JPH0223974B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion scattering spectrometer that irradiates a sample with an ion beam and performs energy analysis on ions emitted from the sample.

When a sample is irradiated with an ion beam, the ions emitted from the sample include ions that were scattered by the irradiated ions hitting atoms on the sample surface, and ions that caused atoms on the sample surface to fly out from the sample due to ion bombardment. be. Each of these ions provides information about the sample, but in this case, the subject of the invention is the former scattered ion, that is, the irradiated ion itself scattered by the sample atoms. . The energy of ions (same ions as the irradiated ions) scattered in a direction that forms a certain angle to the irradiation direction of the irradiated ions can be determined by considering the elastic collision between the irradiated ions and the atoms on the sample surface and applying the law of conservation of momentum. From this, we can determine the mass of atoms on the sample surface,
Therefore, surface analysis of the sample becomes possible.

Ion scattering spectrometry is performed with an apparatus configuration as shown in FIG. 1 is an ion gun, 2 is an irradiation ion beam, 3 is a sample, and an energy analyzer 4 is mounted at a certain angle, for example, perpendicular to the irradiation ion beam 2.
is arranged, and the ions that have passed through the energy analyzer 4 are detected by the ion detector 5.
An energy analyzer is like a concentric double spherical shell electrode, and of the ions that enter through the entrance slit, only those ions with a specific energy determined by the voltage between the double spherical shell electrodes exit from the exit slit. The energy value is scanned by changing the voltage between the double electrodes, or by keeping this voltage constant and changing the potential difference between the sample and the midpoint potential of the double electrodes. When energy scanning is performed with this configuration, the record of the output of the ion detector 5, that is, the energy spectrum of ions emitted from the sample, generally takes the form shown in FIG. In this spectrum, the large peak at a low energy location is the ion of the atoms that make up the sample itself, which is ejected from the sample by ion bombardment, and the scattered ion peak that is the problem in this invention is It is an extremely small thing that sits on top of a peak, and is exaggerated in the diagram for ease of viewing, but in reality, the peak is very small and difficult to see. Some of the scattered ion peaks have large energy and appear far away from the peak (because the sample contains various elements). Peaks like this are easy to find and their spectral intensities can be easily measured, but peaks like are superimposed on unnecessary (interfering) ion peaks, making it difficult to detect their presence and also difficult to quantify their intensity. be.

Therefore, the present invention has been made with the object of providing a scattered ion spectrometer that can remove unnecessary ions and obtain the energy spectrum of purely scattered ions in scattered ion spectroscopy.

To remove unnecessary ions and extract only scattered ions, a mass spectrometer is installed between the energy analyzer and the ion detector, taking advantage of the fact that the scattered ions are the same as the irradiated ions and have a known constant mass number. Just place it. For this reason, it is conceivable to arrange a quadrupole mass spectrometer between the energy analyzer and the ion detector. Here, a quadrupole mass spectrometer has an optimal energy range for incident ions, and if the energy range is outside of this range, the separation ability decreases. On the other hand, since the ions emitted from the energy analyzer retain the energy they had when they entered the energy analyzer, the energy of the ions entering the quadrupole mass analyzer increases with the energy scan of the energy analyzer. changes significantly. For this reason, the mass spectrometer only functions optimally in a certain limited energy range during the energy scanning process in the energy analyzer.

The present invention solves the above-mentioned problems by allowing a quadrupole mass spectrometer to function optimally over the entire energy scan range, and by completely separating scattered ions and unnecessary ions over the entire energy scan range. The aim is to increase the detection sensitivity of spectra and improve quantitative performance.

The present invention allows the quadrupole mass spectrometer to have a certain ground potential so that a deceleration electric field acts on ions between the energy analyzer and the mass spectrometer,
Ion scattering in which the intensity of this deceleration electric field is changed in conjunction with the energy scan of the energy analyzer so that the energy of ions incident on the mass spectrometer remains at a constant value that is optimal for mass spectrometry regardless of the energy scan. The present invention provides a spectroscopic device. The present invention will be explained below with reference to Examples.

FIG. 3 shows an embodiment of the present invention. 1 is an ion gun, 2 is an irradiation ion beam, 3 is a sample, and 4 is an energy analyzer. The configuration up to this point is the first one.
This is the same as the normal ion scattering spectrometer shown in the figure. 5 is an electron multiplier tube for ion detection, and 6 is a quadrupole mass spectrometer disposed between the energy analyzer 4 and the ion detector 5. 7 is a power source for applying a high frequency voltage and a DC voltage between each electrode of the quadrupole mass spectrometer 6 so as to pass only scattered ions, that is, ions having the same mass as the irradiated ions. The potential on the central axis of a quadrupole mass spectrometer is equal to the external potential unless a bias is applied to the mass spectrometer as a whole with respect to the external potential. 8 is a DC power supply for applying a DC bias potential to the entire mass spectrometer 6 so that the potential on the center line of the analyzer 6 has a constant potential with respect to the energy analyzer 4; It is connected to the positive terminal of the energy scanning variable DC power supply 9 of the analyzer 4 and has the same potential as the energy analyzer 4. Therefore, there is a constant potential difference between the energy analyzer 4 and the mass analyzer 6 provided by the DC power supply 8, and the electric field based on this potential difference causes ions to travel from the energy analyzer 4 to the mass analyzer 6. Slowed down. The energy analyzer 4 keeps the voltage applied between the double spherical electrodes constant so that the intermediate potential is the potential given to the sample 3 by the power source 9, and performs energy scanning by changing the voltage of the power source 9. I'm going. Therefore, in this case, since the energy of the ions emitted from the energy analyzer 4 is constant, the output voltage of the power source 8 may be fixed at an optimal value. energy analyzer 4
When performing an energy scan by changing the voltage between the double electrodes while keeping the potential as a whole at 0, the energy of the ions exiting the energy analyzer 4 changes according to the energy scan. It is necessary to change the output of the power supply 8 that provides a ground bias potential to the energy scan.

FIG. 4 shows another embodiment of the present invention. In this figure, the same reference numerals are given to the parts corresponding to those in FIG. 3, and the explanation of each part will be omitted. In this example, the overall ground bias of the quadrupole mass analyzer 6 is zero, whereas the overall potential of the energy analyzer 4 is semi-fixed to a certain value by the power supply 10. A constant ion deceleration electric field is formed between the energy analyzer 4 and the mass analyzer 6. In this case, energy scanning is performed by changing the overall potential of the irradiation ion optical system and the sample 3 using the scanning variable DC power supply 11, and the voltage between the dipoles of the energy analyzer 4 is kept constant.

The ion scattering spectrometer of the present invention has the above-mentioned configuration and uses a quadrupole mass spectrometer to remove interfering ions from scattered ions, so the mass spectrometer is inexpensive and the ion scattering spectrometer has the above-mentioned configuration. Since the energy of the ions to be detected can be set to the optimal value for mass spectrometry, interfering ions can be completely removed, and the resulting energy spectrum, as shown in Figure 5, has no peak in Figure 2, and is composed of scattered ions. Detection sensitivity and quantification are improved (especially for light elements with low energy).

[Brief explanation of drawings]

Figure 1 is a block diagram showing the basic configuration of the ion scattering spectrometer, Figure 2 is an example of the ion energy spectrum obtained with the above equipment, Figures 3 and 4.
The figures are block diagrams showing different embodiments of the apparatus of the present invention, and FIG. 5 is a diagram showing an example of an energy spectrum obtained by the apparatus of the present invention. 1...Ion gun, 3...Sample, 4...Energy analyzer, 5...Ion detector, 6...Quadrupole mass spectrometer, 8, 10...Between the energy analyzer and the mass spectrometer A power source that provides a potential difference.

Claims (1)

[Claims] 1 A quadrupole mass spectrometer set to pass only ions of the same mass as the scattered ions is placed between the energy analyzer and the ion detector, and the An ion scattering spectrometer in which a power source is connected to provide a potential difference between the two, and the potential difference is set so that the energy of ions entering the quadrupole mass spectrometer is optimal for mass analysis.