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SEMI C3-0699 © SEMI 19 86, 1999 7 It is assumed that the resu l ts of such a calculation must not exceed the specification f or t he product being analyzed. 6.10 Notes — Any special requirem e n ts for any sectio n withi…

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SEMI C3-0699 © SEMI 1986, 1999 6
The introduction of a gaseous sample into a carrier gas
stream is accomplished by means of a sample injection
valve. Valves for this purpose can be any of several
types, although the most commonly used are either
rotary or diaphragm valves using loops of stainless steel
tubing of a known volume. It is not necessary to
diagram such sample introduction systems for a
procedure unless the introduction system is unique to
the application by way of special conditions for safety
or other reasons critical to the accuracy of the sampling
technique.
6.3 Separations — It is an acceptable and common
practice to quantitate several gaseous impurities with a
single gas chromatographic separation. Occasionally a
single injected sample volume will undergo
"multidimensional" separation to achieve the necessary
analysis. Rotary valves, diaphragm valves or Dean's
pressure switching again are used to move impurities
from one separation medium to another, or from one
column to another. Where multidimensional techniques
are used, they should be accompanied by flowpath
diagrams which clearly indicate valving and their
appropriate positions. The valving sequences used
should have adequate explanation to clarify the
separations.
6.4 Columns — Columns used are generally of 3.2
mm (1/8 in.) o.d. and 2.2 mm (0.085 in.) i.d. stainless
steel of varying lengths and packed with one of many
solid supports. Columns may be specified by length and
packing material if these standard dimensions apply. If
another dimension or material is used for the column
itself, it should be specified by material type, and by
o.d. and i.d. in mm. Packing materials should be
specified by material, % coating and coating type if
applicable, and mesh size. Capillary columns are
assumed to be fused silica unless otherwise specified
and should be specified by i.d. in mm, film thickness in
µm, and length in meters. Column temperatures and
applicable program rates should be given for each
independently heated zone in degrees Celsius.
6.5 Carrier and Support Gases — Carrier and support
gas flow rates for all separations should be specified.
Carrier and support gases used should fall into the
general purity requirements in Table 2 and purity need
not be specified unless the analysis has specific purity
requirements for safety, accuracy, or component
lifetime. Flows should be specified in mL/min or
L/min, or as linear velocity for open tubular capillary
columns.
6.6 Detectors — Detector technolo gy should be
specified, and alternative detection may be assumed
equivalent for detectors of like selectivity and
sensitivity. Table 2 gives a reference of relative
detector sensitivity and is provided as a guideline only.
Detector parameters are less likely to be easily
formatted since detector technologies vary widely in
their specific parameters. All elements critical to
achieving like sensitivity must be included, such as
temperature, make-up gases and their flows, flame,
combustion or reaction gas ratios or flows, voltages,
currents, or any additional settings as outlined by the
detector manufacturer.
6.6.1 Detection limits must be speci fied for each
impurity for the actual methodology used. Because the
lower detection limit can be greatly influenced by
retention time for any impurity, it is important that the
detection limit be derived for the impurity within the
context of the method, and not solely on the
detectability of the detector. Detection limits are
assumed to be calculated on a mole/mole basis.
6.7 Operating Procedures — The standard procedure
assumed for the gas chromatographic analysis of most
gases is as follows:
1. Inject the calibration standard onto the column
using a gas sampling valve. Record the retention
time(s) and peak area(s) for all impurities detected.
2. Analyze the sample to be tested in the same
manner as the calibration standard.
3. Repeat 1.
4. Compare the average peak area of the calibration
standard with that of the sample being tested. (See
Calculation of Concentration, in Section 6.9.)
6.7.1 The method should specify an y additional valve
switching or special parameters which are necessary for
the successful analysis of the impurities specified for
the procedure. It must also specify the order of elution
if multiple impurities are detected.
6.8 Calibration — Calibration for these analytical
procedures is generally by external, single point
calibration. Calibration gas mixtures should be
specified and are assumed to be within the range
specified in Section 2.26. Calibration standards are
assumed to be made in a balance of gas representative
of the sample unless otherwise specified. If calibration
techniques other than external, point calibrations are
used, they must be described.
6.9 Calculation of Concentration — The calculation of
the concentration of impurity within the sample is based
on a comparison of the average peak area of the
impurity in the calibration standard, to the average peak
area of the impurity within the sample, based on the
formula:
Sample Peak Are
a
Standard Peak Are
a
×
Concentratio
n
of Standard
=
Concentratio
n
of Sample
SEMI C3-0699 © SEMI 1986, 19997
It is assumed that the results of such a calculation must
not exceed the specification for the product being
analyzed.
6.10 Notes — Any special requirements for any
section within gas method may be included here. Notes
should reflect the minimum requirements to
successfully achieve the desired detection limits with
the equipment specified.
1.1 Impurity analyzed - description of method (e.g., gas
chromatograph with thermal conductivity detector).
1.1.1 Detection Limit - (mole/mole)
1.1.2 Instrument Parameters
1.1.2.1 Column(s):
Adsorbent, mesh size, length in meters, (dimensions if
other than 1/8 in. by 0.085 in.)
1.1.2.2 Carrier Flow: mL/min, gas type
1.1.2.3 Support Gases:
1.1.2.4 Sample Volume: mL
1.1.2.5 Temperatures:
Detector: °C
Columns: °C
Other Equipment: °C
1.1.3 Calibration Standard - amount ppm (or ppb)
impurity, balance if other than helium.
1.1.4 Operating Procedure (Parameters)
1.1.4.1 Order of elution
1.1.4.2 Special instructions
1.1.5 Notes
1.1.6 Figures
Figure 1
Format for Gas Chromatographic Method
7 Special Analyses
7.1 Resistivity Measurement — The American Society
of Testing and Materials (ASTM) is developing a
method to measure resistivity in substrates. This
method may be referenced when it is finalized.
7.2 Metal Analysis of Gaseous Silicon Compounds
7.2.1 Because of the importance of t race elemental
impurities impacting silicon device characteristics,
there is an increasing need for the detection and
quantitative analysis of low-level impurities in the
silicon materials used in device fabrication. Some of
these materials are gaseous silicon-containing
compounds, such as silane and the chlorosilanes. For
elemental analysis by FTIR or PLS, a compound must
first be converted to a solid form such as a single
crystalline rod or disc. For the quantitative
determination of metals and some non-metallic
elements, the gases can be passed through a series of
bubblers containing high-purity DI water or dilute
acids. The aqueous media can be concentrated and
analyzed by suitable techniques such as ICP or AA
spectroscopy. In both cases, the recovery is assumed to
be 100% efficient or, in other words, there is no loss of
any impurity from the silicon source.
7.2.2 FTIR (Fourier Transform Infrared)
Spectroscopy, PLS (Photoluminescence Spectroscopy)
and NAA (Neutron Activation Analysis) are probably
the most useful tools for the detection and analysis of
trace quantities of elemental impurities in solid silicon
materials. NAA requires special silicon material
specimens to be submitted to neutron irradiation in a
nuclear reactor and the analysis facility to be approved
by the Nuclear Regulatory Commission (NRC) and
other government agencies. In contrast, FTIR and PLS
do not require special governmental regulations, and the
instrumentation is available on the open market.
7.2.3 An FTIR spectrometer is an infrared
spectrometer in which a Michelson Interferometer is
used in place of a grating or prism. The simplicity of
the Michelson Interferometer, with only one moving
part, an oscillating mirror, along with a He-Ne laser as a
reference, provides nearly absolute frequency accuracy.
This translates into a high spectral resolution. FTIR has
greater detection efficiency since the energy-wasting
slits required for dispersive spectrometers are not used.
With a microcomputer to control the functions and to
perform data processing, signal averaging is used to
improve the signal-to-noise ratio. All these features lead
to good reproducibility and rapid measurement results
compared with conventional IR techniques.
7.2.3.1 As FTIR is a transmission met hod, it requires a
single crystalline silicon specimen with flat, parallel,
mirror-polished surfaces. For oxygen in silicon, the
absorption peak at 9 microns is used for quantitative
analyses. For carbon in silicon, the absorption band at
16 microns is used. Both measurements may be
performed at room temperature. (The carbon
determination has strong interference from the silicon
phonon band, but can be resolved with high purity,
carbon-free standards.) For the determination of
shallow donors and acceptors, FTIR measurements
must be made at liquid helium temperatures, but the
through-put is low. Although the operation of today's
FTIR instrument is relatively simple, the interpretation
of the results through software and associated
problems/solutions is not. Quantitative analysis is based
upon the measured percent transmission at the
characteristic wavelength and compared to standards.
Detection limits at about 10-12°K are in the 10
11
to 10
13
atoms/cc for shallow donors and acceptors, 3.1 × 10
14
atoms/cc for oxygen, and 2 × 10
15
atoms/cc for carbon.
SEMI C3-0699 © SEMI 1986, 1999 8
Table 2 Carrier Gases for GC Instruments
Detector Gas Detection Level
0 - 100 ppt 100 ppt - 100
ppb
100 ppb - 100
ppm
100 ppm - 1% 1% - 10% 10% - 100%
TCD/USD Ar N/A N/A 99.9999% 99.999% 99.998% 99.995%
H
2
N/A N/A 99.9995% 99.999% 99.99% 99.99%
He N/A N/A 99.9995% 99.9995% 99.999% 99.99%
N
2
N/A N/A 99.9995% 99.9995% 99.998%
< 0.5 ppm O
2
99.998%
HID/DID He N/A 99.9999% 99.9999% N/A N/A N/A
He* N/A 99.995% 99.995% N/A N/A N/A
FID He N/A N/A 99.9995% 99.999% 99.998% 99.99%
N
2
N/A N/A 99.999%
< 0.05 ppm
THC
99.999%
< 0.05 ppm
THC
99.998%
< 0.5 ppm THC
99.998%
H
2
** N/A N/A 99.9995%
< 0.2 ppm THC
99.999%
< 0.5 ppm THC
99.99%
< 0.5 ppm THC
99.99%
Air** N/A N/A HC Free
< 0.1 ppm THC
Zero Air
< 1 ppm THC
Zero Air
< 1 ppm THC
Blended Air
FPD He N/A 99.9995% 99.999% N/A N/A N/A
N
2
N/A 99.999%
< 0.05 THC
99.998%
< 0.5 ppm THC
N/A N/A N/A
H
2
** N/A 99.995%
< 0.2 ppm THC
99.999%
< 0.5 ppm THC
N/A N/A N/A
Air** N/A HC Free
< 0.1 ppm THC
Zero Air
< 1 ppm THC
N/A N/A N/A
RGD Ar 99.999%
< 1 ppm H
2
/CO
99.999%
< 1 ppm H
2
/CO
99.999%
< 1 ppm H
2
/CO
99.999%
< 1 ppm H
2
/CO
N/A N/A
N
2
99.999%
< 1 ppm H
2
/CO
99.999%
< 1 ppm H
2
/CO
99.999%
< 1 ppm H
2
/CO
99.999%
< 1 ppm H
2
/CO
N/A N/A
Air Zero Air
< 1 ppm H
2
/CO
Zero Air
< 1 ppm H
2
/CO
Zero Air
< 1 ppm H
2
/CO
Zero Air
< 1 ppm H
2
/CO
N/A N/A
ECD N
2
99.9995% 99.998%
< 0.5 ppm O
2
99.998%
< 0.5 ppm O
2
N/A N/A N/A
CH
4
/Ar EC Grade
< 1 ppb Total
Halocarbons
EC Grade
< 1 ppb Total
Halocarbons
EC Grade
< 1 ppb Total
Halocarbons
N/A N/A N/A
PID He N/A 99.9995% 99.995% N/A N/A N/A
N
2
N/A 99.9995% 99.998% N/A N/A N/A
MS/MSD H
2
99.9995%
< 0.2 ppm THC
99.999%
< 0.5 ppm THC
99.999%
< 0.5 ppm THC
99.99%
< 0.5 ppm THC
99.99%
< 0.5 ppm THC
99.99%
< 0.5 ppm THC
Ar 99.999% 99.998% 99.998% 99.998% 99.998% 99.998%
He 99.9995% 99.999% 99.999% 99.995% 99.995% 99.995%
N
2
99.9995% 99.998% 99.998% 99.998% 99.998% 99.998%
*purge gas
**combustion gases