JPH06150865A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To minimize damage on a sample caused by excessive electron beam radiation. CONSTITUTION:A primary electron beam 2 is radiated to a sample 5 while scanning it by a scanning coil 4, and a secondary electron, a reflected electron or the like created at that time is detected by a detector 7. In a scanning electron microscope to display an image according to image contrast on a display device 9 according to this detected signal, scanning speed of the primary electron beam 2 and a detecting signal quantity of the detector 7 are integrated by an integrator 14, and the scanning coil 4 is controlled by a scanning speed controller 15 based on the result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique relating to a microscope, and more particularly to a technique effective for use in a scanning electron microscope for observing semiconductor devices and the like.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a conventional scanning electron microscope.

An electron gun 1 for emitting a primary electron beam 2 is attached to a ceiling portion of a casing 3 (inside of which a vacuum atmosphere is provided), and a scanning coil 4 is arranged along the passage of the primary electron beam 2. The sample 5 is arranged at the destination of the primary electrons, and the sample 5 is placed on the table 6.

A detector 7 for detecting the signal 10 from the sample 5 is attached to the side wall of the housing 3. An amplifier 8 is connected to the detector 7, and a display device 9 is connected to the amplifier 8.

In the above structure, the sample 5 is irradiated with the primary electron beam 2 emitted from the electron gun 1. At that time,
The primary electron beam 2 scans the sample 5 at a constant speed by being deflected by the magnetic field generated by the scanning coil 4. By this scanning, the signal 5 excited by the primary electron beam 2 is emitted from the sample 5.

This signal 10 includes secondary electrons, backscattered electrons, X
Lines, cathodoluminescence, etc., which are detected by the detector 7 and converted into electric signals, and further amplified by the amplifier 8 to a level at which image contrast is formed. Further, it is processed into a signal for display on the display by the display device 9, and an image corresponding to the surface shape of the sample 5 (for example, a black and white image in which a bright part and a dark part are distinguished by contrast) is displayed on the display screen.

[0007]

According to the study of the present inventor, the prior art of irradiating a sample having an insulator formed on its surface with a primary electron beam and detecting the secondary electrons thereof and displaying it as an image Has a problem that a high contrast part in an image has a large amount of signal, and a low contrast part has a small amount of signal, resulting in a poor S / N ratio (signal to noise ratio).

FIG. 5 is an explanatory diagram showing the generation of the image contrast obtained from the amplifier 8.

As shown, a hole 11 (for example,
When a contact hole) is formed, the portion of the hole 11 is different from the other portion in image contrast (signal amount) and S.
/ N ratio becomes small. In this case, it is desirable that the S / N ratio does not decrease and is constant, but it depends on the signal amount and becomes smaller as the signal amount decreases.

FIG. 6 is a sectional view showing the state of charging that occurs when a sample of an insulator is scanned with a scanning electron microscope.

When the sample 5 is a semiconductor element, the insulator 13 is formed on the substrate 12, and the hole 1 is formed in the insulator 13.
1 is formed. When the surface of the sample 5 is irradiated with the primary electron beam 2 by the electron gun 1, the insulator 13 is negatively charged. Due to this charging, the electrons emitted to the deep portion of the hole 11 are confined inside and cannot go outside. Therefore, the signal amount is reduced and the contrast is reduced.

For example, in the case of inspecting a resist residue on the bottom of a contact hole in the manufacturing process of a semiconductor device, charge-up of an insulator occurs, the contrast and S / N ratio become small, and it becomes difficult to see the desired portion. .

In this case, if an attempt is made to obtain a sufficient S / N ratio in the low contrast portion, the high contrast portion will be irradiated with more electron beam than necessary, resulting in charge-up of the sample or the like. This will cause electron beam damage.

Therefore, an object of the present invention is to provide a technique capable of minimizing damage to a sample due to excessive electron beam irradiation and preventing a decrease in S / N ratio.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0016]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

That is, the sample is irradiated with a primary electron beam while being scanned by the scanning means, and secondary electrons, backscattered electrons and the like generated at that time are detected by the detector, and an image based on the image contrast is formed based on this detection signal. It is a scanning electron microscope for displaying or printing, and is provided with control means for changing the scanning speed of the primary electron beam according to the detection signal amount of the detector.

[0018]

According to the above-mentioned means, the scanning speed is increased for the bright portion of the detection signal (the portion having a large amount of signal) to reduce the electron beam irradiation amount, and conversely, the dark portion of the detection signal (the portion of the signal). For a portion where the amount is small), the scanning speed is slowed to increase the electron beam irradiation amount so that the bright portion of the detection signal is less likely to be charged. As a result, the S / N ratio becomes constant, and it becomes possible to easily observe a sample with a large contrast, which was difficult to observe due to halation in the past, and to minimize the damage of the sample due to excessive electron beam irradiation. It becomes possible to stop.

[0019]

1 is a block diagram showing an embodiment of a scanning electron microscope according to the present invention. Note that, in FIG. 1, the same reference numerals are used for the same components as those shown in FIG.

In this embodiment, an integrator 14 is connected to the amplifier 8, a scanning speed controller 15 is connected between the integrator 14 and the scanning coil 4, and calculation is performed between the integrator 14 and the display device 9. The feature is that the part 16 is connected.

The integrator 14 measures the time required for the signal amount to reach a certain constant value (hereinafter referred to as the integration time). This integration time is obtained by integrating so that it becomes longer when the hole 11 is dark and becomes shorter when the surface of the insulator 13 is bright. As a result, the bright / dark state of the irradiation portion of the primary electron beam 2 can be detected.

With respect to the integration time obtained by the integrator 14, the scanning speed controller 15 controls the scanning coil 4 to slow the scanning speed when the integration time is long and to increase the scanning speed when the integration time is short. By doing so, the signal amounts emitted from all the locations on the sample 5 can be made the same.

As a result, as shown in FIG. 2, the irradiation charge amount becomes lower in the portion having a lower image contrast, that is, in the portion of the insulator 13, and as shown in FIG. 3, the portion of the insulator 13 is less likely to be charged. Then, the electrons in the hole 11 jump out to the outside and can be detected by the detector 7. This makes it possible to obtain a sufficient contrast (= integration time) while keeping the S / N (square root of signal amount) ratio constant as shown in FIG.

As shown in FIG. 2, the shape of the contrast is opposite to the conventional one (the hole 11 is higher than the insulator 13). The contrast of the portion 11 is processed so as to be lower than that of the insulator 13, so that the image appearing on the screen of the display device 9 has the same appearance as the conventional one.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, in the above embodiment, the scanning speed is controlled according to the integration time of the integrator 14, but
The [irradiation time / pixel] by the electron gun 1 may be controlled.

In the above embodiment, the scan image is displayed on the display, but it may be printed by a printer.

[0028]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.
It is as follows.

That is, the sample is irradiated with the primary electron beam while being scanned by the scanning means, and secondary electrons, reflected electrons, etc. generated at that time are detected by the detector, and an image based on the image contrast is formed based on this detection signal. In the scanning electron microscope for displaying or printing, since the control means for changing the scanning speed of the primary electron beam according to the detection signal amount of the detector is provided, the S / N ratio becomes constant. In addition, it becomes possible to easily observe a sample having a large contrast, which has been difficult to observe due to halation in the past, and it is possible to minimize damage to the sample due to excessive electron beam irradiation.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing characteristics of contrast and irradiation charge amount by the scanning electron microscope of the present invention.

FIG. 3 is a cross-sectional view showing a charging state of a sample by irradiation with a primary electron beam according to the present invention.

FIG. 4 is a configuration diagram showing an example of a conventional scanning electron microscope.

FIG. 5 is an explanatory diagram showing characteristics of contrast and irradiation charge amount by a conventional scanning electron microscope.

FIG. 6 is a cross-sectional view showing a charging state of a sample by irradiation with a primary electron beam by a conventional scanning electron microscope.

[Explanation of symbols]

 1 Electron Gun 2 Primary Electron Beam 3 Case 4 Scanning Coil 5 Sample 6 Table 7 Detector 8 Amplifier 9 Display Device 10 Signal 11 Hole 12 Substrate 13 Insulator 14 Integrator 15 Scanning Speed Controller 16 Computing Unit

Claims (3)

[Claims] 1. A sample is irradiated with a primary electron beam while being scanned by a scanning means, secondary electrons and backscattered electrons generated at that time are detected by a detector, and an image based on image contrast is formed based on this detection signal. A scanning electron microscope for displaying or printing, characterized by comprising control means for changing the scanning speed of the primary electron beam according to the amount of detection signals of the detector. 2. The control means measures the time required for the signal amount to reach a certain constant value, and the scanning speed control which controls the scanning means based on the output signal of the integrating means. The scanning electron microscope according to claim 1, further comprising means. 3. The scanning electron microscope according to claim 2, further comprising arithmetic means for calculating the reciprocal of the integrated output of the integrating means, and displaying or printing based on the output.