JP2000208084A - Scanning charged particle beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning charged particle beam device capable clearly performing image observation even when a charged region exists on the surface of a sample. SOLUTION: The intensity of a secondary electron signal is reduced according to the intensity of an absorption current by means of a computing unit 17. Such a computation can be accomplished by using, for instance, an adder as the computing unit 17. As a result, when a charged region is scanned by a primary electron beam, the absorption current is reduced, and a secondary electron detection signal is abnormally intensified, but the intensity of the secondary electron detection signal is reduced according to the small value of the absorption current. Therefore, the luminance in the charged region of the sample is abnormally intensified, so that the observation of the whole image on a cathode-ray tube 15 is prevented from being hindered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning type charged particle beam apparatus such as a scanning electron microscope which scans an electron beam on a sample and displays an image based on a signal from the sample. The present invention relates to a scanning charged particle beam apparatus suitable for observing a sample to be measured.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a scanning electron microscope as a scanning type charged particle beam apparatus, wherein 1 is an electron gun. The electron beam EB generated from the electron gun 1 is narrowly focused on the sample 4 by the focusing lens 2 and the objective lens 3. The electron beam EB is deflected by the scanning coil 5, and the irradiation position of the electron beam on the sample 4 is scanned.

The scanning coil 5 is supplied with a two-dimensional scanning signal from a beam scanning controller 6. The sample 4 is moved by a motor 8 driven by a sample stage controller 7.
It is mounted on a moving stage 9 that can be moved in two-dimensional directions of X and Y.

Secondary electrons generated by irradiating the sample 4 with the electron beam EB are detected by a secondary electron detector 10. The detection signal of the detector 10 is supplied to a frame memory 12 after being converted into a digital signal by an AD converter 11.

[0005] Reference numeral 13 denotes an address generator for selecting the coordinates of the storage pixel when the detection signal is stored in each pixel of the frame Mary 12, and this generator 13 is provided with an electron supplied from the beam scanning controller 6. An address signal is created by a signal corresponding to the scanning signal of the beam EB. The signal stored in the frame memory 12 is read out, converted into an analog signal by the DA converter 14, and then supplied to the cathode ray tube 15. The operation of such a configuration will now be described.

When observing a secondary electron image, two-dimensional scanning of the electron beam EB is performed on the sample 4. Secondary electrons generated based on the irradiation of the sample 4 with the electron beam EB are detected by the detector 10. The detection signal is an AD converter 11
Is stored in a pixel-corresponding storage area at an address corresponding to the scanning position of the electron beam EB in the frame memory 12 via

[0007] The video signal is stored in each pixel of the frame memory 12 in this manner. The stored video signal is read out and passed through the DA converter 14 to the cathode ray tube 1.
5, the secondary electron image of the sample is displayed on the cathode ray tube 15.

[0008]

In the above-mentioned scanning electron microscope, if there is a non-conductive area on the sample surface, a charging phenomenon occurs in the sample area due to the current of the primary electron beam. When a primary electron beam is further irradiated on the area where the charging phenomenon has occurred, the amount of secondary electrons generated from the area increases, and the luminance of the detected image signal becomes abnormally large. As a result, in the image on the cathode ray tube, the charged region is observed to be shining white, and the image becomes difficult to see as a whole.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a scanning charged particle beam capable of clearly observing an image even when a charged region exists on the surface of a sample. The realization of the device.

[0010]

A scanning electron microscope according to a first aspect of the present invention comprises a focusing lens for focusing a charged particle beam on a sample, and a scanning device for scanning an irradiation position of the charged particle beam on the sample. Means, a detector for detecting a signal emitted from the surface of the sample by irradiating the sample with a charged particle beam, an amplifier for amplifying a current absorbed by the sample, and a function of the intensity of the sampled current signal from the amplifier. And a calculator for adjusting the intensity of a detection signal from the detector, and displaying an image based on the signal calculated by the calculator.

In the first invention, secondary electrons and reflected electrons obtained from the surface of the sample are detected, an absorption current signal of the sample is obtained, and secondary electrons and reflected electrons are obtained according to the intensity of the absorption current signal of the sample. The intensity of the detection signal is adjusted, an image is displayed based on the adjusted signal, and the phenomenon that abnormally high luminance on the display screen is prevented.

A scanning charged particle beam apparatus according to a second aspect of the present invention uses an adder as an arithmetic unit in the first aspect of the present invention. A scanning charged particle beam device according to a third aspect of the present invention, in the first aspect of the invention, is configured to supply an absorption current signal to a computing unit via a low-pass filter.

According to a fourth aspect of the present invention, in the scanning charged particle beam apparatus according to the first aspect, the amplification degree of the amplifier of the absorption current is variable.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows an example of a scanning electron microscope according to the present invention, and the same or similar parts as those in the conventional apparatus of FIG.

In FIG. 2, reference numeral 1 denotes an electron gun. The electron beam EB generated from the electron gun 1 is narrowly focused on the sample 4 by the focusing lens 2 and the objective lens 3. The electron beam EB is deflected by the scanning coil 5, and the irradiation position of the electron beam on the sample 4 is scanned.

The scanning coil 5 is supplied with a two-dimensional scanning signal from a beam scanning controller 6. The sample 4 is moved by a motor 8 driven by a sample stage controller 7.
It is mounted on a moving stage 9 that can be moved in two-dimensional directions of X and Y.

Secondary electrons generated by irradiating the sample 4 with the electron beam EB are detected by a secondary electron detector 10. The detection signal of the detector 10 is supplied to the arithmetic unit 17 after being amplified by the amplifier 16. The arithmetic output signal of the arithmetic unit 17 is supplied to the frame memory 12 after being converted into a digital signal by the AD converter 11.

Reference numeral 13 denotes an address generator for selecting a coordinate of a storage pixel when a detection signal is stored in each pixel of the frame Mary 12, and this generator 13 is an electron generator supplied from the beam scanning controller 6. An address signal is created by a signal corresponding to the scanning signal of the beam EB. The signal stored in the frame memory 12 is read out, converted into an analog signal by the DA converter 14, and then supplied to the cathode ray tube 15.

An amplifier 18 for the absorption current of the sample 4 is connected to the sample stage 9. The signal amplified by the amplifier 18 is supplied to a low-pass filter 19, and the signal that has passed through the low-pass filter 19 is supplied to the computing unit 17 to be operated on a secondary electron detection signal. The operation of such a configuration will now be described.

When observing a secondary electron image, two-dimensional scanning of the electron beam EB is performed on the sample 4. Secondary electrons generated based on the irradiation of the sample 4 with the electron beam EB are detected by the detector 10. The detection signal is stored in a pixel-corresponding storage area of an address corresponding to the scanning position of the electron beam EB in the frame memory 12 via the AD converter 11 via the amplifier 16 and the arithmetic unit 17.

The video signal is stored in each pixel of the frame memory 12 in this manner. The stored video signal is read out, and is passed through the DA converter 14 to the cathode ray tube 1.
5, the secondary electron image of the sample is displayed on the cathode ray tube 15.

By the way, normally, when charging occurs, the intensity of the secondary electron detection signal increases, while the absorption current of the sample 4 decreases relatively as compared with a state where no charging occurs on the sample. For this reason, in the embodiment of FIG.
7, the intensity of the secondary electron signal is reduced according to the intensity of the absorption current. Such an operation is performed by, for example, the arithmetic unit 1
7 can be achieved by using an adder.

As a result, when the charged area is scanned with the primary electron beam, the absorption current becomes small and the secondary electron detection signal becomes abnormally large. The intensity of the electronic detection signal is reduced. Therefore, it is possible to prevent the luminance from becoming abnormally high in the charged region of the sample, and obstructing the observation of the entire image on the cathode ray tube 15.

After the absorption current of the sample is amplified by the amplifier 18 and supplied to the low-pass filter 19, the low-pass filter 19 passes only the signal in the frequency band of the absorption current and has a high frequency as a noise component. Cut the signal.

It is effective to appropriately adjust the amplification degree of the amplifier 18 and the pass band of the low-pass filter 19.
That is, if this adjustment is optimally performed, it is possible to prevent the signal component of the fine structure on the sample based on the secondary electron detection signal from disappearing or being weakened by the calculation in the calculator 17 in the non-charged region. it can.

Although the embodiment of the present invention has been described in detail, the present invention is not limited to this embodiment. For example, although secondary electrons are detected, reflected electrons may be detected. Also, a scanning electron microscope that irradiates a sample with an electron beam has been described as an example,
The present invention can also be applied to an apparatus that irradiates a sample with an ion beam.

[0027]

As described above, in the first invention,
Detects secondary electrons and reflected electrons obtained from the surface of the sample, obtains an absorption current signal of the sample, and adjusts the intensity of the secondary electron and reflection electron detection signals according to the intensity of the absorption current signal of the sample. Since the image is displayed based on the signal obtained, on the display screen corresponding to the charged sample area,
It is possible to prevent a phenomenon in which the luminance is abnormally high, and to obtain an image that is always easy to see even if a non-conductive area exists on the sample.

In the scanning charged particle beam device according to the second invention, the same effect as that of the first invention is achieved because the adder is used as the arithmetic unit in the first invention. Third
The scanning charged particle beam device according to the invention of claim 1 is
In the present invention, since the absorption current signal is supplied to the arithmetic unit via the low-pass filter, it is possible to adjust the secondary electron and reflected electron signals without the influence of noise.

In the scanning charged particle beam apparatus according to the fourth aspect of the present invention, since the amplification degree of the amplifier of the absorption current is variable in the first aspect of the invention, the image signal in the non-charged area is not adversely affected. Such adjustment is possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a conventional scanning electron microscope.

FIG. 2 is a diagram showing an example of a scanning electron microscope according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electron gun 2 focusing lens 3 objective lens 4 sample 5 scanning coil 6 beam scanning controller 7 stage controller 8 motor 9 moving stage 10 detector 11 AD converter 12 frame memory 13 address generator 14 DA converter 15 cathode ray tube 16 , 18 Amplifier 17 Operation unit 19 Low-pass filter

Claims (4)

[Claims] A focusing lens for focusing the charged particle beam on the sample; a scanning unit for scanning an irradiation position of the charged particle beam on the sample; and a sample surface by irradiating the sample with the charged particle beam. A detector for detecting the emitted signal, an amplifier for amplifying the current absorbed by the sample, and a calculator for adjusting the intensity of the detection signal from the detector in accordance with the intensity of the absorption current signal of the sample from the amplifier. And a scanning charged particle beam apparatus configured to display an image based on a signal calculated by the calculator. 2. The scanning type charged particle beam apparatus according to claim 1, wherein the arithmetic unit is an adder. 3. The scanning type charged particle beam apparatus according to claim 1, wherein the absorption current signal is supplied to an arithmetic unit via a low-pass filter. 4. The scanning electron microscope according to claim 1, wherein the amplification degree of the amplifier for amplifying the absorption current is variable.