JPS5815732B2 - sekisouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement for increasing the sensitivity of a mass spectrometer using a photographic plate.

Mass spectrometers that use photographic plates are used in solid-state analysis mass spectrometers such as spark mass spectrometers and ion microanalyzers, but because the sensitivity of photographic plates to ions is low, there is a drawback in terms of analytical sensitivity. be.

The present invention aims to provide an apparatus in which the detection sensitivity of a mass spectrometer using this photographic plate is greatly improved.

In the following, conventional technology will be described in the case of an ion microanalyzer.

When the surface of a solid sample is irradiated with an ion beam, the surface is sputtered and at the same time, ions are also emitted from the sample surface at a certain rate.

If we mass analyze these emitted ions (secondary ions),
It is possible to identify the constituent elements on the sample surface and determine their concentration.

In addition, when detecting trace impurities or trace constituent elements, as shown in Figure 1, a photographic plate, which can be expected to have a temporal integration effect for detecting secondary ions, is used, or Secondary electron multipliers have been used for detection.

However, it is necessary to further increase the detection sensitivity for detecting trace elements and detecting elements with low ionization efficiency, and there has been a demand for the development of a more sensitive device.

FIG. 1 shows a conventional example of a solid surface analyzer that uses a photographic plate to detect secondary ions.

Primary ions 2 generated and accelerated by an ion source 1 are focused by a lens 3 and then irradiated onto a sample 5.

The deflection plates 4 and 4' function to deflect and irradiate the primary ions 2 to an arbitrary analysis point on the sample 5.

Secondary ions 6 emitted from the sample 5 due to the impact of the primary ions 2 are efficiently extracted by an extraction electrode 7, and then passed through a slit 9 where they are focused by an electrostatic lens 8 and subjected to partial object point correction. The energy is further dispersed by the electric field applied to the fan-shaped deflection electric field electrode 10.

Each of the energy-dispersed secondary ions 6 receives a different deflection in the magnetic field 11 according to the difference in their mass-to-charge ratio, making an angle of 45 degrees with respect to the incident end surface of the magnetic field of each secondary ion 6. focused on a plane.

Therefore, by placing the photographic plate 12 on this surface where each secondary ion is focused, all the secondary ions 6 can be recorded on the photographic plate at the same time.

In FIG. 1, when the object point 5 on the sample is placed at the front focus of the fan-shaped deflection electric field and the deflection angle φe of the electric field is selected to be 31°51', the secondary ions 6 emitted from the electric field become a parallel beam.

Such a combination of object point (analysis point on sample 5) electric field 10 and magnetic field 11 is described by Mattauch and Herzog.
This is an excellent method developed in 1934 by Matt.
It is called ch-Herzog type.

The slit 9 is for regulating the spread of the ion beam entering the electric field, and the slit 9' is for regulating the energy width of the secondary ion beam 6 entering the magnetic field 11.

On the other hand, in addition to the photographic plate 12 for recording the secondary ions 6, the intensity of the magnetic field 11 is changed (mass scanning) using an electric detector 13 to determine the relationship between the mass-to-charge ratio and the secondary ion intensity (i.e. Mass spectra) can also be recorded.

The slit 9'' is a baffle (slit) to prevent ions with different mass-to-charge ratios from entering the detector 13 at the same time. 351 ft G true film (ASAloo) and a dry plate for electron beam detection cannot be used.

This is because the probability that secondary ions 6 will enter these films and dry plates is very small, resulting in low sensitivity.

Therefore, what is normally used as the photosensitive plate 12 for detecting ions 6 is a photographic plate for light exposure, with the gelatin film emulsion removed from the surface, and the ion beam is formed using particles for detection (for example, AgBr).
The system is designed to record data as accurately as possible.

In other words, ions have difficulty penetrating into substances (only a few K
Since the energy is eV (eV, the probability of penetration is small), the detection sensitivity is lower than that of light or electron detection, and the detection method is also difficult.

FIG. 2 shows an example of analysis of metal alloys recorded on dry plate 12.

Ll, L2. L3 is the difference in ion beam exposure time (L
l<L2<La).

B+, Mg+, Niju, and Fe+ on the horizontal axis represent ions of metal alloy components (boron, magnesium, potassium, iron), respectively.

Note that the scale on the horizontal axis indicates the mass-to-charge ratio.

On the other hand, FIG. 3 is a mass spectrum of the same alloy as that shown in FIG. 2, recorded by the detector 13 of FIG. 1.

Here, the scale on the horizontal axis indicates the mass-to-charge ratio.

A comparison between FIG. 2 and FIG. 3 shows that the photographic plate in FIG. 2 has higher sensitivity than the differential method in FIG. 2 due to the integral effect.

However, even if this photographic plate method is used, the sensitivity is still not sufficient for practical use, and in actual cases, even higher sensitivity detection of trace elements is required.

As a method to meet this expectation, (1) the amount of primary ions 2 is increased to increase the absolute amount of secondary ions 6;

(2) The type of secondary ion 2 is an active ion. (3)
Increase the energy of primary ions 2.

(4) Increase secondary ion collection efficiency.

(5) Increase the transmittance of the electric field and magnetic field of secondary ions.

(6) Countermeasures such as increasing the sensitivity of the photographic plate have been considered, and although various studies and prototypes have been attempted, no satisfactory conclusion has yet been reached.

The present invention was made in response to such a demand, and after performing mass spectrometry on secondary ions from the surface of a solid sample, the obtained ion image is converted and amplified into an electron image using a channel plate, and By detecting and recording this amplified secondary electron image, secondary ions of trace elements can be detected and recorded with high sensitivity.

By converting secondary ions into secondary electrons and amplifying them in this way, it becomes possible to detect and record mass spectra using ordinary dry plates and 35 g films that have been conventionally used for photography with electron microscopes.

That is, the detection sensitivity of a photographic plate from which surface emulsion has been removed for one ion is about 1/Zoo inferior to the detection sensitivity of a normal plate or film for one electron.

The present invention takes this point into consideration and attempts to detect the ion image after converting it into an electron image.

Another great advantage is that if the electrons are converted into electrons and then multiplied, a high multiplication factor of about 1000 times can be obtained with a normal channel plate.

In a Mat tauch-Herzog type double focusing mass spectrometer, in which ions with different mass-to-charge ratios are focused on the same surface, the focal point of secondary ions is on the surface, so a channel plate is placed at that position. This allows a plurality of ions to be simultaneously and independently converted into electrons and multiplied through channels at different positions.

However, if these secondary electrons are then converted into light using a film or phosphor and then recorded on the film or detected electrically, the ions can be 102 to 10 times more powerful than the conventional method of directly recording ions with a photographic plate. The above detection sensitivity can be obtained.

Examples of the present invention will be described in detail below.

FIG. 4 shows an embodiment of the present invention, and shows a conventional device (
Compared to FIG. 1), the part of the detector for the secondary ions 6 that have passed through the magnetic field 11 is different.

Secondary ions 6 have different mass-to-charge ratios (Mm+>Mn
+>M2+>M1+), different trajectories are drawn in the magnetic field 11.

Secondary ions emitted from the magnetic field 11 are transferred to the channel plate 14
After being incident on , it is converted into secondary electrons.

After being multiplied in the channel, the secondary electrons exit the channel plate 14 and are irradiated onto the photographic film 15, where they are detected and recorded.

FIG. 5 shows a sketch of the channel plate 14.

FIG. 6 shows an enlarged view of a portion of the channel plate 14.

One channel of the channel plate has a diameter of 10 to 1
It consists of a hollow glassy substance about 5 μm in length and 2 to 3 dragons in length.

The channel plate is formed by folding each channel into a plate shape.

A lead wire 16 is attached to the ion incident surface of this channel plate, and a lead wire 16' is attached to the opposite surface.

Set the lead wire 16 to O potential and +IKV to the lead wire 16'.
The gain of the channel plate was 103 when .

By using this method, the secondary ion 6 in Fig.
Compared to the conventional method of detecting directly with a photographic plate, we were able to obtain a sensitivity of 103.

Therefore, it has become possible to detect trace impurities that were previously undetectable, and it has also become possible to shorten the measurement time to about 1/100 to obtain the same detection sensitivity as before.

FIG. 1 shows another embodiment in which an antistatic wire 21 is placed in front of the photographic film 15 of FIG.

This anti-static wire 21 is used to shield static electricity so that the electric field caused by charges that have been charged up on the photographic film 15 does not adversely affect the trajectory of the incident electron beam, and is operated in accordance with a well-known method. is kept at a constant potential (usually placed at ground potential, but considering its role, it does not necessarily have to be at ground potential, and it is sufficient if it is kept at a constant potential).

For example, if the wire 21 is kept at a negative potential with respect to the lead wire 16', the secondary electrons 20 emitted from the channel plate 14 are accelerated by the field applied between the lead wire 16' and the wire 21. The image is then recorded by irradiating the photographic film 22.

This wire 21 is a thin metal wire, and is stretched obliquely or at right angles so as not to be parallel to the ion beam image.

The reason for this is to prevent the wire 21 from overlapping with the ion beam image (spectral lines as shown in FIG. 2).

Note that, instead of this wire 21, a thin metal wire may be woven into a net shape and used.

If a sufficiently thin wire is used as the conductive wire or net, the incident electron beam can be guided onto the photographic film with almost no loss.

Also, since this conductive wire or mesh is kept at a constant potential, it does not itself cause any fluctuations in the electron beam trajectory.

Alternatively, a conductive material (for example, carbon, Nesa film, etc.) may be deposited on the surface of the film 22 for antistatic purposes.

FIG. 8 shows another embodiment of the present invention for observing secondary ion images.

After converting the secondary ions 6 mass-separated by the magnetic field 11 into secondary electrons by the channel plate 14 and further multiplying them,
Secondary electrons 20 emitted from channel rate 14
When the secondary electrons 20 are made to collide with a surface of a glass 19 on which a Nesa coating layer 18 is applied and then a phosphor 17 is applied thereon, the secondary electrons 20 are converted into light by the phosphor 17.

That is, light is emitted to the position of the phosphor 11 in accordance with the position of the primary ions 6 and their intensity.

By observing these lights on the surface of the phosphor 11,
The intensity and position of the secondary ions 6 can be detected.

Conventionally, secondary ions were directly irradiated onto the phosphor for the purpose of observing secondary ions 6, but the luminous efficiency of the ions was about 1/I 00 lower than that of the electrons.
Direct observation of ion images has not been effective because phosphors also deteriorate over time due to sputtering caused by ions.

FIG. 9 shows another embodiment in which a photographic film 22 is placed behind the fluorescent screen of FIG.

Since the secondary ions 6 are finally converted into light by the phosphor 17, the photographic film 22 can be one for ordinary light.

In this method, the mass spectrometry section is vacuum isolated by the glass 19, so the photographic film 22 can be placed in the atmosphere, and (1) it is possible to prevent the deterioration of the vacuum level of the mass spectrometry section due to the conventional insertion of a photographic plate. , (2) The film 22 can be placed in the atmosphere, making the movement and movement mechanism of the film 22 easier. (3) The mass spectrometer can now be subjected to an operation of baking out the adsorbed gas, which allows for high It has become clear that there are significant advantages not seen before, such as the ability to achieve a vacuum and the ability to reduce background ions.

FIG. 10 shows a new lens 23 placed between the glass 19 and the photographic film 22 in the embodiment shown in FIG.
An example will be shown in which the image of No. 7 is enlarged and recorded on the film 22.

According to this embodiment, by enlarging and recording ion beak images that are close to each other on the phosphor 17 on the film 22, the spectral image can be viewed directly on the film with the naked eye.

FIG. 11 shows yet another embodiment of the invention.

Secondary ions M n + subjected to mass spectrometry in the magnetic field 11.

Channel plates 14 and 14' with different mm
After being converted into electrons and amplified, they are emitted as secondary electrons 20 and 20'.

The secondary electrons 20 and 20' are accelerated by a channel plate and a wire 21, and then irradiated onto a photographic film 22 and recorded.

Since voltages are independently applied to the channel plates 14 and 14' through the lead wires 24 and 24', 16 and 16', the gain of the channel plates differs depending on the applied voltage.

Therefore, if the ion strengths of Mn+ and Mm+ are significantly different, it is possible to adjust the intensity of secondary electrons reaching the film by changing the voltage applied to the channel plate.

In other words, if you increase the applied voltage to detect ions with very low intensity, and lower the applied voltage to detect ions with strong intensity, you can keep the exposure level of the film almost the same and easily select the exposure time. becomes.

Also, from this example, the same result can be obtained by dividing the channel plate into two or more pieces, by placing a phosphor instead of photographic film and using photographic film after converting it into light, or by converting the intensity of light into an electrical signal. You can expect good results.

Furthermore, when a phosphor is used, a single channel plate may be sufficient as long as a plurality of wires are provided in front of the phosphor so that a voltage can be applied independently to each wire.

This is because when accelerating secondary electrons between the wire and the channel plate, the luminous effect of the phosphor differs depending on the difference in acceleration voltage.

For this purpose, high applied voltage for weakly intense ions,
By applying a low voltage to ions with high intensity, it is possible to obtain approximately the same amount of light on the phosphor.

In this way, the exposure degree of the film can be made almost the same as in the case of the photographic film, and the exposure time can be easily selected.

Commercially available channel plates have a diameter of 2.5
Most of them are relatively small disk-shaped, ranging from CIIL to about 10cIrL, and large-sized ones like the one shown in FIG. 5 need to be specially manufactured.

To obtain the effect of the present invention using a commercially available small channel plate, a commercially available disc-shaped channel plate is cut into a square or rectangle as shown in FIG. 12, and this can be moved at a constant speed along the photographic plate 22. It's good to do it like this.

Let the length of the photographic plate be y, and the width of the channel plate be x.

Also, the gain of the channel plate is A, the sensitivity of the photographic plate to ions is BI, and the sensitivity to electrons is B.
If E, then the sensitivity multiplication factor G in this method is given by:

Generally BE>J, and the gain A of the channel plate is 1000 or more, so for example, if the length y of the photographic plate 22 is 30CrrL, the width of the channel plate
Even in the case of cIn, a value of G of 100 or more can be easily obtained.

[Brief explanation of drawings]

Figure 1 shows an example of a conventional solid state analyzer that analyzes the surface of a solid sample, and Figure 2 shows the intensity of secondary ions obtained on a photographic plate when a metal alloy is analyzed using the equipment shown in Figure 1. 3 shows a mass spectrum of secondary ions obtained by electrical detection when a metal alloy is analyzed using the apparatus shown in FIG. 1, and FIG. 4 shows an embodiment of the mass spectrometer of the present invention. Fig. 5 is a sketch of a channel plate used in the present invention, Fig. 6 is an enlarged sketch of a part of the channel plate, and Figs. 7 to 12 are views of main parts showing other embodiments of the present invention. be. In the figure, 1... ion source, 2...
Primary ion, 3... Electrostatic lens, 4,4'...
...Deflection plate, 5...Sample, 6,6'...
...Secondary ion, 7...Secondary ion extraction electrode, 8...Electrostatic lens, 9°9', 9''...
...Slit, 10...Deflection electric field electrode, 1
1... Magnetic field, 12... Photographic plate, 13
...Ion collector, 14,14'...
... Channel plate, 15... Photographic film, 16, 16'... Lead wire, 17...
... Phosphor, 18 ... Nesa coating layer, 19
...Glass plate, 20,20'...Secondary electron, 21...Wire, 22...Photographic film, 23...Optics lens, 24.24
'······Lead.

Claims (1)

[Claims] 1. Means for generating sample ions and emitting them in a beam, means for mass-separating the ion beam using a magnetic field, and recording an image of the mass-separated ion beam on a photographic plate. In the apparatus having the means, a channel plate is installed in front of the photographic plate to convert the ion beam image into an electron beam image, and the detection sensitivity is increased by recording this electron beam image on the photographic plate. A mass spectrometer characterized by: 2. In the apparatus described in claim 1, a thin conductive wire or net is installed between the channel plate and the photographic plate, and by keeping this at a constant potential, the channel plate is charged by charging the photographic plate. A mass spectrometer characterized in that the electron trajectory from the to the photographic plate is bent and the image is prevented from being distorted. 3 In the apparatus set forth in claim 1, a fluorescent plate made of a glass surface coated with fluorescent paint is installed after the channel plate, and the electronic image formed by the channel plate is further converted into an optical image by the fluorescent plate, which is then photographed. A mass spectrometer characterized in that a photographic plate can be used in the atmosphere at all times by capturing images. 4. A mass spectrometer according to claim 1, characterized in that the small channel plate is moved along the photographic plate at a constant speed.