JPS6188436A - liquid metal ion source - Google Patents

Abstract

PURPOSE:To achieve prolonged stable emission of ions by continuously supplying the substance to be ionized in a liquid metal ion source which has a container for storing the substance, a feeder and an auxiliary heater for melting the substance. CONSTITUTION:In the liquid metal ion source of this invention, a molten substance 2 to be ionized held in a reservoir 24 is discharged from the pointed end of a needle-like emitter chip 12 and a lead-out electrode 20 is used to lead out ions 22. The liquid metal ion source also has a container 32 for storing particles 2' of the substance to be ionized, a feeder 34 having a spiral rotary shaft 34a, and an auxiliary heater 33 having a receiver 51 heated by feeding currents to current introduction terminals 52 and 52'. The substance to be ionized is supplied into the reservoir 24 while being heated and molten and while controlling the supply of the substance. Accordingly, it is possible to continuously produce ions from the substance for a long time. Furthermore, it is also possible to achieve a constant characteristic of ion emission by preventing any temperature variation.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to the groove construction of a liquid total bending ion source provided with a preheating section for an ionized substance, and is particularly suitable for long-term continuous operation of fine ion implantation. Concerning a suitable liquid metal ion source.

[Background of the invention]

The ion beam emitted from the liquid metal ion source is focused to submicron size, and this is used in fields such as submicron dry processes (maskless doping, ion beam exposure, ion beam processing, etc.) and submicron surface analysis. The application of this has recently attracted attention. Particularly in the field of electronic devices, impurities (e.g., boron, phosphorus, arsenic, etc.) can be directly implanted (also called implantation, doping) into a narrow region on the surface of a semiconductor substrate without using a mask, and conventional masks can be used. This method is attracting a lot of attention because it enables implantation into minute regions that could not be achieved with traditional ion implantation, and because it promises to greatly simplify the semiconductor process.

The operating principle and typical basic configuration of this liquid total bending ion source are detailed in Japanese Patent Application Laid-Open No. 125998/1982, but the operating principle will be briefly described here.

First, a substance to be ionized (liquid metal) is supplied to an emitter with a sharply pointed tip, which has been melted by gravity heating, electron beam impact, laser light, etc. When a high voltage is applied between the emitter and the extraction electrode, an electric field concentrates at the tip of the emitter. As a result, the liquid metal at the tip of the emitter becomes a TayLor Co.
A conical projection called r+a) is formed, and the ion beam is extracted from its tip.

When such an ion source is used in various fields, it is important that the ion source can stably extract a target ion beam for a long period of time.

These conventional ion sources have the following problems. In other words, (1) It is necessary to keep the entire amount of ionized material loaded in the ion source in a molten state at all times, so if the ionized material is solid, powdered, or has a high melting point, the power consumption for heating it will increase. is big.

(2) When the heater current is constant, the temperature of the ionized substance increases as the ionized substance decreases, and the ion release characteristics change, such as an increase in the total ion current value.

(3) When the ionized substance is an alloy of metals with significantly different vapor pressures, the ratio of the alloy composition changes due to selective evaporation due to long-term heating.

(4) The amount of ionized material loaded is limited by the size of the reservoir or crucible and the heating capacity, which is a factor in determining the life of the ion source.

(5) If ion release cannot be expected due to consumption of the ionized substance, the vacuum must be broken once and the ionized substance must be replenished from the outside. If ion emission is interrupted once, ionized material is replenished, and ion emission is resumed, it will take a long time for ions to be stably emitted immediately after the emission is resumed, and the emitted ion current characteristics of the extraction voltage will change. It's different compared to before the interruption. In addition, replenishment work also takes time.

[Purpose of the invention]

An object of the present invention is to provide a liquid metal ion source that can stably emit ions and operate continuously for a long time.

[Summary of the invention]

The ion source of the present invention includes a reservoir for holding a substance to be ionized in a molten state, and is arranged so as to emit ions of the substance to be ionized in a molten state supplied from the reservoir from its tip. an extraction electrode for extracting ions from the tip of the emitter by concentrating a high electric field at the tip of the emitter; a reservoir for a substance to be ionized; and a reservoir for a substance to be ionized from the reservoir to the reservoir. It is characterized by comprising a transfer means for transferring the substance and a preheating section for melting the substance to be ionized.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure shows the basic configuration of a liquid metal ion source equipped with an ionizable substance preheating section according to the present invention. In the figure, 2.2' is an ionized substance reservoir or crucible, 4 is a heating part (heater), and 12
22 is a needle-shaped emitter chip, 22 is an ion beam, 32 is a storage section for ionized substances, 34 is a means for transporting ionized substances, and 33 is a preheating section for ionized substances according to the present invention.

37a, 37b are movement paths for ionized substances, 20 is an ion extraction electrode 14, 16.18.35 is a power source, 8.8'
1 is a current introduction terminal, and 10 is a circular hole.

Furthermore, all of the power supplies except the power supplies 14, 16, 18, and 35 are housed in the vacuum container 36.

This liquid metal ion source uses a method in which an ionized substance is melted by electrical heating, and the ionized substance 2
The reservoir portion 24 also serves as the heating portion 4, and resistance heating is performed by energizing the heating portion 4 made of metal, carbon, etc.
The heat melts the ionized material 2. The tip of the needle-like emitter tip 12 is sufficiently wetted with the molten ionized substance 2.

Therefore, by applying a negative high voltage to the ion extraction electrode 20, the ionized substance 2 attached to the tip of the needle-shaped emitter tip 12 is ionized, and the ion beam 2 is
2 is drawn.

In this example, NiB and Keckel-boron alloy (melting point: about 1000° C.) were used as the ionized substance 2'. The heater is made of carbon, and its shape is such that there is a recess in the center of the heater 4 in order to avoid scattering of the ionized substance 2 from the movement path 37 of the ionized substance 2 on the heater 4.
4, and has a shape that also serves as a reservoir for the ionized substance 2. In addition, in order to increase the heat generation efficiency of the heater 4,
The width of the heater 4 between the reservoir portion 24 and the current introduction terminals 8, 8' is reduced to about 1 mm. Note that the plate thickness of this heater 4 is 0.2 a+m. The loading capacity of N i B stored in this recess 24 is approximately 5 mm, and the time (life) until stable ion release can no longer be expected is approximately 10 mm.
It was 0 hours. Of course, this lifetime depends on the amount of ions released (
It is not a fixed value because it depends on the total emitted ion current value) and the amount of evaporation due to heating of the ionized substance.

The ionized substance storage section 32 has a larger capacity than the reservoir section 24 of the heater 4, and in this embodiment, about 2 cm3 of granular or powdered NiB crushed to a maximum diameter of about 0.5 ml11 is contained inside the ionized substance storage section 32. It is installed.

In this example, as a specific example of the means for transporting ionized substances,
A helical rotating shaft 34a as shown in FIG. 2 was used.

The amount and timing of supply of the ionized substance 2 to the reservoir section 24, the amount of rotation of the helical rotating shaft 34a, and the amount of supplied ionized material to the preheating section 33 are measured in advance, and the amount of helical rotation 34a is adjusted. By causing ionized substance 2
' was supplied to the preheating section 33 in an amount of about 2 mm3 at about every 50 hours, and was heated and melted in the preheating section 33. in this case,
The preheating section 33 does not always need to be in a heated state, and only when the preheating section 33 is supplied with the ionized substance 2, ff1
Just activate fi35. Further, it is desirable that the temperature of the preheating section 33 is approximately the same as that of the reservoir section 24.

Here, in a liquid metal ion source having a storage section 32 for the ionized substance 2 independently of the reservoir section 24 for melting the ionized substance 2 or the heater 4, a preheating section 33 is used.
6 Explain the significance of the need for ionized substance 2' in a conventional liquid metal ion source.
3, and a reservoir 2 in which the ionized substance 2' is in a molten state.
4 or unmelted ionized substance to be replenished onto the heater 2
When the ionized substance 2' is introduced using the transfer means 34, the unmelted ionized substance 2' is added all at once. Naturally, the temperature of the ionized substance 2 in the molten state drops rapidly. This temperature drop may change ion emission characteristics such as the emitted ion current value, or in extreme cases, ion emission may stop.

Fluctuations in ion emission characteristics pose a problem in that when fine ion implantation is performed, the characteristics of the semiconductor into which the ions are implanted also change. As a method of reducing this temperature drop, a means 34 for transporting the ionized substance 2' that supplies the ionized substance in small amounts is considered. The relationship between the temperature of the molten ionized substance 2 and time at this time is as shown in Figure 3(b), although the temperature change is not as drastic when the ionized substance 2' is introduced all at once as shown in Figure 2(a). As shown in
If vtt amount of ionized substance 2 is supplied at short intervals such as + tz + ti + ta, the fluctuation in temperature drop becomes smaller. (However, in Figure 1, T1 is the temperature of the molten ionized substance 2.) However, this problem of temperature drop has not been solved, and there is a need for a means of replenishing the ionized substance 2' that does not cause temperature fluctuations at all. Ta.

Various methods can be considered for heating the ionized substance 2 in the pre-excitation heating section 33. For example, as shown in FIG. 4(a), there is a method of electrically heating a thin metal plate 40 processed so as to be able to receive the ionized substance 2 transferred by the transfer means 34, or as shown in FIG. 4(b). There is a method in which a receiver 41 processed to receive the unmelted ionized substance 2' is heated by radiant heat from a heater 42 that surrounds it.

The preheating section of this embodiment will be described below with reference to FIG. 5. The preheating section 33 of this embodiment includes a receiver section 51 that receives and holds the unmelted ionized substance 2 transferred by the transfer means 34, and current introduction terminals 52 and 52'.
The receiving part 51 also serves as a heater heated by electricity, and the receiving part 51 can melt the unmelted ionized substance 2' held in the receiving part 51. This receiver is part 51
is made of molybdenum (MO), which is a type of high melting point metal, and is made of a plate with a thickness of 0.1 mm. Furthermore, the upper opening is 3 to 4
It has a 7 mm or U-shaped cross section, and the longitudinal direction is approximately 2 mm.
It has a slightly inclined structure at 0o+m. This inclination allows the ionized substance 2 melted on the receiver portion 51 to flow into the reservoir 24 for the molten ionized substance 2 .

With such a structure, the unmelted ionized substance 2' transferred from the storage section 32 is heated to 1 to 1 on the preheating section 33.
It can be melted in 2 minutes and supplied to the reservoir 24, so that the temperature of the molten ionized substance 2 in the reservoir 24 is
As shown in FIG. 3(c), there was almost no change.

〔Effect of the invention〕

According to the present invention, a large amount of ionized substance can be stored by increasing the capacity of the storage section for solid powder or liquid ionized substance, and stable ion release can be performed continuously for a long time by continuous replenishment. I can do it. Moreover, since the storage section is independent of the heating section and the reservoir section, it is not necessary to keep the entire amount of the ionized substance loaded in the ion source in a molten state at all times, and power consumption can be kept at the same level as in the past. In addition, the ionized substance can be replenished inside the vacuum container, so
Changes in ion emission characteristics before and after replenishment caused by interruption of ion ejection for replenishment of the ion beam from outside the vacuum can be avoided. Moreover, when the ionized substance is an alloy of metals with significantly different vapor pressures, selective evaporation due to long-term heating can be avoided by continuously replenishing the ionized substance from the storage section. Furthermore, by providing a pre-heating section for the ionized substance, it is possible to replenish the reservoir at approximately the same temperature as the molten ionized material in the reservoir, without changing the ion release characteristics, and for a certain period of time. By supplying the ions to the reservoir at intervals, stable ion release can be performed continuously for a long period of time.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a liquid metal ion source according to the present invention, FIG. 2 is a diagram showing an embodiment of a means for transporting ionized substances, and FIGS. 3(a), (b), and (c) are views showing ionized substances. FIG. 4(a) and (b) are schematic planting diagrams for explaining the preheating section according to the present invention; FIG. FIG. 1 is a configuration diagram showing an embodiment of a pre-excitation heating section of the present invention. 2.2'... Ionized substance, 4... Heating section, 1o.
...Circular hole, 12...Acicular emitter tip, 20...
- Extraction electrode, 22... Ion beam, 24... Reservoir, 32... Storage section, 33... Preheating section, 34
... Transfer means, 34a... Spiral rotation shaft, 35.
...Power source, 36...Vacuum container, 40...Metal plate, 4
1... Uke is part, 42... Hi Fig. 3 (Yu 9 Far seat 1 z 5 Ro

Claims (1)

[Claims] 1. A reservoir for holding a substance to be ionized in a molten state; an emitter arranged to emit ions of the substance to be ionized in a molten state supplied from the reservoir from its tip; A liquid metal ion source consisting of an extraction electrode for extracting ions from the tip of the emitter by concentrating a high electric field between the emitters, a reservoir for a substance to be ionized, and a transfer of the substance to be ionized from the reservoir. 1. A liquid metal ion source characterized by comprising: a transfer means for ionizing a substance; and a preheating section for melting a substance to be ionized.