JPH07130327A - Laser ionized neutral particle mass spectrograph and laser ionized neutral particle mass spectrometry - Google Patents

Abstract

PURPOSE:To provide a laser inoized neutral particle mass spectrograph and a laser ionized neutral particle mass spectrometry that can quantitatively determine the mass of a sample highly accurately. CONSTITUTION:The spatial shape of a pulse laser 18 generated from a pulse laser generator 17 is changed through the variable opening width 19 of a slit 20. A neutral particle 16 from a neutral particle generator 15 is ionized by radiating the pulse laser of changed spatial shape on the neutral particle, and a light excited ion 22 is thus generated. The mass of the light excited ion is separated by a mass spectrograph 24, and the mass-separated ion is detected by an ion detector 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser ionization neutral particle mass spectrometer and laser ionization neutral particle mass for irradiating a neutral particle of an analyte with a pulsed laser to measure a mass spectrum of photoexcited ions generated. Regarding analysis method.

[0002]

2. Description of the Related Art As a typical trace analysis method for a solid sample, there is a secondary ion mass spectrometry method for detecting secondary ions sputtered from the surface by an ion beam. But,
Since secondary ions have extremely low generation efficiency and large element dependence, secondary ion strength is not proportional to the element concentration in the sample, and there is a problem in quantification. On the other hand, the amount of neutral particles sputtered at the same time as secondary ions is overwhelmingly larger than that of secondary ions, and is proportional to the original element concentration, so neutral particle mass spectrometry that detects it is This is a highly quantitative analysis method. In particular, the laser ionization neutral particle mass spectrometry method, in which neutral particles are ionized by a high-intensity laser and subjected to mass analysis, is known as a method with good ionization efficiency.
As a laser ionization neutral particle mass spectrometer capable of depth direction analysis, there is a laser ionization neutral particle mass spectrometer (JP-A-3-291559). The principle configuration of this device will be described below.

FIG. 6 is a diagram showing the configuration of the conventional laser ionization neutral particle mass spectrometer described above. In FIG. 6, the ion beam generator 1 generates a continuous primary ion beam 2. Then, after focusing the continuous ion beam 2 using the electrostatic lens 3, it is vibrated by the scanning electrode 4,
An impact is given while scanning the surface of the solid sample 5. Neutral particles 6 are solid sample 5 due to the impact of continuous primary ion beam 2.
Is sputtered from the surface. The neutral particles 6 are
The pulsed laser light 8 generated from the pulsed laser generator 7 is ionized in the vicinity of the focus focused by the lens 9 to become photoexcited ions 10. The photoexcited ions 10 are extracted by the extraction electrode 11, mass-separated by the mass analyzer 12 using a magnetic field or an electric field, and then converted into electric pulses by the ion detector 13 and counted by the pulse counter 14.

In the conventional device as described above, the spatial shape of the pulse laser beam 8 is fixed to a constant shape.

[0005]

In the above-mentioned prior art, although the spatial shape of the pulse laser 8 is constant, the ionization cross-section of the neutral particles 6 is different depending on the type of analyte, so that the neutral particles 6 are different. The proportion of photoexcited ions 10 that are ionized differs. Therefore, in the prior art, even when the same amount of the analyte is quantified, the intensity of the photoexcited ion 10 is different, so that the proportional relationship is not established between the amount of the analyte and the intensity of the photoexcited ion, and the accuracy is high. It was difficult to quantify.

The present invention has been made in view of the above,
An object of the invention is to provide a laser ionization neutral particle mass spectrometer and a laser ionization neutral particle mass spectrometry method capable of quantifying the amount of an analyte with high accuracy.

[0007]

In order to achieve the above object, the laser ionization neutral particle mass spectrometer of the present invention comprises:
A pulse laser generator for generating pulsed laser light and irradiating the neutral particles of the analyte in vacuum with the pulsed laser light to ionize the neutral particles to generate photoexcited ions, wherein the photoexcited ions are mass-produced. A laser ionization neutral particle mass spectrometer having a mass analyzer for separation, and an ion detector for detecting ions mass-separated by the mass analyzer, the space of pulsed laser light generated from the pulsed laser generator. The gist is to have slit means having an opening width that changes so as to change the shape.

Further, the laser ionization neutral particle mass spectrometry method of the present invention is a laser ionization neutral particle mass spectrometry method for mass-separating and detecting neutral particles of an analyte ionized by pulsed laser light in a vacuum. The pulsed laser light is a pulsed laser light that has passed through a slit, the opening width of the slit is changed to change the spatial shape of the pulsed laser light, and a pulse detected within a predetermined time after the change. The gist is to measure the neutral particle intensity of the analyte ionized by the laser light.

Furthermore, the laser ionization neutral particle mass spectrometry method of the present invention is a laser ionization neutral particle mass spectrometry method for mass-separating and detecting neutral particles of an analyte ionized by pulsed laser light in a vacuum. The pulsed laser light is a pulsed laser light that has passed through a slit, and the dependence of the detected intensity of the ionized neutral particles on the opening width of the slit is measured to determine the ionization cross-sectional area of the neutral particles. After obtaining, the gist is to correct the detection intensity by the ionization cross section.

[0010]

In the laser ionization neutral particle mass spectrometer of the present invention, the spatial shape of the pulsed laser light generated from the pulsed laser generator is changed by the slit means whose opening is changed, and the pulsed laser light whose spatial shape is changed is changed. Are irradiated to neutral particles of the analyte to generate photoexcited ions, the photoexcited ions are mass-separated, and the mass-separated ions are detected.

Further, in the laser ionization neutral particle mass spectrometry method of the present invention, the opening width of the slit is changed to change the spatial shape of the pulsed laser light, and the pulse detected within a predetermined time after the change. The neutral particle intensity of the analyte ionized by the laser light is measured.

Further, in the laser ionization neutral particle mass spectrometry method of the present invention, the pulsed laser light is pulsed laser light that has passed through the slit, and the opening width of the slit at the detection intensity of the neutralized particles ionized by the pulsed laser light. After measuring the dependence on and obtaining the ionization cross section of neutral particles,
The detection intensity is corrected by the ionization cross section.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing the arrangement of a laser ionization neutral particle mass spectrometer according to the first embodiment of the present invention. In FIG. 1, neutral particles 16 are generated from a neutral particle generator 15. On the other hand, a part of the pulse laser 18 generated from the pulse laser generator 17 passes through the slit 20 having a variable opening width 19, is condensed by the lens 21, and is irradiated on the neutral particles 16. The neutral particles 16 are ionized near the focal point of the pulse laser 18 to become photoexcited ions 22. The photoexcited ions 22 are extracted by the extraction electrode 23 to which a voltage is applied, and are mass-separated by the mass analyzer 24 using a magnetic field or an electric field. The photoexcited ions 22 mass-separated by the mass analyzer 24 are converted into electric pulses by the ion detector 25 and counted by the pulse counter 26. In this embodiment, the opening width 19 of the slit 20 is
Can be changed to change the spatial shape of the pulse laser 18, and the dependence of the intensity of the photoexcited ions 22 on the aperture width 19 can be measured.

Next, a second embodiment will be described with reference to FIG. In FIG. 2, the ion beam generator 2
A primary ion beam 28 is generated from 7. Then, after focusing the ion beam 28 using the electrostatic lens 29,
It is vibrated by the scanning electrode 30, and the surface of the solid sample 31 is scanned and impacted. By this operation, the neutral particles 32 are released from the surface of the solid sample 31. On the other hand, a part of the pulse laser 34 generated from the pulse laser generator 33 is
The light passes through a slit 36 having a variable opening width 35, is condensed by a lens 37, and reaches directly above the solid sample 31. In the area where the pulse laser 34 is focused, the neutral particles 32 are
The photoexcited ions 38 are ionized.

The photoexcited ions 38 are extracted by an extraction electrode 39 to which a voltage is applied, and are mass separated by a mass analyzer 40 using a magnetic field or an electric field. Mass spectrometer 40
The photoexcited ions 38 subjected to the mass separation are pulsed by the ion detector 41 and counted by the pulse counter 42. In the present embodiment, by changing the opening width 35 of the slit 36, the spatial shape of the pulse laser 34 reaching directly above the solid sample 31 is changed, and the photoexcited ions 3 are generated.
The dependence of the intensity of 8 on the opening width 35 can be measured.

Next, a third embodiment will be described with reference to FIG. In FIG. 3, an ion beam generator 58
The primary ion beam 43 from the above is focused by the electrostatic lens 59, vibrated by the scanning electrode 60, and strikes while scanning the surface of the solid sample 44. Then, the primary ion beam 43
Neutral particles 45 are released from the surface of the solid sample 44 by the impact of. On the other hand, a part of the pulse laser 47 generated from the pulse laser generator 46 passes through the slit 49 having the variable opening width 48 and reaches immediately above the solid sample 44.
The neutral particles 45 are ionized by a part of the pulse laser 47 to become photoexcited ions 50. The photoexcited ions 50 are extracted by the extraction electrode 61, mass-separated by the mass analyzer 62, converted into electric pulses by the ion detector 63, and counted by the pulse counter 56.

In this embodiment, the movable portion 51 of the slit 49 is
Is attached to the pulse motor 52, the electric signal 54 for operating the pulse motor 52 is sent to the pulse controller 55 by the computer 53, and the pulse motor 52 is operated by the pulse controller 55. Can be moved to change the opening width 48.

The photoexcited ions 50 counted by the pulse counter 56 within a predetermined time are taken into the computer 53 as an electric signal 57, and the dependence of the intensity of the photoexcited ions 50 on the aperture width 48 is automatically measured. You can

FIG. 4 shows Kr for ⁶⁹ Ga neutral particles.
This is an example of measuring the dependence of the photoexcited ion intensity on the opening width of the slit when ionized by an F excimer laser. The laser wavelength λ = 248 nm in this experiment corresponds to a photon energy of 5.0 eV, and the Ga ionization energy is 6.0 eV. Therefore, the number n of photons required for Ga ionization is n. = 2. That is,
In this example, the number n of photons required for ionization of Ga is 2. Therefore, in the region corresponding to the region A in FIG. 8, the photoexcited ion intensity is proportional to the 2n-1 = 3th power of the aperture width. In this experiment, λ = 248 nm, f = 30 cm, A = 15 mm, ∫
{T (t)} ⁿ dt = 6.7 ns, and at the point corresponding to point B in FIG. 8, B _Ga = 0.6 mm and F _Ga = 3.8 ×
Since it is 10 ²³ s ^-1 ,

## EQU1 ## σ _Ga = (λ ² f ² / AB _Ga F _Ga ) ⁿ / ∫ {T (t)} ⁿ dt = 4 × 10 ^-50 cm ⁴ s.

FIG. 5 (a) shows that a semiconductor sample containing Ga is sputtered by an ion beam,
The sample was scraped from the surface to generate neutral particles of Ga as an analyte, and the photoexcited ion intensity detected among photoexcited ions generated by ionizing the neutral particles by a pulse laser was scraped. It is plotted against depth. Using σ _Ga obtained in relation to FIG. 4, the correction coefficient k _Ga can be obtained according to k _Ga = v _Ga / (m ′ · σ _Ga · B ^2n-1 ), and this k _Ga Using Ga
The concentration c _{Ga of} is calculated according to c _Ga = k _Ga · I _Ga . By using this correction, the Ga concentration distribution in the depth direction shown in FIGS. 5A to 5B is obtained.

FIG. 7 is a diagram showing the relationship between the intensity and concentration of photoexcited ions of the analyte in the case of the conventional method and in the case of the present invention.

As shown in FIG. 7, in the conventional method, even if the spatial shape of the pulsed laser is constant, the ionization cross-sections of the neutral particles of each analyte are different depending on the type of the analyte, so that they are ionized. Difference occurs in the
A proportional relationship was not established between the amount c _i and the intensity I _{i of the} photoexcited ion, and highly accurate quantitative analysis could not be performed. But,
As described above, the slit having a variable opening width is used to measure the dependence of the intensity I _i of the photoexcited ion on the opening width B when the spatial shape of the pulsed laser light is changed. seeking ionization cross section sigma _i neutrals things i, advance correction coefficient seeking sigma _i k _i
If the intensity I _{i of the} photoexcited ion is corrected by this correction coefficient k _i , the amount c _{i of the} analyte can be obtained from the corrected intensity k _i · I _{i of} the photoexcited ion. This will be described with reference to FIG.

FIG. 8 shows theoretically expected curves for the dependence of the intensity of photoexcited ions on the aperture width. In region a of FIG. 8, the photoexcited ion intensity I _i of the analyte i, the amount c _i of the analyte i, the ionization cross-section σ _i of neutral particles of the analyte _i, and the analyte i. Between the velocity v _i of the neutral particles, the photon flux F of the laser passing through the slit, and the aperture width B, I _i = m · c _i · σ _i · F ⁿ · B ^n-1 / v The relationship of _i is established. Where n is the minimum number of photons required to ionize one neutral particle of the analyte i,
m is a proportional constant. Further, since F is proportional to B, the following relationship holds: I _i = m ′ · c _i · σ _i · B ^2n-1 / v _i . Here, m ′ is a proportional constant. v
_{Since i} is obtained by another method, σ _i and m ′ may be obtained to obtain c _i from I _i .

The other opening width of the slit is A, the wavelength of the laser is λ, the focal length of the lens is f, and the time distribution of the laser light intensity is T (t). T (t) is standardized and its maximum value is 1. If the value of the aperture width B at point B in FIG. 8 is B _i and the photon flux of the laser is F _i ,

[Formula 2] σ _i · (AB _i F _i / λ ² f ² ) ⁿ · ∫ {T
(T)} ⁿ dt = 1. The integration is performed over the emission time of one laser pulse. Therefore σ _i is

## EQU3 ## σ _i = (λ ² f ² / AB _i F _i ) ⁿ / ∫ {T
(T)} ⁿ dt. Here, λ, f, and A are determined by experimental conditions, and T (t) is obtained by another measurement.
If the values of B _i and F _i are obtained from the measurement results as shown in FIG. 8, σ _i can be obtained.

In order to obtain m ', a known amount of the analyte s is prepared and the measurement as shown in FIG. 8 is performed. The same measurement result as in FIG. 8 was obtained for the analyte _s, and the ionization cross-section σ was obtained from the values of the opening widths B _s and F _s at the point B.
_s

## EQU4 ## σ _s = (λ ² f ² / AB _s F _s ) ⁿ / ∫ {T
(T)} ⁿ dt, and then at an arbitrary aperture width B of region a,
Using the intensity I _{s of the} photoexcited ion, the known concentration c _s, and the velocity v _{s of} neutral particles obtained from other measurements,
m ′ is obtained by m ′ = v _s / (c _s σ _s B ²ⁿ⁻¹ ) · I _s , and the correction coefficient k _i of the analyte _i is k _i = v _i / (m ′ · σ _i · B ^2n-1 ). By this k _i ,
When the intensity I i of the photoexcited ion of the unknown amount of the analyte _i is corrected, the amount c _{i of the} analyte can be accurately quantified from c _i = k _i · I _i .

[0027]

As described above, according to the present invention,
The spatial shape of the pulsed laser light generated from the pulsed laser generator is changed by the slit means whose opening changes.
The pulsed laser light is irradiated because the pulsed laser light with the changed spatial shape is applied to the neutral particles of the analyte to generate photoexcited ions, and the photoexcited ions are mass-separated and the mass-separated ions are detected. The ionization cross section of neutral particles can be obtained from the measurement result of the intensity of photoexcited ions when the spatial shape of is changed, and the correction coefficient is obtained in advance using the ionization cross section of this neutral particle. By measuring the intensity of the photoexcited ion by the correction coefficient, the amount of the unknown analyte can be obtained from the intensity of the photoexcited ion corrected, and the amount of the analyte can be quantified with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a laser ionization neutral particle mass spectrometer according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a laser ionization neutral particle mass spectrometer according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a laser ionization neutral particle mass spectrometer according to a third embodiment of the present invention.

FIG. 4 is a diagram showing the slit aperture width dependence of the measured photoexcited ion intensity.

FIG. 5 is a diagram showing an example in which the amount of the analyte is obtained from the photoexcited ion intensity through the correction of the present invention.

FIG. 6 is a diagram showing a configuration of a conventional laser ionization neutral particle mass spectrometer.

FIG. 7 is a diagram showing the relationship between the intensity and concentration of photoexcited ions of an analyte in the case of a conventional method and the case of the present invention.

FIG. 8 is a diagram showing the slit aperture width dependence of theoretically expected photoexcited ion intensity.

[Explanation of symbols]

 15 Neutral Particle Generator 16 Neutral Particle 17 Pulse Laser Generator 18 Pulse Laser 19 Opening Width 20 Slit 23 Extraction Electrode 24 Mass Spectrometer 25 Ion Detector 26 Pulse Counter

Claims (3)

[Claims] 1. A pulse laser generator for generating pulsed laser light and irradiating the neutral particles of an analyte in vacuum with the pulsed laser light to ionize the neutral particles to generate photoexcited ions, A laser ionization neutral particle mass spectrometer having a mass analyzer for mass-separating the photoexcited ions, and an ion detector for detecting ions mass-separated by the mass analyzer, which is generated from the pulse laser generator. A laser ionization neutral particle mass spectrometer, comprising slit means having an opening width that changes so as to change the spatial shape of pulsed laser light. 2. A laser ionization neutral particle mass spectrometry method for mass-separating and detecting neutral particles of an analyte ionized by pulsed laser light in a vacuum, wherein the pulsed laser light is a pulse passing through a slit. Neutral particles of the analyte ionized by the pulsed laser light that is laser light, the spatial shape of the pulsed laser light is changed by changing the opening width of the slit, and is detected within a predetermined time after the change. A laser ionization neutral particle mass spectrometry method characterized by measuring intensity. 3. A laser ionization neutral particle mass spectrometry method for mass-separating and detecting neutral particles of an analyte ionized by pulsed laser light in a vacuum, wherein the pulsed laser light is a pulse passing through a slit. Laser light, measuring the dependence of the detection intensity of the ionized neutral particles on the opening width of the slit, after obtaining the ionization cross section of the neutral particles, the detection intensity by the ionization cross section Method for laser ionization neutral particle mass spectrometry characterized by correction.