JPH02288138A - Flashing system of electric field emitting electron gun - Google Patents

Abstract

PURPOSE:To have proper flashing always by setting the flashing voltage or time on the basis of the drawout voltage when a specified period of time has elapsed since the previous flashing. CONSTITUTION:An electric field emitting type electron gun according to the present invention is composed of an emitter 1, power supply 2 for weak flashing, power supply 3 for strong flashing, switches 4, 5, drawout electrode 6, accelerating electrode 7, power supply 8 for drawout voltage, control circuit 9, current sensor 10, and a drawout voltage adjusting knob 1. The surface roughness of the emitter 1 is judged through comparison of the current drawout voltage with the max. drawout voltage, while the control circuit 9 makes judgement about whether the next flashing is to be weak or strong. Thus the next flashing strength is decided automatically to secure good performance of flashing at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a field emission type electron gun, and particularly to its flushing method.

[Prior Art] Field-emission electron guns are widely used as electron guns in electron microscopes, etc., but as time passes, gas molecules present in vacuum may adhere to the emitter surface or the electron beam may The collision of ions creates unevenness, which results in unstable extraction current and deterioration in the quality of the obtained image. Therefore, when a field emission electron gun is first used and at regular intervals after use, an appropriate amount of current is passed through the emitter to heat it, remove gas molecules attached to the emitter surface, and generate positive ions. The emitter surface is smoothed by removing the unevenness caused by the collision.

This is flushing, and is performed by a configuration as shown in FIG. In Fig. 3, 1 is the emitter of the field emission type electron gun, 2 is the weak flushing power supply, 3 is the strong flushing power supply, 4.5 is the switch, 6 is the extraction electrode,
Reference numeral 7 indicates an accelerating electrode, and 8 indicates a power source for bowing out voltage.

As shown in Figure 3, there are two types of flushing power supplies: a weak flushing power supply 2 that supplies a relatively small current, and a strong flushing power supply 3 that supplies a relatively large current. 4, when you select which power source to use and turn on the switch 5 for flushing, the emitter 1 - switch 5 -
A closed circuit is formed between switch 4 - power source 2 for weak flushing or power source 3 for strong flushing - emitter 1, and a current flows through emitter 1 to heat it and perform flushing. Although not shown in FIG. 3, an appropriate voltage is applied to the accelerating electrode 7 in order to obtain a predetermined beam accelerating voltage. Further, the voltage applied to the extraction electrode 6 is set by the operator adjusting the voltage of the extraction voltage power source 8.

Flushing is performed in this way, but 2
The reason why different types of flushing power supplies 2.3 are provided to enable weak flushing and strong flushing is as follows.

When performing flushing, if a relatively large current is applied by the strong flushing power supply 3, gas molecules on the surface of the emitter 1 can be removed and unevenness can be smoothed out compared to when the weak flushing power supply 2 is used. is performed well, but the diameter of the tip of emitter 1 increases,
In order to obtain the same beam current, it is necessary to increase the extraction voltage. However, at this time, if the voltage of the accelerating electrode 7 is lower than the voltage of the extraction electrode 6 and a decelerating electric field is used, the intensity of the decelerating electric field becomes larger and the beam is greatly decelerated. Therefore, a problem arises in that the aberration becomes large.

Therefore, weak flushing is usually used to prevent the diameter of the tip of the emitter 1 from increasing, remove attached gas molecules, and remove unevenness, which results in a lot of noise in images such as electron microscope images, and deteriorates the quality. It is equipped with two types of @ sources so that strong flushing can be performed if the water level drops.

[Problems to be Solved by the Invention] However, the decision as to whether to perform weak flushing or strong flushing depends largely on the operator's experience, which requires skill and is troublesome.

In addition, in order to eliminate the above-mentioned trouble, strong flushing has always been performed after performing weak flushing for -number of times, but the timing of strong flushing does not necessarily depend on the number of weak flushing. Flushing cannot be carried out properly because it has to be determined based on the amount of gas molecules adsorbed on the emitter, the degree of unevenness on the emitter surface, etc. .

The present invention solves the above-mentioned problems, and aims to provide a flushing method for a field emission electron gun that can always perform proper flushing.

[Means for Solving the Problems] In order to achieve the above object, the flashing method of the field emission type electron gun of the present invention adjusts the flashing voltage based on the extraction voltage when a predetermined usage time has elapsed since the previous flashing. [Function and Effects of the Invention] According to the present invention, it is possible to set the amount of voltage to be applied or the amount of time to let the current flow during the next flushing. Since it is determined automatically, not only can proper flushing be performed, but also the operator's troublesomeness can be eliminated, and good images can always be obtained.

[Example code] Examples will be described below with reference to the drawings.

FIG. 1(a) is a diagram showing the configuration of one embodiment of the flushing method of a field emission type electron gun according to the present invention, and in the figure, 9
10 is a control circuit, 10 is a current detector, and 11 is a draw-out voltage adjustment knob, and the same parts as in FIG. 3 are given the same numbers. Further, FIG. 1(b) is a diagram showing a flowchart of processing performed by the control circuit 9. As shown in FIG.

In the device shown in FIG. 1, when the operator adjusts the draw voltage with the draw voltage adjustment knob 11, the control circuit 9 detects the rotation angle of the draw voltage adjustment knob 11 and uses a rotary switch (not shown), etc., for example. By switching the taps, the setting of the extraction voltage power source 8 is performed. Further, the control circuit 9 takes in the beam current with the current detector 10, displays the beam current value on a display (not shown), and lights up a lamp when the beam current is within a predetermined range.

Next, how to decide whether to perform weak flushing or strong flushing when performing the next flushing will be explained with reference to the flowchart in FIG. 1(b).

At some point, when the operator presses the switch 5 to perform flushing, the control circuit 9 detects the press of the switch 5 (step S1) and waits for a predetermined N time (step S2). The value of N can be arbitrarily set within the range of about 1 to 10 hours, but the time must be such that the beam current can be stably obtained, and about 3 hours may suffice. When N hours have passed since the switch 5 was pressed, the control circuit 9 takes in the value of the extraction voltage V at that time (step S3).
. Since the control circuit 9 recognizes the extraction voltage based on the position of the extraction voltage adjustment knob 11, this value may be used. Next, the control circuit 9 compares the extraction voltage V with a preset maximum value v,8 of the extraction voltage (step S4), and if the extraction voltage V is larger, the value of v, , 8 is determined in step S5. is updated to the value of the extraction voltage V and the process of step S6 is performed, otherwise the process of step S6 is directly performed. In step S6,
The control circuit 9 selects the values of (V, , -V) and a predetermined value vR.
As a result, the value of (V,, WuV) is v1
If it is 1 or more, it is determined that the next flushing should be strong flushing, and the switch 4 is connected to the strong flushing power supply 3 side, and the value of (V, , -V) is set to VR.
If it is less than that, it is determined that the next flushing should be weak flushing, and the switch 4 is connected to the weak flushing power source 2 side.

The above process allows the next flushing to be performed properly for the following reasons.

The emission of electrons from the emitter 1 is not uniform from the emitter surface, and in particular, many electrons are emitted from the sharp parts.

Therefore, if the surface of emitter 1 has many irregularities, more electrons will be emitted than if the emitter surface is smooth, and the beam current will increase accordingly, which is necessary to obtain the same beam current. The extraction voltage V may be lower when the emitter surface is uneven than when the emitter surface is smooth. In other words, it is possible to know the state of the unevenness of the emitter surface by the value of the extraction voltage V, and this is utilized in the present invention, and this is done in step S6 in FIG. 1(b). This is the process. That is, the state of the unevenness on the surface of the emitter 1 is determined by comparing the current extraction voltage V with the maximum extraction voltage V, .

Note that the necessity of step S5 is clear. because,
This is because Vl, 8, which is initially set, is a provisional maximum extraction voltage value, and is not an actual value.

Furthermore, the validity of detecting the extraction voltage V when the beam current is stable is also clear. In other words, since the obtained beam current value becomes stable over time, the operator must adjust the voltage adjustment knob 11 until the beam current stabilizes so that the beam current falls within a predetermined range. This is because the extraction voltage is not adjusted after the beam current is stabilized, but remains at a constant value.

In the embodiment shown in FIG. 1, the control circuit 9 determines whether the next flushing will be a weak flush or a strong flush, and based on the determination, the control circuit 9 switches the switch 4.
The system only performs a switching operation, and when to perform flushing is left to the operator's discretion. That is, when the operator determines that it is time to perform flushing by observing an electron microscope image or the like, he or she presses the switch 5. As a result, the switch 5 forms the above-mentioned closed circuit for a predetermined period of time. This is done because the time from the previous flushing to the next flushing varies depending on the condition of the surface of the emitter 1, and cannot be uniquely determined by the passage of time. However, it is natural that the time interval for flushing can be set appropriately and the flushing can be performed automatically by the control circuit 9. In the above embodiment, two power supplies for flushing are used, but more power supplies can be used. It is obvious that it is also possible to switch between the two.

The first embodiment has been described above, and next, the second embodiment will be described with reference to FIG. Note that in FIG. 2, the same parts as in FIG. 1 are given the same numbers.

In the system shown in Figure 1, the flushing intensity is changed by switching the flushing power supply, but in the system shown in Figure 2, the strength of the flushing is changed by controlling the flushing time. It is something.

Therefore, the control circuit 21 controls the maximum extraction voltage V determined in step S10 of FIG. 2(b). .

The flushing time, that is, the time during which the switch 22 in FIG. 2(a) is turned on, is determined based on the difference between the voltage V and the current extraction voltage V (step 511). To determine the flushing time, a table defining the relationship between the values of (V, , -V) and the flushing time is stored in advance in the internal memory of the control circuit 21, and step S
The flushing time may be determined by referring to the table from the difference value determined by IO.

In this case, it is preferable that the flushing power source 23 be capable of supplying a relatively large current. This is because if a power supply that can only supply a relatively small current is used, the temperature of the emitter 1 may not rise above a certain level even if flushing is performed for a long time, and there is a possibility that good flushing cannot be performed.

As described above, according to the present invention, since the next flushing strength is automatically determined, the operator only has to judge when to perform flushing based on an electron microscope image, etc., compared to the conventional method of determining the flushing strength. This will free you from that hassle.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a diagram showing the configuration of another embodiment of the present invention, and FIG. 3 is a diagram for explaining a conventional flushing method. 1... Emitter of field emission type electron gun, 2... Power source for weak flushing, 3... Power source for strong flushing, 4.
5... Switch, 6... Extracting electrode, 7... Accelerating electrode, 8... Extracting voltage power supply, 9... Control circuit, 10... Current detector, 11... Extracting voltage Adjustment knob. Figure 1 (a) Applicant JEOL Ltd. Agent Patent attorney Hideo Sugai (5 others) (b) ] U Figure (a) (b) Figure 1

Claims (1)

[Claims] (1) A flushing method for a field emission electron gun, characterized in that the flushing voltage or flushing time is set based on the extraction voltage when a predetermined time has elapsed since the previous flushing.