Plasma source ion implanting apparatus using the same

Details Plasma source ion implanting apparatus using the same Plasma source ion implanting apparatus using the same

2000-02-01

2001-10-02

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

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

Plasma generating

C315S111210, C315S111510, C315S111810, C313S362100, C204S298070

Reexamination Certificate

active

06297594

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma source which supplies a plasma to an ion beam and neutralizes the ion beam by electrons of the plasma to prevent the target from being charged, in an ion beam irradiation apparatus (e.g., an ion implanting apparatus) for radiating an ion beam toward a target, more particularly, relates to a means for preventing high energy electrons from being contained in the discharged plasma, and the ion implanting apparatus using the plasma source.
2. Description of the Related Art
In carrying out a process, e.g., ion implanting process, to implant into a targets for example, a semiconductor wafer, by radiating an ion beam to the target, a problem arises in which the target is positively charged (charged up) by the positive charge of the ion beam.
In order to solve the charge-up problem, JP-A-5-234562 and JP-A-5-47338 disclose that a plasma source is located near a target. Plasma is supplied to an ion beam. The ion beam is neutralized by electrons in the plasma, to thereby prevent the charging of the target. Incidentally, the plasma source used for such purpose is also called an ion beam neutralizer.
The plasma source will be described with reference to a drawing.
FIG. 6
shows an apparatus in which a conventional plasma source is attached to an ion beam irradiation apparatus.
In the apparatus, an ion beam
34
is irradiated on a target
36
that is held by a holder
38
within a vacuum container
32
, whereby a process of ion implanting, ion beam etching or the like is applied to the target
36
. The target
36
is a semiconductor wafer, another substrate, or the like.
As shown in
FIG. 6
, a hole
33
is formed in a side wall of the vacuum container
32
, which is located near the target
36
. A plasma source
2
is attached to a portion on the vacuum container
32
, which is located near the hole
33
, while an insulating member
30
is interposed therebetween.
The plasma source
2
of the ECT (electron cyclotron resonance) type is composed of a plasma chamber
4
of metal for generating a plasma
20
, a gas introducing pipe (gas introducing means)
10
for introducing a gas
12
for plasma generation, such as argon or xenon, into the plasma chamber
4
, an antenna (microwave introducing means)
14
of metal for introducing a microwave
15
at 2.45 GHz into the plasma chamber
4
, and a magnetic coil
18
for generating along a plasma emission direction
22
a magnetic field B having an intensity high enough to cause an electron cyclotron resonance within the plasma chamber
4
(the intensity: approximately 87.5 mT when the frequency of the microwave
15
is 2.45 GHz) Reference numeral
16
is a connector.
To make it easy to extract the plasma
20
into the vacuum container
32
, provision is preferably made of means for applying a DC voltage (extraction voltage) from a DC extraction power supply
28
to between the plasma chamber
4
and the vacuum container
32
in a state that a positive polarity of the extraction voltage is set at the vacuum container
32
.
The front side of the plasma chamber
4
consists of a front board
6
with a plasma emission aperture
8
in this instance. A plasma
20
that is efficiently generated by microwave discharging and electron cyclotron resonating operations within the plasma chamber
4
flows out through the plasma emission aperture
8
into the vacuum container
32
, and is supplied to the ion beam
34
(this is called a plasma bridge.). Through the plasma bridging operation, the ion beam
34
is neutralized by the electrons in the plasma
20
, to thereby suppress formation of positive charges at the target
36
, which results from the ion beam irradiation.
The plasma source
2
uses the microwave
15
, not the filament, for the generation of the exposure unit
20
. Therefore, there is no fear that the target
36
is contaminated with the materials of the filament that are sputtered out through the plasma emission aperture
8
.
Further, the inner wall of the plasma chamber
4
and the antenna
14
are covered with insulating covers
24
and
26
, respectively. With use of the covering, there is no fear that the metal plasma chamber
4
, the front board
6
and the antenna
14
are sputtered by the plasma
20
to thereby contaminate the target
36
.
In the thus constructed plasma source
2
, when energy of electrons contained in the plasma
20
is high, the high energy electrons reach the target
36
and possibly charges negatively (charges up) the target up to a voltage corresponding to the electron energy. Some technical measure should be taken for the negative charging of the target
36
.
Recently, the transistors (FETS) formed in the surface of the target wafer are remarkably reduced in size (e.g., one side of each of them is about 0.18 &mgr;m), and its gate oxide film is extremely thinned (e.g., about 5 nm). For this reason, it is necessary to set the charge-up voltage at an extremely low voltage (e.g., about 5V or lower). Otherwise, the charge-up voltage causes the breakdown of the transistors, possibly resulting in reduction of a production yield in fabricating the transistors and deterioration of product reliability.
In the plasma source
2
mentioned above, within the plasma chamber
4
, the magnetic field B for the electron cyclotron resonance is generated along the plasma emission direction
22
in which the plasma flows out through the plasma emission aperture
8
. Accordingly, the electrons in the plasma
20
within the plasma chamber
4
are accelerated by the electron cyclotron resonance along the magnetic field B. The high speed (i.e., high energy) electrons are extracted through the plasma emission aperture
8
since the plasma emission aperture
8
is located along the acceleration direction of the electrons. Those electrons are supplied to the ion beam
34
, and reaches the target
36
. As a result, a problem of increase of the charge-up voltage of the target
36
arises.
The energy of the electrons in the exposure unit
20
supplied from the plasma source
2
is distributed over a range from several eV to 100 eV, as will be described in detail later referring to FIG.
4
. Therefore, the charge-up voltage of the target
36
could be increased up to a value near 100V at maximum.
SUMMARY OF THE INVENTION
Accordingly, the present invention has an object to prevent high energy electrons from being contained in the emission plasma.
The plasma source of the present invention has magnetic field generating means for generating within a plasma chamber a magnetic field causing the electron cyclotron resonance in a direction crossing a direction in which a plasma is flows out through the plasma emission aperture.
The electrons that are accelerated by the electron cyclotron resonance within the plasma chamber move along the magnetic field having the direction crossing the plasma emission direction. Therefore, those electrons hit the inner wall of the plasma chamber to disappear. Accordingly, only electrons of low speed in the plasma, which are diffused in a region in the vicinity of the plasma emission aperture, are extracted through the plasma emission aperture. In this way, high energy electrons are prevented from being contained in the emission plasma.


REFERENCES:
patent: 4727293 (1988-02-01), Asmussen et al.
patent: 4788473 (1988-11-01), Mori et al.
patent: 4874497 (1989-10-01), Matsuoka et al.
patent: 4911814 (1990-03-01), Matsuoka et al.
patent: 5107170 (1992-04-01), Ishikawa et al.
patent: 5280219 (1994-01-01), Ghanbari
patent: 5399871 (1995-03-01), Ito et al.
patent: 5430355 (1995-07-01), Paranjpe
patent: 5545257 (1996-08-01), Vella
patent: A-5-47338 (1993-02-01), None
patent: A-5-234562 (1993-09-01), None

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