JPH0252828B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage measuring device using an electron beam. In particular, the present invention relates to improvements in voltage measuring devices using electron beams that utilize the property that the kinetic energy of secondary electrons depends on the potential of a sample irradiated with the electron beam.

Samples whose voltage is difficult to measure by conventional means,
For example, as a voltage measuring device that measures the voltage of a desired area on the surface of an integrated circuit having a fine pattern.
A voltage measurement device whose basic principle is to irradiate the sample with an electron beam, detect the amount of secondary electrons generated by this, and regard the change in the amount of secondary electrons as a change in the potential of the sample. There is.

The basic configuration of an example of this type of voltage measuring device is shown in FIG. In the figure, 1 is a vacuum container that is the outer box of the apparatus, and 2 is an electron gun that irradiates a sample 4 with an electron beam 3 and generates secondary electrons 5. 6
is an extraction electrode and is at a more positive potential than sample 4. Further, 7 is a deceleration electrode for analysis, which has a function of controlling the amount of secondary electrons incident on the secondary electron amount detector 8.

The distribution of the amount of secondary electrons with respect to the energy possessed by the secondary electrons in a voltage measuring device having such a configuration is as shown in Figure 2a, and this distribution curve is plotted along the X axis, that is, the energy axis, with the potential of the sample as a parameter. It is thought that the object moves in parallel along the . In the figure, curves A and B are for the case where the sample voltage is, for example, 5V and 0V, respectively. The amount of secondary electrons incident on the secondary electron amount detector is the total amount of secondary electrons with energy above a certain value, and the amount of secondary electrons incident on the secondary electron amount detector is the deceleration voltage for analysis. Therefore, Fig. 2a is controlled by
It can be converted as shown in Figure b. In the figure, curve A′,
B' corresponds to curves A and B, respectively, when the sample voltages are, for example, 5V and 0V.

Therefore, all the elements other than the potential of the sample and the voltage of the deceleration electrode that can affect the amount of secondary electrons are kept constant, and only the voltage of the deceleration electrode is changed as a parameter to change the potential. If the deceleration voltage that keeps the output of the secondary electron amount detector constant is determined for multiple samples, the difference in deceleration voltage △V (Fig. 2b
), it should be possible to determine the potential difference between the samples.

However, according to the results of experiments, the curve representing the relationship between the output of the secondary electron quantity detector and the voltage of the deceleration electrode for analysis, that is, the deceleration voltage, is not as shown in Fig. 2b, but often as shown in Fig. 3. . That is, for some reason, the function form of the output of the secondary electron amount detector versus the deceleration voltage changes irregularly as the deceleration voltage changes. In the figure, curves A″ and B″ are respectively curves.
Corresponds to A′ and B′, and the sample voltage is e.g. 5V, 0V.
This is the case. In other words, when the deceleration voltage is changed, the above function form changes irregularly.
This tendency significantly reduces the measurement accuracy of the voltage measuring device having the above configuration.

The present invention is aimed at solving this problem, and is a voltage measuring device using an electron beam, which has a characteristic that the function form of the output of a secondary electron quantity detector versus the analytical deceleration voltage does not change following the deceleration voltage. Our goal is to provide the following. The gist thereof is to arrange a buffer electrode having a similar shape to the extraction electrode and the deceleration electrode for analysis concentrically with these electrodes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A voltage measuring device using an electron beam according to an embodiment of the present invention will be described below with reference to the drawings, and the configuration and unique effects of the present invention will be clarified.

First, as a result of various studies on the reasons for the irregular change in the function form mentioned above, we found that a certain proportion of secondary electrons
It is assumed that this is because when passing through the deceleration electrode, some fraction of the secondary electrons that fly in a direction that is not perpendicular to the deceleration electrode and therefore have energy close to the limit condition do not reach the detector. Furthermore,
It is presumed that this abnormality in the flight direction of the secondary electrons is affected by the direction of the electric field between the extraction electrode and the deceleration electrode. In other words, normally around +1KV is applied to the extraction electrode to attract secondary electrons, but
The speed of secondary electrons is usually controlled by applying a voltage of about -10 to 0 V to the deceleration electrode for analysis. As a result, the velocity of the secondary electrons rapidly decreases in this section, and because both electrodes are mesh-like, the direction of the electric field between the two electrodes is no longer perpendicular to the gap between the electrodes. It is presumed that secondary electrons whose flight direction is not perpendicular to the electrode surface are generated, causing the above-mentioned asymmetrical change in the function form.

Based on this estimation, in order to eliminate the above drawback, a third electrode (buffer electrode) is provided between the extraction electrode and the deceleration electrode, and this
Thinking that it would be effective to apply a positive voltage of about 100V, we prototyped a voltage measurement device using an electron beam with the structure shown in Figure 4, and after repeated experiments, we found that the voltage applied to the buffer electrode was 50V.
It was confirmed that generally good results were obtained at about ~100V. In the figure, 1 to 8 are the same as those shown with the same numbers in FIG. It has the shape of , and is arranged concentrically with both electrodes.

As explained above, according to the present invention,
In a voltage measuring device using an electron beam, which has an extraction electrode and an analysis deceleration electrode, each having a hemispherical mesh shape with a different radius and arranged concentrically, and which detects the amount of secondary electrons. , between both electrodes,
A hemispherical net-like buffer electrode is placed concentrically with both electrodes, which improves energy resolution, is unaffected by changes in the deceleration voltage, and improves analytical characteristics of the electron beam voltage measuring device. can be provided.

Note that the voltage to be applied to the buffer electrode is determined in relation to the deceleration voltage.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the basic configuration of a voltage measuring device using an electron beam in the prior art.
Figures 2a and b are supplementary graphs for explaining the voltage measurement principle of the voltage measuring device using an electron beam shown in Figure 1, and Figure 3 is a supplementary graph for explaining the drawbacks of the voltage measuring device using an electron beam in the prior art. FIG. 4 is a conceptual diagram showing the basic configuration of a voltage measuring device using an electron beam according to an embodiment of the present invention. 1... Vacuum container which is an outer box, 2... Electron gun, 3
...Electron beam, 4...Sample, 5...Secondary electron,
6...Extraction electrode, 7...Deceleration electrode for analysis, 8
...Secondary electron amount detection device, 9...Buffer electrode.

Claims (1)

[Claims] 1. An extraction electrode and an analytical deceleration electrode arranged concentrically, each having a hemispherical mesh shape with a different radius, and an electron emission device that irradiates the sample with an electron beam placed at the center of the hemispherical mesh electrode. and a detection device that detects the secondary electrons that have passed through the hemispherical mesh electrode, and the electron beam is generated by utilizing the property that the energy of the secondary electrons depends on the potential of the sample that is irradiated with the electron beam. A voltage measuring device using an electron beam, characterized in that the voltage measuring device using an electron beam has a hemispherical mesh buffer electrode arranged between the extraction electrode and the analysis deceleration electrode concentrically with the electrode.