Liquid purification or separation – With alarm – indicator – register – recorder – signal or... – Responsive to fluid flow
Reexamination Certificate
2002-10-31
2004-12-14
Popovics, Robert James (Department: 1724)
Liquid purification or separation
With alarm, indicator, register, recorder, signal or...
Responsive to fluid flow
C210S097000, C210S103000, C210S106000, C210S193000, C210S220000, C210S408000, C210S411000, C210S416100, C210S490000, C210S502100, C210S739000, C210S745000, C210S777000, C210S791000
Reexamination Certificate
active
06830679
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of filtering and mainly relates to a filtration device for removing objects of removal from fluids with which very minute objects of removal of mainly 0.15 &mgr;m or less are contained in a colloidal solution (sol).
BACKGROUND OF THE INVENTION
Presently, diminishing the amount of industrial waste, separate collection and recycling of industrial waste, and preventing release of industrial waste are considered to be ecologically-important topics and business issues as society moves towards the 21st 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 that are objects of removal, shall be hereinafter referred to as “wastewater.” The objects of removal are eliminated from wastewater by an expensive filtration system or a similar system. Wastewater is thereby recycled as a clean fluid, and the removed objects or substances that cannot pass through the filtration system are disposed of as industrial waste. In particular, water is sent back to a natural setting, such as a river or sea, or recycled after being 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, wastewater treatment techniques are important in terms of recycling and preventing environmental contamination, and an immediate demand exists for a filtration system that incurs low initial and running costs.
By way of illustration, wastewater treatment as practiced in the field of semiconductors shall now be described. When a plate member formed, for example, from a metal, a semiconductor, or ceramic, is ground or abraded, an abrasion (or grinding) jig or the plate member is subject 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 onto the plate member.
More specifically, in the process of dicing or back-grinding of plate-like semiconductor material; e.g., a semiconductor wafer, pure water is made to flow over the semiconductor wafer. In a dicing machine, a shower of pure water is made to flow over a semiconductor wafer, or pure water is squirted onto a dicing blade from a discharge nozzle in order to prevent an increase in the temperature of the 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 back-grinding.
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 recovered.
In a current process for manufacturing a semiconductor, wastewater, in which objects of removal (i.e., waste) primarily consisting of Si are mixed, is disposed of according to one 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, polyaluminum chloride (PAC) or aluminum sulfate (Al
2
(SO
4
)
3
) is mixed in the wastewater as a coagulant to generate a reaction product with Si and the wastewater is filtrated to remove this reaction product.
Under the method that employs a filter and a centrifugal separator in combination, the wastewater is filtrated, the concentrated wastewater is processed by the centrifugal separator to recover the silicon waste as sludge, and the clear water resulting from filtration of the wastewater is released to a natural setting or is recycled.
For example, as shown in
FIG. 11
, wastewater discharged during a dicing operation is collected into a raw water tank
201
and is sent by a pump
202
to a filtration unit
203
. A ceramic-based or organic-based filter F is provided in filtration unit
203
, and the filtrated water is delivered via a pipe
204
to a collected water tank
205
for recycling. Alternatively, the filtrated water is released to a natural setting.
In filtration unit
203
, since clogging of filter F occurs, washing is carried out periodically. For example, a valve B
1
connected to raw water tank
201
is closed, a valve B
3
and a valve B
2
, for delivering washing water from the raw water tank are opened, and filter F is cleaned by a reverse flow of water from collected water tank
205
. The resultant wastewater containing a high concentration of Si waste is returned to raw water tank
201
. Also, the concentrated water in a concentrated water tank
206
is transported via a pump
308
to centrifugal separator
209
and is thereby separated into sludge and separated fluid. The sludge comprising Si waste is collected into a sludge recovery tank
210
and the separated fluid is collected into a separated-fluid tank
211
. After further accumulation of the separated fluid, the wastewater in separated-fluid tank
211
is transported to raw water tank
201
via pump
212
.
These methods have also been employed for the recovery of waste resulting from grinding or abrasion of a solid or plate-like member formed essentially from a metal material, such as Cu, Fe, Al, etc., or from grinding or abrasion of a solid or plate-like member formed from ceramic or other inorganic material.
Chemical-mechanical polishing (CMP) has come to be employed as a new semiconductor processing technology.
This CMP technique enables
(1) the realization of smooth device surface shapes; and
(2) the realization of structures with embedded materials that differ from the substrate.
With regard to (1) above, fine patterns are formed precisely using lithography techniques. The combined use of techniques for affixing Si wafers enables materialization of three-dimensional IC's.
With (2), embedded structures are made possible. Since priorly, a technique of embedding tungsten (W) has been employed in multilayer wiring of IC's. With this technique, W is embedded by a CVD method in a trench of an interlayer film and the surface is made smooth by etching back. However, smoothing by CMP has come to be employed recently. Other examples of application of this embedding technique include damascene processes and element separation.
Such CMP techniques and applications are described in detail in “Science of CMP,” published by Science Forum Co., Ltd.
A mechanism for a CMP process shall now be described briefly. As shown in
FIG. 12
, a semiconductor wafer
252
is placed on an abrasive cloth
251
placed over a rotary table
250
, and irregularities of the wafer
252
surface are eliminated by performing lapping, polishing, and chemical etching while pouring on an abrasive (slurry)
253
. Smoothing is achieved by chemical reactions induced by a solvent included in abrasive
253
and by mechanical abrasive actions of the abrasive cloth and the abrasive grains in the abrasive. Foamed polyurethane or non-woven fabric, etc., is used, for example, as abrasive cloth
251
. The abrasive has abrasive grains of silica, alumina, etc., mixed in water containing a pH regulator and is generally referred to as slurry. Lapping is performed while pouring on this slurry
253
and applying pressure onto abrasive cloth
251
while rotating wafer
252
. A dressing part
254
, maintains the abrading ability of abrasive cloth
251
and constantly keeps the surface of abrasive cloth
251
in a dressed condition. Numerals
202
,
208
, and
212
indicate motors and
255
to
257
indicate belts.
The above-described mechanism is arranged as a system as shown for example in FIG.
13
. This system largely comprises a wafer cassette loading
Iinuma Hirofumi
Iseki Masahiro
Tsuihiji Motoyuki
Umezawa Hiroyuki
Morrison & Foerster / LLP
Popovics Robert James
Sanyo Electric Co,. Ltd.
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