JPH0789148B2 - 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 of measuring the film thickness of an oxide film or the like formed on the surface of a sample such as a semiconductor in an atmosphere open to the atmosphere, the sample surface is irradiated with light and the thin film on the sample is passed by irradiation of light. There is a known method in which electrons emitted to the outside are introduced into the electron detection unit, the number of emitted electrons is counted by utilizing the gas discharge phenomenon caused by the introduced electrons, and the film thickness is measured based on the number of emitted electrons. (Japanese Patent Application No. Sho 59-118818, etc.)

(Problems to be Solved by the Invention) However, in such a conventional electron counter, a high voltage is applied to the anode ring arranged in the electron detector to generate a gas discharge by the electrons emitted from the sample. The number of electrons is counted from the pulse change of the anode voltage due to this gas discharge, but the method of determining the first lattice voltage and the second lattice voltage when the anode voltage is changed is not clear, and the optimum state Therefore, it was difficult to efficiently count the emitted electrons.

(Means for Solving Problems) The present invention has been made in view of such problems in the related art. Even if the anode voltage is changed, the grid voltage is always set to the optimum state, which is efficient and stable. An object of the present invention is to provide an electronic counting device capable of performing a counting operation.

In order to achieve this object, in the present invention, the second grid voltage G2 is varied for each of a plurality of different first grid voltages G1 = V1a, V1b, V1c, ... Lattice voltage detecting means for detecting the second lattice voltage G2 = V2a, V2b, V2c ... At which the peak value of N is obtained, and a plurality of second lattice voltages G2 = V2a, V2b, V2c detected by the lattice voltage means. The setting means for selecting the second lattice voltage that gives the maximum count rate Nmax and the corresponding first lattice voltage from among these and setting them as optimum values is provided.

(Operation) According to the configuration of the present invention as described above, even when the anode voltage is changed, the optimum values of the first lattice voltage and the second lattice voltage that maximize the electron counting efficiency at the anode voltage at that time are determined. It can be set accurately, for example, by obtaining the optimum grid voltage for the anode voltage in advance and storing it in a memory or the like,
If the anode voltage is determined, the optimum lattice voltage can be uniquely read from the memory and set, and efficient and stable operation can be compensated.

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

First, the configuration will be described. 1 is an electronic detection unit, which has a metal case 3 having a detection window 2 opened at the bottom thereof.
Is grounded. An anode ring 4 is arranged in the case 3, and a high voltage of, for example, Va = 3.4 KV is applied to the anode ring 4 from a high voltage power supply 23, and the anode voltage Va from the high voltage power supply 23 is If necessary, for example
It can be varied within the range of Va = 3.0KV to 4.0KV.

A first grid electrode 5 and a second grid electrode 6 are sequentially arranged on the detection window 2 side of the anode ring 4.

The output of the first pulse generator 20 is connected to the first grid electrode 5, and the first pulse generator 20 applies the first grid voltage G1, for example, G1 = 100V, to the first grid electrode 5. The output of the second pulse generator 22 is connected to the second grid electrode 6, and the second pulse generator 22 outputs the second grid voltage G2 as, for example,
G2 = 80V is applied.

To the first pulse generator 20 and the second pulse generator 22, the output of an amplifier 18 for extracting the voltage change of the anode ring 4 via a capacitor C is connected.

The voltage applied to the anode ring 4 falls in a pulsed manner as shown in FIG. 2 (a) due to the gas discharge that occurs when electrons are introduced from the detection window 2, and the first fall of the anode voltage is changed by the amplifier 18. When applied to the pulse generator 20, the first
As shown in FIG. 2 (b), the pulse generator 20 has a rectangular wave pulse having a quenching voltage Vq increased by a predetermined voltage ΔV in order to prevent gas discharge from the first grid voltage G1 up to then. Is output over the quenching time Te. Here, the voltage ΔV that gives the quenching voltage Vq is set to, for example, ΔV = 300V, and therefore, when a voltage pulse is received, the voltage G1 of the first grid electrode 5 is 100V up to that point.
Changes from 300V to 400V.

On the other hand, when the second pulse generator 22 receives the voltage pulse from the amplifier 18, as shown in FIG.
A rectangular pulse is generated that changes the grid voltage G2 to -30 V over the quenching time Te. For example, the second grid voltage G2
= 80V, a square wave pulse with 110V lower is generated.

The action of the rectangular wave pulse over the quenching time Te by the first pulse generator 20 and the second pulse generator 22 is
When the electrons emitted from 10 approach the anode ring, the high electric field in the vicinity of the anode ring 4 accelerates the electrons to cause a gas discharge phenomenon.
By increasing the quenching voltage Vq over the quenching time Te, the potential difference between the anode ring 4 and the first lattice electrode 5 is reduced by, for example, ΔV = 300V, which causes light or cations generated by gas discharge. Prevent secondary electrons from reaching the discharge voltage and prevent avalanche discharge.

On the other hand, the output of the rectangular wave pulse that is reduced to −30 V over the quenching time Te of the second pulse generator 22 captures and neutralizes the cations generated by the gas discharge accompanied by the amplification action by the second lattice electrode 6. This prevents cations from reaching the sample 10 and affecting the photoelectron emission action, and at the same time blocks the introduction of electrons from the outside.

Further, a light source device 9 is arranged on the side of the electron detector 1,
The sample 10 set on the sample table 8 is irradiated from the light source device 9 with a single wavelength light having a predetermined wavelength obliquely from above. The light source device 9 includes a light source 11 such as a deuterium lamp, a monochromator 12 that converts the wavelength from the light source 11 into a single wavelength, and slits 13 and 14 for adjusting the light intensity before and after the monochromator 1. There is.

Further, counting means as a measuring circuit for counting the number of electrons based on the voltage pulse output from the amplifier 18 of the electron detector 1.
24 is provided, and the counting means 24 outputs, for example, an electronic counting rate (cps) per unit time. The output of the counting means 24 is given to the calculating means 26, which calculates the first grid electrode 5 and the second grid electrode 5 based on the electron counting rate N obtained from the counting means 24.
A calculation control process for setting the grid power supply of the grid electrode 6 to an optimum value is performed. Further, in this embodiment, the arithmetic means 26 also has a function of varying the voltage of the high voltage power supply 23 and setting the anode voltage applied to the anode ring 4 to an optimum value. A display means 28 is provided following the computing means 26, and the electronic counting rate N obtained by the counting means 24 is displayed on the display means 28 as it is, or formed on the surface of the sample 10 provided in the computing means 26. The film thickness T based on the calculation result of the calculation means for calculating the film thickness T of the formed oxide film or the like is displayed. Further, the wavelength may be changed and the work function may be displayed.

Here, the calculation control process for setting the electrode voltage of the first grid electrode 5 and the second grid electrode 6 to the optimum value by the calculation means 26 is as follows.

(A) With the anode voltage Va set on the anode ring 4 by the high-voltage power supply 23 set to an appropriate value, as shown in the drawing, the sample stage 8
The sample 10 to be the reference is set to, and in this state, the first grid voltage G1 by the first pulse generator 20 is G1 = V1a, V1b, V1c, ...
As described above, for example, G1 = 80 to 120V is gradually changed in a range, and the first grid voltage is fixed to each of the first grid voltages V1a, V1b, V1c ,. G2 is varied in the range of G2 = 40 to 110V, for example.

(B) The second lattice voltages V2a, V2b, V2c, ... Which obtain the peak value of the count rate N when the second lattice voltage G2 is varied in the range of G2 = 40 to 110V, for example, are detected.

(C) The maximum count rate Nm among the second lattice voltages V2a, V2b, V2c, ... Which give the peak value of the count rate obtained in (B) above.
The second grid voltage that gives ax and the corresponding first grid voltage are selected.

(D) The first and second pulse generators 20, 2 are set with the first and second lattice voltages obtained in (C) as optimum lattice voltages.
Set to 2.

Next, the operation of the embodiment of FIG. 1 will be described with reference to the flowchart of FIG.

First, in the processing from blocks 30 to 36 in FIG. 3,
The calculation means 26 controls the high-voltage power supply 23 to set the optimum anode voltage Va applied to the anode ring 4.

As shown in FIG. 1, the setting process of the optimum anode voltage is as follows.
With the sample 10 serving as an appropriate reference set on the sample stage 8, the light source device 9 irradiates it with monochromatic wavelength light of a predetermined wavelength to emit electrons, and the electrons emitted from the sample 10 are introduced into the electron detector 1. The counting means 24 measures the counting rate.

That is, in the initial state, the calculating means 26 sets the anode voltage Va by the high voltage power supply 23 to the minimum value Va = 3.
It is set to 0 KV, and the anode voltage Va is increased from this initial state as shown in block 30. The electronic counting rate N obtained from the counting means 24 is compared with the threshold value No determined by the background noise in the next discrimination block 32 against the rise of the anode voltage in the block 30, and the electronic counting rate N is equal to or more than the threshold value No. When it is determined that the above condition is satisfied, the anode voltage at this time is detected as the discharge start voltage Vs, and the process proceeds to the next block 34. In block 34, a voltage obtained by adding a half of the predetermined plateau voltage width Pw to the discharge start voltage Vs is calculated as the optimum anode voltage Vao, and in the next block 36, the high voltage power supply is set to the optimum anode voltage Vao. Control 23.

Here, the count rate N when the anode voltage Va is changed is the fourth
It becomes the characteristic shown in the figure, and if the anode voltage Va is increased,
A count rate exceeding the threshold value No determined by the background noise is obtained at a certain voltage, and the voltage exceeding this threshold value No is detected as the discharge start voltage Vs. Further, when the anode voltage is increased, the counting rate N is changed within a certain range against the change of the anode voltage.
Is a substantially constant value, and the range in which the count rate N remains constant with respect to this change in the anode voltage is defined as the plateau voltage width Pw. Further, when the anode voltage is increased beyond the plateau voltage width Pw, the count rate N rapidly increases and the count becomes impossible.

The plateau voltage width Pw giving the range of the anode voltage at which the counting rate shown in FIG. 4 is substantially constant is the variation ΔV of the first lattice voltage G1 giving the quenching voltage Vq shown in FIG. 2 (b).
Given as a voltage range equal to. Therefore, the optimum anode voltage obtained in block 34 in the flow chart of FIG.
As Vao, the voltage at the center of the plateau width Pw in the characteristic curve shown in FIG. 4 is set as the optimum anode voltage Vao.

Referring to FIG. 3 again, when the setting up to the optimum anode voltage Vao is completed by the processing up to the block 36, the first grid voltage G1 is set to the initial voltage Va in the next block 38.
For example, since the first grid voltage G1 is variable in the range of G1 = 80 to 120V, V1a = 80V is set.

In this way, with the first grid voltage G1 set to the initial voltage of G1 = V1a, the second grid voltage G2 is changed in the range of 40 to 110V in the next block 40. Then, in the next block 42, the count rate N when the second grid voltage G2 in the block 40 is changed is monitored, and G2 = V2a is detected as the second grid voltage G2 at which the count rate N becomes maximum. Subsequently, in a determination block 44, it is checked whether or not the final setting of the first grid voltage is completed. If the final setting is not completed, the process returns to the block 46, and the first grid voltage G1 up to that point is set to the predetermined voltage ΔV1. In addition, a new first grid voltage is set, and the processes of blocks 40 and 42 are repeated in the same manner.

FIG. 5 shows blocks 40 to 40 in the flow chart of FIG.
It is a characteristic graph which showed the relation of the count rate N to the 2nd lattice voltage G2 obtained by processing of 46.

The characteristic graph of FIG. 5 shows that the first grid voltage G1 is V1a, V1b,
V1c, ..., V1g, which is varied in seven steps, shows the relationship of the count rate N when the second lattice voltage G2 is varied at each first lattice voltage. As is clear from this characteristic graph,
The second grid voltage G2 that gives the peak value Na, Nb, ... Ne of the count rate N obtained by varying the second grid voltage G2 when the grid voltage G1 is constant is G2 = V2a, V2b ,. It can be detected as V2g.

Referring again to FIG. 3, if the final setting of the first grid voltage G1 is determined in the decision block 44, the process proceeds to the next block 48, for example, as shown in FIG. 5, the second grid voltage V2a. ,
The second lattice voltage G2, which gives the maximum count rate Nmax, such as V2e, is detected from V2b, ... V2g. Then in block 50 the second grid voltage G2 = V2e and V detected in block 48
The first grid voltage G1 = V1e corresponding to 2e is set in the first pulse generator 20 and the second pulse generator 22 as the optimum grid voltage.

The setting process of the optimum grid voltage is completed by the above process, but in the flowchart of FIG.
At 52, the electron detection unit 1 is set to the background counting mode to obtain the electron counting rate. In this background counting mode, as shown in the signal waveform diagram of FIG. 6, the voltage applied to the second grid electrode 6 by the second pulse generator 22 is set to −30.
The state is fixed to V and the introduction of electrons from the outside is blocked, and therefore, the mode is in which only the electrons generated like noise inside the electron detector 1 are counted.

If the counting rate that gives the background noise by setting the background counting mode is counted in the block 52, the counting rate N is compared with the threshold value No of the background noise in the next decision block 54. If it is smaller, it is considered that the optimum setting process of the grid voltage has been normally performed, and the setting process ends. On the other hand, when the count rate N in the background counting mode is greater than the threshold value No, the process proceeds to block 56 to issue an alarm and prompt the adjustment of the electronic detection unit 1 itself.

When the setting process of the optimum lattice voltage as described above is completed, the measurement sample is set on the sample table 8 and the measurement process for measuring the work function of the sample or the film pressure formed on the sample surface is performed. Like

In the above embodiment, the optimum grid voltage is set in accordance with the flow chart shown in FIG. 3 according to the flow chart shown in FIG. Although the case where the processing is performed in real time has been taken as an example, in an actual device, the anode voltage is varied and the corresponding grid voltage setting processing shown in FIG. The first grid voltage and the second grid voltage are obtained, the results are stored in advance in a memory with the anode voltage as an address, and the optimum grid voltage corresponding to the anode voltage is read out from the memory to set the first pulse generator 20 and the second grid voltage. Second
It may be set in the pulse generator 22.

Further, the above embodiment is an example in which the optimum anode voltage is set by detecting the discharge start voltage by changing the anode voltage and applying a voltage of 1/2 of the plateau voltage width. The invention is not limited to this, and the optimum lattice voltage setting process may be performed in the same manner with the anode voltage set manually or by an appropriate method.

(Effect of the invention) Second grid in which the peak value of the electron count value is obtained by varying the second grid voltage G2 applied to the second grid electrode for each of the plurality of different first grid voltages G1 applied to the first grid electrode A grid voltage detecting means for detecting the voltage G2, and a second grid voltage G2 and a first grid voltage G2 corresponding to the second grid voltage G2 giving the maximum count value from the plurality of second grid voltages G2 obtained by the grid voltage detecting means. Lattice voltage G1
Since the setting means for selecting and setting as the optimum value is provided, even when the anode voltage is changed in accordance with the change of the measurement condition, for example, the change of the atmospheric pressure or the temperature or the change of the distance between the sample and the electron detector. In addition, it is possible to obtain the optimum grid voltage setting state that maximizes the counting rate with respect to the anode voltage at that time, and it is possible to efficiently and stably perform electron counting with respect to changes in measurement conditions, and the reliability of the device. Can be greatly improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, FIG. 2 is a signal waveform diagram showing changes in the anode voltage, first and second lattice electrode voltages in the electron detection section, and FIG. 3 is the present invention. FIG. 4 is a flow chart showing an optimum grid voltage setting process according to FIG.
FIG. 5 is a characteristic graph diagram showing the relationship of the counting rate N to the second lattice voltage G2 with the first lattice voltage G1 as a parameter, and FIG. 6 is a signal waveform diagram showing the electrode voltage in the background counting mode. . 1: Electron detection part 2: Detection window 3: Case 4: Anode ring 5: First grid electrode 6: Second grid electrode 8: Sample stand 9: Light source device 10: Sample 11: Light source 12: Monochromator 13,14: Slit 18: Amplifier 20: First pulse generator 22: Second pulse generator 23: High voltage power supply 24: Counting means 26: Arithmetic means 28: Display means

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Claims (1)

[Claims] 1. An electron detector in which an anode ring to which a high voltage is applied is arranged in a case having a detection window on one side, and a first grid electrode and a second grid electrode are sequentially arranged on the detection window side of the anode ring. A first lattice voltage G1 having a predetermined positive voltage so that electrons emitted from a sample irradiated with light are introduced into the electron detection unit from the detection window to the first lattice electrode and the second lattice electrode. And an electron counter for counting the number of electrons based on the gas discharge caused by the introduced electrons by applying a second positive voltage G2 which is a predetermined positive voltage lower than the first negative voltage G1. A plurality of different first grid voltages applied to the first grid electrode
A second lattice voltage G2 for obtaining a peak value of the electron count value by varying the second lattice voltage G2 applied to the second lattice electrode for each G1.
Detecting means for detecting a grid voltage, a second grid voltage G2 giving a maximum count value from a plurality of second grid voltages G2 obtained by the grid voltage detecting means, and a first grid voltage corresponding to the second grid voltage G2. An electronic counting device comprising a setting means for selecting the grid voltage G1 and setting it as an optimum value.