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SEMI E45-1101 © SEMI 1995 , 2001 4 with an ele mental standard is carried out (blank — 0.5 µ g/L – 1 µ g/L). 8.6.3 A detection limit for sodi um and copper bet ter than 5 × 10 9 atoms/cm 2 (approxim ately 0.1 µ g/L for G…

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SEMI E45-1101 © SEMI 1995, 20013
and controlled ambient (e.g., ISO Class 4 (as defined in
ISO 14644-1)).
7.2 The VPD and the advisable drying chamber(s) shall
have opening(s) made of PVDF, PFA, PTFE or similar
resistant and pure polymer materials that are not
attacked by HF. The chamber(s) may contain one or
more wafer stacks. After evacuation, the chamber shall
be flushed with filtered N
2
until the complete drying of
the microdroplet residue is achieved.
7.3 For the aliquots of standard stock and scanning
solutions, validated micropipettes shall be used. DIN
12650 Part 6 provides an applicable validation
procedure.
8 Procedure
These procedures show the determination of Na, Ca,
Cu, and Fe on a silicon wafer surface with
VPD/GFAAS, VPD/ICP-MS and VPD/TXRF. For
achieving best detection limits, VPD/GFAAS and
VPD/ICP-MS shall be used for NA and Cu whereas
VPD/TXRF shall be used for Ca and Fe.
8.1 Test Requirements — The evaluation of the
minienvironment and the analysis shall be carried out
under appropriate clean conditions. Any potential for
cross contamination shall be checked in advance.
Possible contamination sources are:
• VPD preparation
• storage
• contaminated GFAAS or ICP-MS vessels
• environment
• measurement methods and collection efficiency of
VPD
• handling
8.1.1 The capability of the analytical lab has to be
checked carefully for compliance with Sections 8.2,
8.6, and 9.
8.2 Surface Conditions and Cleaning Procedure —
Polished silicon wafers with the following
specifications must be used:
• Specific resistivity = 1–100 Ωcm
• CZ crystal growth method
• Cleaned to leave a native oxide with hydrophilic
surface conditions and with Na, Ca, Cu, and Fe
concentrations lower than 1 × 10
10
atoms/cm
2
8.2.1 Wafer cleaning must be done less than ten
minutes before any further processing. This restricted
time limitation is necessary to ensure cross
contamination avoidance.
8.3 VPD Preparation — The vessel for (opening > 25
cm
2
) inside the VPD box is filled with 25 vol-% HF by
mixing DI water with 50 vol-% VLSI-grade
hydrofluoric acid (see SEMI C28) allowing
hydrofluoric acid of between 25 to 50 wt % to be used.
The wafers are then exposed to the hydrofluoric acid
vapor. Allow wafers exposure to hydrofluoric acid
vapor for 15 to 30 minutes, at which time the wafer
should become hydrophobic due to oxide removal. The
liquid reaction products are collected by rolling a DI
water droplet over the whole wafer surface using up to
100 µL for advisable machine operation or an
appropriate volume for manual operation. Any cross
contamination is minimized by using DI water as
solvent.
8.4 Collection Procedure — An automatic scanning
procedure is preferable, but if the collection procedure
is manual the following procedure should be used.
8.4.1 Use appropriate method to exclude the wafer
edge.
8.4.2 A droplet of collecting agent, usually ultra-pure
hydrofluoric acid or another reagent or a combination
of reagents, is rolled over the whole surface of the
wafer in a parallel pattern.
8.4.3 The same droplet is then moved over the whole
surface, this time in a pattern orthogonal to the first.
8.4.4 Finally, the droplet is rolled in a spiral pattern
from the wafer periphery to its center.
8.5 Pre-analysis Procedure
8.5.1 GFAAS Analysis — The wafer droplet is diluted
to 500 µL.
8.5.2 TXRF Analysis — The droplet is evaporated on
the wafer surface in a clean environment at room
temperature under a nitrogen purge.
8.5.3 ICP-MS Analysis — The wafer droplet is diluted
to 500 µL.
8.6 Sodium and Copper Analysis by GFAAS
8.6.1 Calibration Standards — 1 µg/L for Na.
8.6.2 The calibration frequency and procedures shall be
in accordance with the requirements of the ISO 9001
quality system. The temperature program for the
graphite furnace (dry, ash, atomize) is optimized for
maximum sensitivity. Volatility (e.g., NaF) should be
avoided by spiking the liquid samples with nitric acid
(VLSI grade—see SEMI C35). Prior to analysis of the
liquid sample, a three-point calibration of the element
SEMI E45-1101 © SEMI 1995, 2001 4
with an elemental standard is carried out (blank — 0.5
µg/L – 1 µg/L).
8.6.3 A detection limit for sodium and copper better
than 5 × 10
9
atoms/cm
2
(approximately 0.1 µg/L for
GFAAS analysis) is recommended.
8.6.4 The detection limit is defined by 3 • σ • R (σ =
standard deviation, R = reciprocal slope of the
calibration curve).
8.6.5 The surface concentration is calculated as
follows:
C
s
= C
1
×
V × NA × 10
-9
/(W × A)
with:
C
s
(atoms/cm
2
): surface concentration
C
1
(µg/L): analyzed concentration
V(mL): volume of diluted sample
NA = 6.023 × 10
23
mol
–1
: Avogadro number
A (cm
2
): wafer surface area
W (g/mol): atomic weight of element (22.99 for
sodium, 86.54 for copper)
8.7 Sodium and Copper Analysis by ICP-MS
8.7.1 Calibration Standards — 1 µg/L for both sodium
and copper.
8.7.2 A detection limit for sodium and copper better
than 5 × 10
9
atoms/cm
2
(e.g., for 200–300 mm wafers)
is recommended.
8.7.3 The detection limit is defined by 3 • σ • R (σ =
standard deviation, R = reciprocal slope of the
calibration curve).
8.7.4 The surface concentration is calculated as
follows:
C
s
= C
1
×
V × NA × 10
-9
/(W×A)
with:
C
s
(atoms/cm
2
): surface concentration
C
1
(µg/L): analyzed concentration
V(ml): volume of diluted sample
NA = 6.023 × 10
23
/mol : Avogadro number
A (cm
2
): wafer surface area
W (g/mol): atomic weight of element (22.99 for
Na, 86.54 for copper)
8.8 Calcium and Iron Analysis by TXRF
8.8.1 Calibration Standards — The ISO 9001 quality
system shall be applied to the calibration. The
instrument is calibrated by analyzing the calibration
wafer. The calibration wafer is prepared by dropping a
solution of metal standard (e.g., Ni or Co) on a clean
wafer surface. The volume of the droplet is the same as
used for VPD preparation (up to 100 µL), and the
resulting surface concentration must be in the lower
10
11
atoms/cm
2
range. The droplet is then evaporated on
the wafer surface at room temperature under nitrogen
purge until the liquid matrix is removed. Its residue is
analyzed by TXRF. The detection limit is defined by 3 •
σ • R (σ = standard deviation, R = reciprocal slope of
the calibration curve). Note that the droplet area must
be smaller than the spot area of the detector.
8.8.2 Reproducibility shall be first established
following the procedure below.
8.8.3 Define a grid of 3 × 3 measurement points with
an inter distance of 3 mm. The reside position, found by
optical inspection, shall be located at the center of the
matrix.
8.8.4 Determine the intensity by short analyses of each
of the nine measurement locations. The analysis area is
at maximum intensity for the standard element of the
calibration wafer.
8.8.4.1 Calibration shall be checked weekly and after
each equipment service (e.g., after an exchange of
filament, anode, or repair of anode) with the same
calibration wafer.
8.8.4.2 The surface concentration is calculated as
follows:
C
s
= RSF
m
× (C
0
/I
0
) × I
with:
C
s
(atoms/cm
2
): surface concentration of analyzed
metal M
I (counts/s): analyzed intensity of metal M
C
0
(atoms
/
cm
2
): surface concentration of standard
metal S (Ni or Co) on calibration wafer
I
0
(counts/s): analyzed intensity of standard metal
S on calibration wafer
RSF
m
: relative sensitivity factor of investigated
metal M to standard metal S
8.8.4.3 The constants RSF
m
are implemented in the
software of the TXRF equipment.
8.9 Sampling Procedure — If the average elemental
concentration for the sampling wafers is higher than the
average elemental concentration plus three standard
deviations for the analyzed reference wafers, then the
sampled minienvironment is considered to cause
significant contamination.
SEMI E45-1101 © SEMI 1995, 20015
8.9.1 Minienvironment Exposure — The following
exposure time for sampling specific minienvironments
shall be used:
Minienvironments used to store wafers: 168 h
Minienvironments as an interface to process tools:
24 h
8.9.2 Minienvironments for Storing Wafers — Fill the
minienvironment with six wafers. Measure wafers by
VPD/GFAAS or VPD/ICP-MS in front, back, and
center slots. Use the adjacent wafers for VPD/TXRF.
8.9.3 Minienvironments for Introducing Wafers to
Process Tools — Introduce six wafers into the
minienvironment. Measure three wafers with
VPD/GFAAS or VPD/ICP-MS, one in the center
position and two at the edge positions opposite to each
other. Use the adjacent wafers for VPD/TXRF. In the
case of single wafer minienvironments, wafers are
processed sequentially. To ensure that no cross
contamination is introduced from conditions prevailing
in storing, transportation, or any of the handling
processes, precautions must be adhered to at all times.
9 Results
9.1 The investigated minienvironment must be
described in detail (e.g., construction, materials, history,
process, cleaning procedures, storage conditions). All
surface concentrations must be fully reported.
9.2 The number of tested sampling and reference
wafers, average elemental concentration, and standard
deviation of the reference wafers, slot positions,
position in the minienvironment, and number of
repeated experiments (if applicable) must be
documented.
9.3 All equipment, tools, and chemicals used must be
specified within the report.
10 Related Documents
10.1 SEMI Standards
SEMI C30 — Specifications and Guidelines for
Hydrogen Peroxide
NOTE 2: Unless otherwise indicated, all documents cited
shall be the latest published versions.
10.2 Other Documents
A. Shimazaki, H. Hiratsuka, Y. Matsushita, S. Yoshii,
Ext. Abs. 16th Conference on Solid State Devices and
Materials, Kobe, 281 (1984).
M. Hourai, T. Nakidomi, Y. Oka, K. Murakami, S.
Sumita, N. Fujino, T. Shiraiwa, Japan Journal of
Applied Physics 27, 12 (1988) L2361.
A. Huber, H.J. Rath, P. Eichinger, T. Bauer, L. Kotz, R.
Staudigl, Diagnostic Techniques for Semiconductor
Materials and Devices, ed. by T.J. Shaffner, D.K.
Schroder, ECS Proc. Vol. 88-20, 109 (1988).
P. Eichinger, H.J. Rath, H. Schwenke, Semiconductor
Fabrication: Technology and Metrology, ASTM STP
990, ed. by D.C. Gupta, American Society for Testing
and Materials, 305 (1989).
C. Neumann, P. Eichinger, Spectrochim. Acta 46B,
1369 (1991).
A. Shimazaki, Defects in Silicon II, ed. by W.M. Bullis,
U. Gösele, and F. Shimura, ECS Proc. Vol. 91-9, 47
(1991).
W. Hub, V. Penka, Microcontamination Conference
Proceedings, San Jose, Oct. 1991, 266.
N. Streckfuss, L. Frey, G. Zielonka, F. Kroninger, C.
Ryzlewicz, H. Ryssel, Fresenius Journal Analytical
Chemistry 343, 765 (1992).
R.S. Hockett, S. Ikeda, T. Taniguchi, Cleaning
Technology in Semiconductor Device Manufacturing,
ed. by J. Ruzyllo, R.E. Novak, ECS Proc. Vol. 92-12,
324 (1992).
L. Fabry, S. Pahlke, L. Kotz, E. Schemmel, Crystalline
Defects and Contamination: Their Impact and Control
in Device Manufacturing, ed. by B.O. Kolbesen, C.
Claeys, P. Stallhofer, F. Tardif, ECS Proc. Vol. 93-15,
232 (1993).
S. Tan, Nuclear Instruments and Materials in Physics
Research B99, 458 (1995).
NOTICE: SEMI makes no warranties or representa-
tions as to the suitability of the standards set forth
herein for any particular application. The determination
of the suitability of the standard is solely the
responsibility of the user. Users are cautioned to refer to
manufacturer's instructions, product labels, product data
sheets, and other relevant literature, respecting any
materials or equipment mentioned herein. These
standards are subject to change without notice.
The user’s attention is called to the possibility that
compliance with this standard may require use of
copyrighted material or of an invention covered by
patent rights. By publication of this standard,
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(SEMI) takes no position respecting the validity of any
patent rights or copyrights asserted in connection with
any items mentioned in this standard. Users of this
standard are expressly advised that determination of
any such patent rights or copyrights, and the risk of
infringement of such rights are entirely their own
responsibility.
Copyright by SEMI® (Semiconductor Equipment and Materials
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