Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR RECOVERY OF WATER AND SLURRY
ABRASIVES USED FOR CHEMICAL AND MECHANICAL
PLANARIZATION
BACKGROUND OF THE INVENTION
Related Applications:
This is a continuation in part of Serial No. 08/870,082, filed June 5,
1997.
Field of the Invention:
This invention relates generally to chemical mechanical processing of
semiconductor wafers, and more particularly concerns a method and apparatus
for
recovery of components of an aqueous chemical and mechanical abrasive slurry
containing finely divided, suspended particles following their use in
processing of
semiconductor wafers.
Description of Related Art:
Semiconductor components are commonly manufactured by layering
electrically conductive and dielectric materials to achieve appropriate
electrical
characteristics for fabrication of multiple electrical components such as
resistors,
capacitors and transistors. Many of these discrete devices are incorporated
into
integrated circuits for use in creating microprocessors, memory chips, logic
circuits,
and the like. Many integrated circuits can be produced on semiconductor wafers
by
layering of dielectric and electrically conductive materials to create
multiple
semiconductor devices in a relatively small area.
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The density of electrical components on such semiconductor devices
has continually increased as trace line widths and element sizes on such
semiconductor devices have narrowed. At one time, for example, trace line
widths on
such devices typically ranged from l~cm to 4~cm. However, in recent years, the
S industry has made significant advances in reducing trace line widths used in
integrated
circuits to less than l~cm. Currently, trace line widths of 0.5 to 0.35 ~m are
common,
and research is being conducted to achieve trace line widths of from 0.25 ~cm
to 0.18
~cm. In addition, the demand for increased memory and computing power has
driven
limits on the number of semiconductor devices per integrated circuit that are
achievable ever higher, resulting in an increase in the number of layers
applied to
semiconductor wafers, while the typical size of the integrated circuits
continues to
decrease. The combination of narrower trace line widths, increased numbers of
layers
of materials and higher densities of semiconductor devices per integrated
circuit has
made such devices increasingly susceptible to failure due to inconsistencies
on
semiconductor wafer surfaces, and it has become increasingly important that
such
semiconductor wafers have surfaces and dielectric layers that are uniformly
smooth.
Methods for chemical mechanical planarization (CMP) have been
developed to polish the surface of semiconductor wafers, and typically involve
rotating the wafer on a polishing pad, applying pressure through a rotating
chuck, and
supplying an aqueous chemical slurry containing an abrasive polishing agent to
the
polishing pad for both surfactant and abrasive action. Abrasive agents that
can be
used in the chemical mechanical slurry include particles of fumed silica,
cesium and
alumina. The chemical mechanical slurry can also include stabilizer or
oxidizer
agents. Fumed silica is typically mixed with a stabilizer such as potassium
hydroxide
or ammonium hydroxide, and is commonly used to polish dielectric or oxide
layers
on the semiconductor wafer. Cesium and alumina are commonly mixed with an
oxidizer agent such as ferric nitrate or hydrogen peroxide, and are typically
used to
polish metal layers, such as tungsten, copper and aluminum, for example.
The slurry and material removed from the various layers of the
semiconductor wafer form a waste stream that is commonly disposed of as
industrial
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waste. The abrasive components constitute approximately 8% to 15% of the raw
waste stream, with the remainder constituting other chemical agents such as
stabilizer
or oxidizer agents, and water. The raw waste stream is typically diluted with
rinse
water to yield a final solids concentration of approximately 1 % to 1.5% in
the waste
stream. However, the disposal of dissolved or suspended solids in the
industrial waste
stream has become a relevant issue due to strict local, state and federal
regulations,
and it would thus be desirable to provide a process and apparatus to remove
abrasive
components from the waste stream for possible removal of heavy metal
components
for separate disposal.
Since, for a significant amount of time, the waste stream contains only
deionized water; it would also be desirable to reclaim the waste stream
supernatant
liquid to permit reuse of the supernatant liquid in the chemical mechanical
planarization process. Ideally, this process would occur at the polisher tool
in order
to effectively reuse the deionized water and simultaneously save costs. While
conventional filtration technology exists for point-of use filtration, this
technology is
not suited for the high probability of suspended matter in the waste stream.
With
conventional filtration, all effluent flow is into the filter at a
perpendicular angle to the
membrane element. The particles embed in the membrane media and the filter
subsequently clogs. This causes high downtime and related operating costs.
Alternatives to point-of use filtration include central plant treatments
such as pH neutralization and the addition of flocculating or settling agents
in
conjunction with filter presses; ultrafiltration or reverse osmosis filtration
systems.
These systems represent a prohibitively costly system for users with just
several
polishing tools and continuing high operation costs. Further, these systems
are based
on the current chemistries and are relatively inflexible to handle future
slurry
requirements. It is therefore desirable to have a process which treats the
primary
suspended particles problem, yet is flexible enough to meet slurry specific
problems.
It is also desirable to have a process that is scalable from pilot production
to full scale
manufacturing. The present invention meets these and other needs.
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SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention provides for the
separation and recovery of abrasive components and fluids from an aqueous
chemical
mechanical slurry used for planarization of semiconductor materials, to permit
the
reuse of the liquid effluent in non-process applications as well as for gray
water for
irrigation, process cooling water, or as make-up water for a reverse osmosis
system,
or safe disposal in the industrial waste stream, as desired.
The invention accordingly provides for a method and apparatus for
recovering clear liquid from an aqueous slurry waste stream and for
concentrating and
recovering particles of abrasive materials from the same aqueous solution. In
the
method and apparatus for the invention, an aqueous slurry waste stream which,
on an
irregular basis, contains an abrasive component is introduced into a particle
detection
device which used one of several technologies to detect the presence of
abrasive
particles. The detection device may use optical, ultrasonic or other similar
detection
techniques to measure the density of the abrasive solids in the effluent
stream or the
turbidity of the effluent stream. Based on the measurement made by the
detection
device, when solids concentrations below a desired threshold are indicated,
the
effluent stream is diverted to one or more small collection tanks. The
collected liquid
is pumped back to the polisher through an apparatus which provides non-process
water to the polisher for reuse as rinse water. Alternatively, when a solids
concentration over the desired threshold is detected, the entire waste stream
is diverted
to an apparatus that separates the solids from the liquid component of the
waste stream
using an ultrafiltration device. The clear liquid is collected in one or more
collection
tanks and used variously for return to the polisher as non-process rinse
water;
backflush water for the ultrafiltration device; or diverted to the facility
industrial waste
treatment system for disposal. With additional treatment (ion-exchange or
elutriation
for copper removal, for example) this liquid may be used for gray-water
applications
such as cooling water or irrigation or as feed water to the facility reverse
osmosis
system for further water usage reduction.
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The apparatus of this invention further provides for recirculating the
waste solids stream from the ultrafiltration device in order to further
concentrate the
solids and effect maximum removal of clear liquid from the waste stream. This
apparatus is capable of concentrating the solids from as little as 0.2% solids
by weight
5 to as high as 50% solids by weight. When the solids content reaches the
preferred
concentration level, the solids waste is diverted to an apparatus where the
solids are
collected in containers for off site disposal or reclamation for reuse in
other industries.
These and other aspects and advantages of the invention will become
apparent from the following detailed description and the accompanying
drawings,
which illustrate by way of example the features of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram of the method and apparatus of a first
embodiment of the invention for recovering liquid and slurry abrasives that
have been
used for chemical mechanical planarization of semiconductor wafers;
Fig. 2 is a sectional view of a separation column of Fig. I;
Fig. 3 is a schematic diagram of the method and apparatus of a second
embodiment of the invention for recovering water and slurry abrasives that
have been
used for chemical and mechanical planarization of semiconductor wafers;
Fig. 4 is a sectional view of the shock tank of Fig. 3;
Fig. 5 is a schematic view of the filter assembly of Fig. 3;
Fig. 6 is a sectional view of the filter of the filter assembly of Fig. 5;
Fig. 7 is a sectional view of a separation column of Fig. 3;
Fig. 8 is a schematic diagram of the method and apparatus of a third
embodiment according to the principles of the invention for recovering liquid
and
slurry abrasives that have been used from chemical mechanical planarization of
semiconductor wafers;
Fig. 9 is a schematic diagram of an apparatus according to the
principles of the invention for detecting solids concentration in the effluent
stream and
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diverting the clear liquid stream to the interface apparatus and back to the
polisher;
Fig. 10 is a perspective view of an ultrafiltration device for use in the
apparatus of Fig 9 or Fig. 1 l; and
Fig. 11 is a schematic diagram of an apparatus according to the
principles of the invention for recovering clear liquid from a slurry abrasive
waste
stream and concentrating the waste stream to maximize the recovery of clear
liquid.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As the density of electrical components and wiring in semiconductor
devices have increased, such devices have become increasingly susceptible to
failure
due to surface irregularities on semiconductor wafers. Conventional methods
utilized
in the industry for chemical mechanical planarization of the surface of
semiconductor
wafers to address this problem commonly result in a wasteful disposal of the
abrasive
agents and water in the slung used for polishing the various layers of the
semiconductor wafers.
As is illustrated in the drawings, the invention is accordingly embodied
in a method and apparatus for recovering particles of abrasive material from
an
aqueous slurry of the particles of abrasive material. Referring to Fig. 1, in
a first
presently preferred embodiment, an apparatus 10 for recovering particles of
abrasive
material from an aqueous slurry of the particles of abrasive material
typically receives
raw waste from inlet line 12 including the aqueous chemical and mechanical
slung
containing abrasive particles and materials removed from planarization of
semiconductor materials in a slurry waste collection tank 14. The quantity of
flow of
the slurry waste can be measured by a flow meter 16 connected to the raw waste
inlet
line. The slung waste in the slurry waste collection tank is preferably
maintained
under conditions of ambient temperature and pressure, and is preferably
maintained
at approximately a neutral pH. The acidity or basicity of the slung waste is
preferably
monitored by a pH meter 18 connected to the slurry waste collection tank.
Electrical signals indicative of the pH of the slurry waste in the
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collection tank can be received by a controller 19 for controlling the
introduction into
the slurry waste collection tank of pH neutralizing agents that are selected
depending
upon the pH of the slurry effluent. Neutralizing agents can include, for
example, an
acid from an acid reservoir 20 dispensed through acid valve 24 controlled by
the
controller, or a base from a base reservoir 22 through base valve 26
controlled by the
controller, or pH buffer agents, all of which are well known to those skilled
in the art.
The slurry waste in the collection tank is typically stirred by a stirrer (not
shown) in
the collection tank that is driven by motor 27. The mixture of slurry effluent
and any
neutralizing agents can be held in the slurry collection tank for a period of
time for
treatment as desired, and then discharged for further processing through the
collection
tank outlet 28. Alternatively, the treated slurry effluent can be discharged
continuously through the collection tank outlet 28.
Flow of the treated slurry effluent from the collection tank can be
facilitated by pump 29 connected between the collection tank outlet and the
treated
slurry effluent line 30 leading to further processing of the slurry effluent.
A pressure
meter 32 and total dissolved solids meter 34 can be connected to the treated
slurry
effluent line for monitoring the condition of the treated slurry effluent.
The treated slurry effluent carried by the effluent line is preferably
drawn by vacuum into one or more process chambers or separation columns 36 for
separating the treated slurry effluent into a portion containing a greater
proportion of
the abrasive particles, and a supernatant portion containing a lesser
proportion of the
abrasive particles. Alternatively, the slurry effluent can be pumped by
positive
pressure through the separation columns. Each separation column has an inlet
38 for
receiving treated slurry effluent, a supernatant outlet line 40 for the
lighter supernatant
portion of the slurry effluent, and a bottom solids outlet 42 for the heavier
portion of
the separated slurry effluent containing a greater proportion of the abrasive
particles.
As is illustrated in Fig. 1, in a presently preferred embodiment, a plurality
of the
separation columns can be connected in series, so that the most upstream
separation
column receives treated slurry effluent from the slurry effluent collection
tank, and
subsequent downstream separation columns receive the lighter supernatant
portion of
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the slurry effluent from an upstream separation column. The most downstream
separation column supernatant outlet carries the processed supernatant for
further
processing.
With reference to Fig. 2, each separation column preferably has a
nozzle 44 for introducing the treated slurry effluent into a cooling portion
45 of the
separation column, surrounded by a cooling coil 46 carrying a flow of coolant.
The
nozzle preferably introduces the slurry effluent into the cooling portion of
the
separation column in a direction tangential to the longitudinal axis of the
separation
column to create a helical or circular flow of the slurry effluent in the
cooling portion
of the separation column. The cooling coil preferably cools the slurry
effluent to a
temperature between about 0°C and about 15°C, facilitating
agglomeration of the
particles.
After the slurry effluent is cooled, it passes through precision machined
openings between two charged electrode plates. Passage of the cooled slurry
effluent
between the negatively charged electrode 48 and the positively charged
electrode 50
results in a change in the electrical properties of the particles, causing
them to
agglomerate, causing the resultant flocs of particles to separate from a
supernatant
liquid portion of the slurry effluent. The slurry effluent then passes through
a second
nozzle 52 that introduces the slurry effluent in a direction tangential to the
longitudinal
axis of the separation column to create a helical or circular flow of the
slurry effluent,
causing a portion of the aqueous slurry containing the agglomerations or flocs
of the
particles to move to the solids settling chamber 54 of the of the separation
column,
while the supernatant liquid remaining in the aqueous slurry exits through the
supernatant outlet 40.
A solids outlet valve 56 allows control of the flow from the bottom
solids outlet 42, so that the portion of the aqueous slurry in the solids
settling chamber
containing agglomerations ofthe particles can be discharged as desired from
the solids
settling chamber through a solids outlet line 58 to a solids collection tank
60, either
periodically or continuously. In a presently preferred embodiment, a plurality
of
separating columns are connected in series such that the supernatant liquid
from a
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supernatant outlet of one separating column passes to the inlet of the next
separating
column in sequence, while the supernatant outlet of the last separating column
in the
sequence carries the supernatant liquid for further processing and collection.
In one currently preferred embodiment, the supernatant liquid from the
separating columns passes via supernatant line 61 to one or more vacuum
chambers
62 connected to a source of vacuum 64. The temperature and pressure of the
supernatant liquid in the supernatant line can be monitored by temperature and
pressure sensors, if desired. In one currently preferred embodiment, the
aqueous
slurry is introduced into the process chamber at ambient temperature and
pressure.
In a presently preferred embodiment, the supernatant liquid line from the
separating
columns is connected to the inlet 66 to a plurality of vacuum chambers, each
of which
has a supernatant outlet 68 to supernatant outlet line 70, leading to inlet 72
to
supernatant liquid collection tank 74. When the supernatant liquid in a vacuum
chamber is subjected to a reduction ofpressure, gas entrapped in the
supernatant liquid
bubbles to the surface of the supernatant liquid. The bubbling of gas to the
surface of
the supernatant liquid is believed to bring particles in the supernatant
liquid into close
proximity to cause further agglomeration of the particles due to van der Waals
attraction among the particles. The agglomerated particles have a higher
specific
gravity than the water in the supernatant liquid, causing them to separate and
precipitate to the bottom ofthe vacuum chamber. Alternatively, gas, such as
clean dry
air, oxygen or nitrogen, for example, can be injected in small quantities into
the
supernatant liquid in the vacuum chamber to further enhance the bubbling of
gas
through the supernatant liquid.
A solids outlet line 76 leading from the bottom of each vacuum
chamber is connected to a solids line 78 leading to solids collection tank. In
a
presently preferred embodiment, an outlet line 80 from solids collection tank
is
connected to carry collected solids and liquid to a centrifugal separator 82.
Liquid
passes from the centrifugal separator to the supernatant collection tank 74.
Liquid
from the solids collection tank 60 pass through the fluid line 84 to filter
press 86,
which also receives concentrated solids from the centrifugal separator via
solids outlet
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line 87 from centrifugal separator. Solids can ultimately be collected via
solids waste
line 88 from filter press 86. Supernatant liquid from the centrifugal
separator flows
via supernatant liquid outlet line 90 to the supernatant liquid collection
tank 74. The
pH of the supernatant liquid can be monitored by pH meter 92 connected to the
5 supernatant liquid collection tank. The supernatant liquid can be collected
through
outlet 94, and can be pumped by a pump 96 through line 98 to one or more
holding
tanks 100 having supernatant outlets 102, where the quantity and quality of
the
supernatant liquid can be monitored, for example, by pH meter 104, total
dissolved
solids meter 106, turbidity meter 108, and flow meter 110.
10 Refernng to Figs. 3 to 7, in a currently preferred second embodiment
of the invention, an apparatus 210 for recovering particles of abrasive
material from
an aqueous slurry of the particles of abrasive material typically receives raw
waste
from inlet line 212 including the aqueous chemical and mechanical slurry
containing
abrasive particles and materials removed from planarization of semiconductor
materials in a slurry waste pH shock tank 214. The quantity of flow of the
slurry
waste can be measured by a flow meter 216 connected to the raw waste inlet
line. The
slurry waste in the slurry waste pH shock tank is preferably maintained under
conditions of ambient temperature and pressure, and is preferably maintained
at
approximately a pH of about 2 to 4. The pH of the slurry waste is preferably
monitored by a pH meter 218 connected to the slurry waste Ph shock tank, as is
shown
in Fig. 3.
Referring to Figs. 3 and 4, electrical signals indicative of the pH of the
slurry waste in the pH shock tank can be received by a controller 219 for
controlling
the introduction into the slurry waste pH shock tank of an acid, such as HCI,
for
example, and other pH controlling agents, in quantities depending upon the pH
of the
slurry effluent. The acid is dispensed from an acid reservoir 220 through acid
valve
224 controlled by the controller, or a base from a base reservoir 222 through
base
valve 226 controlled by the controller, or pH buffer agents. The slurry waste
in the
pH shock tank is typically stirred by a stirrer 221 in the pH shock tank that
is driven
by motor 227. The mixture of slurry effluent and any neutralizing agents can
be held
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in the slurry pH shock tank for a period of time for treatment as desired, and
is
typically held in the shock tank for a period of time ranging up to about 1
hour. The
acidified aqueous slurry is then discharged for further processing through the
pH
shock tank outlet 228 to the pH balance tank 214'.
As is illustrated in Fig. 4, the slurry waste pH shock tank 214 has a
stirrer 221 propeller at end of a stirrer shaft 223 which also serves as a
cathode for
applying an electrical potential through the acidified aqueous slurry to
change the
electrical properties of the particles to facilitate agglomeration and
flocculation of the
particles. A wire mesh anode grid 225 is disposed in the shock tank around the
stirrer
shaft cathode, and is electrically connected with the base of the shock tank,
which also
serves as an anode. The voltage that is applied to the aqueous slurry in the
shock tank
is typically about 12 to 5,500 volts, although higher voltages may be even
more
effective. The shock tank also has a supernatant overflow outlet 229 for
relief of
excess aqueous slurry in the shock tank. A cooling jacket (not shown)
typically of
coils similar to those for the cooled process chamber preferably is used
around the pH
shock tank to cool the temperature of the aqueous slurry to a range of between
about
0°C and about 15°C. Electrophoresis is accomplished in the pH
shock tank radially,
driving the particles through the separation anode grid. Outside the stirnng
zone
within the mesh grid, the particles agglomerate and fall to the bottom of the
tank, and
are drawn to the bottom of the tank by the anode plate at the bottom of the
tank. The
agglomeration process is enhanced by chilling the aqueous slurry to a
temperature
between about 0°C and about 1 S°C, which decrease the effects of
Joule heating and
connective mixing caused by the electrophoretic process. Supernatant liquid
can also
be drawn off from the top of the pH shock tank to be neutralized and recycled
with
supernatant from other parts of the process.
Refernng to Fig. 3, the acidified solids/fluid solution is drawn off from
the bottom of the pH shock tank under vacuum to the pH balance tank 214', and
is
mixed with untreated waste slurry received via inlet line 212', and
neutralizing agents
added to the pH balance tank. Electrical signals indicative of the pH of the
slurry
waste in the pH balance tank can be received by a controller 219' for
controlling the
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introduction into the slurry waste pH balance tank of pH neutralizing agents
that are
selected depending upon the pH of the slurry effluent. Neutralizing agents can
include, for example, an acid such as HCI, for example, from an acid reservoir
220'
dispensed through acid valve 224' controlled by the controller, or a base,
such as
sodium bicarbonate (Na2C03), from a base reservoir 222' through base valve
226'
controlled by the controller, or pH buffer agents, all of which are well known
to those
skilled in the art. The slurry waste in the pH balance tank is typically
stirred by a
stirrer 221' in the pH balance tank that is driven by motor 227'. The mixture
of slurry
effluent and any neutralizing agents can be held in the slurry pH balance tank
for a
period of time for treatment as desired, and then discharged for further
processing
through the pH balance tank outlet 228'. Alternatively, the treated slurry
effluent can
be discharged continuously through the pH balance tank outlet 228'. A cooling
jacket
(not shown) typically of coils similar to those for the cooled process chamber
and the
pH shock tank preferably is used around the pH balance tank to maintain the
temperature of the pH neutralized aqueous slurry within a range of about
0°C to about
15°C for increasing the rate of agglomeration. Outside the agitation
zone of the
stirrer, agglomerated particles fall to the bottom of the pH balance tank.
The effluent from the pH balance tank then preferably is preferably
drawn under vacuum to a first self cleaning reversible gross particle filter
assembly
230 and then to a second self cleaning reversible filter assembly 230' which
is
substantially identical to the filter assembly 230, as is illustrated in Figs.
3 and 5. The
filter assemblies 230 and 230' will be described in detail with reference to
the filter
assembly 230 shown in Fig. S. The self cleaning gross particle filters operate
by
forcing a fluid flow through the filter containing a mufti-layered filter
material that
traps gross particles. After a timed interval, the flow can be reversed
through the
filter, causing the gross particles previously captured in the filter media to
flow out
and to drop into a collection chamber. By repeating this process, the filters
collect
gross particles, and reduce the need for frequent filter replacement.
The effluent from the pH balance tank outlet 228' is thus connected to
filter assembly inlet 256 of the filter assembly, which includes a series of
flow control
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valves 231 a-231 f connected to the inlet 256 that can be opened and closed to
direct
the flow of pH neutralized slurry through the filter 232 connected between the
two
filter manifolds 233a,b. As is shown in Fig. 6, in a currently preferred
embodiment,
the filter contains a sequence of symmetrically arranged layers of filter
media 234a-g,
S with the gradation of the filter media being from coarsest to finest from
the outside
layers to the inside layer. Thus, the filter contains two outside gross filter
media
234a,g respectively adjacent to a medium filter media 234b,f, followed
respectively
by an adjacent medium/fme filter media 234c,e, on either side of the innermost
fine
filter media 234d. Other similar arrangements of filter media may also be
suitable.
Thus, in operation, the filter assembly can be operated in either of two
configurations
allowing the direction of flow through the filter to be reversed periodically
to flush
gross particles from the filter, allowing the gross particles to be discharged
through
the filter assembly solids outlet 258. In an exemplary first configuration,
valves 231 a,
b, d, f are closed and valves 231c and a are open, allowing flow from right to
left
through the filter. Filtered supernatant flows up through the supernatant
liquid outlet
235. After a period of time for collecting gross particles on the right side
of the filter,
the valve configuration can be changed to a reversed flushing configuration in
which
valves 231 a, c and a are closed, and valve 231 d is temporarily opened and
valve 231 f
temporarily closed to allow gross particles to be flushed to the right through
to the
solids outlet 258. Thereafter, valve 231d can be closed, and valve 231f
opened, to
allow flow in a normal second flow configuration from left to right through
the filter
and up through the supernatant liquid outlet 235. After a period of time for
collecting
gross particles on the left side of the filter, the valve configuration can be
again
changed back to the original flow configuration for flushing of the filter, in
which
valves 231 b, d, f are closed, valve 231c is open, allowing flow from right to
left
through the filter, and valve 231 a is temporarily opened and valve 231 a
temporarily
closed to allow gross particles to be flushed to the left through to the
solids outlet 258.
Thereafter, valves 231 a, b, d, f are closed and valves 231 c and a are open,
in the
normal first flow configuration, allowing flow from right to left through the
filter, and
filtered supernatant flows out through the supernatant liquid outlet 235.
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The treated slurry effluent carried by the effluent line is preferably
drawn by vacuum through an inlet 238 into one or more process chambers or
separation columns 236 for separating the treated slurry effluent into a
portion
containing a greater proportion of the abrasive particles, and a supernatant
portion
containing a lesser proportion of the abrasive particles. As is illustrated in
Fig. 3, in
a presently preferred embodiment, a plurality of the separation columns can be
connected in series, so that the most upstream separation column receives
treated
slurry effluent from the slurry effluent collection tank, and subsequent
downstream
separation columns receive the lighter supernatant portion of the slurry
effluent from
an upstream separation column. The most downstream separation column
supernatant
outlet carries the processed supernatant for further processing and
collection. Each
separation column has an inlet 238 for receiving treated slurry effluent, a
supernatant
outlet line 240 for the lighter supernatant portion of the slurry effluent,
and a bottom
solids outlet 242 for the heavier portion of the separated slurry effluent
containing a
greater proportion of the abrasive particles.
With reference to Fig. 7, each separation column typically has a solids
outlet end cap 255 and a supernatant liquid outlet end cap 257. for
introducing the
treated slurry effluent into a cooling portion 45 of the separation column,
surrounded
by a cooling coil 46 carrying a flow of coolant. A nozzle 252 receiving the
aqueous
slurry flow from the inlet preferably introduces the slurry effluent into the
cooling
portion of the separation column in a direction tangential to the longitudinal
axis of
the separation column to create a helical or circular flow of the slurry
effluent in the
cooling portion of the separation column. The cooling coil preferably cools
the slurry
effluent to a temperature between about 0°C and about 15°C,
facilitating
agglomeration of the particles, causing a portion of the aqueous slurry
containing the
agglomerations or flocs of the particles to fall out of suspension to the
solids settling
chamber 254 at the bottom of the separation column, while the supernatant
liquid
remaining in the aqueous slurry exits through the supernatant outlet 240. The
accumulated solids can be either periodically purged or continuously drawn by
vacuum from the separation columns to a gross solids collection tank 260.
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Refernng to Figs. 3 and 7, a solids outlet valve 256 allows control of
the flow from the bottom solids outlet 242, so that the portion of the aqueous
slurry
in the solids settling chamber containing agglomerations of the particles can
be
discharged as desired from the solids settling chamber through a solids outlet
line 258
5 to a gross solids collection tank 260, either periodically or continuously.
In a
currently preferred embodiment, the effluent from solids outline 258 is drawn
to the
gross solids collection tank by a vacuum gravity vessel 261 connected to a
vacuum
source 264. The gross solids collection tank can be emptied while fluid flow
continues through the separating columns.
10 In a currently preferred embodiment, the supernatant liquid from the
separating columns passes via supernatant outlet line 240 to one or more
vacuum
gravity vessel 262 connected to the source of vacuum 264. In one currently
preferred
embodiment, the aqueous slurry is introduced into the process chamber at
ambient
temperature and pressure. In a presently preferred embodiment, the supernatant
liquid
15 line from the separating columns is connected to the inlet 266 to a
plurality of vacuum
gravity vessels, each of which has a supernatant outlet 268 connected to the
fine
sludge collection tank 270, having an outlet 272.
An outlet line 280 from solids collection tank is connected to carry
collected solids from the outlet of the gross solids collection tank and fine
sludge from
the fine sludge collection tank outlet and liquid remaining in the gross
sludge and fine
sludge to a centrifugal separator 282. The lighter liquid fraction separated
in the
centrifugal separator is conducted to the supernatant collection tank 274.
Concentrated solids are conducted to a dryer 286 via the solids outlet line
287 from
the centrifugal separator. Solids can ultimately be collected via solids waste
line 288
from the dryer. Supernatant liquid from the centrifugal separator flows via
supernatant liquid outlet line 290 to the supernatant liquid collection tank
274. The
supernatant is drawn from the centrifuge, through an optional I7V light source
and ion
exchange resin bead to remove dissolved solids, into the supernatant liquid
collection
tank for final processing. The pH and total dissolved solids of the
supernatant liquid
can be monitored by pH meter 292 and total dissolved solids metering station
293,
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respectively, connected to the supernatant liquid collection tank. The
supernatant
liquid can be collected through outlet 294, and can be pumped by a pump 296
through
line 298, which can be provided with one or more filters 297.
In the case of silica-based and TEOS based slurries, the flocculated
material may be recovered for reuse of the silicon or TEOS in the slurries. In
the case
of alumina-based slurries, the flocculated material may also be recovered for
reuse of
the silicon in the slurries. Due to metallic impurities, it is unlikely that
alumina-based
slurries can be reclaimed for use in the semiconductor industry. In the case
where
TEOS or silica-based and alumina or cesium-based slurries are combined, then
the
flocculated material is treated as alumina-based solids for reuse or disposal.
The reuse
or disposal of the silicon, alumina and other metals and the required purity
for any
such reuse is well known to those skilled in the art of slurry manufacture.
Referring to Fig. 8, in a currently preferred third embodiment of the
invention, a method and apparatus are provided first for the recovery of clear
liquid
from an aqueous waste stream that may contain abrasive materials, and then for
the
removal of the solids from the aqueous solution. The apparatus 300 for
detecting the
concentration of abrasive solids in an aqueous waste stream receives raw waste
from
a polisher 302 including the aqueous slurry containing abrasive particles and
materials
removed from planarization of semiconductor materials. The apparatus 300 is
located
in a location of close proximity to the polishing tool, and generates a signal
304 to a
control unit 306 controlling valve 308 for directing the effluent from the
detector
apparatus 300. When the abrasive solids concentration is below a desired
threshold,
the entire effluent stream is diverted by the valve 308 to an apparatus 310
for reuse in
non-critical rinsing applications in the polishing tool. When the abrasive
solids
concentration is above the desired threshold, the entire effluent stream,
including the
aqueous slurry containing abrasive particles and materials removed from
planarization
of semiconductor materials, is diverted by the valve 309 to an apparatus 312
which
can be the concentrator apparatus of Figs. 1-2 or Figs. 4-7, to further
separate the clear
liquid component from the abrasive solids and concentrates the abrasive solids
for
disposal. The clear liquid from the concentrator apparatus 312 is returned via
line 313
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to the concentration detection apparatus 300 for recycling or to the
industrial waste
treatment system 314 for disposal. The concentrated abrasive solids and
materials
removed from planarization of semiconductor materials are diverted to an
apparatus
316 for alternatively filling one of several waste collection containers 317
which,
S when filled, are removed for off site processing 318.
Referring to Figure 9, in another presently preferred embodiment, an apparatus
320 for detecting the concentration of abrasive and other materials in an
aqueous
solution receives raw aqueous effluent possibly containing an aqueous slurry
of
abrasive particles in a solids detection device 322 where the incoming flow
324 and
effluent pH 326 are also measured. The solids detection device utilizes
optical,
ultrasonic or similar detection techniques to detect turbidity and/or
particulate density:
The solids detection device generates a signal 328 to a control unit 330
controlling
valve 332 for directing the effluent from the solids detection device. If the
incoming
effluent stream contains solids under a desired threshold, the entire effluent
stream is
diverted by valve 332 to one or more collection tanks 334; otherwise, the
entire
effluent stream containing abrasive solids is diverted by valve 332 to one or
more
collection tanks 336 for local filtration. From tank 336, effluent containing
abrasive
solids and materials from polishing semiconductor wafers is transferred by
pump 338
through an ultrafiltration device 340 of either ceramic or sintered metal
construction,
as illustrated in Fig. 10. The ultrafiltration device is preferably
manufactured from
ceramic or sintered metal, although other materials of construction such as
polysulfone
may alternatively be used. After a single pass, the aqueous solution
containing
abrasive solids and materials from polishing semiconductor wafers is sent by
drain
342 to a solids concentrator apparatus for further processing. The clear
liquid from
this ultrafiltration device is collected in the one or more collection tanks
334. An
electronic interface of the control unit with the polisher indicates when non-
process
equipment rinse water is required by the polisher 344. Upon receipt of a
signal from
the polisher, pump 346 draws clear liquid from one or more collection tanks
334, and
pumps the liquid through flow meter 348 and valve 350 to return to the
polisher as
non-process equipment rinse water. When adequate reclaimed water is not
available
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from collection tanks 334, additional rinse water is obtained by opening the
deionized
water by-pass valve 352. When the supply in the collection tank 334 is
sufficient to
meet the demand of the polisher, the excess is diverted to the industrial
waste
treatment system through an overflow drain 354.
Refernng to Fig. 11, the apparatus 360 for concentrating the abrasive
solids in the waste stream receives an aqueous solution from the solids
detection
apparatus 362 into one or more concentration tanks 364. The solids content in
this
tank is monitored on a continuous basis by a solids concentration measurement
device
366 while the pH of the liquid is monitored continuously by the pH sensor 368.
While
the solids concentration is below a desired threshold and the fluid level in
the tank is
below the level sensor 370, pump 372 recirculates the aqueous solution through
an
ultrafiltration device 374 such as the one shown in Fig. 10. The
ultrafiltration device
374 is preferably manufactured from ceramic or sintered metal, although other
materials of construction such as polysulfone may alternatively be used. The
retentate
375 from the ultrafilter is returned to the concentration tank 364 for re-
filtration while
the permeate 377 or clear liquid from the ultrafiltration device 374 is sent
to either the
industrial waste treatment system (not shown) or back to the solids detection
apparatus
362 for use as non-process equipment rinse water, or to a backflush water
collection
tank 379 through valve 376. The ultrafiltration device 374 is backflushed
periodically
(preferably every 10 to 20 minutes) by diverting the waste stream at valve 378
to an
apparatus for collection of the solids waste (not shown) and opening valve 380
for a
short period of time. Backflush water is drawn by pump from the backflush
water
collection tank (not shown) and used to pressurize the back side of the
ultrafiltration
device. This causes possible embedded particles to break away from the
ultrafiltration
element and return to the concentration tank 364.
When the solids concentration reaches the desired threshold, or when the fluid
level in the concentration tank 364 reaches the level sensor 370, the flow
from pump
372 is diverted by valve 378 to apparatus for collection of the solids waste
(not
shown).
It will be apparent from the foregoing that while particular forms of the
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19
invention have been illustrated and described, various modifications can be
made
without departing from the spirit and scope of the invention. Accordingly, it
is not
intended that the invention be limited, except as by the appended claims.
