JPS58194237A - Scanning type electron microscope - Google Patents

Abstract

PURPOSE:To secure a uniform image on the same condition, by cutting a secondary electron signal into two separate portions, low frequency and high frequency, while installing a signal correction device regulating the high frequency portion according to the magnitude of the low frequency portion and thereby forming the image with the corrected signal. CONSTITUTION:A signal correction device 4 for turning a detection secondary electron signal S2 into a correction secondary electron signal S3 for correction is installed in addition. This correction device 4 is fitted with a low-pass filter 42 which passes only a delay circuit 41 having the signal S2 delayed for the specified time long and a low frequency constitutent and calculates a difference between a delay signal S41 and a low frequency signal S42 with a differential amplification circuit 43. On the other hand, also it calculates a difference between a reference level signal S45 of the specified voltage value and the low frequency signal S42 with a differential amplifier 46, then amplifies a high frequency signal S43 with an amplifier 44 in accordance with a gain correction signal S46 out of this differential amplifier 46 and transmits the correction secondary electron signal S3 to a display unit 3. With this, a uniform image can be secured by using the secondary electron signal uninfluenced by any external cause.

Description

[Detailed description of the invention] fil Technical field of invention The present invention relates to a signal processing device for a scanning electronic mirror mirror.

(2) Background of the technology Scanning electron micro-defect (hereinafter referred to as SEM) is used for surface inspection of objects, compositional analysis of objects, and electron beam groping for measuring the characteristics of semiconductor devices. .

In such applications of SEM, improvements in resolution, reliability of obtained signals, etc. are required.

(3) Conventional technology and problems FIG. 1 shows a schematic configuration of a conventional SEM.

In SEMI, a high-voltage power source is applied to an electron gun to generate an electron beam, the electron beam is focused by an electron lens, and a sample on a stage is irradiated with the focused electron beam. At this time, the secondary electrons generated from the sample surface are
The detected secondary electron signal S2 is obtained by converting it into an electrical signal using a detector composed of a photomultiplier tube. This detected secondary electron signal S2 has the property of changing in response to changes in the unevenness, composition, or potential of the sample surface.

The detected secondary electron signal S2 is converted into a deflection signal S from the XY deflection signal generator 2 that controls the scanning of the sample surface by the electron beam.
By applying the voltage to the observation surface water device 3 that operates in synchronization with 1, unevenness and unevenness are created on the screen of the display device 3 such as a cathode ray tube.
Images showing changes in composition or potential can be obtained.3 However, the conventional SEM described above has problems with the overall light weight due to fluctuations in the electron beam, movement of the stage on which the sample is placed, and fluctuations in the arm and arm conditions. There is a problem in that, due to a significant decrease or partial unevenness in the amount of light, the entire image on one screen may be different from other cases under the same conditions, or unevenness may occur partially on one screen.

The fact that a uniform image cannot be obtained under the same conditions causes a secondary problem in that the observer misjudges or deteriorates the observation ability.

(4) Purpose of the Invention The purpose of the present invention is to remove noise components from a secondary electronic signal on which noise components due to external causes such as fluctuations in an electron beam are superimposed, and to perform correction based on the noise components. An object of the present invention is to provide a scanning electron microscope device that forms an image using a secondary electron signal that is not dependent on secondary electron signals.

(5) Structure of the Invention In the present invention, in a scanning electron microscope device that irradiates an electron beam onto a sample, detects the emitted secondary electrons, and forms an image using the detected secondary electrons No. 18, Separates the secondary electron signal into a low frequency component signal and a high frequency component signala
t. A signal correction device is provided to adjust the magnitude of the high frequency component signal according to the magnitude of the low frequency component signal, and an image is formed using the secondary electronic signal corrected by the signal compensation device. There is provided a scanning electron microscope device characterized by the following.

(6) Embodiment of the Invention FIG. 2 shows a scanning electronic microscopic sewing device as an embodiment of the invention. Compared to the apparatus shown in FIG. 1, the apparatus shown in FIG. 2 is further provided with a signal correction device 4 for correcting the detected secondary electron signal S2 into a corrected secondary electron signal S3.

An embodiment of the circuit diagram of the signal correction device 4 is shown in FIG. The signal correction device 4 includes a delay circuit 41 that delays the detected secondary electronic signal S2 received from the SEM 1 by a predetermined time, and blocks the high frequency components of the detected secondary electronic signal S2 from passing through and allows only the low frequency components to pass. Loaf 4 filter 42 as a low frequency component extraction circuit, and a differential amplifier as a high frequency component extraction circuit that calculates the difference between the delayed secondary electronic signal 841 from the delay circuit 41 and the low frequency component signal 842 from the low pass filter 42. 43, reference level signal 84 with a predetermined voltage value
Reference signal generation circuit 45 that generates 5, low frequency component value 0
The differential amplifier 46 calculates the difference between s42 and the reference level signal 842, and the high frequency component signal 843 from the differential amplifier 43 is amplified based on the gain correction signal 846 from the differential amplifier 46 and sent to the display device 3 for correction secondary It consists of an amplifier 44 that sends out an electronic signal S3.

Next, the operation of the apparatus shown in FIG. 3 will be described with reference to FIGS.

The detected secondary electronic signal 81 illustrated in FIG. Even if the amplitude of the electronic signal has no low frequency components, the PI.

P2. P3. A case where there is a difference as shown in P4 is shown.

Such a detected secondary electron signal S1 is passed through the low-pass filter 4.
2, as shown in FIG. 4 (6).

A low frequency component signal S42 containing only low frequency components is obtained. The detected secondary electronic signal S1 is also delayed by the delay circuit 41 so as to match the passage time of the low/arm filter 42.

Therefore, as the output of the differential amplifier 43, a signal 843 containing only high frequency components is obtained by subtracting the signal S41 of FIG. 4-) from the signal S2 of FIG. 4-).

Amplitudes P1', P2', and P3' of the high frequency component signal 843.

, P4' is not uniform as in this example,
It is also possible to amplify f343 and use it in the display device 3 as the corrected secondary electron signal S3.

However, in this embodiment, as shown in FIG. 4(C), P1' should originally have the same amplitude.

P2', P3', and P4' are still affected, and the status of S43 does not indicate the original state of secondary electron generation. Therefore, it is necessary to correct the signal 843, and this is done as follows.

The aforementioned low frequency component signal 842 and the reference level signal 845 from the reference signal generation circuit 45 are compared by the differential amplifier 46 to obtain a gain correction signal S46, as shown in FIG. 4(b).

The amplifier 44 receives the r-in correction signal 846 and changes the amplification gain of the signal S.43 in accordance with the gain correction signal.

In other words, when 846 is positive, the gain decreases from the standard gain, and when 846 is negative, the gain becomes larger than the standard gain, and the amount of change in these gains is the absolute value of 846. K has become dependent on me. On the other hand, if the amplitudes are originally the same, the amplitudes of the corrected secondary electron signals S3 will be the same amplitude P1'', as shown in FIG. 4(a).
P2'.

P3' and P4'' are corrected.

The image on the display device 3 obtained using the nine-corrected secondary electron signal S3 obtained above is uniform and free of unevenness. Therefore, even if the detected secondary electron signal s2 contains fluctuations in relatively low frequency components, changes in amplitude, etc. due to some reason, a signal equivalent to the secondary electron signal in a normal state can be obtained, and observation errors can be reduced. Can be removed.

In the above explanation, for clarity,
We have described the cases of amplitudes PI', P2', P3'', and P4'', but these signals are unique depending on the shape of the object's surface, the composition of the object, etc., and each signal is as described above. The corrected image is formed on the display device 3.

The reference level signal 845 can be adjusted to an appropriate voltage level from the reference signal generating circuit 45, and a gain correction signal 846 of an appropriate magnitude can be obtained. This allows adjustment of the entire image.

In carrying out the present invention, various modifications can be made in addition to those described above. For example, in the embodiment of FIG.
Although the delay circuit 41 and the differential amplifier circuit 43 are used as the high frequency component extraction circuit for extracting the secondary electronic signal of the high frequency component, these may be replaced with a noise/bus filter.

(7) Effects of the Invention According to the present invention, noise components are removed from a secondary electronic signal on which noise components due to external causes such as fluctuations in the electron beam are superimposed, and correction is performed based on the noise components. A scanning electron microscope device is provided that can form images using secondary electron signals that are not dependent on secondary electron signals.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional scanning electron microscope device, FIG. 2 is a schematic diagram of a scanning electron microscope device as an embodiment of the present invention, and FIG. 3 is a diagram of a signal correction device in FIG. A circuit diagram as an example, Fig. 4-) to (ω is a sign characteristic diagram in the device shown in Fig. 3. (Explanation of the signs) 1... Electron microscope, 2... Deflection signal generator, 3・
. . . Display device, 4 . Circuit, 46...Differential amplifier. Patent applicant Fujitsu Limited Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Uchida, Yukio Patent attorney Akira Yamaguchi Figure 4 (d) 53

Claims (1)

[Claims] 1. In a scanning electron microscope device that irradiates a sample with an electron beam, detects the emitted secondary electrons, and forms an image using the detected secondary electron signal, the secondary electron signal is converted into a low frequency component signal. A signal correction device that separates the nuclear high frequency component signal into high frequency component signals and adjusts the magnitude of the nuclear high frequency component signal according to the magnitude of the low frequency component signal is provided, and an image is created using the secondary electron signal corrected by the signal compensation device. A scanning electron microscope device whose special purpose was to enable the formation of