JP2001176409A - Ion source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable prolongation of service of filament, while taking advantage of the use of trimethylindium or triethylindium gas as the raw material gas. SOLUTION: This ion source ionizes a raw material gas 28, containing indium within a plasma formation chamber 2, by making use of thermal electrons produced from a filament 8 and extracts an ion beam 16 containing indium ions. In addition, the raw material gas 28 is either trimethylindium or triethylindium gas, and a filament 8 is composed of tantalum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, for indium ion implantation into a semiconductor substrate, and ionizes a source gas containing indium in a plasma generation vessel by utilizing thermoelectrons generated from a filament. The present invention relates to an ion source for extracting an ion beam containing indium ions, and more specifically, to a means for extending the life of a filament.

[0002]

2. Description of the Related Art In recent years, attention has been paid to indium ion implantation into a semiconductor substrate (for example, a silicon substrate or a gallium arsenide substrate).

[0003] For example, as an ion source used in such an application, a source gas containing indium is ionized in a plasma generation vessel by using thermoelectrons generated from a filament (hot cathode) to form an ion beam containing indium ions. There is a so-called hot cathode type ion source for extraction.

In the case of using a gasified material such as indium chloride (InCl ₃ ) as a source gas for such an ion source, there are the following problems. That is, these compounds are deliquescent (that is, they absorb and dissolve moisture in the air).
Therefore, the inner wall of the plasma generation container is immediately contaminated by the melted material, and it becomes difficult to evacuate the plasma generation container and thereby generate plasma. In addition, since an acid is generated by the dissolution, the inner wall of the plasma generation vessel is corroded. Further, even if the dissolved matter is removed by cleaning, it takes much time and effort.

[0005] Metal indium (I) is used as a raw material gas.
In the case of using gasified substances such as n), there is a problem that an oven at a high temperature (for example, a heating temperature of about 800 ° C. to 1000 ° C.) is required for gasification because these substances have a low vapor pressure. .

On the other hand, trimethylindium [I
n (CH ₃ ) ₃ ] or triethylindium [In (C
₂ H ₅ ) ₃ ] does not require the use of a high-temperature oven for gasification because the vapor pressure is somewhat high. Moreover, since there is no deliquescence, the inner wall of the plasma generation container is not stained or corroded. Because of these advantages, it is very convenient to use these gases as source gases.

[0007]

However, in the above-mentioned hot cathode type ion source, an ion beam containing indium ions is extracted by using the above-mentioned trimethylindium gas or triethylindium gas as a source gas. After a short time (for example, 1 hour ~
It was found that the filament deteriorated in about several hours) and the life was exhausted. As this filament, a tungsten filament usually used for an ion source was used.

The following is a description of the degradation process of the filament. First, as in the example shown in FIG. 2, many voids (voids) 32 are generated inside and on the surface of the filament 30, and the surface of the filament 30 becomes uneven. When such voids 32 are generated and grown, the distribution of the surface temperature of the filament 30 during operation of the ion source gradually becomes uneven, and at the same time, local deterioration of the filament 30 progresses, and the portion 34 becomes thin. This further promotes non-uniformity of the temperature distribution, and the portion 34 becomes thinner rapidly, and as a result, the life of the filament 30 is shortened at an accelerating rate, leading to disconnection.

As described above, it has been found that the use of trimethylindium gas or triethylindium gas as a raw material gas has many advantages as described above, but has a serious problem that the life of the filament is short.

Accordingly, an object of the present invention is to make it possible to extend the life of the filament while taking advantage of the use of trimethylindium gas or triethylindium gas as a raw material gas.

[0011]

The ion source according to the present invention comprises:
The source gas is trimethyl indium gas or triethyl indium gas, and the filament is made of tantalum.

In the above-mentioned gases other than the trimethylindium gas or the triethylindium gas, the above-mentioned rapid deterioration of the tungsten filament is not observed, and this is peculiar to the combination of the tungsten filament with the trimethylindium gas or the triethylindium gas. It is considered to be a phenomenon of.

When the reason was considered, activated hydrogen or activated carbon was generated by plasmatization of trimethylindium gas or triethylindium gas, and when these acted as hot cathodes, the temperature became high between the metal crystals of the tungsten filament. This is considered to be due to intrusion, whereby a large number of voids are generated inside and on the surface of the tungsten filament.

On the other hand, when the filament is formed of tantalum (Ta), it has been confirmed that the life thereof is much longer (for example, about 5 to 6 times or more as described later) than that of tungsten. Was.

Considering the reason, in the tantalum filament, while maintaining the metal crystal state,
Because the active hydrogen and activated carbon can be stored,
This is presumably because voids are less likely to be generated than tungsten filaments. Tantalum can store as much as 740 volumes of hydrogen, for example, in the dark glowing state.

[0016]

FIG. 1 is a sectional view showing an example of an ion source according to the present invention.

This ion source is a hot cathode electron bombardment type ion source, more specifically, a so-called Bernus type ion source, and includes a plasma generation container 2 also serving as an anode, and a plasma generation container 2 in the plasma generation container 2. A U-shaped filament (hot cathode) 8 provided on one side, a reflective electrode 10 provided on the other side in the plasma generation container 2, and an ion extraction slit 4 provided on a wall surface of the plasma generation container 2. It has. Near the outlet of the ion extraction slit 4, an extraction electrode 14 for extracting an ion beam 16 from the plasma 12 generated in the plasma generation container 2 is provided. A magnetic field generator 18 that generates a magnetic field B in the axial direction is disposed outside the plasma generation container 2. 24 and 25 are insulators.

The filament 8 is made of tantalum in this embodiment. As a comparative example, an experiment using a conventional filament made of tungsten was also performed.

In the plasma generation vessel 2, a plasma 12
As a result, a source gas (source gas) 28 serving as a source of the ion beam 16 is introduced through the gas introduction port 6 provided on the wall surface of the plasma generation container 2 and the gas introduction pipe 26 connected thereto in this example. . In this example, a trimethylindium gas was used as the source gas 28.

In such an ion source, the filament 8 is heated by the filament power supply 20 while evacuating the inside and outside of the plasma generation container 2 and introducing the raw material gas 28 into the plasma generation container 2 at an appropriate flow rate. To generate thermoelectrons and to apply an arc discharge voltage between the filament 8 and the plasma generation container 2 from the arc power source 22.
And an arc discharge occurs between the source gas 28
Is ionized to generate a plasma 12. Then, an ion beam 16 containing indium ions is extracted from the plasma 12.

The reflection electrode 10 repels the electrons emitted from the filament 8 and acts to increase the ionization efficiency of the gas, and hence the generation efficiency of the plasma 12.

In such an ion source, when the life of the filament 8 was compared, the life of the tungsten filament used conventionally was only one hour to several hours, whereas the life of the tantalum filament was 30 hours. There were ~ 40 hours or more. That is, it was confirmed that the life of the tantalum filament was about 5 to 6 times longer than that of the tungsten filament.

Moreover, since trimethylindium used as the source gas 28 has a relatively high vapor pressure as described above, it is not necessary to use a high-temperature oven for gasification. For example, gasification can be performed by evacuation of a container containing solid trimethylindium at room temperature. Moreover, since trimethylindium has no deliquescence,
The inner wall of the plasma generation container 2 is not stained or corroded by the melt. Therefore, the ion source can be stably operated for a long time, the life of the ion source is long, and maintenance such as cleaning can be simplified.

Since triethylindium gas is also an organic metal gas similar to trimethylindium gas,
When the source gas 28 is a triethylindium gas, the same effect as described above can be obtained.

The source gas 28, that is, trimethylindium gas or triethylindium gas, may be introduced into the plasma generation vessel 2 by itself, or may be Ar.
, Ne or the like may be introduced together with an inert gas (rare gas). If introduced together with the inert gas, the plasma generation vessel 2
It is possible to reduce the flow rate of the source gas 28 while securing the total gas flow rate (that is, the sum of the source gas 28 and the inert gas) necessary for the continuous continuation of the plasma 12 and the desired ion beam quantity of indium ions. Therefore, the influence of the raw material gas on the filament 8 is further reduced, and the life of the filament 8 can be further extended.

The present invention is not limited to the above-mentioned Bernas-type ion source, but may be any other ion source having a filament, such as a Kauffman type, a Freeman type, a bucket type (multipole magnetic field type), a hot cathode PIG type, etc. Can be applied to the ion source.

[0027]

As described above, according to the present invention, the advantage of using trimethylindium gas or triethylindium gas as a raw material gas, that is, there is no need to use a high-temperature oven, and the inner wall of the plasma generation vessel is dissolved This makes it possible to extend the life of the filament while taking advantage of the fact that the filament is not contaminated or corroded.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an ion source according to the present invention.

FIG. 2 is a diagram schematically illustrating an example of a filament whose surface has become uneven due to generation of voids.

[Explanation of symbols]

 2 Plasma generation container 8 Filament 16 Ion beam 28 Source gas

Claims (1)

[Claims] 1. An ion source for using a thermoelectron generated from a filament to ionize a source gas containing indium in a plasma generation vessel to extract an ion beam containing indium ions, wherein the source gas is trimethylindium gas or triethyl. An ion source which is indium gas and wherein said filament is made of tantalum.