JPH0393143A - Elementary analyzer for minute quantity of microwave plasma - Google Patents

Abstract

PURPOSE:To improve the ratio of a signal to noise so as to enhance detection sensitivity by coaxially connecting a microwave unit to a plasma sampling system using a cylindrical conductor in such a manner that the central axes thereof accord with each other. CONSTITUTION:A microwave circuit 10 and a plasma sampling cone 31 are coaxially connected by a cylindrical conductor 20 in such a manner that the central axes thereof accord with each other. Namely, the cylindrical conductor 20 is activated to prevent microwave power supplied from the tip ends of a discharge tube 16 and outer conductor 13 from leaking into the atmosphere from a space between the cone 31 and the conductor 20. Even a fine signal can be accurately detected if the microwave power is large, thereby enhancing detection sensitivity of an analyzer.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a microwave plasma trace element analyzer for analyzing trace elements used in the fields of semiconductors, living organisms, etc. Regarding prevention of microwave leakage and prevention of abnormal voltage generated in plasma. [Prior art] A typical conventional ultratrace element analyzer using atmospheric pressure microwave plasma is Spectrochemika Acta, 42B, 5.
(1987) pp. 705 to 712 (especially
Fig. on page 707. 2). Figure 2 shows its schematic structure. here. 10 is T M
,,. The microwave three-dimensional circuit section consists of a resonant cavity, etc., and 16 is a discharge tube made of quartz or the like. 30 is a plasma sampling system, 31 is a sampling cone, 3
4 is a mounting board for the sampling cone.

50 is an ion extraction system, 51 is a schema, 52 is a mounting substrate for the schema, and 53 is an ion extraction electrode. Also. 60 is a quartz tube.

In this conventional device, plasma is generated in the discharge tube 16 by microwave power (360 W) supplied to the cavity (microwave three-dimensional circuit) 10. At this time, a sample to be analyzed is introduced into the discharge tube 16, and is dissociated, excited, and ionized by the plasma generated in the discharge tube 16. The sample ions obtained by this ionization are extracted through an orifice provided in the sampling cone 31 and the schema 51, accelerated by a negative voltage applied to the ion extraction electrode 53, and subjected to mass analysis by a mass filter. In addition, in order to reduce the mixing of N2 from the atmosphere into the plasma, a quartz tube 60 is provided between the microwave three-dimensional circuit 10 and the plasma sampling cone 31 to shield the plasma from the atmosphere side. There is.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into consideration the leakage of microwaves from the space between the cavity 10 and the sampling cone 31, which not only causes radio wave interference but also reduces the signal-to-noise ratio, resulting in extremely small amounts of trace elements. There was a problem that it could not be detected with high sensitivity.

Furthermore, when the microwave power is increased to 400 W or more in order to directly analyze a solution sample with high sensitivity, the cavity 10
A high frequency electric field is generated between the sampling cone 31 and the ion energy distribution f (E) in the plasma.
There were also problems such as abnormalities and the inability to stably and sensitively detect trace elements.The purpose of the present invention is to solve the above-mentioned problems.

[Means to solve the problem]

In order to achieve the above purpose, as shown in FIG. The conductors 20 (composed of 21 to 25) are concentrically connected so that their central axes coincide.

Further, the tip of the microwave three-dimensional circuit 10 (the tip of the outer conductor 13) and the plasma sampling cone 3
For example, as shown in FIG.
After dividing the cylindrical conductor parts 22 and 24 into 24 parts and setting the gap d by fitting the two cylindrical conductor parts 22 and 24, the two parts can be fixed with, for example, screws 23 so as to be completely conductive even to high frequency current. I made it.

[Effect]

The cylindrical conductor 20 is designed to shield microwave power radiated from the tip of the discharge tube 16 and the outer conductor 13 from leaking into the atmosphere from the space between it and the plasma sampling cone 31. works. As a result, even if the microwave power becomes large (400W
Above) Even extremely small signals can be detected accurately, and the detection sensitivity of the analyzer can be greatly improved.

Further, the cylindrical conductor 20 is arranged on the inner and outer conductors 12.1.
3, etc., and a certain plasma sampling system 30 from the plasma sampling cone 31, etc., are operated so as to be axially symmetrical and at the same potential not only in terms of DC but also in terms of high frequency. do. As a result, no abnormal potential is generated in the plasma, and no abnormal elementary reactions occur (the ion energy distribution f (E) does not become abnormal), allowing highly sensitive and accurate quantitative analysis.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Here, 10 is a three-dimensional circuit section for generating microwave plasma, which can be used to directly analyze a solution sample with high sensitivity using large power (400 W or more).
As shown in Application No. 4 and Japanese Patent Application No. 01-038219, a flat waveguide 11, an inner conductor 12, an outer conductor 13, a ventilation port 14, a cooling gas introduction system 15, a discharge tube 16, and a sample introduction tube 17 It consists of etc. Reference numeral 20 denotes a cylindrical conductor portion made of Cu or the like according to the present invention, and is composed of a cylindrical conductor portion (I) 21 and a cylindrical conductor portion (II) 24, which are connected to the plasma sampling system 30 and the microwave stereo, respectively. It is electrically and mechanically fixed to the circuit part 10 axially symmetrically,
Furthermore, these have overlapping parts (fitting parts) and can be electrically and mechanically connected and fixed at multiple locations using screws 23, for example. The connection/fixing method is not limited to the above. Further, at least one of the cylindrical conductor portions (1) and (II) includes:
A plurality of ventilation holes 22 and 25 are provided at equal intervals. Reference numeral 30 denotes a plasma sampling system, which includes a sampling cone 31, a cooling plate 32 for cooling the cone, a vacuum vessel 34 to which these are attached, and the like. The sampling cone 31 and the vacuum container 34 are made of SUS, and the cooling plate 32 is made of Cu or the like. Note that the cooling plate 3
2 and the vacuum vessel 34 are preferably provided with cooling water passages 33 and 35. The ion extraction system 40 comprising the ion extraction electrode 41, the ion accelerating electrode 42, and the substrate 43 to which they can be attached is as detailed in Japanese Patent Application No. 63-283602 and Japanese Patent Application No. 01-23835. The sample ions generated by these are then subjected to mass analysis using a mass filter. Note that the configurations and shapes of the microwave three-dimensional circuit section 10, the plasma sampling system 30, and the ion extraction system 40 are not limited to those described above. Furthermore, although the above explanation was about a qualitative analysis device,
When applied to an emission spectrometer, a vacuum ultraviolet light source, or a plasma source in plasma processing, the three-dimensional circuit section 10 and the vacuum container 34 are connected by the cylindrical conductor 20, for example, via the plasma sampling cone 3l. The effect of doing so is basically the same. At this time, the shape of the plasma sampling cone 31 may be modified depending on the purpose. Moreover, if the gap d is constant, the cylindrical conductor portion (1
) and (II) may be used as one unit (in that case, screws 2-3 etc. are not required). [Effects of the Invention] According to the present invention, by coaxially connecting the microwave three-dimensional section 10 and the plasma sampling system 30 with the cylindrical conductor 20 so that their central axes coincide, plasma generation can be achieved. Microwave leakage of large power (4 0
0 W or more), the signal-to-noise ratio is improved, the detection sensitivity is improved, and safety and health problems are eliminated.

Furthermore, it is possible to prevent an abnormal voltage that occurs between the microwave three-dimensional circuit section 10 and the plasma sampling system 30 at the time of high power (400 W or more), and the ion energy distribution f (E) in the plasma does not become abnormal. This method has the important effect of allowing extremely trace amounts of elements to be analyzed stably and accurately.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the main part of an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the main part of the prior art. DESCRIPTION OF SYMBOLS 10... Microwave three-dimensional circuit part, 11... Flat waveguide, 12... Inner conductor, 13... Outer conductor, 14...
Ventilation port, l6...discharge tube, 20...cylindrical conductor part,
2l... Cylindrical conductor portion (I), 24... Cylindrical conductor portion (II), 23... Screw (fixing tool). 22.2
5... Ventilation port, 30... Plasma sampling system,
31... Plasma sampling cone, 32... Cooling plate, 34... Vacuum container, 41... Ion extraction electrode, 42... Ion accelerating electrode. II 74 7 I12: AtL4*riJ ss sound p20 cylindrical punch JO dera

Claims (1)

[Claims] 1. In an ultratrace element analysis device using microwave plasma, a cylinder whose central axis coincides with the microwave three-dimensional circuit section of the plasma generation section and the sampling cone for sampling plasma, ions, etc. A microwave plasma ultratrace element analysis device characterized by being connected by a shaped conductor. 2. The microwave plasma trace element analysis apparatus according to claim 1, wherein the length of the cylindrical conductor is variable. 3. The microwave plasma trace element analysis apparatus according to claim 1 or 2, wherein the cylindrical conductor is provided with a plurality of ventilation holes.