JPS63292555A - Electron beam apparatus - Google Patents

Abstract

PURPOSE:To make it possible to improve S/N (signal v.s. noise) ratio of secondary electron output by cyclically and intermittently radiating electron beams, and applying lock-in amplification method, after detecting AC-modulated secondary electrons emitted from this irradiated part by a scintillator or a secondary electron multiplying tube. CONSTITUTION:Electron beams emitted from a power source 1 and an electron gun 2 reach a sample 11 through an electron lens system 3, a chopping electrode 4 to form a cyclic and intermittent wave, an aperture 5 and a scanning coil 6. Secondary electrons emitted from the sample 11 as the result of incident electron beams, is AC-demodulated by the scintillator or a secondary electron multiplying tube 8 to be detected. The AC-modulated secondary electron signal is, further, output to a CRT 10 through a lock-in amplifier 9. A secondary electron beam image with good S/N ratio is obtained by applying this kind of lock-in amplification, even if an electron beam incident current is reduced in the same way as in the case that an electron beam incident current is reduced for the purpose of preventing electrification.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention uses an electron beam to perform surface observation and analysis and LSI
The present invention relates to an electron beam device that performs surface analysis such as testing.

2. Description of the Related Art Conventionally, in an electron beam apparatus such as a scanning electron microscope, when a sample is irradiated with an electron beam, secondary electrons emitted from the sample are detected and outputted without signal processing.

Problems to be Solved by the Invention However, in the above configuration, when an electron beam is irradiated onto an insulating material sample, the insulating material sample becomes electrically charged (charged up), and the intensity of secondary electrons emitted from the insulating material sample decreases. becomes weaker, and the S/N ratio (signal-to-noise ratio) deteriorates. In order to prevent this deterioration, the amount of charging can be reduced by reducing the electron beam incident current IP, but in this case as well, the secondary electron intensity becomes weaker and the S/N ratio deteriorates.

Means for Solving the Problems The present invention provides a means for irradiating a local surface of a sample with a periodic and intermittent electron beam (-order electrons), and a means for irradiating a local surface of a sample with an alternating current modulated secondary electron beam emitted from this primary electron irradiation section. This is an electron beam device consisting of a scintillator or a secondary electron multiplier for detecting secondary electrons, and a lock-in amplification method for extracting an output after detecting secondary electrons.

A working sample is irradiated with a periodic and intermittent electron beam, and the AC-modulated secondary electrons emitted from the irradiated area are detected by a scintillator or secondary electron multiplier, and then a lock-in amplification method is applied. By using this method, it is possible to improve the S/N (signal-to-noise) ratio of the secondary electron output when the electron beam incident current is reduced.

The lock-in amplification method used here will be described.

After a sample is irradiated with a periodic and intermittent electron beam, secondary electrons emitted from the sample are AC-modulated by the intermittent electron beam and output from a scintillator or a secondary electron multiplier. When the AC modulated secondary electron output is narrowband amplified and phase detected, unmodulated noise,
Since the dark current is not amplified, the SIN ratio is improved.

Embodiment Figures show an embodiment of the present invention applied to a scanning electron microscope. In the figure, an electron beam emitted from a power source 1 and an electron gun 2 passes through an electron lens system 3, chops 'Ki4, aperture 5, and forms a periodic and intermittent waveform.
It reaches the sample 11 via the scanning coil 6. Secondary electrons emitted from the sample 11 as a result of the incidence of the electron beam are AC-modulated and detected by the scintillator or the secondary electron multiplier tube 8 . The AC modulated secondary electronic signal is outputted to the CRT lo through the lock-in increase/disposal 9. By using lock-in amplification, in the present invention, even when the electron beam incident current is reduced in the same way as in the conventional case where the electron beam incident current is reduced to prevent static electricity, the present invention can provide a second signal with a good S/N ratio. A secondary electron beam image is obtained.

In addition, although the Example uses a scanning electron microscope, charging of the sample surface can be prevented and the S/N ratio can be improved even when using other surface potential measurement methods.

As described in detail, according to the present invention, when a sample is charged in a measurement in which the sample is irradiated with an electron beam and secondary electrons are detected, the charge can be reduced by reducing the electron beam incident current. Not only can this be prevented, but it can also be improved against deterioration of the S/N ratio, which has great practical effects.

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[Brief explanation of drawings]

The figure is a configuration diagram showing an embodiment in which the electron beam device of the present invention is applied to a scanning electron microscope. 1...Power supply, 2...Electron gun, 3...
...electronic lens system, 4...electrode for chopping, 5...aperture, 6...scanning coil, 7.°/°°° chopping power supply,
8...Scintillator or secondary electron multiplier, 9
...Lock-in amplifier, 1o...C,
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Claims (1)

[Claims] means for irradiating the local surface of the sample with periodic and intermittent primary electrons; means for detecting secondary electrons emitted from the primary electron irradiation section; means consisting of a scintillator or a secondary electron multiplier; An electron beam device consisting of a lock-in amplifier that extracts the output after detecting the next electron.