JPH0736322B2 - Field emission type ion beam generator - Google Patents

Description

The present invention relates to a field emission type ion beam generator, and more particularly to an apparatus for stabilizing an ion beam.

“Prior Art” The emitter used in an EHD (Electro Hydro Dynamics) field ion source (hereinafter referred to as “EHD type ion source”) is a liquid metal (for example, a tungsten wire whose tip is electropolished to about 0.5 μmφ). , Gallium, etc.), and when a direct current voltage (emission voltage) of several KV is applied between this emitter and the ectostractor, the strong electric field formed at the tip of the tungsten needle forming the emitter causes the so-called tailor Cone (Ta
ylor Cone) to form a conical protrusion. An electric field is concentrated at the tip of the conical protrusion, and the liquid metal at the tip of the needle is field-evaporated and extracted as gallium ions, for example.

In the EHD type ion source using such an emitter, a stabilizing circuit is provided between the emitter and the extractor in order to enhance the stabilization of the ion beam. FIG. 3 shows a conventional example of such a device, in which 1 is an emitter for emitting an ion beam, E ₁ is its heating power supply, and E ₂ is an acceleration power supply. 2 is an extractor, 3 is a cathode,
Reference numeral 4 is a detector for detecting the amount of the ion beam emitted from the emitter 1. The signal (emission current) detected by the detector is input to the stabilizing circuit 5, and the negative feedback circuit in the stabilizing circuit keeps the emission current constant. 6 is a current setting volume for setting the emission current.

[Problems to be Solved by the Invention] When setting a desired emission current in the device configured as described above, the emission voltage applied between the emitter 1 and the extractor 2 by operating the current setting volume 6. Was set to the emission voltage at which the emission current to be set flows.

However, there are cases where the emission current to be set cannot be flowed depending on the combination of the magnitude of the emission current to be set and the value of the emission current immediately before the setting. Hereinafter, such a case will be described.

First, the relationship between the emission voltage and the emission current in such a device will be described.

When the current setting potentiometer 6 is operated to gradually increase the emission voltage applied between the emitter 1 and the extractor 2 from 0 V, the emission voltage e and the emission current i change as shown in FIG. That is, when the emission voltage e gradually increased from 0V, emission current i to the emission voltage reaches ex ₁ (KV) is hardly flows rapidly emission when emission voltage reaches ex ₁ (KV) Current i ₁ flows. This is because the liquid metal that wets the tip of the emitter of the field emission type ion beam generator is almost hemispherical due to the surface tension when the emission voltage is not applied, and the emission voltage is applied in this state. However, when the voltage is less than ex ₁ (KV), a strong electric field to the extent that field evaporation occurs is not formed, but when a certain large emission voltage ex ₁ (KV) is applied, a strong electric field is formed. , The attractive force by the electric field exceeds the surface tension, and the liquid metal that wets the tip of the emitter forms a conical protrusion (Taylor cone) as described above, and the electric field concentrates on the tip of the Taylor cone, This is because the liquid metal of (1) is field-evaporated and extracted as ions.

Next, the current setting volume 6 is operated to further increase the emission voltage. In this way, when the emission voltage e is raised from the state where the emission current once flows rapidly, the emission current i increases substantially in proportion to the emission voltage e. At this point, when the emission current larger than the value i ₁ when the emission current suddenly flows is stable and the emission voltage is lowered by operating the current setting potentiometer 6,
Until ex ₁ is reached, the emission current i decreases in accordance with the relationship between the emission voltage e and the emission current i shown by the solid line in FIG. However, if the emission voltage is further lowered after the emission voltage reaches ex ₁ ,
The emission current does not become 0, and as shown by the broken line in FIG. 4, the emission current flows approximately in proportion until it reaches ex ₂ . Then, when the emission voltage becomes lower than ex ₂ , the emission current stops flowing. This is because even if the emission voltage is lowered once the Taylor cone as described above is formed and a certain stabilization time has passed, a certain voltage value ex
Up to ₂ , the Taylor cone is maintained (that is, a hysteresis phenomenon occurs), but when the voltage value ex ₂ or less, the Taylor cone cannot be maintained, and the liquid metal at the tip of the emitter depends only on the original surface tension. This is because it will return to a hemispherical shape. In emission current i ₂ flowing when the emission voltage reaches ex _2, referred to emission current i ₂ at this emission off current, the emission voltage ex ₂ and emission-off voltage, while the emission voltage 0 (KV ), The emission current i ₁ when the emission current suddenly flows is called the emission on-current, and the emission voltage ex ₁ is called the emission on-current. Further, when the emission voltage is raised again while the emission voltage is being lowered in this way, if the emission voltage at that time is larger than the emission off current ex ₂ , the emission current increases substantially in proportion. However, if it is smaller than the emission off voltage ex _2, even if the voltage is raised again, the emission current does not flow until the emission voltage reaches the emission on voltage ex ₁ as shown by the solid line in FIG. Of course, at this time, if the emission voltage is raised above the emission-on voltage ex ₁ , the emission current increases substantially in proportion to the emission voltage. When increasing the emission voltage e from a value between the emission off voltage ex ₂ and the emission on voltage ex ₁ , as described above, the emission on current i ₁
If it is not the case that the emission voltage is raised again while the emission voltage is being lowered from the state where a larger current is flowing stably, just as when raising from 0 (KV), emission current does not flow until the emission voltage reaches the emission-on voltage ex _1, abruptly flows when reaching the emission turn-on voltage ex _1, then, the emission current was approximately proportional to the increase in emission voltage increases.

Now, in the device configured as described above, since the emission voltage and the emission current have the above relationship, when the emission current is set to a value larger than the emission on current value i ₁ flowing at the emission on voltage ex _1. , And when setting the emission current flowing at the emission voltage between the emission on voltage ex ₁ and the emission off voltage ex ₂ from the state where the emission current larger than the emission on current i ₁ is flowing stably, By operating the setting volume 6 to set the emission voltage applied between the emitter 1 and the extractor 2 to the emission voltage through which the emission current to be set flows, the emission current to be set can be flowed without any problems. .

However, for example, in an ion beam device or the like, in order to focus the ion beam finely, the emission current is often set to be smaller than the emission on current i ₁ flowing at the emission on voltage ex ₁ from the beginning. In addition, the current setting volume 6 can be operated to set the emission voltage applied between the emitter 1 and the extractor 2 to the emission voltage at which the emission current to be set flows. Absent.

It is an object of the present invention to provide a device having a simple structure capable of passing an emission current to be set even in such a case.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a stabilization for controlling the potential between the emitter and the extractor so that the emission current has a set emission current value. In a field emission type ion beam generator provided with a circuit,
The emission current setting means, the reference current generating means, a comparator for comparing the current from the emission current setting means with the current from the reference current generating means, and the current value from the emission current setting means is the emission-on current value. When it is lower, a circuit for supplying a current having a value larger than the emission on current value to the stabilizing circuit in place of the current from the emission current setting means for a certain period by the signal from the comparator is provided.

EXAMPLES Examples of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a diagram for explaining an operating state, and in FIG. 3, the same components as those of the conventional example are designated by the same reference numerals.

In FIG. 1, reference numeral 7 is a comparator to which a signal from the current setting potentiometer 6 is input to one terminal and a signal from the second current setting potentiometer 8 is input to the other terminal. Reference numeral 9 is a timer circuit connected to the first comparator 7, and a stabilization circuit 5 is provided by a signal from the comparator.
The period signal corresponding to the time when the response of is stable is output.
A switching circuit 13 switches the signal supplied to the stabilizing circuit 5 in response to the signal from the timer circuit 9, and is either a signal set by the third current setting volume 14 or a signal set by the current setting volume 6. And is supplied to the stabilizing circuit 5.

In the device configured as described above, the emission current immediately before the setting is smaller than the emission on current i ₁ flowing at the emission on voltage ex ₁ , and the emission current immediately before the setting is a current value larger than the emission on current i _1. An operation in the case where the emission current is set to be smaller than the emission-on current i ₁ flowing at the emission-on voltage ex ₁ when the current value is not lowered from the state where the emission is stable is described.

First, the emission voltage at which the desired emission current ik to be set by operating the second current setting volume 8 flows
Set the same voltage as exk. Further, by operating the third current setting volume 14, a voltage exp larger than the emission-on voltage ex ₁ is set. The set of each voltage is set according to the characteristic of the emission voltage / emission current shown in FIG. 2 which is measured in advance.

In this state, by operating the current setting potentiometer 6, the emission voltage at which the desired emission current ik flows
Set exk. In the setting operation, when the emission voltage reaches the emission voltage exk to be set, the comparator 7 makes the signal level from the current setting volume 6 equal to the signal level corresponding to the voltage set by the second current setting volume 8. When this is detected, the timer circuit 9 is activated. Then, the switching circuit 13 switches to the side of the third current setting potentiometer 14 for a predetermined period by the signal from the timer circuit 9. By this switching, the stabilizing circuit 5 operates so that a voltage (pxp) larger than the emission-on voltage ex _{1 is} applied between the emitter 1 and the extractor 2 for a predetermined period. By applying the voltage, the liquid metal that wets the tip of the emitter forms a Taylor cone as described above, and is stabilized during the predetermined period. Therefore, the electric field is concentrated at the tip of the tailor cone, and the liquid metal in that portion is field-evaporated and extracted as ions,
The emission current ip (current flowing at the emission voltage exp) set by the third current setting volume 14 flows during the predetermined period. When the signal from the timer circuit 9 is no longer input to the switching circuit 13 after a preset period, the switching circuit 13 switches to the current setting potentiometer 6 side. Then, the edging current changes according to the relationship between the solid line and the dotted line shown in FIG. 2, and the stabilizing circuit 5 is provided so that the emission current ik by the emission voltage exk set by the current setting potentiometer 6 flows.
Works.

It should be noted that when the emission current is set to a value larger than the emission on current value i ₁ flowing at the emission on current ex ₁ , and when the emission current is a large current equal to or larger than the emission on current i ₁ flows stably. When setting the emission current flowing at the emission voltage between the emission on voltage ex ₁ and the emission off voltage ex ₂ , the emission current is set by the current setting potentiometer 6, and the emission voltage corresponding to the set current is stable as it is. Since it is sufficient that the voltage is applied between the emitter 1 and the extractor 2 from the conversion circuit 5, the switching circuit 13
Is always kept switched to the current setting potentiometer 6 side. For example, the second current setting volume 8
If the emission voltage exmax is set so that the maximum current imax flows, the emission current set by the current setting potentiometer 6 is always smaller than this current, so the timer circuit 9 does not operate, and for that reason Switching circuit 13
Does not switch to the third current setting volume 14 side.

[Effects of the Invention] As described in detail above, according to the present invention, the emission current smaller than the emission on-current is changed from the state in which the emission current larger than the emission on-current is not stably flowing due to the simple configuration. Even if the emission voltage for flowing is set, the set emission current can be made to flow.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a diagram for explaining an operation state of an apparatus according to the present invention, FIG. 3 is a diagram showing a conventional example, and FIG. It is a figure which shows the relationship between the emission voltage and the emission current in such a device. 1: Emitter, 2: Extractor, 3: Cathode, 4: Detector, 5: Stabilization circuit, 6: Current setting volume, 7: Comparator, 8: Second current setting volume, 9: Timer circuit, 13 : Switching circuit, 14: Third current setting potentiometer

Claims (1)

[Claims] 1. A field emission type ion beam generator provided with a stabilizing circuit for controlling a potential between an emitter and an extractor so that the emission current has a set emission current value. A reference current generating means, a comparator for comparing the current from the emission current setting means with the current from the reference current generating means, and when the current value from the emission current setting means is lower than the emission on current value. A field emission type ion beam generator comprising a circuit for supplying a current having a value larger than an emission on current value to the stabilizing circuit instead of the current from the emission current setting means for a certain period of time according to a signal from the comparator. .