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SEMI F98-0305 © SEMI 2005 4 analyzers at a sufficient distance upstr eam of the central diverter point, or provide a sufficient buffer/quarantin e volume. 8.3 Temperat ure — Hot wate r effluent from rinse tanks on wet be…

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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

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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

NOTICE: SEMI makes no warranties or representations as to the suitability of the standards set forth herein for any

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Users are cautioned to refer to manufacturer's instructions, product labels, product data sheets, and other relevant

literature, respecting any materials or equipment mentioned herein. These standards are subject to change without

notice.

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