JP2001050916A - Method and apparatus for measurement of work function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and an apparatus, in which a sample is irradiated with an ion beam so as to measure work function. SOLUTION: When a selected work-function measuring point is irradiated with an ion beam, gas molecules which are adsorbed to the surface of a sample are measured immediately because the ion beam is irradiated. After that, from the measuring point on the sample, secondary electrons which sufficiently reflect the work function of the sample are emitted. A control means 21 controls an analysis energy setting means 23. The analysis energy setting means 23 continuously changes (sweeps) the analysis energy of an electron spectroscope 20 within a certain range, while the work-function measuring point is being irradiated with the ion beam. An energy-spectrum acquisition means 22 obtains a spectrum in the measuring point, on the basis of a signal which is sent from the electron spectroscope 20. By the control means 21, a spectrum which is obtained by the energy-spectrum acquisition means 22 is displayed on a display means 27.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a work function measuring method and a work function measuring device for obtaining a work function of a sample.

[0002]

2. Description of the Related Art As a method of obtaining a work function of a sample,
Some methods use secondary electrons emitted from a sample by electron beam irradiation. This method will be described below.

When an electron beam is irradiated on the surface of a solid sample, electrons having an energy distribution as shown in FIG. 1 are generated. The portion having the largest intensity on the lowest energy side among them is “true secondary electron” or simply “secondary electron” for short.
is called.

FIG. 2 is an enlarged view of the lowest energy portion of the secondary electrons in FIG. Here, assuming that the energy at which the secondary electrons appear is Eonset, the intensity of the secondary electrons sharply increases from the point beyond Eonset. This Eon
set is determined by the work function Φs of the solid sample, the work function Φsm of the electron spectrometer for detecting secondary electrons, and Eb,
Eonset = Eb + Φs−Φsm Eb is Eb = e
In Vb, e is the elementary charge (1.6 × 10 ⁻¹⁹ C), Vb is the absolute value of the negative bias voltage applied to the sample, and the electron spectrometer has a vacuum level (the outermost surface of the spectrometer). Is adjusted based on the reference potential). Note that FIG. 2 is displayed with the vacuum level of the electron spectrometer as the coordinate origin.

[0005] The work function Φsm of the electron spectrometer can be determined by measuring Eonset for a sample whose work function is known. Therefore, if Φsm is known, the work function of the unknown sample can be measured by measuring Eonset for the sample whose work function is unknown.

The work function measuring method using an electron beam has been described above. However, according to this method, the electron beam can be narrowed down, so that it is possible to analyze a minute part.

[0007]

On the other hand, when performing such a conventional work function measuring method, there are the following disadvantages.

A) Since the work function Φs of the solid sample is extremely sensitive to gas adsorption on the solid surface, it is essential to provide a means for cleaning the sample surface, for example, an ion etching apparatus.

B) In addition, since the gas must not be immediately adsorbed on the sample surface after the sample has been cleaned by the ion etching apparatus, the vacuum tank must be compatible with an ultra-high vacuum, and the apparatus becomes expensive. .

C) Accurate measurement is difficult for a sample that is easily damaged by electron beam irradiation.

It is an object of the present invention to provide a work function measuring method and a work function measuring device which solve such a problem.

[0012]

A work function measuring method according to the present invention that achieves this object irradiates a sample with an ion beam, detects secondary electrons emitted from the sample by the ion beam irradiation, and obtains an energy spectrum. Is obtained, a secondary electron appearance energy at which secondary electrons appear is obtained from the obtained energy spectrum, and a work function of the sample is obtained based on the secondary electron appearance energy.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the work function measuring method described above, there has been no example examined so far when an ion beam is used instead of an electron beam.

At this time, when the present inventor tried, the work function of the sample can be measured in exactly the same way as in the case of electron beam irradiation, even if Eonset of secondary electrons generated by ion beam irradiation is used. I understand.

An embodiment of the present invention for obtaining a work function of a sample using an ion beam will be described below with reference to the drawings.

FIG. 3 is a diagram showing an example of the work function measuring device of the present invention.

In FIG. 3, reference numeral 1 denotes an ion beam irradiating means.
The apparatus includes a gas ion gun 2, a focusing lens 3, a deflector 4, and an objective lens 5.

Numeral 6 denotes a vacuum container of the gas ion gun 2. Helium gas stored in a gas storage chamber 7 is introduced into the vacuum container 6 through a gas flow control valve 8. Vacuum container 6
The gas pressure in the chamber is measured by a pressure measuring device (not shown), and a gas flow regulator (not shown) connected to the pressure measuring device maintains the gas pressure in the vacuum vessel 6 at a predetermined pressure. The gas flow control valve 8 is controlled so as to be controlled.

A vacuum vessel 6 has a filament 9 for generating electrons, an ionization chamber 10, and an extraction electrode 1 for extracting cations generated in the ionization chamber 10.
1 is arranged.

The filament 9 is connected to an emission current control unit 12 and the emission power source 1
3 is connected to the ionization chamber 10. Further, the ionization chamber 10 is connected to an extraction electrode 11 maintained at a ground potential via an ion acceleration power supply 14.

In such a gas ion gun 2, the filament 9 is heated by the emission current control unit 12 and the potential of the filament 9 is changed to the ionization chamber 1.
The emission power source 13 is set to a negative potential with respect to 0.
Is controlled, thermions generated in the filament 9 are accelerated toward the ionization chamber 10 and enter the ionization chamber. Therefore, the helium gas in the ionization chamber 10 is ionized by being irradiated with the electrons, and ions are generated.

The ion accelerating power source 14 is set so that the potential of the ionization chamber 10 becomes positive with respect to the extraction electrode 11.
Is controlled, the cations generated in the ionization chamber 10 are accelerated toward the extraction electrode 11, and the ion beam passing through the extraction electrode 11 is focused by the focusing lens 3 and the objective lens 5.

A sample chamber 15 is connected to the ion beam irradiation means 1, and a sample 16 is arranged in the sample chamber 15. The sample 16 is mounted on a sample stage 17, and the sample 16 is provided with a bias voltage applying device 1.
8, so that a negative bias voltage is applied.

A secondary electron detector 19 and an electron spectrometer 20 (signal detecting means) such as an electrostatic hemispherical energy analyzer are arranged inside the sample chamber 15, and their detection signals are controlled. Sent to the means 21. This control means 21 is an energy spectrum obtaining means 2 for obtaining an energy spectrum based on the output of the electron spectroscope 20.
2 is provided.

The analysis energy of the electron spectroscope 20 is set by the analysis energy setting means 23, and the analysis energy setting means 23 is controlled by the control means 21.

In the figure, reference numeral 24 denotes a deflection signal generating means for supplying a deflection signal to a deflection power supply 25. The deflection signal generating means 24 is controlled by the control means 21. Also, 26
Is input means, and 27 is display means, all of which are connected to the control means 21.

Reference numeral 28 denotes an exhaust device for exhausting the sample chamber 15.

The configuration of the apparatus shown in FIG. 3 has been described above. Next, the operation of this apparatus will be described.

First, the operator inputs an instruction to acquire a secondary electron image using the secondary electron detector 19 through the input means 26. When this input is performed, the control means 21 controls the deflection signal generation means 24,
Sends a deflection signal to the deflection power supply 25 to cause the ion beam to scan the sample two-dimensionally. As a result, the focused ion beam that has passed through the extraction electrode 11 is
Scanned dimensionally.

Secondary electrons are emitted from the sample 16 by the ion beam irradiation. The secondary electrons are detected by the secondary electron detector 19, and the detected signal is transmitted to the control means 21.
Sent to The control means 21 causes the display means 27 to display a secondary electron image of the sample 16 based on the transmitted signal.

In the apparatus shown in FIG. 3, a rare gas, helium gas, is selected as an ion species so that the sample surface is not modified by ion beam irradiation. The acceleration power supply 14 is controlled to reduce the ion energy. For this reason, even if the sample is irradiated with the ion beam for acquiring the secondary electron image, the sample is not damaged by the ion beam.

When the secondary electron image is displayed on the display means 27, the operator selects a point at which the work function is to be measured within the range of the visual field by using the input means 26 while viewing the secondary electron image. I do.

When the work function measurement point on the sample is selected in this way, the control means 21 controls the deflection signal generation means 2
4, and the deflection signal generation means 24 sends a deflection signal for irradiating the ion beam to the work function measurement point to the deflection power supply 25.

As a result, the ion beam irradiates the selected measurement point, and the ion beam irradiation immediately removes the adsorbed gas molecules on the sample surface. Thereafter, secondary electrons sufficiently reflecting the work function of the sample are emitted from the measurement points of the sample. As described above, during the work function measurement of the sample, it can be considered that the ion irradiation itself cleans the sample surface. Therefore, it is not necessary that the vacuum tank can maintain a high vacuum beyond the vacuum tank.

Further, the control means 21 controls the analysis energy setting means 23, and the analysis energy setting means 23 operates when the ion beam is irradiated on the work function measurement point.
The analysis energy of the electron spectrometer 20 is continuously changed (swept) within a certain range. As described above, the detection signal of the electron spectroscope 20 is sent to the control means 21, and the energy spectrum obtaining means 22 of the control means 21 obtains a spectrum at the work function measurement point based on the sent signal.

Then, the control means 21 causes the display means 27 to display the spectrum obtained by the energy spectrum obtaining means 22. FIG. 4 shows the spectrum. The operator visually calculates the secondary electron appearance energy Eonset from the spectrum, and obtains the calculated Eonset.
To obtain the work function Φs at the measurement point.

Although the apparatus shown in FIG. 3 has been described above, in such an apparatus, since the ion irradiation itself cleans the sample surface, the work function can be measured even when the vacuum chamber is at a relatively low vacuum. Further, unlike the work function measurement method using electron beam irradiation, there is no need to attach two electron irradiation devices and an ion etching device.

The efficiency of secondary electron emission by ion irradiation is not much different from that of electron beam irradiation at a high accelerating voltage (1 keV or more) even if the ion accelerating voltage is very low (50 eV or less). Therefore, even if ions having sufficiently low energy are used, there is no hindrance to the measurement of Eonset, and the sample is hardly damaged by ion irradiation. By the way, in the case of irradiating an electron, although the sample damage due to the electron irradiation is reduced as the energy becomes lower, the secondary electron emission efficiency is remarkably reduced at the same time, so that the measurement of Eonset becomes difficult.

As described above, an example of the present invention has been described, but the present invention is not limited to this example.

For example, in the above-described example, the spectrum is displayed and the Eonset is obtained visually, but the Eonset may be obtained automatically by the apparatus.
As an example, a means may be provided for obtaining the energy at which the second derivative of the spectrum becomes zero based on the output of the energy spectrum obtaining means, and the obtained energy may be used as the secondary electron appearance energy Eonset. Further, a means for calculating the work function of the sample from Eonset = Eb + Φs−Φsm based on the output of the means for calculating the secondary electron appearance energy may be provided. With such means, the work function of the sample can be automatically obtained. FIG. 5 shows a spectrum obtained by the energy spectrum obtaining means.
set indicates the energy at which the second derivative of the spectrum becomes zero.

Although helium gas is used in the above example, a rare gas such as argon, krypton, or xenon may be used.

In the case of monitoring the change of the work function when different ions are irradiated on the surface of the sample, not only rare gas ions but also all the ions of interest are added to the sample. Irradiation may be performed.

When Φs ≧ Φsm holds, Vb = 0 may be used in principle. In this case, a bias voltage applying device is not required. However, the work function of the spectroscope usually depends on the work function of the sample. Since the value is not so small as compared with the function and may be reversed, a bias voltage applying device is indispensable practically. The same result can be obtained by applying a bias of the opposite polarity to the entire spectroscope instead of applying a bias voltage to the sample, but in practice, the former is often easier to realize.

[Brief description of the drawings]

FIG. 1 is a diagram showing an energy distribution of electrons generated from a sample when the sample is irradiated with an electron beam.

FIG. 2 is an enlarged view of the lowest energy portion of the secondary electrons in FIG.

FIG. 3 is a diagram showing an example of the work function measuring device of the present invention.

FIG. 4 shows a spectrum obtained by an energy spectrum obtaining means.

FIG. 5 shows a spectrum obtained by an energy spectrum obtaining means.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ion beam irradiation means, 2 ... Gas ion gun, 3 ... Focusing lens, 4 ... Deflector, 5 ... Objective lens, 6 ... Vacuum container, 7 ... Gas storage room, 8 ... Gas flow control valve, 9 ... Filament, DESCRIPTION OF SYMBOLS 10 ... Ionization chamber, 11 ... Extraction electrode, 12 ... Emission current amount control part, 13 ... Emission power supply, 1
4 ... Ion acceleration power supply, 15 ... Sample chamber, 16 ... Sample, 17
... Sample stage, 18 ... Bias voltage applying device, 19 ...
Secondary electron detector, 20: electron spectrometer, 21: control means,
22: Energy spectrum acquisition means, 23: Analysis energy setting means, 24: Deflection signal generation means, 25: Deflection power supply, 26: Input means, 27: Display means, 28: Exhaust device

Claims (3)

[Claims] A sample is irradiated with an ion beam, secondary electrons emitted from the sample by the ion beam irradiation are detected to obtain an energy spectrum, and a secondary electron in which secondary electrons appear from the obtained energy spectrum. A work function measurement method comprising: obtaining an electron appearance energy; and obtaining a work function of the sample based on the secondary electron appearance energy. 2. An ion beam irradiator for irradiating a sample with an ion beam, a signal detector for detecting secondary electrons emitted from the sample by the ion beam irradiation, and an output of the signal detector. A work function measuring apparatus, comprising: an energy spectrum obtaining unit for obtaining an energy spectrum; and a display unit for displaying the energy spectrum based on an output of the energy spectrum obtaining unit. 3. An ion beam irradiator for irradiating a sample with an ion beam, a signal detector for detecting secondary electrons emitted from the sample by the ion beam irradiation, and an output of the signal detector. A work function measuring apparatus, comprising: an energy spectrum obtaining unit that obtains an energy spectrum; and a unit that obtains secondary electron appearance energy at which secondary electrons appear based on an output of the energy spectrum obtaining unit.