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SEMI F60-0301 © SEMI 2001 4 standard. A minimum sputtering etch cleaning of the SPC sa mple of ≥ 10 nano meter s is re co mmend ed in order to rem ove surface contamination, the oxide passive layer and establish equilibr…
SEMI F60-0301 © SEMI 20013
9.2 Statistical Process Control Material — A nominal
316L material with a composition range within the
guidelines of ASTM A276. The composition of the
bulk material should be determined by methods
consistent with ASTM A751.
10 Safety Precautions
10.1 This test method does not purport to address the
safety considerations associated with use of high
voltage, vacuum, and X-ray producing equipment. The
method assumes an ESCA analyst with knowledge of
instrumentation and associated safety precautions.
11 Test Specimen
11.1 Specimens are to be sectioned to appropriate size
for the particular ESCA instrument using a clean, dry
hacksaw or dry low speed bandsaw. Any sample
preparation shall avoid introducing contamination onto
the surface to be measured. In addition, preparation
must avoid excessive heating of the sample, i.e., the
surface temperature shall not exceed 50
o
C, to avoid
oxide growth or change in surface composition.
11.2 Sample preparation should preferably be done by
the component manufacturer. Following sectioning the
sample(s) are to be cleaned and packaged per the
manufacturer’s standard final cleaning and packaging
procedures.
11.3 If sample preparation is done by other than the
manufacturer, the sample(s) may be cleaned in DI
water. If the sample(s) are not to be analyzed
immediately they should be packaged by wrapping in
clean metal foil or sealing in cleanroom quality nylon
bags.
11.4 If sample preparation is done by other than the
manufacturer this shall be stated in the report narrative
and the analytical results are not to be interpreted as
indicative of the manufacturer’s quality of cleaning and
packaging procedures. A note to this effect shall be
included in all tables of reported results of the
composition of the surface.
11.5 After preparation, samples should be analyzed
promptly, with allowance for shipping times and
queuing time at the analyst.
12 Preparation of Apparatus
12.1 Instruments shall be routinely tested in
accordance with manufacturer recommendations to
assure proper performance. The instrument vacuum
shall be 1.0E-7 Torr or better during the analysis.
13 Calibration and Standardization
13.1 Proper instrument calibration is necessary to
provide the most accurate and reproducible results,
particularly if results are compared among different
laboratories. Instrument calibration for sensitivity
factors and binding energies shall be performed in
accordance with the instrument manufacturer
recommendations or other accepted method, such as
that provided in ASTM E902.
13.2 The general ESCA calibration procedures
described above are suitable for most analyses and
provide reasonably accurate relative quantitative
information regarding the surface chemistry. However,
in order to establish the most accurate measurement
practical and to maintain the desired level of
reproducibility over time, an application-specific
statistical process control (SPC) shall be established for
this test method to determine the appropriate sensitivity
factors for Cr, Fe, Ni and Mo in 316L stainless steel.
The bulk composition of the SPC material should have
an assay consistent with the acceptable composition
range of 316L for Cr, Fe, Ni and Mo, as set forth in
ASTM A276. The bulk composition of the SPC
material should be determined by methods consistent
with ASTM A751. The relative sensitivity factors
established for the quantification of data should reflect
the nominal composition of the bulk 316L SPC
standard after a sputter cleaning sufficient to remove
any surface contamination and the oxide passive layer.
A ± 3σ relative precision should be established from a
minimum of 10 SPC measurements with the following
tolerances:
Cr ± 10%
Fe ± 10%
Ni ± 25%
Mo ± 30%
As referenced from ASTM A276-97, a typical 316L
material has a composition range in terms of wt% of:
Cr 16–18
Ni 10–14
Mo 2–3
C < 0.03
Mn < 2.0
P < 0.045
S < 0.03
Si < 1.0
N< 0.1
Fe Balance.
Note that ESCA data is reported in atomic percent.
13.3 The sputter conditions established for the SPC
surface cleaning shall be the same as those established
for the ESCA depth profile measurement part of this
SEMI F60-0301 © SEMI 2001 4
standard. A minimum sputtering etch cleaning of the
SPC sample of ≥ 10 nanometers is recommended in
order to remove surface contamination, the oxide
passive layer and establish equilibrium. Note that the
degree of preferential sputtering and other ion etching
artifacts are a function of the matrix material and the
ion gun conditions.
13.4 Calibration frequency of the application specific
SPC should be designed to establish a record of the
reproducibility and accuracy of the measurement, as
reflected by the nominal composition of the 316L
standard. A minimum frequency of one per week is
recommended, or immediately prior to performing a
measurement in accordance with this test method.
13.5 A sputter rate calibration shall be performed prior
to an ESCA profile measurement conducted in
accordance to this test method. The ion sputter rate
determination shall be made using standard thin films
of 100 nanometers or less of SiO
2
on Si. The method of
determining the thickness of the oxide film shall be
based upon the oxygen concentration profile. The
oxide – substrate interface shall be specified as the
point at which the oxygen concentration decreases to ½
its maximum value in the SiO
2
film, ignoring the first
sputter cycle.
13.6 Multiple samples may be analyzed following a
single sputter rate determination if the ion gun
parameters have not been adjusted and the ion gun
performance is documented as stable over the period in
question.
14 Procedure
14.1 As-Received Surface Analysis— The sample is to
be mounted in accordance with manufacturer's
recommendations and in a manner consistent with ultra-
high vacuum surface analytical procedures. Some of
these practices are detailed in ASTM-E1078. The area
to be analyzed should be mounted parallel to the sample
holder surface so that TOA is well known.
14.1.1 Place the sample in the ESCA introduction
chamber for pump down. Transfer to the analytical
chamber at the manufacturer's recommended base
pressure. Align the sample with respect to the X-ray
beam and analyzer so that optimum count rate from the
desired analytical location is obtained. The use of a
collimated high voltage electron beam to align the
sample should be avoided, as this may pyrolyze surface
carbon and potentially alter surface oxide chemistry.
The surface area to be analyzed should be free of
visible particles and large defect features, if possible.
14.1.2 A beam size as close to 1 mm as possible
should be used to ensure measurement of a
representative surface. If surface curvature is great
(e.g., < 1/4" tubing), a smaller beam may be employed.
Elemental survey data (0–1100 eV) are to be measured
from the sample surface to determine the elements
present and their approximate surface abundance. A
high throughput analyzer setting may be used to obtain
a signal to noise ratio (S/N) sufficient to detect common
surface contaminants such as sulfur and phosphorus at
one atomic percent or better.
14.1.3 Using instrument settings sufficient to provide
a FWHM peak width of 1.0 eV or less on Au (4f
7/2
),
measure chromium, iron, and carbon regions. A typical
region width is 20 eV. Suggested ranges are as follows:
Cr (2p
3/2
) from 570 to 590 eV, Fe (2p
3/2
) from 700 to
720 eV, and C (1s) from 275 to 295 eV. Signal to noise
ratios of greater than 20 are suggested.
14.1.4 A consistent method of data reduction of high-
resolution surface spectra is necessary in order to
provide meaningful comparison of the relative Cr:Fe
ratios.
14.1.5 The spectra shall be charge compensated with
respect to the maximum of the Cr (2p
3/2
) set to 577 eV.
An iterated Shirley method of background subtraction
shall be applied to the Fe (2p
3/2
) and Cr (2p
3/2
) spectral
regions, using a minimum of three iterations.
14.1.6 The curve fit regions shall typically extend
from:
Cr (2p
3/2
) 570–582 eV
Fe (2p
3/2
) 704–717 eV
14.1.7 The curve fit peak parameters should be
initialized as follows:
Cr (2p
3/2
) Peak Position FWHM % gaussian
1 574 1.5 80
2 576.5 2.0 80
3 577.5 2.0 80
Fe (2p
3/2
) Peak Position FWHM % gaussian
1 707 1.0 80
2 708 1.0 80
3 710 1.4 80
4 711.5 1.4 80
5 713 1.4 80
14.1.8 The curve fit routine should apply the following
tolerances for the band limit parameters of all peaks
defined above:
FWHM delta
≤ 0.2 eV
% gaussian delta
≤ 10%
Curve fit position delta
≤ 0.25 eV
14.1.9 An automated form of data reduction is
recommended to enhance reproducibility and minimize
SEMI F60-0301 © SEMI 20015
analyst subjectivity associated with the curve fit
procedure. If it is necessary to deviate from the curve
fit parameters outlined above in order to obtain a
satisfactory curve fit it should be noted in the formal
report. Possible sources for the anomalous behavior
include an excessive concentration of iron oxide or a
sufficiently aged sample surface, such that the oxide
surface chemistry and structure has modified.
14.2 Depth Profile Analysis— The ESCA depth
profile may be performed following acquisition of the
initial as-received surface survey scan and high-
resolution spectra using the same sample x-y position
and take-off angle of 35°.
14.2.1 The depth profile may be acquired in either
continuous mode (simultaneous sputter etching and data
acquisition) or alternating sputter etch/data acquisition
mode. The following acquisition windows are
recommended:
Spectral line Lower limit Range
C 280 eV 15 eV
O 525 eV 15 eV
Cr 570 eV 15 eV
Ni 848 eV 15 eV
Fe 700 eV 25 eV
14.2.2 If only an elemental compositional profile is
acquired, any pass energy may be selected as long as
the remaining acquisition parameters defined by the
number of sweeps, step size and dwell time result in ≤
1.0at% detection of the matrix elements followed in the
depth profile.
14.2.3 The composition profile should extend far
enough into the depth of the sample to reach the base
metal composition of the 316L material, but a minimum
of 100Å from the surface as referenced to the calibrated
sputter rate in SiO
2
.
15 Calculations and Interpret ation of Results
15.1 Most manufacturers supply software for
determination of elemental composition. The elemental
composition should be calculated using sensitivity
factors appropriate to the instrument, each element, and
resolution settings for each measurement.
15.2 The total Cr/Fe ratio is calculated by adding peak
areas from all species of each element, adjusting for
different numbers of scans and sensitivity factors, and
dividing the Cr result by the Fe result. The Cr oxide/
Fe oxide ratio is calculated in a similar manner, except
that only peaks 2 and 3 for Cr and only peaks 3 through
5 for Fe (oxide species) are used. The formulas are as
follows:
Total Cr/Fe = (Σ Cr peak areas)/# Cr scans/Cr sensitivity factor
(Σ Fe peak areas)/# Fe scans/Fe sensitivity factor
Cr Oxide/ = (Σ
Cr oxide peak areas)/# Cr scans/Cr sens. factor
Fe Oxide (Σ Fe oxide peak areas)/# Fe scans/Fe sens. factor
16 Reporting Results
16.1 As-Received Surface Results — A tabular
summary of the elemental composition of all elements
detected in the surface survey spectrum is to be
supplied with the associated elemental survey spectrum.
If sample preparation has been done by other than the
component manufacturer all tables of as-received
surface analysis results shall include a note stating:
“Sample preparation was not performed by the
component manufacturer. Results are not to be
interpreted as indicative of the component
manufacturer’s quality of cleaning and packaging
procedures.”
16.1.1 Tabular summaries of total Cr/Fe ratio and Cr
oxide/ Fe oxide are also to be supplied, with associated
Cr(2p
3/2
), Fe(2p
3/2
), and C(1s) narrow region spectra.
16.1.2 Acquisition parameters, including
manufacturer, model and TOA; X-ray source (Al or
Mg); beam size; and other pertinent settings are to be
supplied. Analyst identity and analysis date are also
required information. Each table and graph must be
clearly labeled with sample identification.
16.2 Depth Profile Results — Compositional depth
profile data plots shall display the atomic concentration
of Fe, Cr, Ni, C, and O at minimum versus the sputter
time or the equivalent depth from the calibrated sputter
rate in SiO
2
.
16.2.1 The method applied to determine the oxide
thickness shall be specified in the report. A commonly
accepted method of quantifying the oxide thickness is
determined as the sputter time/depth at which the
oxygen concentration decreases to ½ the maximum
value. The carbon thickness may be determined
similarly.