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SEMI MF1727-0304 © SEMI 2003, 2004 2 3.7 Wafers, parti cularly <111> orientati on, may show lower shallow-pit defect density when the back surface of the wafer is gettered. Backsid e gettering should be noted in th…

SEMI MF1727-0304 © SEMI 2003, 2004 1

SEMI MF1727-0304

PRACTICE FOR DETECTION OF OXIDATION INDUCED DEFECTS IN

POLISHED 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 1727-97. Last previous edition SEMI MF1727-02.

1 Purpose

1.1 Defects induced by thermal processing of silicon

wafers may adversely influence device performance

and yield.

1.2 These defects are influenced directly by

contamination, ambient atmosphere, temperature, time

at temperature, and rate of change of temperature to

which the specimens are subjected. Conditions vary

significantly among device manufacturing technologies.

The thermal cycling procedures of this practice are

intended to simulate basic device processing

technologies. Oxidation cycles other than specified

herein, or multiple oxidation cycles, may sometimes

more accurately simulate device-processing procedures.

The results obtained may differ significantly from those

obtained with the specified oxidation cycles.

1.3 The geometry of some patterns revealed by this

practice suggests that they are related to the crystal

growth process while others seem related to surface

preparation or thermal cycling conditions.

1.4 This practice is suitable for acceptance testing

when used with referenced practices and methods.

2 Scope

2.1 This practice covers the detection of crystalline

defects in the surface region of silicon wafers. The

defects are induced or enhanced by oxidation cycles

encountered in normal device processing. An

atmospheric pressure oxidation cycle representative of

bipolar, metal-oxide-silicon (MOS) and CMOS

technologies is included. This practice reveals strain

fields arising from the presence of precipitates,

oxidation induced stacking faults, and shallow etch pits.

Slip is also revealed that arises when internal or edge

stresses are applied to the wafer.

2.2 Application of this practice is limited to specimens

that have been chemical or chemical/mechanical

polished to remove surface damage from at least one

side of the specimen. This practice may also be applied

to detection of defects in epitaxial layers.

2.3 The surface of the specimen opposite the surface to

be investigated may be damaged deliberately or

otherwise treated for gettering purposes or chemically

etched to remove damage.

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 practices and determine

the applicability of regulatory or other limitations prior

to use.

3 Limitations

3.1 Material having residual work damage in the

polished surface exhibits visible patterns when the

procedures of this practice are used. Usually, edge

damage, lapping damage, tool marks, or scratches are

easily identified by the location and pattern observed.

3.2 Contamination not removed by preparatory

cleaning procedures or deposited following cleaning,

may become visible after oxidation and preferential

etching.

3.3 Slip may be introduced by differential expansion at

the points of wafer support in the furnace boat. Slip

radiating from the points of support may be assumed to

originate from this boat pinch and not be inherent in the

unprocessed wafer. Slip may also be caused by large

thermal gradients imposed across a wafer by fast

insertion or removal from the furnace.

3.4 If the oxidation furnace or apparatus is

contaminated, it can cause extraneous artifacts or

defects.

3.5 Striations, helical features on the surface of a

silicon wafer, are ascribed to periodic dopant

incorporation differences occurring at the rotating solid-

liquid interface during crystal growth. These features

are visible to the unaided eye after preferential etching,

seem continuous under 100× magnification, and may be

confused with ring patterns of oxidation stacking faults.

3.6 Otherwise identical wafers with different back

surface conditions may yield different results by this

practice.

SEMI MF1727-0304 © SEMI 2003, 2004 2

3.7 Wafers, particularly <111> orientation, may show

lower shallow-pit defect density when the back surface

of the wafer is gettered. Backside gettering should be

noted in the sample classification when data are

reported.

4 Referenced Standards

4.1 SEMI Standards

SEMI C3.19 — Standard for Hydrogen (H

) 99.9995%

Quality

SEMI C28 — Specifications and Guidelines for

Hydrofluoric Acid

SEMI C54 — Specifications and Guidelines for

Oxygen

SEMI MF1241 — Terminology of Silicon Technology

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

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Defect-related terminology may be found in SEMI

MF1241.

6 Summary of Practice

6.1 Wet oxidation is used to generate or highlight

defects, or both, in silicon wafers. This oxidation may

also simulate simple device production processes.

6.2 The defects are revealed subsequently by

preferential etching and examination by interference

contrast microscopy according to referenced SEMI

standards.

7 Apparatus

7.1 Oxidation Furnace — furnace shall be consistent

with the intended process application and shall sustain a

designated temperature with uniformity less than ± 5° C

over a zone at least 0.3-m long.

1 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

7.2 Steam Source — Wet oxidation shall be carried out

using a pyrogenic steam generator to provide steam.

7.3 Working Chamber — A pure, fused quartz, silicon

carbide, or silicon tube of an inside diameter sufficient

to hold the specimen wafers. The inlet end shall be

fitted with the appropriate pyrogenic torch apparatus.

The exhaust end shall be fitted to exhaust the process

gases to satisfy applicable environmental requirements

and prevent back streaming of outside air into the

working chamber.

7.4 Wafer Boat — A quartz, silicon or silicon carbide

fixture for holding the specimen wafers either parallel

or perpendicular to the gas flow in the furnace.

7.5 Pickup Tool — A manual or automated transfer

tool fitted with a nonmetallic material such as quartz or

TFE-fluorocarbon. The pickup tool shall be

constructed so that no metal can contact the specimen

wafer.

8 Reagents and Materials

8.1 Purity of Reagents — Chemicals shall conform to

the assay and impurity levels of Grade 1 SEMI

Specifications where they exist. Reagents for which

SEMI specifications have not been developed shall

conform to the specifications of the Committee on

Analytical Reagents of the American Chemical

Society,

where such specifications are available.

Gases shall conform to the purity requirements of the

cited SEMI specifications. 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.

8.2 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 Hydrofluoric Acid — Concentrated, in accordance

with Grade 1 of SEMI C28.

8.4 Hydrogen Gas — In accordance with SEMI C3.19,

for use in pyrogenic steam generator.

8.5 Oxygen Gas — In accordance with SEMI C54, for

use both as furnace ambient and in pyrogenic steam

generator.

2 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.

SEMI MF1727-0304 © SEMI 2003, 2004 3

9 Sampling

9.1 Select specimens to represent the lot to be tested as

specified in producer/consumer agreements.

10 Specimen Preparation

10.1 Commonly this practice may be used for wafers

as they are received; however, the parties using this

practice may establish a uniform cleaning procedure

before oxidation.

11 Preparation of Apparatus

11.1 The oxidation furnace tube (working chamber)

and associated quartzware shall be maintained in a state

suitable for producing oxides appropriate for the

process for which the wafers are being tested.

11.2 Immediately before use, clean the pickup tool

using standard industry practices.

12 Procedure

12.1 Handle wafers only with a clean, nonmetallic

pickup tool or automated transfer unit to avoid

scratching or contaminating the surface.

12.2 Oxidize the wafers by the thermal sequence listed

in Table 1 or by a process acceptable to both producer

and consumer.

12.2.1 Caution — Pyrogenic steam oxidation uses

heated hydrogen and oxygen to grow a wet oxide layer.

Improper or uncontrolled combination of these gases

can result in fire or explosion.

12.2.2 Preheat the furnace to the push temperature.

Table 1 Oxidation Procedure

Step Function Conditions

Ambient Dry Oxygen

Temperature 800° C

1. Push (Load)

Push Rate 200 mm/minute

Ambient Dry Oxygen

Ramp Rate + 5° C/minute

2. Temperature

Ramp

Final Temperature 1100° C

Ambient Steam (wet oxide)

Temperature 1100° C

3. Oxidation

Time 60 minute

Ambient Dry Oxygen

Ramp Rate –3° C/minute

4. Temperature

Ramp

Final Temperature 800° C

Ambient Dry Oxygen

Temperature 800° C

5. Pull (Unload)

Pull Rate 200 mm/minute

12.2.3 Load the specimen wafers into the wafer boat,

being careful to avoid binding, scratching, or

contamination.

12.2.4 Insert the boat into the hot zone at the rate called

for in the thermal sequence being employed. The wafer

boat shall be centered in the uniform hot zone.

12.2.5 Follow the ramp up, oxidation, ramp down, and

pull procedures as specified in the thermal sequence

being employed.

12.2.6 Because silicon wafers and quartz accessories

are extremely hot when they are removed from the

oxidation furnace, allow the materials adequate time to

cool before handling.

12.3 Transfer the room temperature wafers from the

quartz boat to a wafer carrier using the pickup tool or

automated transfer unit.

12.4 Remove the thermal oxide layer using

hydrofluoric acid for 2 min followed by water rinse and

spin dry.

12.4.1 Caution — Hydrofluoric acid solutions are

particularly hazardous and specific preventive measures

must be strictly observed. Safety or protective gear

should be worn while handling acid solutions. Safety

requirements vary, but the essential items are: plastic

gloves, safety glasses, face shield, acid gown, and shoe

covers.

12.5 Select and use an appropriate etching solution as

described in SEMI MF1809 to allow defect delineation

while removing 4 µm (or another amount as agreed

upon between the parties to the test) of silicon from the

surface being evaluated.

12.6 Count and report the density of observed defects

using SEMI MF1810.

13 Keywords

13.1 defects; dislocation; epitaxy; hillock;

imperfections; oxidation; preferential etch; shallow pit;

silicon; slip; stacking fault; swirl