JPH02174047A - Scanning type electron microscope - Google Patents

Abstract

PURPOSE:To detect only reflected electrons occurring near the surface of a sample and obtain a reflected electron image emphasized with the information near the surface by decreasing the extraction angles of detectors to the preset angle or below. CONSTITUTION:A finely squeezed electron beam 3 is fed into a sample 4 through the surface of the sample 4, and reflected electrons 5a and 5b are generated. Detectors 1a and 1b are arranged at symmetrical positions with respect to the incident electron beam 3, their extraction angles 2a and 2b are set to 5 deg. or below with the same magnitude. Signals obtained by the detectors 1a and 1b contain the composition information and the irregularity information and are divided into the composition information and the irregularity information when electrically added or subtracted, and they are intensity-modulated and displayed on a CRT synchronously with the electron beam. The composition image and irregularity image sensitive to the surface structure are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a scanning electron microscope, and more particularly, to a scanning electron microscope particularly intended for observing the fine structure of a surface.

[Prior art] When it is desired to observe the fine structure of the surface with particular emphasis using a conventional scanning electron microscope (hereinafter referred to as SEM), the accelerating voltage of the electron beam is lowered to prevent the electrons from penetrating into the sample. By setting conditions where the depth was shallower, more electrons were emitted from areas closer to the surface, and this was detected and observed. There is also a method of observing only surface information by reducing the angle between the sample surface and the axis through which the detector views the sample surface (hereinafter referred to as the take-out angle).

[Problem to be solved by the invention] Of the electrons detected by the SEM, reflected electrons are electrons with relatively high energy among the electrons emitted from the sample, and the incident electrons are scattered and reflected by the sample surface. The depth of generation is approximately 10 nm from the surface, although it depends on the accelerating voltage of the incident electrons.

Changing the accelerating voltage of the electron beam changes the penetration depth of the electron beam; when the accelerating voltage is high, there is a lot of reflected electron information from deep parts, and conversely, when the accelerating voltage is low, there is a lot of information closer to the surface. As a result, an image sensitive to surface microstructure is obtained.

When incoming electrons are incident perpendicularly to the sample surface, the ratio of reflected electron intensity to incident electron intensity has a corresponding relationship with the atomic number of the sample, and as the atomic number increases, this ratio also increases.

In this way, information on the composition of the sample can be obtained from information on the ratio of reflected electron intensity obtained from the sample.

On the other hand, when the backscattered electron detector is placed in a direction inclined to the incident electron beam, the intensity of the backscattered electrons increases if the sample surface is tilted toward the detector, and decreases if the sample surface is tilted in the opposite direction. This allows us to understand the geometrical unevenness of the sample surface. If two backscattered electron detectors are installed symmetrically to the incident electron beam and electrical signals from the left and right detectors are electrically added or subtracted, composition information can be obtained from the left and right detectors. The incoming signal has the same magnitude and polarity, whereas the information on unevenness has the opposite polarity even if the absolute value of the signal is the same. Therefore, in this way, composition information and unevenness information can be detected separately from reflected electrons.

This is widely used as a method for observing surface composition and irregularities.

However, since the backscattered electrons have a certain generation depth, information regarding these compositions or irregularities can only be obtained at a certain depth. Therefore, when it is desired to observe the fine structure of the surface with particular emphasis, even if the accelerating voltage is lowered as described above, the detection of information on the surface structure cannot be said to be sufficiently emphasized.

The present invention has been made in order to solve the conventional problems as described above, and aims to provide a scanning electron microscope that can effectively detect only the reflected electrons generated on the very surface of a sample. purpose.

[Means for Solving the Problems] The present invention includes a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a finely focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, and a means for scanning a sample surface with a narrowly focused electron beam, In a scanning electron microscope, the two detectors are equipped with two detectors for detecting backscattered electrons, and means for modulating the brightness of the detected backscattered electrons and displaying them on a CRT. This is a scanning electron microscope characterized in that each of the microscopes is disposed at a position where the angle between the axis from which the sample is viewed and the surface of the sample is 5 degrees or less.

[Function] The gist of the present invention is to detect only the backscattered electrons generated on the very surface of the sample by reducing the take-off angle of the detector to a predetermined angle or less, thereby emphasizing information on the surface. The objective is to obtain a backscattered electron image.

With reference to FIG. 2, a qualitative explanation will be given of the effect of increasing the detection sensitivity of the surface.

In FIG. 2, it is considered that by irradiating the sample surface with the electron beam 3, backscattered electrons reflected from a portion up to several depths are generated equidirectionally in all directions. Among these, AO occurs on the very surface and is almost parallel to the surface.
The reflected electrons traveling in the D direction are detected by the detector 1. However, the reflected electrons generated at A1 and traveling in the A+D direction have a long distance to reach the sample surface, lose energy in the process, and have a high probability of being absorbed by the sample. Therefore, by reducing the extraction angle 2, only the foul electrons generated on the very surface can be effectively detected by the detector. In addition, in the figure, Zm is the electron beam penetration depth, and
is the depth of the backscattered electron generation region.

When the extraction angle 2 is θ, the distance β that the reflected electrons generated at the depth X travel to reach the surface is [=x/sin θ. here! If ≧1, X≦0.1, then θ≦5
．． It becomes 7°.

If the distance from the backscattered electron generation position to the sample surface is one period or more, the backscattered electrons lose energy and are absorbed by the sample, and if the depth is 0.1 #l or less, it is sufficient to be considered surface information. From this, it can be seen that when the extraction angle is 5° or less, information in which reflected electrons on the very surface are emphasized is increased by one.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of a scanning electron microscope according to the present invention. A finely focused electron beam 3 generated from an electron gun (not shown) enters the sample from the surface of the sample 4 and generates reflected electrons 5a and 5b. The detectors 1a and 1b are arranged at symmetrical positions with respect to the incident electron beam 3, and their extraction angles 2a and 2b have the same magnitude and are less than 5 degrees.

The signals q'd by the detectors 1a and 1b include composition information and unevenness information, and are separated into composition information and unevenness information by electrical addition or subtraction. Then synchronize with the electron beam and C
By displaying on RT, a composition image and an uneven image sensitive to the surface structure were obtained.

[Effects of the Invention] As explained above, the present invention has a mechanism that effectively detects only the backscattered electrons generated on the very surface of the sample, so information that more reliably reflects the surface microstructure can be obtained. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram qualitatively showing the principle of the present invention. 1, la, lb...detector 2, 2a, 2b...extraction angle 3...electron beam 4...sample 5a, 5b...backscattered electron 7m...electron beam penetration depth ...Depth of backscattered electron generation area

Claims (1)

[Claims] (1) A means for scanning the sample surface with a narrowly focused electron beam, and two detectors arranged symmetrically with respect to the axis of incidence of the electron beam on the sample surface to detect reflected electrons emitted from the sample. In a scanning electron microscope equipped with a means for modulating the brightness of the detected backscattered electrons and displaying them on a CRT, the two detectors are configured to measure the angle between the axis of the sample surface and the sample surface. A scanning electron microscope characterized in that both are arranged at positions where the angle is 5° or less.