured in a glass container 16 (16A, 16B) as a vacuum container, a laser pulse light source 10, and reference numerals 11 to 13.
And a device for generating an oblique voltage represented by On one end side of the glass container 16 (on the side of the container 16A), a laser incident window 9 and a pressing spring 17 for fixing the sample 1 to one end in the glass container 16 so that the laser pulse light from the laser incident window 9 is irradiated. And the other end (container 16B
Side), a vacuum pump 18 for evacuation for maintaining the vacuum inside the glass container 16 is connected, and the fluorescent screen 5 on which a swept image of emitted photoelectrons emitted from the sample 1 is formed as a streak image is formed. And an output surface plate 50 on which the phosphor screen is formed. Inside the glass container 16, a limiter aperture electrode 2 for passing only emitted photoelectrons emitted almost perpendicularly from the sample 1, a deflecting electrode 4 for deflecting the emitted photoelectrons, and passing through the limiter aperture electrode 2 A focusing electrode 3 for focusing the photoelectrons,
An anode 6 for accelerating photoelectrons that have passed through the limiting aperture electrode 2 is provided. Further, a potential is applied to the sample 1 from an external power supply via a lead wire penetrating the wall of the glass container 16. A variable potential is applied to the focusing electrode 3 from an external power supply via a lead wire, and the focusing electrode 3 is adjusted so as to minimize the spot size on the phosphor screen 5. In this case, the voltage between the sample and the anode is 10 KV, and the anode is grounded. One of the deflection electrodes 4 on the output side of the anode 6 is grounded, and an oblique voltage is applied to the other via a lead wire. Note that the end of the glass container 16 to which the sample 1 is fixed is detachable so that the sample 1 can be replaced. In order to maintain a higher vacuum state, a ring 19 is provided between the container 16A and the container 16B.
Although a and 19b are used, a higher vacuum state can be maintained by pressing a copper ring with a metal flange instead of the ring. The distance L between the limiter aperture electrode 2 of the glass container 16 and the sample 1 must be sufficient to reflect the energy difference in the travel time difference. In this case, the distance L is set to 100 mm. The voltage applied during this period is set to 100 V, and the opening diameter of the limit aperture electrode 2 is set to 100 μm.

The oblique voltage generator comprises a PIN diode 11 into which the laser pulse light from the laser pulse light source 10 is reflected and reflected by the half mirror 15, a delay circuit 12, and an oblique voltage generation circuit 13. . The oblique voltage generated by the oblique voltage generator is applied to the deflection electrode 4 and passes through the limit aperture electrode 2 to sweep the focused and accelerated photoelectrons.

Next, the operation of the embodiment will be described.

First, 1 ps from the laser pulse light source 10
Is incident on the sample 1 and photoelectrons having various emission energies are emitted substantially simultaneously, and are slowly accelerated by a low voltage of 100 V applied between the sample 1 and the limit aperture electrode 2. Of these emitted photoelectrons, only those emitted almost vertically from the sample 1 pass through the limit aperture electrode 2. Furthermore, the emitted photoelectrons that have passed through the limit aperture electrode 2 are focused by the focusing electrode 3 and enter between the deflection electrodes 4.

On the other hand, a part of the ultrashort pulse laser light is reflected by the half mirror 15 and is incident on the PIN diode 11 to generate an electric pulse. Further, the electric pulse is delayed by an appropriate amount by the delay circuit 12, and then the oblique voltage generating circuit 13 is triggered to generate an oblique voltage. This oblique voltage is applied to the deflection electrode 4 via a lead wire passing through the glass container 16. Since this oblique voltage decreases with the passage of time, the voltage applied to the deflecting electrode 4 also decreases, and the emitted photoelectrons that arrive at the deflecting electrode 4 later in time are swept downward in the drawing. Then, a streak image is formed on the phosphor screen 5. It should be noted that those that are not emitted almost vertically from the sample 1 are captured by the limiting aperture electrode 2 and are not formed as streak images on the phosphor screen 5. Also, photoelectrons emitted not vertically but almost vertically from the sample 1 are not captured by the limiting aperture electrode 2, but are not spread on the fluorescent screen 5 because they are focused by the focusing electrode 3. Measurement errors can be eliminated.

In the above embodiment, in order to enhance the resolution, the inner walls of the glass container 16 are coated with metals 8a and 8b such as Al so that the speed of the emitted photoelectrons does not fluctuate due to the electric charge generated on the surface of the glass container. To form a wall electrode. In the case of the embodiment of FIG.
The potential of the wall electrode 8a is the same as that of the sample. In addition, as the travel time difference electron emission energy is different is more remarkable, it may be the voltages V ₁ between the sample 1 and limiter proboscis aperture electrode 2 to a negative voltage. Further, M
By arranging the CP 7 on the surface of the phosphor screen 5, the emitted photoelectrons swept by the deflection electrode 4 can be more brightly focused on the phosphor screen 5 as a streak image. According to the configuration of such an electron spectroscopic device, an energy resolution of 0.5 meV or less can be obtained when the emission energy of the emitted photoelectrons is in the range of 0 to 10 eV.

In the above-described embodiment, the excitation energy beam for emitting photoelectrons substantially simultaneously from the sample 1 is an ultrashort pulse laser beam. However, the present invention is not limited to this. Irradiation with an ultrashort electron beam is also possible. is there. Also, X-ray, ultraviolet,
Visible light and the like can also be used. Further, as a method of applying a deflection voltage to the deflection electrode 4, a so-called push-pull sweep in which oblique voltages having opposite phases are applied to both deflection plates is also possible. Further, also in the case where ions emitted from the sample 1 are ions, if anions are anions, a voltage having a forward polarity may be applied in the same manner as in the above-described embodiment. A voltage may be applied. Further, instead of the MCP 7 and the phosphor screen 5, an electron beam impact type solid-state imaging device may be arranged on the inner surface of the output surface.

[0026]

As described above, according to the present invention,
In the process of traveling in the drift space, the charged particles emitted from the sample generate a travel time difference based on the speed difference in the acceleration direction among the initial velocities at the time of ejection. For this reason, the electric field is swept to different angles in the process of passing through the deflecting electrode that changes monotonically with time, so that the transit time difference generated according to the initial velocity in the drift space appears as it is spatially resolved on the output face plate. Further, by providing the aperture means and the focusing means, only the charged particles emitted from the sample in a certain direction can be incident on the output face plate with high resolution. In the present invention, the energy distribution of only the photoelectrons emitted almost vertically passing through the limit aperture electrode is obtained by a streak method using a deflection electrode. Therefore, it is possible to provide an electron spectrometer capable of obtaining high resolution.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating the operation and principle of an electron spectroscopy apparatus according to the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is a diagram showing a main part of FIG. 2;

FIG. 4 is a diagram showing an embodiment of the electron spectroscopy apparatus according to the present invention.

FIG. 5 is a diagram illustrating a conventional configuration.

[Explanation of symbols]

 1: Sample, 2: Electrode (Limiting aperture electrode), 3: Electron lens system, 4: Deflection electrode, 5: Phosphor screen.

Continuation of the front page (56) References JP-A-2-20563 (JP, A) JP-A-50-112188 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 49 / 44-49/48 H01J 37/244 H01J 37/252 H01J 37/05

Claims (4)

(57) [Claims] 1. A space from a sample held by a sample holding unit to an output face plate is held in a vacuum state, and the sample is irradiated with pulsed energy rays, and charged particles released from the sample by the irradiation are irradiated with a pulsed energy beam. In a device for measuring the energy distribution of charged particles, which is deflected in the direction perpendicular to the traveling direction after drifting and is guided to the output face plate, a voltage for performing the drift and acceleration is applied and emitted from the sample in a substantially vertical direction. A limiting aperture electrode having an opening through which only the charged particles pass, a deflection electrode to which a sweep voltage for performing the deflection is applied, and the limiting electrode provided between the limiting aperture electrode and the deflection electrode. A focusing means for focusing a beam of charged particles on the output face plate. 2. The apparatus according to claim 1, further comprising an electron lens provided between said sample and said limiter aperture electrode to focus charged particles from said sample on said limiter aperture electrode. For measuring the energy distribution of charged particles. 3. The pulsed energy beam is an ultrashort pulse light repeated at a constant time interval, and the sweep voltage is synchronized with the repetition period while a predetermined time is delayed from the emission of the ultrashort pulse light. The charged particle energy distribution measuring device according to claim 1, wherein the device is configured to change monotonically. 4. The apparatus according to claim 1, wherein a fluorescent surface is formed on the output face plate.