Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
2000-01-21
2001-05-01
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C315S111410, C156S345420
Reexamination Certificate
active
06225746
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application corresponds to and claims the priority of Japanese Patent Application No. 11-56067, filed in Japan on Mar. 3, 1999, and the entire contents of which are hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of Industrial Application
The present invention relates to a plasma processing system having an improved plasma source capable of supplying ions, electrons, neutral radicals and ultra-violet and visible light useful for chemical vapor disposition (CVD) or etching processes in the fabrication of devices on semiconductor wafers in semiconductor industry.
2. Discussion of Related Art
Plasma sources are an indispensable tool for the present and future semiconductor wafer processing in semiconductor industry. Three important conditions of such sources are higher plasma density, higher radial uniformity of the plasma over the wafer surface, and large-area plasma. In this respect, conventional high density plasma sources have limited applications owing to their design rules. This matter is explained by reference to a helical resonator plasma having a conventional geometry. A schematic diagram of the conventional helical resonator plasma source producing high density plasma is shown in FIG.
8
. Since only the plasma generation process is of interest, a wafer holding stage, a vacuuming port and vacuum components are not shown in FIG.
8
. The helical resonator plasma source has a helical coil
51
made of metal and wound around a dielectric tube
52
which is usually made of quartz. One end of the helical coil
51
, usually the lower end, is grounded while the other end is open. The length of the helical coil is L
1
=&lgr;/4, where &lgr; is the wavelength of the rf frequency applied to the helical resonator and n is an integer. A metal cylinder
53
, usually made of aluminum, is placed around the helical coil
51
. The metal cylinder
53
, the helical coil
51
, and the dielectric tube
52
are placed coaxially on a top plate
59
of a process chamber
55
. This top plate
59
is made of metal and has a circular hole with a diameter equal to the diameter of the dielectric tube
52
. A process gas is fed through a gas inlet port
58
formed at the upper end of the dielectric tube
52
. An rf power generated from an rf power source
57
is fed to a point
54
on the helical coil
51
through a matching circuit
56
. The rf power source
57
operates at a constant frequency that lies usually in the range of 1 MHz to 40 MHz. When the length of the helical coil
51
is taken as an integral multiple of a quarter of the wavelength, the composite structure begins to resonate. At this condition, the electromagnetic field within the helical coil
51
can ignite and maintain a plasma in the dielectric tube
52
at lower pressures.
A wafer holder is arranged at the lower end of the process chamber
55
. A wafer to be processed is loaded on the wafer holder. The plasma generated within the dielectric tube
52
is mainly diffused toward the wafer in the process chamber
55
through the circular hole of the top plate
59
.
First, a major problem concerning the configuration of the above-mentioned high density plasma source making the helical resonator plasma is in the controllability of radial plasma uniformity. The plasma is generated in the small-diameter dielectric tube
52
and then introduced into the large-diameter process chamber
55
. Once the high density plasma enters into the process chamber
55
, the plasma generated various species, for example, ions, electrons, etc., diffuse radially outward in addition to their flight downstream. This diffusion process yields a nonuniform plasma density across a radial line of the process chamber
55
as shown in FIG.
8
.
FIG. 8
shows the plasma density distribution characteristic of the plasma diffused in the process chamber
55
. The lateral axis means a distance in a radial direction across the process chamber
55
and the longitudinal axis refers to the plasma density. As shown by the plasma density characteristic curved line
60
in
FIG. 8
, the plasma density is at a high level at the center position while it is at a low level at the outer edges. Thus, the plasma diffused into the process chamber
55
from the dielectric tube
52
becomes nonuniform in the radial direction of the process chamber
55
. Even though a large-diameter dielectric tube is used instead of the dielectric tube
52
, the above problem can not be solved. Thus, without additional hardware, for example, magnetic multipole confinement, a radially uniform plasma can not be obtained with the above helical resonator plasma source.
Secondly, the open end of the helical coil
51
has a higher voltage when the helical coil
51
begins to resonate. This higher voltage causes generation of a capacitively coupled plasma that in turn results in sputtering the wall of the dielectric tube
52
, which is close to the open end of helical coil
51
. This causes a contamination of the plasma.
Because of these qualities, the conventional helical resonator plasma source has limited application in plasma assisted wafer processing, especially in large-area wafer processing. In order to avoid the above mentioned disadvantages, the configuration of helical resonator plasma source has to be improved.
OBJECTS AND SUMMARY
An object of the present invention is to provide a helical resonator plasma source that yields a radially uniform plasma in the downstream and which eliminates the localized sputtering of the dielectric tube wall.
A plasma processing system of the present invention has a helical resonator where a helical coil is placed, and a plasma process chamber where a wafer holder is arranged at a lower position and a wafer to be processed is loaded on the wafer holder. The helical coil
15
is made of a metal with a length of n&lgr;/4 where n is an integer and &lgr; is the wavelength of the rf frequency applied to the helical coil. The plasma processing system further comprises a reactor including the helical resonator and the process chamber, wherein the helical resonator has a vertical bar for introducing a gas, which is fixed to a top plate of the helical resonator and connected to a gas inlet port. A partition wall divides the reactor into the helical resonator and the process chamber. The partition wall is comprised of an outer metal ring, a circular central plate, and a doughnut-shaped dielectric plate between the outer metal ring and the central metal plate. The circular central metal plate is fixed to the top plate using the vertical bar and includes a gas reservoir and a plurality of gas inlet ports. In the above configuration, the helical coil is placed around the vertical bar and has a diameter (D) that satisfies d
1
<D<d
2
, where d
1
and d
2
are the inner and outer diameters of the doughnut-shaped dielectric plate.
In accordance with the plasma processing system, a ring-shaped or doughnut-shaped plasma is generated below the doughnut-shaped dielectric plate in the process chamber. The ring-shaped or annular plasma lies in an annular region, and is diffused in the downstream toward the wafer to become a uniform plasma in the radial direction.
In the plasma processing system, preferably, the central metal plate is electrically grounded or electrically isolated.
In the plasma processing system, the central metal plate is preferably supplied a rf power or a DC bias voltage.
In the plasma processing system, the central metal plate is preferably grounded through an inductor and a variable capacitor connected in series.
In the plasma processing system, the helical coil preferably has several turns, or at least two turns, with its axis extending in a vertical direction.
In the plasma processing system, the lower end of the helical coil, which is closest to the doughnut-shaped dielectric plate, is preferably connected to the ground, while the other end that lies farthest from the dielectric plate is open.
In the plasma processing system, the outer metal ring, the doughnut-shaped di
Anelva Corporation
Burns Doane , Swecker, Mathis LLP
Vu Jimmy
Wong Don
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