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SEMI MF1630-0704 © SEMI 2004 1 SEMI MF1630-0704 TEST METHOD FOR LOW TEMPE RATURE FT-IR ANALYSIS OF SINGLE CRYSTAL SILICO N FOR III-V IMPURITIES This test method was technically approved by th e Global Silicon Wafer Commi…

SEMI MF1618-1104 © SEMI 2004 10

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SEMI MF1630-0704 © SEMI 2004 1

SEMI MF1630-0704

TEST METHOD FOR LOW TEMPERATURE FT-IR ANALYSIS OF

SINGLE CRYSTAL SILICON FOR III-V IMPURITIES

This test method 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 March 14, 2004. Initially available at

www.semi.org

May 2004; to be published July 2004. Original edition published by ASTM International as ASTM F 1630-

95. Last previous edition SEMI MF1630-00.

1 Purpose

1.1 Electronic grade polysilicon producers and users

rely on LTFT-IR spectroscopy to evaluate polysilicon

for quality assurance and research purposes.

1.2 LTFT-IR spectroscopy identifies and quantitates

boron, phosphorus, aluminum, arsenic, indium,

antimony, and gallium.

1.3 LTFT-IR spectroscopy can be applied to FZ, CZ, or

other single crystal silicon (either doped or undoped) up

to the concentration limits given in Section 2.2.

1.4 The measurement of carbon in silicon at low

temperature can be accomplished concurrently in

accordance with SEMI MF1391. The carbon can be

measured at lower concentrations at <15 K than is

possible at room temperature because the two-phonon

band transmission is increased by a factor of two

allowing greater throughput to the detector that results

in an increased signal to noise ratio. Also the carbon

adsorption band narrows from a FWHM of 5 to 6 cm

−1

to a FWHM of 2.5 to 3.0 cm

−1

at these low

temperatures.

2 Scope

2.1 This test method covers the determination of

electrically active boron, phosphorus, arsenic,

aluminum, antimony, and gallium concentration in

single crystal silicon.

2.2 This test method can be used for silicon in which

the impurity/dopant concentrations are between 0.01

ppba and 5.0 ppba for each of the electrically active

elements.

2.3 The concentration for each impurity/dopant can be

obtained by application of Beer’s Law. Calibration

factors are given for each element.

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 The sample specimen must be colder than 15 K for

measurement of electrically active species. If the

sample specimen is mounted on a cold finger, care must

be taken to obtain good contact between the sample

specimen and the cold finger for efficient heat transfer.

The oxygen absorption lines at 1136 cm

−1

and 1128

−1

are sensitive to temperature and can be used to

determine the specimen temperature.

When the

sample specimen is less than 15 K the net absorbance at

1136 cm

−1

is three times larger than the net absorbance

at 1128 cm

−1

. A ratio of greater than three is obtained

for temperatures below 15 K.

3.2 Without sufficient incident white light the

compensated donors and acceptors will not absorb.

Therefore, the white light intensity must be great

enough to completely neutralize all the compensated

donors and acceptors. The intensity of the white light

necessary must be determined for each system. The

user should increase the intensity of the white light until

further increase in intensity no longer affects the

area/height of the electrically active impurity/dopant

peaks.

3.3 Water vapor absorption interferes with the

measurement of several peaks. Consequently, the

background spectrum should be collected at least daily.

The entire light path, including the sample chamber,

must be purged to remove moisture. Special care

should be taken whenever a sample specimen is

changed so that the moisture level in the sample

chamber or elsewhere in the light path is not affected.

3.4 Oxygen level in Czochralski silicon can be high

enough to exhibit thermal donor absorption lines.

These lines fall between 400 cm

−1

and 550 cm

−1

and

can interfere with aluminum (473 cm

−1

), gallium (548

−1

), and occasionally arsenic (382 cm

−1

). Thermal

donors can be removed by annealing the sample

specimen.

1 Rome, J. J., “Calibration Relationships for Optically Measuring the

Concentrations of Boron, Gallium and Indium in Silicon,” Thesis,

School of Engineering, Air Force Institute of Technology (1982), pp.

46–47.

SEMI MF1630-0704 © SEMI 2004 2

3.5 Multiple internal reflections can produce a

secondary interferogram and baseline oscillations.

Changing the sample specimen thickness, the surface

preparation, or the resolution can eliminate the

secondary interferogram and the baseline oscillation.

3.6 High antimony levels interfere with the 320 cm

−1

boron absorption line. Antimony' s strongest absorption

line is 293 cm

−1

, but a secondary absorption line occurs

at 320 cm

−1

4 Referenced Standards

4.1 SEMI Standards

SEMI MF723 — Practice for Conversion Between

Resistivity and Dopant Density for Boron-Doped,

Phosphorus-Doped, and Arsenic-Doped Silicon

SEMI MF1241 — Terminology of Semiconductor

Technology

SEMI MF1391 — Test Method for Substitutional

Atomic Carbon Content of Silicon by Infrared

Absorption

SEMI MF1723 — Practice for Evaluation of

Polycrystalline Silicon Rods by Float-Zone Crystal

Growth and Spectroscopy

4.2 ASTM Standards

E 131 — Terminology Relating to Molecular

Spectroscopy

E 168 Practices for General Techniques of Infrared

Quantitative Analysis

E 177 — Practices for Use of the Terms Precision and

Bias in ASTM Test Methods

E 275 — Practice for Describing and Measuring the

Performance of Ultraviolet, Visible, and Near-Infrared

Spectrophotometers

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 General definitions for terms related to infrared

absorption spectroscopy are found in ASTM

Terminology E 131.

5.2 Definitions for terms related to silicon materials

technology are found in SEMI MF1241.

2 Annual Book of ASTM Standards, Vol 03.06, ASTM International,

100 Barr Harbor Drive, West Conshohocken, PA 19428. Telephone:

610-832-9500, Fax: 610-832-9555, Website:

www.astm.org

3 Annual Book of ASTM Standards, Vol 14.02.

5.3 Abbreviations and Acronyms

5.3.1 FT-IR — Fourier transform infrared

(spectrometer).

5.3.2 FWHM — full width of an absorption peak

expressed in cm

−1

at half its absorbance magnitude as

measured from the baseline.

5.3.3 LTFT-IR — low temperature, Fourier transform

infrared (spectrometer).

5.4 Definitions

5.4.1 background spectrum, n — in FT-IR instruments,

the single-beam spectrum obtained without a specimen

in the infrared light path that is usually obtained with

only nitrogen, dry air, or a vacuum in the beam.

5.4.2 baseline, n — a straight line interpolation between

points on either side of the absorption peak of the

absorbance spectrum.

5.4.3 electrically active elements, n — dopants or impu-

rities in silicon that are members of either Group III

(boron, aluminum, gallium, and indium) or Group V

(phosphorus, arsenic, antimony, and bismuth) of the

periodic table.

5.4.4 sample spectrum, n — the ratio of a spectrum

obtained with the test specimen in the IR beam to a

background spectrum.

6 Summary of Test Method

6.1 A sample specimen of single crystal silicon is

cooled to less than 15 K. Under these conditions the

number of free carriers becomes negligibly small and

the IR spectrum of the sample exhibits a series of

absorption bands that are characteristic for each shallow

impurity species.

6.2 The sample specimen is illuminated with an

incident white light source to flood the silicon with

photons of greater energy than the silicon band gap to

allow neutralization of compensated impurities.

6.3 An infrared beam is directed through the sample

specimen and a transmitted spectrum is collected. The

spectrum is ratioed to the background spectrum and

then converted to an absorbance spectrum.

6.4 Baselines are constructed at one of the characteristic

absorption bands for each impurity/dopant to be

measured.

4 Kolbesen, B. O., “Simultaneous Determination of the Total

Content of Boron and Phosphorus in High-Resistivity Silicon by IR

Spectroscopy at Low Temperature,” Appl. Phys . Lett. 27, 353–355

(1975).

5 Baber, S. C., “Net and Total Shallow Impurity Analysis of Silicon

by Low Temperature Fourier Transform Infrared Spectroscopy,” Thin

Solid Films 72, 201–210 (1980).