ASTM F1528-94(1999)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 1528 – 94 (Reapproved 1999)
Standard Test Method for
Measuring Boron Contamination in Heavily Doped N-Type
Silicon Substrates by Secondary Ion Mass Spectrometry
This standard is issued under the fixed designation F 1528; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.2 primary ions—ions created and focussed by an ion
gun onto the specimen surface to sputter ionize surface atoms.
1.1 This test method covers the determination of total trace
3.1.3 secondary ions—ions that leave the specimen surface
boron contamination in the bulk of single crystal, heavily
as a result of the primary ion beam sputter ionizing the
doped n-type silicon substrates using secondary ion mass
specimen surface atoms.
spectrometry (SIMS).
3.1.4 secondary ion mass spectrometry—mass spectrometry
1.2 This test method can be used for silicon in which the
performed upon secondary ions from the specimen surface.
dopant concentrations are less than 0.2 % (1 by 10 atoms/
cm ) for antimony, arsenic or phosphorus. This test method is
4. Summary of Test Method
especially applicable for silicon where boron, the p-type
4.1 Secondary ion mass spectrometry (SIMS) is utilized to
dopant, is an unintentional contaminant at trace levels (<5 by
14 3
determine the bulk contamination of boron in single crystal,
10 atoms/cm ).
heavily doped n-type silicon substrates. Specimens of single
1.3 This test method can be used for silicon in which the
crystal silicon (one silicon specimen with very low boron
boron contamination is greater than two times the SIMS
12 concentration, such as a high resistivity n-type float-zone
detection limits that is approximately between 5 by 10
3 13 3
silicon specimen, to be used as an instrumental BLANK; one
atoms/cm and5by10 atoms/cm depending upon the
calibration specimen made of a bulk-doped boron silicon
instrumentation type described herein.
wafer; and the test specimens) are loaded into a sample holder.
1.4 In principle, different sample surfaces can be used, but
An oxygen primary ion beam is used to bombard each
the precision estimate was taken from data on polished etched
specimen. The positive secondary ions are mass analyzed. The
surfaces.
BLANK silicon sample is sputtered to achieve instrumental
1.5 This standard does not purport to address all of the
background. The samples are then analyzed for boron and
safety concerns, if any, associated with its use. It is the
silicon in a sequential manner throughout the holder. The ratio
responsibility of the user of this standard to establish appro-
of the measured boron and silicon secondary ion intensities
priate safety and health practices and determine the applica-
+ + + +
(B /S ) is calculated for each specimen. The (B /Si ) ratios of
bility of regulatory limitations prior to use.
the test specimens are then converted to boron concentrations
+ +
2. Referenced Documents by linear scaling from the (B /Si ) ratio of the calibration
specimen that has a known boron concentration. No crater
2.1 ASTM Standards:
measurement is required.
E 122 Practice for Choice of Sample Size to Estimate a
Measure of Quality of a Lot or Process
5. Significance and Use
3. Terminology 5.1 SIMS can measure the boron contamination in heavily-
doped n-type substrates where this contamination can result in
3.1 Definitions of Terms Specific to This Standard:
autodoping at the epitaxial silicon-substrate interface.
3.1.1 ion mass spectrometry—the separation and counting
5.2 This test method can be used for process control,
of ions by their mass-to-charge ratio.
research and development, and materials acceptance purposes.
1 6. Interferences
This test method is under the jurisdiction of ASTM Committee F-1 on
Electronics and is the direct responsibility of Subcommittee F01.06 on Silicon
6.1 Boron adsorbed on the surface can interfere with the
Materials and Process Control.
boron measurement.
Current edition approved July 15, 1994. Published September 1994.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 1528 – 94 (1999)
6.2 Boron adsorbed from the SIMS instrument chamber to 10. Calibration
the surface can interfere with the boron measurement.
10.1 The calibration standard must be present with bulk
14 3
6.3 The specimen surface must be flat in the specimen boron concentration between 1 and 10 by 10 atoms/cm as
determined by some other measurement that is agreed upon by
holder windows so that the inclination of the specimen surface
the parties.
with respect to the ion collection optics is constant from
10.2 Each calibration standard specimen must be the same
specimen-to-specimen. Otherwise, the accuracy and precision
size and have the same polished surface as the test specimen.
can be degraded.
10.3 Each BLANK specimen must be the same size and
6.4 The accuracy and precision of the measurement degrade
have the same polished surface as the test specimen.
significantly as the roughness of the specimen surface in-
creases. This degradation can be avoided by using polished
11. Procedure
etched surfaces.
11.1 Specimen Loading:
6.5 Variability of boron in the calibration standards can limit
11.1.1 Load the specimens into the SIMS sample holder
the measurement precision.
checking to see that the specimens are flat against the backs of
6.6 Bias in the assigned boron concentration of the calibra-
the windows and cover the windows as much as is possible. A
tion standard can introduce bias into the SIMS measured
specimen load includes: one BLANK silicon specimen, one
boron.
calibration specimen, and the test specimens.
11.2 Instrument Tuning:
7. Apparatus
11.2.1 Turn on the instrument in accordance with the
manufacturer’s instructions.
7.1 Magnetic Sector SIMS Instrument, equipped with an
11.2.2 Fill the liquid nitrogen or helium cold trap if cooling
oxygen primary ion source, electron multiplier detector, and
equipment is used as stated in 7.2.
Faraday cup detector or daley detector capable of measuring
11.2.3 Analytical Conditions:
positive secondary ions. The SIMS instrument should be
11.2.3.1 Use a focused oxygen primary-ion current and
adequately prepared (that is, baked) so as to provide the lowest
adjust the contrast diaphragm and field aperture to maximize
possible instrumental background.
+ 8
the Si -ion count rate. The rate must be greater than 1 by 10
7.2 Liquid Nitrogen or Liquid Helium Cooled Cryopanel,
counts/s as measured on the Faraday cup or daley detector, and
that surrounds the test specimen holder in the analysis chamber
with no raster.
−8
if the analysis chamber vacuum is 10 torr or higher. For
11.2.3.2 Typical first raster test conditions are several hun-
−8
instruments with vacuum less than 10 torr the cooling is not
dred microns by several hundred microns depending upon the
required.
beam radius, (typical condition is 250 by 250-μm raster) to
7.3 Test Specimen Holder—A test sp
...