JPS5834894B2 - scanning electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scanning electron microscope that uses a cathode ray tube equipped with an electromagnetic deflection coil as a display device.

In recent years, scanning electron microscopes have increased the scanning speed,
The dynamics of the sample can be observed as a flicker-free image on the display.

In this case, the current flowing through the deflection coil also changes faster, but since the deflection coil has self-inductance, there is a limit to the improvement in scanning speed.

Therefore, to reduce the self-inductance, it is necessary to reduce the number of turns of the coil or connect the coils in parallel, but in either case, the deflection current must be increased, and the Loss (heat generation) will occur.

Therefore, when the deflection current is a sawtooth wave, the loss is lower than when it is constant at the maximum value.01 Also, when the scanning speed is fast and when the scanning speed is slow, the latter generates more heat. There will be more.

For this reason, the display device of a conventional scanning electron microscope reaches a considerably high temperature, and a water/metal or empty drive mechanism is required to prevent damage to other circuits.

On the other hand, when the scanning speed is fast and slow, the amount of electron beam per unit area and unit time on the fluorescent screen of the cathode ray tube is different, so the brightness is higher in the latter than in the former. There is the inconvenience of having to adjust the brightness every time the mode is switched.

The present invention aims to solve the above-mentioned drawbacks, and will be described in detail below based on actual cases shown in the drawings.

In FIG. 1, reference numeral 1 denotes an electron gun, and an electron beam from this electron gun is focused by focusing lenses 2 and 3 and projected onto a sample 4.

5a and 5b are deflection coils to which a scanning current is supplied from a scanning power source 6 via an amplifier (magnification adjuster) 7, whereby the electron beam two-dimensionally scans a certain area on the sample 4. do.

The scanning power supply 6 has a scanning speed of multiple stages (at least two stages).
It is also possible to generate a constant current for fixing the electron beam to a specific point on the sample.

Secondary electrons and reflected electrons generated at the electron beam irradiation point of the sample 4 are detected by a detector 8 and supplied to a brightness modulation grid of a cathode ray tube 10 via an amplifier 9.

A scanning signal is sent from the scanning power supply 6 to the deflection coil 11 of the cathode ray tube via an amplifier 12 and a switching device 13, so that a scanning image of the sample 4 is projected onto the cathode tube. .

Reference numeral 14 denotes a mode selection circuit, in which the operator selects a desired scanning speed (fast scanning or slow scanning) or spot mode (a mode in which the electron beam is stopped at a fixed point on the sample), and the scanning power supply 6 is controlled based on this selection. be done.

A signal is sent from the mode selection circuit to the switching control circuit 15, which generates a pulse signal with a constant periodic pulse width when the scanning speed is selected below a certain value or when the spot mode is selected, and controls the switching control circuit 15. Device 1
3 and blanking circuit 16.

The switching device 13 switches the deflection current from the scanning power source 6 between zero or constant current to supply the cathode ray tube 10.
It will be sent to the deflection coil 11 of.

2a is the sawtooth wave signal from the power supply 6, and 01b is the deflection current after passing through the switching device 13.

3a shows the constant current from the power source 6, and b is the deflection current after switching.

On the other hand, during the time period other than when the deflection current passes through the switching device 13, or during the period when zero current or constant current is applied, the blanking circuit 16 operates and the electron beam of the cathode ray tube 10 is cut off.

With the above configuration, it is possible to make the conduction time and the cut time of the deflection current due to switching approximately the same, or the latter can be made longer, so the average deflection current can be reduced compared to the conventional method. The amount of heat generated can be significantly reduced.

As a result, it is possible to achieve power saving and to reduce the thermal influence on other circuits, thereby making it possible to simplify the cooling mechanism.

Furthermore, since the average amount of electron beams irradiated onto the phosphor screen per unit time is also reduced, the disadvantage of increased brightness due to slow scanning speed is eliminated.

It should be noted that the switching speed does not need to be constant, but is determined by the ratio of the energization time to the cut time (
(corresponding to the pulse width) and the repetition frequency may be made variable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIGS. 2 and 3 are diagrams for explaining the operation of a portion of the apparatus shown in FIG. 5a and 5b...Deflection coil, 6...
Scanning power supply, 10...Cathode ray tube, 11...
- Cathode ray tube deflection coil, 13... switching device, 14... mode selection circuit, 15...
...Switching control circuit, 16...Blanking circuit.

Claims (1)

[Claims] 1. Electron generation source, electron lens system to narrowly focus the electron beam and project it onto the sample, deflection coil to scan the electron beam on the sample, power supply to supply scanning current to the deflection coil, electron A display device comprising a detector for detecting information generated from each part on a sample by radiation irradiation, and a deflection coil into which an output signal of the detector is introduced as a brightness modulation signal and a scanning current is supplied from the scanning power supply. When the electron beam spot is scanned at low speed or stopped at an arbitrary point, the current supplied to the deflection coil of the display device is switched between zero or a constant current, and the deflection current is zero or constant. A scanning electron microscope characterized in that the brightness of a display device is blanked when an electric current is applied.