Review of Water Use and Water Conservation Technology in by adz11579

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									             Review of Water Use and Water Conservation
                  Technology in High-Tech Industry
Wen-Shyong Lin1* Chien-Hung Chen2 Pei-Lin Chang3 Kon-Tsu Kin4 Shiuh-
            Tyng Tseng5 Kuo-Hung Lee6 Chun-Wei Chen7
1.Researcher, Industrial Technology Research Institute, Energy and Environment Research
  Laboratories, Rm.112, Bldg.24, 195, Sec.4 Chung Hsing Rd., Chutung, Hsinchu, Taiwan,
  R.O.C. 310, e-mail:franklin@itri.org.tw
2.Associate Researcher, Industrial Technology Research Institute, Energy and Environment
  Research Laboratories, Rm.112, Bldg.24, 195,Sec.4 Chung Hsing Rd. Chutung, Hsinchu,
  Taiwan, R.O.C. 310, e-mail:7chchen@itri.org.tw
3.Researcher, Industrial Technology Research Institute, Energy and Environment Research
  Laboratories, Rm.112, Bldg.24, 195, Sec.4 Chung Hsing Rd. Chutung, Hsinchu, Taiwan,
  R.O.C. 310, e-mail:PLChang@itri.org.tw6
4.Lead Researcher, Industrial Technology Research Institute, Energy and Environment
  Research Laboratories, Rm.112, Bldg.24, 195, Sec.4 Chung Hsing Rd. Chutung, Hsinchu,
  Taiwan, R.O.C. 310, e-mail:kinkontsu@itri.org.tw
5.Technician, Southern Taiwan Science Park Administration, No. 3, Nanke 3rd Rd.,
  Sinshih Township, Tainan County, Taiwan,R.O.C. 741, e-mail:sttseng@stsipa.gov.tw
6.Director, Southern Taiwan Science Park Administration, No. 3, Nanke 3rd Rd., Sinshih
  Township, Tainan County, Taiwan, R.O.C. 741, e-mail:khlee@stsipa.gov.tw
7.Deputy Director-general, Southern Taiwan Science Park Administration, No. 3, Nanke
  3rd Rd., Sinshih Township, Tainan County, Taiwan, R.O.C. 741, e-mail :
  lkk@stsipa.gov.tw

                                         Abstract
      High-tech electronics industry is one of the star industries in Taiwan, which includes
semicondustor foundry and manufactories of IC chips, TFT-LCD and LED.
Microelectronics industry requires large quantity of ultrapure water (UPW) for various
process uses. In chip manufacturing, besides fab capacity and yield, the size, line width and
mask layer of the wafer directly impact the total water consumption of the plant. A large
semiconductor or TFT-LCD manufacturing plant consumes couple thousand tons of water a
day. In IC manufacturing process, most water is used in UPW cleaning and chemical
mechanical polishing (CMP), which comprises 80 to 85% of the total water use. Another
5~20% is used in the center and local scrubbers or as the back-up water for the cooling
towers. Therefore, process water and the water used in the utility system are the two prime
targets for improvement in water conservation in microelectronics industry. Because the
yield relies heavily on the quality of the UPW, usually between 17.5~18.5M-cm, the key to
efficient water management lies on the operation mode of the water purification system,
including the rate of pure water production, pure water supply system, back-wash
frequency, selection of back-wash water source, reclamation of the spent backwash water
                                           C3-33
from mid- and back-stage, concentrates from the UF and RO processes, EDI electrode
wastewater etc. This study intends to autopsy the water use and to identify the potential
targets for water conservation for the high-tech industries, emphasizing on water balance
efficiency, unit water consumption, water production rate, efficiency in segregation of
spent rinse water, recycle of process water, and conductivity control of the blow-down from
cooling towers.
Keywords: reclaimed water, water conservation, ultrapure water, reused water,
concentrate, segregation of spent rinse water, recovery rate

                                   1. Introduduction
     High-tech electronics is one of the six most water-consuming industries. With the
developments in economics and technology, the demand for high quality water is
increasing tremendously. In respond to the escalating demand for water and the increasing
scarcity in water sources along with the legislative restriction in building new dams, the
Taiwan government has set a target for water conservation in individual industry. Many
electronic industries have been required to raise their water recovery rates. In response, the
Hsin-chu Science-based Industrial Park (HSIP) has adjusted its annual water conservation
goal from two million tons in 2003 to ten million tons in 2007.
     Wafer manufacturing and packaging industry comprise 80% of the IC industry in
Taiwan. They consume large quantity of ultrapure water (UPW) in wafer cleaning which is
a pivotal process in product yields. With the advancement in technology, the line width in
wafer becomes narrower and the level of integration becomes thicker. To maintain good
yield, more chemical cleaning and the accompanying more demand for the purity of the
UPW are required, which contradicts the philosophy of green technology. High-tech
industries are now seeking more efficient water reclamation system to meet the rapidly
increasing demand for water quality and to reduce the water consumption simultaneously.

    2. Water use and developments in water and wastewater treatment
                              technology

2.1 Characteristics of water use in manufacturing process
      Large quantity of UPW along with cleaning chemicals are used to rinse off the
impurities from the wafer surface. With the development in electronics technology, the
demand for UPW has grown at a phenomenal pace, driven by the size reduction in
microchips, the high level of integration and the more planalized wafer surface. The
traditional multi-stage batch cleaning method can no longer meet the requirement for 1-
micron platform. In addition, the batch mode cleaning promotes cross pollution. The high
water-consumption nature of the high-tech manufacturing is further challenged by the water
shortage and environmental issue in Taiwan. Therefore, the industry must reduce the water
consumption as well as increase the percentage of water reuse. The specification of water
use in high-tech industry is given in Table 1.


                                           C3-34
             Table 1 Roadmap of water use in high-tech manufacturing process
             Year of Intrduction               2000         2003       2005     2007
           Technology node (nm)                180          130        100        65
       Total Oxidizable Carbon (ppb)             2           <1        <0.5     <0.4
              Bacteria (CFU/L)                  <1           <1         <1       <1
              Total silica (ppb)                 1            1        <0.5     <0.2
         Cation / anion metals (ppt)            20          <20         10       <10
          Particles>0.05μs (pcs/ml)              2            2         <1      <0.5
     It is anticipated that wet cleaning remains the major cleaning mode for the wafer
productions in the next few generations. The criteria for wafer surface cleanness are listed
in Table 2.
                          Table 2 Criteria for wafer surface cleanness
                 Year of Intrduction                   2003         2005       2007
               Technology node (nm)                    130           100        65
           Critical particle diameter (nm)              50           40        32.5
          Critical particle count (#/wafer)             59           97         82
         Surface carbon (1010 atoms/cm2)                1.8          1.4        1.2
        Back surface particle diameter (nm)             0.2          0.2       0.16
       Back surface particle count (#/wafer)            600          400        200
     Recently, many innovative technologies in cleaning such as cleaning under room
temperature and washing by ozone and hydrochloric acid alternatively have been proposed
to reduce the use of water and chemicals. In addition, the single-stage cleaning mode has
replaced multi-stage cleaning to meet the demand for high purity and planarization. The
production values per unit water consumption for IC manufacturing from year 1998 to 2000
is presented in Fig. 1 along with three other categories of manufacturing. The daily water
consumptions by IC and TFT-LCD manufacturing are given in Fig. 2.




           Fig. 1 Comparison of production values per unit water consumption
                          among four categories of industry.

                                          C3-35
                              25
                                     IC industries
    (ten thousand tons/day)

                                     LCD industries

                              20
    Water consumption




                              15



                              10



                              5
                              2002          2003         2004   2005            2006
                                                        Year
Fig. 2 Trends in the water consumption in IC and LCD industries between 2002 and 2006.
2.2 Evolution of water use and wastewater treatment in high-tech manufacturing
      The trend in water use in developed countries has indicated their focus on water
conservation. The aims are to enhance the efficiency of water use, to reduce the water cost
and to develop new wastewater treatment technology. The NSF/SRC Enginner Research
Center for Environmentally Benign Semiconductor Manufacturing of USA, cofounded by
UC Berkeley, MIT,University of Arizona and Stanford University, has over thirty members,
mostly world-class semiconductor manufacturers such as Intel, TI, HP and Applied
Materials. The mission of the center is to research and develop new wastewater treatment
and recycling technologies for electronics industry to minimize its environmental impact.
In Taiwan, most researches in regard to water conservation in high-tech industries have
been conducted in ITRI. The prospect of potential cleaning process and water treatment in
semiconductor industries is revealed in Fig. 3 and Fig. 4.
      The development of water treatment technologies in high-tech industries development
is illustrated in Fig. 5. In response, ITRI has reviewed existing and potential technologies
for wafer cleaning process and proposed the following list of prospectice research topics:
       1.Removal of photo-resistance by ozone:
         (1)High concentration ozone module at (O3) > 50ppm.
         (2)Bubbling ozone for 8-in and above chip manufacturing
         (3)Development of PR removal tools in packaging process.
       2.Dry cleaning:
         (1)Confirmation tests for reactivity and uniformity of gas phase.
         (2)Cleaning of large size glass material and high uniformity.

                                                      C3-36
               (3)Development of high uniformity photo-excitation platform for TFT-LCD.
             3.Cleaning by super-critical fluid:
                  (1)Development of CNT-FED cleaning and activation module and recipe.
                  (2)SCCO2supercritical carbon dioxide cleaning of three diode CNT-FED
                     Field<3V/μm,Ja>10mA/cm2..
                  (3)Development of high efficiency porous membrane module for water treatment.
                  (4)Development of purification technology of complex porous adsorbent:
             4.Surface modification of environmentally friendly Germanium base material.
               (1)Removal of micro-pollutants from Germanium surface.
               (2)Roughness control of Germanium surface.
               (3)Integrated test for Germanium parts.
             5.Cleaning by organic water:
                  (1)Preservation of raw food by oxidizing organic water.
                  (2)Elemination of residual pesticides from vegetables and fruits by washing with
                     organic water.
                  (3)Cleaning by oxidizing micro-bubbling.
                  (4)Organic farming with function water.

                                                                                                            Fundamental research : Stanford(USA), IMEC (BE)
                                                                                                           基礎研究: Stanford(USA),
                                                                                                      aning Equipment research : SC fluids systems (USA)
                                                                                             ition Cle             IMEC(BE)
         (1) Ultra-Low k 製程技術瓶頸
          (1) Technical issues of ultra-lowK process                                  nts Add
                                  Moisture                                    Surfacta               Cle
                                                                                                           設備研發: SC Fluids
                                                                                                        aning
                                                                                                  s
                                                                                          al Fluid                 Systems(USA)
            Damaged Layer        Absorption

                                                                              Super-critic             •SCCO2多孔性材質
                                                                                        ‧The scCO2 porous material
                                                                                         •SCCO2 多孔性材質  •光阻去除技術
                     Plasma-treated                                • SCCO2實驗模
                                                            ‧Establish scCO2 module.•除水技術,除銅技術 •電性分析技術
                                                                                       ‧Material analysis technology.
                     POSG              pattern collapse              組建立
                          Si           for dense lines      ‧System stability verify. •材料分析技術 analysis technology.
                                                                                        ‧Material
                                                                   • 系統穩定性測試
                                                            ‧PR removal technology. ‧Electrical reliability research.Samco (JP) : Ushio, Samco (JP)
                                                                                                        Equipment development
                                                                                                      設備研發: Ushio,
                                                                                                g
          (2) Technical issues of 65nm                                                al Cleanin
           (2) photo engraving. process
               65奈米顯影製程瓶頸
                                                                            Dry Chemic                    • UV-assisted ultra-thin
                                                                                                            oxide growth
                                                                                •UV-assisted PR removal
                                                          •UV-O3 dry clean
                                                                                                基礎研究: IMEC(BE), Tohoku U. (JP) Tohoku U(JP).
                                                                                                 Fundamental research : IMEC (BE),
                                                                                                 Equipment research Semitool, FSI,
                                                                                                設備研發: Semitool, FSI,: Micron (USA) Micron (USA)
                        TMAH
                                                              O3/H2-UPW Cleaning
                                                      •P/R Stripping           •Pre-gate Cleaning    •Pre-gate interface layer control
                                                      •Post-etch Cleaning      •Post CMP Cleaning    •Ultra-thin gate oxide growth

                                                                        Dilute RCA Clean
                                      RCA Clean (H2SO4,H2O2 , HCl)
Water                                                                                                                                2010
       用 製 2
consumption
                                      2002                    2004                   2006                   2008
       水 程
of processs 4
       量
     ( L/cm2) 6

                   Fig. 3 Prospect of potential cleaning process in semiconductor industries.




                                                                             C3-37
       Fig. 4 The development of water treatment technologies in high-tech industries.
      New processes and materials are being developed to meet the future trend for zero
pollution, resource conservation, environmental protection and sustainable development, as
illustrated in Fig.5.




            Fig. 5 The future trend of development in IC and LCD industries.
                                         C3-38
                             3. Rational water recovery rate
     In Taiwan, minimum water recovery has been imposed on the high-tech manufacturers.
An even higher water recovery is required for those newly built plants. The fulfillment of
the target water recovery is used as the basis for the evaluation of the new strategic
industries. However, water recovery can not reflect the true water use. Some fabs
manipulate the calculation of water recovery by using different mathematical models.
Comparison of water recoveries, as a result, becomes a mere formality.
     Current method for water recovery calculation does not guarantee plants with high
water recovery being more environmentally-friendly. However, when the government set
an unrealistically high water recovery, the manufacturers are forced to advance the level of
wastewater treatment. Any increase in water recovery implies a considerable increase in
expense for water reclamation while the technology for wastewater treatment must be
improved. A statistic on the variation of component cost with water recovery rate in
semiconductor manufacturers of Japan indicates that the lowest total treatment cost
occurred at 75% water recovery, as revealed in Table 3 and Fig. 6. As a result, most
manufacturers automatically adjust the water recovery to 75% although the Japanese
Government did not clearly authorize the water recovery. The calculation was based on the
water rate of Japan. By replacing it with the water rate of Taiwan, the water rate of the
lowest cost shifts to zero, a indication that the water rate of Taiwan is too low to reflect the
actual supply and demand of water use. In other words, there is no incentive for water
conservation. On the other hand, the calculation on Japanese semiconductor
manufacturering has come to a conclusion that the capital cost for a fab for 100% water
recovery is twice that for zero water recovery, suggesting that zero discharge does not
conform to economic efficiency.
  Table 3 Water treatment cost of various recovery rate in semiconductor manufactory in
                                          Japan.
                                                                Cost unit : yen (Japan)
         Recovery Rate(%)                  0%        30%       50%        75%       100%

   Initial Cost                           100        105        130       130        200
   Electric Power                         150        150        125       125        200
   Chemical, Steam, Cooling water         100         75        75         75        250
   Supplies / Consumables                 250        250        275       275        300
   TOC reduction equipments                 0         0         75        125        150
   Outsourcing                              0         0          0          0        125
   City Water                             450        425        225       150         30
                Total Cost                950        900        775       750       1055



                                            C3-39
   Fig. 6 Water treatment cost of various recovery rate in semiconductor manufactory in
                                            Japan.
      Therefore, to increse the efficiency of water use by means of water reuse, the water
recovery rate must be rationized. Indices for water recovery must be clearly defined and
characterized to draw up a reasonable formula for water recovery calculation to reflect the
efficiency of water use and to serve as a tool for promoting efficient water use. A joint
research by ITRI and the HSIP has concluded a rational water recovery rate of 70~75% for
the high-tech industry. The economic benefits evaluation of water conservation of a typical
high-tech industry in Taiwan is shown in Fig. 7.




    Fig. 7 Economic benefit evaluation of water conservation in a high-tech industry.
                                          C3-40
        4. Efficiency in drain water segregation and trouble shooting
     The segregation of spent rinse waters with different pollutant concentration and the
water standards for water reuse are closely related to the water recovery rate. In general,
TOC and conductivity are used as the criteria for water reuse. The scheme of drain water
systems optimization is given in Fig.8.




                                                              M o d e l T y p e :F C -3 0 0 0
                                                              E Q C o d e :W J D 0 2

                                                                                                      F u n c tio n :                                                                        F u n c tio n :                                                  F u n c ti o n :                                    F u n c tio n :
                                                                                                      1 . L i g h t e tc h w ith H F / D I W                                                 1 . L i g h t e tc h w ith H F / D I W                           1 . R o b o t c h u c k s w i tc h                  1 . C h u c k C l e a n in g
                                                                                                      2 . R in s e s w it h D I W                                                            2 . R in s e s w it h D I W                                      ( s in g l e h a n d / b a t h h a n d )                & D ry in g
                                                                                                      3 . D r i e s w i th I P A v a p o r                                                   3 . D r i e s w i th I P A v a p o r




                                                                                                                 L P D 1 U n it                                                                      L P D 2 U n it
                                                                                                          B a th T y p e : O v e r f l o w                                                    B a th T y p e :O v e r f lo w
                                                                                                           B a th M a te r ia l :P V C                                                         B a th M a te r ia l :P V C
                                                                                                                                                                                                                                                                                                               C H C L /C T C U n it
                                                                                                           B a th C a p a c i ty :3 5 L                                                        B a th C a p a c i ty :3 5 L
                                                                                                                                                                                                                                                                                                             B a th T y p e :O v e rflo w
                                                                                                                                                                                                                                                                                                             B a t h M a te r ia l :P T F E
                                                                                                                                                                                                                                                                                                            B a th C a p a c i ty :3 .0 × 2 L
                                                                                                                                                                                                                                                                   C W S U n it




                                                                                      Q u ic k D u m p                                                                         Q u ic k D u m p                                                                                                          G r a v i ty
                                                                          程 式 控 制                                                                                    程 式 控 制
                                                                                           14        16                                                                            17        19
                                                                                                                            drain                                                                               d r a in
                                                                                                15                         s w it c h                                                   18                                                                                                                  20
                                                                                                                      51                                                                                   6 1 s w it c h
                                                                                                                             box                                                                                 box                                                                                                                         27

                                                                                       IP A L                                                                                  IP A L
                                                                                                                 52                                                                                   62
                                                                                           PW R                       53                                                           PW R                    63
                                                                                                                                                                                                                                                                                                      FW L
                                                                                                             FW L            54                                                    W WR                          64
                                                                                           W W R/                                                                                                 FW L                                                                                              W W R /P W R                            FW H
                                                          藍 色 字 體 為                        PW R
                                                                                                                                                                                   /P W R
                                                                                                                   HW R                                                                                 HW R
                                                          F a c il it y D a t a                                    HW R                                                                                 HW R
                                                                                                                     V a t d r a in                                                                       V a t d ra in
                                                                                                                      FW H                                                                                 FW H
                                                                                                                                                       IP A
                                                                                                                                        2                                                                                   3                          IP A                                                                  4




                                                                                                                                                           1:3 0 0




                                                                                                                                                                                                                                                  1:3 0 0
                                                          紅 色 字 體 為                        W W R/                                                                         IP A L    W W R/                                                                                                                 PW R                             FW H
                                                                                  IP A L                                           D IW         49% H F                                                             D IW
                                                                                            PW R                                                                                     PW R                                                     49% H F
                                                           建 議 改 管                                                AW H            3 0 L /M                                                            AW H         3 0 L /M                                                                                               D IW




                                                                                                                                               1:1 5




                                                                                                                                                                                                                                      1:1 5
                                                                                                                                                                                                                                                                                                                         2 6 L /M
                                                                                                                                        3 5% H 2O                                             FW L              FW H        3 5% H 2O
                                                                                                      FW L                 FW H                        2                                                                                      2




                                                                                   力晶二廠 WFD01/WDS01 機台水樣分析報告

                                                                        1. 取樣時間:2002/9/27                                                                            3:00~8:00 pm

                                                                        2. 取樣機台:FC3000/WFD01 及 WING300/WDS01
                                                                        3. 取樣點:(1) WFD01 機台 WB TANK2 (QDR unit) Tube no. 31
                                                                               (2) WFD01 機台 LPD unit Tube no. 39
                                                                               (3) WFD01 機台 CHCL/CTC unit Tube no. 41
                                                                               (4) WDS01 機台 HQDR1 BATH Tube AWR
                                                                               (5) WDS01 機台 C/W BATH Tube AWR
                                                                               (6) WDS01 機台 RD2 BATH Tube PWR
                                                                        4. 樣品採集、保存及收藏:
                                                                           血清瓶/PVC 瓶收集,4℃保貯。

                                                                        5. 分析項目:Fluoride / TOC

                                                                        6. 分析儀器:Hach A4000 / Anatel A2000 / Suntex Conductivity Meter

                                                                        7. 分析前處理:依儀器偵測範圍進行水樣稀釋

                                                                        8. 分析結果:
                                                                                                                                                                                                                                分析結果
                                                                取樣點                                                    樣品標號                                                                         F
                                                                                                                                                                                                            -
                                                                                                                                                                                                                                         TOC                    電導度值
                                                                                                                                                                                                  (ppm)                                  (ppb)                  (μs/cm)
                                                                       (1)        FWL Drain (FWL)                                                                                                   94                                     --                     680
                                                                       (2)        PWR Drain (PWR/WWR)                                                                                               --                                  105020                    2.1
                                                                       (3)        FWL Drain (AWR/FWL)                                                                                              ND                                      --                     2.1
                                                                                  AWR Drain 1 (WWR/AWR)
                                                                                                                                                                                                        --                                        1261                     13.4
                                                                                  (200/1200sec)
                                                                       (4)
                                                                                  AWR Drain 2 (WWR/AWR)
                                                                                                                                                                                                        --                                        1107                       2.6
                                                                                  (850~900/1200sec)
                                                                                  AWR Drain (WWR/AWR)
                                                                       (5)        (繼 HP1→HQDR 之後 chuck                                                                                               ND                                                199                   2.0
                                                                                  清洗排放水)
                                                                                  PWR Drain (PWR/WWR)
                                                                                  (RD2 洗槽用水量 40L/min×
                                                                       (6)                                                                                                                              --                                    27594                          1.2
                                                                                   3~5min,排至 IPAL;Idle 水
                                                                                   流量 10 L/min,排至 PWR)




                        Fig. 8 Optimization of drain water systems
                                          C3-41
      Different streams of spent water are segregated by the automatic monitoring system
for treatment and reuse. To lower the risk of contamination by the recycled rinse water, the
fab is recommended to incorporate a system for trouble shooting and an automatic control
system like the one given in Fig. 9.




                        Fig. 9 The procedure for trouble shooting.

             5. Assessment of potential water conservation targets

5.1 Unit water consumption
     Unit water consumption must be compared on the same product and the same front-
end utilization, as well as the age of the production station and the function in raw and
drain water. A year 2005 survey conducted by the industrial park shows that the average
unit water consumption for 6-in, 8-in and 12-in wafers are 0.79, 4 and 7.3 tons/wafer,

                                          C3-42
respectively. The unit water consumption for LED crystal is 0.2266 ton/wafer, for nickel-
plated aluminum plate is 0.025 ton/wafer, and for wireless card is 0.94 liter/set. Average
nitrogen consumption is 0.00052 L/T. The front-end utilizations of plants used in the
survey are all above 80%.
5.2 Production rate of water purification system
     In electronic industry, water purification system is a critical component which
produces the ultra-pure water for wafer cleaning. The water use and discharge of the UPW
system affect the water consumption and water recovery tremendously. Therefore, analysis
and control of the pure water production is extremely important to efficient water
conservation. Low water production wastes water resources, while high water production
shortens the membrane life and increases the cost for water purification. Therefore, the
operation parameters must be optimized. Most water purification systems target their water
production rate in the range of 65% to 85%, depending upon the original design of the
system.
5.3 Efficiency in drain water segregation
      Different streams of spent water from wet stations are separated by concentration. The
criteria for either collection or discharge is determined by each plant. The quality and
volume of the recovered water are closely related to the water recovery of the process.
Therefore, each plant must establish an efficient drain water segregation system. The
survey conducted by the HSIP has pointed out that most fabs experience an uneven
distribution of stream segregation, normally between 11 and 100%, among which 47% are
under 50% efficiency.
5.4 Backflow water
     Backflow water is the pure water which flow through the process yet is not used due
to low front-end utilization, over production of pure water, or idle station. The backflow
water is either recycled back to the water purification tank or overflow into discharge. The
survey mentioned in the previous section has found that the UPW production is usually
preset at 1.5 to 4 times the actual need for processing. The discharge of backflow water
means a waste of water resource. Although the water can be conserved by recycling back
to the water purification system, energy is still wasted. Therefore, the plant should control
the water production carefully in compliance to the water need for processing. A safe ratio
for water production/processing water need is between 1.5 and 2.
5.5 Conductivity control of blow-down
     Most plants in the industrial park adopt the cleaner stream of concentrate from the
membrane treatment (ROR) as back-up water for cooling towers. The conductivity of the
ROR is around 30 to 50μS/cm. By setting the conductivity of blow-down at around 1000
μS/cm, the tower concentration cycle is 20, which surpasses the requirement for water
conservation, namely, 4 to 5 concentration cycle. However, there is still room for further
increase in concuctivity. In general, the conductivity of the blow-down can be controlled at
1800 to 2000μS/cm. Most fabs in HISP set the conductivity control between 1000μS/cm
and 1800μS/cm, although some manufacturers have no control at all. Conductivity control
of the blow down may be an alternative for cooling tower operation.
                                           C3-43
                                     6. Summary
     1.Because C/T (Cooling Tower) and wet scrubbers are the major water uses in the
       public utility system of the high-tech industry, the optimization of their operation
       plays an important role in water conservation. Optimal operation curves of C/T and
       scrubber in regards to operation parameters including water quality of C/T (EC, Ca
       and pH), concentration cycle,temperature of the cooling tower effluent, and pH for
       recycling water in wet scrubber,must be established.
     2.The water recovery criteria for plants built after 1999 is set as 85%. Some
       manufacturers,however, have trouble reaching the target till now. For those who
       have successfully raised the reclamation rate from 75% to 85%, the cost has
       severely over the benefit of investment. The key technology lies at the reclamation
       of the Cu-CMP and scrubber discharge. These manufacturers should be recognized
       and their experience in water conservation can be shared with others. In the mean
       time, the Science Park Administration needs to rationize the recovery criteria as
       well as to encourage the achievement by rewards.
     3.If without treatment,the internal recycling water of the scrubber and any pre-set
       internal recycling process water should not be included in the calculation of water
       balance. However, most manufacturers in the science park include these streams in
       the calculation in order to raise the calculated recovery rate.
     4.To meet the water recovery criteria set by the science park administration, the
       manufacturers must invest heavily before they can acquire an effective technology
       for water reclamation. The administration can consider to establish a reasonable
       investment technology and reclamation guideline to achieve the goal for water
       conservation without sacrificeing the profit.

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