JPH0797486B2 - Method for manufacturing field emission ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention applies a high electric field to the tip of the needle electrode by heating and melting a substance to be ionized such as metal to wet the tip of the needle electrode. The present invention relates to a field emission type ion source that emits an ion beam.

Since the field emission ion source can obtain a thin ion beam of 0.1 μm or less, it has attracted a great deal of attention for nanofabrication. Further, it can be applied to maskless ion implantation, milling, X-ray mask correction, and the like.

[Conventional technology and problems]

The field emission ion source heats and melts a substance to be ionized and supplies it to the tip of a needle electrode, forms a thin coating of the substance there, and when a high electric field is applied to the tip of the needle electrode, the coating is The electric field produces a protrusion called a Taylor cone, from which ions are emitted. If the leakage of the substance to be ionized into the needle electrode is not uniform, a stable ion beam cannot be obtained. In order to stabilize the ion beam, a method of providing a feed back circuit in the power source of the extraction electrode and a method of providing a control electrode between the needle electrode and the extraction electrode have been proposed (Japanese Patent Laid-Open No. 56-102046). ).

However, even with such a method, it is not possible to suppress spike-like noise that occurs once every several minutes, and it has been difficult to always maintain the current fluctuation rate at 1% / 10 minutes or less.

An object of the present invention is to provide a method of manufacturing a field emission type ion source capable of obtaining a stable ion beam.

[Means for solving problems]

The present inventors have accomplished the present invention as a result of various studies on aging after assembling a field emission type ion source to achieve the above object.

That is, the present invention is a needle electrode, a storage unit for storing a substance to be ionized, a heating unit for heating the needle electrode and the storage unit, and a drawer for applying an electric field to the tip of the needle electrode. A field emission ion source comprising electrodes, wherein the field emission ion source is treated in the following first to third steps.

First step: The heating is performed in a vacuum without applying the electric field, and the temperature of the storage section reaches a temperature higher than the operating temperature by 50 ° C. or more.

Second step ... The electric field is applied while maintaining the temperature and vacuum of the first step.

Third step: The temperature of the storage is lowered to the operating temperature while maintaining the vacuum and applying the electric field.

Hereinafter, the present invention will be described in detail. In the present invention, the operating temperature is the temperature of the storage section when the field emission type ion source (hereinafter referred to as ion source) of the present invention is used,
It is determined by the experiment described below.

That is, the ion source that has completed the assembly and stores the desired substance to be ionized is first heated to melt the substance to be ionized in the storage unit, and the temperature of the storage unit is set to 40 ° C or higher than the melting point of the substance.
Increase the temperature by 0-700 ℃. Next, an extraction voltage is applied to the extraction electrode, and the extraction voltage is adjusted so that the ion current value is about 5 to 10 μA. Then, by adjusting the heating power source, the fluctuation rate of the ion current at that time is measured while the temperature of the storage part is gradually lowered. The temperature at which the ion source is preheated varies depending on the substance to be ionized, and it is desirable to raise the temperature as high as possible within the range where the vapor pressure does not increase.

As a result of the above experiment, the temperature of the storage section when the fluctuation rate of the ionic current is the smallest is the desired operating temperature. Of course, the operating temperature varies depending on the structure of the ion source, the material and size of the needle electrode, and the type of ionized substance, but it can be obtained in advance by the method described above.

Next, the temperature of the storage unit in the first step is higher than the operating temperature.
The temperature should be higher than 50 ° C. 50 from operating temperature
If it is not higher than ℃, there is no effect of stabilizing the ion beam. Further, the upper limit of the temperature of the storage part varies depending on various conditions, but generally, when the temperature is higher than the operating temperature by 300 ° C. or more, the substance to be ionized with the needle electrode or the storage part causes a remarkable reaction, or the substance to be ionized. Is significantly vaporized, which is not preferable.

In this temperature range, the substance to be ionized spreads well on the tip of the needle electrode. In this state, the viscosity of the substance to be ionized is reduced, so that when the extraction voltage is applied to the extraction electrode in the second step, the tip of the needle electrode can be completely covered with the substance to be ionized. . If the ion beam is emitted at a temperature higher than the operating temperature, a stable ion beam cannot always be obtained, but if the temperature of the storage section is then lowered to the operating temperature in the third step, the ion beam will be stabilized. If you hold this state for at least 10 minutes,
A thin and uniform coating of the substance to be ionized is formed on the tip of the needle electrode to complete the ion source.

The ion source thus obtained can be directly put into use as it is. Also, when not in use immediately, the power may be turned off and left. When the ion source manufactured in this way is used next time, a stable ion beam can be obtained only by heating it to a predetermined operating temperature and applying an extraction voltage to the extraction electrode. Also, if the ion source is misused and the ion beam is emitted at a temperature that is too low or if a discharge is generated, the coating of the substance to be ionized at the tip of the needle electrode is disturbed and the ion beam becomes unstable. Sometimes. In such a case, the ion beam can be stabilized by performing the processes from the first step to the third step. As described above, the method for producing an ion source according to the present invention can be used as a method for repairing a disordered ion source.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIG.

Example 1 A needle-shaped electrode 3 was prepared by forming a tungsten carbide sintered body into a rod shape of 0.5 × 0.5 × 4.7 mm, and having a longitudinal end made by a mechanical polishing method to have a cone angle of 30 ° and a radius of curvature of 1 μm. The tantalum reservoir 2 was attached to the needle electrode, and the heating supports 7a and 7b were provided on the needle electrode base 5.

As a substance 1 to be ionized, a needle electrode and a part of the reservoir were immersed in an Au ₆₀ Si ₂₆ Be ₁₄ (atomic ratio) alloy melted in a crucible made of boron nitride. Filled.

The environment of this ion source was set to a vacuum with a vacuum degree of 3 × 10 ⁻⁵ Pa, the temperature of the storage part was set to 800 ° C., and the fluctuation rate of the ion current at 800 ° C. was measured and found to be 2% / 10 minutes. As a result of measuring the fluctuation rate of the ion current while gradually lowering the temperature, as shown in the ion source a in FIG. 2, it was 2% / 10 minutes at 720 ° to 800 ° C, but 1% / at 700 to 490 ° C. It took 10 minutes.

Next, when a similar experiment is performed using another ion source b having the same structure and the same ionized substance, as shown in FIG.
At ℃, the current fluctuation rate was 1.5% / 10 minutes, but 750 to 500 ℃
In the range of 1%, it was 1% / 10 minutes. From these results, when the substance to be ionized is Au ₆₀ Si ₂₆ Be ₁₄ , 700-500 ℃
Is a stable temperature range, and 700 ° C is especially desirable operating temperature. Therefore, first, the temperature of the storage unit 2 was set to 800 ° C. while maintaining the above-mentioned vacuum and maintained for 10 minutes (first step).

After that, an extraction voltage of 4.24 KV was applied between the needle-shaped electrode and the extraction electrode 10 to emit an ion beam 11 of 10 μA for 10 minutes (second step). Then, raise the temperature of the storage to 700
The temperature was lowered to ℃ (3rd step).

The ion source manufactured in this way is extended at an operating temperature of 700 ° C.
I used it for 00 hours. During that time, the power is stopped for 30 days due to interruption of use.
Despite the number of turns, the ion current fluctuation rate during that time was 1% / 10 minutes or less.

Example 2 An experiment was conducted in which the ion source prepared in Example 1 was intentionally broken down to increase the fluctuation rate of the ion current and repaired by the method of the present invention. That is, when the ion source b prepared in Example 1 is gradually heated while applying an extraction voltage at 400 ° C. to eject ions, the temperature of the storage part is 800 ° C. and the ion current fluctuation rate is 7%. / 10 minutes or more.
This is because the substance to be ionized is discharged at a low temperature and has a high viscosity, so that the uniform coating of the substance to be ionized is disturbed. The instability of the ion source was stopped and the storage temperature was lowered to 300 ° C or lower.

First, the temperature of the storage section was heated to 800 ° C. in the environment of this ion source in a vacuum state with a vacuum degree of 3 × 10 ⁻⁵ Pa (first step). Next, an extraction voltage of 4.25 KV was applied (second step).
Then, while maintaining the vacuum and continuing to apply the extraction voltage, as shown in FIG. 3, the temperature was lowered from 800 ° C. to 700 ° C., and ion beam emission of 60 μA was performed for 1 minute (3rd step).
Process). By the above processing, the ion current fluctuation rate of this ion source returned to a stable state of 1% / 10 minutes.

Example 3 A structure of the ion source shown in FIG. 1 was prepared by using a tip of a tungsten wire having a diameter of 0.15 mm, which was sharpened to have a radius of curvature of 1 μm or less by electrolytic polishing as a needle electrode 3.

Gallium was melted in an alumina crucible and the acicular electrode and the reservoir were dipped in the crucible to fill the reservoir with gallium.

When the practical operating temperature of this ion source was determined by the method described in Example 1, it was 500 to 600 ° C. The environment of this ion source was set to a vacuum degree of 7 × 10 ⁻⁵ Pa, and the temperature of the storage section was first set to 650 ° C. and maintained for 15 minutes (first step). Next, an extraction voltage of 5.22 KV was applied between the needle-shaped electrode and the extraction electrode, and ion emission with an ion current of 20 μA was performed for 10 minutes (second step).

Gradually lower the temperature to 600 ℃ in the storage section and confirm that the current fluctuation rate is 1% / 10 minutes or less.
Hold for 3 minutes (3rd step). The ion source produced by such treatment is 500-60 after 700 hours.
At an operating temperature of 0 ° C., an ion current of 5 to 10 μA could be obtained with a stability of a current fluctuation rate of 1% / 10 minutes or less.

〔The invention's effect〕

The ion source manufactured through the treatment steps of the first step to the third step of the present invention is excellent in the stability of the ion current, and can be used without performing an aging operation.

[Brief description of drawings]

FIG. 1 is an explanatory view of an ion source of the present invention, FIG. 2 and FIG.
The figure is a graph showing the relationship between the heating temperature of the ion source used in the examples and the current fluctuation rate. Reference numeral 1 ... a substance to be ionized, 2 ... a storage unit, 3 ...
Needle electrode, 4 ... Needle electrode tip, 5 ... Needle electrode base,
6 ... Adhesive, 7a, 7b ... Heating support, 8a, 8b ... Conductive support, 9a, 9b ... Conductive partition, 10 ... Extraction electrode, 11
...... Ion beam, 12a, 12b ...... Insulation material, 13a, 13b ...... Nut, 14 ...... Connecting rod, 15a, 15b …… Strip plate, 16a, 16b …… Electrode, 17 …… Heating power supply, 18 …… Drawer power supply

Claims (1)

[Claims] 1. A needle electrode, a storage unit for storing a substance to be ionized, a heating unit for heating the needle electrode and the storage unit, and a drawer for applying an electric field to the tip of the needle electrode. A field emission ion source comprising an electrode, wherein the field emission ion source is treated in the following first to third steps. First step: The heating is performed in a vacuum without applying the electric field, and the temperature of the storage section reaches a temperature higher than the operating temperature by 50 ° C. or more. Second step ... The electric field is applied while maintaining the temperature and vacuum of the first step. Third step ... Maintaining a vacuum and lowering the temperature of the reservoir to the operating temperature while applying the electric field.