Plasma generator using microwave

Details Plasma generator using microwave Plasma generator using microwave

2002-09-12

2004-04-06

Vo, Tuyet T. (Department: 2821)

Electric lamp and discharge devices: systems

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

Plasma generating

C315S111710, C219S121430, C219S121360, C219S121390, C219S121400

Reexamination Certificate

active

06717368

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a plasma generator using microwave and more particularly to such plasma generator used, for example, to wash or etch surface of a workpiece such as metallic piece, semiconductor or insulator or to coat the surface of such workpiece with thin film.
BACKGROUND ART
The plasma generator of RF (radio frequency power source) parallel-plate type as shown in
FIG. 6
of the accompanying drawings has been most extensively used to generate processing plasma free from magnetic field.
This plasma generator
10
of well known art comprises a plasma generating chamber
11
containing therein a pair of conductive parallel plates
12
a
,
12
b
adapted to be power-supplied from a high-frequency power source
13
so that plasma
14
may be generated between the parallel plates
12
a
,
12
b
. Referring to
FIG. 6
, reference numeral
15
designates a vacuum pump and reference numeral
16
designates a gas charging line.
The plasma generator
20
of RF induction type as shown in
FIG. 7
has been also extensively used.
This plasma generator
20
of well known art comprises a plasma generating chamber
21
provided therearound with a high frequency coil
22
adapted to be power-supplied from a high-frequency power source
23
so that plasma
24
may be generated within the plasma generating chamber
21
.
Referring to
FIG. 7
, reference numeral
25
designates an auxiliary field coil, reference numeral
26
designates a vacuum pump and reference numeral
27
designates a gas charging line.
An example of the conventional plasma generators using microwave is the plasma generator of surface wave excitation type as shown in FIG.
8
.
This plasma generator
30
of well known art comprises wave guide tubes
31
, a plasma generating chamber
32
and a dielectric plates
33
interposed between the wave guide tubes
31
and the plasma generating chamber
32
so as to define dielectric windows. With such construction, the surface wave is generated on the surfaces of the dielectric plates
33
facing the plasma generating chamber
32
as power Po in the form of microwave is supplied from the wave guide tubes
31
and this surface wave ionizes gaseous molecules and thereby generates plasma
34
.
Referring to
FIG. 8
, reference numeral
35
designates a vacuum pump and reference numeral
36
designates a gas charging line.
The plasma generator
10
of
FIG. 6
is disadvantageous in that the plasma
14
has a diameter of 0.2 m or less, an electron density of 1×10
11
cm
−3
or less and a plasma density homogeneity of ±5% or less. As a result, both the plasma area and the electron density are too low to be used for surface processing of semiconductors and/or spray-coating with a thin film.
The plasma generator
20
of
FIG. 7
is more advantageous than the plasma generator
10
so far as the electron density is concerned. However, it is impossible to obtain the plasma of homogeneous high electron density unless complicated adjustment is carried out by application of DC or high frequency auxiliary magnetic field by the auxiliary field coil
25
.
The plasma generator
30
of
FIG. 8
is necessarily accompanied with increased cost because a thickness of the dielectric plates
33
should be sufficiently increased to protect the plasma generating chamber
32
from ambient pressure if it is desired to enlarge the plasma area. Furthermore, it is difficult for this plasma generator
30
to ensure the desired homogeneity of the plasma density.
In view of the situation as has been described above, it is a principal object of the present invention to provide a plasma generator constructed so that the microwave energy may be used to improve the homogeneity of plasma density as well as the electron density and to ensure plasma having a large area.
SUMMARY OF THE INVENTION
The object set forth above is achieved, according to the present invention, by a plasma generator adapted to supply microwave energy into a plasma generating chamber to generate plasma within the plasma generating chamber, said plasma generator comprising a plurality of wave guide tubes arranged in parallel one to another to supply microwave energy, each of the wave guide tubes being formed with a plurality of coupling ports arranged intermittently in an axial direction of the wave guide tube and dimensioned so that coupling coefficient thereof become gradually higher toward a distal end of the wave guide tube, and a plurality of dielectric windows provided through the plasma generating chamber in association with the respective coupling ports of the wave guide tubes.
According to the present invention, the coupling ports are dimensioned so that these ports may have coupling coefficients gradually increasing toward the distal ends of the respective wave guide tubes and thereby microwave energy radiated through the respective coupling ports of the respective wave guide tubes may be uniformized.
Accordingly, by appropriately selecting the intervals of the plural wave guide tubes as well as the intervals of the coupling ports, plasma of high and uniform density can be generated by the microwave energy radiated through the coupling ports and the associated dielectric windows into the plasma generating chamber.
Area of the plasma generated in the manner as has been described above can be enlarged by providing the respective wave guide tubes with a plurality of the coupling ports.
The dielectric windows can be separated one from another in association with the respective coupling ports and therefore the size of the windows can be limited. This feature is advantageous also from the view point of the manufacturing cost.
The wave guide tubes are provided with a plurality of the coupling ports of circular or square shape and diameters of these circular or square ports formed through each of the wave guide tubes are gradually enlarged so as to have the coupling coefficient gradually increasing as closer to the distal end of the wave guide tube the coupling ports are.
The plasma generating chamber is formed at positions corresponding to the respective coupling ports of the respective wave guide tubes with openings communicating with the respective coupling ports so that these openings are blocked off by the dielectric plates and thereby the plasma generating chamber is sealed hermetically.
Furthermore, there are provided a plurality of wave guide tubes, each of these wave guide tubes being formed with a plurality of coupling ports adapted to uniformize the microwave energy radiated through these ports and thereby plasma of a large area is generated with high and uniform density.
The invention allows the dielectric windows to be separated one from another and the dielectric windows as thin as possible can be used. In consequence, the plasma generator using microwave can be easily implemented at a rational manufacturing cost.


REFERENCES:
patent: 5529632 (1996-06-01), Katayama et al.
patent: 6558635 (2003-05-01), Minaee et al.

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