JP2707097B2 - Method and apparatus for ionizing sputtered neutral particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for ionizing sputtered neutral particles suitable for high sensitivity and improvement of quantitative accuracy in a secondary ionic material analysis method for analyzing solid materials. Regarding the device.

[Conventional technology]

In this type of neutral ionization method, for example, an inert gas for discharge is caused to flow through the entire sample chamber in which a sample is placed to generate plasma, thereby ionizing sputtered neutral particles from the sample. ing. That is, the entire sample chamber is a plasma space, and an extraction electrode is provided outside the plasma space. Secondary ions from the sample are guided to the mass spectrometer (" Electronic Materials ", Special Issue, Latest Results of Ultra-High-Speed GaAs Devices, December, p.35 (1985)).

[Problems to be solved by the invention]

The prior art described above does not consider the following points.

1) The entire sample chamber is in contact with the plasma, and contamination from the sample chamber walls is mixed, making it difficult to perform trace analysis and true element identification.

2) Since the carrier gas for exciting and sustaining the discharge is supplied, the masking effect of the carrier gas itself and the impurity element in the carrier gas increase the background and limit the detection limit.

3) Since the sample in the high pressure (10 ^-3 to 10 ^-4 Torr) of the carrier gas is irradiated with the temporary ion beam, the primary ion beam is scattered by collision with gas molecules, and the beam diameter becomes extremely large. It becomes difficult to analyze minute parts.

An object of the present invention is to solve the above-mentioned problems of the conventional method and to improve the accuracy of micro-analysis and quantification.

[Means for solving the problem]

The above object can be achieved by employing the following method. For ionization of sputtered neutral particles, a shield electrode having the same potential as the sample is provided so as to surround the sample, and a high-frequency voltage or a DC voltage is applied between the discharge electrode and the sample,
Plasma is locally generated in the vicinity of the primary ion irradiation part of the sample, thereby ionizing neutral particles of sputter. The discharge is excited and sustained by the partial pressure of the sample composition element produced by the neutral particles of sputter. The ions thus generated are extracted by a high-frequency electric field and a DC electric field used for discharge excitation and sustaining, accelerated by an electric field applied to an accelerating electrode arranged at a later stage, and guided to a mass spectrometer. The ions guided to the mass spectrometer are separated there and detected in a mass-to-charge ratio. In this case, the discharge excitation high-frequency electric field and the DC electric field are applied to the secondary ion extraction electrode while fixing the sample potential. In this way, ionization of the neutral particles of the sputter and effective extraction of the generated ions are performed.

That is, the present invention relates to a secondary ion mass spectrometry,
A sputtered neutral particle ionization method in which a high-frequency electric field or a pulsed electric field is applied between the sample and the secondary ion extraction electrode to plasma the sputtered particles, and the plasma neutralizes the sputtered neutral particles. is there.

Further, the present invention provides a secondary ion mass spectrometer,
The present invention is an apparatus for ionizing sputter neutral particles including means for applying a high-frequency electric field or a pulse electric field for converting sputter particles into plasma between a sample and a secondary ion extraction electrode.

[Action]

As described above, the sample and the secondary ion extraction electrode are used as they are as discharge electrodes, and when a high frequency voltage or a DC high voltage is applied to both, a plasma is locally generated in the primary ion beam irradiation unit. In this case, this plasma generation is caused by an increase in local partial pressure due to sputter neutral particles.

For this reason, since the plasma is localized, contamination from the sample chamber wall does not occur. In addition, a carrier gas is not required for discharge excitation and sustaining, thereby increasing a detection limit,
Further, scattering of the primary ion beam can be prevented.

Therefore, it is possible to improve the accuracy of micro-analysis and quantitative analysis.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 shows an overall configuration of an ion microanalyzer (IMA) used as an embodiment, and FIG. 2 shows details of a sample peripheral portion which is a main part of the present invention.

In FIG. 1, (a) is a primary ion beam irradiation system, which comprises an ion source 1, a condenser lens 2, an objective lens 3, a deflection electrode 4, a sample 5, and the like. The role of the primary ion beam irradiation system is to focus and deflect the ion beam 6 emitted from the ion source 1 and irradiate an arbitrary point on the sample with a fine beam.

(B) is a secondary ion mass spectrometry system, in which secondary ions 19 generated on the sample are reflected by the entrance slit 11 of the mass spectrometer.
Lens 10, sector electric field 12, energy selection slit 13, sector magnetic field 14, collector slit 1
5, Neutral particle removal deflection electrode 16 and deflection slit slit 1
7 and an ion detector 18. Secondary ions 19 emitted from the sample are slit by the lens 10
The light is focused to 11, guided to a mass spectrometer composed of sector electromagnetic fields 12 and 14 and an energy selection slit 13, and mass-separated by a collector slit 15. The specific ions that have passed through the collector slit 15 are detected by a neutral particle removing deflection electrode 16, a deflection slit 17, and an ion detector 18.

FIG. 2 shows a main part of the present embodiment, and shows details in the vicinity of the sample including a power supply. A hemispherical metal shield mesh 8 for shielding an external electric field is mounted around the sample. The metal shield mesh 8 plays a role of preventing interference such as discharge between the peripheral portion other than the extraction electrode 7.
The post-acceleration electrode 9 is a secondary ion generated near the sample surface.
It has a role of leading 19 to the mass spectrometry system (b).

The principle of operation is as follows. A positive or negative secondary ion accelerating voltage is supplied from the DC power source 20 to the sample 5 depending on the polarity of the secondary ions (positive or negative ions). A high frequency voltage of 28 MHz and 10 Watt is applied to the secondary ion extraction electrode 7 from a high frequency power supply 21. On the other hand, a high density sputtered particle cloud is locally formed from the sample surface irradiated with the primary ions by sputtering. When the high-frequency electric field is applied between the sample 5 and the extraction electrode 7 in this state, a local plasma is generated by sputtered particles at the primary ion irradiation portion of the sample surface. Thereby, the sequentially sputtered neutral particles are ionized, and 80 to 90% of the sputtered neutral particles are ionized. Here, the extraction electrode 7
A case where a high-frequency voltage was applied was described above, but a similar plasma was formed even with a high-voltage pulse of, for example, 3 KV and a pulse width of 5 μs to 100 μs, which demonstrates that ionization of neutral particles occurs efficiently.

Next, examples in which the present invention is applied to GaAs and AuSi compounds will be described. The measurement conditions in this example are as shown in Table 1.

The frequency was measured in the range of several MHz to several tens of MHz, and it was found that effective ionization occurred in each case.

Table 2 shows an example of the results of the quantitative measurement performed on the above-described samples, in comparison with the results obtained by the conventional secondary ion analysis method. From the table, the conventional secondary ion analysis In the method, there is a large difference of about 3 to 4 digits due to a difference in the ionization rate (a value obtained by dividing the number of ionized particles by the number of all sputtered particles) between As ⁺ , Ga ^+, and Au ⁺ Si ⁺ . On the other hand, according to the technique of the present invention, it can be seen that the difference between the two has a value almost equal to one. This can be said to demonstrate that the technique of the present invention works extremely effectively on ionization of sputter neutral particles in consideration of the fact that the total sputtering amount matches the composition ratio.

 The effects obtained from this embodiment are as follows.

(1) Almost 100% ionization of sputtered neutral particles is possible, so that the ionization rate due to elements and the matrix effect can be reduced.

(1) High sensitivity analysis is possible by improving the ionization rate.

As described above, according to the present embodiment, the ionization of the neutral particles, which was not used for the analysis in the past, caused about 100
There is an effect that the absolute sensitivity is improved by a factor of about two and the difference in ionization rate for each element is extremely small, so that the quantitative accuracy is improved.

Conventionally, Cs ⁺ and O ₂ ⁺ have been used as primary ion species and negative and positive ions have been detected as secondary ions, respectively, for the purpose of improving the analysis sensitivity of negative and positive elements. In order to utilize this effect, in the conventional method, _two ion sources for Cs ⁺ and O ₂ ⁺ were used as primary ion sources. In the present invention, only one kind of primary ion is required, which is effective in reducing the cost of the apparatus and operability.

Further, by irradiating the same primary ion beam, the analysis of negative and positive elements can be performed with high sensitivity at the same place, which speeds up material analysis and significantly improves the reliability of analysis results.

〔The invention's effect〕

As described above, according to the method and the apparatus for ionizing sputtered neutral particles according to the present invention, the sample and the secondary ion extraction electrode are used as they are as the discharge electrodes, and a high frequency voltage or a DC high voltage is applied to both. Thereby, plasma is locally generated in the primary ion beam irradiation unit. In this case, an increase in the local partial pressure due to the neutral particles of the sputter is an excitation source in this plasma generation.

For this reason, since the plasma is localized, contamination from the sample chamber wall does not occur. In addition, a carrier gas is not required for discharge excitation and sustaining, thereby increasing a detection limit,
Further, scattering of the primary ion beam can be prevented.

Therefore, it is possible to improve the accuracy of micro-analysis and quantitative analysis.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an embodiment when the present invention is applied to a secondary ion analysis method, and FIG. 2 is a configuration diagram showing an embodiment of a main part thereof. DESCRIPTION OF SYMBOLS 1 ... Ion source, 2 ... Condenser lens, 3 ... Objective lens, 4 ... Deflection electrode, 5 ... Sample, 6 ... Primary ion beam, 7 ... Secondary ion extraction electrode, 8 ... Shield electrode , 9 ... post-acceleration electrode, 10 ... convergent lens,
11… Slit, 12… Sector electric field, 13… Energy slit, 14… Sector magnetic field, 15… Collector slit, 16… Deflecting electrode, 17… Aperture, 18… Detector, 19
...... Secondary ion beam.

Continuation of the front page (56) References JP-A-47-45793 (JP, A) JP-A-61-263039 (JP, A) JP-A-62-264544 (JP, A) JP-A-54-158294 (JP, A) , A) JP-A-61-116742 (JP, A)

Claims (3)

(57) [Claims] In a secondary ion mass spectrometry, a high-frequency electric field or a pulse electric field is applied between a sample and a secondary ion extraction electrode to convert sputtered particles into plasma, and the plasma neutralizes sputtered neutral particles. Of neutralizing sputtered neutral particles. 2. The method according to claim 1, wherein the sample potential is kept constant as a secondary ion accelerating voltage, and a high-frequency voltage or a pulse voltage is applied to the extraction electrode. 3. A sputter neutral particle ionization apparatus comprising a secondary ion mass spectrometer and a means for applying a high frequency electric field or a pulse electric field for converting sputter particles into plasma between a sample and a secondary ion extraction electrode.