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SEMI MF1366-0305 © SEMI 2003, 2005 1 SEMI MF1366-0305 TEST METHOD FOR MEASURING OXYGEN CONCENTRATION IN HEAVILY DOPED SILICON SUBSTR ATES BY SECON DARY ION MASS SPECTROMETRY These test methods were techni cally approved …
SEMI MF1239-0305 © SEMI 2003, 2005 7
oxygen concentration, partial precipitation occurs (in this transition region, oxygen reduction changes rapidly with
increasing initial oxygen concentration); at high initial oxygen concentration, full precipitation occurs (in this
region, oxygen reduction is proportional to initial oxygen concentration).
12.2.2.6 Compare the curves obtained for each group. If the data for each group falls within a band of suitable
width, consider the groups equivalent.
13 Report
13.1 Report the following for each group tested:
13.1.1 Identification of group (lot number, location of measurement point on wafer, center or edge, etc.),
13.1.2 Dates of initial and final oxygen measurement and of the heat treatment and identification of operators for
measurement and heat treatment,
13.1.3 Identification of infrared spectrophotometer used,
13.1.4 Table of initial and final oxygen concentrations for each wafer measured, and
13.1.5 Averages and standard deviations of the initial oxygen content and oxygen reduction for each group tested.
13.2 In addition, if Method 2 was used, report the following:
13.2.1 Table of average initial oxygen concentration and average oxygen reduction for each bin in each group, and
13.2.2 Graph of average oxygen reductions against average initial oxygen concentrations for each group.
14 Precision
14.1 Wafers from six different groups with different back surface conditions were processed in two laboratories and
combined. Both Cycles A and B were used. Measurements of initial and final oxygen concentrations on all wafers
tested were made at two other laboratories.
14.2 The wafers within each group did not meet the 2-wafer per 0.5 ppma interval required by these test methods.
14.3 Nevertheless, from the plots reproduced as Figures 2 through 5, both measurement laboratories (that employed
different FT-IR spectrophotometers for making the oxygen determinations at the center of the wafers only)
concluded that the wafers from Groups V1, V3, V4, V5, and V6 were essentially equivalent but those from Group
V2 had increased precipitation in the transition region.
15 Bias
15.1 No reference standards are available for precipitated oxygen, so it is impossible to determine bias except for
that of the individual oxygen measurements. Bias of the individual oxygen measurements should be determined in
accordance with the procedures of the test method utilized.
16 Keywords
delta [O
i
]; interstitial oxygen; oxygen precipitation; oxygen reduction; silicon ; [O
i
]
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SEMI MF1366-0305 © SEMI 2003, 2005 1
SEMI MF1366-0305
TEST METHOD FOR MEASURING OXYGEN CONCENTRATION IN
HEAVILY DOPED SILICON SUBSTRATES BY SECONDARY ION MASS
SPECTROMETRY
These test methods were technically approved by the Global Silicon Wafer Committee and are the direct
responsibility of the North American Silicon Wafer Committee. Current edition approved for publication by
the North American Regional Standards Committee on December 10, 2004. Initially available at
www.semi.org January 2005; to be published March 2005. Original edition published by ASTM
International as ASTM F 1366-92. Last previous edition SEMI MF1366-02.
1 Purpose
1.1 The presence of oxygen can be beneficial to certain manufacturing operations by preventing the formation of
process-induced defects. Oxygen is introduced into silicon wafers during the crystal growing process. Hence, it is
very important to control the oxygen content of silicon crystals.
1.2 SIMS can measure the oxygen concentration in heavily-doped silicon substrates used for epitaxial silicon where
the free carrier concentration obscures the infrared absorption and prevents the normal use of the infrared
measurement as a characterization technique for the commercial production of silicon.
1.3 The SIMS measurement allows for the production of controlled oxygen content in heavily-doped silicon
crystals.
1.4 This test method can be used for process control, research and development, and materials acceptance purposes.
2 Scope
2.1 This test method covers the determination of total oxygen concentration in the bulk of single crystal silicon
substrates using secondary ion mass spectrometry (SIMS).
2.2 This test method can be used for silicon in which the dopant concentrations are less than 0.2% (1 × 10
20
atoms/cm
3
) for boron, antimony, arsenic, and phosphorus (see SEMI MF723). This test method is especially
applicable for silicon that has resistivity between 0.0012 and 1.0 ·cm for p-type silicon and between 0.008 and 0.2
·cm for n-type silicon (see SEMI MF43).
2.3 This test method can be used for silicon in which the oxygen content is greater than the SIMS instrumental
oxygen background as measured in a float zone silicon sample, but the test method has a useful precision especially
when the oxygen content is much greater (approximately 10× to 20×) than the measured oxygen background in the
float zone silicon.
2.4 This test method is complementary to infrared absorption spectroscopy that can be used for the measurement of
interstitial oxygen in silicon that has resistivity greater than 1.0 ·cm for p-type silicon and greater than 0.1 ·cm
for n-type silicon (see SEMI MF1188). The infrared absorption measurement can be extended to between 0.02 and
0.1 ·cm for n-type silicon with minor changes in the measurement procedure.
1
2.5 In principle, different sample surfaces can be used, but the precision estimate was taken from data on chemical-
mechanical polished surfaces.
NOTICE: This standard does not purport to address safety issues, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate safety and health guides and determine the
applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 Oxygen from silicon oxide, carbon oxide, and water on the surface can interfere with the oxygen measurement.
3.2 Oxygen adsorbed from the SIMS instrument chamber to the surface can interfere with the oxygen measurement.
1 Hill, D. E., “Determination of Interstitial Oxygen Concentration in Low-Resistivity n-type Silicon Wafers by Infrared Absorption
Measurements,” J. Electrochem. Soc. 137, 3926 (1990).
SEMI MF1366-0305 © SEMI 2003, 2005 2
3.3 There are no effects upon the oxygen ion yield from the dopants for dopant densities less than 1 × 10
20
atoms/cm
3
.
2
3.4 The SIMS oxygen instrumental background as measured on the float zone silicon specimen should be as low as
possible and stable before the analyses are begun.
3.5 The specimen surface must be flat in the specimen holder windows so that the inclination of the specimen
surface with respect to the ion collection optics is constant from specimen to specimen. Otherwise, the accuracy and
precision can be degraded.
3.6 The accuracy and precision of the measurement significantly degrade as the roughness of the specimen surface
increases. This degradation can be avoided by using chemical-mechanical polished surfaces.
3.7 Variability of oxygen in the calibration standards can limit the measurement precision.
3.8 Bias in the assigned oxygen of the calibration standards can introduce bias into the SIMS measured oxygen.
4 Referenced Standards
4.1 SEMI Standards
SEMI MF43 — Test Methods for Resistivity of Semiconductor Materials
SEMI MF723 — Practice for Conversion between Resistivity and Dopant Density for Arsenic-Doped, Boron-
Doped, and Phosphorus-Doped Silicon
SEMI MF1188 — Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption
4.2 ASTM Standard
E 122 — Practice for Choice of Sample Size to Estimate a Measure of Quality for a Lot or Process
3
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Definitions
5.1.1 IOC-88 — calibration factor
4
for infrared absorption measurements of oxygen in silicon that gives a value
equivalent to that found by the SIMS method.
5.1.2 ion mass spectrometry — the separation and counting of ions by their mass-to-charge ratio.
5.1.3 primary ions — ions created and focussed by an ion gun onto the specimen surface to sputter ionize surface
atoms.
5.1.4 secondary ions — ions that leave the specimen surface as a result of the primary ion beam sputter ionizing the
specimen surface atoms.
5.1.5 secondary ion mass spectrometry — mass spectrometry performed upon secondary ions from the specimen
surface.
6 Summary of Test Method
6.1 SIMS is utilized to determine the bulk concentration of oxygen in single crystal silicon substrate.
2 Bleiler, R. J., Chu, P. K., Novak, S. W., and Wilson, R. G.,“ Study of Possible Matrix Effects in the Quantitative Determination of Oxygen in
Heavily Doped Czochralski Silicon Crystals,” Seventh International Meeting on Secondary Ion Mass Spectrometry, SIMS VII (John Wiley and
Sons, 1990), p. 507.
3 Annual Book of ASTM Standards, Vol 14.02, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Telephone: 610-
832-9500, Fax: 610-832-9555, Website:
www.astm.org
.
4 Baghdadi, A., Bullis, W. M., Croakin, M. C., Li Yue-zhen, Scace, R. I., Series, R. W., Stallhofer, P., and Watanabe, M., “Interlaboratory
Determination of the Calibration Factor for the Measurement of the Interstitial Oxygen Content of Silicon by Infrared Absorption,” J.
Electrochem. Soc. 136, 2015–2034 (1989). Baghdadi, A., Scace, R. I., and Walters, E. J., “Semiconductor Measurement Technology: Database
for and Statistical Analysis of the Interlaboratory Determination of the Calibration Factor for the Measurement of the Interstitial Oxygen Content
of Silicon by Infrared Absorption,” NIST Special Publication 400-82, July 1989.