JPH01186743A - Electric field emission type scanning electron microscope - Google Patents

Abstract

PURPOSE:To make it possible to obtain a clear sample image in which the intensity variation of the primary electron beam is canceled by deflecting the primary electron beam radiated on the sample during the retrace period into a correcting signal, and detecting the signal. CONSTITUTION:When a switch 14 is opened or closed synchronously to the retrace signal, a voltage is applied to a deflector 13 from a DC power source 15 synchronously to the signal, the primary electron beam 2 is deflected out of the optical axis, and the intensity of the electron beam is detected by an electron beam detector 16. The detected signal is fed to a division circuit 8 together with an image signal of a sample 5 detected by the secondary electron detector 9. The signal is operated by the division circuit 8, fed to a cathode-ray tube 11, and displayed as a sample image. In such a way, a clear sample image in which the intensity variation of the primary electron beam 2 is almost all canceled can be displayed regardless of the variation of the emission pattern.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a field emission scanning electron microscope, in particular, which corrects fluctuations in the electron beam from a field emission electron gun to obtain a clear sample image. Regarding equipment.

[Prior Art] In a scanning electron microscope equipped with a field emission electron gun (hereinafter abbreviated as FEG), the intensity of the electron beam emitted from the FEG, that is, the total emission current changes with time, so as shown in Fig. 4. This structure prevents the sample image from being affected by changes in electron beam intensity.

In FIG. 4, reference numeral 1 denotes an FEG, and a primary electron beam 2 emitted from the FEG is narrowly focused by a converging lens 3 and scanned two-dimensionally over a sample 5 by a deflection coil 4. Reference numeral 6 denotes an electron beam detector having an electron beam passage hole 6a formed in the shape of a diaphragm as shown in FIG. The detector 6 detects the electron beam 2a at the very periphery of the primary electron beam 2 irradiated onto the sample 5. This detection signal is sent to the divider circuit 8 via the current amplifier 7 as a probe current signal P. On the other hand, for example, secondary electrons e accompanying the irradiation of the sample 5 with the primary electron beam 2 are detected by the secondary electron detector 9 and amplified by the amplifier 10, and then sent to the dividing circuit 8 as a video signal S. It will be done. Here, if the probe current signal intensity P is proportional to the intensity of the primary electron beam 2 irradiated onto the sample 5 with the same proportionality constant over time, then
The signal from the rain detector is input to the divider circuit 8 and the ratio (S/P
) and displays this signal on the cathode ray tube 11 to which the scanning signal is supplied from the scanning signal generation circuit 12 based on this ratio signal, the change in the primary electron beam intensity included in the video signal S is canceled. and does not appear on the sample image.

[Problems to be solved by the invention] By the way, in the device configured in this way, the electron beam detector 6
As mentioned above, what is detected is the electron beam 2a only at the periphery of the primary electron beam 2, and the intensity change of the electron beam 2a is equal to the intensity change of the electron beam at the center irradiated onto the sample 5. It is said that However, since the emission pattern of the field emission electron gun changes over time, the ratio of the amount of current at the center and the periphery of the primary electron beam 2 actually changes over time. Therefore, it is not possible to correctly cancel the intensity change (noise) of the primary electron beam, and a clear sample image cannot be obtained. Further, in such a device, it is necessary to correctly arrange the electron beam passage hole 6a of the electron beam detector 6 on the optical axis, but the work to correctly arrange the electron beam detector 6 on the optical axis is complicated. It is. Furthermore, since the probe current is detected only in the periphery of the primary electron beam 2, the detection current is weak and the S/N ratio is poor.
It is not possible to cancel the intensity change of the second electron beam with high precision, and it is not possible to obtain a clear sample image.

The present invention has been made in view of the above points, and an object of the present invention is to provide a field emission type scanning electron microscope that can cancel changes in the primary electron beam intensity and obtain a clear sample image.

[Means for Solving the Problems] The present invention for achieving the above object uses a field emission type electron gun that emits an electron beam in an electric field, and a field emission type electron gun that emits an electron beam in an electric field, and a method for scanning a sample with the electron beam. information detection means for detecting information; and deflection means for deflecting the electron beam off the optical axis during a retrace period of a scanning signal in order to detect fluctuations in the electron beam current from the field emission type electron gun. , an electron beam detection means for detecting the intensity of the electron beam deflected off the optical axis by the deflection means; a storage means for temporarily storing the signal detected by the electron beam detection means; The present invention is characterized by comprising means for correcting fluctuations in the information signal due to fluctuations in the electron beam based on the signal from the storage means and the signal from the information detection means.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and the same components as those of the conventional device shown in FIG. 4 are given the same numbers. In FIG. 1, reference numeral 13 indicates the primary electron beam 2 emitted from the FEGI during the retrace period (t) of the scanning signal shown in FIG.
l) a deflector for deflecting the optical axis off the optical axis, the deflector 1
3 is applied with a deflection voltage from a DC power supply 15 via a switch 14. Further, since the switch 14 is supplied with a switching signal synchronized with the retrace period as shown in FIG. 2 (b) from the scanning signal generation circuit 12, the switch 14 is synchronized with this retrace signal. to open and close the switch. 16 is an electron beam detector arranged off the optical axis, and when the switch 14 opens and closes in synchronization with the retrace signal, a voltage is applied to the deflector 13 from the DC power supply 15 in synchronization with this signal. Ru. Therefore, the primary electron beam 2 is deflected off the optical axis as shown by the dotted line in FIG.
detected by. The signal detected by the electron beam detector 13 is amplified by an amplifier 17 composed of a current/voltage converter and an amplifier circuit, and then held for a certain period of time by a sample-and-hold circuit 18 and divided as a probe current signal P'. The signal is sent to the calculation circuit 8. The division circuit 8
Since the image signal S from the sample 5 detected by the secondary electron detector 9 is also supplied to the image signal S, the image signal S is calculated by the dividing circuit 8 (S/P i) and is supplied to the cathode ray tube 11 and displayed as a sample image. be done.

By the way, in the apparatus configured in this way, the electron beam intensity of the primary electron beam 2 irradiated onto the sample 5 is deflected by the deflector 13 during the retrace period and detected by the electron beam detector 16. 1 detected by the electron beam detector 16
Since the electron beam intensity of the secondary electron beam 2 is the same as the electron beam intensity of the primary electron beam 2 irradiated onto the sample 5, the video signal S is proportional to the probe current signal P' with the same proportionality constant over time. There will be. Therefore, when the signal is displayed on the cathode ray tube 11 by the dividing circuit 8, a clear sample image is displayed in which the intensity change of the primary electron beam 2 is almost canceled out, regardless of the fluctuation of the emissidine pattern. In addition, instead of detecting only the electron beam in the very periphery of the primary electron beam 2 irradiated onto the sample 5 as in the conventional device, the electron beam intensity is monitored for the primary electron beam 2 itself irradiated onto the sample 5. Since the primary electron beam fluctuations are detected with high accuracy, correction for primary electron beam fluctuations can be performed with high precision based on this sufficiently strong signal. Furthermore, in the apparatus configured in this manner, unlike the conventional apparatus, the electron beam detector is not arranged on the optical axis, so there is no need to perform complicated operations such as alignment.

FIG. 3 is a diagram for explaining another embodiment of the present invention. In the embodiment shown in FIG. 1, a primary electron beam 2 is deflected by a deflector 13, and an electron beam detector 16 is arranged outside the optical axis.
However, as shown in FIG. 3, one deflection plate of the deflector 19 can be used as an electron beam detector 19a, and The primary electron beam 2 is bent more strongly. Due to this deflection, the primary electron beam 2 is deflected as shown by the dotted line in FIG. 3, and is detected as a probe current signal by the electron beam detector 19a. Therefore, even in the apparatus configured in this way, since the video signal from which electron beam fluctuations have been removed is input to the cathode ray tube 11, the cathode ray tube 11
A clear image of the sample is displayed, with changes in the intensity of the primary electron beam canceled out.

[Effects of the Invention] As detailed above, according to the present invention, the primary electron beam irradiated onto the sample is deflected during the retrace period and detected as a correction signal. A field emission scanning electron microscope is provided that can obtain a clear sample image with intensity changes canceled.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of one embodiment of the present invention, FIG. 2 is a diagram for explaining the present invention, FIG. 3 is a diagram for explaining another embodiment of the present invention, and FIG. 4 is a diagram for explaining another embodiment of the present invention. FIG. 5 is a diagram for explaining a conventional example, and FIG. 5 is a diagram for explaining an electron beam detector of a conventional device. 1: FEG, 2: Primary electron beam, 3: Focusing lens, 4: Deflection coil, 5: Sample, 8: Division circuit, 9: Secondary electron detector, 10: Amplifier, 11: Cathode ray tube, 12: Scanning signal generation circuit, 13: deflector, 14: switch, 15: DC power supply, 16: electron beam detector, 17: amplifier, 18: sample and hold circuit. 19: Deflector, 19a Two-electron beam detector. Patent applicant: JEOL Ltd. Figure 1

Claims (1)

[Scope of Claims] 1) A field emission type electron gun that emits an electron beam in an electric field, an information detection means that detects information from the sample obtained by scanning the sample with the electron beam, and the field emission type electron gun. a deflection means for deflecting the electron beam off the optical axis during the retrace period of a scanning signal in order to detect fluctuations in the electron beam current from the electron gun; and electrons deflected off the optical axis by the deflection means. An electron beam detection means for detecting the intensity of the beam, a storage means for temporarily storing the signal detected by the electron beam detection means, a signal from the storage means and a signal from the information detection means. and means for correcting fluctuations in the information signal due to fluctuations in the electron beam. 2) The field emission type scanning electron microscope according to claim 1, characterized in that the deflection means for deflecting the electron beam and the electron beam detection means also serve as the field emission type scanning electron microscope.