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Description  |
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This invention relates to plasma reactor equipment and, in particular, to
the construction of a readily assembled and disassembled reactor.
BACKGROUND
In the prior art, plasma reactors come in a variety of shapes, e.g.
parallel plate and barrel types, and a variety of capacities, e.g. single
wafer and batch. Typically, the reactor comprises a quartz, aluminum, or
stainless steel chamber with aluminum electrodes positioned therein. In a
recent advance in the art, as described in U.S. Pat. No. 4,209,357, a
single wafer, parallel plate reactor is provided with an interior or upper
plasma electrode which serves both as an RF (radio frequency) electrode
and as a gas manifold. While providing increased uniformity and other
advantages, the reactor is expensive to make due to the precise machining
and alignment of the various parts which make up the electrode/manifold.
The processes run in plasma reactors have become more complex and use a
variety of gases. As is known, a plasma contains the source gas or gases
as well as intermediate products and by-products. Sometimes a successful
process is obtained by only slight shifts in the chemical balance in the
reactor. A problem exists in that the chemicals used or found in a process
can chemically attack the materials used to make the chamber. Another
problem is that the chamber, particularly the electrodes, is subject to
physical attack by the plasma, e.g. what is known as back sputtering. Yet
another problem is that certain materials react to form coatings on parts
of the chamber, particularly the electrodes. These three problems combine
for a fourth wherein subsequent operations, particularly with different
chemicals, cause deposits or materials from the chamber to deposit on the
semiconductor wafer therein, contaminating it, or to upset the chemical
balance of the reaction.
These problems can be minimized by careful choice of materials and
reagents, as well as routine cleaning of the chamber. This makes ease of
assembly and disassembly an important feature of a reactor, both for
cleaning and for changing at least the electrode materials.
In view of the foregoing, it is therefore an object of the present
invention to provide an improved plasma reactor which is more easily
assembled and disassembled.
Another object of the present invention is to provide a plasma reactor
having readily removable electrodes.
A further object of the present invention is to provide a plasma reactor
having interchangeable electrodes of different materials, with one set
being chosen for a particular process.
Another object of the present invention is to provide a plasma reactor
having electrodes coated with a material resistant to the plasma reaction.
A further object of the present invention is to provide a plasma reactor
having electrodes coated with a material intended to contribute to the
plasma reaction.
Another object of the present invention is to provide a plasma reactor
having interchangeable electrodes of the same material for reducing the
downtime associated with cleaning the reactor.
A further object of the present invention is to provide an improved plasma
reactor having an electrode/manifold member of simplified construction.
SUMMARY
The foregoing objects are achieved in the present invention wherein a
plasma reactor comprises a shell attached to a frame wherein the shell
comprises passageways and a plenum for gas. The interior of the shell
defines a broad, shallow counterbore. An electrode member abuts the
shoulder around the counterbore, thereby defining a second plenum. The
electrode member comprises a plurality of apertures in the central portion
thereof for gas flow in a first direction and a second plurality of
apertures in a peripheral portion thereof for gas flow in a second
direction. The electrode member may comprise metallic and/or non-metallic
materials. The electrode member is held in place by retaining ring means
which attaches to the shell by suitable fastening means. The lower
electrode of the reactor is part of the closure mechanism for the chamber
and receives the semiconductor wafer or other article to be treated. The
fastening means are readily accessible when the reactor is open yet are
outside the sealed volume when the reactor is closed.
A more complete understanding of the present invention can be obtained by
considering the following detailed description in conjunction with the
accompanying drawings, in which:
FIG. 1 illustrates a plasma reactor in accordance with the prior art.
FIG. 2 illustrates a preferred embodiment of a plasma reactor in accordance
with the present invention.
FIG. 3 illustrates an alternative embodiment of a plasma reactor in
accordance with the present invention.
FIG. 1 illustrates, in slightly more detail, the construction of the plasma
reactor described in U.S. Pat. No. 4,209,357. Specifically, reactor 10
comprises a frame 11 to which is fastened chamber body 12, retaining ring
13, and isolation ring 14. Wafer ring 15, which typically comprises a
ceramic, sits atop lower electrode 16 which forms the closure mechanism
for the reactor. Lower electrode 16 is RF hot and receives the RF energy
from connector 21 and attachment bolt 22. RF connector 21 comprises a
coaxial cable, the outer portion of which is connected to RF shield 23.
Frame 11 comprises an enlarged bore through which the lower electrode
assembly passes. Interconnecting RF shield 23 and frame 11 are a plurality
of conductive fingers 24, suitably disposed about the interior of the bore
in frame 11. RF shield 23 is isolated from lower electrode 16 by isolation
disc 25. A suitable seal, such as O-ring 26, seals lower electrode 16 to
isolation ring 14, thereby sealing the enclosed volume of the reactor.
Within the reactor volume, the interior or upper electrode assembly
comprises an upper electrode 17 and a manifold plate 18.
In assembling a reactor constructed as illustrated in FIG. 1, manifold
plate 18 is fastened to chamber body 12 by fasteners 33 suitably
positioned around the periphery thereof. Similarly, upper electrode 17 is
fastened to manifold plate 18 by another plurality of fastening means such
as bolt 34. Isolation ring 14 is temporarily held in place while retaining
ring 13 is secured to chamber body 12 by another plurality of fastening
means such as bolt 31. The thus completed chamber assembly is then
fastened to a frame 11 by way of another plurality of bolts 32. Typically,
eight or more bolts are used for each plurality.
Manifold plate 18 is rarely flat after being attached to chamber body 12.
The machining of the plurality of apertures and channels in manifold plate
18 causes distortions thereof. Further, improper torque on bolts 33 which
attach plate 18 to chamber 12 may cause further distortions in plate 18.
In assembling the reactor illustrated in FIG. 1 the torque applied to
bolts 33 and 34 are used to correct for any non-planarities in electrode
17, which must be planar and uniformly spaced from lower electrode 16.
Also, the passageways in upper electrode 17 and manifold plate 18 must be
carefully aligned.
As can be appreciated from the foregoing, the reactor of FIG. 1, while
providing improvements over prior art reactors, is difficult to
disassemble, clean, and reassemble quickly. Further, the metal to metal
contact between upper electrode 17 and manifold plate 18 must be carefully
maintained across the entire area of contact to prevent leakage or mixing
or supply and exhaust gases. Further, the reduced diameter portion of
upper electrode 17, which provides clearance for bolts 34, causes a plasma
region which is not as well defined as desired due to the large volume
around the sides of upper electrode 17. Also, during disassembly of
reactor 10 virtually all seals for the chamber must be broken, not only
large seals 26 and 27 but also the plurality of smaller seals associated
with the reactor such as the water and gas seals. It is particularly
smaller seals, which are not intended to be made and broken repeatedly,
that may cause difficulty in operating the reactor.
These disadvantages are overcome with the reactor illustrated in FIG. 2.
Specifically, reactor 50 comprises a frame 51 to which chamber body or
shell 52 is attached by a plurality of fastening means such as bolt 81.
Typically, depending upon the diameter of the shell, eight to twelve bolts
would be used to fasten shell 52 to frame 51. Within shell 52, a plurality
of passageways 57 communicate with a central plenum 58 through which gases
are typically exhausted by member 72 which is connected to a suitable
vacuum pump. Also, within shell 52 is passageway 73 which communicates to
the outside of shell 52 by way of connection fitting 71. A source of one
or more gases is connected to fitting 71. Alternatively, a plurality of
passageways 73 can be provided so that the interior of shell 52 acts as
the mixing chamber. Shell 52 forms a broad, shallow counterbore having
shoulders 59.
Upper electrode 56 is abutted against shoulders 59 to form plenum 61 within
chamber 52. The electrode is plain, i.e. characterized by the absence of
any means for fastening it, e.g. enlarged bores for bolts, threaded
portions or the like. Electrode 56 must be held in place by another,
appropriately shaped member which is adapted for being fastened to shell
52. As illustrated in FIG. 2, isolation ring 54 holds electrode 56 in
place and retaining ring 53 is attached to shell 52, fastening both
electrode 56 and isolation ring 54.
Upper electrode 56 comprises a plurality of bores such as bores 68 which
communicate from one major surface of electrodes 56 to the other in a
predetermined pattern across the central area of electrode 56. The lower
surface of electrode 56, in turn, preferably comprises a large shallow
counterbore defined as annular shoulder 64 which determines the spacing
between the major surface of electrode 56 and lower electrode assembly 55.
Lower electrode assembly 55 is not shown in detail as its construction can
be similar to the construction of the lower electrode assembly described
in FIG. 1. When the reactor is closed, i.e. when electrode assembly 55 is
positioned as shown, chamber 65 is formed above lower electrode assembly
and is the volume in which the plasma is formed.
Around the peripheral portion of electrode 56 is formed a plurality of
bores 69 which communicates with passageways 57. In a preferred embodiment
of the present invention, the pheriphery of electrode 56 is of reduced
thickness to form an annular chamber 63 between shoulder 62 and shell 52.
Annular chamber 63 communicates by way of passageway 57 with plenum 58. In
so doing, it is not necessary to align bores 69 with corresponding
portions of passageways 57, thereby consideralby simplifying the
construction of a plasma reactor in accordance with the present invention.
Reactor 50 is readily disassembled by opening the chamber, and removing
bolts 82, of which there are typically eight. Retaining ring 53 is removed
and isolation ring 54 is removed. This done, electrode 56 is then simply
removed and the disassembly process is completed. Thus, it is not
necessary to remove shell 52 from frame 51 nor is it necessary to break
the plurality of seals for vacuum, gas, and water lines. O-ring seals 83
and 84 are intended for opening and closing and, even if worn, are readily
replaced. Further, there is no metal to metal seal as in the chamber of
the prior art. In addition, fastening members 82 are all outside the seal
formed by O-ring 84 and thus can comprise any suitable material for
fastening members, since they are not subject to attack by the plasma.
Thus it is apparent to those of skill in the art that the construction of
chamber 50 is considerably simplified from that of the prior art, not only
in the number of fasteners used but also in their location. Further, the
construction of the electrode is simplified and the sealing of the chamber
is also simplified. In addition, the seals for vacuum, gas, and water
lines need not be broken each time the reactor is disassembled, thereby
increasing the reliability of each of those joints. Also, the upper
electrode has a greater area in contact with the shell, thereby improving
the heat sinking of the elctrode and increasing the temperature control of
the electrode.
Electrode 56 may comprise any suitable material and may readily be
interchanged with other electrodes of the same outline, for example, to
vary the spacing between electrode 56 and lower electrode assembly 55.
This is readily accomplished by changing the depth of the counterbore,
i.e. the height of shoulder 64. Further, electrode 56 may comprise any
suitable material appropriate for the particular reaction taking place.
For example, the most commonly used material is aluminum. However,
materials such as anodized aluminum or stainless steel can also be used.
In addition, electrode 56 can have the lower major surface thereof coated
with a suitable material to either enhance the plasma reaction or to help
electrode 56 withstand the plasma within chamber 65.
Alternatively, as illustrated in FIG. 3, electrode 96 may comprise a
non-metallic member having a metal coating 97 formed thereon. In this
case, it is necessary for metal layer 97 to be electrically connected with
shell 52. This can be accomplished a number of ways, such as forming a
conductive layer 98 on the upper portion of shoulder 62 for engaging a
suitable contact (not shown) connected to a nearby portion of shell 52.
Conductive layers 97 and 98 are readily connected by a conductor in one or
more of bores 69. In so doing, one obtains a plasma electrode which is
much less expensive to produce and can be disposed of rather than cleaned,
if desired. As an example, but not by way of limitation, electrode 96 may
comprise acetal plastic (Delrin), polyterafluoroethylene plastic (Teflon),
or cermaic, e.g. alumina, having a coating of aluminum formed thereon.
There is thus provided by the present invention an improved plasma reactor
which is substantially simpler to construct and maintain and, in addition,
enables one to interchange electrodes to obtain the most compatible
materials for the particular process being accomplished.
Having thus described the invention it will be apparent to those of skill
in the art that various modifications may be made within the spirit and
scope of the present invention. For example, while illustrated in a
preferred embodiment as a single wafer, parallel plate reactor for
processing semiconductor wafers, it is understood that any article or
plurality of articles may be processed in a reactor in accordance with the
present invention.
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