Microwave plasma generator

Details Microwave plasma generator Microwave plasma generator

2001-04-09

2002-06-11

Mills, Gregory (Department: 1763)

Coating apparatus

Gas or vapor deposition

With treating means

C118S7230ME, C118S7230MR, C315S111210, C156S345410

Reexamination Certificate

active

06401653

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a plasma generator for generating plasma by means of microwave discharge. This plasma generator is well suited for use in, for instance, processes of etching and ashing on a semiconductor wafer placed in a processing chamber in which a plasma gas is introduced or of cleaning of the chamber.
2. Description of the Related Art
This prior art plasma generator is described below with reference to FIG.
10
. In
FIG. 10
, a reference numeral
100
represents a rectangular-sectional waveguide, at an opening of one end side of which is mounted a microwave power source (not shown) for introducing a microwave to the interior of this rectangular waveguide.
Reference numerals
102
and
104
represent cylindrical conductors connected vertically in a tube-axial direction to the walls of the respective open tubes of the rectangular waveguide
100
, one cylindrical conductor
102
of which has a gas inlet
102
a
for introducing plasma and the other cylindrical conductor
104
of which has its opening
104
a
connected to the processing chamber now shown.
A reference numeral
106
represents a cylindrical insulator, which is inserted through the rectangular waveguide
100
vertically in its tube-axial direction and mounted in both of the cylindrical conductors
102
and
104
and also which has its portion positioned in the rectangular waveguide
100
serving as a plasma generating portion
106
a.
A reference numeral
108
represents a movable terminal which can move in the tube-axial direction so that the plasma generating portion
106
a
of the cylindrical insulator
106
may have a stronger microwave field therein.
In such a plasma generator, when a microwave is introduced into the rectangular waveguide
100
and a plasma gas is introduced through the gas inlet
102
a
in the cylindrical conductor
102
, plasma is generated due to microwave discharge in the internal space of the plasma generating portion
106
a
of the cylindrical insulator
106
.
The plasma thus generated in the cylindrical insulator
106
is introduced to, for example, a semiconductor wafer positioned in a processing chamber connected to the opening
104
a
so that this wafer may be etched or ashed or that the chamber may be cleaned.
In the prior art plasma generator, however, since a microwave inside the rectangular waveguide
100
travels perpendicular to the surface of the plasma generating portion
106
a
of the cylindrical insulator
106
, its field acts parallel with the plasma. Accordingly, the microwave has a strong reflected wave power.
To guard against this, conventionally, a matching device is typically attached to the rectangular waveguide
100
to utilize its matching action for suppressing the reflected wave power of the microwave (microwave matching), which is, however, not always easy and is time consuming.
The matching is thus difficult and time consuming, thus leading to problems of inefficiencies of, for example, semiconductor wafer processes, in short, various operations utilizing plasma.
In addition, a large and heavy body of the matching device itself makes it inconvenient to handle it and its high price also increases the costs of the apparatus as a whole.
Also, the prior art plasma generator has poor radiation of the heat generated along with the generation of plasma, thus leading to disabled supply of a high microwave power problematically.
That is, since plasma occurs at a portion (plasma generating portion
106
a
) of the cylindrical insulator
106
that portion is positioned in the rectangular waveguide
100
, the heat due to plasma is generated locally. Moreover, thus locally generated heat is construction-wise difficult to radiate to the outside, so that if plasma is generated by supplying a high microwave power, the cylindrical insulator
106
is highly heated locally and may be damaged. For this reason, the prior art has been impossible to supply a high microwave power.
In order to inhibit the cylindrical insulator
106
from being highly heated locally, a cooling fan may possibly be provided for cooling the plasma generating portion
106
a
, in which case, however, a required large capacity of the cooling fan would enlarge the apparatus as a whole. Further, such a cooling fan, if used in a clean room for manufacturing of semiconductor devices in which the plasma generator is mounted, may disturb the surrounding atmosphere problematically.
Also, although the cylindrical insulator
106
may possibly be of a double-tube construction so that a cooling medium may be distributed therethrough to radiate the heat, the cylindrical insulator
106
is generally made of a relatively brittle glass tube and also exposed to hot plasma and have the atmospheric pressure applied thereon from the outside because of its internal vacuum state, thus being subject to damages due to heat and pressure. For this reason, the cylindrical insulator
106
must be designed in case of damages, in which case in turn the cooling medium may come into the apparatus to thereby spread its leakage throughout the apparatus, so that such a heat radiating construction could not have been employed.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to facilitate microwave matching.
Another object of the invention is to facilitate microwave matching without utilizing a matching device to thereby eliminate the necessity of using it, thus making it easy to handle the apparatus as a whole, and also to reduce the costs of the apparatus.
A further another object of the invention is to cool the apparatus reliably with a simple construction.
The other objects, features, and advantages of the invention will become clear from the following description.
A plasma generator according to the invention comprises, as shown in
FIG. 1
, a rectangular waveguide (
2
) in which a microwave is introduced, a coaxial tube (
4
) connected in a T shape to the rectangular waveguide (
2
) through their respective openings (
2
b
and
42
c
), a vacuum-sealing window (
6
) for blocking the openings (
2
b
and
42
c
) with an insulating material to thereby vacuum-seal the interior of the coaxial tube (
4
) against the rectangular waveguide (
2
), and an insulator (
16
) arranged in the coaxial tube (
4
) as linked to the vacuum-sealing window (
6
).
According to the invention, the insulator (
16
) is provided at a boundary between plasma and a microwave so that the electric field of the microwave may not run parallel with the plasma. Accordingly, the microwave can be absorbed by the plasma more easily to thereby reduce its reflected wave power. Moreover, by adjusting the shape of the insulator (
16
), the impedance of the total load can be kept roughly constant against large fluctuations in plasma impedance caused by transitional ignition of the plasma, changes in its process, etc., thus eliminating the conventional necessity of difficult microwave matching by use of a matching device in the rectangular waveguide (
2
), thus making more easy and efficient a variety of operations with plasma. In addition, it is possible to make it more easy and convenient to use the apparatus even with a large and heavy matching device and also reduce the costs of the apparatus.
Preferably the invention has such a double-tube construction that the above-mentioned coaxial tube (
4
) may consist of an inner conductor (
41
) and an outer conductor (
42
) disposed external of the inner conductor (
41
) radially with a predetermined gap therebetween and also such an annular construction that the above-mentioned insulator (
16
) may be mounted on the outer periphery of the above-mentioned inner conductor (
41
).
By this construction as a whole, a microwave power can be efficiently supplied from the insulator toward a plasma generating space (
19
) of the radially opposing gap between the inner conductor (
41
) and the outer conductor (
42
), thus increasing the plasma generation efficiency in that space preferably.
In this case, the above-mentioned inner conductor (
41
) may

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