JPH06103626B2 - Mass spectrometer for focused ion beam - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass spectrometer in an apparatus for performing physical properties, composition analysis, fine processing, surface modification, etc. of a minute region by using a focused ion beam.

[0002]

2. Description of the Related Art In the field of semiconductors, since a huge amount of information is processed by a computer, it is required to increase the memory / calculation ability and the information processing speed. Therefore, the development of high integration of IC is progressing from LSI to VLSI and to three-dimensional IC. In studying such an IC process, an ion beam focused to a micro size is an extremely effective means. On the other hand, in the analysis, it is extremely important to analyze the atomic distribution in the microscopic region. Therefore, the Rutherford backscattering method (RBS) and the particle excitation X-ray method with a resolution of less than 1 μm using a focused ion beam with high energy are used. (PIXE) and other analytical techniques are being improved in function. FIG. 7 shows an example of the configuration of a conventional high-energy focused ion beam device used as an analyzer. In FIG. 7, the electrostatic accelerator 1
Then, if helium gas is used for the ion source 2, for example, He
Ions containing ⁺ and He ²⁺ are generated, and when an accelerating voltage of, for example, 1 MV is applied to the accelerating tube 3, the ions are accelerated and He ⁺ becomes 1
MeV and He ²⁺ become a high energy ion beam 4 of 2 MeV and emerge at high speed and high energy. They are supplied to the objective collimator 5, narrowed down to a few tens of μm, and enter the Wien (E × B) type mass analyzer 6 as an analysis component of ion species beam energy. In the Wien type mass spectrometer 6, the electromagnet coil 7 and the window electromagnet yoke 8 are used.
He ⁺ under a certain condition on the electric field created under the electrode distance d by applying a voltage + V / 2, −V / 2 to the magnetic field B created by Only the ions go straight, the other ions are deflected and the analysis electrode 9
Alternatively, it collides with the ion selection slit 10 on the outlet side to neutralize the electric charge and is discharged as exhaust gas. Denoted at 11 is a He ⁺ beam deflecting electrode. Only the straight He ⁺ ions enter the quadrupole electromagnet lens 12 and are focused.
A beam spot is made incident on a target (measurement sample) 14 therein. The ions scattered by the interaction of the He ⁺ ions with the measurement sample 14 or the excited fluorescent X-rays are energy-analyzed by the detector 15 in the chamber 13, and the physical property data of the sample can be obtained. Further, by applying a voltage to the deflection electrode 11, the spot position can be scanned, and two-dimensional analysis can be performed.

[0003]

In the above focused ion beam apparatus, the Wien type mass analyzer 6 for directly advancing only a specific ion species (He ⁺ ion) from the ion beam 4 incident from the electrostatic accelerator 1 is The cross-sectional shape is as shown in FIG. 3, and since the vacuum duct 30 and the electrode pairs 34 and 35 are included, the magnetic pole gap Mg has to be increased, and there is a problem that the entire device becomes large. Also, the electrodes 34, 3
It was difficult to accurately fix No. 5 to the magnetic pole pairs 36 and 37 in the electromagnetic field orthogonal type. That is, since it is difficult to fix the electrode pair 34, 35 and the vacuum duct 30, and the magnetic poles 36, 37, and the vacuum duct 30 to the cylindrical vacuum duct 30 with high precision, the vacuum duct 30 is adjusted in the circumferential direction. A mechanism was provided for fine adjustment, which made the device complicated and large. The problem of increasing the size of the entire device due to the fact that the magnetic pole gap Mg cannot be reduced will be described.
FIG. 4 shows a schematic diagram of the mass spectrometer 6, and FIGS. 5 and 6 show sectional views perpendicular to and parallel to the ion beam direction. As shown in FIG. 4, the mass spectrometer 6 includes magnetic poles 36, 37 and electrodes 3 which are orthogonal to each other in the direction of the ion beam.
4 and 35, the electromagnetic field orthogonal type is configured. Figure 5
In the region 33 where the ion beam passes, the electrode 3
It is located at a central position surrounded by 4, 35 and magnetic poles 36, 37. Electric force lines 42 and magnetic force lines 43 in this region 33
Are electrodes 34, 35 and magnetic poles 36, 37, which are opposed to each other.
The distribution density is vertical and uniform. However, as the distance from the center of the region 33 increases, the lines of electric force 42 and lines of magnetic force 43 become curved and the distribution density is not uniform. The size of the region 33 for obtaining the above-mentioned uniform distribution density is determined by the electrode gap Eg and the electrode cross-section aperture ratio (interelectrode gap Eg / electrode width Ew). The same applies to the magnetic pole gap Mg and the magnetic pole sectional aperture ratio. If the passage area 33 of the ion beam is larger than the uniform electromagnetic field distribution area, it affects the minimum ion beam diameter after focusing as an inspection. In the structure as shown in FIG. 5, the magnetic pole gap Mg becomes large, so that the magnetic pole width Mw needs to be made large in order to reduce the sectional aperture ratio.
This becomes more serious in the direction parallel to the beam axis shown in FIG. 6 because the beam must pass through the non-uniform region of the magnetic field at the end face of the magnetic pole, which becomes more serious. It is necessary to make the vessel length L) sufficiently small. In the conventional device, since the magnetic pole gap Mg is about 4 cm, the analyzer length is about 40 cm. Therefore, in order to downsize the device, it is necessary to reduce both the magnetic pole gap Mg and the electrode gap Eg. SUMMARY OF THE INVENTION It is an object of the present invention to provide a mass spectrometer that realizes both the magnetic pole gap Mg and the electrode gap Eg to be small, and that has the conventional problems of miniaturization and easy setting of the electromagnetic field orthogonal type. .

[0004]

According to the present invention for achieving the above object, an electric field and a magnetic field are applied in directions orthogonal to the direction of an ion beam incident from an ion accelerator so that only a specific ion species travels straight. And a parallel plate electrode pair having an electrode cross-sectional aperture ratio (electrode gap / electrode width) capable of giving a uniform electric field distribution density in a direction orthogonal to the beam direction of the ion beam, A parallel magnetic pole pair having a magnetic pole cross-section aperture ratio (magnetic pole gap / magnetic pole width) capable of giving a uniform magnetic field distribution density in a direction orthogonal to the beam direction of the ion beam and the electric field distribution direction is set in the magnetic field direction of the electrode pair. Of the magnetic pole pair is larger than the gap of the magnetic pole pair, and the gap width of the magnetic pole pair in the direction of the electric field is larger than the gap of the electrode pair. It is.

[0005]

According to the present invention, an electrode pair having an electrode sectional aperture ratio capable of providing a uniform electric field distribution density in a direction orthogonal to the beam direction of an ion beam, and an electrode pair orthogonal to the ion beam direction and the electric field distribution direction. A magnetic pole pair having a magnetic pole cross-sectional aperture ratio capable of giving a uniform magnetic field distribution density in a direction,
In order to arrange the above condition, a part of the electrode pair having an electrode width exceeding the ion beam passage region width is embedded in a magnetic pole pair having a magnetic pole width also exceeding the ion beam passage region width. To be realized. At this time, in order to avoid electrical conduction between the electrodes, this was made possible by using a material having a high volume resistivity as the magnetic pole material. Therefore, both the electrode and the magnetic pole gap can be reduced without impairing the sectional aperture ratio of the electrode and the magnetic pole, so that the sectional size and the longitudinal size of the device can be reduced. In order to realize this configuration, if a part of the electrode is inserted and fixed in the slit provided in the magnetic pole, the relative positioning accuracy of the magnetic pole of the electrode is improved. Further, if the portion of the electrode embedded in the magnetic pole is made of a ferromagnetic material, the disturbance of the magnetic field due to the provision of the slit can be suppressed.

[0006]

EXAMPLES Next, specific examples will be shown to provide an understanding of the present invention. FIG. 1 is a sectional view of a mass spectrometer according to an embodiment of the present invention. FIG. 2 is a perspective view showing a configuration example of electrodes. As shown in FIG. 1, in this embodiment, the magnetic poles are composed of the magnetic poles 21,
21 and permanent magnets 22 and 22 for exciting this are window-shaped, and a vacuum duct 26 is arranged in the center thereof. If, for example, a ferrite material (volume resistivity 1 × 10 ⁷ Ω / m) is used as the magnetic pole material, a part of the electrodes 23, 23 is embedded in the magnetic poles 21, 21 as shown in the figure. You can According to this configuration, the electric resistance between the electrodes is in the unit of MΩ, and the insulation between the electrodes 23 and 23 can be maintained. The volume resistivity of this magnetic pole should be at least 1
A high resistivity of 0 ⁴ Ω / m or more is required. Otherwise, the resistance value between the electrodes 23, 23 will be in the unit of kΩ, and when the electrode voltage is several hundred volts, it will reach several hundred mA, and the power consumption will be several watts or more. Issues arise. As shown in the figure, according to the configuration of this embodiment,
For the vacuum duct 26, which is the passage area of the ion beam,
With a sufficient size, the gap can be made small without impairing the sectional aperture ratio, and the orthogonal arrangement relationship between the electrodes 23, 23 and the magnetic poles 21, 21 can be carried out accurately. The disturbance of the magnetic field distribution due to the electrodes 23, 23 being buried in the magnetic poles 21, 21 does not cause a problem if the width of the slit is sufficiently smaller than the magnetic pole gap Mg. Therefore, it is desirable that the electrodes 23, 23 be manufactured as thin as possible. Note that, as shown in FIG. 2, the exposed portions of the electrodes 23, 23 are made of a conductive material such as copper, and the portions embedded in the magnetic poles 21, 21 are made of an iron material having a magnetic permeability close to that of ferrite. If the material is used, the disturbance of the magnetic field in the magnetic poles 21 and 21 can be made negligible. Further, in the present embodiment, the example in which the vacuum duct 26 is provided between the electrodes 23, 23 and the magnetic poles 21, 21 has been shown, but the mass analyzer according to the present configuration can be constructed in a small size, so that the whole vacuum duct is used. It can also be stored.

[0007]

As described above, according to the present invention, the gap between the electrode and the magnetic pole can be made small while keeping the sectional aperture ratio small, so that the size of the entire device can be reduced to 1/2 of the conventional size. The size can be reduced to 1/4, and since no vacuum duct is interposed between the electrode and the magnetic pole, they can be positioned and fixed with high precision. Therefore, the alignment after the incorporation into the focused ion beam device is easy, and the obtained beam spot diameter can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of an electrode of the embodiment apparatus.

FIG. 3 is a cross-sectional view of a conventional device.

FIG. 4 is a schematic diagram of a conventional device.

FIG. 5 is a cross-sectional explanatory view of a conventional device.

FIG. 6 is a vertical cross-sectional explanatory view of a conventional device.

FIG. 7 is a configuration diagram of a conventional focused ion beam apparatus.

[Explanation of symbols]

 21 ... Magnetic pole 23 ... Electrode 26 ... Vacuum duct Eg ... Electrode gap Ew ... Electrode width Mg ... Magnetic pole gap Mw ... Magnetic pole width

Claims (3)

[Claims] 1. A mass spectrometer of an electromagnetic field orthogonal type in which an electric field and a magnetic field are applied in a direction orthogonal to the direction of an ion beam incident from an ion accelerator to cause only a specific ion species to go straight, A parallel plate electrode pair having an electrode cross-sectional aperture ratio (electrode gap / electrode width) capable of giving a uniform electric field distribution density in a direction orthogonal to the direction, and orthogonal to the beam direction of the ion beam and the electric field distribution direction A parallel magnetic pole pair having a magnetic pole cross-sectional aperture ratio (magnetic pole gap / magnetic pole width) capable of giving a uniform magnetic field distribution density in a magnetic field direction. A mass spectrometer for a focused ion beam, characterized in that the gap width thereof is larger than the electrode pair gap. 2. The magnetic pole pair is made of a ferromagnetic material having a volume resistivity of 10 ⁴ Ω / m or more, and a slit in the magnetic field direction is formed in the magnetic pole pair, and both ends of the electrode pair are inserted into the slit. The mass spectrometer for a focused ion beam according to claim 1. 3. An electrode pair, both ends of which are made of a ferromagnetic conductor, and the other portions are made of a non-magnetic conductor.
A focused ion beam mass spectrometer as described.