JPH05182620A - Device for monitoring filament condition of electron gun - Google Patents

Abstract

PURPOSE:To grasp the filament condition, and obtain an appropriate electron beam, and prevent the short life of the filament lifetime by outputting the electron beam under the condition stored by a computer, and monitoring the emission current thereafter with the computer. CONSTITUTION:A CPU 1 sets the filament current, the bias voltage, and the accelerating voltage at the condition, that the electron beam is output to a filament power source 4 and a bias power source 5 and a high voltage generating unit 3, automatically on the basis of the stored data. Thereafter, the content of an emission current detector 6 is feedbacked to the CPU 1, and a real measured value is taken, and the CPU 1 compares the emission current reference value with the real measured value to judge the various filament conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for automatically detecting an abnormal state of a filament in a tungsten filament exchange type electron gun in an electron microscope or the like.

[0002]

2. Description of the Related Art A conventional tungsten filament exchange type device monitors an abnormal state of a filament by manually adjusting a filament current, a bias voltage and an acceleration voltage and visually observing an emission meter (emission current). It required skill to judge the condition.

[0003]

The above-mentioned prior art requires a delicate attachment when replacing the tungsten filament, and depending on the attachment method, an appropriate electron beam cannot be obtained, and the life of the filament is shortened. There was a problem that it was not possible to easily judge the quality of the filament attachment.

Further, since the filament current, the bias voltage, and the accelerating voltage are manually adjusted, the conditioner such as the current and voltage setting values being too large or too small is not constant and the filament abnormal condition is judged by the operator. There is also the problem of making it more uncertain.

An object of the present invention is to output an electron beam under a condition stored by a computer, and then monitor the emission current by the computer to grasp the filament state to obtain an appropriate electron beam and the filament life. It is to prevent the short life of.

[0006]

In order to achieve the above object, a computer starts to store a state (emission current reference value) that a reference electron beam will output, and then stores the stored data (filament). Automatically set using current, bias voltage, acceleration voltage). The computer determines the various filament states by comparing the emission current at that time with the above-mentioned emission current reference value.

[0007]

By reading the emission current by the computer and comparing the read value with the reference value, it is possible to quickly determine an abnormality such as a defective filament attachment setting, disconnection, or discharge. In addition, the method does not malfunction because it is based on a simple comparison between the measured value and the reference value.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation and configuration of the present invention will be described below with reference to FIGS.

Abnormal states of the filament include excessive setting of the filament, excessive setting of the filament, disconnection of the filament, and discharge in the electron gun. If these abnormal states occur, an appropriate electron beam is emitted. Can't get Further, these abnormal states can be judged to some extent by monitoring the emission current.

The present invention utilizes this emission current and will be described in detail below.

The horizontal axis of FIG. 1 represents the filament current, and the vertical axis represents the emission current. A curve 1a shows a state in which the filament current and the accelerating voltage are adjusted to obtain a reference electron beam after the bias voltage is set to 0 V in a normal filament setting state (a filament attachment position reference state) ( Judgment as to whether the electron beam is the reference is manually adjusted by a skilled person or application number 1-180342.
No. 1-295762), and the bias voltage (0 V) filament current, accelerating voltage, and emission current at this time are stored in a central processing unit (hereinafter referred to as CPU). The emission current value stored at that time is used as the current reference value. The feature of this apparatus is that the emission current reference value (curve 1a) shown above is stored and set by the CPU in advance, and then the emission current is measured and the filament state is monitored based on the following determination criteria. If is determined to be an abnormal filament state, warning processing (display of the state contents, etc.) or automatic bias voltage adjustment is performed.

A. When the measured emission current value is zero (14a in FIG. 14), it is determined that the filament is broken.

B. The measured emission current value is a predetermined value X (see the curve 2 in FIG. 1 from the emission current reference value.
If it is larger than a), it is determined that the filament setting is too protruding. Also, since the bias voltage is 0V, C
The PU increases the bias voltage at a predetermined interval to suppress the emission current and automatically adjust it to the current reference value.

C. The measured emission current value is a predetermined value Y (see the curve 3 in FIG. 1 from the emission current reference value.
If less than a), it is determined that the filament is set too far.

D. If the actually measured emission current value fluctuates near the emission current reference value (Fig. 1 emission current reference value + X emission current reference value -Y, the current is not stable), it is determined that the discharge is inside the electron gun.

According to the present invention, by monitoring the filament state by the above-described method, it is possible to always obtain an optimum electron beam, and excessive current flows too much, and the life of the filament is shortened due to discharge in the electron gun. It also prevents. Next, the configuration of an apparatus for carrying out this method will be described with reference to FIG.

FIG. 2 is a block diagram of a scanning electron microscope of a tungsten filament exchange type, and 1 is a CPU.
That is, the CPU automatically sets the filament current, the bias voltage, and the acceleration voltage by using the stored data in a state where the electron beam will be output to the filament power source 4 and the bias power source 5 and the high voltage generation unit 3. To do. (Fig.1.1
(emission current reference value shown in a)) After that, the content of the emission current detector is fed back to the CPU, the measured value is taken in, and the emission current reference value and the measured value are compared by the method described above to determine the various filament states. The CPU makes the judgment.

More specifically, the electron beam generated from the filament 8 heated by the heating means is accelerated by an accelerating voltage applied between the filament and the anode electrode 10, and is provided between the filament and the anode electrode. In an apparatus for controlling an electron beam by applying a bias voltage to the Wehnelt electrode 9, after setting the bias voltage to 0 V, the filament current and the acceleration voltage are adjusted to obtain an appropriate electron beam. The CPU starts to store this state, and thereafter the filament state is monitored by the method described above.

FIG. 3 shows a logic (flow chart) diagram for monitoring the filament state of the electron gun.

[0020]

According to the present invention, the computer monitors the filament state, so that the abnormal state of the filament can be accurately grasped, and it becomes possible to obtain an appropriate electron beam. Further, it is effective in preventing excess current from flowing too much and shortening the life of the filament due to discharge in the electron gun.

[Brief description of drawings]

FIG. 1 is a diagram showing a filament current on the horizontal axis and an emission current on the vertical axis.

FIG. 2 is a configuration diagram of a tungsten filament exchange type scanning electron microscope.

FIG. 3 is a logic (flow chart) diagram for automatically monitoring a filament state.

[Explanation of symbols]

1a to 3a ... Emission current value, 1 ... CPU, 2 ... D
/ A converter, 3 ... high-voltage generator, 4 ... filament power supply,
5 ... Bias power supply, 6 ... Emission current detector, 7 ...
・ Deflector, 8 ... Filament, 9 ... Wehnelt, 10
... anode, 11 ... electron gun, 12 ... mirror body, 13 ... sample,
14 ... Secondary electron detector, 15 ... Image amplifier, 16 ... CR
T, a ... Electron beam, b ... Secondary electron.

Claims (5)

[Claims] 1. In a tungsten filament exchange type electron gun for an electron microscope or the like, a filament set at a reference mounting position is used as a first step, and a filament current and an acceleration voltage are adjusted after setting a bias voltage to 0V. The computer stores the states of the high voltage generator such as the emission current value (current reference value), the bias voltage (0V), and the filament current. As a second step, the filament of an electron gun is characterized in that the filament is automatically heated by using the above-mentioned data stored in the computer in the first step and the state is monitored by comparing and judging the emission current with a reference value. Condition monitoring device. 2. In claim 1, when the electron beam is automatically obtained, the emission current is monitored, and when the emission current that should flow to the current reference value is not flowing, it is judged as a filament disconnection and a warning such as lamp lighting is given. A filament state monitoring device for an electron gun, which is characterized by performing processing. 3. The method according to claim 1, wherein when the electron beam is automatically obtained, the emission current is monitored and the emission current to flow to the current reference value is too small (current reference value-
[alpha] or less), a filament state monitoring device for an electron gun, which is configured to determine that the setting of mounting the filament is too much, and perform warning processing such as warning or lighting of a lamp. 4. The method according to claim 1, wherein when the electron beam is automatically obtained, the emission current is monitored, and if there is too much emission current near the current reference value (current reference value + α).
As described above, the electron gun is characterized in that it is judged that the mounting setting of the filament is too protruding, and the computer automatically adjusts the bias voltage to suppress the emission current to a value close to the current reference value and to perform a warning process. Filament condition monitoring device. 5. The electron gun according to claim 1, wherein when the electron beam is automatically obtained, the emission current is monitored, and the emission current that should flow to the current reference value fluctuates near that value (current reference value ± α). A filament condition monitoring device for an electron gun, which is characterized by performing a warning or a warning process such as lighting a lamp by determining that the discharge has occurred.