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SEMI F98-0305 © SEMI 2005 3 ultimately through a semi permeable memb rane that isolates the fee d water ch annel from adjacent circulating water flows (“concentrate channels”) that sweep away the impurities entering thro…

SEMI F98-0305 © SEMI 2005 2

4.2 Other Standards

“Strategies for Water Reuse Reduction in Semiconductor Manufacturing”, Technology Transfer 97013232A-ENG

2004 International Technology Roadmap for Semiconductors

NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.

5 Terminology

5.1 Acronyms and Abbreviations

5.1.1 UPW — Ultrapure Water

5.2 Definitions

5.2.1 spent water — any discharge water that is consumed or processed and is ready to be discharged to drain.

5.2.2 UPW reclaim — the reuse of spent water as feed water for a process different from the one that discharged it,

e.g. RO reject fed into cooling towers.

5.2.3 UPW recycle — the reuse of spent water as feed water for the same process that discharged it (Point-of-

Discharge (POD) recycling), or the plant UPW system.

5.2.4 UPW reuse — the secondary use of spent water.

6 Design Components and Elements

6.1 Collection of Waste Streams — The most common collection system includes fab-wide gravity collection

piping using PVC or PVDF transfer piping and associated pipe racks and tunnels to the collection tanks. Proper

venting is also critical to correct operation. The system may also include a reclaim pit, pumps, tanks, and controls.

Separate holding tanks are used for each grade of water or type of waste stream so that routing of waste and types of

treatment can be matched to specific needs (see Figure 1).

6.1.1 A key consideration for the design of a water reuse system is the ability to separate different grades of water

and collect each type of effluent. Typical types of segregation include: segregation of clean rinse water from acid

waste; separation of waste streams that contain organics, (e.g. from IPA drying); and isolation of waste streams that

require specific treatment such as for hydrofluoric acid, CMP processing, copper solutions, or phosphoric acid.

6.1.2 A recent initiative by semiconductor fabs encourages tool manufacturers to include multiple drain lines within

the tool so that waste streams can be easily segregated. Diverter valves can be used to segregate chemicals and are

also useful when organics exceed recommended levels. Tool manufacturers can also incorporate plumbing and

treatment modules for returning spent water discharged from a tool as feed water for that tool (Point of Discharge

[POD] recycling). Purchasing tools with recycle hardware already built-in eliminates the need for users to design

and install customized water reuse systems unique to their site.

6.2 Treatment of Waste Streams — In addition to choosing the most effective and technically sound design choices,

other considerations for treatment choices include easy access to all major components for operations and

maintenance, availability of consumables and spare parts, and a high level of automation and reliability. There are

several choices related to treatment choices:

6.2.1 TOC (total oxidizable carbon) destruction by UV is commonly used for removal of organics found in reclaim

waters and is sometimes combined with ozone or hydrogen peroxide.

6.2.2 Activated Carbon or other adsorbents (e.g. GAC) are used for removal of organics and decomposed

hydrogen peroxide, and is a common type of treatment in recycle water systems.

6.2.3 Electrodeionization (EDI) enables ion exchange reactions to be carried out continuously, without off-line

regeneration, by introducing a dc electric field across the resin bed. This electric filed is oriented transverse to the

direction of water flow through the ion exchange column. Under the influence of the applied electric field, impurity

ions, chemically captured by the ion exchange reactions, drift from resin bead to neighboring resin bead and

1 International SEMATECH, 2706 Montopolis Drive, Austin, TX 78741, USA, Website: www.sematech.org

SEMI F98-0305 © SEMI 2005 3

ultimately through a semipermeable membrane that isolates the feed water channel from adjacent circulating water

flows (“concentrate channels”) that sweep away the impurities entering through the semipermeable membranes.

This continuous regeneration action eliminates the need to take ion exchange columns off-line for resin regeneration

and also eliminates the need for storing regeneration chemicals on site.

6.2.4 Reverse Osmosis Membrane Treatment provides extremely high rejection of dissolved ions (charged atoms

and molecules), organic (carbon containing) compounds, silica (silicon containing) compounds, and virtually

complete rejection of suspended contaminants, but will not reject dissolved gases and volatile organic compounds as

well. For reclaim systems, special types of high rejection or low fouling RO membranes may be selected.

6.2.5 Often RO Systems are combined with ion exchange processes either with the purpose of increasing the

recovery rate of the RO or by combining the high efficiency of a membrane process with the lower fouling potential

of ion exchange resins, e.g. Weakly Acidic Cation Resin (WAC) is designed to remove Ca and Mg ions in the

water. The system design should reflect that most of the contaminants of rinse waters are anionic in nature and may

foul RO membranes, but recycling water may be mixed with other water qualities and may therefore contain

hardness, which can react with the Fluoride of the recycling water.

6.2.6 Biological processes are used to treat water with higher organic contents. They can be either fixed bed

systems or fluidized bed systems. These processes typically require both upstream and downstream processes, such

as neutralization, and maintaining a stable feed concentration for the biological process upstream and removal of

bacteria downstream. The operation of such systems is quite sensitive, but most of the organics used in

semiconductor manufacturing can be treated by such systems, including TMAH and chemicals used for lithography

and stripping.

6.2.7 Other Treatment — Includes microfiltration, ultrafiltration, and other types of water treatment typically used

to protect RO Membranes. Pretreatment equipment may include media filtration (bulk suspended solids removal),

1–5 micron cartridge filtration (polishing step for suspended solids removal), sodium-cycle cation exchange

(softening, to remove scale-forming cations), acid injection (to minimize cellulose acetate membrane damage and/or

to control carbonate scales), scale inhibitor injection (to control scaling), and sulfite ion injection (to remove

oxidizing agents).

6.3 Monitoring — TOC, pH, conductivity, and temperature are typical parameters that can be monitored on-line

and tracked over time to optimize performance. The set points and level of monitoring depends on the chemistries

being used and what the ionic and organic loads are in each waste stream after the application and the treatment. To

ensure the accuracy of certain on-line measurements, a minimum residence time and volume of sample is required

and can be provided through the use of a buffer station and separate sample tanks. Other parameters such as fluoride

levels, specific organics, and oxidants from undeveloped ammonia must be measured in the laboratory.

7 Grades of Water Effluent

7.1 Rinse Water — The second and third rinses from wafer cleaning processes are sufficiently high quality to be

reused without further treatment either for make-up water in a UPW system, or directly for use in a lower grade

application such as CMP cleaning.

7.2 Non-treated Reclaim Water — Is a lower grade of water with possible applications including fab air pollution

abatement scrubbers, fab point-of-use hazardous gas burn boxes, and drain flushing for CMP drains.

8 Special Issues

8.1 Difficulty of Identifying and Treating Organics — It is difficult to evaluate rinse waters after solvent use. Real

time, on-line instruments are not available to easily quantify and identify the complete composition of the organic

molecules for proper segregation. In addition, treatment of waste water containing organics is more difficult in

some cases, depending on the organic molecules being removed or converted.

8.2 Managing Excursions — Excursions in reuse water quality can occur due to various reasons such as human

error in operating non-automated manufacturing equipment.

8.2.1

It is important to detect and redirect such water before it can contaminate the system for which it directed for

reuse or possibly even damage the treatment equipment. Excursions from organics are particularly difficult because

they cannot be detected in real time. Two methods have been used to compensate for this delay: locate the

analyzers at a sufficient distance upstream of the central diverter point, or provide a sufficient buffer/quarantine

volume.

8.3 Temperature — Hot water effluent from rinse tanks on wet benches can provide a challenge in recycling

treatment systems, as temperature can be an important variable to water recycling system performance and can cause

an increase in bacteria growth. This issue is influenced by seasonal variations in ambient temperature. Heat

exchangers for process waters can be added to a recycle system in order to keep the system at a steady state.

8.4 Discharge Permits — One aspect of water reuse that can have significant economic impact relates to site

effluent and local discharge permits. As water reuse increases, contaminant concentrations in the site effluent will

also increase due to the reduced volume of the wastewater. If site water reuse is great enough, these higher

concentrations may approach the limits of the local wastewater discharge permits and need to be closely monitored.

9 Economic Considerations

9.1 General — Potential cost savings are available from the introduction of reuse water systems. One type of

savings can be measured from the actual cost of the water being replaced. The cost savings depends on the grade of

water being replaced and the original cost of producing that grade of water at that location. Additional savings can

often be realized in maintenance costs (e.g. membrane cleaning) given that the reclaim water is generally of better

quality than incoming water. Models for evaluating the economics of a reclaim or recycle water application have

been developed in the industry.

UPW Plant

Recycling

Plant

Fab

Reclaim

Plant

Other users

Waste water

treatment plant

Waste water

Lightly

contaminated

Contaminated

Very

contaminated

Raw water

NOTE: Courtesy of German UPW standard VDI 2083 Part 13

Figure 1

Schematic of Basic Reclaim Water System