JPS60140642A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To obtain an extreme-magnification wide-visual field reflection electron image with uniform brightness by providing a means to compensate a change of the average level of output signals due to the scanning of electron rays. CONSTITUTION:A magnification control signal directing the magnification variable circuit 4, and a scanning signal from a scanning signal generating circuit 3 is fed to a deflection coil 2 after being converted into a large-amplitude signal. An arithmetic circuit 5 generates an output by adding output signals of all detection elements Dmn. At the same time, the control signal from the control section 6 is also fed to a switching circuit 9, which is made a conductive state, and the correction signal from a correction signal generating circuit 8 is fed to an intensity correcting circuit 7. The correction signal generating circuit 8 generates a correction signal compensating a decrease of the average level of the outputs of an adding circuit due to a decrease of the solid angle based on the scanning signal from the scanning signal generating circuit 3. Accordingly, an extreme-magnification wide-visual field reflection electron image with uniform brightness can be displayed on a CRT10.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scanning electron microscope equipped with a backscattered electron detector consisting of a plurality of detection elements arranged two-dimensionally.

Backscattered electron images of a sample are obtained by detecting the backscattered electrons generated when the sample is irradiated with an electron beam, but recently, it has become possible to obtain both high-resolution, high-magnification images and ultra-low-magnification wide-field images of the sample. Demand for scanning electron microscopes capable of co-observation has increased. In order to meet these demands, multiple backscattered electron detection elements are arranged two-dimensionally near the sample to form a large reflection detector. By narrowing the area and extracting only the output signals from some of the detection elements, it is possible to detect backscattered electrons that deviate significantly from the direction that forms the relationship between the sample surface and the mirror surface, which causes a reduction in resolution. In addition, when trying to obtain a very low magnification wide field of view, in order to detect a sufficient amount of backscattered electrons and obtain an image with less uneven brightness, it is necessary to use a signal based on the sum of the output signals of all detection elements. to obtain a sample image. However, when horizontally scanning the electron beam FB in the direction of arrow 1'' in Fig. 1 to obtain an extremely low magnification wide-field image of the sample S, the position of the backscattered electron generation point, that is, the irradiation point of the electron beam on the sample, is P+, P2,
P3, the solid angles from the backscattered electron generation point to the detection surface of the backscattered electron detector are φ1, φ2, . It becomes φ3,
It will change. Therefore, in the conventional device, the obtained extremely low magnification wide-field image is dark because the solid angle is small near the 23rd point, and the solid angle is large near the 11th point, as shown in Figure 2. As the amount of electrons incident on the detection element increased, it became brighter, and there was still unaccountable unevenness in brightness.

The present invention aims to solve these conventional drawbacks and provide a scanning electron microscope that can obtain not only high-resolution, high-magnification images, but also very low-magnification, wide-field backscattered electron images with uniform brightness. There is.

The present invention consists of a means for two-dimensionally scanning an electron beam on a sample, and a plurality of two-dimensionally arranged detection elements for detecting backscattered electrons scattered from the sample by irradiation with the electron beam. A detector, a magnification switching means for switching the observation magnification by changing the size of the scanning area of the electron beam on the sample, and a number of detection elements used in conjunction with the magnification switching by the magnification switching means. In an apparatus comprising means for switching, and means for displaying a sample image based on an output signal of the backscattered electron detection element that is scanned in synchronization with the electron beam, It is characterized in that it includes means for compensating for changes in the average level.

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 3 is for showing one embodiment of the present invention, and in the figure 1
is an objective lens, and the electron beam EB focused by this objective lens 1 is irradiated onto the sample S. 2 is electron beam E
This deflection coil 2 is supplied with a sawtooth scanning signal as shown in FIG. 4(a) from a scanning signal generating circuit 3 via a variable magnification circuit 4. D is a large number of backscattered electron detection elements D arranged two-dimensionally.
IIIn (m= 1. 2. 3. 4. n= 1.
2. 3) is a backscattered electron detector consisting of: The output signal from each backscattered electron detection element Dm11 is amplified by a corresponding amplifier, A, mn, and then subjected to arithmetic processing such as signal selection or addition in an arithmetic circuit 5. In this arithmetic circuit 5, the output signals from which detection elements are to be added are determined based on a control signal from the control section 6.

Further, a magnification control signal is supplied from the control section 6 to the variable magnification circuit 4, and the observation magnification is controlled. The output signal of the arithmetic circuit 5 is supplied to a brightness correction circuit 7. Reference numeral 8 denotes a correction signal generation circuit, to which the output signal from the scanning signal generation circuit 3 is supplied, the correction signal generation circuit 8 generates a signal based on the output signal from the scanning signal generation circuit 3. A correction signal as shown in FIG. 4(C) is created. This correction signal is supplied to the brightness correction circuit 7 via the switch circuit 9, and is added to the output signal from the arithmetic circuit 5 in the brightness correction circuit 7. The output signal from the brightness correction circuit 7 is supplied to the grid G of the cathode ray tube 10. A scanning signal is supplied to the deflection coil C of the cathode ray tube 10 from the scanning signal generating circuit 3.

In such a configuration, first, when attempting to observe a high-resolution, high-magnification image of the sample S, a magnification control signal for setting the magnification to a specific high magnification is supplied from the control unit 6 to the variable magnification circuit 4. Ru. As a result, the horizontal scanning signal and sawtooth vertical scanning signal as shown in FIG. 4(a) are converted into small amplitude signals and then supplied to the deflection coil 2. Therefore, an extremely narrow area of the sample S is two-dimensionally scanned by the electron beam EB, and the reflected electrons generated at this time are incident on the detector D and detected. At this time, an arithmetic control signal is supplied from the control section 6 to the arithmetic circuit 5, and the arithmetic circuit 5 is configured to take out, for example, only the output signal from the central detection element D23. Further, the control signal from the control section 6 is supplied to the switch circuit 9, and the switch circuit 9 is brought into a non-conducting state. Therefore, the output signal from the detection element [ ) 23 from the arithmetic circuit 5 passes through the brightness correction circuit 7 as it is and is supplied to the cathode ray tube 10 . The IC displays a high-resolution, high-magnification image on the cathode ray tube 10. Next, when attempting to observe a wide field of view with very low magnification of the sample S, a magnification control signal instructing low magnification is supplied from the control unit 6 to the variable magnification circuit 4, and a fourth A scanning signal as shown in FIG. 3(a) is converted into a large amplitude signal in the variable magnification circuit 4 and then supplied to the deflection coil 2. At this time, a control signal is supplied from the control section 6 to the arithmetic circuit 5, and as a result,
The arithmetic circuit 5 adds the output signals of all the detection elements Dmn and outputs the sum. Therefore, the arithmetic circuit 5 obtains a video signal whose average level decreases with horizontal scanning as shown in FIG. 4(b). At the same time, the control signal from the control section 6 is also supplied to the switch circuit 9, so that the switch circuit 9 is rendered conductive so that the correction signal from the correction signal generation circuit 8 is supplied to the brightness correction circuit 7. The correction signal generation circuit 3 generates a correction signal as shown in FIG. 4(C) based on the scanning signal from the scanning signal generation circuit 3. Therefore, the signal g from the arithmetic circuit 5 as shown in FIG. After being corrected, it is supplied to the cathode ray tube 10. Therefore, the cathode ray tube 10 displays an extremely low magnification wide-field backscattered electron image without uneven brightness.

In the above-described embodiment, the reduction in the average level of the output of the adder circuit due to the reduction in the solid angle is corrected, but the amplification factor of the amplifier that amplifies the output signal of the adder circuit is adjusted to the output of the correction signal generation circuit. It may be changed based on the signal.

As mentioned above, in the scanning electron microscope of the present invention,
The signal obtained by adding each detection element is corrected according to the change in the position where the backscattered electrons are generated, and the change in the average level of the signal due to the change in position is compensated for, so there is no unevenness in brightness. It is possible to display ultra-low magnification wide-field backscattered electron images.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams for explaining the drawbacks of conventional scanning electron microscopes, Figure 3 is a diagram for showing an embodiment of the present invention, and Figure 4 is the same as that shown in Figure 2. Each circuit element j of one embodiment,
FIG. 3 is a diagram for illustrating another output signal. EB: Electron beam, S: Sample, D: Detector, 1: Objective lens, 2: Deflection coil, 3: Scanning signal generation circuit, 4: 18 rate variable circuit, 5: Arithmetic circuit, 6: Control unit, 7: Brightness correction circuit, 8: Correction signal generation circuit, 9: Switch circuit, [)
mn: detection element, :Amn: amplifier. Patent applicant JEOL Ltd. Representative Ito-husband Figure 4

Claims (3)

[Claims] (1) Backscattered electrons consisting of a means for two-dimensionally scanning an electron beam over a sample, and a plurality of two-dimensionally arranged detection elements for detecting backscattered electrons scattered from the sample by irradiation with the electron beam. A detector, a magnification switching means for switching the observation magnification by changing the size of the scanning area of the electron beam on the sample, and a number of detection elements used in conjunction with the magnification switching by the magnification switching means. In an apparatus comprising means for switching, and means for displaying a sample image based on an output signal of the backscattered electron detection element that is scanned in synchronization with the electron beam, A scanning electron microscope characterized in that it is equipped with means for compensating for changes in average level. (2) The means for compensating for changes in the average level of the output signal due to scanning of the electron beam includes a circuit for generating a correction signal based on the signal for scanning the electron beam;
A scanning electron microscope according to claim 1, further comprising a circuit for changing the level or amplification gain of the output signal based on a correction signal from the circuit. (3) A patent comprising means for switching the operating state of the means for compensating for changes in the average level of the output signal due to scanning of the electron beam in conjunction with switching the number of detection elements used. A scanning electron microscope according to claim 1).