JPH0641979B2 - Electronic counter - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electron 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 film thickness of an oxide film or the like on the surface of a sample such as a semiconductor, electrons are emitted to the outside through a thin film on the sample by irradiating the sample with light. There is known a method of counting the film thickness by an electronic detection unit to measure the film thickness (Japanese Patent Application No. 59-118818, etc.).

By the way, in such an electronic measuring device, there is a problem that the counting error becomes large due to the influence of the humidity in the electronic detection unit, and in order to solve this, dry gas such as dry air is put in the electronic detection unit. It is thought that injection will eliminate the influence of humidity.

(Problems to be Solved by the Invention) However, when injecting dry gas into the electronic detection portion, the gas flow rate was manually adjusted while watching the instruction of the flow meter, so that a large amount of gas was flowed. If it is too much, the gas may be wasted, or the amount of gas may be too small to generate noise due to the influence of humidity, which may make it impossible to supply a necessary and sufficient amount of gas.

(Means for Solving Problems) The present invention has been made in view of such conventional problems, and enables stable electronic measurement by eliminating a measurement error due to the influence of humidity in the electronic detection unit. An object of the present invention is to provide an electronic measuring device capable of supplying an optimum amount of dry gas.

In order to achieve this object, in the present invention, a gas supply means for injecting a dry gas such as dry air into the electron detection part, a background counting mode for prohibiting the introduction of electrons from the sample side into the electron detection part And a flow rate control means for controlling the supply amount by the gas supply means so that the value of the number of electrons (counting rate) measured by this measuring means is minimized. It was done like this.

(Operation) According to such a configuration of the present invention, the supply flow rate of the dry gas such as dry air is set to, for example, zero when the background counting mode in which the introduction of electrons from the sample side into the electron detection unit is prohibited is set. Gradually increase, the humidity in the electronic detector decreases as the gas flow rate increases, and the count rate as background noise generated by the decrease in humidity also decreases. By setting the saturation flow rate at which the counting rate does not decrease even if it is performed as the optimum supply flow rate, the gas supply shortage and the gas supply excessively are eliminated.

(Embodiment) FIG. 1 is an explanatory view showing an embodiment of the present invention.

First, the structure will be described. Reference numeral 1 denotes an electron detecting portion, which has a metallic case 3 having a detection window 2 opened at the bottom, and this case 3 is grounded to serve as a cathode. An anode ring 4 is arranged in the case 3, a high voltage power supply 23 is connected to the anode ring 4, and a high voltage of, for example, 3.4 KV is applied.
A first grid electrode 5 to which a voltage of, for example, 100 V is applied is installed between the anode ring 4 and the case 3, and a sample 10 arranged opposite the first grid electrode 5 and the detection window 2 of the case 3. In between, the second voltage applied with, for example, 80V
Grid electrodes 6 are arranged.

On the other hand, a light source 13 is provided in the light source device separately arranged with respect to the electron detection unit 1, and a spectroscope 14 for monochromatic light from the light source 13 and a slit 1 arranged before and after the spectroscope 14 are provided.
The monochromatic light from the spectroscope 14 which has slits 15 and 16 and whose light intensity is adjusted by the slits 15 and 16 is radiated onto the surface of the sample 10 obliquely from above.

On the other hand, the measurement circuit unit includes an amplifier 18 connected to the anode ring 4 of the electron detection unit 1 via a capacitor C, and a first circuit is provided between the output of the amplifier 18 and the first grid electrode 5.
A pulse generator 20 is provided. First pulse generator 20
Is a predetermined time width Te, for example Te = 3 ms, on the first grid electrode 5 when a pulse voltage is generated on the anode ring 4.
Then, a rectangular wave pulse increased by 300 V is sent to increase the voltage of the first grid electrode 5 from 100 V to 400 V as shown in the ALL mode of FIG. 2 (b).

A second pulse generator 22 is provided between the output of the amplifier 31 and the second grid electrode 6, and the second pulse generator 22 receives, for example, a time width Te when a pulse voltage is generated in the anode ring 4. Then, the rectangular wave pulse down by -110V 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 the ALL mode in the signal waveform diagram of FIG. 2 (c). Let

The time width Te and the peak voltage of the rectangular wave pulse 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,
This counting means 24 counts the number of pulse voltages generated in the anode ring 4. The output of the counting means 24 is given to the calculating means 26, and as the calculating means 26, for example, a microcomputer is used. The calculating function of the calculating means 26 is such that, if the count number (counting rate) of the electronic pulse per second in the counting means 24 is N, the counting means 2
The thin film 1 in the sample 10 in response to the output count number N of 4
The film thickness T of 0B is calculated by the following equation.

| 0g N = | 0g N1-T / 2.30λ ...
(1) where λ is the mean free path (angstrom) of electrons in the thin film, and N1 is the number of counts (counting rate) when the film thickness is zero.
The thickness T of the thin film 10b is sent to the display means 28 such as a CRT printer, and the thickness T of the thin film 10b which is the calculation result of the calculation means 26 is displayed on the display means 28.

In contrast to the electronic measuring device including the electron detecting section 1, the illumination optical system for the sample 10 and the measuring circuit, in the present invention, a gas for supplying dried gas such as dry air into the electron detecting section 1 is further provided. A supply pipe 30 is provided, and a dry gas from a dry air generator or the like that generates dry air by drying dry air packed in an air cylinder (not shown) or silica gel is pressurized to the gas supply pipe 30. Supplied.

A flow rate adjuster 32 for controlling the gas flow rate is provided in the middle of the gas supply pipe 30 for supplying the dry gas into the electron detector 1. As the flow rate adjuster 32, for example, an electric valve that adjusts the opening degree by driving a motor can be used.

In order to operate the flow rate adjuster 32 provided in the gas supply pipe 30, a flow rate adjuster 34 is provided, and for the flow rate controller 34, the number of electrons per second obtained by the calculator 25 from the calculator 25 is provided. Pulse count number (counting rate) N
Is supplied, the flow rate control device 34 gradually turns the flow rate adjuster 32 from zero flow rate in a state where the measurement mode of the electronic detection unit 1 is set to the background measurement mode (BG mode), and the calculation means 26 is operated. It is possible to detect the state in which the count number N obtained through the decrease is saturated to the minimum value, and the adjusted opening degree at that time is held.

Further, since the flow rate control device 24 sets the background counting mode to the electronic detection unit 1, the second pulse generator 2
2 has a function of fixing the applied voltage of the second grid electrode 6 to −30 V and prohibiting the introduction of electrons into the electron detection unit 1 from the sample 10 side.

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

First, prior to the measurement of the film thickness T of the thin film 10b of the sample 10, the measurement mode of the electron detector 1 is set to the background counting mode by operating the flow rate controller 34. That is, in the normal ALL mode in which the number of electrons emitted from the sample 10 is detected, the electrons emitted by the irradiation of the light energy on the sample 10 enter the electron detection unit 1 through the detection window 2 and
It passes through the second grid electrode 6 set to 0V and the first grid electrode 5 set to 100V, and is attracted to the anode ring 4. When the emitted electrons approach the anode ring 4, the anode ring 4
Since a strong electric field is generated in the vicinity of by the high voltage, electrons are accelerated by this electric field to cause a gas discharge phenomenon. As a result, the voltage applied to the anode ring 4 is reduced by the gas discharge, as shown in FIG. 2 (a), and a voltage pulse is generated.

The voltage pulse generated in the anode ring 4 is amplified by the amplifier 18, and then the first pulse generator 20 and the second pulse generator 2 are amplified.
2 and each generate a rectangular pulse. That is,
The first pulse generator 20 generates a rectangular wave pulse having a voltage of 300 V and a time width Te, and applies it to the first grid electrode 5,
The voltage of the grid electrode 5 is increased from 100V to 400V. As a result, the potential difference between the anode ring 4 and the first lattice electrode 5 is reduced by 300 V, whereby the secondary electrons due to light or cations generated by the gas discharge action cannot reach the discharge voltage and the avalanche. Discharge is prevented.

On the other hand, the second pulse generator 22 is -1 over the time width Te.
A rectangular wave pulse of 10 V is applied to the second grid electrode 6,
The voltage of the second grid electrode 6 is reduced from 80V to -30V.
As a result, the cations generated by the gas discharge with the amplifying action are captured and neutralized by the second lattice electrode 6, whereby the cations are thin film 10b of the sample 10 and the sample body 1.
It is prevented from reaching 0a and affecting the emission action of low energy electrons. Further, the electrons from the outside are blocked from entering the electron detector 1.

On the other hand, in the background counting mode when adjusting the gas flow rate, the anode ring 4 is used in the ALL mode described above.
Each time it receives an electronic pulse from
By setting the second pulse generator 22 applying the voltage falling to −30 V to the second grid electrode 6 to the fixed voltage generation state of −30 V and keeping the applied voltage of the second grid electrode 6 at −30 V. A closed state is created in which the introduction of electrons into the electron detection unit 1 is prohibited from the sample 10 side through the detection window 2.

Therefore, in this background counting mode, the counting operation of the electron pulse (noise amount) by the electrons generated only in the electron detecting section 1 is performed.

Therefore, in the flow rate control device 34, after setting the voltage generation state of −30 V in the second pulse generator 22, the flow rate regulator 32 is gradually opened from the state of zero flow rate and the dry gas is supplied through the gas supply pipe 30. A dry gas such as air is supplied to the electron detector 1.

FIG. 3 is a characteristic graph showing a change in the electron count rate N when the flow rate Q of the dry gas is gradually increased from zero, and the humidity of the electron detector 1 decreases as the gas flow rate increases. Therefore, the count rate N as background noise due to humidity also decreases. At this time, even if the supply flow rate of the dry gas is increased beyond a certain flow rate QS, the count rate as background noise does not decrease any more, and the state becomes saturated. Therefore, in the flow rate control device 34, if the flow rate Qs at which the count rate is saturated is reached,
At that point, the flow rate adjustment is stopped and the flow rate Qs at which the background noise is saturated is maintained. As a result, the electron detection unit 1 is supplied with a dry and minimal amount of gas that minimizes background noise due to humidity. In this state, the background counting mode is released and the ALL mode is set. As a result, the measurement process of the film thickness T or the like based on the count value N of the number of electrons emitted by the irradiation of the light energy on the sample 10 is performed.

In the above embodiment, the flow rate controller 32 controls the flow rate regulator 32 to gradually increase the gas flow rate from zero flow rate to control the optimum flow rate Qs at which the background noise is saturated. The optimum flow rate Qs may be set by gradually reducing the flow rate from the state where the flow rate regulator 32 is fully opened.

In the above embodiment, the automatic flow rate control device 34 automatically sets the optimum flow rate Qs. However, the flow rate control device 34 is caused to display the count rate N so that the display result becomes the minimum value. Alternatively, the flow rate regulator 32 may be adjusted manually.

(Effects of the Invention) As described above, according to the present invention, the supply flow rate of a dry gas such as dry air is set in the background counting mode in which the introduction of electrons from the sample side into the electron detection unit is prohibited. For example, the saturation flow rate is set as the optimum supply flow rate so that the count rate does not decrease even if the gas flow rate is further increased from the zero flow rate. It is possible to obtain the optimum gas supply amount setting state in which the background noise due to the humidity is kept to a minimum, the noise component increases due to insufficient gas supply, and waste due to excessive gas supply can be eliminated.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, and FIG. 2 is a signal waveform diagram showing the time change of the voltage waveform of each part in the ALL mode during sample measurement and the background counting mode during flow rate adjustment, FIG. 3 is a characteristic graph showing the relationship of the count rate (background noise) with respect to the adjusted flow rate. 1: Electron detection part 2: Detection window 3: Case 4: Anode ring 5: First grid electrode 6: Second grid electrode 10: Sample 10a: Sample body 10b: Thin film 13: Light source 14: Spectroscope 15, 16: Slit 18: Amplifier 20: 1st pulse generator 22: 2nd pulse generator 23: High voltage power supply 24: Counting means 26: Computing means 28: Display means 30: Gas supply piping 32: Flow rate regulator 34: Flow rate control device

Claims (1)

[Claims] 1. An electron counter for counting the number of electrons by irradiating a sample with light and introducing electrons emitted from the sample into an electron detector, wherein the electron detector is dried with dry air or the like. Gas supply means for supplying gas, measuring means for measuring the number of electrons in the background counting mode in which introduction of electrons from the sample side into the electron detecting section is prohibited, and background counting mode obtained by the measuring means An electronic counting device, comprising: a flow rate control means for controlling the amount of gas supplied by the gas supply means so that the measured value in step 1 is minimized.