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SEMI F68-1101 © SEMI 2001 2 5.1.13 ppm — parts per million, volume basis 5.1.14 psi — pounds p er squa re inc h 5.1.15 psia — pounds per square inch absolute 5.1.16 psig — pounds p er sq uare inc h gauge 5.1.17 R a — su …
SEMI F68-1101 © SEMI 20011
SEMI F68-1101
TEST METHOD FOR DETERMINING PURIFIER EFFICIENCY
This test method 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 27, 2001. Initially available at www.semi.org September 2001; to be
published November 2001.
1 Purpose
1.1 The purpose of this document is to define a test
method to quantify the efficiency of a purifier for
removal of an active gaseous impurity from a matrix
gas.
2 Scope
2.1 To determine the efficiency of a gas purifier to
remove a given impurity species. Efficiency tests are
performed by adding ppm levels of gaseous impurities
to a pure matrix gas and monitoring the effluent of the
test purifier for active impurity species. Tests are done
at supplier recommended flow rate, operating
temperature and pressure.
2.2 To establish a method of determining instantaneous
purifier efficiency.
2.3 The test method applies to point of use (POU) and
large scale purifiers.
2.4 This method is for UHP efficient removal of low
level contaminants.
2.5 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 and safety health practices and determine
the applicability of regulatory limitations prior to use.
3 Limitations
3.1 The inherent limitation to this method is the limit
of detection (LOD) of the analytical instrument
employed by the user.
3.2 This test method can only be used to compare
purifier efficiency results if the user application for
flow rate, pressure, and temperature are the same as the
test conditions. Different user and/or different
operating conditions may result in different purifier
performance results.
3.3 In testing mixtures of impurities, some impurities
may influence the efficiency results of other impurities.
Discussion with the manufacturer is highly
recommended prior to testing.
3.4 The test method does not apply to particulates.
3.5 This test method will provide efficiency
information only for impurities that are used in the
challenge gas.
4 Referenced Standards
4.1 SEMI Standards
SEMI E29 — Standard Terminology for the Calibration
of Mass Flow Controllers and Mass Flow Meters
SEMI F6 — Guide for Secondary Containment of
Hazardous Gas Piping Systems
SEMI F22 — Guide for Gas Distribution Systems
SEMI F33 — Method for Calibration of Atmospheric
Pressure Ionization Mass Spectrometer (APIMS)
4.2 ANSI Standards
1
ANSI B46.1 — Surface Texture (Surface Roughness,
Waviness, and Lay)
NOTE 1: Unless otherwise indicated, all documents cited
shall be the latest published versions.
5 Terminology
5.1 Abbreviations and Acronyms
5.1.1 APIMS — atmospheric pressure ionization mass
spectrometer
5.1.2 °C — degrees Celsius
5.1.3 DUT — device under test
5.1.4 °F — degrees Fahrenheit
5.1.5 in — inch
5.1.6 kPa — kiloPascal
5.1.7 LOD — limit of detection
5.1.8 m — meter
5.1.9 MFC — mass flow controller
5.1.10 NMHC — non methane hydrocarbons
5.1.11 POU — point of use
5.1.12 ppb — parts per billion, volume basis
1 American National Standards Institute, New York Office: 11 West
42nd Street, New York, NY 10036, USA. Telephone: 212.642.4900;
Fax: 212.398.0023 Website: www.ansi.org
SEMI F68-1101 © SEMI 2001 2
5.1.13 ppm — parts per million, volume basis
5.1.14 psi — pounds per square inch
5.1.15 psia — pounds per square inch absolute
5.1.16 psig — pounds per square inch gauge
5.1.17 R
a
— surface roughness average (as defined in
ANSI B46.1)
5.1.18 R
a,max
— surface roughness maximum (as
defined in ANSI B46.1)
5.1.19 s — second
5.1.20 sccm — standard cubic centimeters per minute
5.1.21 slpm — standard liters per minute
5.1.22 UHP — ultra high purity
5.2 Definitions
5.2.1 activation — the process of initially preparing the
purifier media to be chemically reactive with gas
impurities.
5.2.2 activation temperature — temperature at which
DUT was initially prepared.
5.2.3 atmospheric pressure ionization mass
spectrometer (APIMS) — an instrument consisting of
an atmospheric pressure ion source where gas phase
impurities are ionized via charge exchange reactions
with the bulk gas. These ions are directed into a
vacuum chamber where they are then separated by a
mass analyzer and detected by an electron multiplier.
5.2.3.1 ion source — the section of a mass
spectrometer used to generate sample ions by electron
impact, chemical ionization, or charge exchange.
5.2.3.2 mass analyzer — a device that utilizes electric
and/or magnetic fields to separate charged particles or
ions according to their mass-to-charge (m/e) ratios.
Examples of mass analyzers include quadrupole,
magnetic and/or electric sector, time of flight, and ion
traps.
5.2.3.3 electron multiplier — a device that detects and
amplifies electro-magnetic phenomena such as
positive/negative ions.
5.2.4 back pressure regulator — a self-contained
device, consisting of a mechanical or electrical sensor
and control device, commonly used in the
semiconductor industry to maintain a constant pressure
upstream of the regulator.
5.2.5 breakthrough — the point in time when an
individual impurity level in the purifier effluent exceeds
the level specified by the manufacturer. Typically in
the range of 1–100 ppb.
5.2.6 challenge gas — a gas mixture containing high
levels of gas impurities. Typically, a challenge gas has
impurities of between 500 ppm to 1% which is used to
shorten the test duration; however, challenges in the
range of 1–10 ppm for the impurities is more
representative.
5.2.7 efficiency — a measure of the ability of a purifier
to remove active impurities from a matrix gas stream.
It is calculated as the ratio of the difference between the
inlet concentration and the concentration of impurity
leaving the purifier to the concentration of impurity
entering the purifier.
5.2.8 gaseous impurities — gas phase elements and
compounds in the gas stream other than the process or
base gas.
5.2.9 impurity analyzer — an appropriate analyzer to
measure the concentration of desired impurities in a gas
stream from the ppm to the percent (%) concentration
range.
5.2.10 inert gas — a gas, which at ambient conditions,
does not react chemically with other materials or
chemicals.
5.2.11 limit of detection (LOD) — lowest concentration
that can be detected by an instrument. LOD is typically
defined as three times the standard deviation of the
mean noise level (see SEMI F6, lower detectable limit
of instrument).
5.2.12 mass flow controller (MFC) — a self-contained
device, consisting of a mass flow transducer, control
valve, and control and signal-processing electronics,
commonly used in the semiconductor industry to
measure and regulate the mass flow of gas (as defined
in SEMI E29).
5.2.13 pure gas — an inert gas, minimum purity of
99.9995%, and less than 1 ppb of each impurity that is
specified to be removed by the DUT.
5.2.14 purifier— generally a catalytic (getter, reactive),
resinous, or diatomaceous material within a pressure
vessel which removes particulate and/or trace gas
impurities from a gas stream (as defined in SEMI F22).
5.2.15 purifier capacity — the total quantity of each
trace gas impurity that may be sorbed by the purifier
media. Defined as liters impurity/liter purifier media.
5.2.16 regeneration — the process of reactivating the
purifier media.
5.2.17 test duration — total time required to complete
the test procedure.
5.2.18 test flow rate — flow rate through DUT (slpm).
SEMI F68-1101 © SEMI 20013
5.2.19 test pressure — pressure immediately upstream
of the DUT.
5.2.20 test temperature — operating temperature of
DUT.
5.2.21 ultratrace analytical instrumentation —
instrumentation that has sufficient sensitivity to
measure all impurities of interest at the specified level
of the customer, the ppb or sub-ppb level.
5.2.22 zero gas — nitrogen, argon, helium or hydrogen
with an estimated level an order of magnitude, or more,
lower than the lowest calibration point for each
impurity of interest (as defined in SEMI F33).
6 Summary of Method
6.1 This method will allow a user to quantify the
impurity efficiency of a point-of-use (POU) or large
scale purifier.
7 Safety Precautions
7.1 This test method may involve hazardous materials,
operations, and equipment. The test method does not
purport to address the safety considerations associated
with its use. It is the responsibility of the user to
establish appropriate safety and health practices and
determine the applicability of regulatory limitations
before using this method.
7.2 Exhaust from the DUT should be properly vented.
7.3 Only the appropriate gas should be used for purifier
testing. Use of inappropriate gases may cause
exothermic reactions and possible explosions.
7.4 Electric discharges or mechanical friction might
trigger combustion within a getter. Avoid situations
where there is an accumulation of electrostatic charge.
7.5 Purifiers are generally designed for use with
impurity levels less than 1% and should not be used to
purify air or other inappropriate gases. Contact the
manufacturer if there is any question as to the
suitability for a particular gas.
7.6 Care should be taken to minimize the purifier’s
exposure to room air (even filtered air). Room air may
chemically react with some purifiers shortening the
purifier lifetime. Follow manufacturer’s installation
procedures.
8 Test Protocol
8.1 Test Conditions
8.1.1 The test should be conducted following
manufacturer’s recommended handling procedures to
activate new media or regenerate existing purifier
media.
8.1.2 The test is to be conducted at a room temperature
maintained between 18°C (64°F) and 26°C (78°F).
Environmental temperature fluctuations within this
range are not expected to have any measurable effect on
the instrumentation used to detect the level of
impurities. Follow instrument manufacturer’s operating
procedures.
8.2 Apparatus
8.2.1 Materials
8.2.1.1 Test Gas — a mixture of pure gas and
challenge gas. The mixture should contain gaseous
impurities of between 1 ppm and 10 ppm.
8.2.1.2 Pressure Regulators — all wetted internal
surfaces, where appropriate, should be made of
electropolished 316L stainless steel with an internal
surface finish of 0.18 µ m (7 µ in) R
a
and 0.25 µ m (10
µ in) R
a,max
, to control system pressures.
8.2.1.3 Pressure Gauge — all wetted internal surfaces,
where appropriate, should be made of electropolished
316L stainless steel with an internal surface finish of
0.18 µ m (7 µ in) R
a
and 0.25 µ m (10 µ in) R
a,max
, to
monitor system pressures.
8.2.1.4 Standard Test Flows — use appropriate mass
flow devices. One MFC with appropriate range of 0–50
slpm for the pure gas is suggested. Various MFCs with
appropriate ranges of 0–25 sccm, 0–100 sccm and 0–1
slpm for the challenge gas are suggested.
8.2.1.5 Tubing — made of electropolished 316L
stainless steel, with an internal surface finish of 0.18
µ m (7 µ in) R
a
and 0.25 µ m (10 µ in) R
a,max
, to transport
gas.
8.2.1.6 Fittings — the appropriate size face-seal fitting
is used.
8.2.1.7 Gaskets — use metal gaskets for all
connections. New gaskets should be used for each new
connection. Use of cleanroom gloves is required when
handling gaskets and fittings.
8.2.2 Instrumentation
8.2.2.1 An APIMS or other ultratrace analytical
instrumentation is used to determine the level of each
gaseous impurity exiting the DUT.
8.2.2.2 An impurity analyzer is used to measure higher
concentrations of impurities such as found in the test
gas.
8.2.2.3 Electronically controlled mass flow controllers
are used to accurately blend the impurity challenge
level.