Method of filtering a fluid

Details Method of filtering a fluid Method of filtering a fluid

2000-03-29

2002-10-08

Drodge, Joseph W. (Department: 1723)

Liquid purification or separation

Processes

Separating

C451S060000, C210S745000, C210S778000, C210S785000, C210S791000

Reexamination Certificate

active

06461524

ABSTRACT:

BACKGROUND OF THE ART
1. Field of the Invention
The present invention relates to a method of filtering a fluid, and more particularly, to a method of removing, from a fluid, very minute objects of removal measuring 0.1 &mgr;m or less.
2. Description of the Related Art
At present, diminishing the amount of industrial waste, separate collection and recycling of industrial waste, and prevention of release of industrial waste are considered to be ecologically-important topics and business issues as society moves toward the Twenty-first century. Some types of industrial waste comprise various types of fluids containing objects of removal; i.e., substances to be removed.
Such fluids are known by a variety of expressions, such as sewage, drainage, and effluent. Fluids, such as water or chemicals, containing substances which are objects of removal will be hereinafter referred to as “wastewater.” The objects of removal are eliminated from wastewater by means of an expensive filtration system or a like system. Thus, wastewater is recycled as a clean fluid, and the removed objects of removal or substances which cannot pass through the filtration system are disposed of as industrial waste. Particularly, water is sent back to a natural setting, such as a river or the sea, or recycled after having been purified so as to meet environmental standards.
Adoption of such a filtration system is difficult because of costs incurred in constructing and running a filtration system, thus posing an environmental problem.
As can be seen from the above description, a technique for disposing of wastewater is important in terms of recycling and prevention of environmental contamination, and immediate demand exists for a filtration system incurring low initial and running costs.
By way of illustration, there will now be described disposal of wastewater as practiced in the semiconductor industry. When a plate member formed from, for example, metal, a semiconductor, or ceramics, is ground or abraded, an abrasion (or grinding) jig or the plate member is subjected to a shower of a fluid, such as water, for preventing an increase in the temperature of the abrasion (or grinding) jig, which would otherwise be caused by friction, for improving lubricity, and for preventing adhesion of abrasion or grinding waste to the plate member.
More specifically, at the time of dicing or back-grinding of plate-like semiconductor material; e.g., a semiconductor wafer, pure water is caused to flow over the semiconductor wafer. In a dicing machine, a shower of pure water is caused to flow over a semiconductor wafer, or pure water is squirted onto a blade from a discharge nozzle, in order to prevent an increase in the temperature of a dicing blade or adhesion of dicing waste onto the semiconductor wafer. For the same reason, a flow of pure water is employed during an operation in which a semiconductor wafer is made thin by means of a back-grinding operation.
Wastewater which has mixed therein grinding or abrasion waste and is discharged from the dicing or back-grinding machine is returned to a natural setting or recycled after having been purified through a filter. Alternatively, concentrated wastewater is collected.
In a current process for manufacturing a semiconductor, wastewater in which objects of removal (i.e., waste) primarily consisting of silicon are mixed is disposed of according to either of two methods; i.e., a coagulating sedimentation method and a method which employs a filter and a centrifugal separator in combination.
Under the coagulating sedimentation method, polychlorinated aluminum (PAC) or aluminum sulfate [Al
2
(SO
4
)
3
] is mixed into wastewater as a coagulant so as to react with silicon, to thereby form a reactant. The wastewater is filtrated by removal of the reactant.
Under the method which employs a filter and a centrifugal separator in combination, wastewater is filtrated, and concentrated wastewater is processed by a centrifugal separator, thereby collecting silicon waste as sludge. Clear water resulting from filtration of wastewater is released to a natural setting or recycled.
For example, as shown in
FIG. 18
, wastewater discharged during a dicing operation is collected into a raw water tank
201
and is sent to a filtration unit
203
by means of a pump
202
. A ceramic-based or organic-based filter F is provided in the filtration unit
203
, and hence which has been water filtrated through the filter F is delivered, by way of a pipe
204
, to a collected water tank
205
wherein the water is recycled. Alternatively, the filtrated water is released to a natural setting.
In the filtration unit
203
, wastewater is supplied to the filter F under pressure, thus clogging the filter F. To eliminate clogging of the filter F, the filter F is periodically cleaned. For instance, a valve B
1
connected to the raw water tank
201
is closed, and there are opened a valve B
3
and a valve B
2
for delivering collected water from the collected water tank
205
. The water supplied from the collected water tank
205
is used for cleaning the filter F. The resultant wastewater containing a high concentration of silicon waste is returned to the raw water tank
201
. Concentrated water in a concentrated water tank
206
is transported to a centrifugal separator
209
by way of a pump
208
. In the centrifugal separator
209
, the concentrated water is separated into sludge and a separated fluid. Sludge consisting of silicon waste is collected into a sludge recovery tank
210
, and the separated fluid is collected into a separated fluid tank
211
. After a separated fluid has been further accumulated in the separated water tank
211
, the separated fluid is transported to the raw water tank
201
by way of a pump
212
.
These methods have been employed even for recapturing waste resulting from grinding or abrasion of a solid or plate-like substance formed essentially from metal material; for example, Cu, Fe, or Al or from grinding or abrasion of a solid or plate-like substance formed from an inorganic substance such as ceramic.
A chemical-and-mechanical polishing (CMP) technique has been adopted as a new semiconductor processing technique. The CMP technique is for smoothing the upper surface of an interlayer dielectric film covering an interconnect in order to materialize an ideal multilayer interconnect structure, wherein irregularities formed in the upper surface of an interlayer dielectric film are chemically and mechanically abraded away.
The CMP technique enables materialization of a smooth device surface. As a result, a minute pattern can be accurately formed on the device through use of the lithography technique. Use of the CMP technique in conjunction with a technique of affixing silicon wafers enables materialization of a three-dimensional integrated circuit.
Second, the CMP technique enables materialization of a structure in which there is embedded material differing from a substrate, thus yielding an advantage of facilitated realization of an embedded interconnect structure. There has been employed a technique of embedding tungsten (W) in a trench of an interlayer film of multilayer interconnect of an IC by means of the CVD technique. The thus-embedded interlayer film is etched back, thus smoothing the surface of the interlayer film. However, smoothing an interlayer film by means of the CMP technique yields an advantage of facilitating a process, and hence the CMP technique has recently come into the limelight.
The CMP technique and applications thereof are described in detail in a periodical entitled “Science of CMP” issued by a science forum.
The mechanism of a machine used for CMP will now be briefly described. As shown in
FIG. 19
, a semiconductor wafer
252
is placed on an abrasive cloth
251
placed over a rotary table
250
. The semiconductor wafer
252
is abraded by being slid over the abrasive cloth
251
while an abrasive (i.e., slurry)
253
is caused to flow over the surface of the semiconductor wafer
252
. Further, the semiconductor wafer
252
is chemically etched, thereby elim

Affiliated with

Also associated with

Rating

Method of filtering a fluid does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of filtering a fluid, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of filtering a fluid will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2949747