JPH1125874A - Gallium ion source and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion beam for a long time, which can operate for a along time at a room temperature, can improve a flashing interval and has a small energy width and superior quality by using a gallium ion source having a standardized X-ray intensity ratio of tungsten to gallium, detected from a side part of a tungsten electrode not higher than a specific value. SOLUTION: A gallium ion source is composed by using a tungsten electrode 1 and assembling a storage part 2 for gallium 3, heater parts 4A, 4B and an electroconductive supporting 5A, 5B. In this gallium ion source, a standardized X-ray intensity ratio of tungsten to gallium detected from a side part of the tungsten electrode 1 is set not more than 2.0. At this time, stable supply of gallium to the tungsten electrode 1 is secured, and as a result, stable ion emission is attained stably for a long time, even at room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium ion source used for an ion microscope, a focused ion beam device, a TEM pretreatment device, and the like.

Circuit formation in the manufacture of semiconductor integrated circuits,
Alternatively, a focused ion beam apparatus equipped with a liquid metal ion source for mask repair and further surface analysis has been developed and spread. As for the liquid metal ion source, so-called liquid metal ion sources using various metals and alloys as ion species are known. Among them, a gallium ion source has been attracting attention as a suitable source for the mask repair and surface analysis.

[0003]

2. Description of the Related Art Gallium is a liquid metal at room temperature, and its ion source has a structure in which, for example, as shown in FIG. 2, a tungsten electrode 1 having a sharp point at its tip and a storage section 2 are welded to a hairpin type filament. Things. FIG.
As shown in FIG. 5, the tungsten electrode 1 penetrates the storage section 2 and is heated by the heating sections 4A and 4B as necessary. The storage 2 is filled with gallium 3,
The gallium 3 spreads on the surface of the tungsten electrode 1, and the tip of the tungsten electrode 1 is wet by the molten gallium 3.

In the gallium ion source described above, when a positive potential is applied to the tungsten electrode 1 and a negative potential is applied to the extraction electrode, the gallium at the tip of the needle-like electrode has a conical shape called a Taylor cone with a potential difference exceeding a certain threshold. Gallium ions are extracted from the tips. The gallium ion source having the structure shown in FIG. 1 is used at a high temperature of about 500 to 600 [deg.] C. by energizing heating when stable ion emission for a long time is required.

However, in the above-mentioned conventional gallium ion source, use at a high temperature not only increases the energy distribution width of the emitted ions, but also has the drawback that the gallium is largely consumed by evaporation and has a short life, so that the gallium ion source cannot be used at room temperature. Has become the current mainstream in the use of gallium ion sources.

The tip of a tungsten electrode used for a gallium ion source is sharpened from a fine wire having a diameter of about 0.15 mm, usually by an electrolytic polishing method using an aqueous solution of sodium hydroxide as an electrolytic solution. Mirror polishing of the side surface.

[0007]

However, when the gallium ion source is operated at room temperature, there is a problem that it is difficult to stably release ions for a long time, and the stable operation of the focused ion beam apparatus is secured. There are serious problems such as the inability to improve the productivity of semiconductor integrated circuit manufacturing equipment.

[0008] In order to ensure stable ion emission of the gallium ion source, it is necessary to smoothly supply liquid metal gallium to the tip of the tungsten electrode. However, during operation at room temperature, since the oxide on the surface of the liquid metal gallium is difficult to volatilize and remove, the flow of the liquid metal gallium from the storage unit to the tip of the tungsten electrode is not smooth, and the gallium does not flow to the electrode tip. Supply and shortage
As a result, there is a problem that the ion emission becomes unstable or the applied voltage becomes extremely high when the ion emission amount is maintained at a predetermined amount.

A gallium ion source whose gallium surface has been once oxidized and ion emission has become unstable can be obtained by performing a flushing operation to temporarily raise the operating temperature.
It is known to return to the same ion emission state again.
However, during the flushing operation, the expensive apparatus is substantially stopped as described above, which is a serious problem in practical use.

The stable ion emission time between the flushing operation and the next flushing operation, that is, the flushing interval is an indicator of the operation at room temperature and is an important indicator for the performance of the gallium ion source. However, there is a problem that the flushing interval is extremely short, for example, several tens of hours.

The present inventors have conducted various studies in view of the above circumstances, and as a result, when the tungsten electrode is roughened at least on its side surface and the gallium coats the tungsten electrode in a specific state, the flushing interval of the gallium ion source is reduced. The present invention has been found to be longer, leading to the present invention. That is, an object of the present invention is to provide a gallium ion source that can operate at room temperature for a long time.

[0012]

That is, the present invention relates to a gallium ion source having a storage for storing gallium to be ionized and a tungsten electrode having a needle-like tip to which gallium is supplied from the storage. The gallium ion source is characterized in that the ratio of the standardized X-ray intensity of tungsten and gallium detected from the side surface of the tungsten electrode is 2.0 or less, and preferably the storage unit and / or the tungsten The gallium ion source has a heating unit for heating an electrode.

Further, according to the present invention, at least the side surface of the tungsten electrode is etched so that the ratio of the standardized X-ray intensities of tungsten and gallium detected from the side surface of the tungsten electrode is 2.0 or less. A method for producing a gallium ion source, which is preferably characterized in that etching is performed using an alkaline aqueous potassium ferricyanide solution.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for measuring X-ray intensity in the present invention using an energy dispersive spectroscopy will be described. FIG. 3 shows the arrangement of the sample and the equipment in the measurement. The measurement conditions were as follows: the acceleration voltage of incident electrons was 20 kV, the electron beam incident angle θ1 was 40 °, the angle θ2 between the detector and the electron source was 90 ° Characteristic X-rays are gallium, Kα rays,
Tungsten is an Lα ray. The measurement area is 2 × 1
0 ^-3 mm ² or more.

In the present invention, the ratio of the standardized X-ray intensities IW / Ga of tungsten and gallium is determined by the respective X-ray intensities IW, IGa, Tw of tungsten and gallium detected from the side surface of the tungsten needle electrode. Then, using the X-ray intensities IW0 and IGa0 of tungsten and gallium themselves measured under the same conditions in advance, it is expressed by the following equation (1).

IW / Ga = (IW / IW0) / (IGa / IGa0) (1)

In the present invention, it is essential that the ratio between the standardized X-ray intensities of tungsten and gallium detected from the side surface of the tungsten electrode is 2.0 or less. Stable supply to the tip of the tungsten electrode is ensured, and as a result, stable ion emission is achieved over a long period of time even at room temperature.

Although the reason for this is not clear, the present inventors have determined that the amount of gallium adhering to the side surface of the tungsten electrode is not less than a certain amount, which is necessary and sufficient for the stable supply of gallium to the tip of the tungsten electrode. I guess it is a condition. In other words, even if a certain amount or more of the gallium layer is present on the surface of the tungsten electrode, for example, in the case where the presence of an oxide in the gallium surface layer impairs the fluidity near the gallium surface layer, the tungsten electrode The flowability of gallium in the vicinity of the surface is not hindered, and stable ion emission can be achieved. Further, in order to achieve the object of the present invention, it is not necessary to particularly define the lower limit of the ratio of the standardized X-ray intensities of gallium and tungsten.

In the method of manufacturing a gallium ion source according to the present invention, at least a side surface of a tungsten electrode is provided with an appropriate surface roughness and shape, and a standard for tungsten and gallium detected from a side surface portion of the tungsten electrode. Any processing method may be used as long as it can be processed so that the ratio of the converted X-ray intensities is 2.0 or less. However, according to the study results of the present inventors, after etching at least the side surface of the tungsten electrode, the tungsten electrode tip is processed into a desired shape by a known processing method such as a mechanical processing method or an electrolytic polishing method. The gallium ion source of the present invention can be easily obtained.

In the etching, it is preferable to perform etching in an alkaline potassium ferricyanide aqueous solution since the gallium ion source of the present invention can be stably obtained. In order to ensure the etching effect of the aqueous potassium ferricyanide solution, the aqueous solution is made alkaline. For this purpose, potassium hydroxide and / or sodium hydroxide can be used.

[0021]

【Example】

[Example 1] An etching solution was prepared by mixing potassium ferricyanide, potassium hydroxide and water in a weight ratio of 1: 1: 20, and a tungsten wire having a diameter of 0.15 mm and a length of 20 mm was immersed and etched at room temperature for 1 minute. As a result, a tungsten wire whose side surface was roughened was manufactured.

Next, the tip of the tungsten wire was electropolished using an aqueous solution of sodium hydroxide as an electrolytic solution to obtain a tungsten electrode having a sharp end for an ion source.

The gallium ion source illustrated in FIG. 1 was fabricated by assembling a gallium storage unit, a heating unit, and an insulator using the tungsten electrode. The gallium ion source was set in a vacuum apparatus having a crucible previously filled with gallium, and evacuated to 7 × 10 ⁻⁷ Torr,
While heating the gallium together with the crucible, energizing the heating unit of the gallium ion source, and immersing the tungsten electrode and the storage unit in gallium in the crucible while heating, the tungsten electrode surface is wetted with gallium and the storage unit is gallium. To obtain a gallium ion source.

With respect to the gallium ion source, the X-ray intensity on the side surface of the tungsten electrode was measured under the following conditions.
The ratio of the standardized X-ray intensities of tungsten and gallium was calculated, and the flushing interval at room temperature with a total emission current of 2 μA was measured. The results are shown in Table 1.

<Method of Measuring X-ray Intensity> The measurement is a measurement to which energy dispersive X-ray spectroscopy is applied, and schematically shows the arrangement of samples and equipment (see FIG. 3). The measurement conditions are as follows: the acceleration voltage of incident electrons is 20 kV, the electron beam incident angle θ1 is 40 °, and the angle θ2 between the detector and the electron source is 90 °. The X-ray intensity is measured in a measurement area of about 2.2 × 10 ⁻³ mm ² at the center of the side surface of the tungsten electrode of the gallium ion source. The detected X-rays are characteristic X-rays of tungsten which is an electrode member and gallium which wets the surface,
Measure IW and IGa.

Further, a container having an appropriate depth is filled with gallium and an electron beam is applied to the gallium itself to measure the X-ray intensity IGa0, and the sample is changed to a tungsten wire having a diameter of 0.15 mm to measure IW0. . The above IGa0
, IW0, IGa, and IW, from the above equation (1),
The ratio IW / Ga of the normalized X-ray intensities of tungsten and gallium is calculated.

<Measurement of Flushing Interval> FIG.
Using a measurement system shown in (1), an extraction electrode made of a perforated metal plate is provided at a position 1.7 mm away from the tip of the tungsten electrode, and ions are emitted by applying a positive voltage to the gallium ion source. Usually, the filament current is 0 A, that is, the device is operated at room temperature without heating.

In order to measure the flushing interval, first, a filament current is supplied, the filament is heated at, for example, about 600 ° C. for several minutes, and then flushing is performed. Then, the extraction voltage Vex is adjusted by a constant voltage operation so that the total emission current becomes 2 μA. A change in the extraction voltage Vex with time is examined, and the time when the ratio Vex / Vex0 with respect to the initial extraction voltage Vex0 reaches 1.3 is defined as a flushing interval.

[0029]

[Table 1]

[Examples 2 to 4] In the same manner as in Example 1, except that the etching time was changed to 10, 30, and 60 minutes (Examples 2, 3, and 4 respectively). Example 1 A gallium ion source was obtained by the same operation.
The same evaluation was performed. The results are shown in Table 1.

COMPARATIVE EXAMPLE As a comparative example, an aqueous solution of sodium hydroxide was used as an electrolytic solution, and the diameter was 0.15 mm and the length was 20 mm.
A side surface of a tungsten wire having a thickness of 1 mm was subjected to mirror polishing by electrolytic polishing, and a tip portion was electrolytically polished to prepare a tungsten electrode for a ion source having a sharp end. The side surface of the tungsten electrode is a mirror surface, which is the same as the tungsten electrode of a conventionally known gallium ion source.
This gallium ion source was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0032]

As is clear from the embodiments, the gallium ion source according to the present invention provides a long-time operation at room temperature, a greatly improved flushing interval, and an ion beam having a small energy width and excellent quality for a long time. Because it can be used, it is very useful for many ion beam utilizing devices including a focused ion beam device.

[Brief description of the drawings]

FIG. 1 Structure of gallium ion source

FIG. 2 is a structural diagram of another gallium ion source.

FIG. 3 is a diagram showing a sample and equipment arrangement when measuring X-ray intensity.

FIG. 4 is a measurement circuit diagram of an ion emission characteristic.

[Explanation of symbols]

 Reference Signs List 1 tungsten electrode 2 storage unit 3 gallium 4A heating unit 4B heating unit 4C heating unit 5A conductive support member 5B conductive support member 5C conductive support member 5D conductive support member 6A partition 6B partition 7B partition 7 insulator

Claims (4)

[Claims] 1. A gallium ion source having a storage unit for storing gallium to be ionized and a tungsten electrode to which gallium is supplied from the storage unit, wherein the gallium ion source includes tungsten and gallium detected from side surfaces of the tungsten electrode. A gallium ion source, wherein the ratio of the normalized X-ray intensities is 2.0 or less. 2. A heating device for heating a storage part and / or a tungsten electrode.
A gallium ion source as described. 3. The method according to claim 1, wherein at least the side surface of the tungsten electrode is etched so that the ratio of the standardized X-ray intensities of tungsten and gallium detected from the side surface of the tungsten electrode is 2.0 or less. For producing a gallium ion source. 4. The method for producing a gallium ion source according to claim 3, wherein the etching is performed using an alkaline aqueous solution of potassium ferricyanide.