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SEMI F48-0600 © SEMI 2000 3 8 Apparatu s 8.1 Mu ffle Furnace With te mpe r a t ure control ranging up t o a minim u m of 700°C and equipped w ith a means to regulate air circulation. 8.2 Microw ave M uffle Furnace 8.3 …
SEMI F48-0600 © SEMI 2000 2
3.2 This procedure anticipates analysis levels in the
ppm (mass/mass) range. Impurities less than 0.1 ppm
may not be detected by this method.
3.3 When extending the method to other elements
recovery should be evaluated during validation. Poor
recovery rates are often found for volatile elements
such as boron (B), arsenic (As), antimony (Sb),
mercury (Hg), gold (Au), and tungsten (W) because of
the relatively high temperature sample preparation
method and poor stability of some elements in aqueous
solution. Elements forming volatile halogenides can be
affected due to the in-situ production of hydrogen
halogenides when halogenated polymers are ashed.
3.4 This is a bulk analysis technique. For leachable
testing or surface analysis refer to the Related
Documents (Section 16) of this method.
3.5 Due to the rapid advances in digestion technology,
consult the manufacturer’s recommended instructions
for guidance when conducting analyses using the DCV
sections of this document.
3.6 DCV techniques can generate gaseous digestion
reaction products, very reactive, or volatile materials at
high pressures. Spontaneous venting which can occur
during sample heating may cause venting of the vessels
with potential loss of sample and analytes. Sample
sizes greater than 0.25 g may accentuate this event.
3.7 In the use of the DCV technique, TiO2, alumina,
and other oxides may not be totally dissolved.
Sequestering of target analyte elements may occur.
3.8 Although this method allows the sampling of small
pieces of polymer that are mechnically removed from a
larger item, obtaining such samples in a clean manner
may be difficult. Multiple sampling, separation and
preparation techniques might be necessary to establish
confidence in the results.
3.9 This document is not intended to supersede
international, national or local codes, regulations, and
laws. Each should be consulted to ensure that the
method meets regulatory requirements in each location.
4 Referenced Standards
4.1 SEMI Standard
SEMI F40 –– Practice for Preparing Liquid Chemical
Distribution Components for Chemical Testing
4.2 ASTM Standard
1
ASTM D4375 –– Standard Practice for Basic
Definitions, Notation, and Symbology for Statistics in
Committee D19 on Water
1 American Society for Testing and Materials, 1916 Race St.,
Philadelphia, PA 19103
NOTE 1: As listed or revised, all documents cited shall be the
latest publications of adopted standards.
5 Terminology
5.1 Acronyms and Abbreviations
5.1.1 AAS/GFAAS — atomic absorption spectroscopy/
graphite furnace atomic absorption spectroscopy
5.1.2 amu — atomic mass unit
5.1.3 DCV digestion in closed vessel
5.1.4 DDA digestion by dry ashing
5.1.5 GFAAS — graphite furnace atomic absorption
spectroscopy
5.1.6 ICP–AES — inductively coupled plasma–atomic
emission spectroscopy
5.1.7 ICP–MS — inductively coupled plasma–mass
spectrometry
5.1.8 ppb — parts per billion by mass (ng/g)
5.1.9 ppm — parts per million by mass (µg/g)
5.1.10 UPW — ultrapure water (see Section 9.4)
6 Summary of Test Method
6.1 Samples previously prepared using SEMI F40 are
ashed or digested under pressure within a digestion
device, and trace inorganics in the residue are dissolved
into acid and UPW. The sample is then analyzed by
ICP–MS, GFAAS, and/or ICP–AES to determine the
inorganic content of the material. This method applies
only to nonvolatile metals (i.e., alkali metals, alkaline
earths, and transition metals).
6.2 Data from different tests can be compared to
determine the inorganic content in different materials
and in the same material from different manufacturers.
7 Significance and Use
7.1 Determining the metallic contamination
concentration in bulk polymer materials used in either
distribution systems for process fluids or products in
direct contact with the wafer is important criterion for
deciding the suitability of a material. For example,
ultrapure water contaminated by distribution system
components may adversely affect microelectronic and
other processes.
7.2 This method measures the total amount of
impurities in the bulk of the material. These impurities
will not necessarily leach into a process fluid stream.
SEMI F48-0600 © SEMI 20003
8 Apparatus
8.1 Muffle Furnace With temperature control
ranging up to a minimum of 700°C and equipped with a
means to regulate air circulation.
8.2 Microwave Muffle Furnace
8.3 Crucibles Made of either platinum or quartz
and with a 30 mL capacity.
8.4 ICP–MS
8.5 GFAAS
8.6 ICP–AES Either simultaneous or sequential
reading type.
8.7 Chemical Fume Hood
8.8 Propane Torch or Appropriate Heating Source
with a minimum temperature of 650°C.
8.9 Device for digestions under a pressure of at least
30 bar (435 psi), with temperature control. This can be
a laboratory microwave-based system or a system based
on other heating sources.
8.9.1 In the case of microwave digestion devices:
Laboratory microwave digestion systems should be
used that possess appropriate temperature control of
chemical reactions. Closed microwave systems must
have controlled pressure relief.
8.9.2 Digestion vessels of appropriate internal volume
should be used and construction should be of
appropriate chemically inert materials. If the vessel is
pressurized, it should be capable of withstanding a
minimum pressure of 30 atm (30 bar or 435 psi), with
controlled pressure relief of reagents and digestion
products.
NOTE 2: Only microwave manufacturer’s approved vessels
for that device should be used.
8.9.3 In case of a laboratory microwave digestion
device: Oscillating turntable to insure homogeneous
distribution of microwave radiation to all vessels.
8.9.4 Filter paper, qualitative or equivalent.
8.9.5 Filter funnel, polypropylene, polyethylene or
equivalent.
8.10 Volumetric flasks, 20 mL or 50 mL capacity or
equivalent.
8.11 Analytical balance, of appropriate capacity, with
a ± 0.0001 g or appropriate precision for the weighing
of the sample. Optionally, the vessel with sample and
reagents may be weighed, with an appropriate precision
balance, before and after microwave processing to
evaluate the seal integrity in some vessel types.
9 Materials
9.1 Argon Gas 99.99% pure or better.
9.2 Standards and Reference Materials
9.2.1 For preparation of multi-element standard
solutions, use NIST
2
, NIST-traceable, or other
appropriate international standards as stock solutions.
9.2.2 From these stock solutions, multi-element
working standard solutions must be prepared daily by
pipeting the appropriate volumes of the trace metal
standards and diluting to the desired concentrations.
NOTE 3: Prepare these working standards using the same
amount of acid as used for the sample.
9.2.3 For validation purposes, use appropriate
international reference materials that match the sample
matrix as close as possible.
9.3 All reagents should be of appropriate purity or
high purity (acids for example, should be sub-boiling
distilled where possible) to minimize the blank levels
due to elemental contamination. If the purity of a
reagent is questionable, analyze the reagent to
determine the level of impurities. The reagent blank
must be less than the minimum detection limit in order
to be used.
9.3.1 Ultrapure Hydrochloric Acid less than 1 ppb for
each trace metal.
9.3.2 Ultrapure Nitric Acid less than 1 ppb for each
trace metal.
9.4 Ultrapure Water
9.4.1 For purposes of this test, references to water
shall be understood to mean ultrapure water as defined
by maximum individual metal and anion impurity
levels of 0.1 ppb or less, nonvolatile residue levels of
0.1 ppm or less, resistivity of 18 megohm-cm or
greater, and reactive silica impurity of less than 1.0 ppb.
10 Precautions
10.1 Safety Precautions
10.1.1 This test method may involve hazardous
materials, operations, and equipment. This 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 to determine the applicability of regulatory
limitations before using this method.
2 National Institute of Standards and Technology, 100 Bureau Dr.,
Gaithersburg, MD, 20899-001 USA, (301) 975-6478,
<www.nist.gov>
SEMI F48-0600 © SEMI 2000 4
10.1.2 Care must be taken in the handling and use of
the acids to avoid acid burns or contamination of the
acid. Acid should be neutralized before disposal.
10.1.3 Care must be taken when using the propane
torch to avoid burns. The torch should not be used near
flammable materials or solvents.
10.1.4 Care must be taken when using the muffle
furnace to avoid burns.
10.1.5 When ashing fluoropolymeric materials, the
ashing must be performed in a fume hood. When
heated, fluoropolymer materials outgas hydrofluoric
acid fumes and may also emit fluoropolymeric particles
which, if inhaled, can cause a condition known as
“polymer fume fever.” If hot fluoropolymer fumes are
inhaled, remove the individual to a well-ventilated area
and seek medical attention.
10.1.6 The outer layers of vessels used in the DCV
technique are frequently not as acid or reagent resistant
as the liner material. To retain the performance and
safety required these outer layers must be neither
chemically degraded nor physically damaged. Routine
examination of the vessel materials may be required to
ensure their safe use.
10.1.7 Only DCV containers with pressure relief or
control mechanisms or containers with suitably inert
polymeric or quartz liners and pressure relief
mechanisms are considered acceptable for use with this
process.
NOTE 4: Only microwave manufacturer’s approved vessels
for that device should be used.
10.1.8 Use of laboratory microwave systems is
required for this method. Users are advised not to use
domestic (kitchen) type microwave ovens or cookware.
Nor should inappropriately sealed containers without
pressure relief for microwave acid digestions be used.
See Section 16.3.1 for additional information on safety
issues concerning the use of laboratory microwave
systems.
10.1.9 Toxic nitrogen oxide(s), hydrogen fluoride, and
toxic chlorine (from the addition of hydrochloric acid)
fumes are usually produced during digestion.
Therefore, all steps involving open or the opening of
digestion vessels must be performed in a properly
operating fume ventilation system.
10.1.10 The analyst should wear appropriate
protective clothing, such as gloves and face protection,
and must not at any time permit a solution containing
hydrofluoric acid to come in contact with skin or lungs.
10.2 Technical Precautions – Digestion by Dry Ashing
(DDA)
10.2.1 Flaming and ashing temperatures must be
controlled so that they do not exceed 650°C to
minimize metal loss due to volatilization. If the
crucible becomes excessively hot for longer than about
one minute during flaming, it may have overheated.
When testing the method for recovery rates, it will
become apparent that the sample has been overheated
from the low recovery of metals.
10.2.2 One method of cleaning the crucibles and
covers is to flame them with a propane torch or other
appropriate heating source until they are sufficiently
hot, allow them to cool, rinse in dilute ultrapure nitric
acid, and then rinse in ultrapure water.
10.2.3 When ashing a sample, take care that all of the
ash residue remains in the crucible.
10.2.4 Several factors concerning selection of crucible
materials should be considered when performing the
DDA technique. For example, the crucible itself can
contribute elevated levels of its own composition into
samples at trace levels. Temperature restrictions are
another factor to consider in the selection of the
crucible material. Corrosion of the crucible during the
decomposition of the sample should also be considered.
For example, in the ashing of fluorinated materials,
platinum is preferred over quartz glass that could be
etched by the liberated hydrogen fluoride.
10.3 Technical Precautions – Digestion in Closed
Vessel (DCV)
10.3.1 Trace analysis requires a thorough cleaning.
One method of cleaning the vessels is to leach with hot
(1:1) hydrochloric acid (greater than 80 C, but less than
boiling) for a minimum of two hours followed with hot
(1:1) nitric acid (greater than 80 C, but less than
boiling) for a minimum of two hours and rinsed with
reagent water and dried in a clean environment.
10.4 Other Technical Precautions
10.4.1 When switching between high concentration
samples and low concentration samples, all crucibles or
digestion vessels should be cleaned according to the
corresponding and recommended cleaning procedure.
This cleaning procedure should also be used whenever
the prior use of the digestion vessels is unknown or
cross contamination from vessels is suspected.
10.4.2 Trace metallic levels of reagent blanks must be
significantly lower than those in the sample in order to
obtain accurate results for the analyte of interest.
10.4.3 Perform sample preparation in a clean
environment and under a fume hood to minimize
contamination.