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SEMI E46-0301 © SEMI 1995 , 2001 3 ground jo int NS8 0 • aluminum foil • 2 metal sa ws • table vice • finely toothed metal file • steel ruler (30 cm ) 10.2 Pr econditioning Procedur e (T h ermal Decontaminat ion) — In or…
SEMI E46-0301 © SEMI 1995, 2001 2
6 Interferences
6.1 To adequately measure organic contaminants from
minienvironments, an extremely sensitive method for
analyzing volatiles is required. At this time, the only
analytical method meeting these requirements is IMS.
The absolute determination of organic contamination by
the IMS method is still limited, especially in the
presence of many analytes, but this proposed test
method permits the comparison of quantitative results
from different laboratories.
7 Apparatus
7.1 Minimum Requirements for the Ion Mobility
Spectrometer — For the successful performance of the
experiments using the IMS instrument, the following
requirements are essential:
— minimum length of the drift cell: 4 cm
— sample inlet has to be lockable (no sniffing
devices)
— sample desorption oven must have a programmable
temperature control
— the electronics must guarantee a linear
amplification of the observed signal
— intensity over at least five orders of magnitude
— documentation of all single measurement results.
7.2 Measuring Parameters — For measurements with
the ion mobility spectrometer, the following parameters
have to be used:
temperature of the desorption furnace: 200°C*
temperature of the drift cell and IMS detector:
205°C*
maximum dwell time or channel length corres-
ponding to minimum time resolution: 80 µs**
measuring time per spectrum: 40 ms*
(for 200 V/cm and 10 cm length of drift cell)
gatewidth: 200 µs**
number of scans: 2000**
drift gas and carrier gas: zero grade (synthetic) air*
• approx. 10 ppm H
2
O*
• max 0.1 ppmv total hydrocarbons*
carrier gas flow: 100 mL/min* (for a diameter of
3.9 mm)
drift gas flow: 500 mL/min** (for a diameter of
4.25 cm)
* specified; ** suggested
8 Reagents
8.1 The chemicals must be of the described quality or
better and supplied with a certificate of analysis.
Benzene: ultrapure quality for trace residue analysis.
Minimum quality: pro analysi.
• content of benzene: min. 99.8%
• content of water: max. 0.02%
• nonvolatile residue: max. 0.0005%
Ethanol: ultrapure quality for trace residue analysis.
Absolute.
• content of ethanol: min. 99.8%
• content of water: max. 0.1%
• nonvolatile residue: max. 0.0005%
DOP: normal pure quality.
• content of DOP: better than 96%
HPB: normal pure quality.
• content of HPB: better than 96%
9 Safety Precautions
9.1 All preparation and measurement work has to be
done according to local regulations for laboratories.
10 Procedure
10.1 Preparation Tools and Auxiliaries — The
following equipment is needed for the preparation of
polymer headspace substrates:
• protective eye wear
• 1 fume cupboard
• 1 butane burner
• 2 pairs of crucible tongs made of stainless steel
• scalpel with changeable blades
• 4 pairs of cross tweezers with tips made of steel
• 1 metal vernier calliper
• Si-wafer-chips: formate 20 × 10 mm
2
• watch glass
• weighing bottle with lid, both made of glass
inner diameter: 80 mm
height: 30 mm
SEMI E46-0301 © SEMI 1995, 20013
ground joint NS80
• aluminum foil
• 2 metal saws
• table vice
• finely toothed metal file
• steel ruler (30 cm)
10.2 Preconditioning Procedure (Thermal
Decontamination) — In order to assure that all
environmental influences are eliminated, all thermal
decontamination procedures described in the following
have to take place immediately before the appropriate
measurements or experiments are performed.
10.2.1 Preconditioning of Aluminum Foil — Two
cross tweezers are flamed with a butane torch in the
fume cupboard (1 min., red heat). A piece of aluminum
foil (20 × 30 cm
2
) is folded multiply and, by using
tweezers, is carefully heated in the flame until fully
converted. After cooling down, the foil is stored on a
fire resistant surface (ceramics preferred).
10.2.2 Preconditioning of Weighing Bottles — The
jaws of the crucible tongs are heated in the butane torch
until they are red hot for two minutes. After a short
cooling period (15 s), the bottom of the weighing bottle
is picked up. For several times, the inner and the outer
surfaces of the glass are heated alternately in the torch
(2 minutes for each run). After approximately 30 s of
cooling down - held in air by the tongs - the flamed
weighing bottle is put down on the preconditioned
aluminum foil. The tongs are allowed to cool for 15 s,
then the lid is prepared in the same way. After 10
minutes of cooling, the lid can be placed on the
weighing bottle.
10.2.3 Preconditioning of Watch Glass — The watch
glass is picked up with preconditioned cross tweezers
and carefully heated in the butane torch for 30 s
(without deformation by melting).
10.2.3.1 Simultaneously, the tips of a second pair of
cross tweezers are heated to red heat. After 30 s, the
watch glass is transferred by these tweezers, carefully
heated for another 30 s to red heat (total heating time, 1
min), and placed on the preconditioned aluminum foil.
After a cooling period of 5 minutes, the watch glass is
picked up with a clean pair of preconditioned cross
tweezers and placed inside the weighing bottle.
10.2.4 Preconditioning of Si-chips — Wafers, as
received, are cut into chips of 20 × 10 mm
2
in size. The
use of cotton gloves is recommended to avoid organic
contamination through fingerprints. Then one Si-chip is
picked up with a pair of cross tweezers and heated to
red hot in a butane torch (30 s). Simultaneously, the tips
of a second pair of cross tweezers are heated to red hot.
After 30 s, the Si-chip is transferred to these tweezers
and heated for another 30 s to red heat (total heating
time, 1 min). After cooling, the Si-chip is transferred
into the preconditioned weighing bottle. The weighing
bottle must be opened and closed only with the
thermally decontaminated crucible tongs.
10.2.4.1 The lid must be placed only on the
preconditioned aluminum foil. Five more Si-chips are
preconditioned as described above and placed into the
weighing bottle. The six Si-chips must not overlap or
touch one another. The Si-chips should be placed on
the preconditioned watch glass.
10.2.5 Preparation of Polymer Material — The table
top vice is mounted on a clean work-bench. The cross
tweezers, the blade of a metal saw, the scalpel, the
metal vernier calliper (within the measuring range), the
steel ruler (in the range of 0 to 3 cm), and the finely
toothed metal file are thermally decontaminated.
Having decontaminated the metal saw, an area of
approximately 50 × 50 mm
2
is sawed off the polymeric
material and fixed with the clean cross tweezers. This
piece of polymer material is then clamped vertically
between the jaws of the vice. An area 12 × 20 mm
2
is
carefully marked with the scalpel and cut out with the
metal saw. Before total separation, the polymer sample
is clamped with cross tweezers while the jaws of the
vice are covered with the decontaminated aluminum
foil. After clamping the polymer sample between the
jaws of the vice, all sides of the polymer sample are
carefully filed to length wit ha metal file (size control
with metal vernier caliper). Then the polymer sample is
placed on a clean watch glass by cleaned tweezers. The
watch glass is positioned on the thermally cleaned
aluminum foil. Both parts are stored inside the
preconditioned weighing bottle which is carefully
closed with its lid. The weighing bottle, within which
the Si-chips are stored, is wrapped in preconditioned
aluminum foil for storage and transportation.
10.3 IMS Measurements Procedure
10.3.1 Blank Measurement — The background signal
level (noise) of the equipment must be defined by
measuring the clean and stabilized IMS-equipment,
without sample, three times for each polarity.
10.3.2 Reference Measurement — All manipulations
etc. with the reference chemicals (Hexaphenylbenzene
and Dioctylphthalate) have to take place entirely in
PFA containers etc. Following equipment is needed:
2 narrow necked flasks (PFA), 250 mL
2 weighing boats (PFA)
! ! low weight, diameter smaller than diameter of
narrow necked flask! !
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2 pipettes (glass), 100 mL
1 micro dropper with changeable tips of 2 µL (may
be PP)
1 micro spatula (metal)
1 micro balance, measuring range 10
-6
g to 1 g at
least
10.3.2.1 Preparation of the reference measurement
with HPB:
10.3.2.1.1 Before the HPB is weighed, the PFA-bottle
and the weighing boat have to be cleaned. For this the
weighing boat and 10 mL benzene are given into the
bottle. The bottle is closed and shaken well for approx.
1 minute. The benzene is discarded. This procedure is
repeated four times. After the last cleaning the empty
open bottle and the weighing boat, placed on a
decontaminated aluminum foil (see Section 10.2.1). are
allowed to dry at room temperature in a fume cupboard
for ten minutes. Then the bottle is closed. The weighing
boat is placed onto the micro balance by thermally
decontaminated cross tweezers. Approx. 5 mg of HPB
are weighed into the weighing boat by use of a
thermally decontaminated micro spatula. The weight is
recorded exactly for the later calculation. The weighing
boat is placed into the PFA bottle by the cross tweezers.
10.3.2.1.2 The volume of the benzene is measured
using a 100 mL-pipette. Before use, the pipette has to
be washed 5 times using 10 mL benzene each time. The
100 mL benzene are filled into the PFA flask, which is
closed immediately.
10.3.2.1.3 First the bottle, now containing HPB and
benzene, is shaken well for three minutes. Often this is
not sufficient for a complete dissolution of the HPB
(visible inspection). To assure complete dissolution, the
PFA flask is placed into an ultrasonic bath for 5
minutes (not longer, because solution may get hot).
Two minutes before the end of that time the preparation
of the silicon chip is started. The piece of silicon is
heated to red heat for one minute, placed on the
thermally decontaminated aluminum foil and given 5
minutes to cool. When the treatment in the ultrasonic
bath is finished, the PFA flask is shaken for three
minutes again, then given 2 minutes for just standing.
10.3.2.1.4 The bottle is opened. By the micro dropper
2 µL are taken from near the surface (tip not more than
1 mm under surface of liquid). The 2 µL are spread
onto the silicon chip in such a way that the liquid on the
chip covers the smallest possible area. Care is to be
taken to prevent large spreading or even dropping off
the liquid (e.g., the Si chip has to be positioned flat).
The liquid is given 5 minutes to evaporate (room
temperature, no extensive blowing of air). Then the
measurement of the HPB reference can be started.
10.3.2.1.5 Before each following HPB measurement
the flask again has to be shaken 3 minutes, 5 minutes
ultrasonic bath, shaking 3 minutes, allow two minutes
of resting. The solution of the HPB in benzene must not
be kept longer than 10 days.
10.3.2.1.6 The reproducibility of the integral value
(see calculation) achieved by this procedure is better
than 4%. Sample measurements shall be performed
only, if the reference measurement has provided a
reproducibility equal to or better than 10%.
NOTE 1: Hexaphenylbenzene has been chosen as a reference
compound because its signal is well-defined and its mobility
value is well separated from the peaks of nearly all other
relevant organic contaminants. It provides positive ions only.
A different reference, Dioctylphthalate, is needed for negative
ions.
10.3.2.1.7 DOP-reference samples: All the same as
HPB, except replacing the benzene by ethanol. The
DOP is weighed using a micro dropper (not spatula).
10.3.2.1.8 The mobility spectrum of dioctylphthalate
is also well separated but there are several peaks due to
thermal decomposition (phthalic anhydride etc.). This
compound is a frequently used plasticizer and therefore
one of the most critical polymer additives.
10.3.3 Measurement of the Headspace Samples —
Positive and negative ions are detected successively in
two separate runs. At least two independent
measurements are carried out for each polarity. Every
measurement to be saved consists of 2000 single scans
and is then repeated. Hence, an automated measurement
is required.
10.3.3.1 The silicon chip is placed in the furnace of
the IMS using thermally decontaminated cross
tweezers. The measurement of the drift time spectrum
(positive or negative polarity) has to be started
immediately after loading the desorption furnace with
the sample (time delay between sample introduction
and starting of the measurement: 15 s).
10.3.4 Termination of the Measurement — The
measurement is terminated when the signal intensity
has decreased to about 10% above the noise of the
blank measurement spectrum. If this point is not
reached after two hours, the measurement should be
terminated; in this case, the investigated sample does
not show suitable material properties.
10.4 Headspace Sampling in Minienvironments —
The crucible tongs are preconditioned as described in
Section 10.2, and the preconditioned aluminum foil is
placed beside the minienvironment that is to be
examined. After opening the minienvironment, the lid
of the weighing bottle is picked up with the crucible
tongs and carefully placed on the aluminum foil. Both