JPH1194780A - Work function measuring method, apparatus therefor and sample holder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure work function regardless of material quality without being affected by a surface state. SOLUTION: A first process wherein the surface of a movable electrode 12 is irradiated with exciting light Lλ, while a wavelength is successively scanned to calculate light energy at a time of the discharge of photoelectrons from the surface of the movable electrode, a second process vibrating the movable electrode 12 in constant frequency so as to allow the same to advance and retreat with respect to a sample S (a) to measure the potential difference between the movable electrode 12 and the sample S, and a third process calculating the value wherein the light energy calculated in the previous process is added to this potential difference (b), are provided.

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, particularly work functions.

[0002]

2. Description of the Related Art In the development of a material having a specific function, a work function is obtained as a means for judging the characteristics of a material. In order to measure such a work function, an electrode oscillating with a constant amplitude is usually opposed to the sample surface, and a surface potential measuring device for measuring a potential difference between the sample and the electrode by a zero-point method, An anode B is provided inside a cathode A having one end opened as shown in Japanese Unexamined Patent Publication No. 1-138450, and a sample S is placed in the opening of the cathode A in a state where an electric field is applied between these two electrodes. A photoelectron emission threshold measurement device is provided which irradiates the surface with light L while sequentially changing the wavelength, and detects the energy of light when the surface is irradiated with light having a photoelectron emission dark value or more.

[0003]

According to the former device,
Although the measurement can be performed by a simple operation of facing the movable electrode to the sample, it is difficult to accurately grasp the characteristics of the sample itself because the measurement result largely depends on the gas molecules attached to the movable electrode. According to the latter device, the work function of the material itself is almost unaffected by gas molecules and the work function of the material itself can be accurately grasped. However, there is a problem that the work function of the elements and molecules constituting the material cannot be measured. The present invention has been made in view of such a problem,
The aim is to propose a method for accurately measuring the properties of a sample, irrespective of the type of sample or the adhesion of gas molecules. Another object of the present invention is to provide an apparatus for performing the above-mentioned measuring method.

[0004]

According to the present invention, in order to solve such a problem, the surface of the movable electrode is irradiated with excitation light while sequentially scanning the wavelength, and photoelectrons are emitted from the surface of the movable electrode. Obtaining light energy at the time of
Vibrating the movable electrode at a constant frequency so as to advance and retreat with respect to the surface of the sample, measuring a potential difference between the movable electrode and the sample, and obtaining a value obtained by adding the light energy to the potential difference. In addition, the work function of the movable electrode itself can be corrected.

[0005]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a first embodiment of the present invention. FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 denotes a vibration-type surface potential measuring device, and reference numeral 2 denotes a photoelectron emission threshold measuring device. In this embodiment, they are integrated into the sample holder 3.

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 the sample. In this embodiment, the sample holder 3
It is integrated into one.

The photoemission threshold value measuring device 2 includes an anode 22 for forming an uneven electric field, a first grid electrode 23 for controlling discharge, and a first grid electrode 23 in an inner space of a cylindrical cathode 21 having an opening 21a at a lower portion. The detection unit 25 includes a two-grating electrode 24 arranged in a vertical relationship.

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

The first grid electrode 23 is connected to a first pulse generator 28
However, a second pulse generator 29 is connected to the second grid electrode 24, and a voltage of about 100 V is normally applied to the first grid electrode 23 as shown in FIG. 2 (a)), a voltage of about 400 V which is continued for a certain time Te is applied (FIG. 2).
(B)) Also, a voltage of about 80 V is applied to the second grid electrode 24 at all times, and a voltage of about −30 V (FIG. 2C) is applied when a pulse due to discharge is detected.

Thus, 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 time Te. To prevent the development of

A light beam generator 30 is arranged near the detector 25. This light beam generator 3
Numeral 0 is composed of a light source 31 and a spectroscope 33 controlled by a signal from a wavelength switching circuit 32, so that a sample or the like can be irradiated with light having a different wavelength.

Numeral 34 denotes an energy detection circuit for detecting 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 ground,
In this embodiment, a support section 35 is provided to hold the sample horizontally 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 from the sample measured by the potential difference measurement circuit 13 and outputs the result. is there.

Next, the operation of the apparatus configured as described above will be described. As shown in FIG.
2 is arranged below the opening 21a of the cathode 21 such that the sample facing surface faces the detecting section 25 of the photoemission threshold value measuring device 2, and irradiates the light Lλ of the light beam generating devices 31 and 33 while changing the wavelength. I do.

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

Since the photoelectrons move to the anode 22 to cause a discharge, if the light energy at this time is detected by the energy detection circuit 34, the work function V0 of the movable electrode 12 is determined.

Thus, the work function V of the movable electrode 12
At the stage when 0 is found, the sample S is placed on the sample holder 3 and opposed to the movable electrode 12 with a gap as shown in FIG. Vibrate as follows.

Naturally, a contact charging phenomenon referred to 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 the two, and Since a capacitor is formed between the sample 12 and the sample S, it forms 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 between the movable electrode 12 and the sample S by the work function calculation circuit 36 comprising measuring means of an ultra-high input impedance. Can be.

As described above, according to the vibration type surface potential measuring device 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. The work function based on the composition of the sample can be accurately measured even for a sample such as a semiconductor that does not match the above.

In the above embodiment, the sample is measured after the work function of the movable electrode is detected. However, after the sample is measured, the work function of the movable electrode is detected and corrected. It is apparent that the same operation and effect can be obtained even if this is done.

In the above-described embodiment, the work function of the movable electrode is directly measured. However, the work function can be measured through a standard sample. That is, the work function of the standard sample whose work function is measured by the photoemission threshold measurement device 2 is determined by the vibration-type surface potential measurement device 1,
The difference between the two measured values is stored as a correction value due to gas adsorption of the movable electrode or the like.

By measuring the sample with the vibration-type surface potential measuring device 1 and correcting the obtained value with the correction value, it is possible to correct an error caused by gas adsorption of the movable electrode 12 or the like.

Further, in the above-described embodiment, the sample holder 3 is connected to the opening 21 of the cathode 21 of the photoemission threshold measuring device 2.
Although it is arranged so as to face a, it may be attached to a transport means so as to be movable.

FIG. 4 shows an embodiment of a work function measuring apparatus utilizing the above-described work function measuring method, and FIG. 5 shows an enlarged view of a measuring region, showing a high impedance. A frame 41 is provided on an upper surface of a main body case 40 having a built-in voltage measuring means, and a measuring mechanism is arranged. A microscope 43 for confirming a position of a sample is positioned in front of the frame 41 so as not to obstruct measurement. It is provided so as to be retractable or removable.

The frame 41 has a front surface on which the control panel 44 is provided and a lateral side opened by a notch portion 41a so that a sample can be inserted and removed. A knob 45 is provided in an area surrounded by the frame 41. A sample mounting table 47 that allows the sample to be moved up and down, and a vibration-type surface potential measurement unit 48 are arranged so as to be located on the upper surface of the sample. The control panel 44 has a dial for setting the potential measured with the standard sample. 56
And a potential display panel 57.

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

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

The window 55 is formed with a slope 55a extending from the lower surface to the upper surface, and at least a surface facing the sample,
Further, a material that is stable against the atmosphere, that is, a gold plating layer in this embodiment, is formed in the region of the window 55.

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 has been measured in advance by the photoemission threshold measuring device as described above is mounted on the sample. It is mounted on a predetermined position of the mounting table 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,
It is positioned at a fixed gap g with respect to the electrode plate 52 (FIG. 8B).

When the vibration-type surface potential measuring unit 48 is operated in this state, the electrode plate 52
, A constant amplitude up and down in the range of 0. In this embodiment, the amplitude is 0.1.
Vibrates at 5 mm or less.

In this measurement process, since the side of the electrode plate 52 is surrounded by the window 55 of the substrate 57 provided with the stable gold surface layer, the electrode plate 52 is not subject to disturbance and the standard sample S Generates a potential of The potential of the standard sample S detected in this manner is displayed on the display panel 57. Therefore, when the potential applied to the electrode plate 52 is adjusted by the dial 45 so that the potential becomes a value measured in advance, the calibration operation is completed. .

When the measurement of the standard sample is completed, the knob 4
5 is operated to take out a standard sample, and a target sample is set in the same manner as described above. Thereby, the gap g between the surface of the sample and the electrode plate 52 of the vibration-type surface potential measurement unit 48 is set to the same value as when the standard sample S was measured.
The work function of a sample can be accurately measured in the atmosphere without requiring a vacuum environment.

The standard sample S is composed of a stable thin gold plate. However, there is a possibility that ions in the atmosphere may adhere to the sample for a long period of time and the potential may change. In the center of the metal plate 60, a recess 61 is formed in which the surface of the standard sample S can be projected and positioned, and the other metal plate 62 has a recess capable of forming a gap between at least the measurement region of the standard sample S. When a standard sample S is prepared and accommodated in a holder 65 in which a standard sample S is sandwiched between two metal plates 60 and 62 and fastened by fastening means such as screws 64, 64, the measurement surface of the standard sample S and the atmosphere are removed. Can be disconnected, 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,
A step of irradiating excitation light while sequentially scanning the wavelength of the surface of the movable electrode to obtain light energy when photoelectrons are emitted from the surface of the movable electrode, and at a constant frequency so as to advance and retreat with respect to the surface of the sample. The method includes the steps of vibrating the movable electrode to measure a potential difference between the movable electrode and the sample, and obtaining a value obtained by adding the light energy to the potential difference, so that the work of the sample is performed regardless of the state of the movable electrode. The function can be measured accurately in the atmosphere.

[Brief description of the drawings]

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

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

FIGS. 3A and 3B are explanatory diagrams illustrating the operation of the above device.

FIGS. 4A and 4B are a front view and a side view, respectively, showing an embodiment of an apparatus using a vibration-type surface potential measurement method.

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

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

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

FIGS. 8A and 8B are diagrams showing the operation of the above-described apparatus in a state before setting a sample and in a measurable state, respectively.

FIGS. 9A to 9C are views showing one embodiment of a standard sample holder suitable for the above-described apparatus, respectively, in a state in which a metal plate constituting the holder and a sample are accommodated.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vibration type surface potential measuring device 2 Photoelectron emission threshold measuring device 3 Sample holder 11 Exciter 12 Movable electrode 25 Measuring part S Sample

Claims (7)

[Claims] 1. A step of irradiating excitation light while sequentially scanning the surface of a movable electrode with a wavelength to obtain light energy when photoelectrons are emitted from the surface of the movable electrode, and moving back and forth with respect to the surface of the sample. A work function measuring method comprising the steps of: vibrating a movable electrode at a constant frequency to measure a potential difference between the movable electrode and the sample; and obtaining a value obtained by adding the light energy to the potential difference. A step of irradiating the standard sample with excitation light while sequentially scanning the wavelength to obtain light energy when photoelectrons are emitted from the standard sample; Vibrating the movable electrode at a constant frequency to measure a potential difference between the movable electrode and the standard sample; and vibrating the movable electrode at a constant frequency so as to advance and retreat with respect to the surface of the sample. A work function measuring method comprising: a step of measuring a potential difference from the sample; and a step of obtaining a value obtained by adding the light energy to the potential difference. 3. A surface potential measuring means comprising: a movable electrode vibrating at a constant frequency so as to advance and retreat with respect to a surface of a sample; a surface potential measuring means comprising means for measuring a potential difference between the movable electrode and the sample; A light beam generating means for irradiating excitation light while scanning a wavelength, a photoelectron detection means for detecting photoelectrons from the sample, and a means for detecting the energy of the excitation light when photoelectrons are detected by the photoelectron detection means A work function measuring device comprising: a photoelectron emission threshold measuring unit comprising: a unit for obtaining a difference between the potential difference and the energy; and a sample holder for supporting a sample so as to face the movable electrode and the photoelectron detecting unit. . 4. A vibrating surface potential measuring means in which an electrode plate is fixed to a free end side of an elastic plate fixed in a cantilever shape also serving as a lead portion of a measured potential, and a maximum displacement point below said electrode plate. A work comprising: a positioning substrate whose lower surface is located slightly below and has a window that exposes the electrode plate; and positioning means that can move up and down with respect to the substrate and contact the sample surface with the substrate. Function measurement device. 5. The work function measuring apparatus according to claim 4, wherein a stable metal layer is formed on the surface of the substrate. 6. A first metal plate having a concave portion capable of projecting and positioning a surface of a standard sample, and a second metal plate having a concave portion capable of forming a gap between at least a measurement region of the sample. And a means for holding the metal plate across the sample. 7. The sample holder according to claim 6, wherein a stable metal layer is formed on the opposing surface of the metal plate.