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SEMI MF2139-1103 © SEMI 2003 1 SEMI MF2139-1103 TEST METHOD FOR MEASURING NITROGEN CONCENTRATION IN SILICON SUBSTRATES BY SECONDARY ION MASS SPECTROMETRY This standard was technically approved by the Global Silicon Wafer…

SEMI MF2074-1103 © SEMI 2003 3

Table 1 Positions for Measurement of Wafer Diameter

Configuration Primary Fiducial Secondary Flat Diameter 1 Diameter 2 Diameter 3

1 270° 180° 45° 135° 165°

2 270° none 0° 45° 135°

3 270° 90° 0° 45° 135°

4 270° 225° 0° 120° 150°

5 270° 135° 0° 30° 60°

Table 2 Wafer Types and Orientations Corresponding to Measurement Configuration of Table 1

Configuration

Conductivity

Type

Orientation Notes

1 p [100] Applies only to [100] p-type wafers, 150 mm and smaller, with secondary

flats

2 p [111] Applies both to [111] p-type wafers, 150 mm and smaller, (without

secondary flats) and to all other notched and flatted wafers without secondary

flats regardless of conductivity type and orientation

3 n [100] Applies only to [100] n-type wafers, 125 mm and smaller, with secondary

flats

4 n [111] Applies only to [111] n-type wafers, 150 mm and smaller, with secondary

flats

5 n [100] Applies only to [100] n-type 150 mm wafers with secondary flats

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SEMI MF2139-1103 © SEMI 2003 1

SEMI MF2139-1103

TEST METHOD FOR MEASURING NITROGEN CONCENTRATION IN

SILICON SUBSTRATES BY SECONDARY ION MASS SPECTROMETRY

This standard 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 July 27, 2003. Initially available at www.semi.org

October 2003; to be published November 2003. Originally published by ASTM International as ASTM

F 2139-01. Last previous edition ASTM F 2139-01.

1 Purpose

1.1 Secondary ion mass spectrometry (SIMS) can

measure in un-annealed, polished Czochralski (CZ)

silicon substrates the nitrogen concentration that may

be intentionally introduced to: (1) increase the V/G

tolerance for grown-in defects free region, where V is

the pull rate and G is the crystal temperature gradient at

the solid-liquid interface;

(2) increase the void-free

denuded zone depth and the bulk micro-defect density

after annealing in hydrogen or argon;

2,3

(3) reduce the

crystal originated particle (COP) size after annealing;

2,3

or (4) enhance the precipitation of oxygen in epitaxial

substrates under reduced temperature processing.

1.2 SIMS can measure total bulk nitrogen in CZ-

silicon, whereas infrared spectroscopy is negatively

affected by the chemical state in oxygen-containing

silicon.

In addition, SIMS can measure the total bulk

nitrogen in p

(B) and n

(Sb) substrates used for

epitaxial silicon, whereas infrared spectroscopy cannot

due to free electron absorption interferences.

1.3 SIMS can measure in un-annealed, polished Float-

zoned (FZ) silicon substrates the nitrogen concentration

1 Iida, M., Kusaki, W., Tamatsuka, M., Iino, E., Kimura, M., and

Muraoka, S., “Effects of Light Element Impurities on the Formation

Grown-In Defects Free Region of Czochralski Silicon Single

Crystal,” in Defects in Silicon III, edited by W. M. Bullis, W. Lin, P.

Wagner, T.Abe, and S. Kobayashi, The Electrochemical Society

Proceedings Series PV99-1 (The Electrochemical Society,

Pennington, NJ, 1999) pp. 499-510.

2 Tamatsuka, M., Kobayashi, N., Tobe, S., and Masui, T., “High

Performance Silicon Wafer with Wide Grown-in Void Free Zone and

High Density Internal Gettering Site Achieved via Rapid Crystal

Growth with Nitrogen Doping and High Temperature Hydrogen

and/or Argon Annealing,” ibid., pp.456-467.

3 Minami, T., Takeda, R., Saito, H., Hirano, Y., Suzuki, O., Nitta, S.

Kashima, K., and Matsushita, Y., “Influence of Void Size on the

Formation of Defect Free Regions in Hydrogen Annealed CZ Silicon

Wafers,” ECS Extended Abstract No.514, 197th Meeting of the

Electrochemical Society, (The Electrochemical Society, Pennington,

NJ, 2000).

4 Shimura, F., and Hockett, R. S., “Nitrogen effect on oxygen

precipitation in Czochralski silicon,” Appl. Phys. Lett. 48, 224-226

(1986).

5 Abe, T., Kikuchi, K., Shirai, S., and Muraoka, M., in Semicon-

ductor Silicon 1981, edited by H. R. Huff, R. J. Kriegler and Y.

Takeishi, (The Electrochemical Society, Pennington, NJ, 1981) pp.

54-71.

that may be introduced to strengthen low oxygen

substrates.

1.4 The SIMS method can be used for process check of

crystal doping, and for research and development.

2 Scope

2.1 This test method covers the determination of total

nitrogen concentration in the bulk of single crystal

substrates using secondary ion mass spectrometry

(SIMS).

6,7

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.

2.3 This test method is for bulk analysis where the

nitrogen concentration is constant with depth.

2.4 This test method can be used for silicon in which

the nitrogen content is 1 × 10

atoms/cm

or greater.

The detection capability depends upon the SIMS

instrumental nitrogen background and the precision of

the measurement.

2.5 This test method is complementary to infrared

spectroscopy, electron paramagnetic resonance, deep

level transient spectroscopy, and charged particle

activation analysis.

The infrared spectroscopy method

detects nitrogen in specific vibrational states, rather

than total nitrogen, and is limited to silicon with doping

concentrations less than about 1 × 10

atoms/cm

. The

6 Hockett, R. S., Evans, Jr., C. A., and Chu, P. K., “The SIMS

Measurement of Nitrogen in Nitrogen-Doped CZ-Silicon,” in

Secondary Ion Mass Spectrometry SIMS VI, edited by A.

Benninghoven, A. M. Huber, and H. W. Huber, (John Wiley & Sons,

New York, 1988) pp. 441-444.

7 Hockett, R. S. and Sams, D. B., “The Measurement of Nitrogen in

Silicon Substrates by SIMS,” in High Purity Silicon VI, edited by C.

L. Claeys, P. Rai-Choudhury, M. Watanabe, P. Stallhofer, and H. J.

Dawson, ECS Proceedings Vol PV 2000-17 (The Electrochemical

Society, Pennington, NJ, 2000) pp. 584-595.

8 Stein, Herman J., “Nitrogen in Crystalline Si,” in Materials

Research Society Symposia Proceedings Vol 59, Oxygen, Carbon,

Hydrogen and Nitrogen in Crystalline Silicon, edited by J. C.

Mikkelsen, Jr., S. J. Pearton, J. W. Corbett, and S. J. Pennycook,

(Materials Research Society, Pittsburgh, PA, 1986) pp. 523-535.

SEMI MF2139-1103 © SEMI 2003 2

charged particle activation analysis detection capability

is limited by an interference from boron.

NOTICE: This standard does not purport to address the

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 Nitrogen on or in the surface silicon oxide can

interfere with the bulk nitrogen measurement.

3.2 Nitrogen adsorbed on the test specimen surface

from the SIMS instrument chamber and fixtures

interfere with the bulk nitrogen measurement by raising

the background signal. The vacuum quality of the

SIMS instrument can be used to minimize this.

3.3 Nitrogen in the SIMS primary Cs beam may be

implanted into the silicon specimen as CsN and thereby

increase the nitrogen background concentration. A

primary beam mass filter may be used to reduce this

interference, but in this case, a reduced Cs beam current

density is needed to maximize the sputter rate.

3.4 Anomalous nitrogen intensity spikes can interfere

with the averaging of signal intensity which is assumed

to be random (see Section 6.9).

3.5 Carbon introduces an interference as

Si at

mass 42 for detecting nitrogen as

Si. This can be

avoided by detecting the nitrogen as

Si at mass 43,

but the signal rate is reduced greatly, about a factor of

20 when the minor isotope of silicon is used. There are

methods to measure the carbon interference, and

subtract this interference. One of the methods to

measure the carbon interference can have its own

interference from high levels of boron dopant.

3.6 The specimen surface must be flat in the specimen

holder window 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.

3.7 The bias 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 wafers.

3.8 Variability of nitrogen in the calibration specimen

can limit the measurement precision.

3.9 Variability from the calibration measurement may

increase the measurement precision of the test

specimen.

3.10 Bias in the assigned nitrogen concentration of the

calibration specimen can introduce bias into the SIMS

measured nitrogen.

3.11 Thermal processing above 800° C of the silicon

substrate may cause diffusion of the nitrogen, so that

the nitrogen concentration is not constant with depth, a

key assumption of this test method.

3.12 Thermal processing of the silicon substrates in a

nitrogen-containing ambient can introduce large

amounts of nitrogen from the ambient deep into the

silicon crystal.

4 Referenced Standards

4.1 ASTM Standards

E 122 — Practice for Calculating Sample Size to Esti-

mate, with a Specified Tolerable Error, the Average for

a Characteristic of a Lot or Process

E 673 — Terminology Relating to Surface Analysis

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Definitions — all terms in this test method are in

accordance with those given in ASTM Terminology

E 673.

6 Summary of Test Method

6.1 SIMS is utilized to determine the bulk

concentration of nitrogen in single crystal silicon

substrate. Specimens of single crystal silicon (one

calibration specimen and the test specimens) are loaded

into a sample holder. 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.

6.2 The calibration sample is analyzed using a cesium

(Cs) primary ion beam and negative ion spectrometry of

Si, or

Si, depending upon the nitrogen isotope

in the calibration sample, to determine a relative

sensitivity factor (RSF) of nitrogen in silicon.

6.3 Each test specimen in the sample holder is

sputtered by the primary cesium ion beam, without

analyzing secondary ion intensities, in order to reduce

the nitrogen background. The amount of time required

for this pre-analysis sputtering depends upon the

instrumentation and the desired background nitrogen

concentration.

9 Available from ASTM International, 100 Barr Harbor Drive, West

Conshohoken, PA 19428-2959, USA. Telephone: 610.832.9585,

Fax: 610.832-9555, Web site:

www.astm.org. ASTM E 122 is

published in Volume 14.02 of Annual Book of ASTM Standards while

ASTM E 673 is published in Volume 3.06.