JPH0573188B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electronic counting device that counts the number of electrons emitted from a sample upon irradiation with light energy.

(Prior art) Conventionally, as a method for measuring the thickness of an oxide film or the like on the surface of a sample such as a semiconductor, the sample surface is irradiated with single-wavelength light of a predetermined wavelength. A method is known in which film thickness is measured by counting the electrons emitted by an electron detector using an electron detection unit (Japanese Patent Application No. 118818/1981, etc.), and an application of this device is to apply light to the surface of metal materials such as aluminum. An electronic counting device has been proposed that can measure the work function of a metal material by measuring the number of electrons emitted when it is irradiated.

(Problem to be solved by the invention) However, in order to measure the work function of aluminum, for example 3.5 eV, using such an electronic counting device, a monochromator irradiates a single wavelength light with the wavelength changed in the range of 150 nm to 500 nm. In this case, an electron counting rate as shown by the solid line in FIG. 7 is obtained.

However, since the work function of aluminum is 3.5 eV, the electron count rate should be obtained only when irradiated with a single wavelength light of 350 nm or less, as shown by the broken line, but in reality, the electron count rate shown in Figure 7 is As shown by the solid line, the electron count rate is obtained even when irradiated with a single wavelength light in the wavelength range larger than 350 nm, and originally, as shown by the broken line, the electron count rate is obtained by irradiation with single wavelength light in the wavelength range below 350 nm. The measurement results that were expected to be obtained could not be achieved.

Therefore, the inventor of the present application conducted various experiments to investigate the cause of this, and came to the conclusion that the cause lies in the spectral characteristics of the monochromator.

In other words, a monochromator originally emits single-wavelength light whose light intensity is concentrated at a predetermined center wavelength, but in reality, when looking at the frequency spectrum of single-wavelength light of, for example, 360 nm, the frequency spectrum shown in Figure 8 is shown. like,
In contrast to the fundamental spectral component with a wavelength of 360 nm, a spectral component as secondary light is generated at half the wavelength of 180 nm, and when aluminum with a work function of 3.5 eV is irradiated with light of a single wavelength of 360 nm, it naturally generates electrons. There should be no emission, but this 180nm
It was confirmed that electrons were emitted due to the secondary light component of , causing an erroneous electron count rate.

(Means for Solving the Problems) The present invention has been made in view of such conventional problems, and it removes the secondary light component contained in the single wavelength light emitted from the monochromator to obtain a measurement sample. An object of the present invention is to provide an electronic counting device that can accurately count the number of electrons depending on the work function of the electron.

In order to achieve this object, the present invention irradiates a sample with single wavelength light in a predetermined wavelength range from a light source device equipped with a monochromator, and introduces the electrons emitted from the sample into an electron detection section to generate electrons. In an electronic counting device for counting numbers, a filter is provided to remove a secondary light component having a half wavelength contained in a single wavelength light emitted from a light source device.

(Function) According to the configuration of the present invention, for example, when the wavelength range of single-wavelength light irradiated onto a sample from a light source device equipped with a monochromator is 200 nm to 400 nm, the secondary light component with an upper limit wavelength of 400 nm is located at 200nm, so by installing a filter that cuts wavelength components below 200nm, the measurement wavelength range can be reduced.
The secondary light component can be removed from irradiation with any single wavelength light between 200nm and 400nm, and the emitted electrons can be accurately detected from the irradiation with wavelength light that depends on the work function of the sample without being affected by the secondary light component. can be counted.

(Example) FIG. 1 is an explanatory diagram showing an example of the present invention.

First, to explain the configuration, 1 is an electron detection section, which is made of a metal case 3 with a detection window 2 opened at the bottom.
The case 3 is grounded. An anode ring 4 is disposed within the case 3, and a high voltage power source 23 is connected to the anode ring 4, to which a high voltage of, for example, 3.4 KV is applied. A first grid electrode 5 is arranged between the anode ring 4 and the case 3, and a voltage of 100V, for example, is applied to the first grid electrode. Furthermore,
A second grid electrode 6 is arranged outside the first grid electrode, and a voltage of 80V, for example, is applied to the second grid electrode.

On the other hand, a light source device 11 arranged separately from the electronic detection section 1 is provided with a light source 12, and a monochromator 13 that converts the light from the light source 12 into single wavelength light.
will be provided. Further, slits 14 and 15 for adjusting the light intensity are provided before and after the monochromator 13, and the single wavelength light from the monochromator 13 whose light intensity is adjusted by the slits 14 and 15 is applied to the sample 10.
The surface is irradiated diagonally from above.

Furthermore, a filter device 3 is provided at the front of the light source device 11.
As shown in FIG. 1a, the filter device 30 is equipped with filters 34a, 34b, 34c, and 34d for cutting secondary light at four locations on the rotating disk 32. The variable wavelength range of monochromatic wavelength light by the installed monochromator 13 is
If it is 150nm to 600nm, filter 34
Filter a has a characteristic of cutting wavelengths of 150 nm or less, filter 34b has a characteristic of cutting wavelengths of 200 nm or less, filter 34c has a characteristic of cutting wavelengths of 250 nm or less, and filter 34d has a characteristic of cutting wavelengths of 250 nm or less.
It has the property of cutting out wavelengths of 300nm or less. Therefore, a filter is selected and used that has cutoff characteristics for wavelengths equal to or less than half of a predetermined wavelength determined by the work function of the sample 10 to be measured. For example, when measuring aluminum with a work function of 3.5 eV and changing the wavelength range of single wavelength light from 200 to 400 nm, in order to prevent electron emission due to secondary light in the wavelength range of 400 nm to 350 nm, 200 nm It is sufficient to select a filter 34d that cuts out the following wavelength ranges.

Referring again to FIG. 1, the measurement circuit section includes an amplifier 18 connected to the anode ring 4 of the electron detection section via a capacitor C, and between the output of the amplifier 18 and the first grid electrode 5. A first pulse generator 20 is provided. The first pulse generator 20
As shown in FIG. As shown in figure b
Increase from 100V to 400V.

Further, a second pulse generator 22 is provided between the output of the amplifier 18 and the second grid electrode 6, and the second pulse generator 22 generates a pulse voltage on the anode ring as shown in FIG. For example, the time range
A rectangular wave pulse lowered by -110V at Te is supplied to the second grid electrode 6, and the voltage of the second grid electrode 6 is lowered from 80V to -30V, as shown in FIG. 2c.

Note that the time width Te and peak voltage of the rectangular wave pulses generated by the first and second pulse generators 20 and 22 can be set arbitrarily.

24 is a counting means connected to the output of the amplifier 18, and the counting means 24 counts the number of pulse voltages generated in the anode ring 4, and outputs, for example, a counting rate per unit time (cps). The number of pulses counted by the counting means 24, that is, the counting rate, is given to the display means 28, which displays the counting rate for the predetermined single wavelength light from the light source device 11.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

Now, assuming that aluminum having a work function of 3.5 eV is used as the sample 10, a monochromator 13 provided in the light source device 11 scans a single wavelength light in the range of 400 nm to 200 nm. On the other hand, the filter device 30 is used to prevent erroneous electron emission due to secondary light between the upper limit wavelength of the measurement wavelength range of 400 nm and the wavelength of 350 nm, at which electron emission starts according to the work function of aluminum as a sample of 3.5 eV. , a filter 34 having a characteristic of cutting secondary light (wavelength 200 nm) with an upper limit wavelength of 400 nm to 200 nm or less.
b is selected so as to be located in front of the light source device 11.

When the sample 10 is irradiated with monochromatic light of a predetermined wavelength from the light source device 11 in such a selected state of the filter device 30, a wavelength of 350 nm or less corresponding to a work function of 3.5 eV for emitting outer shell electrons of aluminum to the outside is emitted. Electrons are emitted from aluminum when it is irradiated with single wavelength light.

Regarding electron emission from aluminum as the sample 10, in the initial state, the first grid electrode 5 of the electron detection unit 1 is set to, for example, 100V, and the second grid electrode is set to, for example, 80V. The electrons enter the electron detection unit 1 through the detection window 2, pass through the second grid electrode 6 and the first grid electrode 5, and are attracted to the anode ring 4 to which a high voltage is applied. When the emitted electrons approach the anode ring 4, a strong electric field is generated near the anode ring 4 due to the high voltage, so the electrons are accelerated by this electric field and cause a gas discharge phenomenon. As a result, the voltage applied to the anode ring 4 due to the gas discharge decreases as shown in FIG. 2a, and a voltage pulse is generated.

The voltage pulse generated on the anode ring is transmitted to the amplifier 18.
After being amplified at , it is applied to a first pulse generator 20 and a second pulse generator 22, each of which generates a rectangular wave pulse. That is, the first pulse generator has a voltage of
A rectangular wave pulse of 300V and a time width of Te is generated and applied to the first grid electrode 5 to increase the voltage of the first grid electrode.
Increase from 100V to 400V. As a result, the electron difference between the anode ring 4 and the first grid electrode 5 is 300V.
As a result, secondary electrons caused by light and cations generated by the gas discharge action cannot reach the discharge potential, and an avalanche of discharge is prevented.

On the other hand, the second pulse generator 22 applies a rectangular wave pulse of -110V to the second grid electrode 6 over a time width Te, and changes the voltage of the second grid electrode 6 from 80V to -
Lower it to 30V. As a result, the cations generated by the gas discharge accompanied by the amplification effect are captured and neutralized by the second grid electrode, whereby the cations reach the sample 10 and affect the emission effect of low-energy electrons. At the same time, it blocks electrons from entering the electron detection section 1 from outside.

Thereafter, the same operation is repeated every time an electron is emitted from the sample 10, and the voltage pulse of the anode ring 4 obtained each time an electron is introduced is counted by the counting means 24, and the counting rate is displayed on the display means 28. I come to do it.

Figure 3 is a graph showing the relationship between the counting rate and the wavelength when a filter 34b that cuts out light with a wavelength of 200 nm or less is used.If the filter is not used, electrons are emitted by secondary light. This results in a wavelength characteristic with an erroneous count rate shown by the broken line, but by using a filter that cuts out the wavelength of 200 nm, the measurement result shown by the solid line can be obtained. In this case, since aluminum with a work function of 3.5 eV is used as sample 10, the secondary light blocking characteristic of the filter can be obtained for the secondary light of single wavelength light with a wavelength of 400 nm or less, and the filter can block the secondary light with a wavelength of 400 nm to around 350 nm. The counting rate is only due to background noise, and when the wavelength reaches 350 nm, electron emission starts and the counting rate increases as the wavelength decreases, and when 200 nm, which is determined by the filter cut characteristics, reaches a single wavelength, the counting rate backs up again. The ground noise becomes depressing.

As is clear from the measurement results shown in Figure 3, by using a filter that cuts out the secondary light component with an upper limit wavelength that exceeds the wavelength at which electron emission starts, which is determined by the work function of the measurement sample, the secondary light component can be reduced. It is possible to obtain the change characteristics of the count rate in a predetermined wavelength range that is not affected, and it is possible to accurately know the work function of the measurement sample from the relationship between the count rate and the wavelength.

Figure 4 is a graph showing the counting results of a suitable metal sample with an electron emission start wavelength near 400 nm; in this case, the scanning wavelength range is from 300 nm to
600nm, and the secondary light has an upper limit wavelength of 600nm.
By selecting the filter 34d that blocks light of 300 nm or less, it is possible to obtain correct measurement results shown by the solid line, as opposed to the conventional measurement results shown by the broken line in which no filter is used.

Incidentally, in the above embodiment, an example was taken in which a filter was provided in the front part of the light source device 11 to block secondary light of a predetermined single wavelength light, but an optical fiber was used instead of the filter. By irradiating the sample 10 with predetermined single-wavelength light through the lens, the secondary light component can be similarly removed. That is, since the wavelength range of light that can be transmitted by optical fibers differs depending on their composition or components, an optical fiber with characteristics that can cut out secondary light components in the wavelength range used for measuring the work function should be selected. By irradiating the sample 10 with light from the light source device 1, it is possible to obtain measurement results similar to those obtained by inserting a secondary light cut filter.

Figures 5 and 6 show a filter device 30 used in the present invention.
In the embodiment shown in FIG. 6, four secondary light cut filters 34a to 34d are arranged on a filter plate and switched by sliding in the direction of the arrow. In the embodiment of FIG. 6, the secondary light cut filters 34a-
The ring member 34d is selectively rotated to a position through which light from the light source passes.

(Effects of the Invention) As described above, according to the present invention, a sample is irradiated with single wavelength light in a predetermined wavelength range from a light source device equipped with a monochromator, and electrons emitted from the sample are introduced into the electron detection section. In the electronic counting device that counts the number of electrons, a filter is installed to remove the secondary light component of 1/2 wavelength included in the single wavelength light emitted from the light source device. Even if the wavelength light contains a secondary light component, it is possible to remove this secondary light component and perform accurate electron emission using only the predetermined single wavelength light, thereby obtaining an accurate counting result of the number of electrons. By accurately knowing when to start counting the number of electrons from a specific wavelength, it is possible to accurately determine the work function of the measurement sample.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the present invention, Fig. 2 is a signal waveform diagram showing the voltage waveform of each electrode in the electronic counting section, and Figs. 3 and 4 are diagrams of the secondary optical cut filter of the present invention. Graph showing the measurement results of the electron count rate with respect to the wavelength obtained by using it, No. 5,
Fig. 6 is an explanatory diagram showing another embodiment of the filter device used in the present invention, Fig. 7 is a graph showing measurement results of the electron count rate for conventional wavelengths, and Fig. 8 is a diagram showing the measurement results of a single wavelength light using a monochromator. FIG. 2 is an explanatory diagram showing a wavelength spectrum of FIG. 1...Electronic detection unit, 2...Detection window, 3...Case, 4
... Anode ring, 5... First grid electrode, 6... Second grid electrode, 10... Sample, 11... Light source device, 12... Light source, 13... Monochromator, 14, 15... Slit, 18... Amplifier, 20... First Pulse generator, 2
2...Second pulse generator, 24...Counting means, 28...
Display means, 30... Filter device, 32... Rotating plate,
34a to 34d...Secondary light cut filter.

Claims (1)

[Claims] 1. An electron device that irradiates a sample with single wavelength light in a predetermined wavelength range from a light source device equipped with a monochromator, introduces electrons emitted from the sample into an electron detection unit, and counts the number of electrons. An electronic counting device comprising: a filter for removing a secondary light component having a half wavelength included in the single wavelength light emitted from the light source device.