JPH01132038A - Mass spectroscope - Google Patents

Abstract

PURPOSE:To make highly accurate mass analysis possible by providing the periphery of an ion beam incident hole of a beam current restricting aperture with a conical protrusion with its apex located at the incident hole. CONSTITUTION:A beam current restricting aperture 4 is provided in its center with an ion beam passing hole 41. The restriction of the ion beam passage restricts the amount of beam current and also works to collimate the beam. It is arranged here such that the aperture 4 is provided with a protrusion with its apex located at the hole 41 and that the periphery of the hole 41 forms the slope A. As a result, particles sputtered and the ion beam reflected at the surface A are diffused in the direction parting from the hole 41 and do not interfere with the ion beam incident in the hole 41. Thus, the contamination of a primary ion beam is lessened and the accuracy of mass analysis is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a mass spectrometer used for mass spectrometry of a solid sample using an ion beam.

(Prior Art) Conventional mass spectrometers of this type emit a primary ion beam such as Ar using an ion gun, and use an ion beam optical system consisting of a focusing lens, an ion beam limiting aperture, etc. to direct this primary ion beam. A common secondary ion mass spectrometer is a secondary ion mass spectrometer that irradiates a sample through a ion beam, detects secondary ions generated from the sample, and performs mass analysis. In this device, the quality of the -order ion beam, that is, the presence of different types of -order ion beams, neutral particles, etc. in the ion beam, has a large effect on the signal-to-noise ratio (NS ratio) of the analysis signal. A high quality ion beam is desired.

Therefore, conventionally, [EX
The quality of the ion beam was improved by using a B (Vienna) filter to remove neutral particles by applying an electric field to the ion beam to deflect the beam and remove neutral particles that do not deflect. .

(Problems to be Solved by the Invention) In the conventional apparatus described above, foreign ions, neutral particles, etc. contained in the ion beam emitted from the ion gun can be removed to some extent. However, the problem arises that the beam current limiting aperture for limiting the ion beam to a predetermined current amount contaminates the ion beam itself.

That is, in the beam current limiting aperture, particles (ions, neutral particles) generated by reflection, scattering, or sputtering of the primary ion beam at the edge portion of the beam entrance hole or the beam limiting surface interfere, and the negative ions It contaminates the beam itself and significantly reduces the quality of the ion beam.

The present invention has been made to address the above-mentioned conventional problems, and an object of the present invention is to provide a mass spectrometer capable of performing highly accurate mass analysis by obtaining an ion beam limiting aperture with a novel shape. .

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention aims to improve the measurement target by passing the primary ion beam emitted from the ion gun through a beam current limiting aperture. In the mass spectrometer that performs mass spectrometry of the sample by setting the ion beam current amount necessary for The gist is:

(Function) According to the present invention, of the ion beam emitted from the ion gun, ions or particles that are sputtered or reflected near the beam entrance of the beam current limiting aperture are removed from the slope of the convex portion around the entrance hole. Since the ions are scattered in a direction away from the entrance hole, interference between the incident ion beam and these ions and particles is significantly reduced. Therefore, the ion beam that has passed through this aperture is effectively current-limited while maintaining high quality, and highly accurate loan analysis can be performed.

(Example) FIG. 1 is a configuration diagram showing a primary ion beam optical system of a mass spectrometer according to an example of the present invention. In the drawing, 1 is an ion gun that emits a primary ion beam such as Ar, 2 is a focusing lens that focuses the ion beam emitted from the ion gun 1, and 3 is a drift tube that focuses the ions focused by the focusing lens 2. The beam is once focused within this tube 3 and then diverged again. - a foreign ion in the next ion (for example, in the case of an Ar+ ion, Ar+“.

Ar++1. An EXB filter for removing (N+, etc.) is generally installed in this part. Reference numeral 4 denotes a beam current limiting aperture having a shape unique to the present invention, which will be described later. A hole 41 through which the ion beam passes is provided in the center, and the beam current is limited by limiting the amount of ion beam passing through. It works to collimate. As shown in the figure, the aperture 4 is provided with a convex portion having the hole 41 as its apex, and the outer periphery of the hole 41 forms a slope A. Therefore, the ion beam and sputtered particles reflected on the A plane are scattered in a direction away from the hole 41 and do not interfere with the ion beam incident on the hole 41. The detailed shapes of J3 and aperture 4 will be described in the explanation section of FIG. 2, which will be described later.

5 is a deflection electrode for deflecting the ions collimated by the aperture 4; At this time, neutral particles contained in the ion beam are not affected by the electric field and are not deflected. Therefore, by detecting only the beam deflected by the electrode 5, neutral particles can be removed. 6
is an electrode for scanning the ion beam that has passed through the deflection electrode 5 and has become a fine probe ion, 7 is an objective lens for focusing the ion beam into a fine illumination, and 8 is a solid sample for irradiating the ion beam. It is.

The primary ion beam that has passed through the optical system as described above irradiates the solid sample 8 and sputters the sample 8, resulting in two
Generates the next ion. By detecting this secondary ion beam, mass spectrometry of the sample can be performed.

Although the beam current limiting aperture is generally made of non-magnetic steel, in this embodiment a material made of tungsten carbide was used. This is because tungsten carbide has a superior surface finish to steel. In other words, in conventional devices, the surface of the aperture hole is generally only subjected to a normal cutting process, and as a result, the ion beam passing through this hole has a halo of scattered particles due to slit scattering, and the ions are This results in a loss of beam uniformity. However, when tungsten carbide is used as the aperture material as in this example,
Excellent surface finishing can be achieved, thereby reducing slit scattering of the ion beam.

However, what is even more important in order to prevent contamination by the ion beam itself and maintain a high-quality ion beam is:
The aim is to optimize the shape of the aperture. Figure 2 shows
This is a partial cross-sectional view showing the structure of the best aperture proposed in this embodiment. Prior to explaining the structure of each part, points taken into consideration for the aperture design of this embodiment will be explained.

a. The surface A that restricts the ion beam needs to be tilted so as to keep some of the incident and reflected ions away from the hole 41 and also keep sputtered particles away. Further, in order to prevent the particles reflected or sputtered from the A surface from being reflected or sputtered again and flying into the vicinity of the hole 41, a drift tube 3 is provided above the aperture 4 to prevent the flying particles from entering.

b. In the upper interior B of the hole 41 (see Fig. 2), only the ion beam scattered larger than the aperture angle θin enters the hole 4.
1, so in order to reduce the number of scattering particles, θ1n should be as close to 90° as possible.

For the same reason as C1, the opening angle θout of the hole 41 must also be made small in order to stop particles passing through.

d. On the other hand, the angle formed by the polished surfaces of surface B and surface C (see FIG. 2) is made as close as possible to 18 Ω° in order to reduce the transmittance of the ion beam.

The C9 divergence angle θout must be larger than the maximum divergence angle of the incident ion beam to avoid scattering of the transmitted ion beam at plane C.

In order to satisfy all of the above conditions, some compromise is essential. In this example, the maximum effect could be obtained under the following conditions.

That is, as shown in FIG. 2, in this embodiment, the opening angle θin of the hole 41 is set to about 10 to 20" to reduce the probability of scattering, and the opening angle θout is set to about 2 to 4 degrees to prevent ions from scattering as much as possible. satisfy.

The inclination of the surface A that reflects the ion beam is approximately 30 to 60.
This prevents reflected or sputtered particles from partially interfering with the ion beam. The diameter d of the hole 41 is 1 to 2111
Assuming that the width of the collimator is 111φ and the width of the collimator is 511 m, the depth De of the frontage portion must be 0.1 to Q and 3 mm in order to satisfy these conditions.

As described above, by providing an appropriate aperture angle at the beam exit, the ion beam with the required current amount passing through the aperture 174 can be held within the divergence angle required for measurement, thereby eliminating unnecessary paths. The ion beam no longer reaches the following optics and sample. Therefore, this device enables fine probe mass spectrometry.

[Effects of the Invention] As described above in detail with reference to embodiments, according to the present invention, contamination of a portion of the ion beam caused by the beam current limiting aperture is significantly reduced. I can do it.

This makes it possible to significantly improve the accuracy of mass spectrometry.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical system according to an embodiment of the present invention;
FIG. 2 is a partially enlarged sectional view of the beam current limiting aperture V shown in FIG. 1. 1... Ion gun 3... Drift tube 4... Beam current limiting aperture 8... Sample 41... Ion beam passage hole

Claims (2)

[Claims] (1) In a mass spectrometer that performs mass analysis of the sample by passing the primary ion beam emitted from the ion gun through a beam current limiting aperture to obtain the amount of ion beam current necessary for the sample to be measured, the beam 1. A mass spectrometer characterized in that a convex portion having an apex at the ion beam entrance hole of a current limiting aperture is provided around the outer periphery of the ion beam entrance hole. (2) The beam limiting aperture is approximately 10 to 20 mm around the beam entrance hole at the entrance hole through which the beam enters and passes through.
The mass spectrometer according to claim 1, wherein the mass spectrometer has an opening of about 2 to 4 degrees around the beam exit side.