JPH0215543A - Contour measuring method - Google Patents

Abstract

PURPOSE:To enable to obtain a height distribution with the secondary expansion of a sample by providing two detectors facing to each other including the sample between them and obtaining the inclining components of surface elements both in the line direction to connect both detectors and in the orthogonal line direction to said line direction within the horizontal surface so as to add and integrate both inclining components. CONSTITUTION:An electron beam 13 injected from an electron gun 12 of a SEM (scanning electron microscope) is injected into a sample 16 through a group of electron lenses 14, a secondary electron 17 is emitted from the sample 16, and the signals detected by means of left and right detectors 18, 19 are arithmetically processed by means of a computer 20; that is, the inclining component of a sample surface element in the line direction of connecting two detectors 18, 19 is obtained using a relational expression between this inclining component and both detecting signals. Using this result and the relational expression indicating that the sum of both detecting signals depends on the angle of the electron beam injecting direction to the normal line direction of the surface element, the inclining component of the surface element in the orthogonal line direction within the horizontal surface against the line direction, and the inclining components in both line directions are added and integrated. The height distribution with the secondary expansion of the sample is thus obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a surface shape measurement method using a scanning electron microscope, and particularly to a surface shape measurement method suitable for measuring the three-dimensional shape of microfabricated objects such as semiconductors, optical disks, and magnetic disks. Concerning a shape measurement method.

[Conventional technology]

Recently, attempts to reconstruct three-dimensional shapes based on image shading information have become popular, and an example of one using SEM (scanning electron microscope) is the Journal of Electron Microscopy of Ele
ctron Microscopy) Volume 34 (19
85), No. 4, pp. 328-337, Tadao Suganuma describes the measurement of surface shape using an SEM equipped with two secondary electron detectors.
aceTopography Using SEM w
ith Two Sec.

ndary E 1actron Detectors
)” was published.

This method detects secondary electrons emitted from the sample.
Two detectors are installed in the SEM, and the two detection signal values are
Utilizing the property that the difference in power is approximately proportional to the slope component of the surface element in the direction connecting the detectors, find the slope on the - line, that is, the differential value in the direction connecting the detectors, and use this as an end. By performing addition and integration from , the cross-sectional shape on the corresponding line is determined.

Specifically, the two left and right detection signal values are IL and I, respectively.
R, the left and right signal values of the flat part used as reference values are I+, , n, IRII, and the correction constant close to ■ is K, then the slope A of the surface element is expressed as follows. .

The slope A of this surface element can also be determined by calibrating in advance to a constant k that most faithfully represents the cross-sectional shape of the sample measured using a sample whose cross-sectional shape is known, as shown in the following equation (2). The standard value IL can be determined by
It can also be determined without using n and IRn.

The direction connecting the two detectors is the X axis, the direction perpendicular to this on the sample surface is the Y axis, and the height direction is the Z axis.
=Y, when scanning the line.

If the slope of point X=j is Aj, then the height Zj of point x=j
By using the fact that is expressed as Y=Y, the cross-sectional shape on the line is determined.

Furthermore, in JP-A-62-6112, an SEM is equipped with four detectors, and the relationship between the output of each detector and the normal direction is determined for a spherical standard sample surface, and then the measurement A method is described in which the normal direction of each point on the sample surface is determined by comparing the output of each detector obtained for the sample with the above relationship, and the three-dimensional shape of the sample is determined based on this normal information. There is.

[Problem to be solved by the invention]

In the former method of the conventional techniques described above, the inclination in the Y-axis direction is not determined. In order to obtain an altitude distribution with a two-dimensional spread, the above-mentioned processing on one line (YO line) is performed over several dozen lines, and a detailed bird map is displayed as viewed from an oblique direction. , but in that case, (3
) Formula 20 is a constant that is arbitrarily set for each line,
The relationship between the altitudes calculated on each line is not fixed.

For this reason, except for those that can be generally considered flat, 2
It was not possible to obtain the altitude distribution in dimensional extent.

In addition, the latter method of the prior art has a different problem to be solved from the present invention, which attempts to measure the surface shape with two detectors, in that the SEM is provided with at least four detectors. do.

An object of the present invention is to provide a surface profile measurement method that uses a SEM equipped with two detectors and can obtain a two-dimensionally spread altitude distribution of a sample from output signal values from these detectors. It's about doing.

[Means to solve the problem]

The above purpose is to make two
The slope component of the sample surface element in the direction of the line connecting the two detectors is calculated using the relational expression between this slope component and the rain detection signal.
Alternatively, find it using a table that summarizes the correspondence between the tilt component and the rain detection signal, and then calculate the angle between the electron beam incident direction and the normal direction of the surface element by the sum of this result and the rain detection signal. Using the relational expression that expresses the dependence of This is achieved by adding and integrating the slope components in both line directions, which are determined by , to determine the surface and shape of the sample.

[Operation] The output signal value of the left detector is IL, the output signal value of the right detector is IR, the direction connecting both detectors in the horizontal plane is the X axis, the direction perpendicular to this is the Y axis, and the height is The direction is the Z axis, and the sample surface is expressed as Z=f(X, Y).

It can be determined using the relational expression, equation (1) or equation (2), that holds true between the signal values IL and IR.

f Next, the slope □ in the Y direction can be found as follows. The sum of IL and In can be regarded as the sum of secondary electrons emitted from the sample, excluding detection loss and the like. It can be written as a unit vector representing the direction of incidence of the electron beam.

V=(0,0,1) here, So, The formula is: Write it like an expression Ru.

Specifically, the arc cosine law is known as a functional form of g. That is, the signal intensity at the flat part on the sample is I.

The result is the following form.

Than this.

It can be solved as follows. The plus and minus signs on the left side of equation (7) can be uniquely determined by determining whether the direction is up or down in the Y direction. For this purpose, it can also be obtained from the formula as follows. When formula (6) is differentiated with respect to X, the following formula is obtained.

XaY can get.

■.

■. Since is an observable quantity, Z of each line, which could not be obtained with conventional technology, can be obtained by integrating the equation. It becomes possible to find the relationship between Z of each line. To more easily obtain the relationship between
The average height difference between adjacent lines may be used.

By using these and performing addition and integration in a certain two-dimensional spread, the altitude distribution in the two-dimensional spread can be obtained.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 2 is a hardware configuration diagram in which two secondary electron detectors are attached to a SEM, for explaining one embodiment of the present invention. An electron beam 13 emitted from an electron gun 12 of a mirror body 11 is converged and deflected by an electron lens system 14, and is incident on a sample 16 on a sample stage 15. Correspondingly, secondary electrons 17 are emitted from the sample 16, and the left detector 1
8. Detected by the right detector 19. The detected signals are processed by the computer 20 operated by instructions from the keyboard 21, and the processed results are displayed on the display 22 together with the detector output signal as required.

FIG. 1 is a flowchart of arithmetic processing in the above embodiment. In processing step 31, the detection signal value IL of the left detector 18 and the detection signal value IR of the right detector 19 are input. In step 32, calculations are made using these aforementioned equations or equations.

In the example shown in FIG. The formula is used.

This X Good luck.

Also ask by searching this It is possible.

The value obtained by a measurement.

(at the flat part of the sample) Calculate.

In the example The formula is used.

next ZIJ can be calculated using the formula.

In step 35, The results, contour line display, bird drawing Display using display etc.

FIG. 3 shows an example of the bird's-eye map display result, and FIG. 4 shows an example of the contour line display result.

〔Effect of the invention〕

According to the present invention, a scanning electron microscope equipped with two detectors has the advantage of being able to obtain a two-dimensionally spread altitude distribution of a sample.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of signal processing according to the present invention, FIG. 2 is a hardware configuration diagram of an example of a JA device implementing the present invention, and FIG. 3 is a diagram showing an example of a bird crossing obtained by the present invention. FIG. 4 is a diagram similarly showing an example of a contour map. Explanation of symbols 11...Mirror body 12...Electron gun 13.
...Electron beam 14...Electron lens system 15.
... Sample stand 16... Sample 17... Secondary electron 18... Left detector 19... Right detector 20... Computer 21... Keyboard 22... Display 31-35.・Processing step

Claims (1)

[Claims] 1. In a method of measuring the surface shape using a scanning electron microscope that scans the sample with an electron beam, detects the emitted secondary electrons, and displays an image with a density corresponding to the detected signal amount,
Two detectors facing each other across the sample are provided, and the slope component of the sample surface element in the line direction connecting both detectors is calculated using the relational expression between the slope component and both detection signal values, or,
It is determined using a table that summarizes the correspondence between the tilt component and both detection signal values, and this result and the sum of both detection signal values depend on the angle that the electron beam incident direction makes with the normal direction of the surface element. Using the relational expression that expresses that A method for measuring a surface shape, characterized in that the surface shape of a sample is determined by adding and integrating the slope components in both of the line directions.