JPH0573189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) 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 formed on the surface of a sample such as a semiconductor, the sample surface is irradiated with light, and the light is emitted to the outside through the thin film on the sample. A method is known in which the film thickness is measured by counting the electrons generated by an electron detector (patent application
59-118818 etc.).

(Problems to be Solved by the Invention) However, in such conventional electronic counting devices, optical members such as lamps and lenses provided in the light source device that irradiates the sample with single-wavelength light are contaminated, or light When light is guided through a fiber, the amount of light irradiated onto the sample changes due to deterioration of the fiber, and there is a risk that accurate measurement of the number of electrons may not be possible.

For example, when measuring the specification function of a sample oxide film from the electron count rate when scanning single-wavelength light from a light source device in a predetermined wavelength range, if there is no decrease in the light intensity in the initial state, the A characteristic of the count rate with a slope α1 with respect to the scanning wavelength was obtained, but when the light intensity decreases, the slope decreases to α2 as shown in Figure 8b, as if the oxide film had become thicker. There was a problem that incorrect measurement results were obtained.

(Means for Solving the Problems) The present invention was made in view of such conventional problems, and even if the amount of light irradiated onto the sample changes due to dirt on the optical member, etc., the amount of light constantly changes. It is an object of the present invention to provide an electronic counting device that can obtain the same counting result of the number of electrons as in the initial state without.

In order to achieve this object, the present invention provides an electronic counting device that irradiates the sample with light and counts the number of electrons by introducing the electrons emitted from the sample into an electronic counting section. a light amount detection means for detecting the amount of light to be detected; a correction coefficient calculating means for calculating a correction coefficient based on the light amount detected in the initial state (reference light amount) and the light amount at the time of measurement; A correction means for correcting the counted value of the number of electrons is provided.

(Function) According to the configuration of the present invention, even if the amount of light irradiated onto the sample decreases due to dirt on the optical member of the light source device or deterioration of the optical fiber, the light intensity can be adjusted based on the change in light amount. By using the correction coefficient, it is possible to obtain the same electron counting result as obtained by irradiation with the reference light amount in the initial state, and it is possible to accurately count the number of electrons without being affected by fluctuations in the light amount.

(Embodiment) FIG. 1 is an explanatory diagram showing one embodiment 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. Case 3
An anode ring 4 is arranged inside, and a high voltage of 3.4 KV, for example, is applied to the anode ring 4 from a high voltage power supply 23. A first grid electrode 5 is arranged between the anode ring 4 and the case 3. The output of the first pulse generator 20 is given to the first grid electrode 5, and when the first pulse generator 20 is not introducing emitted electrons from the sample 12, the first pulse generator 20 applies a voltage of, for example, 100V to the first pulse generator.
The voltage is applied to the grid electrode 5, and when the introduction of electrons emitted from the sample 12 causes a gas discharge phenomenon in the vicinity of the anode ring 4 and the amplifier 18 generates an electron pulse as shown in FIG. For a predetermined quenching time τ, the pulse generator 20
A rectangular wave pulse increased to 300V is generated, and the first grid electrode 5 is applied to 400V for the quenching time τ.
Keep it. In this way, the voltage of the first grid electrode 5
When increased from 100V to 400V, the potential difference between the anode ring 4 and the first grid electrode decreases by 300V,
As a result, secondary electrons caused by light and cations caused by the gas discharge effect caused by the introduction of emitted electrons cannot reach the discharge voltage, and an avalanche of discharge is prevented.

On the other hand, a second grid electrode 6 is arranged outside the first grid electrode 5, and the output of the second pulse generator 22 is applied to the second grid electrode 6. The second pulse generator 22 applies a voltage of, for example, 80 V to the second grid electrode 6 when no emitted electrons are introduced, and the introduction of emitted electrons causes a gas discharge phenomenon as shown in FIG. 2a. When a voltage pulse is applied from the anode ring 4 via the amplifier 18, as shown in FIG. 2c, a rectangular pulse of -110V, for example, is output for a quenching time τ. The second grid electrode 6 receives the -30V rectangular wave pulse for this quenching time τ, and the grid voltage up to that point is
As the voltage decreases from 80V to -30V, the cations generated by the gas discharge accompanied by the amplification effect are captured and neutralized by the second grid electrode 6. As a result, the cations reach the sample 10 and the sample 10 This prevents the photoelectron emission from being affected, and also blocks electrons from being introduced into the electron detection section 1 from the outside.

On the other hand, a sample stage 13 is provided below the detection window 2 of the electron detection section 1, and the sample 12 set on the sample stage 13 is irradiated with predetermined single wavelength light from a light source device 7. The light source device 7 includes a light source 8 such as a deuterium lamp, a monochromator 9 that converts the light from the light source 8 into a single wavelength, and further includes slits 10 and 11 before and after the monochromator 9 for adjusting the light intensity.
has been established. The monochromator 9 has a function of scanning single wavelength light in a predetermined wavelength range, for example, from 150 nm to 600 nm, and by this wavelength scanning, it is possible to obtain measurement results for determining the work function of the sample 12, for example.

A light receiving element 15 is installed at the position where the light from the light source device 7 is irradiated on the sample stage 13 when the sample 12 is not set. It is possible to detect the amount of light from the light source device 7 before measurement.

On the other hand, the voltage pulse generated by the gas discharge phenomenon near the anode ring 4 due to the introduction of electrons emitted from the sample 12 is amplified by the amplifier 18 and then applied to the counting means 24. By counting the number of electrons, for example, the electron counting rate (cps) is determined.

Following the counting means 24, a calculating means 26 is provided, and the calculating means 26 is given the number N of electrons counted by the counting means 24 and the amount of light measured by the light amount measuring means 16. The electronic count value is corrected based on the amount of light detected by the measuring means 16 and displayed on the display means 28.

Here, the correction arithmetic processing by the arithmetic means 26 will be explained as follows, along with its operation.

FIG. 3 is a graph showing the change in light amount when the monochromator 9 of the light source device 7 scans the sample 12 with single wavelength light in a predetermined wavelength range.

As shown by the solid line A in the graph, in the initial state, the light source 8 and lenses of the light source device 7 are free of dirt, so the amount of light when wavelength scanning is performed with the monochromator 9 is Obtained as the maximum amount of light.

Incidentally, the spectral characteristics of the light source 8 are not constant at each wavelength, and exhibit intensity changes as shown, for example, by curve A in FIG. 3.

Therefore, the calculation means 26 corrects the electronic count value in response to the fluctuation in the spectral intensity of the light source device 7 so that it becomes a constant reference light amount W ₀ given by the light amount W ₀ at the wavelength λ ₀ , for example.

That is, the monochromator 9 performs wavelength scanning in the wavelength range λ ₀ to λ _o , and each wavelength λ ₀ , λ ₁ , λ ₂ . . .
The light amount W ₀ , W ₁ , at each of λ _i , ...λ _o
W _{2 ,} . _{. . Wi ,} .

K ₀ = W ₀ /W ₀ K ₁ = W ₀ /W ₁ K ₂ = W ₀ /W ₂・ ・ ・ K _i = W ₀ /W _i・ ・ ・ K _o = W ₀ /W _o …(1) On the other hand, the number of electrons N ₀ measured by the counting means 24 is the number of electrons in the time excluding the quenching time τ, which is the dead time, as shown in FIG _{. N0}・τ) ...(2) However, N: Number of emitted electrons _N0 : Number of measured electrons τ: Quenching time τ as dead time as quenching time
The number N of emitted electrons is calculated by correcting the number of electrons.

Then, the calculation means 26 calculates the number N of emitted electrons obtained by the equation (2) at each scanning wavelength.
Using the correction coefficient of the corresponding wavelength given by equation (1), the true number of emitted electrons N _t obtained by irradiation with the reference light amount W ₀ is determined as N _t =N·K _i (3).

Next, as shown by the broken line B in FIG. 3, the light source device 7
When the amount of light irradiated onto the sample 12 decreases due to dirt on the optical member, etc., the monochromator 9 scans single wavelength light in the wavelength range λ ₀ to λ _o prior to measuring the sample 12, and the light amount measuring means 16, the light quantity characteristics with respect to the scanning wavelength as shown by the broken line B in FIG. 3 are determined.

Once the light amount of the broken line B, where the light amount has decreased in this way, is found in the scanning wavelength range, the denominator in equation (1) above is replaced with W ₀₁ ~ W _o1 to find the correction coefficient K ₀ ~ K _o , and then The number N of emitted electrons is calculated from the number N ₀ of measured electrons from the sample 12 obtained by the counting means 24 using the above equation (2), and then the correction coefficient K _i calculated using the equation (1) is calculated.
is used to calculate the true number of emitted electrons N _t at the measurement wavelength λ _i from the above equation (3).

As a result, deterioration of the light source 8 in the light source device 7,
Or, even if the amount of light irradiated to the sample 12 decreases due to dirt on the optical member, etc., the true number of emitted electrons will always be the same as when the sample 12 is irradiated with the same amount of light as the initial state (however, the spectral sensitivity is corrected to a constant value).
N _t can be calculated.

Furthermore, in the case of the light amount measuring means 16 in FIG.
When the amount of light detected by the light receiving element 15 falls below a predetermined threshold level, an alarm signal may be output to prompt cleaning of the optical system or replacement of the light source 8.

FIG. 4 is an explanatory diagram showing another embodiment of the present invention, and this embodiment is characterized in that light is irradiated onto the sample 12 from the light source device 7 through an optical fiber 30. shall be.

In this embodiment as well, as in the embodiment shown in FIG. is detected, and the calculating means 26 calculates the true number of electrons N _t emitted, which is the same as when irradiated with the amount of light in the initial state, and displays it on the display means 28.

FIG. 5 is an explanatory diagram showing another embodiment of the present invention. In this embodiment, the light from the light source device 7 is irradiated onto the sample 12 through the optical fiber 30, and the optical fiber 30 It is characterized in that optical fibers are branched and connected to each of the entrance side and the exit side to provide light receiving elements 15a and 15b.

In this embodiment, the light emitted from the light source device 7 is converted into an electrical signal by the light receiving element 15a and measured by the light amount measuring means 16, and the light passing through the optical fiber 30 is converted into an electrical signal by the light receiving element 15b. The converted light quantity is then measured by the light quantity measuring means 16, and when a change in light quantity occurs from the light receiving output of the light receiving element 15a, it can be determined that the light source device 7 is dirty or the light source has deteriorated. When a decrease in the amount of light is detected from the output, it can be seen that the decrease in the amount of light is due to deterioration of the optical fiber 30. Of course, the correction based on the amount of light detected by the calculating means 26 is performed using the amount of light obtained based on the light receiving output of the light receiving element 15b that receives the light passing through the optical fiber 30.

Note that the above embodiment takes as an example the case where the single wavelength light from the light source device is scanned and used in a predetermined wavelength range, but the single wavelength light is fixed at a specific wavelength and used. In this case, the correction coefficient for correcting the light intensity to the initial state is calculated based on the light intensity measurement from the light source prior to measurement, and the number of emitted electrons obtained in sample measurement is corrected to the true number of emitted electrons. can do.

Further, in the embodiments shown in Figs. 4 and 5, an optical fiber is used, but the present invention is not limited to this, and the light from the light source is focused with a lens and irradiated onto the sample. It may be hot.

Furthermore, in the above embodiment, when measuring the amount of light, the light amount sensor was fixed to the sample stage.
The present invention is not limited thereto, and for example, as shown in FIG. 6, the light receiving element 15 as a light amount sensor may be made movable, and may be moved from the initial position 15a to the illustrated measurement position during measurement. Furthermore, as shown in FIG. 7, when the light receiving element 15 is fixed to the sample stage 13, the sample stage 13
may be made movable and moved from the initial position 13a to the illustrated measurement position during measurement.

(Effects of the Invention) As described above, according to the present invention, in an electronic counting device that counts the number of electrons by irradiating a sample with light and introducing electrons emitted from the sample into an electron detection section, a light amount detection means for detecting the amount of light irradiated on the object; a correction coefficient calculation means for calculating a correction coefficient based on the initial state light amount detected by the light amount detection means and the light amount at the time of measurement; Since a correction means is provided to correct the counted value of the number of electrons based on the above, it is possible to prevent deterioration of the light source in the light source device, dirt on the optical components, and furthermore, deterioration of the optical fiber when the sample is irradiated with light using the optical fiber. Even if the amount of light decreases due to such factors, it is possible to always obtain the same counting result as the number of electrons emitted by light irradiation in the initial state where there was no decrease in the amount of light.
A stable counting operation can be performed over a long period of time without being affected by variations in light amount.

[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 applied to each electrode provided in the electron detection section of Fig. 1, and Fig. 3 is a light intensity versus light source wavelength. FIGS. 4 and 5 are explanatory diagrams showing other embodiments of the present invention, and FIGS. 6 and 7 show embodiments in which the light amount sensor or sample stage of the present invention is movable. FIG. 8 is a graph showing conventional measurement results of the number of electrons with respect to wavelength due to variations in light intensity. 1...Electronic detection unit, 2...Detection window, 3...Case, 4
... Anode ring, 5... First grid electrode, 6... Second grid electrode, 7... Light source device, 8... Light source, 9... Monochromator, 10, 11... Slit, 12... Sample, 13
...sample stage, 15, 15a, 15b...light receiving element, 1
6... Light quantity measuring means, 18... Amplifier, 20... First pulse generator, 22... Second pulse generator, 23... High voltage power supply, 24... Counting means, 26... Arithmetic means, 28
...display means, 30...optical fiber.

Claims (1)

[Claims] 1. In an electronic counting device that irradiates a sample with light and introduces electrons emitted from the sample into an electron detection section to count the number of electrons, the amount of light irradiated onto the sample a light amount detection means for detecting the amount of light; a correction coefficient calculation means for calculating a correction coefficient based on the initial state light amount detected by the light amount detection means and the light amount at the time of measurement; and a correction coefficient calculation means for calculating the number of electrons based on the correction coefficient. An electronic counting device characterized by comprising a correction means for correcting numerical values.