JPS5811075B2 - electronic microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron microscope equipped with a scanning image observation device.

A device that is a conventional electron microscope but has the function of a scanning electron microscope has been realized.

In such an apparatus, the sample is placed at the center of the objective lens, similar to a normal electron microscope, and when observing a scanned image, the objective lens is strongly excited, and the forward magnetic field formed in front of the sample is converted into a secondary magnetic field. It is used as an electron focusing means, and a deflection means provided above the objective lens is used to two-dimensionally scan the electron beam on the sample.

However, in such a device, there is no problem when the objective lens is strongly excited, but when it is used with OFF or weak excitation, the detector for detecting the secondary electrons generated from the sample is installed above the objective lens and near the electron beam path. As a result, the distance between the detector and the detector inevitably became longer, and a decrease in the detection efficiency of secondary electrons was unavoidable.

Therefore, especially during high-speed scanning, the amount of signal per pixel is insufficient, resulting in a loss of image quality.

As a result of repeated studies and experiments in order to solve the above-mentioned conventional problems, the present inventor provided a cylindrical body (for example, a contamination prevention tube) surrounding the electron beam passage around and above the sample, and the cylindrical body We discovered that applying a positive potential to the sample can improve the secondary electron detection efficiency.

FIG. 1 is a sectional view showing an embodiment of the present invention based on this discovery, and will be explained in detail below.

In FIG. 1, numerals 1 and 2 are an upper magnetic pole piece and a lower magnetic pole piece, respectively, which constitute an objective lens.

Reference numeral 3 denotes a sample to be observed, which is inserted from above or from the side of the upper magnetic pole piece 1 and placed in a magnetic field created by the upper and lower magnetic pole pieces 1 and 2, respectively.

Reference numeral 4 denotes a deflection coil provided above the objective lens for scanning the micro-diameter electron beam EB irradiated onto the sample 3.

A secondary electron detector 5 consisting of a scintillator, a photomultiplier tube, a collection electrode, etc. is provided above the deflection coil 4 and faces toward the electron beam path.

The secondary electrons generated from the electron beam irradiation point on the sample 3 are collected near the electron beam path by the forward magnetic field of the objective lens, and are collected by the secondary electron detector 5 while moving spirally around the path, where they are detected. be done.

Reference numeral 6 denotes a contamination prevention tube arranged to surround the sample, and the contamination prevention tube 6 is held in a heat-insulated manner by the upper magnetic pole piece 1 via a heat-insulating material 7.

The contamination prevention cylinder 6 is kept at a low temperature by a cooling mechanism (not shown), and traps organic gas and the like present near the sample to prevent contamination of the sample.

Further, the contamination prevention tube 6 is maintained at a positive potential of about 10 V with respect to the sample 3 by a DC power source 8.

When observing a scanned image in the configuration as described above.

A finely focused electron beam is deflected onto the sample 3 by the deflection coil 4.
Dimensionally scanning is as described above.

Secondary electrons generated from the surface of the sample 3 due to the two-dimensional scanning are focused by an electrostatic lens effect caused by an electric field formed between the sample and the contamination prevention cylinder 6, and are efficiently guided above the objective lens. Further, the secondary electrons are attracted by the electric field for collecting secondary electrons directed toward the electron beam path from the secondary electron detector 5, and are guided to the detector 5 and detected.

FIG. 2 shows an example of measuring the change in secondary electron detection efficiency according to the potential Vs applied to the pollution prevention cylinder 6.

As can be seen from the figure, it is recognized that the detection efficiency is improved in the positive potential range up to about Vs=20V compared to the conventional case (when Vs=Ov).

Therefore, if the detection signal obtained from the secondary electron detector 5 is supplied to the display device, an image with a good signal-to-noise ratio can be obtained even during high-speed scanning.

It is assumed that the reason why the detection efficiency decreases when Vs exceeds 20 V in FIG. 2 is because the electric field is concentrated between the sample and the lower end of the contamination prevention tube.

Therefore, the position of the fold 6a provided on the inner surface of the pollution prevention cylinder,
If the electric field is not concentrated only between the lower end of the contamination prevention tube and the sample, but is distributed above the sample by making the size appropriate, detection efficiency can be increased to even higher potentials. be able to.

In the above-mentioned embodiment, a positive potential was applied to the contamination prevention tube, but
Needless to say, the present invention is not limited to this, and a separate cylindrical body may be provided.

As detailed above, according to the present invention, the secondary electron detection efficiency can be improved, and in particular, if a positive potential is applied to the contamination prevention tube, the configuration can be extremely simplified.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the potential applied to the pollution prevention cylinder and the detection efficiency. 1: Upper magnetic pole piece, 2: Lower magnetic pole piece, 3: Sample, 5: Secondary electron detector, 6: Contamination prevention cylinder, 7: Heat and insulation material, 8: DC power supply.

Claims (1)

[Claims] 1. A sample is placed between the upper magnetic pole and the lower magnetic pole of the objective lens,
In an electron microscope in which an electron beam is two-dimensionally scanned over the sample and secondary electrons generated from the sample are guided to a detector placed above the objective lens and detected, the sample and the electrons above it are detected. A cylindrical electrode surrounding the wire passage is provided,
An electron microscope characterized in that the cylindrical electrode is configured to apply a positive potential to a sample. 2. The electron microscope according to claim 1, wherein the cylindrical electrode also serves as a contamination prevention tube provided around the sample.