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SEMI F61-0301 © SEMI 2001 4 be configu red in a double-pass arra ngement cons isti ng of tw o RO membrane unit s in series. Permeate (filtered w ater) from the first RO unit is sent to the second RO unit to b e filtered …

SEMI F61-0301 © SEMI 20013

4.2.39 UPW (ultra pure water)  the highest purity

water produced by a semiconductor water treatment

system, which is sent to the end users for use in

manufacturing.

5 General Requirements

5.1 Materials



Components of the UPW system

must be appropriate to the application and conform to

electrical, mechanical, and purity requirements, as well

as the corrosive properties of the UPW chemistry.

These requirements are defined by the physical

installation environment, local and national code

interpretations, process requirements, and delivery

specifications.

5.2 System Installation  The UPW system is

installed according to a protocol that ensures

mechanical integrity, leakproof operation, and no or

minimal contamination being added from distribution

throughout the system.

5.3 Acceptance Tests  Acceptance tests are

conducted on each subsystem or system produced. Such

tests may include performance demonstrations,

demonstrations of reliability criteria, and achievement

of purity standards. Such tests are the basis for

acceptance or rejection by the purchaser against a pre-

negotiated set of criteria for the performance of the

system.

5.4 Qualification Testing  Qualification testing may

include tests for resistivity, temperature, pressure, TOC,

dissolved oxygen, particle levels, bacteria, total silica,

dissolved silica, non-volatile residue, ions, and metals.

5.5 Monitoring  UPW systems are monitored for

continuing performance against desired and achievable

levels of quality. Action limits are generally set to

determine when system performance suggests that

corrective action is required.

5.6 UPW specifications  UPW systems are generally

guaranteed to deliver a certain quality of water on an

ongoing basis. The guaranteed performance is

established in advance between the UPW equipment

manufacturer and the system owner. Both qualification

testing and monitoring testing use the guaranteed

specifications to determine the parameters and levels of

purity to be tested.

5.7 Recycle/Reclaim Opportunitie s



There can be

several opportunities for using water within a UPW

system, and should be recognized during the design

phase when possible. Examples are; use of 1

pass

reject for cooling tower make-up water, returning UF

reject to Primary or Feed water Tank, re-use of last

stage rinse waters as UPW for lower grade use areas,

i.e., CMP, isolation of CMP waste stream, for possible

reclaim/reuse.

6 Source Water

6.1 Raw Water



is the raw material from which

UPW is made. Untreated raw water is natural water

that is obtained from a surface source such as a lake or

river, or from a ground water source. The raw water to

a UPW system is most frequently treated Municipal

Drinking Water.

6.2 Municipal Drinking Water  Most natural raw

waters must be treated in order to produce drinking

water that meets federal and state requirements. There

are upper limits for inorganic contaminants (e.g.,

asbestos, arsenic, copper, and lead), pesticides, volatile

organic chemicals (e.g., benzene, trichloroethylene,

toluene, and xylene), turbidity, microbiological

contaminants, and radiological contaminants (e.g.,

radon 226, radon 228, tritium, and strontium 90).

Municipal Water Treatment may utilize only

chlorination, or filtration and chlorination for certain

ground water sources. For many surface water sources,

coagulation (injection of aluminum or iron salts),

flocculation (injection of a long-chain polymer),

sedimentation, lime or lime/soda ash softening,

filtration, chlorination or chloramination (chlorine plus

ammonia) and other steps may be required.

7 Major Treatment Processe s

7.1 Pretreatment includes all of the water treatment

steps ahead of the Reverse Osmosis Membrane

Treatment step. These steps are primarily required to

protect the membrane units from scaling with sparingly

soluble salts, fouling with living or non-living

suspended particles, or chemical attack by pH,

oxidizing agents or other dissolved contaminants.

Pretreatment equipment may include media filtration,

micro filtration, or ultrafiltration (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), activated carbon

filtration (to remove oxidizing agents and certain

organic molecules), and sulfite ion injection (to remove

oxidizing agents).

7.2 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. Reverse osmosis (RO) units may

SEMI F61-0301 © SEMI 2001 4

be configured in a double-pass arrangement consisting

of two RO membrane units in series. Permeate

(filtered water) from the first RO unit is sent to the

second RO unit to be filtered again. It is not

uncommon for the permeate from a double-pass RO

unit to have a resistivity reading up to 0.5–4 Megohm-

cm, with less than one milligram per liter of organic

and silica contaminants. The more contaminants

removed in the membrane treatment step, the lower the

loading on the Polishing steps.

7.3 Volatiles Removal  The removal of dissolved

oxygen, carbon dioxide, other gases, and volatile

organic compounds is a necessary treatment step. The

removal of these volatile contaminants is accomplished

to acceptable levels in vacuum degasifiers and in

membrane degasification units. The removal of

volatiles that can form ions and the removal of volatile

organic compounds reduce the loading on downstream

Polishing equipment.

7.4 Polishing  The relatively low level of

contaminants that were not removed in the Membrane

Treatment and Volatiles Removal steps are polished

down to acceptable levels in the Polishing steps. Ionic,

organic, and silica contaminants are removed in

typically two stages of Ion Exchange in series (primary

beds and polishing beds). Organic compounds,

measured as TOC (Total Organic Carbon, or Total

Oxidizable Carbon), that are found downstream of the

RO membrane units may be subjected to TOC

Reduction ultraviolet (UV) irradiation (185 nanometer

low pressure units or medium pressure units) to convert

most of them into ionic compounds that can be

effectively removed by Primary Ion Exchange Units

(usually consisting of Separate Beds, Mixed Beds or

EDI/CDI/E-Cell). TOC compounds that exit the

primary ion exchange units are typically subjected to

TOC reducing UV irradiation to break them into

ionized compounds to be removed by the Polishing Ion

Exchange Units. The vast majority of all living

suspended particles (mainly bacteria) that enter any 254

nm UV unit are inactivated. Downstream filters with a

pore size of less than or equal to 0.45 micron remove

the inactivated bacterial bodies. The final filter prior to

Distribution typically has a pore size of less than 0.2

micron.

8 Distribution

8.1 Distribution is frequently comp osed of one or

more Loops. Each loop consists of UPW that

continuously recirculates through appropriate piping

from the final filters, to the manufacturing areas

requiring UPW (end users), and back to a tank located

within the Polishing section to be polished again. The

UPW to the end-user area is commonly called the

Supply. The UPW that travels from the end-user area

back to the water treatment area is commonly called the

Return. Ozone may be injected into the Supply and/or

Return line to control microbiological contaminants and

also to enhance the action of TOC breakdown in

downstream TOC reducing UV units. Sometimes ozone

is injected into the Supply line for similar reasons

(requires de-ozonation at the end-use points).

Sometimes the UPW in the distribution loop is heated

(hot loop) for particular processes.

8.2 Basic System Components

8.3 General  Each UPW system contains certain

basic components and a variety of design options to

meet particular customer and facility needs. An

example of a UPW system is shown in Figure 1

attached.

9 Related Documents

9.1 SEMI Standards

SEMI F4 — Guide for Standard Performance,

Practices, and Sub-Assembly for High Purity Piping

Systems and Final Assembly for Semiconductor

Manufacturing Equipment

SEMI F31 — Guide for Bulk Chemical Distribution

Systems

SEMI S2 — Environmental, Health, and Safety

Guideline for Semiconductor Manufacturing Equipment

9.2 SIA

National Technology Roadmap For Process Chemicals

1 Semiconductor Industry Association, 181 Metro Drive, Ste 150, San

Jose, CA 95110, USA

Feed

Water

≤

≤ 5

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≤

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≤ 1

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≤

≤ 1

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≤

≤ 0.02

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Figure 1

Schematic of a Typical Ultrapure Water System

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