JPH0754683B2 - Antistatic method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an antistatic method for an insulator sample in a scanning electron microscope (SEM) and a secondary ion mass spectrometry (IMA).

[Conventional technology]

The scanning electron microscope (SEM) is configured as shown in FIG. In the figure, 1 is an electron gun, 2 is a plurality of lens groups, 3 is a secondary electron detector, 4 is a sample and sample stage, 5 is an amplifier, 6 is a contrast adjusting circuit, and 7 is a CRT.
Is.

In such a configuration, the electrons emitted from the electron gun 1 are converged as a minute spot on the sample 4 by the lens group 2. The focused fine beam is scanned on the sample 4 in synchronization with the electron beam of the CRT 7. On the other hand, the secondary electrons generated on the sample 4 by being irradiated with the primary electrons are detected by the secondary electron detector 3 and used as a video signal of the CRT 7.

In this way, the surface shape, atomic number and potential contrast of the sample 4 can be obtained.

The principle of secondary ion mass spectrometry (IMA) will be described with reference to FIG. 1 is an ion gun, 2 is a focusing lens system, 3
Is a mass spectrometer, 4 is a sample, 5 is a CRT, and 6 is a data processor.

In such a configuration, the ion beam 7 emitted from the ion source 1 is finely bundled by the lens system 2 and irradiates the sample 4. The secondary ions, which are based on the sample atoms and are emitted from the sample upon irradiation, are detected by the mass spectrometer by dividing them into mass / charge ratios. This enables identification and quantitative analysis of elements or molecules contained in the sample. The two-dimensional elemental image of the sample surface is scanned by synchronizing the primary ion beam 7 with the electron beam scanning of the CRT 5 and the secondary ions emitted from each point of the sample are separated by the mass spectrometer 3 to obtain a specific ion intensity as a video signal. It is obtained by using as.

In the above apparatus or method, when the sample 4 is an insulator, it is necessary to avoid the charging phenomenon. Generally, the secondary electron yield η generated by electron irradiation to an insulator changes depending on the energy of incident electrons, and is 1 in the region of 500 to several Kev.
The above values are shown. When η is 1 or more, the charging phenomenon does not occur, and the charging phenomenon is avoided by limiting the energy of the primary electron beam to a low value.

[Problems to be solved by the invention]

Such an antistatic method avoids the charging phenomenon by limiting the energy of the primary electron beam and leaves no room for energy selection. As is well known, the resolution of a scanning electron microscope (SEM) depends on the primary beam diameter,
The primary beam diameter changes depending on the acceleration voltage, that is, the beam energy. As described above, the conventional insulator observation method has a problem that a low acceleration (energy) beam has to be used at the expense of resolution.

It is an object of the present invention to provide an antistatic method in insulator analysis that is independent of the acceleration voltage (or energy) of the primary beam.

[Means for solving problems]

In order to achieve such an object, the present invention basically utilizes a charged particle induced conduction phenomenon by ionized atoms or electrons generated by electron or ion beam irradiation and causes a charge to flow from the generated conductive layer. This is achieved by creating a conductive thin film for avoiding charge accumulation. A conductive thin film is superposed on and adhered to a conductive layer generated by a primary charged particle beam used for observation or analysis to generate an outflow path for charges and prevent charging.

That is, the present invention is, in a scanning electron microscope or scanning ion microanalyzer, to form a conductive thin film to be grounded in the periphery of an insulating sample, leaving at least an observation region or an analysis region, and a beam of the device. The scanning region covers at least a part of the conductive thin film.

[Action]

The antistatic method configured as described above achieves the above-mentioned object by two means: generation of a conductive layer by irradiation of primary charged particles and formation of a charge outflow path of the primary charged particles.

The formation of the conductive layer is based on the following principle.
If the density of the primary charged particles is Jp (A / cm ² ), the range of the primary charged particles is Rp, the ionization voltage of the sample constituent atoms is Ei, and the energy of the primary charged particles is Ep, the number of induced charges Δn is approximately Is expressed by the following equation (1).

That is, a conductive layer having a resistance value depending on the number of charges Δn generated in the sample is formed on the irradiation surface of the sample.

The charge outflow path is formed by forming a conductive thin film that is electrically contacted with the conductive layer generated as described above and grounded at the other end.

In this case, it is important that the electrical contact between the conductive layer and the conductive thin film is made sufficiently. Therefore, the beam scanning region of the scanning electron microscope or the like is subjected to beam scanning so as to cover at least a part of the conductive thin film, and the thickness of the conductive thin film allows the primary incident charged particles to pass therethrough, and It is set to a value that can retain the energy required for charge generation.

〔Example〕

An embodiment of the antistatic method according to the present invention will be described below with reference to FIG. 1 when applied to observation of an insulator by a scanning electron microscope. In the figure, 1 is a primary charged beam, 2 is a deflection electrode for deflecting the primary charged beam, 3 is an insulator sample, 4 is a conductive material such as Au or Al formed on the surface of the insulator sample 3. Shows a thin film. The conductive thin film 4 is formed, for example, in a lattice shape as shown in the drawing, and exposes the observation or analysis region 5 of the insulator sample 3.

The conductive thin film 4 is grounded. Specifically, for example, a holding tool (not shown) of the insulator sample 3 is brought into contact with the conductive thin film 4, and the holding tool itself is grounded. It has the same structure.

When observing an insulator in such a configuration, first, the observation target portion 5 is exposed on the surface of the sample 3 to form the conductive thin film 4. Next, the sample 3 is placed on the sample stand of the scanning electron microscope, and the conductive thin film 4 is grounded. Finally, electron beam scanning is performed over the deflection area (area indicated by reference numeral 6 in FIG. 1) centering on the exposed portion of the sample 3 and covering the conductive thin film around the exposed portion to form an observation image. .

In this way, under the conditions shown in Table 1, for example,
When observing an inorganic insulating material typified by Al ₂ O ₃ sinter, a polymer film such as vinyl and mica, and a biological sample, a stable SEM with no charging phenomenon is observed in any case.
The image was obtained.

Further, also in the scanning ion microanalyzer, as a result of performing as in the above example,
It has been found that stable mass spectra and depth analyzes are possible at approximately the above mentioned energy and scan regions.

In the above-mentioned embodiment, the conductive thin film 4 is formed in a lattice shape to form the observation or analysis region of the plurality of insulator samples 3, but the invention is not necessarily limited to this.
Of course, the conductive thin film may be formed so as to form only one observation or analysis region.

〔The invention's effect〕

As is clear from the above description, according to the antistatic method of the present invention, it is possible to reduce the acceleration voltage (or energy) regardless of the acceleration voltage (or energy) of the primary charge beam in the insulator analysis. You will be able to do without it.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the antistatic method according to the present invention, FIG. 2 is a diagram showing the structure of a scanning electron microscope (SEM), and FIG. 3 is a secondary ion mass spectrometry (IMA) method. It is explanatory drawing which shows a principle. 1 ... Charged particle beam, 2 ... Deflection electrode, 3 ... Insulator sample, 4 ... Conductive thin film, 5 ... Observation / analysis area, 6 ...
… Scan area.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Bibliography Sho 63-111748 (JP, U) Hiroyoshi Soejima "Electron beam microanalysis" (sho 62-2-28) Nikkan Kogyo Shimbun P. 193-202

Claims (1)

[Claims] 1. A scanning electron microscope or a scanning ion microanalyzer, in which at least an observation region or an analysis region of an insulating sample is left and a conductive thin film is formed to be grounded, and a beam scanning of the device is performed. An antistatic method, characterized in that a region covers at least a part of the conductive thin film, and the thickness of the conductive thin film is set to be equal to or less than a transmission thickness of a charged particle beam of the apparatus.