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SEMI C55-1104 © SEMI 2004 2 7 Physical Constants 7.1 The phys ical constants of ca rbon dioxide are given in Table 2 (for infor mation only). Table 2 Phy sical Constants (for information on ly) Metric Units US Units Mole…

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1 SEMI C55-1104 © SEMI 2004
SEMI C55-1104
SPECIFICATION FOR LIQUID CARBON DIOXIDE (CO
2
) USED IN NEAR
CRITICAL, CRITICAL AND SUPERCRITICAL APPLICATIONS, ≥ 99.99%
QUALITY
This specification was technically approved by the Global Gases Committee and is the direct responsibility of
the North American Gases Committee. Current edition approved by the North American Regional Standards
Committee on July 11, 2004. Initially available at www.semi.org September 2004; to be published
November 2004.
1 Purpose
1.1 The purpose of this document is to provide a
specification for liquid carbon dioxide (CO
2
) that is
used in near critical, critical and supercritical
applications in the semiconductor industry.
2 Scope
2.1 This document provides purity requirements for all
grades of liquid carbon dioxide that are used in near
critical, critical and supercritical applications in the
semiconductor industry.
2.2 If analytical methods are not complete, the
requirements are presented as a guideline.
NOTE 1: Minimum purity requirements. Some applications
may require higher purity.
NOTICE: 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 and health practices and to determine
the applicability of regulatory or other limitations prior
to use.
3 Description/Definition
3.1 Carbon dioxide is a non-flammable, colorless,
odorless compound that is stable at ambient conditions
(25
o
C, 1 bar). Supercritical carbon dioxide exists at a
temperature and pressure that exceeds the critical point
of carbon dioxide. Near critical carbon dioxide exists
in the liquid phase at a pressure that meets or exceeds
the critical pressure and a temperature that is below its
critical temperature but above a reduced temperature
(absolute temperature divided by absolute critical
temperature) of approximately 0.75.
4 Terminology
4.1 None.
5 Specifications
Table 1 Quality: ≥99.99%
Impurities Maximum Acceptable Level
Water 20 ppmv
Total Hydrocarbons
expressed as Methane (THC)
50 ppmv
Particles
#1
Soluble and Insoluble
Compounds Containing
Metals (Na, Fe, Ni, Cu, Cr,
Co, Ca, Mn, W, Mo) (each)
0.1 ppmw
#1: To be determined between supplier and user.
6 Referenced Standards
6.1 SEMI Standards
SEMI C10 — Guide for Determination of Method
Detection Limits
SEMI C15 — Test Method for ppm and ppb Humidity
Standards
SEMI F33 — Method for Calibration of Atmospheric
Pressure Ionization Mass Spectrometer (APIMS)
6.2 ASTM Standard
1
E 1747-95(2000) — Guide for Purity of Carbon
Dioxide Used in Supercritical Fluid Applications
NOTICE: Unless otherwise indicated, all documents
cited shall be the latest published versions.
1 American Society for Testing and Materials International, 100 Barr
Harbor Drive, West Conshohocken, Pennsylvania 19428-2959, USA.
Telephone: 610.832.9585, Fax: 610.832.9555, Website:
www.astm.org.
SEMI C55-1104 © SEMI 2004 2
7 Physical Constants
7.1 The physical constants of carbon dioxide are given
in Table 2 (for information only).
Table 2 Physical Constants (for information only)
Metric Units US Units
Molecular Weight 44.01 44.01
Sublimation Point at 1
atm (14.7 psia)
-78.5
o
C -109.3
o
F
Triple Point Temperature -56.6
o
C -69.9
o
F
Triple Point Pressure 5.1 atm 75.1 psia
Critical Temperature 31
o
C 87.8
o
F
Minimum Near Critical
Temperature
-45.0
o
C -49.1
o
F
Critical Pressure 73 atm 1070 psia
Density of gas at 21.1
o
C
(70
o
F) and 1 atm
1.823 kg/m
3
0.1138 lb/ft
3
Density of Saturated
Liquid at 25
o
C
713 kg/m
3
44.5 lb/ft
3
8 Analytical Procedures
8.1 Water — This procedure is for the determination of
trace moisture (water) in carbon dioxide using an
analyzer, such as a continuous flowing phosphorus
pentoxide hygrometer.
8.1.1 Detection Limit — 100 ppbv or better
8.1.2 Instrument Parameters
8.1.2.1 Flow Requirements — Use appropriate flow, as
recommended by manufacturer.
8.1.3 Calibration Standard — The analyzer shall be
calibrated by reference to a standard gas calibration
mixture containing a moisture content close to the
expected value of the gas under test, in accordance with
the instrument manufacturer’s instructions. This
calibration standard may be prepared using the
procedure described in SEMI F33, Sections 13.2.2 and
13.2.3 and tested using the procedure described in
SEMI C15.
8.1.4 Sample System
8.1.4.1 The sample line and associated valves must be
clean and moisture free. They must be constructed
from high cleanliness materials, such as electropolished
stainless steel. The sample line should be purged dry if
exposed to ambient moisture. The baseline moisture
level should be less than 0.1 ppm.
8.1.4.2 Draw a continuous liquid sample from the
source. The sample line should be insulated so that the
sample does not boil due to heat infiltration. The
distance between the sample point and the analyzer
should be as small as possible to minimize boil-off.
8.1.4.3 Heat the sample so that it is completely
vaporized, leaving absolutely no liquid or solid carbon
dioxide or water residue.
8.1.4.4 Maintain the sample temperature at the
analyzer inlet above its condensation point. A sample
temperature of 40
o
C is recommended.
8.1.4.5 Figure 1 illustrates one potential sampling
configuration.
FROM
LIQUID
CO2
SYSTEM
VENT
VENT
HEATED
TUBING
THERMOCOUPLE
FORWARD
PRESSURE
REGULATOR
PRESSURE
GAGE
THC
DETECTOR
MOISTURE
A
NALYZE
R
Figure 1
Potential Hydrocarbon and Water Sampling System
3 SEMI C55-1104 © SEMI 2004
8.1.5 Operating Procedure
8.1.5.1 Follow the procedures specified in the
instrument manufacturer’s manual.
8.1.5.2 Allow the system to run until a stable reading is
obtained for 20 minutes.
8.1.5.3 Read and record the concentration of moisture
indicated on the moisture analyzer, in ppmv. The result
obtained shall not exceed the value specified in Section
5 of this specification.
8.2 Total Hydrocarbons — This procedure is for the
determination of total hydrocarbons expressed as
methane in carbon dioxide using a total hydrocarbon
analyzer.
8.2.1 Detection Limit — 100 ppbv or better.
8.2.2 Instrument Parameters
8.2.2.1 Flow Requirements — Use appropriate flow, as
recommended by manufacturer.
8.2.3 Calibration Standard — 1 ppmv methane in
nitrogen.
8.2.4 Sampling System
8.2.4.1 The sample line and associated valves must be
clean and hydrocarbon free. They must be constructed
from high cleanliness materials, such as electropolished
stainless steel. The sample line should be cleaned if
exposed to hydrocarbons, such as oils or greases.
8.2.4.2 Draw a continuous liquid sample from the
source. The sample line should be insulated so that the
sample does not boil due to heat infiltration. The
distance between the sample point and the analyzer
should be as small as possible to minimize boil-off.
8.2.4.3 Heat the sample so that it is completely
vaporized, leaving absolutely no liquid or solid carbon
dioxide or water residue. Note that if detection of
heavy hydrocarbons (>C10) is important, it may not be
feasible to completely vaporize the sample. Therefore,
a concentrator method, such as that described in ASTM
E 1747, Section 6, may be required.
8.2.4.4 Maintain the sample temperature at the
analyzer inlet above its condensation point. A sample
temperature of 40
o
C is recommended.
8.2.4.5 Figure 1 illustrates one potential sampling
configuration.
8.2.5 Operating Procedure
8.2.5.1 Follow the procedures specified in the
instrument manufacturer’s manual.
8.2.5.2 Allow the system to run until a stable reading is
obtained for 20 minutes.
8.2.5.3 Read and record the concentration of
hydrocarbons as methane indicated on the total
hydrocarbon analyzer, in ppmv. The result obtained
shall not exceed the value specified in Section 5 of this
specification.
8.3 Metals — This procedure is for the determination
of insoluble and soluble metals in carbon dioxide using
inductively coupled plasma-mass spectroscopy (ICP-
MS), ICP-AES. Specific components to be monitored
are Na, Fe, Ni, Cu, Cr, Co, Mn, Ca, Mo and W.
NOTE 2: The specified method does not detect volatile
metals.
8.3.1 Detection Limit — Determined per SEMI C10.
8.3.2 Instrument Parameters
8.3.3 Calibration Standards — Consult with
instrument manufacturer instructions. All instrument
calibration standards should be prepared from NIST-
traceable reference standards.
8.3.4 Sampling System
8.3.4.1 Two sample preparation methods are approved
for metals analysis. These are a residue method and a
filtration method. The user may select between these
techniques based on convenience, economic
considerations, or other situation specific conditions.
8.3.4.1.1 Residue Method — A CO
2
sample is
transferred to an ambient pressure vessel and allowed to
sublime. The remaining metal residue is dissolved in
nitric acid.
8.3.4.1.1.1 The sample line and associated valves must
be clean and metal particle free. They must be
constructed from high cleanliness materials, such as
electropolished stainless steel.
8.3.4.1.1.2 The sample system must be purged with
high-purity nitrogen prior to and after sampling. Prior
to sampling, the entire sampling system should be
purged by allowing high purity nitrogen to flow through
the system at 5–10 psig for a minimum of three
minutes.
8.3.4.1.1.3 When the purge is complete, draw a
sufficient mass of liquid carbon dioxide sample from
the source to obtain a meaningful metals level. A valve
should be installed in the sample line to flash the liquid
sample from the operating pressure to near ambient
pressure. This will cause the sample to form a
solid/vapor mixture. This mixture should then be
directed to the bottom of a vented sample flask. The
sample flask should have a volume of 100 ml and
should be composed of polypropylene or other suitable
materials. It should be cleaned prior to use using DI
water.