JP3664872B2 - Scanning electron microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention has been to prevent the influence of vibration caused by sound, about the scanning electron microscope.
[0002]
[Prior art]
In scanning electron microscopes, higher resolution has progressed, and it has become important to reduce image blur due to external vibration. Therefore, for example, vibration isolation technology that absorbs mechanical vibration from the floor on which the electron microscope is installed, or vibration that detects this vibration and cancels the vibration is positively applied to the main body of the electron microscope. active control system for removing the effects have been developed.
[0003]
[Problems to be solved by the invention]
In addition to the mechanical vibration described above, the scanning electron microscope is also vibrated by noise, which affects the image and hinders high-resolution image observation, or restricts the observable magnification. In order to eliminate the influence of the noise on the image, the scanning electron microscope or the like is covered with an acoustic shielding box so that the noise does not enter the box.
[0004]
The acoustic shielding box can easily cope with the sound of high frequency components, but the acoustic phase becomes longer as the frequency becomes lower. Therefore, the thickness of the acoustic shielding box must be increased and heavier. Therefore, depending on the noise component, the acoustic shielding box becomes large and heavy, which is problematic in terms of the size of the installation location and load resistance. Further, since the lens barrel is put in the box, the operability of the apparatus is also deteriorated.
[0005]
The present invention has such has been made in view, an object of, without a sound insulating box, to achieve effectively can be reduced scanning electron microscope of the noise on the image by the acoustic is there.
[0006]
[Means for Solving the Problems]
For example, when noise (sound) is applied to the scanning electron microscope, noise appears on the observation screen. There are the following two main factors that cause noise on the screen. First, the case where the noise is loud regardless of the acoustic frequency. The second is a sound having a frequency that matches the natural frequency of the scanning electron microscope itself, and noise is further enhanced by this sound.
[0007]
When the first and second factors were compared, it was confirmed that the influence appears on the image at a lower sound pressure in the case of the second factor than the first factor. FIG. 1 shows an example of the relationship between the acoustic frequency and the amount of noise. The horizontal axis represents the acoustic frequency and the vertical axis represents the noise amount. As for the amount of noise, peaks A, B, and C appear at the natural frequencies a, b, and c of the scanning electron microscope. For this reason, the influence of vibration due to noise can be significantly reduced by effectively reducing the second factor.
[0008]
Therefore, the scanning electron microscope based on the invention of claim 1, a thin focused electron beam over the specimen two-dimensionally scanned, the image based on the obtained signal with the scanning of the electron beam on the sample the scanning electron microscope so as to display, measuring means for measuring the sound pressure frequency of the natural frequency of the scanning electron microscope main body portion disposed in a position close to the scanning electron microscope, the sound pressure measured by the measuring means and conversion means for converting the amount of noise in the image, the reverse phase signal of the converted amount of noise signals, and a circuit to create for the natural frequency of the frequency of the scanning electron microscope, from the circuit The present invention is characterized in that the amount of noise on the image is reduced on the basis of the signal having the opposite phase.
[0009]
According to the first aspect of the present invention, the sound pressure of the natural frequency of the scanning electron microscope is measured, the measured sound pressure is converted into the amount of noise in the image, and the signal having the opposite phase of the converted signal of noise amount To reduce the amount of noise on the image.
[0010]
Scanning electron microscope based on the invention of claim 2 is the invention of claim 1, that based on an inverse phase of the signal noise of the signal, to correct the scanning signal of an electron beam, to reduce noise in the image It is characterized by.
[0011]
Scanning electron microscope based on the invention of claim 3 is the invention of claim 1, based on an inverse phase of the signal noise of the signal, to generate a sound, it is characterized by reducing the noise in the image .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 shows a scanning electron microscope to which the present invention is applied. In FIG. 1, reference numeral 1 denotes an electron gun. An electron beam EB generated from the electron gun 1 and accelerated is finely focused on the sample 4 by the condenser lens 2 and the objective lens 3.
[0013]
Further, the electron beam EB is scanned in the X and Y directions by the deflection coil 5. A scanning signal is supplied from the X direction scanning circuit 6 to the X scanning coil of the deflection coil 5, and a scanning signal is supplied from the Y direction scanning circuit 7 to the Y scanning coil of the deflection coil 5. The X direction scanning circuit 6 and the Y direction scanning circuit 7 are controlled by a scanning control circuit 8.
[0014]
Secondary electrons generated from the sample by irradiation of the sample 4 with the electron beam EB are detected by the secondary electron detector 9. The detection signal of the secondary electron detector 9 is amplified by the amplifier 10 and then supplied to the cathode ray tube 11.
[0015]
Reference numeral 12 denotes an acoustic measurement unit including a microphone, and the sound pressure value measured by the acoustic measurement unit 12 is stored in the sound pressure memory 13. The value stored in the sound pressure memory 13 is supplied to the arithmetic circuit 14 and converted into an influence degree (noise amount) on the image with respect to the sound pressure of each frequency.
[0016]
The noise amount obtained by the arithmetic circuit 14 is supplied to the correction signal adjustment circuit 15, and a correction signal supplied to the X direction scanning circuit 6 and the Y direction device circuit 7 is created. The operation of such a configuration will be described next.
[0017]
When observing a scanning electron microscope image, the electron beam from the electron gun 1 is finely focused on the sample 4 by the condenser lens 2 and the objective lens 3, and the X scanning circuit is set at the scanning speed and magnification set by the scanning control circuit 8. 6 and a Y scanning circuit 7 supply a scanning signal to the deflection coil 5. As a result, a predetermined area on the sample is two-dimensionally scanned by the electron beam EB.
[0018]
Secondary electrons generated from the sample by irradiation of the sample 4 with the electron beam EB are detected by the secondary electron detector 9. The detection signal of the secondary electron detector 9 is amplified by the amplifier 10 and then supplied to the cathode ray tube 11 synchronized with the scanning signal, so that a scanning image of the sample is displayed on the cathode ray tube 11.
[0019]
Next, an operation for reducing the influence of noise will be described. First, at the place where the scanning electron microscope is installed, the sound pressure measurement unit 12 measures the sound pressure of the sound having a frequency corresponding to the natural frequency of the scanning electron microscope. The measured sound pressure is stored in the sound pressure memory 13.
[0020]
The sound pressure value stored in the memory 13 is supplied to the arithmetic circuit 14. The arithmetic circuit 14 converts the measured sound pressure at each frequency into an influence degree (noise amount) on the image. 3 shows the relationship between the sound pressure and the amount of noise. FIG. 3 (a) shows the relationship with the peak A at the frequency a in FIG. 1, and FIG. 3 (b) shows the relationship with the peak B at the frequency b in FIG. FIG. 3C shows the relationship with respect to the peak C at the frequency c in FIG.
[0021]
The noise amount converted by the arithmetic circuit 14 is supplied to the correction signal adjustment circuit 15. The correction signal adjustment circuit 15 creates a signal in which the phase of the frequency is reversed with respect to the converted noise amount signal, and supplies the signal to the X direction scanning circuit 6 and the Y direction scanning circuit 7. Note that it is desirable to correct the phase difference with a volume (CPU control) that shifts the phase before applying a signal to each scanning circuit. As a result, the phase of the frequency to be added is corrected on the observed image so that the noise of the image is minimized.
[0022]
Such generation of the correction signal and adjustment of the phase difference are performed for each frequency of each natural frequency of the scanning electron microscope. As a result, the image displayed on the cathode ray tube 11 is one in which noise due to noise is remarkably reduced.
[0023]
FIG. 4 shows another embodiment of the present invention. The same or similar components as those in the scanning electron microscope of FIG. In this embodiment, the first speaker 18 connected to the X direction acoustic drive circuit 17 and the second speaker 20 connected to the Y direction acoustic drive circuit 19 approaching the scanning electron microscope main body 16. And are provided.
[0024]
The sound from the first speaker 18 is used to cancel noise generated in the X direction. The sound from the second speaker 20 is used to cancel noise generated in the Y direction. A signal from the correction signal adjustment circuit 15 is supplied to the acoustic drive circuit 17 in the X direction and the acoustic drive circuit 19 in the Y direction.
[0025]
In such a configuration, the amount of noise converted by the arithmetic circuit 14 is supplied to the correction signal adjustment circuit 15. In the correction signal adjustment circuit 15, a signal in which the phase of the frequency is reversed with respect to the converted signal of the noise amount is created and supplied to the X direction acoustic drive circuit 17 and the Y direction acoustic drive circuit 19. It should be noted that the phase difference is preferably corrected with a volume (CPU control) that shifts the phase before supplying a signal to each acoustic drive circuit.
[0026]
As a result, the signal from the X direction acoustic drive circuit 17 generates a sound from the first speaker 18 that reduces noise on the image due to noise in the X direction, that is, a sound that cancels the noise. Noise on the directional image is reduced. Further, the signal from the Y direction acoustic drive circuit 19 generates a sound from the second speaker 20 that reduces noise on the image due to noise in the Y direction, that is, a sound that cancels the noise. Noise on the image is reduced.
[0027]
Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, when the amount of noise on the image due to vibration is obtained, the frequency of noise may be divided by image processing to perform each correction. Specifically, the noise on the periodic image may be determined by performing processing such as Fourier transform. Since the period at this time is extracted from the image, an error occurs due to various noises, but each correction may be performed with a frequency value having a natural frequency close to the obtained period.
[0028]
Further, the adjustment of the phase difference is not performed manually, but it is also possible to automatically perform the image processing so that the noise component is minimized. Furthermore, noise removal by noise according to the present invention may be performed not only for fixed noise but also for changing noise. In that case, the value of the frequency corresponding to the natural frequency of the scanning electron microscope main body is monitored, correction processing is performed using a value corresponding to the sound pressure, and noise is removed.
[0029]
Furthermore, in the above description of the embodiment, the removal of noise in the X and Y directions has been described. However, noise in the Z direction may be removed in the same manner.
[0030]
【The invention's effect】
According to the first aspect of the present invention, the sound pressure of the natural frequency of the scanning electron microscope is measured, the measured sound pressure is converted into the amount of noise in the image, and the signal having the opposite phase of the converted signal of noise amount Since the amount of noise on the image is reduced based on the above, image noise due to noise can be effectively reduced by a small correction process.
[0031]
Scanning electron microscope based on the invention of claim 2 is the invention of claim 1, based on an inverse phase of the signal noise of the signal, to correct the scanning signal of the electron beam, so as to reduce the noise in the image Therefore, image noise due to noise can be effectively reduced by a small correction process.
[0032]
Scanning electron microscope based on the invention of claim 3 is the invention of claim 1, based on an inverse phase of the signal noise of the signal, to generate a sound, since the reduce the noise in the image, Image noise due to noise can be effectively reduced by a small correction process.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a relationship between an acoustic frequency and a noise amount.
2 is a diagram showing an example of a scanning electron microscope in accordance with the present invention.
FIG. 3 is a diagram illustrating a relationship of a correction amount with respect to sound pressure.
FIG. 4 is a diagram showing another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electron gun 2 Condenser lens 3 Objective lens 4 Sample 5 Deflection coil 6 X direction scanning circuit 7 Y direction scanning circuit 8 Scan control circuit 9 Secondary electron detector 10 Amplifier 11 Cathode ray tube 12 Sound pressure measurement unit 13 Sound pressure memory 14 Operation Circuit 15 Correction signal adjustment circuit

Claims (3)

A scanning electron microscope main body in a scanning electron microscope in which an electron beam narrowed on a sample is two-dimensionally scanned and an image is displayed based on a signal obtained by scanning the sample with the electron beam. measuring means for measuring the sound pressure frequency of the natural frequency of the approximated arranged scanning electron microscope in a position to, and conversion means for converting the sound pressure measured by the measuring means to the noise amount of the image, is converted and the reverse phase signal of the noise amount of the signal, and a circuit to create for the natural frequency of the frequency of the scanning electron microscope, to reduce the amount of noise in the image based on an inverse phase of the signal from the circuit configured by scanning electron microscopy as. Based on the opposite phase of the signal of the noise of the signal, to correct the scanning signal of an electron beam, scanning electron microscope of claim 1, wherein which is adapted to reduce the noise on the image. Based on the opposite phase of the signal of the noise amount of the signal to generate a sound, scanning electron microscope of claim 1, wherein which is adapted to reduce the noise on the image.

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