JPH053011A - Electronic microscope device - Google Patents

Abstract

PURPOSE:To observe an insulator specimen without accumulation of harmful electrons, by radiating cation beams onto the same position as the electron beam irradiation position on the specimen. CONSTITUTION:Through control made by a calculator 6 via an electron-gun X-Y axis scan circuit 4 and a control circuit 5, a convergence electron beam 1 from an electron gun 2 is made to radiated the surface of a specimen 12 along predetermined scanning lines. The secondary electron 13 generated at this time are detected by a detector 3. The intensity variations of the secondary electron 13 are processed in the calculator 6 to form a secondary electron image of the specimen 12 on a display section 7. At this time, cation beams 8 are made to radiated and re-scan a straight electron scan trajectory via an ion-gun X-Y axis scan circuit while the amount radiated is controlled via an ion-gun control circuit 11 to such an extent as would timely neutralize a negative charge accumulated on the specimen through radiation of the convergence electron beam 1. Since the secondary electrons 14 produced upon radiation of the cation beams 8 cause a decrease in the resolution, the calculator 6 is made inoperative, at the time of cation beam radiation, by the secondary electron detector 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope apparatus for observing the surface condition of a measurement sample by detecting secondary electrons generated by irradiation of the measurement sample with an electron beam.

[0002]

2. Description of the Related Art Electron microscope devices equipped with a secondary electron detector include scanning electron microscopes and transmission electron microscopes. Here, an example of a scanning electron microscope will be described.
In a scanning electron microscope, a focused electron beam (diameter: 10Å) emitted from an electron gun is irradiated onto a measurement sample while scanning in the XY axis directions. At this time, the intensity of secondary electrons generated is detected by a secondary electron detector. The intensity change in the X and Y axis directions is processed by a computer and combined on a CRT to obtain an enlarged image of the measurement sample.

In the secondary electron generation referred to here,
Mainly, the electrons that have been excited into the vacuum through the solid state of electrons excited to a higher energy than the valence band or the vacuum level. When the excitation energy E of the secondary electrons (proportional to the electron acceleration voltage of the device) increases, it can be derived from the formula (1) that the intensity Q _k (E) of the secondary electrons decreases.

[0004]

[Equation 1]

The ratio (secondary electron generation efficiency) δ of the secondary electron generation amount to the focused electron beam incident amount is expressed by the equation (2) with respect to the focused electron beam incident angle θ.

[0006]

[Equation 2]

Δ has a maximum value (δ≈1.5 to 2) at E _Po = 600 eV to 1 keV, and as E _Po increases,
It is known that δ gradually decreases. Where δ <1
It can be seen that negative charges (electrons) are accumulated in the sample in the energy range of E _Po (≈1.5 to 2 keV) or more.
In the case of a conductor sample, these accumulated electrons escape from the sample holder to ground through the sample, but in the case of an insulator sample they accumulate in the sample.

On the other hand, the relationship represented by the equation (3) is established between the resolution d of the microscope and the wavelength λ of light.

[0009]

[Equation 3]

Further, it is known that the wavelength of electrons accelerated by the voltage PV in an electron microscope is represented by the equation (4).

[0011]

[Equation 4]

Therefore, in order to improve the ordinary resolution d, an acceleration voltage of 20 to 50 kV is often used for the scanning electron microscope.

As described above, when an insulator sample is analyzed by using a normal scanning electron microscope, the incident electron beam is bent due to the negative charge accumulated in the measurement sample due to the irradiation of the focused electron beam, or Since it did not reach the sample, the path of the primary electron beam itself was obstructed and measurement was difficult. Therefore, in the case of measuring an insulator sample, pretreatment such as coating the surface of the sample with a conductor such as platinum, gold, or carbon was necessary to provide a ground to prevent accumulation of electrons.

[0014]

SUMMARY OF THE INVENTION The present invention provides an electron microscope capable of observing an insulator sample without accumulating harmful electrons.

[0015]

A feature of the electron microscope apparatus of the present invention is that it is provided with an ion gun for emitting a positive ion beam and a means for irradiating the sample with a positive ion beam at the same position as the electron beam irradiation position. is there.

[0016]

The current I flowing through the sample when the sample is irradiated with cations is approximately given by equation (5). Ar ⁺ and Ga ⁺ are suitable as such cations.

[0017]

[Equation 5]

Generally, the second term (I _P (δ _i ⁻ −δ) of the equation (5) is
_i ⁺ )) is smaller than the first term (I _P (δ _e -1)) and can be ignored. That is, I is approximated to (I _P (δ _e −1)), and when the positive primary ions are irradiated, the secondary electron generation efficiency δ _e is smaller than 1 and I> 0, so that the insulator sample If the current I
Does not flow through the sample and a positive charge is accumulated.

Therefore, when the insulator sample in which electrons are accumulated by the electron beam is irradiated with an appropriate amount of positive ion beam, the accumulated electrons are neutralized by the positive charge generated at this time.

[0020]

1 shows the structure of a scanning electron microscope apparatus as an embodiment of the present invention. In this embodiment, an electron gun 2 that emits a focused electron beam 1 that is narrowed down, a secondary electron detection device 3,
An electron gun XY axis scanning circuit 4, an electron gun control circuit 5, a computer 6 and a display unit 7 are used in a normal scanning electron microscope apparatus, and an ion gun 9 for emitting a positive ion beam 8 and an ion gun XY for controlling irradiation thereof are provided. An axis scanning circuit 10 and an ion gun control circuit 11 are added.

First, as in the prior art, the focused electron beam 1 emitted from the electron gun 2 under the control of the computer 6 through the electron gun XY axis scanning circuit 4 and the electron gun control circuit 5 causes the surface of the sample 12 to be measured. It is irradiated along the scheduled scan line,
Secondary electrons 13 generated at that time are detected by the secondary electron detection device 3. The information on the change in the intensity of the secondary electrons 13 is processed by the computer 6, and the secondary electron image of the measurement sample 12 is obtained on the display unit 7.

At this time, when the measurement sample 12 is an insulator, electrons tend to be accumulated in the measurement sample 12 by irradiation with the focused electron beam 1. In order to suppress this accumulation, Irradiation is performed for each short time, and the electrons accumulated within this short time are immediately neutralized by irradiation with the positive ion beam 8. That is, the measurement sample 12 is irradiated with the positive ion beam 8 from the ion gun 9 controlled by the computer 6 similarly to the focused electron beam 1 through the ion gun XY axis scanning circuit 10 and the ion gun control circuit 11. More specifically, the irradiation of the positive ion beam 8 is rescanned through the ion gun XY axis scanning circuit 10 on the immediately preceding electron beam scanning locus so that the focused electron beam 1 has the same value as the scanned position. The irradiation amount is controlled through the ion gun control circuit 11 to such an extent that the negative charges accumulated in the measurement sample 12 by the irradiation of the focused electron beam 1 are neutralized at any time. At this time, the secondary electrons 1 generated by the irradiation of the positive ion beam 8
4 causes a reduction in the resolution of the scanning electron microscope measurement, and therefore the secondary electron detection device 3 is controlled by the computer 6 so as not to operate when the positive ion beam 8 is irradiated.

FIG. 2 shows the operation timing of one scanning line of the electron gun 2, the ion gun 9 and the secondary electron detection device 3 controlled by the computer 6 through the respective control circuits.
An example of a chart is shown. In this example, scanning and irradiation of the focused electron beam 1 and the positive ion beam 8 on the measurement sample 12 are alternately repeated so that the secondary electron detection device 3 operates only while the focused electron beam 1 is irradiated. Controlled.

The unit irradiation period T of the focused electron beam 1 is appropriately about 1 to 100 msec in order to prevent the electrons from excessively accumulating on the measurement sample 12 and exerting a great influence on the measurement. That is, when the focused electron beam 1 is irradiated for a longer time than this, the total amount of accumulated electrons in the entire scanning region at this time becomes large, and the focused electron beam 1 itself is bent due to the influence of the focused electron beam 1 and the measured sample 12 has a predetermined amount. This is because the scanning line is not irradiated, which hinders accurate measurement. Further, the irradiation of the positive ion beam 8 is adjusted by the computer 6 in accordance with the amount of negative charges accumulated in the measurement sample 12 so that the irradiation intensity and the irradiation time are appropriate. After finishing the measurement on one scan line,
The measurement is repeated on the next scanning line as in the normal scanning electron microscope measurement.

In this way, the focused electron beam 1 scans and irradiates the measurement sample 12 without being affected by electron accumulation, and only the secondary electrons 13 generated at that time are selectively emitted by the secondary electron detection device 3. To be detected. As a result, the intensity change of the secondary electrons 13 in the XY axis directions is image-processed by the computer 6 in synchronism with scanning, and a secondary electron image as a magnified image of the measurement sample 12 is obtained on the display unit 7 with high accuracy.

In this embodiment, the ion gun XY axis scanning circuit 10 and the ion gun control circuit 11 for controlling the positive ion beam 8 are provided separately from those for the focused electron beam 1, but the control software of the computer 6 is used. By making some changes,
The positive ion beam 8 may also be controlled by the electron gun XY axis scanning circuit 4 and the electron gun control circuit 5 itself.

[0027]

According to the present invention, the insulator sample can be observed without accumulating harmful electrons, and therefore the measurement can be performed without pretreatment of the measurement sample such as vapor deposition of a conductor. ..

[Brief description of drawings]

FIG. 1 is a block diagram showing an electron microscope apparatus according to an embodiment of the present invention.

FIG. 2 is a timing chart showing the control operation of the apparatus of this embodiment.

[Explanation of symbols]

 1 Focused Electron Beam 2 Electron Gun 3 Secondary Electron Detector 4 Electron Gun XY Axis Scanning Circuit 5 Electron Gun Control Circuit 6 Computer 7 Display 8 Positive Ion Beam 9 Ion Gun 10 Ion Gun XY Axis Scanning Circuit 11 Ion Gun Gun Control Circuit 12 Measurement sample 13 Secondary electron generated by irradiation of focused electron beam 1 Secondary electron generated by irradiation of positive ion beam 8

Claims (1)

Claims: 1. An electron gun for irradiating a measurement sample with an electron beam,
In an electron microscope device equipped with a secondary electron detection device for detecting secondary electrons generated by irradiation of the electron beam, an ion gun emitting a positive ion beam, and the electron beam irradiation position in the measurement sample at the same position as the electron beam irradiation position. An electron microscope comprising: a means for irradiating a positive ion beam; and a means for controlling the irradiation amount of the positive ion beam to the extent that the electrons accumulated in the measurement sample are neutralized by the electron beam irradiation. apparatus.