Plasma chamber with erosion resistive securement screws

Details Plasma chamber with erosion resistive securement screws Plasma chamber with erosion resistive securement screws

1998-10-30

2002-04-30

Bueker, Richard (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With microwave gas energizing means

C118S7230AN, C118S7230ER

Reexamination Certificate

active

06379491

ABSTRACT:

FIELD OF THE INVENTION
The present application pertains to plasma treatment chambers such as those used in semiconductor integrated circuit fabrication.
BACKGROUND OF THE INVENTION
FIG. 1
shows a plasma chamber which may, for example, be used in the fabrication of semiconductor integrated circuits. As shown, a wafer W (e.g., on which one or more semiconductor integrated circuits are formed) is positioned between first and second electrodes e
1
and e
2
located at opposite sides of the chamber. The wafer W is also located between north m
1
and south m
2
poles of a magnet also on opposite sides of the chamber, which sides are orthogonal to the sides at which the electrodes e
1
and e
2
are located. A low pressure gas G is introduced into the plasma chamber through an inlet port, such as a shower head S. A voltage source V applies an oscillating voltage (of, for example, 13.58 MHz) across the electrodes e
1
and e
2
to produce an electric field E directed between the two electrodes e
1
and e
2
. This tends to cause the molecules of the low pressure gas G to gyrate in a cycloid motion. The north and south poles m
1
and m
2
of the magnet introduce a magnetic field B directed between the two poles, which magnetic field B is orthogonal to the electric field E. This tends to increase the collisions of the gyrating molecules thereby completely ionizing them to form the plasma P over the wafer W. A coolant C, such as liquid He, may be circulated on the underside of the wafer W to cool it during treatment.
FIG. 2
shows a more detailed view of certain parts of an actual plasma chamber
100
, such as the MXP Centura™, distributed by Applied Materials, Inc.™, located in Santa Clara, Calif. The chamber
100
has cylindrically shaped sidewalls
105
. A cathode
110
is located at the bottom of the chamber
100
. A pedestal
120
is secured to the cathode
110
. (Actually, additional parts may be secured to the cathode
110
between the cathode
110
and the pedestal
120
, such as an O-ring and aluminum sheet interface. These are omitted for sake of brevity.) The pedestal
120
is secured by screwing screws through the holes
122
of the pedestal
120
and the holes
112
of the cathode
110
. A quartz pedestal liner ring, not shown, may then be placed in the chamber
100
surrounding the pedestal
120
(for purposes of improving the uniformity of the flow of the plasma gas over the entire wafer W). A transparent quartz cover or focus ring
150
may then be secured to the top of the chamber
100
to form a gas-tight seal, thereby confining the plasma P within the chamber
100
and isolating the wafer W from external contamination. As shown, the quartz cover or focus ring
150
is secured by screwing screws
130
through holes
132
to the chamber
100
or another part secured therein (not shown for sake of brevity). A quartz cap
140
may be placed on top of each screw
130
.
The wafer W may be secured to the pedestal
120
in one of two ways. The pedestal
120
can be an electrostatic chucking pedestal. Such a pedestal
120
can generate an electrostatic charge that holds the wafer W in place during treatment Alternatively, an ordinary pedestal
120
may be used. In such a case, the wafer W is then clamped to the pedestal
120
using a clamping ring
160
. As shown, the clamping ring
160
has plural tips
170
which extend radially towards the interior of the ring
160
. The dimensions of the clamping ring
160
are such that the ring
165
thereof has a greater diameter than the wafer W and does not touch the wafer. Rather, only the tips
170
contact and touch the wafer W. The tips
170
have holes
172
to enable screwing the clamping ring
160
to the pedestal
120
using (e.g., metal) screws
131
(which in turn are covered by graphite plugs, not shown) so that the tips
170
contact and press down on the wafer W, thereby holding it in place.
Plasma treatment is commonly used to etch structures on the wafer, such as polycrystalline silicon (poly) and oxide structures. Specifically, wafer structures not to be etched are typically covered with a mask whereas wafer structures to be etched are left exposed. The treatment using the plasma erodes the exposed structures.
Such a plasma erosive effect is also incurred by the various parts within the chamber
100
. This reduces the life time of the parts. Moreover, because such pats are eroded while treating the wafer, the eroded material of the parts is introduced in the plasma chamber
100
as a contaminant. This tends to reduce the yield of the semiconductor integrated circuits formed from the treated wafers. Two parts specifically subject to the plasma erosive effect are the screws
130
, used to secure the quartz focus ring or cover
150
(and, theoretically, can be used to secure other objects within the plasma chamber
100
), and the clamping rings
160
.
FIG. 3
shows the screw
130
and cap
140
assembly in greater detail. The screw
130
includes a threaded shaft
135
and a head
137
affixed to, and integral with, the top of the screw
130
. The screw
130
is preferably made of a polyimide material, such as the material marketed under the brand name Vespel™ by DuPont Engineering Polymers,™ located in Newark, Del. The screw head
137
has a concave shape. Specifically, the screw head
137
has a recess or slot
139
formed therein for receiving a screw driver blade. As such, the screw head
137
has sharp “pointed” edges
131
and
133
, which edges
131
and
133
each have a small surface area.
The screw
130
, in particular, the screw head
137
, is subject to erosion by the plasma. (The shaft
135
is typically completely screwed into another object within the chamber
100
such as the hole
132
. Thus, only the screw head
137
is exposed to the plasma of the chamber
100
.) In an effort to extend the lifetime of the screw
130
, a protective quartz cap
140
is typically placed over the screw. The quartz cap
140
has an opening
141
which is dimensioned larger than the screw head
137
so that it can be placed over, and can cover, the screw head
137
.
There are several problems with the screw
130
and quartz cap
140
assembly. First, it is difficult to make a cap
140
that fits tightly on the screw
130
. This has two consequences. Specifically, some plasma is able to reach the screw
130
and erode it. The eroded material produces a build up of contaminating particles within the opening
140
. This contaminates the wafer. In addition, the useful life of the screw
130
is limited to only about
100
hours before it is too badly eroded to be reused.
Second, during use, the vibration of the chamber
100
can dislodge the caps
140
causing one or more to be damaged or lost under (or within) one of the many removable parts of the machine (only some of which are shown in FIG.
1
). As the quartz caps
140
are quite expensive (e.g., around U.S. $40 each), this substantially increases the cost of semiconductor integrated circuit manufacture.
In addition, the chamber
100
is utilized in an application in which contamination is controlled. The operator of the chamber must therefore wear protective gloves while inserting and screwing in the screws
130
. As this requires both placement of the screw in a hole and use of a screw driver, the operation requires a large amount of time, thereby reducing the amount of time that the chamber
100
can be utilized in the fabrication process.
It is an object of the present invention to overcome the disadvantages of the prior art.
SUMMARY OF THE INVENTION
This and other objects are achieved by the present invention. According to one embodiment, an apparatus is provided for treating a wafer under fabrication with an erosive plasma, in a contamination controlled environment. The apparatus includes a chamber for containing the wafer to be treated by the plasma, and for isolating the wafer from contaminants external to the chamber during treatment. The chamber also includes one or more plasma erosion resistive screws. Each screw has a shaft secured within the chamber so that the sh

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