JPS63167256A - Electron counting device - Google Patents

Abstract

PURPOSE:To count electrons efficiently and stably against variations of measure ment conditions by selecting a 2nd grating voltage which is obtained by a grat ing voltage detecting means and provides the largest counted value, and a 1st grating voltage corresponding to it, and obtaining the best grating voltage. CONSTITUTION:Electrons emitted by a sample 10 irradiated with light are admitted into an electron detection part provided the 1st and 2nd grating electrodes 5, 6 and counted. An arithmetic means 26 sets the electrode voltages of grating electrodes 5 and 6 to optimum values. While an anode voltage is set for an anode ring 4 by a high-voltage power source 23, a reference sample 10 is set first and the 2nd grating voltage is varied by plural 1st grating voltages to detect the 2nd grating voltage with which the peak value of the counted value is obtained. Then, the 2nd grating voltage corresponding to the maximum counted value and the 1st grating voltage corresponding to the 2nd grating voltage are selected and set as optimum values.

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 formed on the surface of a sample such as a semiconductor in an open atmosphere, the sample surface is irradiated with light, and the light passes through the thin film on the sample. A known method is to introduce electrons emitted to the outside into an electron detection section, count the number of emitted electrons using the gas discharge phenomenon caused by the introduced electrons, and measure the film thickness based on the number of emitted electrons. (Patent Application No. 59-118818, etc.)
.

(Problems to be Solved by the Invention) However, in such conventional electronic counting devices, a high voltage is applied to the anode ring placed in the electron detection section, and a gas discharge is generated by the electrons emitted from the sample. The number of electrons is counted from the pulse change in the anode voltage caused by this gas discharge, but it is not clear how to determine the first grid voltage and the second grid voltage when changing the anode voltage, and it is difficult to determine the optimal state. It was difficult to efficiently count emitted electrons.

(Means for Solving the Problems) The present invention has been made in view of these conventional problems, and it is possible to efficiently and stably maintain the grid voltage by always setting the grid voltage to the optimum state even if the anode voltage is changed. An object of the present invention is to provide an electronic counting device capable of performing counting operations.

To achieve this objective, the present invention uses a plurality of different first grid voltages G1=V1a, Vlb.

The second grid voltage G2 is varied every time VlC, . . . to obtain an electronic count value, for example, the peak value of the electron count rate N. Second grid voltage G2 = grid voltage for detecting V2a, V2b, V2C, . . . A detection means and a plurality of second grid voltages G2=V2a, V2b, V detected by the grid voltage detection means
2C --- The second which gives the maximum number rate N maX
A setting means for selecting a grid voltage and a first grid voltage corresponding thereto and setting the grid voltage as an optimum value is provided.

(Function) According to the configuration of the present invention, even when the anode voltage is changed, the optimum values of the first grid voltage and the second grid voltage that maximize the efficiency of electron counting at the current anode voltage can be determined. It can be set accurately, for example, by determining the optimal grid voltage for the anode voltage in advance and storing it in a memory etc.
Once the anode voltage is determined, the optimum grid voltage can be uniquely read out from the memory and set, ensuring efficient and stable operation.

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

First, to explain the configuration, 1 is an electron detection section, which has a metal case 3 with a detection window 2 opened at the bottom.
is grounded. An anode ring 4 is arranged inside the case 3, and an anode voltage is applied to the anode ring 4 from a high voltage power supply 23.
For example, a high voltage of Va=3.4 KV is applied as a, and the anode voltage Va from the high voltage power supply 23 can be varied in the range of Va=3.0 KV to 4.0 KV as necessary. can.

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

The output of an amplifier 18 is connected to the first pulse generator 20 and the second pulse generator 22, which extracts the voltage change of the anode ring 4 via a capacitor C.

The voltage applied to the anode ring 4 falls in a pulse-like manner as shown in FIG. 1 given to the pulse generator 20,
The first pulse generator 20, as shown in FIG. 2(b),
In order to prevent the first lattice voltage G1 from being charged by the gas, a rectangular wave pulse is outputted over the quenching time Te to a predetermined voltage valve Δ<i>t and a fenching pressure *q. Here, the voltage ΔV that gives the fenching pressure VQ is set to, for example, ΔV=300V, and therefore, when receiving the voltage pulse, the voltage G1 of the first grid electrode 5 is increased by 300V from 100V to 400V. Changes to

On the other hand, when the second pulse generator 22 receives a voltage pulse from the amplifier 18, as shown in FIG. Generates a rectangular pulse that changes. For example, the second
Assuming that the grid voltage G2=80V, a rectangular wave pulse lowered by 1'lOV will be 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 such that when the electrons emitted from the sample 10 approach the anode ring, a high electric field near the anode ring 4 is generated. The electrons are accelerated and cause a gas discharge phenomenon, but the first pulse generator 20 increases the quenching pressure to Vq over the quenching time Te, thereby increasing the contact between the anode ring 4 and the first grid electrode 5. The potential difference is lowered by, for example, Δ=300V, thereby preventing light generated by the gas discharge and secondary electrons caused by positive ions from reaching the discharge voltage, thereby preventing an avalanche of discharge.

On the other hand, the output of the rectangular wave pulse lowered to -30V over the quenching time Te of the second pulse generator 22 is such that the second grid electrode 6 captures and neutralizes the positive ions generated by the gas discharge accompanied by the amplification effect. , this causes the cations to become sample 10
At the same time, it prevents electrons from reaching the photoelectrons and affecting the emission action of photoelectrons, and at the same time blocks the introduction of electrons from the outside.

Furthermore, a light source device 9 is arranged on the side of the electron detection section 1,
A light source device 9 irradiates a sample 10 set on a sample stage 8 with single wavelength light of a predetermined wavelength obliquely from above. The light source device 9 includes a light source 11 such as a deuterium lamp, and a light source 1.
It is provided with a monochromator 12 that converts the wavelength from 1 to a single wavelength, and further provided with slits 13 and 14 in front of the monochromator 12 for adjusting the light intensity.

Further, a counting means 24 is provided as a measuring circuit for counting the number of electrons based on the voltage pulse outputted from the amplifier 18 of the electron detection section 1, and the counting means 24 has an electron counting rate per unit time (cps), for example. The output of the counting means 24 is given to the calculating means 26, and the calculating means 26 calculates the first electronic count rate N obtained from the counting means 24.
An arithmetic control process is performed to set the grid power sources of the grid electrode 5 and the second grid electrode 6 to optimal values. Furthermore, in this embodiment, the calculation means 26 also has the 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. Following the calculation means 26 is the display means 2.
8 is provided, and the display means 28 displays the electron counting rate N obtained by the counting means 24 as it is, or the calculation means 26 displays the thickness of the oxide film etc. formed on the surface of the sample 10. The film thickness T based on the calculation result of the calculation means that calculates T is displayed. Alternatively, the wavelength may be varied and the work function may be displayed.

Here, the calculation control process by which the calculation means 26 sets the electrode voltages of the first grid electrode 5 and the second grid electrode 6 to optimal values is as follows.

(A) With the anode voltage Va set in the anode ring 4 set to an appropriate value by the high-voltage power supply 23, the reference sample 110 is set on the sample stage 8 as shown in the figure, and the first pulse is generated in this state. G1=V
1a.

For example, G1=8, such as Vlb, v1C2...
The second grid voltage G2 is varied stepwise in the range of 0 to 120V, and with the first grid voltage fixed to each of the first grid voltages v1a, V1b, v1c, . . .
It is variable in the range of 40 to 110V.

(B) Set the second grid voltage G2 to, for example, G2=40 to 110V.
The second grid voltages V2a and V2b provide the peak value of the counting rate N when varied within the range of .

V2c, ... is detected.

(C) Second grid m pressure that provides the peak value of the counting rate obtained in (B) above, and a second grid voltage that provides the maximum counting rate N max from among V2a, V2b, V2C, --. select the first grid voltage.

(D> The first and second pulse generators 20 set the first grid voltage and the second grid voltage obtained in the above (C) as the optimum grid voltage.
．． Set to 22.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to the flowchart shown in 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 a to be applied to the anode ring 4.

This optimum anode voltage setting process is as shown in Figure 1.
With a sample 10 serving as an appropriate reference set on the sample stage 8, monochromatic light of a predetermined wavelength is irradiated from the light source device 9 to emit electrons, and the electrons emitted from the sample 10 are introduced into the electron detection section 1. The counting rate is measured by the counting means 24.

That is, in the initial state, the calculation means 26 adjusts the anode voltage Va from the high-voltage power supply 23 within the voltage variable range of 3.0 to 4.0 degrees. OKV
The lowest value Va is set to 3.0 KV, and the anode voltage Va is increased from this initial state as shown in block 30. In response to the increase in anode voltage in block 30, in the next judgment block 32, the electron counting rate N obtained from the counting means 24 is determined by the background noise.

When it is determined that the electron counting rate N is equal to or higher than the threshold value No, the anode voltage at this time is set as the discharge starting voltage V.
It is detected as S and the process proceeds to the next block 34. block 3
In block 4, a voltage obtained by adding half the voltage of the predetermined plateau voltage width Pw to the discharge starting voltage VS is calculated as the optimum anode voltage VaO, and in the next block 36, the high voltage power supply 23 is set to the optimum anode voltage vaO. control.

Here, the counting rate N when changing the anode voltage ■a has the characteristics shown in Figure 4, and as the anode voltage Va is increased, the threshold N determined by background noise at a certain voltage
A counting rate exceeding o is obtained, and the voltage exceeding this threshold value No is detected as the discharge starting voltage vS. Furthermore, when the anode voltage is increased, the counting rate N remains approximately constant within a certain range with respect to changes in the anode voltage; The range is defined as a plateau voltage width Pw. Further, when the anode voltage is increased beyond the plateau voltage width pw, the counting rate N rapidly increases and becomes impossible to count.

The plateau voltage width PW that provides the anode voltage range in which the counting rate is approximately constant as shown in FIG. It is given as an equal voltage width. Therefore, the third
The optimum anode voltage Va is determined in block 34 in the flowchart of the figure.

Therefore, 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 yao.

Referring again to FIG. 3, once the optimum anode voltage yao has been set through the processing up to block 36, the first grid voltage G1 is set to the initial voltage Va in the next block 38. For example, the first grid voltage G1 is G1=80~1
Since it is variable within a range of 20V, it is set to V1a=80V.

With the first grid voltage G1 set to the initial voltage of G1=V1a in this way, in the next block 40, the second grid voltage G2 is varied within a range of, for example, 40 to 110V. Then, in the next block 42, the counting rate N when the second grid voltage G2 in the block 40 is varied is monitored, and the second grid voltage G2 at which the counting rate N becomes maximum is set as G
2=Detect V2a. Next, in the determination block 44, it is checked whether the final setting of the first grid voltage has been completed, and if the final setting has not been completed, the process returns to block 46, and the predetermined voltage Δ is added to the first grid voltage G1 up to that point. (2) 1 is added to set a new first grid voltage, and the process of blocks 40 and 42 is repeated in the same manner.

FIG. 5 shows block 40 in the flowchart of FIG.
It is a characteristic graph showing the relationship between the counting rate N and the second lattice voltage G2 obtained in the processing of 46 to 46.

The characteristic graph in FIG. 5 shows that the first lattice voltage G1 to V1a
, Vlb, v1C2...vlg, and shows the relationship between the counting rate N when the second grid voltage G2 is varied at each first grid voltage. Peak value N of the counting rate N obtained by varying the second grid voltage G2 when the first grid voltage G1 is constant
a, Nb, ... -Ne second grid voltage G2
is G2=V2a.

It can be detected as V 2b, ...■2g.

Referring again to FIG. 3, once the final setting of the first grid voltage G1 is determined in the determination block 44, the process proceeds to the next block 48, where the second grid voltage V2a is determined as shown in FIG. , V2b, ---V2! A second grid voltage G2, for example V2e, which provides the maximum counting rate NmaX is detected from IJ. Then in block 50, the second grid voltage G2=V2e and V2e detected in block 48
First grid voltage G1=V1e@optimum grid voltage corresponding to first pulse generator 20 and second pulse generator 2
Set to 2.

The above process completes the optimum grid voltage setting process, but in addition, in the flowchart of FIG. 3, block 5
2, the electron counting rate is determined by setting the electron detection unit 1 to the background divisor mode.

In this background counting mode, as shown in the signal waveform diagram of FIG. Therefore, the mode is set in which only the electrons generated as noise inside the electron detection section 1 are counted.

After counting the counting rate that gives background noise by setting the background counting mode in block 52, in the next judgment block 54, it is compared with the background noise threshold No.
If it is smaller, it is assumed that the grid voltage optimum setting process has been performed normally and the setting process is terminated. On the other hand, when the counting rate N in the background counting mode is greater than the threshold value No, the process proceeds to block 56 where an alarm is issued to urge adjustment of the electronic detection section 1 itself.

When the process of setting the optimum grid voltage as explained above is completed, the measurement sample is set on the sample stage 8 and the measurement process is performed to measure the work function of the sample or the film pressure formed on the sample surface. It becomes like this.

In the above embodiment, when using the device, the optimum grid voltage is set under the calculation control by the calculation means 26 according to the flowchart shown in FIG. Although this was an example of processing in real time, in actual equipment, the anode voltage is varied, and the corresponding grid voltage is set for each anode voltage by the process of setting the optimum grid voltage shown in Figure 3. The first grid voltage and the second grid voltage are determined, and the results are stored in advance in a memory with the anode voltage as the address.The corresponding optimum grid voltage is read out from the memory when the anode voltage is set, and the first pulse generator 20 and It may also be set in the second pulse generator 22.

Furthermore, in the above embodiment, the discharge starting voltage is detected by varying the anode voltage, and the optimal anode voltage is set by applying a voltage that is 1/2 of the plateau voltage width. The invention is not limited to this, and the optimum grid voltage setting process may be performed in exactly the same manner with the anode voltage set manually or by an appropriate method.

(Effects of the Invention) As explained above, according to the present invention, the second grid voltage is varied for each of a plurality of different first grid voltages, and the second grid voltage at which the peak value of the electronic count value is obtained is detected. A grid voltage detection means and a plurality of second voltages obtained by the grid voltage detection means.
Since a setting means is provided for selecting a second grid voltage that gives the maximum count value from among the grid voltages and a first grid voltage corresponding to this second grid voltage and setting it as the optimum grid voltage, changes in measurement conditions can be avoided. For example, even if the anode voltage is changed due to changes in atmospheric pressure or temperature, or changes in the distance between the sample and the electron detection section, the optimal grid voltage setting state that maximizes the counting rate for the anode voltage at that time can be set. you can get
Electronic counting can be performed efficiently and stably in response to changes in measurement conditions, and the reliability of the device can be greatly improved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an embodiment of the present invention, Fig. 2 is a signal waveform diagram showing changes in anode voltage and first and second grid electrode voltages in the electron detection section, and Fig. 3 is an explanatory diagram showing an embodiment of the present invention. A flowchart showing the process of setting the optimum grid voltage according to FIG. 4, a graph showing the relationship between the electron count rate and the anode voltage,
Fig. 5 is a characteristic graph showing the relationship between the counting rate N and the second grid voltage G2 using the first grid 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 unit 2: Detection window 3: Case 4: Anode ring 5: First grid electrode 6: Second grid electrode 8: Sample stage 9: Light source device 10: Sample 11: Light source 12: Monochromator 13.14 Nislit 18: Amplifier 20: First pulse generator 22: Second pulse generator 23: High voltage power supply 24: Counting means 26: Calculating means 28 Second display means

Claims (1)

[Claims] Electron detection in which an anode ring to which a high voltage is applied is arranged in a case with 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. In an electronic counting device for introducing electrons emitted from a sample irradiated with light into the electron detection section and counting the number of electrons based on a gas discharge generated by the introduced electrons, the electronic counting device has a plurality of different A grid voltage detection means for detecting a second grid voltage from which a peak value of an electronic count value is obtained by varying a second grid voltage for each first grid voltage, and a plurality of second grids obtained by the grid voltage detection means. An electronic counting device comprising: a setting means for selecting a second grid voltage that gives a maximum count value from among the voltages and a first grid voltage corresponding to the second grid voltage and setting the selected value as an optimum value.