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SEMI E46-0301 © SEMI 1995 , 2001 2 6 Interfer ences 6.1 To adequ ately measure organi c c onta minants f r om minie nviro nme nts, a n extr emel y se nsit ive met hod for analyzing volatiles is required. At this time, th…
SEMI E46-0301 © SEMI 1995, 20011
SEMI E46-0301
TEST METHOD FOR THE DETERMINATION OF ORGANIC
CONTAMINATION FROM MINIENVIRONMENTS USING ION MOBILITY
SPECTROMETRY (IMS)
This test method was technically approved by the Global Metrics Committee and is the direct responsibility
of the European Equipment Automation Committee. Current edition approved by the European Regional
Standards Committee on December 20, 2000. Initially available at www.semi.org February 2001; to be
published March 2001. Originally published in 1995.
1 Purpose
1.1 The purpose of this test method is to provide an
analytical procedure—Ion Mobility Spectrometry
(IMS)—for the determination of organic contamination
from minienvironments which has the capability of
testing their construction material.
2 Scope
2.1 Silicon wafers passed through or stored in
minienvironments may be affected by organic
contamination originating from construction materials.
Knowledge of this contamination assists the decision
about the application of minienvironments in
semiconductor manufacturing.
2.2 Ion Mobility Spectrometry was chosen as the
method to determine this contamination because it
provides an easy, widely applicable, fast and sensitive
way to measure organic contamination on surfaces.
2.3 Furthermore, IMS provides the possibility of
checking the contaminating effects of processing,
chemical carryover, and the characterization of future
polymeric materials for use in semiconductor
technology.
2.4 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 determine
the applicability of regulatory limitations prior to use.
3 Referenced Documents
3.1 SEMI Documents
SEMI E19 — Standard Mechanical Interface (SMIF)
SEMI Minienvironment Terminology Workshop
Proceedings, April 2, 1993
4 Terminology
4.1 Box/Cassette/Minienvironment/Pod
4.2 DOP — Dioctylphthalate
4.3 Headspace — The volume above the sample
containing the gas to be analyzed
4.4 HPB — Hexaphenylbenzene
4.5 IMS — Ion Mobility Spectrometry
4.6 IMS/MS — Ion Mobility Spectrometry/Mass
Spectrometry
4.7 NS — Standardized Ground Jo int
4.8 SMIF (Standard Mechanical Interface) — The
interface plane between a pod and another
minienvironment as per SEMI E19.
4.9 PFA — Polyfluoroalkoxy
4.10 PP — Polypropylene
5 Summary of Method
5.1 This test method defines a fast, sensitive technique
for the determination of organic contamination from
minienvironments. The contamination is measured
directly from the silicon surface. Three important
aspects are covered:
a. Contamination due to the minienvironment alone,
b. Contamination from the use of minienvironments
for wafer processing, and
c. Contamination from future materials to be used in
semiconductor technology.
5.2 Silicon wafers are either placed in the
minienvironment or used for headspace sampling
experiments. The sample is heated and the target
compound is either desorbed or outgassed. These
compounds are swept by the carrier gas into the Ion
Molecule Reactor. Here the molecules are chemically
ionized under atmospheric pressure. The target ions are
separated in a drift cell by electrophoreses in the
gaseous state and detected by an electrometer.
Additionally, a quadrupole mass spectrometer could be
used as a second detector. The result is a quantitative
value for the total amount of organic surface
contamination.
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! !