JPS61263039A - Mass spectrometer - Google Patents

Abstract

PURPOSE:To increase the yield of secondary ions, by making a secondary ion mass spectrometer of an ionization chamber containing a filament provided at an open end of a cylindrical magnet, a cylindrical reticulate grid and a repeller. CONSTITUTION:A secondary ion mass spectrometer is made of an ionization chamber 8 containing a cylindrical magnet 12 provided outside a cylindrical reticulate grid 10, an annular filament 14 disposed at one open end of the magnet, a convergence lens system 16 disposed at the other open end, and a repeller 18 provided outside them. The spectrometer is located in such a position that particles 6 emitted from a sample 2 stimulated by primary ions from an ion source can be introduced into the spectrometer. The grid 10 and the repeller 18 are set at positive potential and negative potential relative to the filament 14, respectively. As a result, neutral particles which would not be effectively used are ionized to greatly enhance the efficiency of ionization.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is an SNMS (S p
utt,ered N eutral Spec
tromet, ry).

(Prior Art) Generally, most of sputtered particles obtained by irradiating a sample with ions are neutral particles, and secondary ions are only a small part of them.

In conventional SIMS (secondary ion mass spectrometry), neutral particles are considered to form noise components and are removed, so the amount of detected signal depends on the yield of secondary ions in sputtered particles. Further, the secondary ion yield is subtly influenced by many factors such as the secondary ion species, the incident angle, the type of sample, and the atmosphere around the emitting part.

As a method to reduce such subtle effects and to ionize and utilize neutral particles discarded in SrMS,
Mainly, the following two types of methods have been proposed.

(1) Neutral particles are ionized by irradiating the neutral particle flux with a concentrated electron beam.

(2) Ionize the neutral particles by introducing the neutral particle flux into the ionized gas.

(Problems to be solved by the invention) The method (1) using electron beam irradiation has the advantage that the equipment is simpler than the method (2) using ionized gas, but Since the electron bombardment is performed in the vertical direction, the ionization efficiency is poor, and the method (2) using ionized gas is far superior in terms of ionization efficiency. Furthermore, according to the method (2) using ionized gas, ions in the ionized gas can be used as a primary ion beam, making it possible to perform sputtering at low acceleration (10 eV to IKeV) and improving depth resolution. However, since the method using ionized gas in 2) uses high frequency (27 MHz) electric field discharge,
There is a problem with a lot of noise.

The present invention aims to construct an SNMS using a method of irradiating neutral particles sputtered from a sample with an electron beam, and to increase its ionization efficiency.

(Means for Solving the Problems) The present invention will be described with reference to FIG. 1 showing one embodiment. A filament (14) provided in one opening of the magnet (12), a cylindrical mesh grid (10) provided inside the cylindrical magnet (12), and electrons from the filament (14) are transferred to the grid ( An ionization chamber equipped with a rippler (18) repelling in the lO) direction is provided at a position where particles generated from the sample can be taken in.

(Operation) The principle of operation of ionization in the ionization chamber (8) in the present invention will be explained with reference to FIG. 3 of the embodiment.

When ionizing neutral particles, the grid (io) is placed at a positive potential with respect to the filament (14), and the repeller (18)
Apply a bias voltage so that it becomes a negative potential. The electrons (22) emitted from the filament (14) pass through the grid (
10), causing a spiral movement along the magnetic lines of force (20), increasing the travel distance of the electrons and lengthening their residence time. Further, since the electrons move in a spiral motion in the traveling direction of the neutral particles, the probability of collision with the neutral particles in the ionization chamber increases, and the ionization efficiency increases.

In addition, since the magnet (12) is cylindrical, the magnetic flux (20)
is concentrated on the central axis. As a result, electrons (22) are also concentrated near the central axis of the ionization chamber.

Many ion generation locations are also distributed along the central axis.

This is convenient when dealing with secondary ion optical systems.

(Example 1) FIG. 1 represents a first embodiment of the invention.

2 is a sample, and an ionization chamber 8 is provided at a position where particles 6 generated from the sample 2 excited by primary ions from the ion gun can be taken in. The ionization chamber 8 uses an electron impact ion source in combination with a magnet, and consists of a cylindrical mesh grid 10, a cylindrical magnet 12, a ring-shaped filament 14, a converging lens system 16, and a liberator 18.

A cylindrical magnet 12 is provided on the outside of the cylindrical mesh grid 10 so as to surround the sides of the grid 10. Magnet 12 may be an electromagnet or a permanent magnet. magnet 1
Of the two openings 2, the opening on the sample side is provided with a ring-shaped filament 14. Further, a converging lens system 1G is provided in the other opening of the magnet 12. 1
8 is a filament 14, a magnet 12, and a converging lens system 16
The filament 14 is provided on the outside of the filament 14.
It has a function of repelling electrons from the ionization chamber 8, returning them to the filament 14 side, and confining them within the ionization chamber 8.

17 is an analyzer of the mass spectrometer.

The filament 14, which is a source of thermoelectrons, has a large effect on the ionization efficiency of neutral particles depending on its installation position. In this embodiment, as shown in FIG.
It is provided at a position where the direction of the magnetic lines of force 20 is reversed near the magnet end face of one of the openings.

This example is used to analyze neutral particles 24 from sample 2.
When used as an NMS, bias voltages are applied to each part as shown in FIG. 4, and the filament 14 is ignited to emit thermoelectrons.

Approximately 10V is applied as V+, and approximately 200V is applied as v3. Further, v4 of the converging lens system 16 is a variable voltage up to about IKV.

The ion optical system in this case is as shown in FIG.
It can be represented by an extraction lens 25 and a converging lens 16a. The extraction lens 25 corresponds to a portion of the ionization chamber 8 excluding the convergent lens system 16, and the convergent lens 16a corresponds to the convergent lens system 16.

In this case, normal secondary ions generated from the sample 2 are not detected as a signal.

Furthermore, when this embodiment is used as a normal SIMS for detecting secondary ions 26 generated from the sample 2, as shown in FIG. Positive potential v5 (0~
By keeping the sample 2 at a more positive potential Vs (approximately IKV) than the ionization chamber, the repeller 18, filament 14, and grid 10 are used as extraction electrodes for the secondary ions 26. in this case,
The filament 14 is not fired, and the converging lens system 16 is the same as in FIG.

The ion optical system in this case is as shown in FIG.
It can be represented by an extraction lens 28 and a converging lens 16a, where the extraction lens 28 corresponds to the repeller 18, the filament 14 and the grid 10, and the converging lens 16a corresponds to the converging lens system 16.

Although FIG. 6 shows the case where the secondary ions 26 are positive ions, the method can also be used when the secondary ions 26 are negative ions.

In that case, the sample 2 and the repeller 18 as an extraction electrode,
A bias voltage may be applied so that the polarity between the filament 14 and the grid 10 and the polarity of the converging lens system 16 are opposite to each other.

In this way, by providing the filament 14 on the sample side, secondary ions from the sample 2 are taken in and the normal SI
It will also be possible to use it as an MS. Note that the influence on the ion optical system due to the combined use of a magnet is not a major problem, considering that the magnetic field is axially symmetrical and the charged particles handled are ions.

(Example 2) FIG. 8 shows a second embodiment.

In the embodiment shown in FIG. 1, the converging lens system 16 is constructed integrally with the ionization chamber, whereas in this embodiment, the ionization chamber 30 and the converging lens system 16 are arranged separately.

The ionization chamber 30 includes a cylindrical mesh grid 10°, a cylindrical magnet 12, a ring-shaped filament 14, and a repeller 32.
It consists of The filament 14 is also provided on the sample 2 side in this embodiment.

The repeller 32 is provided inside the magnet 12.

The ionization chamber 30 includes a cylindrical mesh grid 10, a cylindrical magnet 12. It is composed of a ring-shaped filament 14 and a repeller 32.

An extraction electrode 34 for extracting ions from the ionization chamber 30 and a deflection electrode 36 for adjusting the direction of the extracted ion beam are provided between the ionization chamber 30 and the converging lens 16. Note that 38 is an ion gun that generates primary ions to excite the sample 2.

FIG. 8 also shows the bias voltage when this embodiment is used as an SNMS for analyzing neutral particles from sample 2. In this embodiment, each part is similar to the embodiment shown in FIG. It can be used as SIMS to analyze positive ions or negative ions by changing the bias voltage.

(Example 3) FIG. 9 shows a third embodiment.

In this embodiment, the ionization chamber 40 is composed of a cylindrical mesh grid 101, a cylindrical magnet 12, a filament 14, and a repeller 18.42.

An extraction electrode 34 is provided between the ionization chamber 40 and the converging lens system 16.

The repeller 18 has the function of returning the electrons to the filament 14 side and increasing the travel distance of the electrons.The repeller 42 prevents the light from the filament 14 from directly entering the sample 2, and also directs the electrons from the filament 14 onto the central axis. It has the ability to concentrate.

FIG. 10 shows bias voltages when this embodiment is used as an SNMS. Potential of sample 2 and propeller 18, 42
Let be the ground. Then, the electric potential v of the filament 14
1 is +IOV, the filament heating power supply v2 is several volts, the potential (electron impact potential) V3 of the cylindrical mesh grid 10 is +200v, and the potential of the extraction electrode 34 is ground when positive ions are taken out.

In this embodiment, since the filament 14 is moved away from the sample 2, there is an advantage that the sample 2 is not heated.

(Effects of the Invention) According to the present invention, an SNMS having the following advantages can be achieved.

(1) Neutral particles, which have not been used effectively in the past, will be used in SIMS, so
The yield of secondary ions is increased compared to S, and various problems regarding quantitative performance in SIMS can be solved.

(2) Since an axially symmetrical magnetic field is used in combination, there is an advantage that the ionization efficiency of neutral particles is increased and the ion generation locations are distributed along the axis.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing the first embodiment, FIG. 2 is a schematic sectional view showing the filament position of the ionization chamber in the same embodiment, and FIG. 3 is a schematic sectional view showing the ionization mechanism of the ionization chamber in the same embodiment. Cross-sectional view. FIG. 4 is a schematic cross-sectional view showing the bias voltage state when the same embodiment is used as an SNMS, FIG. 5 is a diagram showing the ion optical system of FIG. 4, and FIG. A schematic cross-sectional view showing the bias voltage state, FIG. 7 is a view showing the ion optical system of FIG. 6, FIG. 8 is a schematic cross-sectional view showing the second embodiment, and FIG. 9 is a schematic cross-sectional view showing the third embodiment. Schematic sectional view, FIG. 1O is a schematic sectional view showing the bias voltage state in the embodiment of FIG. 9. 2...Sample, 8.30.40...Ionization chamber 10...
・Grid, 12...Magnet, 14...Filament, 18...Repeller.

Claims (3)

[Claims] (1) A cylindrical magnet that is axially symmetrical with respect to the ion optical system, a filament provided in one opening of this cylindrical magnet, a cylindrical mesh grid provided inside this cylindrical magnet, and the A mass spectrometer, wherein an ionization chamber equipped with a repeller that repels electrons from a filament in the direction of the grid is provided at a position where particles generated from a sample can be taken in. (2) The mass spectrometer according to claim 1, wherein the filament is provided in the sample-side opening of the cylindrical magnet. (3) The mass spectrometer according to claim 1, wherein the filament is provided at the ion exit side opening of the cylindrical magnet.