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SEMI MF1389-0704 © 2004 2 3 Limitations 3.1 Variations in Excitation Inten sity — The extrinsic bound exciton (BE) and in trinsic free exciton (FE) luminescence features do not va ry at the same rate with excitation inte…

SEMI MF1389-0704

TEST METHODS FOR PHOTOLUMINESCENCE ANALYSIS OF SINGLE

CRYSTAL SILICON FOR III-V IMPURITIES

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 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 1389-92.

Last previous edition SEMI MF1389-00.

1 Purpose

1.1 Electronic-grade polycrystalline silicon producers

and users require information regarding impurities for

quality assurance as well as for research and

development purposes. Polysilicon is float-zoned and a

sample from the zoned rod is analyzed following these

test methods to obtain impurity densities that can be

related to the impurity content of the starting material

(see SEMI MF1723).

1.2 Photoluminescence analysis identifies and

quantifies the electrically active dopant impurities in

monocrystalline silicon. These test methods address

boron, phosphorus, arsenic, and aluminum, found as

impurities in electronic grade silicon.

1.3 These test methods can be applied to doped and

undoped float-zoned or Czochralski material.

2 Scope

2.1 These test methods cover the simultaneous

determination of electrically active boron, phosphorus,

arsenic, and aluminum content in low-dislocation

monocrystalline silicon.

NOTE 1: These chemical species can also be determined by

the low temperature infrared analysis procedure of SEMI

MF1630.

2.2 These test methods can be used for samples that

have dopant densities between approximately 1 × 10

and approximately 5 × 10

atoms/cm

2.3 The concentrations obtained using these test

methods are based on an empirically determined

relationship of the logarithm of the concentration to the

logarithm of specific luminescence line-intensity ratios.

2.4 The empirical relationship established assumes a

constant sample excitation level for all measurements

on a given instrument.

2.5 To accommodate differences in instrumentation,

two methods are included. Test Method A refers to

procedures appropriate for dispersive infrared

spectrophotometers operating under the high sample

excitation conditions and Test Method B refers to

procedures appropriate for Fourier transform

instruments operating under low excitation conditions.

2.5.1 Typical calibration curves for each test method

are provided. These curves are modified for each

instrument using the analysis of standard samples as

reference data. Once modified, the curves for a given

instrument should produce sample dopant density

values that agree with other similarly operated

instruments using the same test method. Data obtained

using Test Method A may not agree with data obtained

using Test Method B, hence values must be reported

with reference to the test method used.

NOTE 2: Several different methods of photoluminescence

analysis are currently in practice worldwide. These test

methods address two of these, one (Test Method A) in use

primarily in Japan

and the other (Test Method B) primarily in

the United States. Recently published works

2,3

describe other

approaches.

2.6 Many laboratories use photoluminescence to

analyze epitaxial layers. However this application

encounters many variables and the underlying physics

is not fully understood; hence these test methods do not

attempt to outline standard practices regarding such

analysis.

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.

1 Test Method A is essentially equivalent to JIS H 0615, Test

Method for Determination of Impurity Concentrations in Silicon

Crystal by Photoluminescence Spectroscopy. This standard is

available from Japanese Standard Association 1-24, Akasaka 4

Chome, Minato-ku, Tokyo 107-0000, Japan. Telephone: 81-(0)3-

3583-8005; Fax: 81-(0)3-3586-2014; Website:

www.jsa.or.jp

2 Colley, P. McL., and Lightowlers, E. C., “Calibration of the

Photoluminescence Technique for Measuring B, P, and Al Concen-

trations in Silicon in the Range 1e12 to 1e15 at/cm 3 Using Fourier

Transform Spectroscopy,” Semiconductor Science and Technology 2,

157–166 (1987).

3 Schumacher, K. L., and Whitney, R. L., J. Electron. Materials

18(6), 681–687 (1989).

3 Limitations

3.1 Variations in Excitation Intensity — The extrinsic

bound exciton (BE) and intrinsic free exciton (FE)

luminescence features do not vary at the same rate with

excitation intensity.

The FE features increase

proportionally with excitation intensity, while the BE

features increase proportionally at low excitation levels

but become more slowly increasing at higher excitation

levels generally above the electron hole droplet (EHD)

onset point. Since the calculated concentrations are

derived from the ratio of extrinsic features to the

intrinsic feature, the ratio will be decreasing as the

excitation intensity is increasing. Thus, if a sample is

measured at a higher excitation level than the

instrument is calibrated for, the calculated

concentration will be artificially low, and vice versa.

3.2 Sample surface damage, bulk defects, or other

lifetime reducers also affect the line-intensity ratios and

overall luminescence intensity owing to their tendency

to reduce the steady state population of excitons, thus

mimicking the effects of a lower excitation intensity.

Other mechanisms related to the presence of these

defects may also introduce decalibrating effects. Some

luminescence features are generated by defects; for

example, those at 6510 and 7050 cm

−1

are typical of

thermally stressed samples. Such features can provide

qualitative information about the presence of defects.

5,6

3.3 The ratios and line widths of the silicon

luminescence features vary strongly with temperature,

hence variations in sample temperature must be

avoided. Corrections for the effects of temperature

variations are included in these test methods (see

Section 7.1).

3.4 Overlapping Spectral Features

3.4.1 The boron B

(BE) feature at 8812.6 cm

−1

overlaps the P

(b′

) feature at 8812.7 cm

−1

causing a

direct error when calculating boron concentration. The

beta-series P

(b′

) line is approximately one-tenth the

intensity of the alpha series P

(BE) line at 8806.6

−1

, so a subtraction based on the amount of

phosphorus present can be made in the boron feature

measurement. An alternative approach is to use the

) boron line, which is free from a coincident

4 Nakayama, H., Nishino, T., and Hamakawa, Y.,“Analysis of the

Excitation Luminescence of Silicon for Characterization of the

Content of Impurities,” Jap. J. Appl. Phys. 19(3), 501–511, (1980).

5 Drozdov, N. A., Patrin, A. A., and Tkachev, V. D.,

“Recombination Radiation on Dislocations in Silicon,” Soviet

Physics, J.Experimental and Theoretical Physics 23(11), 597 1976).

6 Suezawa, M., Sasaki, Y., Nishina, Y., and Sumino, K., “Radiative

Recombination on Dislocations in Silicon Crystals,” Jap. J. Appl.

Phys. 20(7), L537 (1981).

phosphorus line, provided the instrument has been

calibrated for this feature.

3.4.2 The antimony Sb

(BE) line falls between the

boron and phosphorus transverse optical (TO) features.

Since the line widths are broad relative to the line

positions of these features, the presence of antimony

affects the apparent intensities of boron and phosphorus

TO features. The no-phonon, (NP) features for these

elements could be used providing the instrument is

calibrated for them.

3.4.3 In general, the broad TO phonon region features

can interfere, particularly when a sample contains

widely differing levels of impurities. For example,

when boron greatly exceeds phosphorus, the P

(BE)

line must be used, and when phosphorus greatly

exceeds boron, one of the approaches described in

Section 3.4.1 must be used.

3.5 Stress in samples can cause NP region feature

splitting and thus affect the established TO/NP line

ratio for a given impurity. The concentrations

calculated from such spectra would be artificially low.

Peak area calculation methods reduce the

measurement' s sensitivity to line splitting effects.

3.6 The calibration curves presented in these test

methods are traceable to resistivity measurements (see

SEMI MF723), neutron transmutation doped, (NTD)

reference material, and low-temperature infrared

absorption spectroscopy (FT-IR) measurements (as a

secondary standard) (see SEMI MF1630). Hence

inaccuracies in the work that produced the calibration

curves impact the accuracy of the PL results.

4 Referenced Standards

4.1 SEMI Standards

SEMI C28 — Specifications and Guidelines for

Hydrofluoric Acid

SEMI C30 — Specifications and Guidelines for

Hydrogen Peroxide

SEMI C35 — Specifications and Guideline for Nitric

Acid

SEMI MF723 — Practice for Conversion Between

Resistivity and Dopant Density for Boron-Doped,

Phosphorus-Doped, and Arsenic-Doped Silicon

SEMI MF1630 — Test Method for Low Temperature

FT-IR Analysis of Single Crystal Silicon for III-V

Impurities

SEMI MF1723 — Practice for Evaluation of

Polycrystalline Silicon Rods by Float-Zone Crystal

Growth and Spectroscopy

4.2 ASTM Standard

D 5127 — Guide for Ultra Pure Water Used in the

Electronics and Semiconductor Industry

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Definitions

5.1.1 defect luminescence lines — those features arising

from defect structures in the silicon.

5.1.2 electron hole droplet (EHD) — the condensed

phase (liquid) of the excitonic gas generated by

photoexcitation.

5.1.2.1 Discussion — The exciton population is

dependent upon excitation intensity and can be raised to

the point where the exciton density is sufficient to allow

condensation of the exciton gas into a liquid like

exciton state.

The existence of EHD luminescence can

be an indirect measurement of excitation power density

on the sample.

5.1.2.2 EHD onset occurs at the point in the sample

excitation intensity curve where the electron-hole-

droplet begins to form.

The EHD luminescence

includes a very broad feature underlying the TO region

impurity lines which, with increasing excitation

intensity, both intensifies and shifts to lower energies

relative to the other silicon luminescence features.

5.1.3 excitons — the electron-hole pairs that give rise to

the luminescence of interest upon recombination at

either a free lattice site (free exciton) or an impurity

atom site (bound exciton).

5.1.4 extrinsic line (X

(BE) or X

(BE)) — the

luminescence that arises from an exciton captured by an

impurity site in the crystal lattice (a bound exciton).

5.1.4.1 Discussion — Its energy is lower than the

intrinsic emission by an amount related to the exciton

binding energy of the impurity at 4.2 K. “X” is the

impurity element symbol and “BE” indicates bound

exciton luminescence line. Extrinsic luminescence also

includes features attributed to bound multi-exciton

complexes (b

, b

, or b

would indicate the first, second

and third bound multi-exciton complex lines,

respectively). In donor luminescence, these complexes

7 Annual Book of ASTM Standards, Vol 11.01, ASTM International,

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

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

www.astm.org.

8 Nakashima, H., and Shiraki, Y., “Role of Shallow Impurities and

Lattice Defects in Nucleation of Electron-Hole Droplets in Si,” Solid

State Comm. 40, 195–197 (1981).

9 Hammond, R. B., and Silver, R. N., “Onsets of the Electron-Hole

Droplet Luminescence in Si,” Phys. Rev. Lett. 42(8), 523–526 (1979).

give rise to two series of lines in the TO region, called

the alpha and beta series. The weaker beta series

features are denoted by an apostrophe after the line

notation (that is, P

(b′

)). See Table 1 and Table 2 for

line locations.

5.1.5 intrinsic line (I

(FE)) — the luminescence that

arises from the silicon itself, with no impurity species

affecting the exciton recombination.

10,11

Table 1 Photoluminescence Line Locations

(Vacuum Wavenumbers)

Silicon Free Exciton (FE) Lines:

(FE) at 8848 cm

−1

(FE) at 8860 cm

−1

(FE) at 9166 cm

−1

Major Shallow Impurity Bound Exciton (BE) Lines:

Element

TO region,

−

NP region,

−

NP/TO region BE

line intensity ratio

Boron 8812.6 9281.3 0.017

(Antimony) (8810.5) (9280.0) (0.010)

Phosphorus 8806.8 9275.4 1.4

Aluminum 8803.4 9271.8 0.7

Arsenic 8801.0 9269.4 2.0

NOTE 1: To convert vacuum wavenumbers to air wavenumbers:

air wavenumber = 1.00030025 × vacuum wavenumber

NOTE 2: To convert wavenumbers to electronvolts:

eV = 1.23985 × 10

−4

× wavenumber

Instrument resolution = 0.5 cm

−1

, sample = FZ silicon.

Table 2 Photoluminescence Line Locations

(Vacuum Wavenumbers) Detailed Listing for Boron

and Phosphorus

Boron Features, cm

−

Phosphorus Features, cm

−

(BE) = 9281.3 P

(BE) = 9275.4

) = 9263.6 P

) = 9246.4

) = 9245.9 P

) = 9223.9

) = 9208.4

) = 9197.8

(BE) = 9130.1 P

(BE) = 9124.4

) = 9112.4 P

(BE-2e) = 8992.8

) = 9095.2

(BE)= 8812.6

′) = 8812.7

) = 8795.0 P

(BE) = 8806.8

10 Tajima, M., “Determination of Boron and Phosphorus Concen-

tration in Silicon by Photoluminescence Analysis,” Appl. Phys. Lett.

32(11), 719 (1978).

11 Tajima, M., “Quantitative Impurity Analysis in Si by the Photo-

luminescence Technique,” edited by J. Nishizawa, Japan Annual

Reviews in Electronics, Computers, and Telecommunications—

Semiconductor Technology (OHM—North Holland, 1982).