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SEMI MF1366-0305 © SEMI 2003, 2005 2 3.3 There are no effects upon the oxygen ion yield from the dopants for dopant dens ities less than 1 × 10 20 atoms/cm 3 . 2 3.4 The SIMS oxygen instrumental background as measured on…

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

atoms/cm

) 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.

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

atoms/cm

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

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

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.

SEMI MF1366-0305 © SEMI 2003, 2005 3

6.1.1 Specimens of single crystal silicon (one float-zone silicon specimen, two calibration specimens, and the test

specimen) are loaded into a sample holder.

6.1.2 The holder with the specimens is baked at 100°C in air for 1 h and then transferred into the analysis chamber

of the SIMS instrument.

6.1.3 A cesium primary ion beam is used to bombard each specimen. The negative secondary ions are mass

analyzed.

6.1.4 The specimens are presputtered sequentially to reduce the instrumental oxygen background.

6.1.5 The specimens are then analyzed, in locations different from the presputtering locations, for oxygen and

silicon in a sequential manner throughout the holder. Three measurement passes are made through the holder.

6.1.6 The ratio of the measured oxygen and silicon secondary ion intensities (O



/Si



) is calculated for each

specimen.

6.1.7 The relative standard deviation (RSD) of the ratio is then calculated for each specimen.

6.1.8 If any specimen other than the float zone specimen has a RSD of the ratio greater than 3%, more analyses are

performed.

6.1.9 The SIMS average O/Si ratios are then converted to infrared-equivalent concentrations by utilizing either the

load-line calibration method

or the load factor calibration method

with the calibration specimens in the load.

7 Apparatus

7.1 SIMS Instrument, equipped with a cesium primary ion source, electron multiplier detector and Faraday cup

detector, and capable of measuring negative secondary ions.

7.1.1 The SIMS instrument should be adequately prepared (that is, baked) so as to provide the lowest possible

instrumental background.

7.2 Cryopane1, liquid nitrogen- or liquid helium-cooled, which surrounds the test specimen holder in the analysis

chamber.

7.3 Test Specimen Holder.

7.4 Oven, for baking test specimen holder.

8 Sampling

8.1 Since this procedure is destructive in nature, a sampling procedure must be used to evaluate the characteristics

of a group of silicon wafers. No general sampling procedure is included as part of this test method, because the

most suitable sampling plan will vary considerably depending upon individual conditions. For referee purposes, a

sampling plan shall be agreed upon before conducting the test. See ASTM Practice E 122 for suggested choices of

sampling plans.

9 Specimen Requirements

9.1 Sample specimens must be flat and smooth on the side used for analysis.

9.2 Sample specimens must be cleaved or diced to fit within the sample specimen holder.

10 Calibration

10.1 The two calibration standards in each load must be lightly doped Czochralski silicon

in which the oxygen

concentration is measured by infrared absorption spectroscopy (see SEMI MF1188), and the measured values of the

5 Goldstein, M., and Makovsky, J., “The Calibration and Reproducibility of Oxygen Concentration in Silicon Measurements Using SIMS

Characterization Techniques,” Semiconductor Fabrication: Technology and Metrology, ASTM STP 990, Dinesh C. Gupta, Ed. (ASTM, 1988) pp.

350–360.

6 Makovsky, J., Goldstein, M., and Chu, P., “Progress in the ‘Load Line Calibration’ Method for Quantitative Determination of [O] in Silicon by

SIMS,” Seventh International Meeting on Secondary Ion Mass Spectrometry, SIMS VII (John Wiley and Sons, 1990) p. 487.

7 Czochralski silicon is available from most silicon substrate suppliers.