Ion source

Details Ion source Ion source

2000-07-21

2003-10-14

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Discharge device load with fluent material supply to the...

Electron or ion source

C315S111210, C118S7230HC

Reexamination Certificate

active

06633133

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ion source to be used to an ion implantation apparatus for producing, for example, a semi-conductor device, using an organometallic gas as a raw gas.
2. Description of the Related Art
This kind of a conventional ion source is shown in FIG.
3
. The similar ion source as this is described in JP-A-9-35648.
This ion source is called as an electron impact ion source, and more specifically a Bernus type ion source. The ion source is furnished with a plasma production container
2
also serving as an anode, a filament
8
(hot cathode) equipped at one side within the plasma production container
2
, a reflecting electrode
10
equipped at the other side within the same, and an ion leading slit
4
provided in the wall of the plasma production container
2
. In the vicinity of an outlet of the ion leading slit
4
, a leading electrode
14
is provided for leading ion beam
16
from the plasma
12
produced within the plasma production container
2
. Outside of the plasma production container
2
, a magnetic field generator
18
is disposed for generating magnetic field B in the axial direction thereof. Numerals
24
and
25
designate insulating materials.
Into the plasma production container
2
, an organometallic gas
28
is introduced as a raw gas (source gas) for making a plasma
12
and ion beam
16
. The organometallic gas
28
is introduced through a gas-introducing inlet
6
provided in the wall of the plasma production container
2
and a gas introducing pipe
26
connected thereto.
The organometallic gas
28
is, for example, gaseous trimethylindium [In(CH
3
)
3
], triethylindium [In(C
2
H
5
)
3
], trimethylgallium [Ga(CH
3
)
3
], triethylgallium [Ga(CaH
5
)
3
] or trimethylantimony [Sb(CH
3
)
3
].
In such an ion source, the inside and the outside of the plasma production container
2
is air-exhausted by vacuum. The filament
8
is heated by a filament electric source
20
. The organometallic gas
28
is introduced into the plasma production container
2
. An arc discharging voltage from an arc source
22
is applied between the filament
8
and the plasma production container
2
. The arc discharge is generated between the filament
8
and the plasma production container
2
. Thus, the organometallic gas
28
is ionized to generate the plasma
12
. Then, the ion beam
16
can be led from this plasma
12
. For example, when the organometallic gas
28
is used as the raw gas, the ion beam
16
containing indium ion or gallium ion can be led.
The reflecting electrode
10
repulses electron emitted from the filament
8
to serve as heightening ionization efficiency of the gas and generation efficiency of the plasma
12
.
There are many cases that the organometallic gas
28
has strong reactivity by itself (trimethylindium is in this case) and that activated molecule or activated atom generated by changing the organometallic gas
28
into the plasma have strong reactivity. In the ion source where the organometallic gas
28
is introduced as it is into the plasma production container
2
, there are problems that (1) parts such as the filament
8
, reflecting electrode
10
and insulating materials
24
,
25
in the plasma production container
2
are affected with quality alteration, whereby the amount of generating the plasma and the amount of generating the ion beam are altered so that lives of these parts are shortened, (2) dirt is easy to occur in the plasma production container
2
, and by the dirt, insulating failures arise between the filament
8
and the plasma production container
2
and other parts, thereby resulting to disturb the stable actuation of the ion source, and (3) maintenance (disassembly, cleaning or the like) should be frequently done for removing the dirt.
To explain more specific examples, if the organometallic gas
28
is trimethylindium gas, there are following problems.
(1) The insulating capacity between the filament
8
and the plasma production container
2
, more specifically of the insulating material
24
decreases by carbon occurring by decomposition of trimethylindium. Accordingly, the arc discharging voltage cannot be normally applied therebetween, and the amount of generating the plasma
12
and the amount of generating the ion beam
16
are altered to be unstable. The electron reflecting actuation at the reflecting electrode
10
is altered to be unstable also by decreasing of the insulating capacity of the insulating material
25
for the reflecting electrode
10
. The amount of generating the plasma
12
and the amount of generating the ion beam
16
are made unstable.
(2) The filament
8
at high temperature is hydrogenated or carbonized and effected with quality alteration by activated hydrogen or activated carbon occurring through decomposition of trimethylindium. The amount of generating thermoelectron from the filament
8
is changed thereby, and the generating amount of the plasma
12
is changed and the generating amount of the ion beam
16
is changed correspondingly. The life of the filament
8
is also shortened.
(3) The filament
8
is embrittled by the activated hydrogen or the activated carbon occurring through brittleness decomposition of trimethylindium, and the amount of generating the thermo-electron from the filament
8
is changed. Thereby, the generating amount of the plasma
12
is changed and the generating amount of the ion beam
16
is also changed. The life of the filament
8
is shortened.
(4) For stabilizing and continuing the plasma
12
with only the trimethylindium gas being the raw gas, it is necessary to supply the trimethylindium gas more than required (that is, more than the amount required for obtaining a desired amount of the indium ion beam). Therefore, excessive indium or carbon existing in the plasma production container
2
increases, and dirt therein becomes larger. The interior of the plasma production container
2
should be frequently cleansed, otherwise the stable actuation of the ion source will be difficult.
(5) Since it is necessary to supply the trimethylindium gas more than required for stabilizing and continuing the plasma
12
, the interior of the gas introducing pipe
26
is contaminated and easily clogged by indium metal caused by thermal decomposition of the gas before being supplied into the plasma production container
2
. As a result, the stable supply of trimethylindium gas is difficult, and the production amount of the ion beam
16
becomes unstable.
Also in the case of the above-mentioned organometallic gases
28
other than the trimethylindium gas, similar problems arise as (1) to (2).
Furthermore, recently, attention has been paid to an indium ion implantation to substrates of a semi-conductor (for example, a silicone substrate or gallium arsenic substrate).
As an ion source to be used to, for example, such purposes, there is an ion source of so-called hot cathode type which uses the thermoelectron generated from the filament (hot cathode) so as to ionize a raw gas containing indium in the plasma production container for leading ion beam containing indium ion.
In a case that a gasified material of such as indium chloride (InCl
3
) is used as the raw gas to the ion source, there will arise problems as follows. Namely, since such compounds have deliquescence (property becoming liquid by absorption of moisture from the air), the inner wall of the plasma production container is instantly contaminated by melted substances. Accordingly, it is difficult to air-exhaust by vacuum the interior of the plasma production container and to produce the plasma. In addition, since acid is generated by melting, the inner wall of the plasma production container is corroded. Many troubles are taken for cleansing melted materials.
In a case that gasified materials of such as metallic indium (In) are used as the raw gas, since these materials are low in a steam pressure, there will occur a problem that an oven of high temperature for gasification (for example

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