Background Statement for SEMI Draft Document #5415
REVISION TO SEMI F63-0211, GUIDE FOR ULTRAPURE WATER USED
IN SEMICONDUCTOR PROCESSING
Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in
reaching an informed decision based on the rationale of the activity that preceded the creation of this Document.
Notice: Recipients of this Document are invited to submit, with their comments, notification of any relevant
patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this
context, “patented technology” is defined as technology for which a patent has issued or has been applied for. In the
latter case, only publicly available information on the contents of the patent application is to be provided.
Background
This document is an update of the existing SEMI F63 ultrapure water guide. The objective is to align it with the
suggestions coming from the International Technology Roadmap for Semiconductors (ITRS) when building or
retrofitting today’s <65nm fabs. The guide supplies both recommended limits as well as supplemental information
about important ultrapure water parameters. Associated analytical methodology references are also contained within.
Since this document is a guide it is not intended to tell the reader what quality of water must be used, rather it
suggests which parameters are important as well as listing the values that can be achieved.
This document is also intended to continue to be updated every two years, keeping it in alignment with the ITRS
development pace. As well, the intent is to continue working closely with the ASTM D19 team (authoring ASTM
D5127) so that all three documents, F63, ITRS and D5127, are complementary to each other. New revision of
ASTM D5127, including SEMI F63 information is being currently balloted by the D19 Committee.
The methodology used in setting the UPW quality parameters for the guide is based on the risk definition of the
ITRS as well as based on the best available UPW treatment and analytical technology. The resulting water quality
guide recommends the UPW characteristics that would mitigate the risks to advanced semiconductor manufacturing
with a reasonable level of investment. When risks are not fully addressed (per ITRS), specific comments have been
added in the supplemental information section that would support the semiconductor fab experts in setting their
UPW quality specifications. In some cases, additional investment may be chosen due to specific factory needs.
Therefore, it is important that the UPW characteristics table will be reviewed together with the supplemental
information section.
Main changes in the updated revision of the document are as follows:
New parameter – pressure stability, has been introduced and explained in the document. There is no value provided
at this point, due to insufficient amount of data from the end user and ITRS. The intent is to add the value in the next
2014 revision as more data is obtained.
Nonvolatile residue limit was included based on the new information about the level of NVR of the successfully
operating fabs. The importance of NVR control has been clarified in Supplemental Information section.
Particle limits have been reduced based on the input from the particle monitoring device suppliers, justifying lower
instrument noise than that assumed in 2010 revision document.
TOC level was reduced from 2 ppb to 1 ppb based on successful experience of modern high volume manufacturing
facilities to achieve and maintain this level. Additional definitions have been provided for organics, based on ITRS
input.
Bacteria specification has been updated for better clarification of the result interpretation. The sample volume has
been updated as well.
Notes:
This document refers to a point of use (POU) water quality.
This document is a guide and therefore complete analytical methods are not contained within. A selected list of
optional methods is found in the related sections.
Reporting Limits from various analytical test methods are used when ITRS suggestions challenged analytical
capabilities. The reporting detection limits have been provided in the parameters table to support the idea of the
feasibility of detection of the respective parameter level. In some cases judgment was applied by F63 task force to
increase the value of the reporting limit to strengthen the confidence in metrology capability. Please refer to the
limitations section and supplementary portion for additional clarification regarding the analytical test methods.
Review and Adjudication Information
Group:
Date:
Time & Timezone:
Location:
City, State/Country:
Leader(s):
Standards Staff:
Task Force Review
UPW Filtration TF/F63 TF
Monday, October 29, 2012
3:00 PM to 5:00 PM, Pacific Time
SEMI Headquarters
San Jose, California
Slava Libman (Air Liquide)/
slava.libman@airliquide.com
Michael Tran (SEMI NA)
408.943.7019
mtran@semi.org
Committee Adjudication
NA Liquid Chemicals Committee
Tuesday, October 30, 2012
1:00 PM to 4:00 PM, Pacific Time
SEMI Headquarters
San Jose, California
Frank Flowers (FMC)/
Frank.Flowers@fmc.com
Frank Parker (ICL)/
Frank.Parker@icl-pplp.com
Michael Tran (SEMI NA)
408.943.7019
mtran@semi.org
This meeting’s details are subject to change, and additional review sessions may be scheduled if necessary. Contact
the task force leaders or Standards staff for confirmation.
Telephone and web information will be distributed to interested parties as the meeting date approaches. If you will
not be able to attend these meetings in person but would like to participate by telephone/web, please contact
Standards staff.
Notice: Additions are indicated by underline and deletions are indicated by strikethrough.
Semiconductor Equipment and Materials International
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DRAFT
SEMI Draft Document #5415
REVISION TO SEMI F63-0211, GUIDE FOR ULTRAPURE WATER USED
IN SEMICONDUCTOR PROCESSING
1 Purpose
1.1 This guide may be used:
 To establish performance criteria when purchasing ultrapure water (UPW) purification equipment.
 To set the process control parameters for UPW-system operation.
 To establish quality expectations for the supplied UPW.
NOTE 1: These suggested guidelines 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 (including
wafer rinsing). UPW purity is therefore critical to the manufacture of semiconductors. This guide provides UPW
quality parameters and background information for the decision-making process related to new or retrofit facilities
that manufacture semiconductors with line widths of 65 nm and smaller.
2.2 The goal of members of the International Technology Roadmap for Semiconductors (ITRS) UPW committee is
to look years ahead on a continual basis to assess the semiconductor industry’s future UPW technology requirements.
In addition to ITRS input, the SEMI committee contributed its knowledge of the feasibility and cost viability of the
technical solutions required to support UPW quality values specified in this guide. .
2.3 The information in this guide has been developed from the following sources:
 ITRS risk assessment with input from facility- and manufacturing-experts and technology providers in the
semiconductor manufacturing industry.
 The results of UPW testing at semiconductor manufacturing sites as measured by independent laboratories that
test high purity water for the semiconductor industry.
 Specifications from water-system equipment manufacturers.
 Input from UPW producers and users at SEMI Standards committee meetings, and also through the balloting
process.
NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their
use. It is the responsibility of the users of the documents to establish appropriate safety and health practices, and
determine the applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 This guide is not intended to define UPW system performance requirements. It only provides a reference set of
parameters and their values, considered to be satisfactory for the advanced semiconductor manufacturing needs. In
some cases the values are limited by the feasibility of the available treatment technology or metrology. It is expected
that semiconductor company experts will define the performance requirements for the UPW system based on
specific manufacturing process sensitivities, with reference to the information provided in this guide.
3.2 The purity of water generated in water systems differs. These guidelines were developed for properly
maintained, state-of-the-art UPW systems as found in high-end semiconductor manufacturing plants and may not
reflect the needs of lesser demanding end-users.
3.3 This guide is not intended to be used to define the criteria needed for selecting process tools.
3.4 This guide defines parameters that apply to the quality of UPW required in semiconductor processing when
proper analytical hookup and tool installation is made.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
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3.5 This guide may include suggested values that are at the detection limit of today’s available, cost-viable,
analytical instrumentation or techniques. UPW system owners, engineers, and technicians are expected to decide
whether the benefits of meeting the suggested values outweigh the associated time and costs. The quality of the data
measured will depend on which testing method and calibration techniques are used. Laboratory or metrology
vendors may be requested to provide additional analytical validation data to confirm detection limits before internal
specification values are set.
4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI C1 — Guide for the Analysis of Liquid Chemicals
SEMI C10 — Guide for the Determination of Detection Limits
SEMI F61 — Guide For Ultrapure Water System Used in Semiconductor Processing
4.2 ASTM Standards1
ASTM D859 — Standard Test Method for Silica in Water
ASTM D4327 — Standard Test Method for Anions in Water by Chemically Suppressed Ion Chromatography
ASTM D4517 — Standard Test Method for Low-Level Total Silica in High-Purity Water by Flameless Atomic
Absorption Spectroscopy
ASTM D5127 — Standard Guide for Ultra Pure Water Used in the Electronics and Semiconductor Industry
ASTM D5173 — Standard Test Method for On-Line Monitoring of Carbon Compounds in Water by Chemical
Oxidation, by UV Light Oxidation, by Both, or by High Temperature Combustion Followed by Gas Phase NDIR or
by Electrolytic Conductivity
ASTM D5391 — Standard Test Method for Electrical Conductivity and Resistivity of a Flowing High Purity Water
Sample
ASTM D5544 — Standard Test Method for On-Line Measurement of Residue After Evaporation of High-Purity
Water
ASTM D6317 — Standard Test Method for Low Level Determination of Total Carbon, Inorganic Carbon and
Organic Carbon in Water by Ultraviolet, Persulfate Oxidation, and Membrane Conductivity Detection
ASTM D7126 — Standard Test Method for On-Line Colorimetric Measurement of Silica
ASTM F1094 — Test Method for Microbiological Monitoring of Water Used for Processing Electron and
Microelectronic Devices by Direct- Pressure Tap Sampling Valve and by the Pre-sterilized Plastic Bag Method
4.3 Other Documents
International Technology Roadmap for Semiconductors (ITRS) 2
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 General terms and acronyms used in this standard are listed and defined in SEMI F61.
6 Use of the Guidelines
6.1 Supplemental information, including recommendations on how to use this document, is provided at the end of
the guide. The supplemental information is critical to understanding the intent of this guide.
1
American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania 19428-2959, USA. Telephone:
610.832.9585; Fax: 610.832.9555; http://www.astm.org
2
http://www.itrs.net
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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6.2 The supplemental information should be considered when making decisions on UPW performance requirements.
Any additional data about manufacturing process sensitivities should also be considered when making a final
decision about appropriate UPW quality.
7 Units
7.1 Parts per million (ppm) is equivalent to µg/mL or mg/L, where 1 L approximately equals 1 kg.
7.2 Parts per billion (ppb) is equivalent to ng/mL or μg/L, where 1 L approximately equals 1 kg.
7.3 Parts per trillion (ppt) is equivalent to pg/mL or ng/L, where 1 L approximately equals 1 kg.
7.4 Micrometer (µ) is a unit of length equal to one millionth of a meter, or one thousandth of a millimeter.
7.5 Colony Forming Units (CFU) is a measurement of bacteria organisms as referred to in ASTM F1094.
8 Description of Parameter Tests
NOTE 2: SEMI Guides do not require analytical data to support analytical methods, therefore the recommendations of specific
analytical methods are only for informational purposes. Alternative methods may also be applicable (see SEMI C1 for analytical
validation methodology).
8.1 Resistivity (megohm·centimeters or MOhm·cm)
8.1.1 Resistivity (conductivity) is measured accurately with only on-line instrumentation. 18.18 MOhm·cm is the
theoretical upper limit for pure water at 25°C.
8.2 Temperature
8.2.1 Temperature stability (K) is defined as a range of the temperature deviation from the facility-specified
temperature target. The temperature is measured with an on-line sensor installed inline.
8.2.2 Temperature gradient (K per interval) is defined as the rate of change of temperature within a specific interval
of time.
8.3 Non-volatile Residue (NVR)
8.3.1 Non-volatile residue (NVR) or a residue after evaporation (usually expressed in units of ppt) is measured
using an online, non-volatile residue monitor.
8.4 Total Organic Carbon (TOC) (usually expressed in units of ppb) also known as Total Oxidizable Carbon
8.4.1 Conductivity cells or infrared photometry can be used to measure the carbon dioxide created by the oxidation
of organic materials.
8.5 Dissolved oxygen (usually expressed in units of ppb) is measured accurately with only on-line instrumentation.
8.6 Particulate Matter (Particles/L)
8.6.1 Currently, accurate trend analysis requires online methods using optical particle counters.
8.7 Bacteria (CFU/L)
8.7.1 Triplicate samples are cultured based on the ASTM F1094 using a minimum sample size of 1 L.
8.8 Silica
8.8.1 Total Silica (usually expressed in units of ppb) is measured by graphite furnace atomic absorption
spectrophotometry (GFAAS), inductively-coupled plasma atomic emission spectroscopy (ICP-AES), or high
resolution-inductively coupled plasma-mass spectroscopy (HR-ICP-MS).
8.8.2 Dissolved Silica (usually expressed in units of ppb as SiO2) is measured by heteropoly blue photometry, or by
ion chromatography.
8.9 Ions and Metals (usually expressed in units of ppt)
8.9.1 Anions and cations such as ammonium, bromide, chloride, fluoride, nitrate, nitrite, phosphate, and sulfate, can
be detected using ion chromatography.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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8.9.2 The 21 elements included in this guide are listed in Table 1.
NOTE 3: Up to 68 elements, including the 21 of interest can be determined by GFAAS, ICP-AES, or ICP-MS.
9 Recommended Ultrapure Water Quality
9.1 Table 1 lists each parameter with its range of performance.
9.2 Table 1 should be considered together with the supplemental information (§ 10).
Table 1 Recommended Ultrapure Water Quality
Typical Linewidth
<0.065 MICRONS
PARAMETER
PERFORMANCE
Limit of Detection (RL)
Resistivity on-line @ 25°C (Mohm·cm)
>18.18
±0.2
Temperature Stability (K)
±1
Not Applicable#3
Temperature Gradient (K/10 min)
<0.1
Not Applicable#3
Pressure stability (bar)
To Be Determined
see § 10.12
TOC on-line (ppb)
<1
0.05
Dissolved Oxygen on-line (ppb)
<10
±0.2
Dissolved Nitrogen on-line (ppm)
8 to 18
±0.3
Dissolved Nitrogen Stability (ppm)
±2
±0.3
Residue after evaporation on-line (ppt)
< 20
<100
On-line Particles > 0.05μ size (#/L)
<200
<100
1 L Sample
<1
1
100 mL Sample
<1
1
Silica – total (ppb)
<0.5
<0.5
Silica – dissolved (ppb as SiO2)
<0.5
<0.1
Ammonium
<50
10
Bromide
<50
10
Chloride
<50
5
Fluoride
<50
5
Nitrate
<50
5
Bacteria (CFU/L)#3
Silica
Ions and Metals (ppt)
Nitrite
<50
5
Phosphate
<50
10
Sulfate
<50
10
Aluminum
<1
0.5
Antimony
<10
0.5
Arsenic
<10
0.5
Barium
<1
0.5
Boron#1
<50
15
Cadmium
<10
0.5
Calcium
<1
0.5
Chromium
<10
0.5
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Typical Linewidth
<0.065 MICRONS
PARAMETER
PERFORMANCE
Limit of Detection (RL)
Copper
<1
0.5
Iron
<1
0.5
Lead
<1
0.5
Lithium
<1
0.5
Magnesium
<1
0.5
Manganese
<10
0.5
Nickel
<10
0.5
Potassium
<1
0.5
Sodium
<1
0.5
Tin
<10
0.5
Titanium
<10
0.5
Vanadium
<10
0.5
Zinc
<1
0.5
#1 Reporting Limits (RL) as reported by the analytical vendors.
#2 The specified value is relative to the absolute temperature target chosen by a semiconductor manufacturing facility and
therefore the accuracy or detection limits are considered to be “not applicable.” The sensor suppliers state that temperature
stability is within 0.1% of the reading for >2 years operation, which is well within the expectations implied by the
specified values.
#3 See §10.8 for additional clarification.
10 Supplemental Information for the Specification Table
10.1 Resistivity
10.1.1 Resistivity is commonly used to indicate UPW purity because it provides an instant response to only
significant change in water quality. It is a well established, relatively inexpensive method, but the absolute values of
resistivity readings are affected by other variables such as probe setup and calibration, sample flowrate, and
temperature variation/compensation. Therefore, resistivity measurements cannot provide an indication of the ionic
contamination at the ppt range, as indicated in Table 1. Reported resistivity-measurement accuracy is usually within
the ±0.2 Mohm·cm range, but in some applications the accuracy may be optimized to a more narrow range and still
be insufficient to indicate trace ionic contamination. The limitations of the resistivity instrumentation should be
taken into account, when specifying the UPW system design.
10.2 Temperature for Immersion Lithography
10.2.1 Based on ITRS analysis, this guide offers a temperature-stability requirement for immersion
photolithography tools, using UPW as an immersion fluid. It represents the maximum rate of change (or gradient) of
the temperature of the cold UPW supplied to the photolithography tool in order for the tool to maintain temperature
stability. In some cases, additional temperature stability requirements, such as <0.1 K/10 min, may be used.
10.2.2 Depending upon the immersion photolithography tool used, the UPW temperature-range requirement for
immersion photolithography can be set within a relatively wide value around room temperature. However, the
temperature gradient is very important for immersion photolithography.
10.2.3 Temperature stability requirements for UPW uses other than immersion photolithography are generally less
stringent than those for immersion photolithography.
10.3 Total Organic Carbon (TOC) (also called Total Oxidizable Carbon)
10.3.1 For the purpose of this guide, Total Organic Carbon is defined as equivalent amount of CO 2 produced from
UV oxidation at 185nm wavelength inside of the UV reactor of a TOC monitoring device. The CO2 is measured
using conductivity cells, which results in a calculated TOC level. It is either assumed that the change in conductivity
is a result of only the CO2 produced from the oxidation of organic compounds present in UPW or the non-CO2
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contributions to conductivity are eliminated or subtracted from the final conductivity measurement and TOC
calculation.
10.3.2 Organic carbon compounds can be broken into the following major groups:
 Natural Organic Matter (NOM) — NOM includes species that either exist naturally in source water or are byproducts of drinking water sterilization.
 Synthetic Organic Matter (SOM) — SOM includes chemical pollutants in the source water, contamination from
components within the UPW system, or trace chemicals introduced via manufacturing rinse-water reclaim. Some
of these organic species can be difficult and expensive to remove using conventional treatment processes.
10.3.3 Benchmarking studies conducted by the UPW ITRS Committee at several semiconductor manufacturing
plants (located throughout the world) have shown that when the TOC levels are controlled to 1 ppb (as
recommended in this specification), no known related defects occur.
10.3.4 The limit of the current metrology for measuring TOC online is 50 ppt, therefore the recommended level of
less than 1 ppb is easily achievable with currently available online instrumentation.
10.3.5 Critical organic compounds - UPW ITRS is currently working on a better definition of the “critical organic
species” that may have higher impact on semiconductor manufacturing. This definition will be based on the Failure
Mode and Effect Analysis (FMEA) taking into account device impact, occurrence, and detection probability (see
additional explanation of FMEA methodology used in Section 10.10). Currently used online, TOC analyzers are
non-specific in their measurement of organic contaminants.
10.3.6 As features of semiconductor devices are scaled down, the oxide thickness is reduced and becomes more
vulnerable to voltage leakage. There is evidence that oxide layers such as native oxide, gate oxide, and tunnel oxide
can be affected by the presence of organic compounds in UPW. Organic compounds containing polar (-OH) groups
form strong bonds with the oxygen of the oxide layer, leading to oxide breakdown and voltage leakage. The
presence of organics on the oxide layers can also lead to poor adhesion of photoresist causing undercutting during
the wet-etching process. This undercutting creates larger windows, or vias, which may short-circuit adjacent metal
lines.
10.4 Dissolved Oxygen
10.4.1 Dissolved oxygen may affect native gate oxide growth and, in higher concentrations, enhance corrosion of
metals such as copper. Although this guide specifies 10 ppb of dissolved oxygen, very critical processes (such as
SiGe device cleaning) may require lower specifications (down to 1 ppb of dissolved oxygen). This can be achieved
only if the cleaning bath is closed to the environment.
10.4.2 Oxygen can be used as a dissolved gas for megasonic cleaning when oxidation is not a concern. The
detection accuracy of the on-line analytical instruments is within ±0.2 ppb, adequately supporting the specified value
of 10 ppb. The UPW section in the 2011 ITRS report (Table 2011 YE3) considers some parameters as process
variables rather than contaminants. Some semiconductor manufactures now treat Dissolved Oxygen (DO) as a
process variable while others consider it a contaminant.
10.5 Dissolved Nitrogen
10.5.1 This guide defines the level of nitrogen necessary for efficient megasonic cleaning and for the lithography
scanner. Some variability of concentration can be tolerated when process engineers determine the specific range for
their facility. Maintaining a 10 ppb dissolved oxygen level in the water implies a dissolved nitrogen level of
approximately 1 ppm, therefore gasification with nitrogen may be required to achieve the desired dissolved nitrogen
concentration. Regassification at the point of use is more economical and easier to control when the incoming level
of dissolved nitrogen is stable. The detection accuracy of on-line analytical instruments is within ±0.3 ppm,
adequately supporting the specified dissolved nitrogen value of 8 to 18 ppm. Dissolved nitrogen stability is
significant for megasonic cleaning and for UPW consumption.
10.6 Non-volatile Residue (NVR)
10.6.1 Measuring NVR online, as described by ASTM D5544, provides an additional, operational, water-quality
parameter. For example, measuring NVR can provide a clear indication of silica (dissolved and colloidal)
breakthrough in ion-exchange beds at a level not detectable by on-line silica analyzers (see § 10.9). ITRS studies
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indicated that colloidal silica may adsorb metals and act as a transport mechanism for metals. The online
measurement of NVR has shown that a change in water quality of as little as 20 ppt of NVR is significant. However,
interference from non-critical organics has been observed. Most current semiconductor UPW systems operate at
<100ppt of NVR. Given the current limitations for both particle measurement and monitoring high-boiling point
organics the measurement of NVR serves as a usual indicator of a stable UPW system. Each semiconductor facility
should evaluate its own need for NVR testing and target values based on existing experience with UPW systems.
10.7 Particles
10.7.1 The ability to measure particles online is a critical parameter for semiconductor manufacturing. Particles can
cause any of the following problems:
 Blocked vias, resulting in chemical damage and epitaxial defects.
 Deposits on the wafer when the pH is low (<3) because particles can overcome the electrokinetic layer around the
wafer.
 Significant damage during the etching process when the thickness of the semiconductor layer is a few Angstroms
(1 Å = 0.1 nm).
 Deposits on wafers caused when residual liquid layers evaporate in the wafer-drying process and deposit any
particles they contain.
10.7.2 Particle metrology has not kept pace with the decreasing line width of semiconductor manufacturing. Current
line widths require the ability to monitor 20 nm particles. However, existing optical particle counters (OPCs) are
only capable of detecting 50 nm particles with a counting efficiency of <5%, and a background count (noise level)
of less than 100 particles per liter (the noise level has been confirmed with leading OPC suppliers). Particle counting
statistics become important as count levels approach the noise level, therefore the OPC setup and performance must
be optimized. The particle value listed in Table 1 of this document considers data averaging over a period of one
hour. Particle levels must consistently be at or near the noise level of any OPC (regardless of any specified level).
10.8 Bacteria
10.8.1 Bacteria can cause the same types of defects as other particles. Bacteria are particularly important during
start up and commissioning, commonly as a result of contamination from newly installed parts. Bacteria cannot be
detected by OPCs because they have a similar refractive index to water. The ASTM F1094 is a reliable, costeffective, and representative method of bacteria detection. Its limitations include long bacteria cultivation time and
possible sample contamination.
10.8.2 ASTM Test Method F1094 provides for running cultures (in triplicate) by concentrating samples on
acceptable filters; sample sizes are 0.1 and 1 liter or larger. Total count of the media is conducted after incubation.
Incubation temperature ranges from 25°C to 28°C and incubation time ranges from 48 hours to 7 days; choice of
both parameters depend on the within-company specifications. The common industry standard is 28 ± 2°C for 48
hours.
10.8.3 Two different sizes (1 and 0.1 liters) of the sample are recommended to address the concern of sample
contamination.
NOTE 4: Only one type of the sample (0.1L or 1 L) is required. Two different volumes are recommended to be used for the
bacteria analyses, as they can help to reconfirm whether contamination (if identified) is related to the UPW or sample
contamination.
10.8.4 The recommended sampling is minimum in triplicates for each set of analyses at the given sample volume
(five samples are recommended for new system commissioning).
10.8.5 It is accepted that if a majority of the samples is non-detect, the result is considered to meet the spec
requirement. The positively detected bacteria in some samples will be viewed as sample contamination during
sampling.
10.9 Silica
10.9.1 Incoming city or raw water is the main source of silica in UPW. Silica may also dissolve from the wafer
surfaces and then be deposited back on the wafers, causing water spotting. Silica is detected by measuring either
reactive silica or total silica. Reactive silica (also known as dissolved silica) is a frequently used online UPW
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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operational parameter. Total silica (dissolved plus colloidal) is an offline measurement. Silica and boron are the first
two anions to break through a mixed bed. Therefore silica is an indicator of anion exchange resin removal efficiency.
If the chemistry within an ion exchange is ideal, reactive silica may transform into colloidal silica, and become a
source of colloidal silica particles. Colloidal silica can also affect the wafer by scavenging metal ions (much like ion
exchange). The specification values for both total and reactive silica are provided at the limit of detection, indicating
that no detectable silica is recommended. Both levels, reactive and total silica, are used to indicate that colloidal
silica is not present.
10.9.2 Typical limits of dissolved silica detection for commercially available instruments are around 0.1 ppb.
Similar levels can be achieved using grab sample analysis.
10.9.3 Reactive Silica is commonly measured by Heteropoly Blue Photometry either online using ASTM D7126 or
by pre-concentrating grab samples using ASTM D859. Total silica is measured by HR-ICP-MS, graphite furnace
atomic absorption spectroscopy (GFAAS) ASTM D4517, or pre-concentration inductively coupled argon plasma
optical emission spectroscopy (ICP-OES).
10.9.4 Colloidal silica is measured indirectly, subtracting reactive silica from total silica. Although a large
percentage of UPW particles may be colloidal silica, detection limits for total silica are too high to be useful as a
substitute method of detecting colloidal silica particles. The measurement of NVR can provide an on-line indication
of the present of colloidal silica. However, the current technology for the measurement of NVR can not discriminate
between the various sources of non-volatile residue.
10.10 Ions and Metals
10.10.1 Metal ions have a significant effect on semiconductor yield for the following reasons:
 Alkali metals can cause the breakdown of dielectrics.
 Transition and heavy metals can lead to crystal defects, minority carrier lifetime issues, and even to surface
sputtering around metal particles.
 Transition metals can impact the p-n-junction.
 Silicide-forming metals can cause dielectric breakdown.
10.10.2 Metals cause gate oxide breakdown and changes in the substrate resistivity.
10.10.3 Metals are removed from the wafer by mechanisms such as the etching of the underlying layer, or the
replacement with H+ ions on the surface at low pH.
10.10.4 Anions can influence metal adsorption behavior.
10.10.5 The ITRS has chosen a methodology similar to a failure mode-and-effect analysis (FMEA) to determine the
acceptable concentration of metals and ions in wafer-cleaning solutions and rinse water. A risk priority number
(RPN) is calculated as a product of the four weighted risk factors for contaminants with values above a critical limit.
Acceptable concentrations are listed in the critical ion lists per chemical and UPW. A lower, permissible, maximum
concentration is also specified. The complete FMEA table can be found in supplementary materials of UPW ITRS.
10.10.6 The following risk factors have been defined as important for the successful manufacturing of
semiconductors:
 Device Impact Factor — Characterizes the severity of the impact on device performance, device reliability or
yield or both, when a specific contaminant is deposited on the wafer surface.
 Occurrence Risk Factor — Characterizes the probability that a specific contaminant occurs in the chemical or
UPW in concentrations that could affect devices on the wafer.
 Deposition Risk Factor — Characterizes the probability that a specific contaminant does deposit on the wafer,
calculated either by a deposition model (diffusion or Pourbaix), or determined in experiments at pH of 7 or both.
 Non-detection Risk Factor — Characterizes the probability that a specific contaminant is not detected either in the
chemical, UPW, or on the wafer.
10.11 Analytical Detection Limits
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10.11.1 Analytical limits of detection must be considered when setting specifications because the specifications
should not be lower than those which can be accurately measured.
10.11.1.1 Detection limits fall into one of the three following categories:
 Instrument Detection Limits (IDLs) — IDLs are statistically based on multiple analytical runs and calculated from
instrument noise or background equivalent concentrations under optimum conditions. Impacts from sampling and
bottle variation are not taken into account. Therefore specifications should not be set to IDLs.
 Method Detection Limits (MDLs) — SEMI C10-0299 defines MDL as “the level at which errors in the
measurement method become large enough such that the preset maximum acceptable risk of seeing the quantified
level, when none of the contaminant in question is present in the sample, is exceeded.” False positives, but not
false negatives, are a concern. MDLs are statistically based and include variations from sampling, bottles, matrix
effects, and sample preparation.
 Reporting Limits (RLs) — RLs are generally set above the MDLs. When possible, as in the case of ions, total
silica, and metals, they are verified by spiking with known concentrations of the analytes of interest to eliminate
false negatives. RLs are set to be achievable on a regular basis in a production analytical environment.
NOTE 5: Overall, RLs > MDLs > IDLs.
10.11.2 The following instrumentation is used for ICP-MS analysis of trace elements:
 Quadrupole ICP-MS (typically collision/reaction cell based), with samples analyzed as received. This is the least
expensive method, but it has the highest MDLs.
 High-resolution ICP-MS, with samples analyzed as received, or with some matrix modification. The
instrumentation is more expensive than quadrupole ICP-MS, but spectral interferences are reduced and MDLs are
lower overall.
 Quadrupole ICP-MS with sample pre-concentration. This has a higher cost and longer turnaround time than the
previous instrumentation, but MDLs and RLs are lower than the ICP-MS methods without pre-concentration.
Not all 2010 ITRS specifications for critical elements can be met by sample analysis without pre-concentration.
All 2010 ITRS critical element specifications are at, or above, the RLs for quadrupole ICP-MS with preconcentration. The pre-concentration method was used for reference of the reporting limits provided in Table 1.
Pressure Stability (+/- 0.3 bar or +/- 4.4 PSIG).
10.12 This guide offers a pressure stability requirement for UPW system design. It is defined as a range of the
pressure deviation from the facility/tool specified pressure target. This is to ensure that the design and operation of
the UPW delivery system to the manufacturing tools is capable of maintaining the pressure within the specified
range.
10.12.1 The pressure is measured with an on-line sensor installed at the point of connection (POC) at required
critical tools.
10.12.2 The Absolute pressure values will be determined by specific tool requirements or site facilities specs.
10.12.3 UPW using tools are becoming increasing sensitive to the actual delivery pressure and variations of the
delivery pressure. Specifically manufacturing tools that have, but are not limited to:
•
Critical timed UPW bath fills.
•
Sensitive UPW spraying operations that require consistent and stable pressures and flows.
•
Exact chemical dilution procedures utilizing UPW line pressure.
10.12.4 Fluctuations in UPW delivery pressures to the tool POC (even minor) are capable of causing differences in
process recipes that will and can reflect an out of control quality indicator.
10.12.5 Due to the increasing size and complexity of modern UPW delivery piping systems, there is frequent risk of
having measurable delivery pressure differentials/variations between different POC locations throughout the Fab
that have a propensity to cause UPW using tools to perform differently. Stable and reliable UPW pressure is a key
variable that is easy and important to minimize to ensure improved and consistent quality.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
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NOTICE: Semiconductor Equipment and Materials International (SEMI) makes no warranties or representations as
to the suitability of the Standards and Safety Guidelines set forth herein for any particular application. The
determination of the suitability of the Standard or Safety Guideline is solely the responsibility of the user. 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. Standards and Safety Guidelines are subject to change
without notice.
By publication of this Standard or Safety Guideline, SEMI takes no position respecting the validity of any patent
rights or copyrights asserted in connection with any items mentioned in this Standard or Safety Guideline. Users of
this Standard or Safety Guideline are expressly advised that determination of any such patent rights or copyrights,
and the risk of infringement of such rights are entirely their own responsibility.
Copyright by SEMI® (Semiconductor Equipment and
Materials International), 3081 Zanker Road, San Jose, CA
95134. Reproduction of the contents in whole or in part is
forbidden without express written consent of SEMI.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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