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SEMI MF1049-0304 © SEMI 2003, 2004 1 SEMI MF1049-0304 PRACTICE FOR SHAL LOW ETCH PIT DETECTION ON SILICON WAFERS This practice was technically approved by the Global Silicon Wafer Committee and is the direct responsibili…

SEMI MF951-0305 © SEMI 2003, 2005 7

12 Precision

12.1 The test method precision is directly dependent on the precision of the individual oxygen measurements. If the

only sources of precision errors are the individual measurements, the radial oxygen variation precision can be

computed for each sampling plan.

13 Bias

13.1 No reference standards are available for oxygen variation, so it is impossible to determine bias except for that

of the individual measurements. Bias of the individual measurements should be determined in accordance with the

procedures of the test methods utilized.

14 Keywords

infrared transmission; interstitial oxygen; oxygen; radial variation; silicon; uniformity; variation

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SEMI MF1049-0304 © SEMI 2003, 2004 1

SEMI MF1049-0304

PRACTICE FOR SHALLOW ETCH PIT DETECTION ON SILICON

WAFERS

This practice 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 December 4, 2003. Initially available at

www.semi.org February 2004; to be published March 2004. Originally published by ASTM International as

ASTM F 1049-87. Last previous edition SEMI MF1049-02.

1 Purpose

1.1 High levels of etch pits are reported

to indicate

metallic contamination that is detrimental to wafer

processing. This can be deduced from the density of

etch pits on the surface of the wafer.

1.2 This practice is used to detect shallow etch pits that

may be related to the level of metallic impurities near

the surface of silicon epitaxial or polished wafers.

2 Scope

2.1 This practice covers detection of high densities of

shallow etch pits on silicon wafers doped either p- or n-

type and with resistivities as low as 0.005 Ω·cm. This

practice is applicable for silicon wafers cut from

crystals grown in either a (111) or (100) crystal

orientation.

2.2 This practice is not recommended for use in defect

density evaluations, but as a subjective means of

estimating defect densities and distributions on the

surface of a polished or epitaxial wafer.

NOTE 1: For determination of shallow and other defect

densities in wafer production environments, use of the

sequence of procedures in SEMI MF 1726, SEMI MF1727,

SEMI MF1809, and SEMI MF1810 is recommended.

2.3 This practice utilizes a thermal oxidation process

followed by a chemical preferential etchant to create

and then delineate shallow etch pits.

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 Etch artifacts are the primary cause of difficulty in

identifying shallow etch pits. Etch artifacts are

generated in various ways such as gas bubble formation

1 Pearce, C. W., and McMahon, R. G., “Role of Metallic Contamina-

tion in the Formation of ‘Saucer’ Pit Defects in Epitaxial Silicon,” J.

Vac. Sci. Tech., 14, 40 (1977).

during etching, improperly cleaned surface prior to

etching, or insufficient etch solution volume.

3.2 Excessive silicon staining (very dark color) during

the preferential etching may obscure or prevent the

development of shallow etch pits on heavily doped p-

type silicon material (<0.2 Ω·cm).

NOTE 2: Light staining will not affect subsequent defect etch

results. However, heavy stains are undesirable.

4 Referenced Standards

4.1 SEMI Standards

SEMI C54 — Specifications and Guidelines for

Oxygen

SEMI C59 — Specifications and Guidelines for

Nitrogen

SEMI C28 — Specifications and Guidelines for

Hydrofluoric Acid

SEMI M17 —Guide for a Universal Wafer Grid

SEMI MF154 — Guide for Identification of Structures

and Contaminants Seen on Specular Silicon Surfaces

SEMI MF1726 — Practice for Analysis of

Crystallographic Perfection of Silicon Wafers

SEMI MF1727 — Practice for Detection of Oxidation

Induced Defects in Polished Silicon Wafers

SEMI MF1809 — Guide for Selection and Use of

Etching Solutions to Delineate Structural Defects in

Silicon

SEMI MF1810 — Test Method for Counting

Preferentially Etched or Decorated Surface Defects in

Silicon Wafers

4.2 ASTM Standard

D 5127 — Guide for Ultra Pure Water Used in the

Electronics and Semiconductor Industry

2 Schimmel, D. G., and Elkind, M. J., “An Examination of the

Chemical Staining of Silicon,” J. Electrochem. Soc., 125, 152 (1978).

3 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

SEMI MF1049-0304 © SEMI 2003, 2004 2

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Definitions

5.1.1 haze — on a semiconductor wafer, non-localized

light scattering resulting from surface topography

(microroughness) or from dense concentrations of

surface or near-surface imperfections.

5.1.1.1 Discussion — Haze due to the existence of a

collection of imperfections of the type that result in

haze cannot be readily distinguished by the eye or other

optical detection system without magnification. In a

scanning surface inspection system, haze and laser-light

scattering events comprise the laser surface scanner

signal due to light scattering from a wafer surface.

5.1.2 shallow etch pits — etch pits that are small and

shallow in depth under high magnification, >200×.

Also known as saucer pits.

6 Summary of Practice

6.1 Silicon wafers, either epitaxial or polished, are

thermally oxidized and preferential etched to reveal

small etch pits, shallow in depth, when observed

through an interference contrast microscope.

6.2 The distribution of the etch pits on the surface of

the wafer is determined and recorded on a diagram.

7 Apparatus

7.1 High-Intensity, Narrow-Beam Light Source —

Tungsten filament with a concentrated beam intensity

greater than 16 klx (1500 fc) and a beam diameter of 20

to 40 mm (0.8 to 1.6 in.) at a position 100 mm (4 in.)

from the light-source housing. The light beam shall not

be collimated and shall be capable of forming an image

of the bulb filament at the lamp focus length.

NOTE 3: Some standard microscope illuminators meet these

requirements.

7.2 Hydrofluoric Acid-Proof Chemical Laboratory

Apparatus — Fluorocarbon, polyethylene, or

polypropylene beakers, graduates, tweezers, eye

protection, apron, gloves, and protective sleeves.

7.3 Wafer Holders — HF acid-proof wafer carriers

which hold wafers. These are required if more than one

wafer is to be etched at a time.

7.4 Optical Microscope — Equipped with interference

contrast attachment. The eyepiece and objective lens in

combination shall give 200× to 1000× magnification.

NOTE 4: Nomarski differential interference contrast is an

example of interference contrast.

7.4.1 Stage Micrometer — With divisions of 0.002 mm

or finer, if an estimate of the shallow etch pit density is

to be made.

7.5 Acid Sink — A fume hood and facilities for

disposing of acids and their vapors.

7.6 Spin Dryer — Used to dry the wafers. Although

this item is not required, it is useful to provide a surface

free of residue artifacts.

8 Reagents and Materials

8.1 Purity of Reagents — Reagents for which SEMI

specifications have not been developed shall conform to

the specifications of the Committee of Analytical

Reagents of the American Chemical Society

. Other

grades may be used provided it is first ascertained that

the reagent is of sufficiently high purity to permit its

use without lessening the accuracy of the determination.

8.1.1 Hydrofluoric Acid (HF) — concentrated, in

accordance with Grade 1 of SEMI C28.

8.1.2 Nitrogen (N

) — 99.998% purity, in accordance

with Grade 4.8 of SEMI C59.

8.1.3 Oxygen (O

) — 99.98% purity, in accordance

with SEMI C54.

8.2 Purity of Water — Reference to water shall be

understood to mean Type E-3 or better water as

described in ASTM Guide D 5127.

8.3 Schimmel Etch for (100) and (111) Surfaces

8.3.1 Chromic Acid Solution — Make a 0.75 M

solution by placing 75 g of chromium trioxide (CrO

) in

a 1-L glass volumetric flask and then add sufficient

water to make a solution volume of 1 L, or 1000 mL.

The solution may be stored up to 6 months in clean

glass, TFE-fluorocarbon, polyethylene, or

polypropylene bottles.

8.3.2 For Test Specimens with Resistivity Greater Than

0.2

Ω

!cm n- or p-Type — Immediately before using,

add 2 parts hydrofluoric acid (HF) to 1 part chromic

acid solution by volume. Prepare and mix in HF-proof

beakers.

8.3.3 For Test Specimens with Resistivity Less Than

0.2

Ω

!cm n- or p-Type — Immediately before using,

4 Reagent Chemicals, American Chemical Society Specifications,

American Chemical Society, Washington, DC. For suggestions on the

testing of reagents not listed by the American Chemical Society, see

Analar Standards for Laboratory Chemicals, BDH Ltd., Poole,

Dorset, U.K., and the United States Pharmacopeia and National

Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,

MD.

5 Schimmel, D. G., “Defect Etch for 〈100〉 Silicon Evaluation,” J.

Electrochem. Soc., 126, 479–483 (1979).