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SEMI MF1982-1103 © SEMI 2003 3 atomic em ission detector (AED). T he nitrogen/p hosphorus t hermionic ioni zation detector (NPD) also respon ds to nitrogen containi ng compounds. NOTE 1: A nitrogen/phosphorus thermionic …

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4.1.6 MS — mass spectrometer
4.1.7 NPD — nitrogen/phosphorus thermionic
ionization detector
4.1.8 TBP — tributyl phosphate, (C
4
H
9
O)
3
PO
4.1.9 TCEP — tris (2-chloroethyl) phosphate,
(ClCH
2
CH
2
O)
3
PO
4.1.10 TD — thermal desorption
4.2 Definitions of Term Specific to This Standard
4.2.1 blank wafer — a thermally-treated wafer
desorbed of any surface organic contaminants.
4.2.1.1 Discussion — In Method A, surface organic
contaminants are desorbed with a rapid thermal
annealer or a high temperature furnace. In Method B
surface organic contaminants are desorbed by purging
them out in the heated quartz chamber unit while
helium gas is flowing as a purge gas.
5 Summary of Test Methods
5.1 Method A
5.1.1 Desorption and GC Analysis — The volatile
organic contaminants on a wafer surface are desorbed
thermally from the wafer surface in a wafer desorption
oven and swept into a sample thermal desorption tube.
The sample thermal desorption tube then is heated for a
set period in the thermal desorption unit and the volatile
organic contaminants desorbed from the sample thermal
desorption tube are swept by a stream of helium to a
cold trap where they are preconcentrated. At the end of
this period, the cold trap is heated rapidly to release the
trapped organics to the GC column head. Sample
components then are separated and eluted out of the GC
column. Then, a portion goes to a phosphorus selective
detector and the remainder goes to a mass spectrometer
(MS). Blank wafers are prepared by purging out any
surface organic contaminants in a rapid thermal
annealer or a high temperature furnace while a purge
gas is flowing.
5.1.2 Identification of Contaminants — Identification
of individual unknown compounds is performed by
correspondence of retention time of their peaks with
that of known compounds. Correspondence of reten-
tion time on a single column should not be regarded as
proof of identity. More precise identification of
individual unknown compounds is performed with MS
by matching their fragmentation patterns with mass
spectra of known compounds in the spectral library.
5.1.3 Quantification — Quantification of total organics
is based on the comparison of the integrated total peak
area of the sample peaks with the area of the external
standard compound, n-C
16
H
34
. Total organophosphorus
content in a sample is quantified by comparing the
sample signal integrated from the phosphorus selective
detector with the signal of the phosphorus standard
compound, tris (2-chloroethyl) phosphate (TCEP) or
tributyl phosphate (TBP). Specified range of standards
is measured periodically, and the result is reported with
blank wafer data.
5.2 Method B
5.2.1 Desorption and GC Analysis — The volatile
organic contaminants on a wafer surface are desorbed
thermally from the wafer surface in a quartz chamber
unit and swept into a glass TD tube. The glass TD tube
then is heated for a set period and a stream of helium
sweeps the volatile organic contaminants desorbed from
the glass TD tube to a cold trap where they are
preconcentrated. At the end of this period, the cold trap
is heated rapidly to release the trapped organics to the
GC column head. Sample components then are sepa-
rated and eluted out of the GC column. Then, a portion
goes to a phosphorus selective detector and the
remainder goes to a mass spectrometer (MS). Blank
wafers are prepared by purging out any surface organic
contaminants in the heated quartz chamber unit, while
helium gas is flowing as a purge gas.
5.2.2 Identification of Contaminants — Identification
of individual unknown compounds is performed by
correspondence of retention time of their peaks with
that of known compounds. Correspondence of
retention time on a single column should not be
regarded as a proof of identity. More precise
identification of individual unknown compounds is
performed with MS by matching their fragmentation
patterns with mass spectra of known compounds in the
spectral library.
5.2.3 Quantification — Quantification of total organics
is based on the comparison of the integrated total peak
area of the sample peaks with the area of the external
standard compound, n-C
16
H
34
. Total organophosphorus
content in a sample is quantified by comparing the
sample signal integrated from a phosphorus selective
detector with the signal of the phosphorus standard
compound, tris (2-chloroethyl) phosphate (TCEP) or
tributyl phosphate (TBP). Specified range of standards
is measured periodically, and the result is reported with
blank wafer data.
6 Apparatus
6.1 Method A
6.1.1 GC Instrument — Utilizes a capillary column to
separate a wide variety of organic compounds coupled
to a mass spectrometer (MS), or a phosphorus selective
detector, or both. Examples of phosphorus selective
detectors are flame photometric detector (FPD), and
SEMI MF1982-1103 © SEMI 2003 3
atomic emission detector (AED). The
nitrogen/phosphorus thermionic ionization detector
(NPD) also responds to nitrogen containing
compounds.
NOTE 1: A nitrogen/phosphorus thermionic ionization
detector (NPD) may also be used as a phosphorus selective
detector. This type of detector also responds to nitrogen
containing compounds. If an NPD is used, the total
organophosphorus reported should exclude any signals due to
nitrogen containing compounds. Often, identification from
the mass spectra can be used to determine whether compound
contains nitrogen or phosphorus, or both.
6.1.2 Sample Thermal Desorption Tubes — Stainless-
steel tubes packed with adsorbent medium, are used to
trap compounds of interest and release them onto a
thermal desorption unit.
NOTE 2: Note that stainless steel is catalytically active and
can corrode with time, affecting recovery for some
compounds. In this case, deactivated stainless steel, glass, or
quartz tubes also can be used. Several adsorbent materials
can be used for trapping organic compounds desorbed from
silicon wafer samples. Some examples are activated carbon,
graphitized carbon, and poly (2,6-diphenyl-p-phenylene
oxide).
6.1.3 Thermal Desorption Unit — Used to desorb
organics from sample thermal desorption tubes. The
thermal desorption unit is coupled to the GC instrument
via a heated transfer line, for example, heated to 225°C
or above.
6.1.4 Thermal Annealer — Or a high temperature
furnace used to obtain a blank wafer (see Section
7.1.1.2 ).
6.1.5 Temperature Controllable Wafer Desorption
Oven — Used to hold and heat a wafer desorption tube.
6.1.6 Wafer Desorption Tube — Stainless-steel tube
with an approximate dimension: 12.7 mm (0.5 in.) in
outer diameter, 9.53 mm (0.375 in.) in inner diameter
and 254 mm (10 in.) in length (see Figure 1), used to
desorb organics from cleaved wafers. Larger tubes may
be used for larger wafer sizes and to increase the
sensitivity of the test (see Note 2).
6.1.7 Analytical Balance
6.1.8 Quartz Plate and Carbide-Tipped Scribe — Used
to cleave wafer samples.
6.1.9 Quick Connect — Used to connect a nitrogen line
to the wafer desorption tube.
6.2 Method B
6.2.1 GC Instrument — Utilizes a capillary column to
separate a wide variety of organic compounds, coupled
to a mass spectrometer (MS) or a phosphorus selective
detector, or both. Examples of phosphorus selective
detectors are flame photometric detector (FPD), atomic
emission detector (AED), or nitrogen/phosphorus
thermionic ionization detector (NPD). The
nitrogen/phosphorus thermionic ionization detector
(NPD) also responds to nitrogen containing compounds
(see Note 1).
6.2.2 Quartz Chamber Unit — Used to desorb organic
contaminants from the wafer surface and transfer them
to a glass TD tube (see Figure 2).
6.2.3 Quartz Chamber — May be used also to purge
out any organic contaminants from a blank wafer.
6.2.4 Glass TD Tube — Packed with adsorbent
medium used to trap compounds of interest and release
them onto a cold trap. Several adsorbent materials can
be used for trapping organic compounds desorbed from
silicon wafer samples. Some examples are activated
carbon, graphitized carbon, and poly (2,6-diphenyl-p-
phenylene oxide).
6.2.5 Cold Trap — Used to concentrate organics
desorbed from glass TD tube and release the organics to
a GC instrument by rapid heating.
7 Procedure
7.1 Method A
7.1.1 Sample Handling and Preparation
7.1.1.1 At all times, avoid manual handling of samples
for analysis to prevent any secondary contamination of
samples. Use stainless steel tweezers for sample
preparation. Use a propane torch to flame stainless
steel tweezers, weigh boats, and other accessories that
come into direct contact with the sample before their
usage.
7.1.1.2 Thermally debsorb any organics from blank
wafers in a rapid thermal annealer or a high temperature
furnace. In order to desorb any organics from blank
wafers, the temperature of a rapid thermal annealer is
kept at 900°C for 15 s, or the temperature of a high
temperature furnace is kept at 700°C for 30 min.
Heating under air or oxygen will make a consistent
organic-free SiO
2
surface. Place the thermally treated
blank wafers directly into petri dishes and wrap the
dishes with organic-free aluminum foil.
7.1.2 Wafer Desorption
7.1.2.1 Clean and precondition sample thermal
desorption tubes in accordance with ASTM Practice
D 6196 prior to attaching to the wafer desorption tube.
7.1.2.2 Turn on the temperature controller for the wafer
desorption oven and wait for the temperature to reach
275°C.
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7.1.2.3 Cleave the wafer sample into strips about 5 to 7
mm wide by scribing a line on the wafer where one
wants it to break and then placing it on a straight wire
and breaking it along the scribed line. The portion of
the wafer sample needed for the analysis changes with
the size of the wafer. For a 100-mm wafer, about half
of its surface area is needed. Larger samples (having
larger surface area) may be used to increase the
sensitivity of the test.
7.1.2.4 Place the wafer strips of wafer into the wafer
desorption tube. Attach a sample thermal desorption
tube to the side of the wafer desorption tube. Connect
the other end of the wafer desorption tube to a nitrogen
line with a flow of 15 to 100 mL/min.
7.1.2.5 Place the wafer desorption tube in the oven and
heat it for 30 min at 275°C. This allows the volatile
organics to be thermally desorbed from the sample
wafer and transferred to the sample thermal desorption
tube.
7.1.2.6 Seal both ends of the sample thermal desorption
tube into the thermal desorption unit or by using caps if
the thermal desorption-GC system is automated. Tubes
must not be left open and exposed to the laboratory
atmosphere. The end caps should be made of a material
that has low outgassing and low reactivity properties,
such as poly tetrafluoroethylene (PTFE), or stainless
steel.
7.1.2.7 Analyze a blank wafer at least daily. Use a
blank wafer treated with the same desorption procedure
just described. Report blank data with the sample data.
7.1.3 GC Analysis
7.1.3.1 Place the sample thermal desorption tube,
which contains organic contaminants desorbed from the
wafer, onto the thermal desorption unit. Enter the
sample information into the computer, and start the GC
analysis.
7.1.3.2 Flow the helium carrier gas through the sample
thermal desorption tube during primary desorption.
Heat the sample thermal desorption tube and sweep out
the target organics contained in the sample to a cold
trap where they are preconcentrated. Two
recommended conditions for heating the sample
desorption tube are as follows. When graphitized
carbon is used as adsorbent material, heat the tube to
400°C and hold at 400°C for 15 min. When poly (2,6-
diphenyl-p-phenylene oxide) is used as adsorbent
material, heat the tube to 270°C and hold at 270°C for
15 min. Cold trap parameters, that is, sorbent, sold
temperature, etc., should be selected such that all target
analytes are retained quantitatively throughout the tube
desorption process, for example, using a cold trap
temperature of −30°C. Refer to ASTM Practice D 6196
for a method for testing desorption efficiency and
analyte recovery. At the end of this period, heat the
cold trap rapidly to 300°C to release the target organics
to the GC column head.
NOTE 3: For higher sensitivity analysis, larger sample sizes
can be used, but clogging by water is possible. In this case, a
subambient cold trap with an adsorbent may be used and
maintained higher than 0°C during trapping to prevent freeze-
up of trap.
7.1.3.3 Separate volatile organics desorbed from the
sample thermal desorption tube by an appropriate
column temperature program. Two recommended
temperature programs are as follows. For high
resolution analysis, using polydimethylsiloxane-coated
column (60 m by 0.25 mm by 0.25–µm film thickness),
heat the column from 40 to 280°C at a rate of 10°C/min
and hold the temperature at 280 °C for 16 min. For
rapid analysis, using polydimethylsiloxane-coated
column (25 m by 0.32 mm by 0.52–µm film thickness),
heat the column from 30 to 265°C at a rate of
12.5°C/min and hold the temperature at 265°C for 16
min.
7.1.3.4 Use n-Hexadecane, n-C
16
H
34
(C
16
), as a standard
for total organic analysis 4
. Use tris (2-chloroethyl)
phosphate, (ClCH
2
CH
2
O)
3
PO (TCEP) or tributyl
phosphate, (C
4
H
9
O)
3
PO (TBP), as a standard for
organophosphorus analysis (see Section 6.1.1 ). These
standards are introduced into the GC system from a
precleaned sample thermal desorption tube. Two-point
calibration method is recommended for checking the
instrument performance. Recommended standards are
two different concentrations of n-C
16
H
34
(C
16
) for total
organic analysis; and, two different concentrations of
tris (2-chloroethyl) phosphate (TCEP) for total
organophosphorus analysis. Recommended frequency
of these measurements is at least once a week.
NOTE 4: AED and FID are recommended for accurate total
carbon quantification.
7.1.4 Quantification
7.1.4.1 Obtain each area below for the calculation of
total organic contaminants. Obtain total organic
contaminants of the sample wafer (A
s
) by summing up
all the peak areas integrated from GC-AED, FID, or
MS chromatogram of the sample wafer. Obtain total
area of the blank wafer (A
b
) by summing up all the peak
areas integrated from GC-AED, FID, or MS
chromatogram of the blank wafer. Obtain the area of
the standard peak (A
c
) integrated from GC-AED, FID,
or MS chromatogram of the standard sample.
7.1.4.2 Obtain each area below for the calculation of
total organophosphorus (TP). Obtain total area of
phosphorus compounds of the sample wafer (A
s
) by