JPH07240165A - Method for regulating field ionization type gas phase ion source, and ion source - Google Patents

Abstract

PURPOSE:To realize a method for regulating a field ionization type gas phase ion source in which an ion beam having a fixed high angle current density can be regularly generated. CONSTITUTION:In field evaporating operation, the difference (Ve-Vm) between a field evaporating voltage Ve and a drawing voltage Vm which can provide a maximum angle current density stored in a computer 13 is read, and the voltage of this difference is applied from a pulse power source 17 to between an emitter 1 and a drawing electrode 2 in superposition with the voltage Vm from a drawing power source 3. Consequently, the surface of the emitter 1 is field-evaporated, and purified. Thereafter, the application of the voltage from the pulse electrode 17 is stopped, and the voltage Vm which can provide the maximum angle current density Bm is applied to between the emitter 1 and the drawing electrode 2 to restart working operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a field ionization type gas phase ion source, in which an ionized gas is supplied to an emitter portion having a high electric field formed at its tip to ionize the gas.

[0002]

2. Description of the Related Art In a field ionization type gas phase ion source, an extraction voltage is applied between an emitter having a sharp tip and an extraction electrode to form a high electric field near the tip of the emitter. Then, an ionized gas such as helium is supplied to the tip of the emitter. The supplied gas atoms are ionized by electric field ionization by the high electric field at the tip of the emitter, extracted by the extraction electrode, accelerated by the acceleration electrode, and extracted as an ion beam. The accelerated ion beam is appropriately focused by a focusing lens, and in the case of an ion beam processing apparatus, the material to be processed is finely focused and irradiated.

Generally, in such a field ionization type gas phase ion source, there is known a method of obtaining a clean surface of the emitter by raising the extraction voltage and field-evaporating the tip of the emitter before the normal operation. Has been. For example, when tungsten is used as the emitter, during electric field evaporation, the electric field at the periphery of the (111) plane of tungsten is sufficient for ionizing gas atoms. Ionization occurs even in the peripheral portion of the (111) plane until the gas atoms are replenished to the region, and the supply of gas atoms to the (111) plane is reduced.

After that, when the electric field is lowered to a certain voltage, a higher surface electric field than the other is applied to the (111) plane slightly protruding from the other crystal planes due to field evaporation, and until then, the peripheral portion of the (111) plane is ionized. The imaged gas atoms have a weak electric field and are hard to be ionized, so that they are replenished by surface diffusion to the (111) plane region at the tip of the emitter.

Due to such a phenomenon, in an ion beam processing apparatus or the like using a field ionization type gas phase ion source, the emitter is adjusted and the extraction voltage is set by the configuration shown in FIG. In the figure, 1 is an emitter formed of tungsten. An extraction electrode 2 is provided close to the emitter 1. An extraction voltage is applied from the extraction voltage power supply 3 between the emitter 1 and the extraction electrode 2. An accelerating electrode 4 has a ground potential, and an accelerating voltage is applied from an accelerating power source 5 between the accelerating electrode 4 and the emitter 1. 6 is a helium gas source, and the helium gas from the gas source 6 is
The ionized gas is supplied to the tip of the emitter 1.
The emitter 1, the extraction electrode 2, the acceleration electrode 4, the gas source 6 and the like constitute a field ionization type gas phase ion source.

The ion beam generated from the ion source is focused by the focusing lens 7 and the objective lens 8 and finely focused on the material 9 to be processed for irradiation. The ion beam with which the material to be processed 9 is irradiated is arbitrarily deflected by the deflector 10, and as a result, the material to be processed is processed by the ion beam having a desired pattern.

A microchannel plate (MCP) 11 is arranged on the optical axis of the ion beam generated from the ion source. A fluorescent surface is provided on the back surface of the MCP 11. Further, the MCP 11 can detect the amount of current of the ion beam, and this detection signal is supplied to the ammeter 12. The value of the ammeter 12 is supplied to the computer 13.
The computer 13 includes an extraction voltage power supply 3, an acceleration power supply 5, and, although not shown, each lens power supply and deflector 10.
Control the deflection control circuit and so on.

A mirror 14 is arranged below the MCP 11 on the optical axis of the ion beam.
Reflects the image of the fluorescent surface on the back of the MCP11,
It acts so as to lead to the camera 15. The image signal obtained by the CCD camera 15 is supplied to the cathode ray tube 16, and the image of the fluorescent surface is displayed on the cathode ray tube 16. The operation of such a configuration will be described below.

First, the processing operation by the ion beam will be described. When the processing operation is executed, the MCP 11 and the mirror 14 are removed from the optical axis of the ion beam. A predetermined extraction voltage is applied from the extraction voltage power supply 3 between the emitter 1 and the extraction electrode 2, and an acceleration voltage is applied from the acceleration power supply 5 between the emitter 1 and the acceleration electrode 4. In this way, a high electric field is formed at the tip of the emitter 1, and helium gas is supplied from the gas source 6 to the tip of the emitter 1.

Helium gas atoms are ionized by field ionization due to the high electric field at the tip of the emitter 1. The ionized gas atoms are accelerated by the acceleration electrode 4 and extracted as an ion beam. This ion beam is focused by the focusing lens 7 and the objective lens 8, and the processed material 9
Is irradiated. The deflector 10 is supplied with a deflection signal corresponding to the processing data from the computer 13 via a deflection control circuit (not shown), and as a result, the material 9 to be processed is processed into a desired pattern by the ion beam.

Prior to the above-described processing operation, the ion source is adjusted so that an ion beam having a sufficient current can be obtained. During this adjustment, the acceleration voltage from the acceleration power source 5 is kept constant. Further, the MCP 11 and the mirror 14 are arranged on the optical axis of the ion beam as shown in the figure. Next, when the extraction voltage from the extraction voltage power source 3 is gradually increased, ionization of gas atoms begins.

At this time, if the extraction voltage and the lens voltage of the focusing lens 7 are raised in conjunction with each other, the field ion image (FIM image) of the emitter 1 can be observed. For example,
When the extraction voltage is increased to about 7 kV, the FIM image is projected on the fluorescent surface on the back surface of the MCP 11. This MCP1
The image of the fluorescent surface on the back surface of 1 is guided to the CCD camera 15 by the mirror 14, and the image signal obtained by the CCD camera 15 is supplied to the cathode ray tube 16, so that the operator receives the FIM image as the cathode ray tube. 16 can be observed.

In the above-mentioned state, the extraction voltage is raised in order to evaporate the tip of the emitter 1 by electric field evaporation. At this time, FI
By observing the M image and confirming the extraction voltage at the time of field evaporation, the extraction voltage is gradually decreased and the ionization is concentrated on the (111) plane at the tip of the emitter. Then, for example, a state where ionization is concentrated on the (111) plane at an extraction voltage of about 6 kV is observed.

As a result, the angular current density in the (111) plane region up to that time increases, and the angular current density shown in FIG. 2 at the optimum voltage determined by the radius of curvature of the (111) plane region and the applied voltage at that time. It has a peak. In FIG. 2, the horizontal axis is the extraction voltage, the vertical axis is the angular current density, Vm is the voltage at which the maximum angular current density Bm is obtained, and Ve is the voltage required for field evaporation.

FIG. 3A shows the operation waveform of the extraction voltage in the ion source of FIG. 1, in which the horizontal axis represents time and the vertical axis represents the extraction voltage. In FIG. 3 (a), when the extraction voltage is gradually increased to cause the first field evaporation, M
An FIM image is observed through the CP 11 and the mirror 14.
When the extraction voltage is further increased, the state of field evaporation is observed in the FIM image, and the field evaporation voltage Ve becomes clear. This voltage value Ve is stored in the computer 13.

After performing the first field evaporation at the voltage Ve,
By reading the ion current from the MCP 11 with the ammeter 12 and the computer 13, the extraction voltage Vm at which the maximum angular current density Bm is obtained is detected. This voltage value Vm is stored in the computer 13. Then, under this voltage value, the ion beam processing apparatus operates normally.

FIG. 3B shows the temporal change in the angular current density corresponding to the change in the extraction voltage shown in FIG. Figure 3 (b)
In, the horizontal axis represents time and the vertical axis represents angular current density. Figure 3
Focusing on (a) and (b), the clean surface of the emitter 1 is exposed and the angular current density is the maximum value Bm at time T1 immediately after the voltage is reduced to Vm after the first field evaporation is completed. Although stable, as time passes, the surface of the emitter is covered with gas molecules due to adsorption of residual gas, and the angular current density decreases as shown in FIG. 3 (b).

Therefore, at the time when the angular current density decreases to a value Bs which is some% of the maximum value Bm, for example, at the time T2a, the electric field evaporation voltage Ve between the emitter 1 and the extraction electrode 2 is controlled by the computer 13. Is applied to perform the second field evaporation. Then, the clean surface of the emitter is obtained again, and then the voltage is lowered to the voltage Vm at which the maximum angular current density Bm is obtained. Hereinafter, such an operation is performed as the third time, the fourth time, ..., And the nth time as a measure against the decrease in the angular current density.

Needless to say, the processing operation is temporarily stopped during each field evaporation of the emitter 1. Further, during the normal processing operation, the current amount of the ion beam is detected indirectly by measuring a part of the ion beam, and the angular current density is constantly decreased to Bs. Have to watch for.

[0020]

The rise time ΔT of the electric field evaporation voltage Ve shown in FIG. 3 (a) is 10 to 20 seconds.
Since a certain amount of time is required, the field evaporation voltage is applied to the emitter 1 for more than the required time, and the field evaporation at the tip of the emitter 1 proceeds excessively every time field evaporation is performed. As a result, the radius of curvature of the emitter could not be controlled accurately, and as shown in FIG. 3B, even if the extraction voltage was set to Vm after the second field evaporation or later, it was obtained after the first field evaporation. There is a problem that the radius of curvature of the emitter cannot be accurately controlled in a stable manner, such as the maximum angular current density Bm not being obtained and the emitter being destroyed by discharge. As a result, a constant maximum angular current density cannot always be obtained, and a constant ion current cannot be obtained. Therefore, when processing is performed using such an ion source, it is difficult to perform processing with high accuracy.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method of adjusting a field ionization type gas phase ion source capable of generating an ion beam having a constant high angular current density. It will be realized.

[0022]

A method of adjusting a field ionization type gas phase ion source according to the present invention comprises an emitter, a means for supplying an ionized gas to an emitter, an extraction electrode, an emitter and an extraction electrode. In an electric field ionization type gas phase ion source equipped with an extraction voltage power supply for applying an extraction voltage between the two, and an acceleration electrode for accelerating the ionized gas from the tip of the emitter, the emitter and the extraction electrode A voltage Ve for field-evaporating the tip of the emitter is applied between them, and then the extraction voltage is lowered to detect the voltage Vm at which the maximum angular current density of the ion beam is obtained.
Each time the angular current density of the ion beam drops to the set value, a voltage Ve is applied between the emitter and the extraction electrode to perform field evaporation of the emitter, and then the extraction voltage is set to Vm. Therefore, the extraction voltage Ve for field-evaporating the emitter is applied in a pulsed manner.

The field ionization type gas phase ion source according to the present invention is for applying an extraction voltage between the emitter, the means for supplying the ionized gas to the emitter, the extraction electrode, and the emitter and the extraction electrode. With the pull-out voltage power supply of
In a field ionization gas phase ion source equipped with an accelerating electrode for accelerating the ionized gas from the tip of the emitter, a pulse power source for generating a pulse voltage and an angular current density of the ion beam are reduced to a set value. Each time
A control means is provided between the emitter and the extraction electrode so as to superimpose the voltage from the extraction power supply and apply the pulse voltage from the pulse power supply.

[0024]

In the present invention, when the angular current density of the ion beam is reduced to the set value, the voltage Ve is applied between the emitter and the extraction electrode to perform field evaporation of the emitter, the voltage is pulsed. Apply.

[0025]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 4 shows an example of an ion beam processing apparatus for carrying out the method of the present invention. The same parts as those of the conventional apparatus of FIG. 1 are designated by the same reference numerals and detailed description thereof will be omitted. The difference from this embodiment and the device of FIG. 1 is that the pulse voltage is applied from the pulse power supply 17 so as to be superimposed on the extraction voltage applied from the extraction voltage power supply 3 to the emitter 1. The operation of such a configuration will be described below.

The processing operation by the ion beam is performed by removing the MCP 11 and the mirror 14 from the optical axis of the ion beam, as in the conventional apparatus shown in FIG. Prior to this processing operation, the ion source is adjusted so that an ion beam with a sufficient current can be obtained. During this adjustment, the acceleration power supply 5
The acceleration voltage from is a constant value. Further, the MCP 11 and the mirror 14 are arranged on the optical axis of the ion beam as shown in the figure. Next, the extraction voltage from the extraction voltage power source 3 is gradually increased, and further the extraction voltage and the lens voltage of the focusing lens 7 are increased in association with each other. This time,
The field ion image (FIM image) of the emitter 1 is displayed on the MCP11,
Observation is performed by the mirror 14, the CCD camera 15, and the cathode ray tube 15.

The first rise in the extraction voltage causes field evaporation at the tip of the emitter 1. This field evaporation is FIM
The field evaporation voltage V when the field evaporation occurs, as observed from the image
Check e. The value of this voltage Ve is calculated by the computer 13
Memorized in. Next, gradually lower the extraction voltage, then M
The detected value of CP11 is measured. Then, the extraction voltage Vm when the maximum angular current density Bm is obtained is confirmed. The value of this voltage Vm is stored in the computer 13. The computer 13 obtains the difference between the stored values of Ve and Vm and stores the difference. After that, set the extraction voltage to Vm,
Perform a predetermined process. Emitter 1 over time
Gas molecules are adsorbed at the tip, and as a result, the angular current density gradually decreases. Therefore, when the angular current density is reduced to the set value Bs lower than the maximum value Bm, the processing operation is temporarily stopped and the second field evaporation operation of the emitter 1 is executed.

In the second field evaporation operation, the difference between Ve and Vm stored in the computer 13 (Ve-
Vm) value is read out, and the voltage of this difference is applied between the pulse power supply 17 and the voltage Vm from the extraction voltage power supply 3 between the emitter 1 and the extraction electrode 2. As a result, the surface of the emitter 1 is field-evaporated and cleaned. afterwards,
The application of the voltage from the pulse power source 17 is stopped, the voltage Vm that provides the maximum angular current density Bm is applied between the emitter 1 and the extraction electrode 2, and the machining operation is restarted.

When the pulse voltage is applied from the pulse power source 17, an extremely short constant pulse width (for example,
By repeatedly applying a voltage having a constant pulse width in the range of 10 to 20 μsec any number of times, the field evaporation voltage Ve can be applied for an optimum time for field evaporation. Therefore,
The electric field evaporation can be finely adjusted by the number of repetitions, and the electric field evaporation is not excessively performed to make the tip of the emitter extremely thick, and conversely, the amount of electric field evaporation is not reduced. Of course, the discharge breakdown of the emitter 1 is prevented. Further, the field evaporation voltage Ve may be applied for an optimum time for field evaporation by adjusting the pulse width arbitrarily.

The electric field evaporation operation of the emitter 1 by applying the pulse voltage described above is executed every time the angular current density of the ion beam is lowered. FIG. 5A shows such a temporal change in the application of the pulsed electric field evaporation voltage Ve and the setting of the extraction voltage Vm, where the horizontal axis is the time and the vertical axis is the extraction voltage. Further, FIG. 5B shows a temporal change of the angular current density corresponding to the change of the extraction voltage of FIG. Figure 5 (b)
In, the horizontal axis represents time and the vertical axis represents angular current density.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, as the ionized atom, argon, nitrogen, oxygen gas or the like can be used other than helium.

[0032]

As described above, according to the present invention, the voltage Ve is applied between the emitter and the extraction electrode every time when the angular current density of the ion beam is reduced to the set value to perform field evaporation of the emitter. In this case, since the voltage is applied in a pulsed manner, the field evaporation voltage Ve can be applied for an optimum time for field evaporation by adjusting the pulse width of the pulse voltage arbitrarily. Therefore, excessive field evaporation does not cause the emitter tip to become extremely thick, or conversely, the field evaporation amount does not decrease. Of course, the discharge breakdown of the emitter is prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional gas phase ion source.

FIG. 2 is a diagram showing a relationship between an extraction voltage and an angular current density.

FIG. 3 is a diagram showing changes over time in the extraction voltage and changes in the angular current density in the conventional device of FIG.

FIG. 4 shows a gas phase ion source according to the present invention.

FIG. 5 is a diagram showing a change in extraction voltage with time and a change in angular current density in the embodiment of FIG.

[Explanation of symbols]

 1 Emitter 2 Extraction Electrode 3 Extraction Voltage Power Supply 4 Acceleration Electrode 5 Acceleration Power Supply 6 Gas Source 7 Focusing Lens 8 Objective Lens 9 Work Material 10 Deflector 11 Micro Channel Plate (MCP) 12 Ammeter 13 Computer 14 Mirror 15 CCD Camera 16 Cathode Ray Tube 17 pulse power supply

Claims (2)

[Claims] 1. An emitter, a means for supplying an ionized gas to the emitter, an extraction electrode, an extraction voltage power supply for applying an extraction voltage between the emitter and the extraction electrode, and a tip portion of the emitter. In a field ionization type gas phase ion source provided with an accelerating electrode for accelerating an ionized gas, a voltage Ve for field-evaporating an emitter tip is applied between an emitter and an extraction electrode, and thereafter,
The extraction voltage is lowered to detect the voltage Vm at which the maximum angular current density of the ion beam is obtained, and thereafter, the voltage Ve is applied between the emitter and the extraction electrode every time the angular current density of the ion beam drops to the set value. The field evaporation of the emitter,
After that, a method of adjusting an ion source for setting an extraction voltage to Vm, wherein the extraction voltage Ve for causing the field evaporation of the emitter is applied in a pulsed manner, the adjustment of a field ionization type gas phase ion source. Method. 2. An emitter, a means for supplying an ionized gas to the emitter, an extraction electrode, an extraction voltage power supply for applying an extraction voltage between the emitter and the extraction electrode, and a tip portion of the emitter. In an electric field ionization type gas phase ion source equipped with an accelerating electrode for accelerating an ionized gas, a pulse power source for generating a pulse voltage and an emitter each time the angular current density of the ion beam drops to a set value. An electric field ionization type gas phase ion source, comprising: a control means for controlling to apply a pulse voltage from a pulse power source so as to be superimposed on a voltage from an extraction power source between the extraction electrode and the extraction electrode.