DISCO Technical Review Mar. 2016

Usefulness of the ultra-compact deionized water recycling unit for dicing saws
Engineering R&D Division, Engineering Support Department, Accessory Equipment Group
Abstract
Ultrapure water is used for cooling and cleaning in the semiconductor manufacturing industry. Thus,
semiconductor manufacturing factories generally install large deionized water manufacturing, drain
recycling, and liquid waste disposal facilities. However, because they are large facilities, there are issues
in flexibility, such as downtime for the entire plant due to regular maintenance or minor improvements. Inthis review, we introduce DWR1722, an ultra-compact deionized water recycling unit for dicing saws,
which is small but realizes a high deionized water recycling rate with low electric power consumption.
1. Introduction
A dicing saw (dicer), which cuts silicon wafers
during the semiconductor manufacturing process,uses deionized water (DI water) for cooling andcleaning. In recent years, the consumption of DI
water has increased in order to clean the wafers
more thoroughly, and the effective use of water
resources is critical in order to reduce
environmental impact. Because of this, theamount of DI water consumed by dicers needs tobe reduced, which can be accomplished byrecycling the water discharged. However, theconventional DI water production and recycling
systems are generally large and expensive
because they have to cover the entire water
systems of the factories. Thus, the operations of
the factory must be completely shut down for
periodic maintenance of the recycling unit;
moreover, it is not easy to enhance the capacity of
the recycling unit on a small scale.

Photo.1 DWR1722

Therefore, we developed the DWR1722, anultracompact DI water recycling unit for dicers
capable of extraordinary energy and water
conservation (Photo 1).

2. Problems of the conventional DI water
recycling units and their solutions
Recycling of wastewater from the dicer as
cutting water requires the following functions:(A) Removal of solids, such as silicon fragments,using a highly efficient filter(B) Sterilization
andorganic
decomposition using a UV lamp

matter(C) Ion removal using an ion exchange resin(D) Water temperature adjustment
refrigerator and a heaterusingaAs shown in Fig. 1, particle sizes of silicon
fragments contained in the wastewater drained
from the dicer are normally below 0.5 µm. Thus,
an extremely fine mesh is required by the filter to1

DISCO Technical Review Mar. 2016

implement function (A). Filtration systems
employed in the conventional DI water recycling
units use filters made of expensive materials, suchas ceramics and organic membranes, and theirstructures are complex and large.

system's structure larger and more complex. It isalso necessary to pass more raw water than
filtrated water, and therefore, a larger pump isrequired. Further, silicon fragments caught by thefilter are discharged as concentrated wastewater.
It is also necessary to install a tank that stores thiswastewater. On the other hand, in dead-end
filtration, fragments accumulate on the filter
surface, which deteriorates its filtration ability.
Therefore, it is necessary to replace the filter
periodically. However, since this method does not
require other systems, it is the simplest filtration
method.

In addition, more space is required in order toimplement functions (B), (C), and (D) using therecycling system, which makes it difficult todesign a compact unit that can be installedadjacent to the dicer in the clean room.

Fig. 1 Particle sizes of silicon fragments
contained in the wastewater from the dicer.

Because of these reasons, the conventional DI
water recycling units are usually large andinstalled outside the clean rooms. This makes it
necessary to secure the installation space and pay
the extra cost of DI water supply and drain piping
work from the dicer to the DI water recycling unit.
Further, expenses are incurred in the treatment ofconcentrated wastewater.

Fig. 2 Cross-flow filtration and dead-end

For these reasons, the DWR1722 employs thedead-end filtration, which enables downsizing.
However, the filters currently available in themarket are not practical because their lifespansare extremely short. Thus, we have developed"CC Filter" (Photo 2), an original filter dedicatedto the filtration of drain water from the dicers. CC
Filter is a disposable filter module having its own
unique structure. With this filter, all the functions
from (A) to (D) can be installed in the DI water
recycling unit with a very small footprint.

We solved these problems and realized a DI
water recycling unit DWR1722 that can beinstalled adjacent to the dicer in the clean room.
The development of this recycling unit focused on
the following points:
1) Ultracompact design
2) Zero wastewater
3) Low power consumption
4) Easy maintenance and operation
2.1
Ultracompact design
Simplifying the structure is essential to downsize
the recycling unit. The filtration method that uses
the ceramic filter or organic membrane mentioned
above is called cross-flow filtration but thedead-end filtration method is also available (Fig.
2). Cross-flow filtration is a system that filtrates
while cleaning the membrane with the power offlowing raw water. Then, other systems, such as
backwash, are combined with it to reduce theclogging of filter. This reduces the frequency withwhich filter needs replacement, but it makes thePhoto.2 CC Filter2

DISCO Technical Review Mar. 2016

temperature control system of the DWR1722
installed adjacent to the dicer is much simpler
because wastewater can be directly controlledfrom the processing point of the dicer. Because ofthe optimized design of each section, theDWR1722 is capable of processing wastewaterfrom two dicers, but the power consumed is half
to one-third of that consumed by the DTU152,
which controls only water temperature.

2.2
Zero wastewater
The recycling rate of conventional DI water
recycling units is generally from 80 to 95%.
Concentrated wastewater that is not recycled
requires further treatment and has to be disposedof as industrial waste with charge. Whenhazardous materials such as gallium arsenide(GaAs) are diced, the treatment of wastewater isparticularly difficult and expensive. Thus, if
100% recycling rate and zero wastewater can berealized, it eliminates the need for a wastewater
treatment system, which provides a greatadvantage.

2.4
Easy maintenance and operation
The DWR1722 is developed to be installedadjacent to the dicer in the clean room and to beused in conjunction with it. Thus, the same
maintenance personnel that perform themaintenance work of the dicer can maintain therecycling unit as well. In order to enhance user
friendliness, a large color touch panel is used foroperation. Screen configurations are designed
such that the structure of the unit can berecognized intuitively. To facilitate thereplacement of the CC Filter and ion exchange
resin, they have a slide-out structure for easy
maintenance in a compact design.

The DWR1722 uses the CC Filter of thedead-end filtration system, thereby achieving zeroconcentrated wastewater. One CC Filter enables
the capture of silicon fragments discharged fromone dicer for a month. The captured silicon
fragments can be disposed of as solids together
with the CC Filter.
Wastewater filtered through the CC Filter
becomes colorless and transparent pure water.
However, in order to recycle it to DI water, it isfurther necessary to remove ion components andorganic matters dissolved in the wastewater.
The ion components can be removed through an
ion exchange resin, but not the organic matter.
The wastewater from the dicer contains a large
quantity of organic substances originating fromthe dicing materials like dicing tapes. Therefore,
if this water is recycled, the concentration oforganic matter increases, which may have anegative impact on the bonding process after
dicing and quality of devices. Thus, an ultraviolet(UV) lamp module specifically designed for theDWR1722 is installed, which enables efficientdissolving of organic matter contained in dicer
wastewater. With this UV lamp module,wastewater is irradiated by UV beams having
wavelengths of 254 nm and 185 nm before
filtering the wastewater through the ion exchange
resin to dissolve organic matter into anorganic-acid level. As a result, recycling rate of
100%Note 1 and zero wastewater can be achieved.

3. Conclusion
The DWR1722 is a DI water recycling unit withexcellent features, such as ultracompactness, zerowastewater, low power consumption, and easy
maintenance and operation, designed to be usedwith dicers. The recycling of DI water is also
demanded by other equipment, such as grinders.
With the help of results from various applications,we plan to develop other recycling units that arecompatible with different types of equipment. We
intend to undertake further efforts to preserve theglobal ecosystem and natural environment
through the realization of resource conservationand zero emission.

Note
1. More precisely, the maximum recycling rate
is approximately 99.5% because around 0.5%of the wastewater vaporizes during dicing.

2.3
Low power consumption
By using the CC Filter of the dead-end filtration
system, power required by the filtration pump canbe minimized. Further, the system for cooling thewater uses the waste heat of the refrigerator
insteadoftheconventional
heater
proportional-integral-derivative (PID) control
scheme. This is particularly helpful in reducing
the power needed for temperature control. The

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