JP3419662B2 - Work function measuring method, work function measuring device, and sample holder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for measuring properties and states of materials, especially work functions.

[0002]

2. Description of the Related Art In the development of a material having a specific function, a work function is determined as a means for determining the characteristics of the material. In order to measure such a work function, an electrode that vibrates with a constant amplitude is generally opposed to the surface of the sample, and a surface potential measuring device that measures the potential difference between the sample and the electrode by the zero-position method is used. As shown in Japanese Patent Laid-Open No. 1-138450, an anode B is disposed inside a cathode A having an opening at one end, and an electric field is applied between the both electrodes. There is used a photoelectron emission threshold value measuring device or the like which is provided and which irradiates the surface with light L while sequentially changing the wavelength and detects the energy of light when light having a photoelectron emission darkness value or more is irradiated.

[0003]

According to the former device,
Measurement can be performed by a simple operation of facing the movable electrode to the sample, but it is difficult to accurately grasp the characteristics of the sample itself because the measurement result is greatly influenced by the gas molecules attached to the movable electrode. With the latter device, the work function of the material itself can be grasped accurately without being affected by gas molecules, but a substance whose work function depends on the Fermi level like a semiconductor material. In that case, there is a problem that the work function of the element or molecule constituting the material cannot be measured. The present invention has been made in view of such problems,
Its purpose is to propose a method for accurately measuring the characteristics of a sample regardless of the type of the sample and the attachment of gas molecules. Another object of the present invention is to provide an apparatus for carrying out the above measuring method.

[0004]

In the present invention in order to solve the Means for Solving the Problems] The problem is irradiated with excitation light while sequentially scanning the wavelength in the standard specimen, when photoelectrons from the standard sample is light emitted a first step of obtaining the energy, the target
A second step of measuring the potential difference between the movable electrode and the standard sample by vibrating the movable electrode at a constant frequency so as to move forward and backward with respect to the surface of the quasi sample, and a test for measuring the work function.
It is movable at a constant frequency so that it moves back and forth with respect to the surface of the material.
It is necessary to vibrate the pole and measure the movable electrode and the work function.
The third step of measuring the potential difference from the sample and the first step
Based on the difference between the potential differences obtained in the step and the second step,
A fourth step of correcting the work function obtained based on the third step is provided, and the work function of the movable electrode itself can be corrected.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described below with reference to illustrated embodiments. FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 is a vibration type surface potential measuring device, and reference numeral 2 is a photoelectron emission threshold measuring device. In this embodiment, the sample holder 3 is integrally incorporated.

The surface potential measuring device 1 comprises a movable electrode 12 attached to an exciter 11 and a potential difference measuring circuit 13 for detecting a potential difference between the movable electrode 12 and a sample. , The sample holder 3 in this embodiment
Is integrated into the.

The photoelectron emission threshold measuring device 2 includes an anode 22 for forming an unequal electric field, a first grid electrode 23 for controlling discharge, and a first grid electrode 23, in the inner space of a cylindrical cathode 21 having an opening 21a at the bottom. The detection unit 25 is provided such that the two grid electrodes 24 are arranged in a vertical relationship.

The anode 22 is supplied with a high voltage from the discharge voltage generating circuit 26 through the high resistance R, which is high enough to cause a discharge between the anode 22 and the cathode 21 when photoelectrons enter the opening 21a. The discharge detection circuit 27 is connected via the capacitor C.

The first grid electrode 23 is a first pulse generator 28.
However, the second grid electrode 24 is connected to the second pulse generator 29, and as shown in FIG. 2, the first grid electrode 23 is constantly discharged with a voltage of about 100 V and is also discharged based on photoelectrons (see FIG. 2 (a)) occurs, a voltage of about 400 V that continues Te for a certain time is applied (see FIG. 2).
(B)) Moreover, a voltage of about 80 V is normally applied to the second grid electrode 24, and a voltage of about −30 V (FIG. 2C) is applied at the stage when a pulse due to discharge is detected.

As a result, the photoelectrons from the sample are drawn into the anode 22 by the potential of the second grid electrode 24, and a discharge corresponding to the number of photoelectrons is generated for a certain period of time Te. To prevent the development of.

A light beam generator 30 is arranged near the detector 25. This light beam generator 3
Reference numeral 0 is composed of a light source 31 and a spectroscope 33 which is controlled by a signal from the wavelength switching circuit 32, and is capable of irradiating a sample or the like with light having different wavelengths.

An energy detection circuit 34 detects the spectral energy of the light beam irradiating the sample when a signal is output from the discharge detection circuit 27.

The sample holder 3 connects the sample to the ground,
In this embodiment, a supporting portion 35 that is held horizontally is provided so that the surface of the sample is parallel to the movable electrode 12, and is connected to the potential difference measuring circuit 13 via a lead wire.

Reference numeral 36 denotes a work function calculation circuit, which adds the work function V0 of the movable electrode 12 measured by the energy detection circuit 34 to the potential difference Vs with the sample measured by the potential difference measurement circuit 13 and outputs the result. is there.

Next, the operation of the thus constructed apparatus will be described. As shown in FIG. 3A, the movable electrode 1
2 is arranged below the opening 21a of the cathode 21 so that its sample facing surface faces the detecting section 25 of the photoelectron emission threshold measuring device 2, and the light Lλ of the light beam generators 31 and 33 is irradiated while changing the wavelength. To do.

When the movable electrode 12 is irradiated with light Lλ having a wavelength having an energy exceeding the work function of the material forming the movable electrode, that is, the photoelectron emission threshold, photoelectrons are emitted from the surface thereof.

Since the photoelectrons move to the anode 22 to cause discharge, the work function V0 of the movable electrode 12 can be found by detecting the light energy at this time by the energy detection circuit 34.

In this way, the work function V of the movable electrode 12 is
When 0 is found, as shown in FIG. 3B, the sample S is placed on the sample holder 3 so as to face the movable electrode 12 with a gap, and the movable electrode 12 is moved back and forth with respect to the sample. To vibrate.

Naturally, a contact charging phenomenon in the field of semiconductor physics occurs between the movable electrode 12 and the sample S, and a potential difference Vs corresponding to a work function difference is induced between them, and the movable electrode Since a capacitor is formed between 12 and the sample S, it constitutes a kind of electrostatic generator.

Therefore, the work function of the sample S can be measured by detecting the potential difference VS corresponding to the work function of the movable electrode 12 and the sample S by the work function calculation circuit 36 including the measuring means of the ultrahigh input impedance. You can

As described above, according to the vibrating surface potential measuring apparatus 1, if the work function of the movable electrode itself is known, the work function can be obtained regardless of the type of the sample. Therefore, the photoemission threshold is the work function. Even for a sample such as a semiconductor that does not match the above, the work function based on the composition of the sample can be accurately measured.

In the above embodiment, the work function of the movable electrode is detected before the sample is measured. However, after the sample is measured, the work function of the movable electrode is detected and corrected. Even if it does so, it is clear that the same operational effect can be obtained.

Further, in the above embodiment, the work function of the movable electrode is directly measured, but it is also possible to measure it through a standard sample. That is, the work function of a standard sample whose work function is measured by the photoelectron emission threshold measuring device 2 is determined by the vibration type surface potential measuring device 1,
The difference between the two measured values is stored as a correction value due to gas adsorption of the movable electrode.

By measuring the sample with the vibration type surface potential measuring device 1 and correcting the value obtained by the correction value, an error caused by gas adsorption of the movable electrode 12 can be corrected.

Further, in the above-mentioned embodiment, the sample holder 3 is attached to the opening 21 of the cathode 21 of the photoelectron emission threshold measuring device 2.
Although it is arranged so as to face a, it may be attached to the conveying means so that it can be moved.

That is, FIG. 4 shows an embodiment of a work function measuring apparatus using the above-mentioned work function measuring method, and FIG. 5 shows an enlarged measuring area, which shows a high impedance. A frame 41 is provided on the upper surface of a main body case 40 having a built-in voltage measuring means, a measuring mechanism is arranged, and a microscope 43 for confirming the position of the sample on the front side of the frame 41 falls over so as not to hinder the measurement. It is provided so that it can be retracted or removed.

The frame 41 has a front surface provided with a control panel 44 and a side opening by a notch 41a so that a sample can be inserted and removed, and a knob 45 is provided in an area surrounded by the frame 41. A sample mounting table 47 that allows the sample to move up and down, and a vibration type surface potential measuring unit 48 are arranged so as to be located on the upper surface of the sample. 56
And a potential display panel 57 is arranged.

The vibration type surface potential measuring unit 48 is shown in FIG.
As shown in FIG. 5, the electrode plate 52 is fixed to the surface of the unit case 49 via the conductive needle arm 51 on the free end side of the plate spring 50 fixed in the shape of a cantilever that also serves as the lead portion of the measurement potential. And a vibrating electrode configured as described above. Electrode plate 52
Is a material that is stable to the atmosphere at least on the surface facing the sample (upper surface in the figure) and has little gas adsorption, gold (A
u) or tungsten (W) plate material.

Returning to FIGS. 4 and 5, the vibration type surface potential measuring unit 48 is fixed to the frame 41 via the mounting substrate 53 with the electrode plate 52 facing downward, and the maximum displacement point of the electrode plate 52 downward. The lower surface 54 is located slightly below the
And, as shown in FIG. 7, the window 5 for exposing the electrode plate 52.
5 and a positioning substrate 57 having a notch 56 for ensuring a visual field for confirmation by the microscope 43.

The window 55 is formed with an inclined surface 55a expanding from the lower surface to the upper surface, and at least a surface facing the sample,
In the area of the window 55 and the window 55, a material that is stable to the atmosphere, that is, a gold plating layer in this embodiment is formed.

In this embodiment, the knob 45 is rotated in one direction to lower the sample mounting table 47, and the standard sample S whose work function is preliminarily measured by the photoelectron emission threshold measuring device is mounted on the sample, as described above. It is placed at a predetermined position on the stand 47 (FIG. 8A).

Next, when the knob 45 is rotated in the other direction until the surface of the standard sample S contacts the positioning substrate 57, the upper surface of the standard sample S contacts the lower surface of the positioning substrate 57,
The electrode plate 52 is positioned with a constant gap g (FIG. 8B).

When the vibrating surface potential measuring unit 48 is operated in this state, the electrode plate 52 is moved to the window 55 of the substrate 57.
Constant amplitude in the range of 0 ..
It vibrates below 5 mm.

In this measurement process, since the side of the electrode plate 52 is surrounded by the window 55 of the substrate 57 having a stable gold surface layer, the electrode plate 52 is not disturbed and the standard sample S Generate a potential of. Since the potential of the standard sample S thus detected is displayed on the display panel 57, the calibration work ends when the potential applied to the electrode plate 52 is adjusted by the dial 45 so as to be a value measured in advance. .

When the measurement of the standard sample is completed, the knob 4
5 is operated to take out the standard sample, and the target sample is set by the same process as described above. As a result, the gap g between the surface of the sample and the electrode plate 52 of the vibration type surface potential measuring unit 48 is set to the same value as when the standard sample S is measured,
The work function of a sample can be accurately measured in air without the need for a vacuum environment.

By the way, the standard sample S is composed of a stable thin gold plate, but since there is a possibility that ions in the atmosphere will adhere and the electric potential will change during a long period of time, it is shown in FIG. As described above, a concave portion 61 capable of projecting and positioning the surface of the standard sample S is formed in the center of the metal plate 60, and a concave portion capable of forming a gap between at least the measurement region of the standard sample S on the other metal plate 62. When the standard sample S is prepared, and the standard sample S is sandwiched between the two metal plates 60 and 62 and housed in a holder 65 which is clamped by tightening means such as screws 64 and 64, the measurement surface of the standard sample S and the atmosphere Can be cut off and the calibration potential can be maintained for a long time. It is desirable to form a stable metal layer such as gold on the opposing surfaces of the metal plates 60 and 62.

[0037]

As described above, according to the present invention ,
The work function of the movable electrode itself and its state can be corrected to accurately measure the work function of the sample.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a voltage change of each electrode of the photoelectron emission threshold measurement device,

3 (a) and 3 (b) are explanatory views showing the operation of the above apparatus.

4 (a) and 4 (b) are respectively a front view and a side view showing an embodiment of an apparatus by a vibration type surface potential measuring method.

FIG. 5 is an enlarged view showing a measurement region of the same device.

6A and 6B are a top view and a side view, respectively, showing an embodiment of a vibration type surface potential measuring unit.

7 (a) and 7 (b) are respectively a front view showing an embodiment of a sample positioning substrate of the same apparatus and a sectional view taken along line AA.

8 (a) and 8 (b) are diagrams showing the operation of the same apparatus in a state before sample setting and a measurable state, respectively.

9 (a) to 9 (c) are views showing an embodiment of a standard sample holder suitable for the above apparatus, respectively, in a state in which a metal plate constituting the holder and a sample are accommodated.

[Explanation of symbols]

1 Vibration type surface potential measuring device 2 Photoemission threshold measurement device 3 Sample holder 11 exciter 12 movable electrodes 25 Measuring section S sample

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Claims (5)

(57) [Claims] 1. A first step of irradiating a standard sample with excitation light while sequentially scanning wavelengths to obtain light energy when photoelectrons are emitted from the standard sample, and advancing / retreating with respect to the surface of the standard sample. A second step of vibrating the movable electrode at a constant frequency so as to measure the potential difference between the movable electrode and the standard sample, and a constant work function so that the work function advances and retreats with respect to the surface of the sample to be measured. The third step of vibrating the movable electrode at a frequency to measure the potential difference between the movable electrode and the sample whose work function is to be measured, and the difference between the potential differences obtained in the first step and the second step. A fourth step of correcting the work function obtained based on the third step, and a work function measuring method comprising: 2. A vibrating surface potential measuring means having a movable electrode plate vibrating at a constant frequency, a lower surface positioned slightly below a maximum displacement point of the movable electrode plate, and the movable electrode plate A work function measuring device comprising a positioning substrate having a window to be exposed and a positioning means capable of moving up and down with respect to the substrate and bringing a surface of a sample into contact with the substrate. 3. The work function measuring device according to claim 2, wherein a stable metal layer is formed on the surface of the substrate. 4. A first metal plate having a recess capable of projecting and positioning the surface of a standard sample, and a second metal plate having a recess capable of forming a gap between at least the measurement region of the sample. And a means for holding the metal plate by sandwiching the sample. 5. The sample holder according to claim 5, wherein a stable metal layer is formed on the facing surface of the metal plate.