JPH046741A - mass spectrometer ion detector - Google Patents

Abstract

PURPOSE:To concurrently perform measurement with both measuring systems while the continuity of the measured values of both measuring systems are held by separating pulses outputted from a preamplifier, and concurrently reading one side with an ion counting system and the other with a DC measuring system. CONSTITUTION:A primary ion beam 4 is focused and radiated to a sample 7, and emitted secondary ions are guided into a mass spectrometer. The desired ions separated by the mass spectrometer are fed to a secondary electron multiplier tube 17, and pulses are generated by a wide-band preamplifier 18. The generated pulses are separated with noises by a discriminator 19 on one side, and the number of pulses is counted by a counter 20. The branched pulses on the other are smoothed by a low-frequency filter 22 and digitally converted by an A/D converter 23. A data processor 21 reads both the counter value and the output value of the A/D converter 23. Both detecting systems can be concurrently operated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the configuration of an ion detector such as a mass spectrometer, and
Regarding ion detection measurement range.

[Conventional technology]

The detectors of conventional mass spectrometers also vary depending on which device the mass spectrometer is combined with. This depends on the polarity, energy, mass number, amount of ions, speed of change in ion amount, etc. of the ions to be detected. Various inventions have been made depending on the purpose.

A general mass spectrometer uses a combination of a secondary electron multiplier tube and a DC amplifier to detect ion beams equivalent to 104 to 1010 cρS. This is the DC measurement method. or.

For mass spectrometers with weak output such as ion microanalyzers, there is a method of counting ions.
The amount of ions equivalent to 10-1 to 107 cps is detected. On the other hand, in the range where the amount of ions is extremely large, it is detected using a Faraday cup and a DC amplifier, and the measurement range is 101 to 1
This is equivalent to 0.5 cps. The range of these three typical detection methods can be expanded somewhat by adding restrictions to measurement factors such as response.

However, even if a plurality of the above ion detection methods are implemented, they are used by switching. Therefore, when the ion detection method is switched, the continuity of measured values is lost. This is extremely inconvenient when, for example, an ion microanalyzer is used to continuously analyze a semiconductor sample in the depth direction, since a measurement range of 8 to 10 orders of magnitude is required.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into consideration the simultaneous operation of a plurality of ion detection methods, and there is a problem that when the ion detection method is switched, the continuity of the measured values is lost.

An object of the present invention is to provide an ion detector for a mass spectrometer that can simultaneously operate two ion detection methods, namely, an ion counting method and a DC measurement method.

[Means to solve the problem]

To achieve the above objective, ions separated by a mass spectrometer are first amplified by a secondary electron multiplier, and then further amplified by a broadband preamplifier.
A pulse of 0 nanoseconds is obtained. The pulses output from this preamplifier are separated from noise by a discriminator and counted by a counter. On the other hand, the output of the preamplifier is branched and passed through a low frequency band filter for analog-to-digital conversion.

If the data processing device reads the count value of the counter and the output of the analog-to-digital converter, the two ion detection methods will be operated simultaneously.

[Effect]

The secondary electron multiplier tube emits a plurality of secondary electrons when one ion is incident on the first-stage dynode. The emitted secondary electrons are accelerated by the acceleration voltage between the stages and strike the next stage dynode, thereby emitting more secondary electrons. By repeating this operation many times, one
It can be amplified to 05 to 106 electron groups. The dispersion of the electron group is about 10 nanoseconds. When this group of electrons is input to a broadband amplifier, it becomes a pulse with a pulse width of about 10 nanoseconds. It is a well-known ion counting method to eliminate noise from this pulse by discretizing it.

When ions enter the secondary electron multiplier tube at a rate of 107 to 108 per second, the output pulses of the broadband amplifier become back-and-forth type, and the number of pulses is no longer proportional to the number of ions. This is the measurement limit of the ion counting method. Therefore, when an amount of ions exceeding this measurement limit is input, the output pulse group of the broadband amplifier is smoothed by a filter to form a low frequency signal, which is converted into an analog-to-digital signal.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained using the blocks shown in FIG. This example concerns an ion microanalyzer. Ions produced by the ion source 1 are accelerated and become a -order ion beam 4, which is focused and irradiated onto the analysis position of the sample 7 by the electrostatic lenses 2 and 6. Secondary ions emitted from the sample surface by this secondary ion beam 4 are accelerated by a secondary ion acceleration power source 8 and introduced into a mass spectrometer constituted by an electric field 11 and a magnetic field 14. The desired ions separated by the mass spectrometer enter the secondary electron multiplier tube 7, generate a large number of secondary electron groups for each ion, and generate pulses in the broadband preamplifier 18. A discriminator 19 separates noise from this pulse signal, and a counter 20 counts the number of pulses. Further, the pulse signal of the wideband preamplifier 18 is branched and passed through a low frequency band filter 22.
The signal is smoothed by the analog/digital converter 23, and converted into a digital value by the analog/digital converter 23. Data processing bag! 21 reads both the counter value and the output value of the analog/digital converter.

FIG. 2 shows the output waveform of the broadband preamplifier.

(,) is a waveform when the number of ions incident on the secondary electron multiplier 17 is relatively small, and the pulse width corresponding to one ion is about 10 nanoseconds.

(b) is a waveform when a very large number of ions are incident on the secondary electron multiplier 17, and is an example in which two pulses overlap. For the waveform (a), the discriminator 19 correctly outputs one pulse to the counter 20, but for the waveform (b), the discriminator 19 also outputs one pulse to the counter, and the number of ions is count down. This (b)
This state is the measurement limit of the discriminator 19 and counter 20.

When the amount of incident ions is large as shown in Figure 2(b),
Since the output of the secondary electron multiplier is unipolar when passed through the low frequency band filter 22, a DC component is obtained by smoothing it. Therefore, this DC component has a value proportional to the number of incident ions unless the secondary electron multiplier 17 and broadband preamplifier 18 are saturated. Therefore, ion detection using both the ion counting method and the DC measurement method is possible at the same time.

〔Effect of the invention〕

According to the present invention, since ion detection using a mass spectrometer or the like can operate using both the ion counting method and the DC measurement method at the same time,
It is possible for the measurement ranges of the two detection methods to partially overlap,
As a result, the dynamic wrench for ion detection expands continuously, and the effects of the present invention are extremely significant.

[Brief explanation of the drawing]

FIG. 1 shows a block diagram of an embodiment of the present invention, and FIG. 2 shows an output waveform diagram of a wideband amplifier. DESCRIPTION OF SYMBOLS 1...Ion source, 2,6.9...Electrostatic lens, 3°10.12.15...Slit, 4...-order ion beam, 5,16...Deflection electrode, 7.・Sample, 8...
Secondary ion acceleration power supply, 11... Electric field, 13... Secondary ion beam, 14... Magnetic field, 17. Secondary electron multiplier,
18... Preamplifier, 19... Discriminator,
20... Counter, 21... Data processing device, 22
-Low frequency band filter, 23.Analog-to-digital converter.

Claims (1)

[Claims] 1. By a secondary electron multiplier, a broadband preamplifier, a discriminator and counter for ion counting, a low frequency band filter and an analog-to-digital converter for direct current measurement. An ion detector for a mass spectrometer, wherein the output signal of the broadband preamplifier is simultaneously output to both the discriminator and the low frequency band filter. 2. A data processing device reads the output value of the counter and the output value of the analog-to-digital converter at the same time, and the output range of the counter and the output range of the analog-to-digital converter partially overlap. An ion detector for a mass spectrometer according to claim 1. 3. The ion counting range is 10^-^1 to 10^7 cps, and the DC measurement range is equivalent to input conversion of 10^6 to 10^1^0 cps, and the measurement range of 10^6 to 10^7 cps can be overlapped. An ion detector for a mass spectrometer according to claim 2.