Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2002-05-24
2004-07-20
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S008000, C451S010000, C451S041000, C451S060000, C451S286000, C451S287000, C451S288000, C451S446000, C222S145100, C222S145500, C222S145700
Reexamination Certificate
active
06764378
ABSTRACT:
TECHNICAL FIELD
This invention relates to chemical-mechanical planarization of semiconductor wafers, and more particularly to fluid flow regulating systems used in such machines.
BACKGROUND OF THE INVENTION
As the level of integration increases on semiconductor wafers, surface irregularities on the wafer have become a serious problem. For example, metallization layers used to form interconnects between the various devices on the wafer may lead to substantial surface irregularities that interfere with the performance of subsequent photolithographic steps on the wafer. In order to flatten these surface irregularities, numerous materials or methods have been developed, such as SOG (Spin on Glass), and reflow. However, since these methods cannot globally planarize the wafer surface and may not sufficiently remove wafer surface irregularities, they have largely given way to the use of polishing techniques to planarize the surface of semiconductor wafers.
In one commonly used technique, known as chemical-mechanical planarization, the semiconductor wafer is mounted in a wafer carrier, and a polishing pad is held on a platen that can be rotated. The exposed surface of the wafer is then pressed against the polishing pad with a prescribed down force, and the polishing pad and/or the wafer are then independently rotated while the wafer carrier is translated across the pad surface. The process is continued until the desired degree of surface uniformity on the wafer is attained. In this technique, the abrasive mechanism is generally provided by a planarization fluid that contains abrasive particles in suspension with a combination of chemical etchants that are formulated to etch and dissolve certain materials that comprise the wafer. Alternatively, the planarization fluid may contain only the chemical etchants, with the abrasive elements embedded in a “fixed abrasive” pad.
The planarization fluids used in chemical-mechanical planarization are most commonly supplied to wafer manufacturers in a commercially prepackaged form, which may be comprised of two or more parts that are combined prior to planarizing a production run of wafers. Once the components are mixed, the planarization fluid is distributed to wafer planarization machines by a planarization fluid distribution system. Numerous disadvantages are present in planarization fluid distribution systems which are explained more fully with reference to the structure and operation of a typical prior art planarization fluid distribution system
10
which is shown in FIG.
1
.
With reference now to
FIG. 1
, carefully measured volumes of planarization fluid components
130
and
132
are combined in a mixing tank
138
to form a planarization fluid
14
. The mixing tank
138
has a mechanical agitator
136
that is driven by an electric motor
134
to mix the components and to keep the abrasive component of planarization fluid
14
in suspension. After the planarization fluid
14
has been sufficiently mixed, the planarization fluid
14
is transferred to a storage tank
12
through line
120
. The storage tank
12
has an outlet pipe
18
for transferring planarization fluid
14
from the tank
12
to a planarization fluid distribution loop
140
. A peristaltic pump
124
that is driven by a motor
122
pumps planarization fluid around the distribution loop
140
. Planarization fluid distribution branches
160
a
-
160
d
allow planarization fluid
14
to be distributed to planarizing machines
126
a
-
126
d
, and the amount of planarization fluid
14
distributed to the machines
126
a
-
126
d
may be controlled by manually actuated valves
150
a
-
150
d
. Although only four planarization machines are shown for clarity of presentation, a larger number of machines may be present in a typical system. By maintaining constant fluid motion in the distribution loop
140
, abrasive settling in the distribution loop
140
is avoided. Moreover, the constant pumping of planarization fluid
14
from storage tank
12
to the distribution loop
140
, together with the return of the unused portion of the planarization fluid
14
to the storage tank
12
through return pipe
16
may keep the abrasive components of planarization fluid
14
sufficiently agitated.
One disadvantage of the prior art fluid distribution system
10
is that it will not permit planarization fluids to be mixed from constituent components close to the machine. The mixing and use of planarization fluid on an as-needed basis is advantageous because the chemical etchants present in the fluid are subject to chemical degradation, and should be used relatively soon after mixing occurs. The combination of fluid components at the machine will generally permit smaller volumes to be mixed which may be more completely consumed in the wafer planarizing process, thus minimizing the waste of planarization fluid.
Another disadvantage of the prior art distribution system
10
is that it cannot accurately regulate the amount of planarization fluid delivered to each machine. Referring again to
FIG. 1
, a peristaltic pump
124
is used to deliver the planarization fluid
14
to the machines
126
a
-
126
d
. Since the peristaltic pump
124
is sensitive to changes in the fluid level in the tank
12
, the amount of fluid delivered to machines
126
a
-
126
d
will vary as the planarization fluid
14
is used. Consequently, the delivery of planarization fluid to machines
126
a
-
126
d
in uniform, precisely regulated amounts cannot be readily accomplished in the prior art system
10
.
Still other problems are inherent in the prior art planarization fluid distribution system
10
. For example, the prior art planarization fluid distribution system
10
requires a minimum volume of planarization fluid
14
in order to operate, and depending on the size of the system, this volume may be considerable. With reference again to
FIG. 1
, it is seen that the planarization fluid distribution system
10
requires that the distribution loop
140
be filled with planarization fluid
14
during operation, and that the storage tank
12
contain a sufficient volume of planarization fluid to permit pumping from the storage tank
12
. Consequently, when all wafer planarization processing is completed, a significant volume of unused planarization fluid is retained within the system
10
. Since the unused planarization fluid loses its effectiveness over time, it cannot be retained for use in planarizing subsequent wafer production runs and is generally discarded. This waste contributes to the overall cost to produce the wafer since commercially available planarization fluid formulations are relatively costly. Still other costs are incurred in discarding the excess planarization fluid, because it must be disposed of as toxic waste.
Still other disadvantages are associated with the prior art planarization fluid distribution system
10
. For example, after the removal and disposal of the excess planarization fluid, the entire distribution system is flushed with deionized water to remove the remaining fluid. However, flushing the distribution system presents still other waste disposal problems since the water used to flush the system generally contains significant concentrations of chemical constituents, as well as abrasives. It must therefore be processed to remove these materials before the water can be discharged into a municipal wastewater disposal system. An additional problem associated with flushing the system is that there is usually no way to remove the de-ionized water that is retained in the distribution system after it is flushed and drained. If the distribution system has a significant volume, considerable amounts of water will remain in the system after flushing. Consequently, the water retained by the system will dilute the fresh planarization fluid mixture when it is transported through the system. This diluted planarization fluid may cause inconsistent planarization results in subsequent wafer production runs.
Finally, abrasive settling problems are not effectively addressed by the prior art planarization flui
Dorsey & Whitney LLP
Hail III Joseph J.
McDonald Shantese
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