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SEMI F75-1102 © SEMI 2002 2 batch samples can prove t ime-consum ing and be prone to sampling error. 4 Referenced Standards 4.1 SEMI Standar ds SEMI F61 — Guide for Ultrapu re Water System Used in Semiconduc tor Processi…
SEMI F75-1102 © SEMI 2002 1
SEMI F75-1102
GUIDE FOR QUALITY MONITORING OF ULTRAPURE WATER USED IN
SEMICONDUCTOR MANUFACTURING
This guide was technically approved by the Global Facilities Committee and is the direct responsibility of the
North American Facilities Committee. Current edition approved by the North American Regional Standards
Committee on August 29, 2002. Initially available at www.semi.org September 2002; to be published
November 2002.
1 Purpose
1.1 These guides provide recommendations for facility
engineers and other manufacturing and quality
professionals who may be responsible for establishing
programs to monitor and control the quality of their
ultrapure water (UPW) systems through to point-of-use
(POU). These guides may be used to help determine the
parameters that should be monitored for UPW that is
produced, distributed and used throughout the
manufacturing facility, and the frequency and location
of testing.
NOTE 1: These suggested guides are published as technical
information and are intended for informational purposes only.
2 Scope
2.1 UPW is used extensively in the production of
semiconductor devices for all wet processing steps.
Ultrapure water systems need to be tested and
monitored to ensure that the UPW being produced
matches the specifications established by the
manufacturing process. The purity of the UPW may
affect device yield unless a wide range of parameters is
closely controlled at the point of distribution (POD).
Semiconductor devices are currently being designed
with smaller linewidths (< 0.13–0.18 µm) and are more
susceptible to low level impurities.
2.2 UPW systems are monitored for continuous
performance for desired and achievable levels of
quality. Action limits are generally set to determine
when system performance data warrants that corrective
action is needed. Table 1 Parameters and Range of
Performance in SEMI F63 may be a useful reference
for establishing quality levels.
2.3 In more critical processes, the quality of the UPW
also needs to be monitored at the POU where the UPW
is in contact with the wafer. The quality of the UPW
should not be expected to be identical to the quality of
the UPW being produced at final filter (FF), which is
not subject to conditions within the tool or distribution
system.
2.4 These guides logically follow the series of SEMI
guides developed for UPW, which include a standard
defining the performance of a UPW system, and a
standard defining the quality of UPW (see reference
section). The Schematic of a Typical Ultrapure Water
System in Figure 1 of SEMI F61 may be a useful
reference for determining sampling points.
2.5 Guides are provided concerning the frequency and
location of sampling for those parameters that are not
available from on-line analyzers. Frequency of
sampling should be based on the specifications set by
manufacturing for the quality of the POD UPW, the
number and locations of on-line analyzers, the stability
of the incoming feed water to the system, and the
historical performance of the UPW system over time.
2.6 These guides may also be used to establish process
control criteria for the incoming feedwater,
performance of UPW system components and POU
rinse baths.
2.7 This standard does not purport to address safety
issues, if any, associated with its use. It is the
responsibility of the users of this standard to establish
appropriate safety health practices and determine the
applicability or regulatory limitations prior to use.
3 Limitations
3.1 These guides have been developed with
consideration of various other sources deemed to be
relevant for this purpose. However this guide was not
intended to be identical to or consistent with any other
industry document or standard.
3.2 Monitoring and testing of recycled or reclaimed
water systems are not specifically addressed in these
guides. Additional test parameters, such as
quantification and identification of organic species in
reclaim water, should be added to monitoring programs
for reclaim and reuse waters.
3.3 Measuring the purity of UPW can prove
challenging. Many on-line instruments (sodium
analyzers, TOC analyzers, silica analyzers, optical
particle counters, non-volatile residue analyzers)
provide very low limits of detection but may not be
capable of being calibrated in the range of detection or
may have very poor accuracy at low levels. On-line
analyzers should primarily be used for trend analysis.
Many tests can still be performed more accurately and
reproducibly in a laboratory environment but taking
SEMI F75-1102 © SEMI 2002 2
batch samples can prove time-consuming and be prone
to sampling error.
4 Referenced Standards
4.1 SEMI Standards
SEMI F61 — Guide for Ultrapure Water System Used
in Semiconductor Processing
SEMI F63 — Guidelines for Ultrapure Water Used in
Semiconductor Processing
NOTE 2: As listed or revised, all documents cited shall be the
latest publications of adopted standards.
5 Terminology
5.1 Abbreviations and Acronyms
NOTE 3: All other abbreviations and acronyms are defined in
the SEMI Compilation of Abbreviations and Acronyms
available at web site, http://www.semi.org/.
5.1.1 CFU — Colony-Forming Units
5.1.2 DO — Dissolved Oxygen
5.1.3 EDI — Electrodionization
5.1.4 EDX — Energy Dispersive X-Ray Microanalysis
5.1.5 FF — Final Filter
5.1.6 IC— Ion Chromatography
5.1.7 NDIR — Non-Dispersive Infrared Analysis
5.1.8 OPC — Optical Particle Counters
5.1.9 POD — Point Of Distribution
5.1.10 RO — Reverse Osmosis
5.1.11 TDS — Total Dissolved Solid
5.1.12 THM — Trihalomethanes
6 Units
6.1 Parts per million (ppm) is equivalent to µg/mL or
mg/L.
6.2 Parts per billion (ppb) is equivalent to ng/mL or
µg/L.
6.3 Parts per trillion (ppt) is equivalent to pg/mL or
ng/L.
7 Use of the Guides
7.1 Monitoring programs should reflect the age and
complexity of the UPW equipment and the needs of the
manufacturing process.
7.2 The quality of UPW at the POU may be negatively
impacted by 1.) contamination sources within a tool, 2.)
the design of the tool, 3.) the materials of construction
of the tool and piping distribution, and 4.)
contamination loading in the bath from build-up after
multiple rinse cycles.
7.3 Sampling methods and contamination control are
of paramount importance when attempting to measure
the listed parameters at very low levels of sensitivity.
7.4 The quality of the data measured may depend on
which testing methods and calibration techniques are
used. Consequently, trends observed in the values may
be more meaningful than absolute values, especially for
certain on-line monitors calibrated for ultrasensitive
detection. In addition, online and offline measurements
may not correlate depending on the measurement
technique and level of sensitivity of the measurement.
8 Tests For Monitoring UPW Production and
Distribution
NOTE 4: Since SEMI Guides do not require analytical data or
methods to support them, the recommendation of specific
analytical methods are only for informational purposes.
Alternative methods may also be applicable.
NOTE 5: See Table 1 at the end of this document for
summary of recommended testing frequency and sampling
points.
8.1 Resistivity (megohm-centimeters)
8.1.1 Resistivity (the inverse of conductivity) is a
general measure of ionic activity and is measured by an
on-line meter. The resistivity of UPW should be
approximately 18.2 mΩcm depending on the resolution
of the instrument.
NOTE 6: 18.25 mΩcm is the theoretical upper limit for pure
water at 25°C.
8.2 Total Oxidizable (Organic) Carbon (TOC) (ppb)
8.2.1 Carbon Sources in Water Supplies
8.2.1.1 Incoming feed water contains both inorganic
and organic carbon. Inorganic carbon as dissolved
carbon dioxide (CO
2
), bicarbonate, and carbonate can
be present at high ppm levels according to the geology
of the water supply. Organic carbon reflects biological
input and man-made contaminants such as oils,
pesticides, and fertilizers. Ground and well waters
normally have significantly lower organic content than
surface waters. To remove the majority of organics,
most UPW systems employ reverse osmosis; anion
exchange resin and ultraviolet (UV) destruction are also
employed to remove organics. Some volatile organics,
such as trihalomethanes (THM), may be controlled by
the use of vacuum degasification. The control of
organics is essential for preventing organic fouling and
maintaining resin beds at high efficiency. In addition,
SEMI F75-1102 © SEMI 2002 3
reduced organic matter will limit the nutrients available
for bacteria growth and thus biofilm development.
Increasing TOC values at the FF can indicate
degradation and/or fouling of system components,
contamination from routine operational maintenance, or
return contamination from the factory. Changes in the
incoming feed water due to seasonal or extreme
weather conditions can also cause increases in TOC
readings.
8.2.2 Method of TOC Measurement for Source Water
8.2.2.1 There are various methods for measuring TOC,
and several TOC analyzers are available. TOC
measurement generally involves the oxidation of
organic materials by means of temperature, UV
radiation, and/or chemicals. The CO
2
produced by these
reactions can then be measured by non-dispersive
infrared analysis (NDIR) or conductivity (resistivity)
differential. The exact method utilized will vary
depending on the TOC instrumentation employed and
the method may also affect the TOC readings as
different methods have different recoveries of various
organics. Some instruments will also require the use of
a carrier gas such as air or nitrogen, while others
measure TOC directly.
8.2.3 Monitoring TOC in the UPW System
8.2.3.1 TOC is a useful test to measure the organic
removal effectiveness of the UPW system components
including Carbon, RO, Degasification, and Ion
Exchange. Suggested measurement points are city
feed, pre and post RO membrane, and final filter, with a
minimum frequency that reflects possible changes in
organics from the feed source or UPW components.
After the RO, TOC drops from low ppm levels in the
source water to mid ppb range, and to single digit ppb
levels after the mixed resin beds and UV TOC
reduction units.
8.2.4 Monitoring TOC at the POU
8.2.4.1 TOC may be measured at the point-of-use to
determine quality changes from the distribution system
and the manufacturing tool. Short wavelength UV (185
nm) is capable of breaking up residual organics into
charged organic molecules. TOC which survives to the
point of use in a UPW system are typically either
“light” molecules or small fragments of larger
molecules such as acetate and formate. While low TOC
means that the UPW system is working effectively to
eliminate the source water organic load, this test is not
an accurate measure of sterility of a UPW system. In
addition, TOC levels at POU can also reflect carryover
from chemical baths and contaminants in cleanroom air.
8.3 Dissolved Oxygen (ppb)
8.3.1 Dissolved oxygen (DO) content can be
controlled, if desired. Rinsing hydrogen passivated
silicon wafer surfaces with high DO UPW can result in
etching of the silicon by the oxygenated UPW and loss
of control of gate oxide thickness.
8.4 Particulate Matter (Particles/L)
8.4.1 Sources of Particles in Ultrapure Water Supplies
8.4.1.1 Particles that adhere to wafer surfaces at each
step of the integrated circuit device manufacture may
impair the application of thin-films and
photolithographic substances, and ultimately cause
discrete and integrated transistors to fail because of
resultant physical imperfections. Particles originate in
the incoming city water and may also be generated
from degradation of the UPW system components or
operational activities. Incoming source water contains a
high level of particles and is initially filtered by
prefilters and mixed media in order to remove gross
physical turbidity in the micron range.
8.4.1.2 Following reverse osmosis, source water
particles have been greatly reduced, as the RO
membranes also reject particles. It is essential to
minimize the particle load to the RO to prevent
membrane fouling and premature or frequent RO
cleanings. From the RO outlet forward in the system,
the particle load in the UPW originates from system
components. Particle sources can be RO membrane
modules, piping components, valves and other similar
control devices, tank linings, resin fines and other
sources where materials are undergoing wear or
degradation and are shedding particles.
8.4.1.3 After the ion-exchange resin beds, increasingly
smaller dimension filters are used in the range 0.2 to 1.0
microns to remove residual particles and resin fines. In
most ultrahigh purity applications, ultra filtration at
10,000 molecular weight is utilized. In most UPW
systems, the presence of significant quantities of sub-
micron particles at the final filter may indicate the
breakdown of upstream UPW system components. In
addition, POU filters on tools can be a source of
contamination if not maintained.
8.4.2 Optical Particle Counters (OPC)
8.4.2.1 On-line methods using laser optical particle
counting technology are recommended for trend
analysis and specification compliance. These
instruments can monitor particles in the 0.03 to > 0.5
micron range depending on the system component
being tested. Particle counting using an OPC requires a
good sample port connection to eliminate false counts.
Good counter maintenance, including annual calibration
and replacement of tubing and fittings is critical
especially if monitoring particles ≤ 0.05 microns. In
order to monitor trend analysis with good statistical