JPS59134539A - Device provided with field emission type electron gun - Google Patents

Abstract

PURPOSE:To reduce a variation in a detecting current even when the lead voltage and accelerating voltage of a field emission electron are largely altered as well as to make a detecting effect improvable, by structuring a device to minimize the variation of an electron flow jumping into a detector in a way of bringing the detector for emission current variations close to the side of an anode. CONSTITUTION:In case of a device provided with a detecting way for both of a field emission type electron gun and a field emission current, an anode surface 3 is set down as a reference, and when a distance of up to a virtual electrode source is set to S while a distance of up to a current detection angle limiting stop 6 to l1 and a distance of up to this stop 6 and a current variation detector 7 to l2 respectively, the electron gun is situated in a position that is set to l1<10mm. and l2<S/5. Since this field emission type electron gun uses both of a first anode and a second anode 3, V0-V1 voltages are impressed between both anodes, having an electrostatic lens action, therefore when the voltage V1 or V0 is largely altered, the distance S of up to the virtual electron source is also altered but doing so aforesaid, even if the distance S is largely altered, a detecting area of the emission current to be detected by the detector 7 will not be altered at all, thus stable current detection comes attainable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a device having a field emission type electron gun, and more particularly to a detection device having an optimal structure for detecting fluctuations in the current of field emission.

[Prior art]

In a conventional detector that detects fluctuations in the emission current of a device having a field emission type electron gun, when the extraction voltage (vl) and the daily velocity voltage (Vo) of field emission electrons are greatly changed, the detection The current detected by the device changes widely, making it difficult to measure the detected current and make effective use of the detected signal.

[Purpose of the invention]

An object of the present invention is to provide a device that can reduce the change in detection current even when the Vo and L voltages are varied widely, thereby increasing the detection effect.

[Summary of the invention]

In the present invention, when the V, Vl voltage is changed over a wide range, the virtual electron source position changes over a wide range. It has a structure that minimizes changes in the flow of incoming electrons.

[Embodiments of the invention]

An embodiment of the invention is shown in FIG.

The field emission type electron gun has a cathode 1, a first anode 2, and a second anode 3.
It consists of When an extraction voltage V111 for extracting electrons is applied between the cathode 1 and the first anode 2, a strong electric field is applied to the surface of the cathode 1, and electrons 4.5 are field-emitted. This emitted electron 4°5 is further accelerated by an accelerating voltage V applied between the cathode 1 and the second anode 3. It is accelerated by 12. Generally, 3 to 8 kV%yoii to 100 kV is used for (1). The accelerated electrons 4 are converged or expanded by an electron lens 8 and focused onto a sample 10 as a probe current 9. In the case of a scanning electron microscope or the like, secondary electrons 14 generated on the surface of the sample 10 are detected by a detector 15 and amplified by an amplifier 16 to form an image signal.

However, the field emission current 4.5 has the disadvantage that the field emission is affected by the condition of the cathode surface and the degree of vacuum near the cathode (generally 10-1° TOrr or less), and the emission current varies greatly. . Therefore, in an apparatus having a field emission type electron gun, a method is adopted in which this current fluctuation is detected and the high dynamic component contained in the image signal is corrected to obtain a true image signal. In FIG. 1, the detector for detecting fluctuations in the radiation current is 7 (=1), this detection signal is amplified by the amplifier 13, and both the output signal and the secondary electron signal 16 are sent to the corrector 17. A method is used to correct the inconvenience. In this device, the fluctuation signal of the radiation current is determined by the angle β−α between the angle β limited by the aperture white that limits the detection angle of the radiation current and the angle α determined by the aperture hole of the current detector 7. The method for detecting the signal 5 incident on the inside is 9, and the radiation current 4 serving as the probe current is an electron flow within the α angle.

In the above-mentioned detection method, the positional relationship among the aperture white, the detector 7, and the electron source 1 is shown in FIG.

Since it is known that detecting the radiation current fluctuation signal 5 and the probe current signal 4 at almost the same signal level increases the effect of correcting fluctuations, the fluctuation signal is detected in FIG. 8. The area of the hole through which the electrons forming the current flow passes is equal to 5t=-c+-;8. =St is desirable.

For this purpose, it is good to adopt the relationship d=5di.

However, since the field emission type electron gun uses the first anode 2 and the second anode 3, aVo -V1 voltage is applied between the two and has an electrostatic lens effect. Because of this effect, when the voltage (2) or the V0 voltage is changed over a wide range, the distance S to the virtual electron source changes over a wide range as shown in FIG. Therefore, the above d.

The condition ``f d,'' is satisfied only at a certain voltage, and the signal from the detector 7 also changes widely, resulting in an insufficient correction signal to the corrector 17. The change in this signal is at the limit aperture r
It can be seen that Rt, its hole diameter d3, the distance t between the limiting diaphragm 6 and the detector 7, and the distance t to the second anode vary widely. That is, the detection angle β-α of the radiation current holds the relationship shown in FIG. '
ml:'d3, and even if the distance of S changes greatly due to the electrostatic lens action, the detection area of the radiation current detected by the detector 7 does not change, making stable current detection possible.

Practical experimental results have shown that it can be used for current detection without any problem even if the current changes by more than 10 rtm (tt).

〔Effect of the invention〕

As explained above, according to the present invention, the distance t0 from the anode to the angle-limiting aperture can be made small, and an apparatus can be obtained that can withstand wide acceleration voltage changes during detection.

[Brief explanation of the drawing]

Figure 1 shows a device with a field emission electron gun and a current fluctuation detector, Figure 2 shows the detection angle to the electron fluctuation detector and the difference in detection diameter due to changes in the virtual electron source, and Figure 3. is a diagram showing changes in the distance S to the virtual electron source. 1... cathode, 2... first anode, 3... second anode,
4... Radiation electron beam (probe electron), 5... Fluctuation detection electron beam, 6... Detection angle limiting aperture, 7... Current detector, 8... Electron lens, 9...・Probe current,
10... Sample, 11... Extraction voltage (V,), 12
... Accelerating voltage (Vo), 13... Amplifier, 14...
・Secondary electron, 15...Secondary electron rod 1 (2) 2nd diagram

Claims (1)

[Claims] 1. In a device having a field emission type electron gun and a means for detecting field emission current, with the anode surface as a reference, the distance to the virtual electron source is S, the distance to the current detection angle limiting aperture 9 is t4, and the aperture is When the distance to the current fluctuation detector is t, t
, (A device having a field emission type electron gun, characterized in that it is within 10 rtrm and is arranged at a position where 11 <-.