JPH1167116A - Liquid metal ion source equipment - Google Patents

Abstract

(57) Abstract: To eliminate the detachment of a needle electrode and to maintain the position and direction of the needle electrode with high accuracy while substantially retaining the advantages of a normal hairpin type with a reservoir. To provide a liquid metal ion source device suitable for a liquid crystal ion source. A needle electrode is fixed to an electric insulator. Around the needle electrode 1, a reservoir 3 in which a wire is spirally wound is provided, and both ends thereof are fixed to the heater 2 by spot welding. The heater 2 is fixed to the columns 6a and 6b by spot welding, and the columns 6a and 6b are fixed to the electric insulator 7. The needle-shaped electrode 1 has a constricted heat resistance portion 9 on the side opposite to the tip.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid metal ion source device, and more particularly, to the manufacture, correction, wiring correction, mask ion implantation, ion exposure, and the like of a mask in a semiconductor manufacturing process.
The present invention relates to a liquid metal ion source device suitable for use in ion etching, deposition, device implantation, and the like, as well as in section extraction of a sample in the analysis field and secondary ion mass spectrometry of a minute region.

[0002]

2. Description of the Related Art A substance to be ionized is kept in a molten state by a heater to wet a needle electrode having a tip having a radius of curvature of about several μm. When a high voltage of kV is applied, the electrostatic force generated by the high voltage on the molten material that wets the tip of the needle electrode overcomes the surface tension, and the molten material becomes ions from the tip of the needle electrode. discharge. This is because a liquid metal ion source (Liquid Metal Ion Source; hereinafter abbreviated as L)
MIS). This is a kind of field evaporation type ion source because ions are emitted in a high electric field. A liquid metal ion source has high brightness because ions are emitted from a point-like region, and focuses ions on a sample surface as a final target into a beam having a diameter of 1 μm or less (generally referred to as a focused ion beam or FIB). Hereinafter, this is referred to as FIB.)

[0003] The ion source of this type, small in comparison with electron impact, vibration type and PIG type ion source used in the ion implantation or the like, emission ion current per unit power consumption is large, 10 ⁵ times higher It has characteristics such as brightness and can almost ionize metals and semiconductors.
For this reason, not only can it be used as an ion source for ion implantation into a semiconductor or the like, but also it is possible to narrow the ion beam to a diameter of 1 μm or less at a high current density of several A / cm ² and use a mask. The application of ion beams to ion implantation techniques and microfabrication techniques has not been realized.

[0004]

At present, three types of field evaporation type ion source devices having such advantages have been tried based on the difference in structure for holding a substance to be ionized.

[0005] One is that a substance to be ionized is put in a container such as a crucible and a needle electrode is protruded from the container, and a heater heats the entire crucible. With this structure, a large amount of the substance to be ionized can be taken, so that the life is long and about 1000 hours can be obtained. However, an extremely large amount of heat is required to heat the entire crucible. However, the material to be ionized is limited to those having a low melting point because of the saving of the crucible material and the power consumption of the heater.

[0006] On the other hand, another structure which is desirable in that there is no restriction on such a material is one using a hairpin type heater as shown in FIG. To briefly explain this, the needle-shaped electrode 1 is simply fixed to the bent portion 2a of the hairpin type heater 2 made of a round wire made of a heat-resistant metal such as tungsten. It adheres by the surface tension in the molten state around the intersection of the needle electrode 1 and the bent portion 2a.

This structure has a great advantage in that the structure is simple, the heater power can be used effectively, and there is no particular limitation on the material to be ionized, but the life is short.

The third structure is a hairpin-type LMIS having a reservoir 3 as shown in FIG. 3. The hairpin-type heater structure is modified to avoid a short life of the hairpin type, and the material to be ionized is changed. This is an LMIS provided with a reservoir 3 for storing. This type is the Japanese Patent Publication No. 58-35.
No. 79 discloses this. The amount of the substance 4 to be ionized adhered to the reservoir varies depending on the degree of wetting of the reservoir with the substance 4 to be ionized, the magnitude of the surface tension, the diameter of the wire, and the like. To prevent short life. However, the mounting portion of the needle electrode 1 is mechanically weak, the spot welding 5 is detached, and the reservoir 4 is easily dropped. In addition, thermal deformation occurs at the spot welds, and there is a problem that it is difficult to mount the needle-shaped electrode 1 while keeping its position and direction with high accuracy.

Ideally, an LMIS can stably emit ions for a long time. On the needle electrode surface when the LMIS is operating ideally, the amount of ionic material consumed as ion emission and the amount of ionic material supplied from the reservoir are balanced, and liquid metal flows smoothly from the reservoir to the tip of the needle electrode. To form a simple flow. If the consumption due to ion emission is greater than the supply of liquid metal to the ion emission part, the ion current decreases under a constant extraction voltage, and the extraction voltage increases under a constant current control. Conversely, if the supply of liquid metal to the ion emitting section is greater than the consumption due to ion emission, the radius of curvature of the liquid metal at the tip of the needle-shaped electrode increases, causing problems such as an increase in extraction voltage and dropping of the liquid metal. Wake up. Most of the problems found in general LMIS are directly caused by insufficient supply of the liquid metal to the ion emitting portion.

As an index indicating the smoothness of the flow of the liquid metal from the reservoir to the tip of the needle electrode, V (drawing voltage)
/ I (ion current). If this is constant with no time change with respect to the resistance of the flow of the liquid metal on the needle electrode surface, the liquid metal on the needle electrode surface balances the amount consumed as ion emission and the amount supplied from the reservoir, It can be said that the liquid metal is flowing smoothly. Conversely, if this value increases over time, the flow resistance of the liquid metal increases for some reason, indicating that the supply from the reservoir cannot keep up with the consumption due to ion emission.

The cause of the shortage of liquid metal supply is LMI
In the structure of S itself, that is, in the structure of LMIS,
In particular, depending on the structure of the needle electrode, the reservoir and the heater, the flow of the liquid metal is slowed down or sometimes caused by the surface resistance of the emitter (needle electrode) when the liquid metal reaches the needle electrode tip from the reservoir. Is to stop. In addition, uneven wetting of the liquid metal on the surface of the needle electrode, specifically, if an impurity layer such as an oxide is formed on the surface of the emitter, the liquid metal and the emitter become poorly wet, and the liquid metal becomes wet. Smooth flow is impeded.

In general, the problem with LMIS is that the molten ionic material does not move continuously and smoothly from the reservoir to the needle electrode tip under constant radiation conditions. In other words, if ions are continuously released under certain conditions, the ion current decreases every certain period of time, and in order to return to the same emission state again,
An operation for temporarily increasing the LMIS operating temperature must be performed. This is usually called a flushing operation. In addition, although there are some differences depending on the structure of the ion gun and the type of the LMIS, there is a difference in the frequency due to the contamination during the ion emission due to oxidation or contamination of materials sputtered by the ions to the LMIS, but a flushing operation is required. . Therefore, the power efficiency of the heater is good, the needle electrode can be heated with low power,
An LMIS having no temperature gradient in the reservoir or the needle electrode is ideal.

Further, the fluctuation of the extraction voltage leads to the fluctuation of the beam diameter and the irradiation position when the FIB is formed.
This is a major problem from a usage standpoint.

When the ion current decreases or the extraction voltage increases, the operator of the FIB apparatus will
The so-called flushing of raising the MIS operating temperature or emitting a large current 10 to 100 times as large as the ion current emitted so far to return to the original ion emission state has been performed empirically.

In the case of the filament type having the reservoir 3 shown in FIG. 3, the needle-like electrode 1 projecting from the reservoir 3 is attached to the bent portion 2a of the filament 2 by spot welding.
In the case of this type, the bent portion 2a has the highest temperature in the flushing, and the reservoir 3 is attached to the bent portion 2a, and there is no escape of heat due to heat conduction. The temperature of the bath 3 is reached. Therefore, the thermal efficiency is very good, and the temperature gradient of one part of the needle electrode is small. However, since the directionality of the needle-shaped electrode 1 is poor, and the needle electrode 1 is weak against impact, the reservoir 3 falls with a slight impact. For this reason, handling of the LMIS requires careful handling, and the direction of the needle electrode 1 may not be aligned at the time of attachment. Also, of course, reproduction is not effective with this type of LMIS. Further, since a deteriorated layer is formed in the spot welded portion 5, the wetting of the liquid metal (Ga) 4 is deteriorated. Therefore, the wetting of the needle electrode 1 may be uneven. This causes deterioration of beam current stability, and is considered disadvantageous for continuously emitting a beam.

It is an object of the present invention to eliminate the detachment of the needle electrode and to maintain the position and orientation of the needle electrode with high accuracy while substantially retaining the advantages of the ordinary hairpin type with a reservoir. It is to provide a suitable liquid metal ion source device.

[0017]

SUMMARY OF THE INVENTION The present invention provides a needle-shaped electrode,
A heater having a liquid metal holding portion for holding liquid metal, and a heater associated with the needle electrode so as to supply the held liquid metal to the tip of the needle electrode; and the needle electrode. And an electric insulator to which a heater is fixed, wherein the needle-like electrode is characterized by a liquid metal ion source device having a thermal resistance portion on a side opposite to a tip thereof.

According to another aspect of the present invention, a needle-shaped electrode and a liquid metal holding portion for holding a liquid metal can be provided, and the held liquid metal can be supplied to the tip of the needle-shaped electrode. A needle associated with the needle electrode, and an electrical insulator to which the needle electrode and the heater are fixed, wherein the needle electrode has a needle opposite to a tip thereof. The liquid metal ion source device has a heat blocking portion formed of a material having a higher thermal resistivity than the electrode.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is based on a hairpin type LMIS having a reservoir as a liquid metal holding portion.
The heater and the needle electrode are fixed to an electric insulator. According to this, since the structure becomes strong, there is no fear that the needle-shaped electrode will come off, and there is no thermal deformation factor. It is kept constant. That is, the ion beam can be stably released over a long period of time.

Further, the needle electrode has a heat resistance portion or a heat cutoff portion on the side opposite to the tip. This can solve the problem when the needle electrode is fixed to the electric insulator. That is, since the escape of heat from the needle electrode to the electrical insulator side can be substantially eliminated or reduced, the temperature gradient between the liquid metal holding part and the needle electrode and the temperature generated in the needle electrode As the gradient becomes smaller, thermal efficiency can be improved and power consumption can be reduced. In addition, uniform evaporation of the liquid metal at the needle electrode, and thus uniform wetting of the needle electrode surface by the liquid metal can be achieved. And
As a result, stable release of ion beams and prolonged life can be expected.

A longitudinal groove exists on the surface of the needle electrode. This inevitably occurs during the manufacturing process. This vertical groove has the effect of promoting the movement of the liquid metal to the tip of the needle-shaped electrode due to surface tension. However, transfer to the electrical insulator by surface tension through the flutes of the liquid metal should be avoided as much as possible. In the embodiment of the present invention, the heat resistance portion or the heat blocking portion blocks the flute at this portion. Therefore, the liquid metal is prevented from moving toward the electric insulator due to surface tension through the vertical groove.

FIG. 1 shows an embodiment according to the present invention.
Heater 2, also called filament, has a diameter of 0.15 mm
And a reservoir 3 as a liquid metal holding part.
And the columns 6a and 6b supporting the reservoir are fixed by spot welding. The reservoir 3 has a diameter of 1.2 mm,
A wire having a length of 3.5 mm is spirally wound around the needle electrode 1. When the liquid metal 4 is Ga, the reservoir ^{3 has} a liquid metal holding capacity of 1.2 mm ³ , which corresponds to a Ga weight of 6 mg and a life of 2000 μA · h.

The columns 6a and 6b are made of Kovar and have a diameter of 12 mm.
It is fixed to a disk-shaped alumina electrical insulator (insulator) 7 mm in thickness and 2 mm in thickness. The needle electrode 1 is made of a black W wire having a diameter of 0.2 mm, and is fixed to an electric insulator 7. The surface of the needle-shaped electrode 1 has a longitudinal groove inevitably generated during the manufacturing process, and has an effect of promoting the movement of the needle-shaped electrode 1 to the tip due to the surface tension of the liquid metal 4. The tip of the needle-shaped electrode 1 is machined into a 70-degree cone, and its surface is roughened by electric field polishing, thereby increasing the surface area to which the liquid metal 4 adheres. Therefore, the surface of the needle-shaped electrode 1 is well wetted with the liquid metal 4 and the liquid metal holding amount is increased.

The liquid metal 4 is connected to the needle electrode 1 from the reservoir 3 by surface tension, and flows on the surface. In order for the liquid metal 4 in the reservoir 3 to flow smoothly to the tip of the needle electrode 1 without interruption even if the amount of the liquid metal 4 decreases, the distance between the reservoir 3 and the needle electrode 1 should be 0.3 mm or less. desirable. Ideally, the reservoir 3 and the needle electrode 1 should be in contact with each other.

An extraction electrode 10 is arranged at a position facing the needle electrode 1. When a high voltage is applied between the two electrodes to concentrate an electric field at the tip of the needle electrode 1, the liquid metal at the tip is ionized. The generated ions are extracted as ion beams through the ion passage holes of the extraction electrode 10.

The needle electrode 1 has a heat resistance portion 9 on the side opposite to the tip. This is specifically 0.13m in diameter
m and a constriction with a length of 1.5 mm. This constriction is formed by electric discharge machining. In the case of electric discharge machining, unnecessary stress is not generated in the needle electrode 1 during the machining process.
The role of the heat resistance portion 9 is to effectively prevent the heat of the needle electrode 1 from escaping to the electrical insulator 7 side.

At the time of flashing, a current is supplied to the heater 2 and the heater 2 itself generates heat. This heat is conducted to the reservoir 3, so that the needle electrode 1 is heated by the conducted heat, together with the self-heating of the reservoir 3.

According to the embodiment shown in FIG. 1, the heater 2 and the needle electrode 1 are fixed to the electric insulator 7. According to this, since the structure becomes strong, there is no fear that the needle-shaped electrode 1 comes off, and since there is no thermal deformation factor, the position and direction of the needle-shaped electrode 1, that is, the position of the ion source and the emission ions The direction is kept constant. That is, ion beam
This allows stable release of the system over a long period of time.

The flushing process is performed so that the needle electrode 1 is heated to 750 ° C. when the liquid metal 4 is Ga. According to the experiment, when the needle electrode 1 does not have the thermal resistance part 9, the electric power required to heat the needle electrode 1 to 750 ° C. is 12W, while when the thermal resistance part 9 is present. Found that the power consumption was 7 W. In addition, the temperature gradient of the needle electrode 1 is reduced
It was found that the temperature could be suppressed from 25 ° C / mm to 25 ° C / mm.

The flushing should ideally be performed so that the temperature of the needle electrode 1 is uniform and the highest. However, the temperature that rises most during the flushing is at the connection between the reservoir 3 and the heater 22, and when there is no heat resistance portion 9, the heat transmitted to the needle electrode 1 is transferred to the electric insulator 7 side. Escape by heat conduction. In this case, since the heat capacity of the electric insulator 7 is large, a large temperature gradient occurs in the needle electrode 1. For this reason, when the needle electrode 1 is heated to 750 ° C., the temperature of the portion of the reservoir 3 where the temperature is high reaches 900 ° C., and the evaporation of the liquid metal 4 (Ga) in that portion is accelerated, and the consumption thereof is reduced. It becomes intense. In addition, if there is a temperature gradient, a portion where evaporation is intense and a portion where it is not necessarily occur.
In this state, as the temperature rises, the surface tension of the liquid metal 4 decreases, and the liquid metal 4 diffuses on the surface of the needle electrode 1, but evaporates immediately in the high temperature portion, and as a result, the liquid metal 4 Remains.

However, when the thermal resistance portion 9 is provided, its thermal resistance is inversely proportional to the cross-sectional area and increases in proportion to its length, so that the temperature gradient between the reservoir 3 and the needle electrode 1 is increased. And the temperature gradient of the needle electrode 1 also becomes smaller. In addition, the heat resistance due to the heat conduction of the needle electrode 1 is reduced due to the thermal resistance portion 9, so that the heat retention effect of the needle electrode 1 after the end of the flushing is increased. It turned out to be the needle electrode 1. At this time, the liquid metal 4 (G
Since a) returns to the reservoir 3 by its own weight, it has been found that even if the liquid metal 4 is biased toward a lower temperature by flushing, it can be returned to the original reservoir 3.

In short, since the escape of heat from the needle electrode 1 to the side of the electrical insulator 7 can be reduced, the temperature gradient between the liquid metal holding portion 3 and the needle electrode 1 and the temperature of the needle electrode 1
The temperature gradient generated in the needle electrode 1 becomes small, the thermal efficiency can be improved and the power consumption can be reduced. In addition, uniform evaporation of the liquid metal at the needle electrode 1 and therefore wetting of the surface of the needle electrode 1 by the liquid metal can be achieved. As a result, the ion beam can be stably released and its life can be prolonged.

The vertical groove existing on the surface of the needle electrode 1 is cut off by the heat resistance portion 9. Therefore, the liquid metal is prevented from moving toward the electric insulator due to surface tension through the vertical groove.

The thermal resistance section 9 may be formed as a thermal cutoff. In this method, the needle-shaped electrode 1 is divided into two parts at the boundary, and a member made of a material having a higher thermal resistance than the needle-shaped electrode 1, such as glass, is put between them to integrate the whole. It can be formed by the following. According to this, because of the so-called heat blocking effect, the effect of preventing heat from escaping can be enhanced, and the temperature gradient generated in the needle electrode 1 can be further reduced.

It should be noted that the liquid metal is not limited to Ga.

[0036]

According to the present invention, it is possible to eliminate the detachment of the needle electrode and to maintain the position and the direction of the needle electrode with high accuracy while substantially retaining the advantages of the ordinary hairpin type with a reservoir. There is provided a liquid metal ion source device suitable for performing the above.

[Brief description of the drawings]

FIG. 1 is a structural view of a liquid metal ion source device showing one embodiment according to the present invention.

FIG. 2 is a structural view of a main part of a known liquid ion source device using a normal hairpin type heater.

FIG. 3 is a structural view of a main part of a known ordinary hairpin type liquid ion source device with a reservoir.

[Explanation of symbols]

1: needle-shaped electrode, 2: heater (filament), 3: reservoir, 4: reservoir as liquid metal holding part, 6a, 6
b: support, 7: electrical insulator (insulator), 9: thermal resistance part (constriction), 10: extraction electrode.

Claims (5)

[Claims] 1. A needle-shaped electrode having a liquid metal holding portion for holding a liquid metal and being associated with the needle-shaped electrode so that the held liquid metal can be supplied to the tip of the needle-shaped electrode. A liquid including a heater and an electrical insulator to which the needle-shaped electrode and the heater are fixed, the needle-shaped electrode having a thermal resistance portion on a side opposite to a tip thereof. Metal ion source device. 2. The liquid metal ion source device according to claim 1, wherein the thermal resistance portion includes a constriction formed in the needle electrode at the portion. 3. The liquid metal ion according to claim 1, wherein the thermal resistance section is provided between the liquid storage section and a fixing section of the needle electrode to the electrical insulator. Source equipment. 4. The liquid metal ion source device according to claim 1, wherein the liquid metal holding section includes a liquid metal holding wire spirally wound around the needle electrode. 5. A needle-shaped electrode having a liquid metal holding portion for holding a liquid metal and associated with the needle-shaped electrode so that the held liquid metal can be supplied to the tip of the needle-shaped electrode. And an electrical insulator to which the needle electrode and the heater are fixed, the needle electrode having a higher thermal resistivity than the needle electrode on the side opposite to the tip thereof. A liquid metal ion source device having a heat blocking portion formed of a material having the same.