JPH04335148A - Auger electron spectroscope - Google Patents

Abstract

PURPOSE:To enable a stage difference between a pulse mode and an analog current mode to be eliminated. CONSTITUTION:A control circuit 12 takes in both an output of a counter circuit 61 in pulse mode and a counter circuit 62 in analog current mode. The control circuit 12 monitors an output flag of a comparison circuit 10 and then enables an output of the counter circuit 61 when the output flag is F1 and an output of the counter circuit 62 when the output flag is F2. Then, a specified processing is performed to a spectrum which is obtained from these two counter circuits 61 and 62, thus enabling a continuous spectrum without any stage difference to be created. Also, the control circuit 12 controls a high voltage which is applied to an electron multiplier 1 for preventing damage when the output flag of the comparison circuit 10 is F3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Auger electron spectrometer, and more particularly to the configuration of a signal processing circuit system for obtaining an energy spectrum of Auger electrons (hereinafter simply referred to as spectrum).

0002

2. Description of the Related Art FIG. 4 is a diagram showing an example of the configuration of a signal processing circuit of a conventional Auger electron spectrometer. Auger electrons emitted from a sample (not shown) are detected by a channeltron or multichannel plate, etc. It is detected and amplified by an electron multiplier 1 as a device.

The output of the electron multiplier 1 becomes pulse-like when the number of Auger electrons per unit time is small.
In this case, the intensity of Auger electrons can be obtained by connecting the switch 7 as shown by the solid line in the figure and counting the pulses by the counting circuit 6 via the pulse amplifier 2. Furthermore, the output of the electron multiplier 1 increases as the probe current applied to the sample increases, and can be detected as a continuous analog current. After the current is amplified by a linear amplifier 3, the current is converted to voltage by a current/voltage converter (hereinafter referred to as an A/V converter) 4, and then the current is converted to a voltage by a voltage/frequency converter (hereinafter referred to as a V/F converter). The intensity of the Auger electrons can be obtained by converting the voltage into a frequency using a converter (referred to as a converter) 5 and counting the frequency using a counting circuit 6. Note that in the following, the former mode in which Auger electron intensity is obtained by a circuit system consisting of a pulse amplifier 2 will be referred to as a pulse mode, and the latter circuit system consisting of a linear amplifier 3, an A/V converter 4, and a V/F converter 5 will be referred to as a pulse mode. The mode in which the Auger electron intensity is obtained using is called the analog current mode.

[0004] Switching the switch 7, ie, selecting whether to obtain Auger electron intensity in pulse mode or analog current mode, sets which mode is adopted depending on the probe current or accelerating voltage applied to the sample. If the count value in pulse mode exceeds a predetermined value, switch to analog current mode, or switch to pulse mode if the count value in analog current mode falls below a predetermined value. It is common to switch between them.

[0005]

By the way, in the configuration shown in FIG. 4, if the dynamic range of the spectrum is wide, one spectrum is obtained using the pulse mode and the analog current mode. that time,
There has been a problem in that a step difference occurs in the spectra obtained in the two modes at the switching position from the pulse mode to the analog current mode and vice versa. The situation is shown in FIGS. 5A and 5B. In FIGS. 5A and 5B, the energy region indicated by "A" indicates the spectrum obtained in pulse mode, the region indicated by "B" indicates the spectrum obtained in analog current mode, and FIG. 5A shows the spectrum obtained in pulse mode. FIG. 5B shows an example where the intensity is higher than the spectrum obtained in the analog current mode, and FIG. 5B is an example of the opposite case. The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an Auger electron spectrometer that can continuously connect a spectrum obtained in pulse mode and a spectrum obtained in analog current mode without creating a step. That is.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the Auger electron spectrometer of the present invention provides a first method for determining the energy spectrum of Auger electrons by pulse counting.
a second counting circuit system that converts the detected current value into a frequency and calculates the energy spectrum of Auger electrons by counting the converted frequency; When the voltage, current, frequency or count value at the position is less than a predetermined threshold, the first
comparing means for outputting a second signal when the output of the comparing means is the first signal; and comparing the energy spectrum obtained by the first counting circuit system when the output of the comparing means is the first signal. 2, the control means makes effective the energy spectrum obtained by the second counting circuit system, and the control means further controls the energy spectrum obtained by the first counting circuit system. and the energy spectrum obtained by the second counting circuit system at the threshold value.

[0007] Furthermore, the Auger electron spectrometer of the present invention includes:
an electron multiplier; a first counting circuit system that obtains the energy spectrum of Auger electrons by pulse counting the output of the electron multiplier; and a first counting circuit system that converts the output current value of the electron multiplier into a frequency; a second counting circuit system that calculates the energy spectrum of Auger electrons by counting the converted frequencies; When the value is less than the first threshold value, the first signal is transmitted; when the value is equal to or more than the first threshold value and less than the second threshold value, the second signal is transmitted; and when the value is equal to or more than the second threshold value, the third signal is transmitted.
comparing means for outputting a signal; and comparing means for outputting an energy spectrum obtained by the first counting circuit system when the output of the comparing means is the first signal, and outputting the energy spectrum obtained from the first counting circuit system when the output of the comparing means is the second signal; It is characterized by comprising a control means for validating each of the energy spectra obtained by the system, and further for controlling a high voltage applied to the electron multiplier when the third signal is present.

[0008]

[Operation] The control circuit 12 takes in both the outputs of the counting circuits 61 and 62. At this time, the control circuit 12 monitors the output flag of the comparator circuit 10, and depending on the content of the flag, the control circuit 12
1 or the output of the counting circuit 62 is enabled, and processing is performed to connect the spectra obtained from these two counting circuits 61 and 62 continuously without any step difference. In addition, the control circuit 1
2 is when the output flag of the comparison circuit 10 is a predetermined value,
The high voltage applied to the electron multiplier 1 is controlled to prevent damage.

[0009]

Embodiments Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 shows the configuration of an embodiment of an Auger electron spectrometer according to the present invention, in which 10 is a comparison circuit, 11 is a D/A converter, 12 is a control circuit, 13 is a high voltage circuit, and 14 is a relay. shows. Note that the same parts as in FIG. 4 are given the same reference numerals.

The control circuit 12 is composed of a microprocessor, and takes in the count values output from the counting circuits 61 and 62 and performs processing to be described later to generate a continuous spectrum. Furthermore, the control circuit 12 generates two digital thresholds TH1 and TH2 having different values. These digital threshold values are converted into analog signals by the D/A converter 11 and provided to the comparison circuit 10. These thresholds will become clear from what will be described later, but the threshold TH1 is a voltage value corresponding to the count value that switches between the region where the pulse mode is adopted and the region where the analog signal mode is adopted, and the threshold TH2 (>TH1 )
is a voltage value corresponding to a count value in a region where the high voltage circuit 13 needs to be controlled. A comparison circuit 10 sets the output of the A/V converter 4 to threshold values TH1 and T.
H2, the output of the A/V converter 4 is equal to the threshold TH
If it is less than 1, the flag F1 is output and TH1
If the value is above TH2 and less than TH2, flag F2 is output, and if it is TH2 or more, flag F3 is output. When the output flag of the comparator circuit 10 is F1, the control circuit 12 adopts the pulse mode and controls the counting circuit 6
1 is enabled, and if it is F2, the analog current mode is adopted and the output of the counting circuit 62 is enabled,
If it is F3, the relay 14 is opened because the area is at risk of destroying the electron multiplier 1.

Next, the operation of the configuration shown in FIG. 1 will be explained.
Here, for ease of understanding, we use the same sample.
Let us consider a case where the count value of Auger electrons is measured when the current applied to the sample, that is, the probe current, is increased while the high voltage applied to the electron multiplier 1 is kept constant. Auger electrons emitted from the sample are converted into electrical signals by an electron multiplier 1, amplified, and input to a pulse amplifier 2 and a linear amplifier 3. The signal amplified by the pulse amplifier 2 is input to the counting circuit 61. Counting circuit 6
1 is the control circuit 1 that counts the input pulses and outputs the counted value.
Output to 2. Further, the signal amplified by the linear amplifier 3 is converted to voltage by the A/V converter 4, and further converted to a voltage by the V/F converter 5.
The signal is converted into a frequency and input to the counting circuit 62. The counting circuit 62 counts the input signals and outputs the counted value to the control circuit 12.

The control circuit 12 simultaneously takes in the outputs of the counting circuits 61 and 62, monitors the flag output from the comparator circuit 10, and operates the relay 14 when it detects that the flag F3 has been output, thereby shutting down the high voltage circuit. 13 and the electron multiplier 1, and the application of high voltage to the electron multiplier 1 is stopped.

At this time, the count values of the counting circuits 61 and 62 change as shown schematically in FIG. 2 as the probe current increases. In FIG. 2, the count value curve 20 corresponds to the count circuit 61.
The count value curve 22 shows the change in the count value due to the counting circuit 62. That is, when the probe current is small, good counting can be performed in the pulse mode, but good data cannot be obtained in the analog current mode due to pulsating current. This situation is shown by broken lines in FIG. However, in analog current mode, the frequency increases as the probe current increases, allowing good data to be obtained, whereas in pulse mode, pulses overlap, and multiple pulses overlap to form a single pulse. As the number of pulses counted increases, it becomes impossible to separate the pulses, and the count value decreases as shown in the count value curve 20. Therefore, a threshold value TH1 is provided to determine which of the count values in the pulse mode and the count values in the analog current mode is valid. This threshold T
As shown in FIG. 2, H1 is set in a region where both pulse mode and analog current mode output good data.

The control circuit 12 includes counting circuits 61, 6
The flag output from the comparator circuit 10 is monitored when taking in the count value from 2. If the flag F1 is output, the pulse mode is enabled, and if the flag F2 is output, the analog current mode is enabled. shall be valid.

However, even if the probe current is the same, the count value in the pulse mode and the count value in the analog current mode generally do not match.
If you just import the count value from 1 or 62,
As described above, and as shown in FIG. 2, a step occurs at the connection between the two count value curves. Such a step is mainly caused by V/
This is thought to be due to the fact that F conversion is performed relatively. That is, in the V/F converter 5, 0V is 0H
Even if the count value is doubled in pulse mode when the probe current changes from IP1 to IP2, the frequency will not be doubled in V/F conversion. is normal, and as a result, the count curves 20 and 22 have different offsets and slopes, as shown in FIG.

Therefore, the control circuit 12 calculates the count value curve 20.
A process is performed to make the effective part 21 and the count value curve 22 into a continuous smooth curve. This process can be performed by various methods, for example, count value curves 21 and 2.
2, find the equation of a straight line that approximates the vicinity of the switching position, match the count value B of the analog current mode at the switching position shown in FIG. 2 with the count value A of the pulse mode, and adjust the slope β of the count value curve 22. This can be done by finding a conversion formula that matches the slope α of the count value curve 21 and converting the count value in the analog current mode into the count value in the pulse mode using the conversion formula.

Next, control of the high voltage applied to the electron multiplier 1 will be explained. The electron multiplier 1 will be damaged if many electrons rush into it. Therefore, as shown in FIG. 2, the threshold value TH2 is set to a count value slightly lower than the count value at which the electron multiplier 1 is damaged, and a voltage corresponding to the threshold value TH2 is applied to the comparator circuit 10. The control circuit is a comparator circuit 10.
When the flag F3 is output, the relay 14, which is normally closed, is opened, and the application of high voltage to the electron multiplier 1 is stopped. This can prevent damage to the electron multiplier 1.

Furthermore, instead of stopping the application of high voltage to the electron multiplier 1 as shown in FIG.
According to this, in the configuration of FIG. 1, the electron multiplier 1 becomes inactive and the measurement ends, whereas the electron multiplier 1 Since it is working, measurements can be continued. An example of its configuration is shown in FIG. In FIG. 3, when the control circuit 12 recognizes that the output flag of the comparison circuit 10 is F3, it gives an instruction to the high voltage circuit 13 to lower the output voltage of the high voltage circuit 13. For example, if the high voltage circuit 13 is capable of continuously varying the output voltage, this instruction can be given by giving an output voltage value, or the output voltage can be switched stepwise into two or more stages. In such cases, this can be done by specifying which stage to use. The high voltage circuit 13 then outputs a voltage according to instructions from the control circuit 12. This can prevent damage to the electron multiplier 1 due to rush current.

Although the case where the probe current is increased has been described above, the above-mentioned processing is performed even when the probe current is kept constant and the energy of Auger electrons detected by an energy analyzer (not shown) is changed. It is clear that even when the dynamic range of the spectrum is wide, a continuous spectrum without any steps can be obtained.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible. For example, in the above embodiment, the threshold value TH
1, TH2 is given as a voltage and compared with the output voltage of the A/V converter 4. This is because voltage comparison can be done inexpensively and easily, and performing voltage comparison is a part of the present invention. This is not the point. Therefore, linear amplifier 3
The comparison may be made using the output of the V/F converter 5, or even the count value that is the output of the counting circuit 62.

Furthermore, in the above embodiment, the linear amplifiers 3, A
Although the A/V converter 4 and the V/F converter 5 are shown as being independent, the A/V converter 4 is connected to the linear amplifier 3.
Alternatively, it may be integrated with the V/F converter 5 to form a current/frequency converter. Note that in the latter case, if the comparator circuit 10 is configured with a voltage comparator circuit, it is necessary to provide a frequency/voltage converter for converting the output of the current/frequency converter into a voltage before the comparator circuit 10. Not even.

[0022]

[Effects of the Invention] As is clear from the above explanation, according to the present invention, the dynamic range of the spectrum is wide, and a continuous energy spectrum can be obtained even when using both pulse mode and analog current mode. be. In addition, one comparison circuit can obtain the switching position between pulse mode and analog current mode and the timing of high voltage control to protect the electron multiplier.
It can be constructed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of FIG. 1.

FIG. 3 is a diagram showing the configuration of another embodiment of the present invention.

FIG. 4 is a diagram showing a configuration example of a conventional signal processing circuit of an Auger electron spectrometer.

FIG. 5 is a diagram for explaining conventional problems.

[Explanation of symbols]

1...Electron multiplier, 2...Pulse amplifier, 3...Linear amplifier, 4...A/V converter, 5...V/F converter, 61, 62
...Counting circuit, 10...Comparison circuit, 11...D/A converter, 1
2...Control circuit, 13...High voltage circuit, 14...Relay.

Claims (3)

[Claims] 1. A first counting circuit system for calculating the energy spectrum of Auger electrons by pulse counting; and a first counting circuit system for calculating the energy spectrum of Auger electrons by converting a detected current value into a frequency and counting the converted frequency. When the voltage, current, frequency, or count value at a predetermined position of the second counting circuit system and the second counting circuit system is less than a predetermined threshold, the first signal is sent, and otherwise, the second signal is sent. comparing means for outputting a signal; and comparing means for outputting an energy spectrum obtained by the first counting circuit system when the output of the comparing means is the first signal, and outputting the energy spectrum obtained from the first counting circuit system when the output of the comparing means is the second signal; 1. An Auger electron spectrometer, comprising: control means that makes effective the energy spectrum obtained by the system. 2. The control means further performs an operation for continuously connecting the energy spectrum obtained by the first counting circuit system and the energy spectrum obtained by the second counting circuit system at the threshold value. 2. The Auger electron spectrometer according to claim 1, wherein the Auger electron spectrometer performs the following steps. 3. An electron multiplier; a first counting circuit system for determining the energy spectrum of Auger electrons by pulse counting the output of the electron multiplier; a second counting circuit system that calculates the energy spectrum of Auger electrons by converting the converted frequency into If it is less than a predetermined first threshold, the first
a comparison means for outputting a second signal when the signal is equal to or greater than the first threshold value and less than the second threshold value, and outputs a third signal when the value is equal to or greater than the second threshold value; When the output of the means is the first signal, the energy spectrum obtained by the first counting circuit system is
control means for validating the energy spectrum obtained by the second counting circuit system when the signal is, and controlling a high voltage applied to the electron multiplier when the signal is the third signal. Features of Auger electron spectroscopy equipment.