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SEMI MF1528-1104 © SEMI 2004 1 SEMI MF1528-1104 TEST METHOD FOR MEASURIN G BORON CONTAMINATION IN HEAVILY DOPED n -TYPE SILICON SUBSTR ATES BY SECONDARY ION MASS SPECTROMETRY This guide was technically approved b y the G…

SEMI MF1527-1104 © SEMI 2003, 2004 20

curve drawn through the experimental data

by more

than 0.0002 (·cm)/(·cm·°C). SEMI MF84 includes a

table of values calculated from this fit and extended

down to 0.0006 ·cm and up to 100 ·cm by taking

smoothed values to avoid the oscillations of the

polynomials in the extreme regions.

R2-5 By substituting these relations into Equation R2-

4, one obtains the following:

082.1

)082.1(

)1(











(R2-14)

R2-6 Estimates of the errors in resistivity measurement

due to uncertainties in diameter, thickness and probe-tip

spacing can be made by inserting the values of a and b

appropriate to the ratios

/D and w/

from Figure

R2-1 and Figure R2-2 into Equation R2-14.

R2-7 It should also be emphasized that uncertainties

due to lateral and axial resistivity inhomogeneity in the

reference wafer are likely to cause significant errors in

resistivity measurement that may be as large or larger

than those discussed in this appendix unless the

material for the reference wafers is carefully selected

for the best possible uniformity.

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representations as to the suitability of the standards set

forth herein for any particular application. The

determination of the suitability of the standard is solely

the responsibility of the user. Users are cautioned to

refer to manufacturer's instructions, product labels,

product data sheets, and other relevant literature,

respecting any materials or equipment mentioned

herein. These standards are subject to change without

notice.

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SEMI MF1528-1104 © SEMI 2004 1

SEMI MF1528-1104

TEST METHOD FOR MEASURING BORON CONTAMINATION IN

HEAVILY DOPED n-TYPE SILICON SUBSTRATES BY SECONDARY

ION MASS SPECTROMETRY

This guide was technically approved by the Global Silicon Wafer Committee and is the direct responsibility

of the North American Silicon Wafer Committee. Current edition approved for publication by the North

American Regional Standards Committee on August 16, 2004. Initially available at www.semi.org

September 2004; to be published November 2004. Original edition published by ASTM International as

ASTM F 1528-94. Last previous edition SEMI MF1528-94 (Reapproved 1999).

1 Purpose

1.1 Frequently it is essential to control the boron level

in heavily-doped n-type substrates used to make

epitaxial wafers because the boron contamination can

result in autodoping at the epitaxial silicon-substrate

interface.

1.2 SIMS can measure the boron contamination in

heavily-doped n-type substrates.

1.3 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

trace boron contamination in the bulk of single crystal,

heavily doped n-type 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 antimony, arsenic or phosphorus

doping. This test method is especially applicable for

silicon where boron is an unintentional p-type

contaminant at trace levels (<5  10

atoms/cm

2.3 This test method can be used for silicon in which

the boron contamination is greater than two times the

SIMS detection limits that is approximately between 5

 10

atoms/cm

and 5  10

atoms/cm

depending

upon the instrumentation type.

2.4 In principle, different sample surfaces can be used,

but the precision estimate was taken from data on

polished etched 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 practices and determine

the applicability of regulatory or other limitations prior

to use.

3 Limitations

3.1 Boron adsorbed on the surface can interfere with

the boron measurement.

3.2 Boron adsorbed from the SIMS instrument

chamber to the surface can interfere with the boron

measurement.

3.3 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.

3.4 The accuracy and precision of the measurement

degrade significantly as the roughness of the specimen

surface increases. This degradation can be avoided by

using polished etched surfaces.

3.5 Variability of boron in the calibration standards can

limit the measurement precision.

3.6 Bias in the assigned boron concentration of the

calibration standard can introduce bias into the SIMS

measured boron.

4 Referenced Standards

4.1 SEMI Standards

SEMI M1 — Specifications for Polished

Monocrystalline Silicon Wafers

SEMI MF1241 — Terminology of Silicon Technology

4.2 ASTM Standard

E 122 — Practice for Choice of Sample Size to

Estimate a Measure of Quality of a Lot or Process

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

1 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

SEMI MF1528-1104 © SEMI 2004 2

5 Terminology

5.1 Definitions

5.1.1 ion mass spectrometry — the separation and

counting of ions by their mass-to-charge ratio.

5.1.2 primary ions — ions created and focused by an

ion gun onto the specimen surface to sputter ionize

surface atoms.

5.1.3 secondary ion mass spectrometry — mass

spectrometry performed upon secondary ions from the

specimen surface.

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.

5.2 For definitions of other terms used in silicon wafer

technology refer to SEMI M1 and SEMI MF1241.

6 Summary of Test Method

6.1 Secondary ion mass spectrometry (SIMS) is

utilized to determine the bulk contamination of boron in

single crystal, heavily doped n-type silicon substrates.

6.1.1 Specimens of single crystal silicon (one silicon

specimen with very low boron concentration, such as a

high resistivity n-type float-zone silicon specimen, to be

used as an instrumental BLANK; one calibration

specimen made of a bulk-doped boron silicon wafer;

and the test specimens) are loaded into a sample holder.

6.1.2 An oxygen primary ion beam is used to bombard

each specimen.

6.1.3 The positive secondary ions are mass analyzed.

6.1.4 The BLANK silicon sample is sputtered to

determine instrumental background.

6.1.5 The samples are then analyzed for boron and

silicon in a sequential manner throughout the holder.

6.1.6 The ratio of the measured boron and silicon

secondary ion intensities (B

) is calculated for each

specimen.

6.1.7 The (B

/Si

) ratios of the test specimens are then

converted to boron concentrations by linear scaling

from the (B

/Si

) ratio of the calibration specimen that

has a known boron concentration.

6.1.8 No crater measurement is required.

7 Apparatus

7.1 Magnetic Sector SIMS Instrument, equipped with

an oxygen primary ion source, electron multiplier

detector, and Faraday cup detector or daley detector

capable of measuring positive secondary ions. The

SIMS instrument should be adequately prepared (that

is, baked) so as to provide the lowest possible

instrumental background.

7.2 Liquid Nitrogen or Liquid Helium Cooled

Cryopanel, to surround the test specimen holder in the

analysis chamber if the analysis chamber vacuum is

8

torr or higher. For instruments with vacuum less

than 10

8

torr the cooling is not required.

7.3 Test Specimen Holder, to keep the specimen(s)

analysis surface planar and perpendicular to the several

kV extraction field, depending on the instrument type.

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.

8.1.1 No general sampling procedure is included as

part of this test method, because the most suitable

sampling plan varies considerably depending upon

individual conditions. See ASTM Practice E 122 for

suggested choices of sampling plans.

8.1.2 For referee purposes, a sampling plan shall be

agreed upon between the parties to the test before

conducting the test.

9 Specimen Requirements

9.1 Sample specimens must be flat and smooth on the

side used for analysis. The surface shall have a polish

etch surface or better (that is, chem-mechanically

polished).

9.2 Sample specimens must be cleaved or diced to fit

within the sample specimen holder.

9.3 A bulk boron-doped silicon calibration specimen is

required.

9.4 A BLANK silicon specimen with boron

concentration below 5  10

atoms/cm

must be

present.

10 Calibration

10.1 The calibration standard must be present with

bulk boron concentration between 1 and 10  10

atoms/cm

as determined by some other measurement

that is agreed upon by the parties.

10.2 Each calibration standard specimen must be the

same size and have the same polished surface as the test

specimen.

10.3 Each BLANK specimen must be the same size

and have the same polished surface as the test

specimen.