Plasma processing apparatus capable of performing uniform...

Details Plasma processing apparatus capable of performing uniform... Plasma processing apparatus capable of performing uniform...

2003-01-21

2004-06-15

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

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

Plasma generating

C315S111510, C156S345480, C118S72300R

Reexamination Certificate

active

06750614

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to plasma processing apparatuses. More particularly, it relates to a plasma processing apparatus which, during plasma discharge, is capable of preventing drift of a discharge current that flows through a gap between electrodes of an electrode pair and further is capable of increasing the effective electrical power in a plasma space.
2. Description of the Related Art
FIG. 13
shows a typical plasma processing apparatus heretofore used for plasma treatment such as chemical vapor deposition (CVD), sputtering, dry etching, and ashing. The plasma processing apparatus in
FIG. 13
has an electrode pair which includes a plasma excitation electrode
4
for exciting plasma and a susceptor electrode
8
facing the plasma excitation electrode
4
. A workpiece W to be plasma-treated is placed between the plasma excitation electrode
4
and the susceptor electrode
8
. The plasma excitation electrode
4
is connected to the power supply side of a radiofrequency (RF) generator
1
through an RF feeder
3
and a matching circuit
2
A. The matching circuit
2
A matches the impedance between the RF generator
1
and the plasma excitation electrode
4
, and is accommodated in a chassis
120
made of a conductive material. The RF feeder
3
and the plasma excitation electrode
4
are enclosed in a housing
21
, also made of a conductive material.
RF power transmitted from the output of the RF generator
1
is sequentially fed into the plasma excitation electrode
4
through the matching circuit
2
A and the RF feeder
3
. A shower plate
5
having many holes
7
is in contact with projections
4
a
on the bottom face of the plasma excitation electrode (cathode)
4
. A gas inlet pipe
17
communicates with a space
6
formed between the plasma excitation electrode
4
and the shower plate
5
. An insulator
17
a
is provided in the middle of the gas inlet pipe
17
, which is made of a conductive material, to insulate the plasma excitation electrode
4
from the gas supply source. Gas from the gas inlet pipe
17
is introduced into a chamber
60
surrounded by a chamber wall
10
through the holes
7
of the shower plate
5
. The upper side of the chamber wall
10
and the plasma excitation electrode
4
are hermetically sealed with an insulator
9
interposed therebetween.
The susceptor electrode
8
is provided in the chamber
60
and serves as the common (i.e., ground) side of the discharge voltage. A workpiece W, such as a wafer, is placed thereon. A shaft
13
supports the susceptor electrode
8
. The lower portion of the shaft
13
and a chamber bottom
10
A are hermetically sealed with conductive bellows
11
. Air is exhausted from the chamber
60
by an exhaust system (not shown).
Since the susceptor electrode
8
can move vertically together with the shaft
13
and the bellows
11
, the distance between the plasma excitation electrode
4
and the susceptor electrode
8
can be adjusted while maintaining a vacuum in the chamber
60
. The lower portion of the shaft
13
is grounded, and the common side of the RF generator
1
is also grounded. The chamber wall
10
has the same DC potential as that of the shaft
13
.
Referring to
FIG. 14
, a matching circuit
2
A is provided between an RF generator
1
and an RF feeder
3
. The matching circuit
2
A includes a plurality of passive devices to achieve impedance matching between the RF generator
1
and a plasma excitation electrode
4
to correspond to changes in a plasma state in a chamber
60
. Specifically, in the example shown in
FIG. 14
, the matching circuit
2
A includes three passive devices, that is, a load capacitor
22
consisting of a vacuum variable capacitor, an inductance coil
23
, and a tuning capacitor
24
consisting of an air variable capacitor. Only one inductance coil
23
is connected between the load capacitor
22
and the tuning capacitor
24
.
In general, in the plasma processing apparatus described above, when drift occurs in a high-frequency current flowing through the gap between the plasma excitation electrode
4
and the susceptor electrode
8
during discharge, the plasma density within the plasma processing chamber
60
changes, resulting in a non-uniform plasma treatment of the workpiece W. Furthermore, the plasma processing apparatus described above has an additional disadvantage of large power loss in the matching circuit due to high parasitic RF resistance in the inductance coil in the matching circuit.
Accordingly, what is needed is an improved plasma processing apparatus which avoids the non-uniform plasma treatment.
SUMMARY OF THE INVENTION
Accordingly, embodiments of the present invention provide a plasma processing apparatus capable of performing uniform plasma treatment of the treatment surface of a workpiece.
Further, by lowering the parasitic RF resistance in an inductance coil of the matching circuit, embodiments of the present invention provide a plasma processing apparatus capable of increasing the plasma-processing capacity by reducing the power loss in a matching circuit and increasing the effective power in a plasma space.
The present invention, in its first aspect, provides a plasma processing apparatus having a plasma processing chamber that accommodates an electrode pair, the electrode pair including a plasma excitation electrode for exciting plasma and a susceptor electrode facing the plasma excitation electrode. A workpiece to be plasma-treated is placed between the electrodes. The plasma processing apparatus further includes a chassis that accommodates an impedance matching circuit, provided in the middle of a supply path for feeding RF power from an RF generator to the plasma excitation electrode. The impedance matching circuit functions matches the impedance between the RF generator and the plasma processing chamber. The chassis serves as a return path from the susceptor electrode to the RF generator. In the return path provided by the chassis, impedances are axisymmetrically equal at a predetermined frequency of the RF power with respect to the direction of a current returning to the RF generator.
While not wishing to be bound by any theory, it is believed that variation in plasma density in the plasma processing chamber is caused by drift in a high-frequency current flowing through the gap between the plasma excitation electrode and the susceptor electrode and that formation of a particular return current path in the chassis, which serves as a return path of the high-frequency current to the RF generator, causes the drift of the high-frequency current. In other words, the return current path particularly in the surface of the chassis is selectively formed along the portion having the lowest impedance at a predetermined frequency of the RF power used for plasma discharge. A discharge current flowing through the gap between the electrodes of the electrode pair varies in density such that the discharge current flows through the shortest path. Thus, making the impedances on the surface of the chassis axisymmetrically equal can prevent or suppress the drift in the gap between the electrodes of the electrode pair.
In accordance with embodiments of the present invention, the chassis may accommodate not only the impedance matching circuit but also other feeders such as an RF feeder from the impedance matching circuit to the plasma excitation electrode. The term “axisymmetric” mentioned above, which will be described below in detail, means not only the generally-defined state in which two points are disposed at equal distances from the central axis thereof on a straight line perpendicular to the central axis, but also the state in which a plurality of points are disposed at equal distances from the central axis thereof on a plane perpendicular to the central axis, the plurality of points also arranged with equal intervals between each other.
The cross-section of the chassis perpendicular to the central axis thereof preferably has a shape of a regular polygon or a circle.
When the quality of the material of

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