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SEMI MF1630-0704 © SEMI 2004 8 NOTICE: SEMI makes no warranties or representations as to the su itability of the standards set forth herein for a ny particular application. The determination of the suitab ility of the st…

SEMI MF1630-0704 © SEMI 2004 7

RELATED INFORMATION 1

DERIVATION OF FACTORS USED IN CALCULATING

CONCENTRATIONS AND DENSITIES OF ELEMENTS IN SILICON

NOTICE: This related information is not an official part of SEMI MF1630. It was developed as non-mandatory

information in ASTM during the initial development of the document in 1994-5. This related information was

approved for publication by SEMI by full letter ballot procedures on March 14, 2004.

R1-1 The factors shown in Table 1 resulted from

several years of corrections and modifications but are

ultimately based on resistivity measurements on silicon

samples. The dopant density, or the concentration of

impurities for this test method, is directly obtained

from the conversion Tables found in SEMI MF723.

R1-2 Baber’s

calibration factors published in 1980,

were the starting point for the current factors.

Corrections or modifications, or both, to his published

data follow in this discussion.

R1-2.1 Baber’s LTFT-IR study utilized the conversion

relations reported by Irvin

in 1962, relating resistivity

and impurity concentrations. Currently, the conversion

tables given in SEMI MF723 are believed to be more

reliable. Corrections to Baber’s factors were made to

reflect these new conversion tables.

R1-2.2 The factors of Baber relate peak heights of the

absorption bands to concentrations. Peak heights are

extremely sensitive to several FT-IR parameters. The

phosphorus band at 316.0 cm

−1

and the arsenic band at

382.0 cm

−1

are very narrow, about 0.25 cm

−1

, and thus

the peak heights of these bands vary greatly with

nominal resolution, type of apodization, degree of zero-

filling, and mechanical strain on the sample. The boron

absorption at 319.6 cm

−1

band used in this test method

is actually a composite of four separate boron

absorption bands. The variability of the measurement

of the absorption bands is reduced considerably when

peak areas are used instead of peak heights. The use of

peak areas is common in the field and their use is

specified in this test method.

R1-2.3 Further minor modifications have been made

over the in the period from about 1985 to about 1995 in

several laboratories that use LTFT-IR spectrometers for

determination of electrically active impurities.

R1-2.3.1 Studies with and without the white light on

the silicon samples, covering a wide range of

concentrations, are valuable as tools to check for

consistency of the boron and phosphorus factors, which

are indeed the most common impurities. With the

absence of white light, the LTFT-IR method shows

7 Irvin, J. C., “Resistivity of Bulk Silicon Diffused Layers in

Silicon,” Bell System Tech. J. 41, 387–410 (1962).

only the net carrier absorption bands at an intensity

proportional to the excess majority carrier

concentration. These data along with the total

impurities obtained with white light on the samples

permitted minor adjustments to the boron or

phosphorus factors, or both.

R1-2.3.2 Silicon samples whose resistivity has been

carefully determined have been measured by LTFT-IR

spectroscopy, and the results used to confirm or slightly

modify the calibration factors.

R1-3 In 1990, a pilot study was conducted in which ten

silicon samples were examined at four different

laboratories by either LTFT-IR or photoluminescence,

or both, and the results compared. Even though each

laboratory used their own factors and modifications of

this test method for determination of impurity

concentrations, the data for boron and phosphorus all

agreed to within ± 20% of the average value. The

factors given in this test method are approximately

equal to the average values from that study.

R1-4 In summary, the factors given in Table 1 are a

result of continued refinement as more and better

measurements have been made. However, they

ultimately correspond to the resistivity measurements

and the conversion to dopant (impurity) concentrations

as given in SEMI MF723. The factors for boron and

phosphorus have the highest degree of certainty since

these two elements are the most commonly measured

and are therefore studied the most. The factors for the

other elements, especially aluminum, antimony,

gallium, and indium, should be considered only

approximations and used only to estimate their

concentrations in silicon.

SEMI MF1630-0704 © SEMI 2004 8

NOTICE: SEMI makes no warranties or

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.

By publication of this standard, Semiconductor

Equipment and Materials International (SEMI)

takes no position respecting the validity of any

patent rights or copyrights asserted in connection

with any items mentioned in this standard. Users

of this standard are expressly advised that

determination of any such patent rights or

copyrights, and the risk of infringement of such

rights are entirely their own responsibility.

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the contents in whole or in part is forbidden without express written

consent of SEMI.

SEMI MF1708-1104 © SEMI 2004 1

SEMI MF1708-1104

PRACTICE FOR EVALUATION OF GRANULAR POLYSILICON BY

MELTER-ZONER SPECTROSCOPIES

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 1708-96. Last previous edition SEMI MF1708-02

1 Purpose

1.1 Polycrystalline silicon is used as the starting

material for growth of large single crystal ingots by

Czochralski methods.

1.2 Although Czochralski grown ingots are intention-

ally doped during crystal growth to the desired

resistivity and type, the dopant levels in the polysilicon

must be known to calculate the amount of dopant to be

added. This practice provides a means to determine the

impurity levels in granular polysilicon to be used for

crystal growth.

1.3 Carbon levels in polysilicon must be known so that

the concentration of carbon in the ingot can be

controlled to a low level.

1.4 This practice has applicability in production control,

quality assurance, materials research, and materials

acceptance.

2 Scope

2.1 This practice describes a procedure to consolidate

granular polysilicon into a solid rod and then to convert

the polysilicon rod into a single crystal by a float-zone

technique. The resultant single crystal ingot is used for

the determination of trace impurities in the polysilicon.

These impurities are acceptor and donor components

(usually boron, aluminum, phosphorus, arsenic, and

antimony) as well as substitutional carbon.

2.2 The useful range of impurity concentration covered

by this practice is 0.002 to 100 parts per billion atomic

(ppba) for acceptor and donor impurities, and 0.02 to 15

parts per million atomic (ppma) for carbon. The

acceptor and donor impurities in a slice taken from the

single crystal ingot are analyzed by photoluminescence

or infrared spectroscopies. The carbon impurity is

determined by analysis of a slice by infrared

spectroscopy.

2.3 This practice is applicable only to evaluation of

polysilicon granules as produced by thermal

decomposition and deposition of silane, or one of the

chlorosilanes, onto high purity seeds of polysilicon in a

continuous or batch fluid bed reactor. The granules are

near spherical in shape and range in size from 200 to

3000 m with a mean size of about 900–1200 m.

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 quartz tubes used in this procedure must be of

high purity, especially in regards to the impurities to be

measured. Boron is of particular concern since it is

always present in quartz and may frequently appear in

uncharacteristically high concentrations in polysilicon.

3.2 All chemicals and gases used in this procedure must

be free of components to be measured or they may give

extraneously high results.

3.3 Loss of single crystal during the zone pass will

produce an ingot that may give unsatisfactory results.

The quality of the infrared or photoluminescence

spectra usually reveals the lack of single crystal.

4 Referenced Standards

4.1 SEMI Standards

SEMI C3.42 — Specification for Argon

SEMI C28 — Specifications and Guidelines for

Hydrofluoric Acid

SEMI C31 — Specification for Methanol

SEMI C34 — Specification and Guideline for Mixed

Acid Etchants

SEMI C35 — Specifications and Guideline for Nitric

Acid

SEMI MF1241 — Terminology of Silicon Technology

SEMI MF1389 — Test Methods for Photoluminescence

Analysis of Single Crystal Silicon for III-V Impurities

SEMI MF1391 — Test Method for Substitutional

Carbon Content of Silicon by Infrared Absorption