JPS6010418B2 - electron beam equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam device equipped with a field emission emitter, and more particularly to an electron beam device that regenerates an emitter deteriorated by ion bombardment or the like by powerful flashing.

In an electron beam device such as a scanning electron beam microscope, the current of all electrons emitted from a field emission emitter is detected, and the voltage between the emitter and the electron beam extraction electrode is controlled so that the current is constant. There is.

However, if a protrusion is generated by ion bombardment on the surface of the emitter part away from the emitter tip, the emitted electron current increases from this part, and even if the total emitted electron current is kept constant, the emitted current from the emitter tip becomes May decrease. In such a case, the probe current that is actually irradiated onto the sample decreases, resulting in a decrease in image quality. Therefore,
In the conventional system, an operator would empirically detect deterioration of the emitter due to such a decline in image quality, and perform so-called strong flashing to regenerate the emitter. Powerful flushing moves the atoms that make up the emitter (ml
gratlon) to remove the protrusions caused by ion bombardment, thereby passing a heating current of considerable power through the emitter.

At this time, the sharpness of the tip of the emitter is also dulled by heating, which is not preferable for concentrating the electric field, so it is desirable to perform strong flashing as few times as possible. However, even if the image quality decreases due to a decrease in the emitter probe current, it has often been discovered that the emitter itself has not deteriorated due to ion bombardment, and the conventional empirical method of detecting inferiority may cause the emitter to deteriorate more than necessary. It was discovered that the lifespan of the emitter was shortened by strong flashing.

Such detection errors are caused by the fact that the action of the lens formed by the electric field between the emitter and the extraction electrode changes as the extraction voltage is changed, in order to keep the total emitted electron current from the emitter constant. This is due to not taking into account the case where the probe current decreases even though the emitted electron current from the emitter tip hardly changes. The present invention has been made in view of these points, and provides an electron beam device that automatically detects emitter deterioration and generates a timing signal for strong flashing in order to automatically perform strong flashing. Embodiments of the scanning electron beam microscope will be described below based on the drawings.

FIG. 1 is for showing an embodiment of the present invention. In the drawing, 1 is a field emission emitter, 2 is an extraction electrode, and 3 is a grounded acceleration electrode.

An extraction voltage is applied between the emitter 1 and the extraction electrode 2 by an extraction power supply 4, and a high voltage is applied between the emitter 1 and the acceleration electrode 3 by an acceleration power supply 5. The electrons 6 extracted by the extraction electrode are accelerated by the accelerating electrode 3 and are further transferred to the sample 8 by the objective lens 7.
It is converged on top. 9 is an aperture used as a probe current detector because a current proportional to the current irradiated to the sample (probe current L) flows, and the output signal of the aperture 9 is sent to the first The signal is supplied to the division circuit 11.

That is, the dividing circuit 11 is supplied with a signal lp/K (where K is a proportionality constant determined by the size of the aperture and the extraction angle of the electron beam). Reference numeral 12 denotes a detection resistor for detecting the total electron current emitted from the emitter 1, and a signal from the detection resistor is introduced into one input terminal of the differential amplifier 13.

A reference signal from a reference power source 14 is introduced into the other input device of the differential amplifier 13. The output signal of the differential amplifier 13 is supplied to the extraction power supply 4, and
changes its output voltage based on the output signal of the differential amplifier 13, and is controlled so that the total emitted electron current of the emitter 1, which is always detected by the detection resistor 12, is a constant value set by the reference power supply 14. . A signal representative of the total emitted electron current L of the emitter from the detection resistor 12 is supplied via an amplifier 15 to a first divider circuit 11 . The first
The output signal of the divider circuit 11 is coupled to a second divider circuit 16. Further, a signal proportional to the drawing voltage of the drawing main source 4 is supplied to a function generator 18 via an amplifier 17. Among the electrons emitted from the tip of the emitter, the ratio L of electrons irradiated to the sample is
L is a function of the extraction electrode Vw, since it is greatly influenced by the action of the lens formed by the electric field between the extraction electrode Vw and the extraction electrode 2. Figure 2 shows that L is theoretically or experimentally determined as a function of Vw, and the function generator 1
Reference numeral 8 denotes a circuit for outputting the above-mentioned L in response to a signal representing the supplied Vw using a broken line or the like;
The output signals from the above are supplied to a second divider circuit 16. The output signal of the divider circuit 16 is introduced into one input terminal of a comparator 19. A reference signal from a reference power supply 20 is also introduced into the other input terminal of the comparator 19. The output signal of the comparator 19 is supplied to a switch circuit 21. The switch circuit 21 is connected in series to a heating power source 22 for powerfully flushing the emitter 1. In such a configuration, switch circuit 21 is normally open so that power from heating power source 22 is not supplied to the emitter.

Now, since the first divider circuit 11 is supplied with a signal lp/K proportional to the probe current through amplifiers 10 and 15, and a signal lo representing the total radiated electron flow from the emitter, its output signal is lp/K1. becomes. The output signal is supplied to one input terminal of the second divider circuit 16, and the second divider circuit 16 receives L(Vw) from the function generator 18.
) is supplied, so the output signal of the second division circuit 16 becomes lp/KI↓. The output signal of the second dividing circuit 16 is supplied to a comparator 19, and if this output signal becomes less than the reference signal from the reference power source 20, a timing signal for strongly flashing the deteriorated emitter 1 is sent from the comparator 19. The signal is output and supplied to the switch circuit 21. Switch circuit 21 is comparator 1
The emitter 1 is closed by the arrival of the timing signal from the heating power source 22, and a heating current from the heating power source 22 is supplied to the emitter 1, thereby performing a strong flushing of the emitter 1. At this time, the extraction power source 4 and the acceleration power source 5 are turned off as is well known. Now, in the above-mentioned scanning electron microscope, a probe current lp/L that compensates for the current lost due to the lens action between the emitter and the extraction electrode is derived for each extraction voltage yw, and this compensated probe current lp/L is derived for each extraction voltage yw. The ratio of the current lp/L to the total radiated electron current L' is lp/
Since the loL is compared with the reference, deterioration of the emitter can always be accurately detected, and based on this, a timing signal for powerful flushing can be generated.

It should be noted that the above-described embodiment is only one embodiment of the present invention, and other embodiments may be adopted when implementing the present invention.

FIG. 3 is for explaining another embodiment, and the same components in FIG. 3 as in FIG. 2 are given the same numbers. In FIG. 3, 23 is a comparator, to which the signal L (Vw) from the function generator 18 and the signal from the reference power supply 26 are supplied. 24 is also a comparator, and the comparator 24 receives the output signal lp/K1 of the first division circuit 11.

and signals from a reference power supply 27 are supplied, and output signals of both comparators 23 and 24 are supplied to an AND circuit 25. The output signal of the AND circuit 25 is supplied to the switch circuit 21. In a device having such a configuration, when the output signal lp/KL of the arithmetic circuit 11 is below the reference value and L(Vw) is below the reference value,
Based on the pulses from both comparators 23 and 24, an output pulse is taken out from the AND circuit 25, and an operation such as closing the switch circuit 21 is performed.

An output pulse is obtained from the AND circuit 25 when the probe current is less than a certain value with respect to the total radiation current set at that time, and the reason for this is that there is almost no contribution from the lens effect. Therefore, even with this configuration, the present invention can be implemented.

Furthermore, the output signal of the first dividing circuit 11 may be directly supplied to the comparator 19, and the output signal of the reference power supply 20 may be controlled based on the signal from the function generator 18. .

Furthermore, although the function generator in the above-described embodiment is constructed from an analog circuit, it may also be constructed from a digital circuit.

Brief Description of the Drawings Fig. 1 is a diagram showing one embodiment of the present invention, Fig. 2 is a diagram showing the relationship between the extraction voltage Vw and L, and Fig. 3 is a diagram showing another embodiment of the present invention. FIG.

1: emitter, 2: extraction electrode, 3: acceleration electrode, 4:
Extraction power supply, 5: Acceleration power supply, 6: Electron, 7: Objective lens, 8: Sample, 9: Aperture, 10, 13, 15, 1
7: Amplifier, 11, 16: Divider circuit, 12: Detection resistor,
14, 20, 26, 27: reference power supply, 18: function generator, 19, 23, 24: comparator, 21: switch circuit, 22: heating power supply, 25: AND circuit.

Next figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. In an apparatus in which the extraction voltage is controlled so that the total emission current of the emitter is constant and is equipped with a probe current detection means for detecting the electron beam current irradiated onto the sample, the distance between the emitter and the extraction electrode is means for substantially determining a signal representing a probe current that compensates for the current lost due to the lens action between the emitter and the extraction electrode based on the signal representing the voltage of the emitter and the extraction electrode, and comparing the signal with a reference value; 1. An electron beam apparatus comprising means for flashing said emitter based on an output signal from said emitter.