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SEMI M11-0704 © SEMI 1988, 2004 3 • Device characteristics that may be affected — leakage and gate oxide integ rity, from crystallogra phic changes. • Detectio n characteristics used for cha racterization — side length a…

SEMI M11-0704 © SEMI 1988, 2004 2

SEMI MF1188 — Test Method for Interstitial Atomic

Oxygen Content of Silicon by Infrared Absorption With

Short Baseline

SEMI MF1239 — Test Methods for Oxygen

Precipitation Characterization of Silicon Wafers by

Measurement of Interstitial Oxygen Reduction

SEMI MF1241 — Terminology of Silicon Technology

SEMI MF1366 — Test Method for Measuring Oxygen

Concentration in Heavily Doped Silicon Substrates by

Secondary Ion Mass Spectrometry

SEMI MF1392 — Test Method for Determining Net

Carrier Density Profiles in Silicon Wafers by

Capacitance-Voltage Measurements with a Mercury

Probe

SEMI MF1393 — Test Method for Determining Net

Carrier Density in Silicon Wafers by Miller Feedback

Profiler Measurements with a Mercury Probe

SEMI MF1726 — Guide for Analysis of

Crystallographic Perfection of Silicon Wafers

SEMI MF1727 — Practice for Detection of Oxidation

Induced Defects in Polished Silicon Wafers

3.2 Other Standards

ANSI/ASQC Z1.4 — Sampling Procedures and Tables

for Inspection by Attributes

ISO 14644-1 — Cleanrooms and associated controlled

environments — Part 1: Classification of airborne

particulates

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

4 Terminology

4.1 Many terms relating to silicon technology are

defined in SEMI MF1241.

4.2 Descriptions of other epitaxial wafer defects

covered in Table 1 are given in SEMI MF154.

4.3 Definitions of selected epi wafer defects, extended

to consider automatic surface inspection are given

below.

4.3.1 mound (epi) — a rounded protrusion on a

semiconductor wafer surface, which may have one or

more partially developed facets (see Figure 1).

1 American Society for Quality Control, 611 East Wisconsin Avenue,

Milwaukee, WI 53202. Website: www.asqc.org.

2 ISO Central Secretariat, C. P. 56, CH-1211 Genève 20,

Switzerland; Website: www.iso.ch; available in the U.S. from

American National Standards Institute, 11 West 42nd Street, 13th

Floor, New York, NY 10036 Website: www.ansi.org.

NOTE 1: Scattering event size reported by SSIS will differ

from the physical size of the object. The figure captions in

the examples highlight this fact. No useful method exists at

the present time to quantify this relationship (see Section

7.3.3.3)

4.3.1.1 Discussion — Related characteristics include

the following:

• Device characteristics that may be affected —

critical feature dimensions, lithographic equipment

focus, gate oxide integrity.

• Detection characteristics used for characterization

— mound height, diameter at 50% height.

• Discrimination characteristics used for

characterization — positive height: 10–100 nm, or

approximately 20% of the epi layer thickness;

diameter: 0.1–6 µm; circular symmetry.

• Specification characteristics used for wafer

qualification — number per wafer, mound height,

height to diameter.

4.3.2 epi stacking fault — a two dimensional effect that

results from a deviation from the normal stacking

sequence of atoms in a crystal. [SEMI MF154, SEMI

MF1727]

NOTE 2: Discrimination and specification characteristics are

given in this section to facilitate equipment development (see

Section 7.3.3.3) and are not intended for use in commercial

wafer specifications.

4.3.2.1 Discussion — Epi stacking faults are typically

linked together into squares in the case of {100}

oriented wafers, and triangles in the case of {111}

oriented wafers. Most stacking faults are nucleated at

the epi layer substrate boundary, though some have

been observed being nucleated further into the epi

growth process. Faults are aligned along specific

crystallographic directions. For {100} wafer the sides

of the faults are aligned along <110> directions. The

length of a side is typically proportional to the epi layer

thickness and related to the crystallographic orientation.

In order to minimize the strain around a stacking fault

contaminants may diffuse to these defects. Some

stacking faults may have an effect on the local growth

rate giving the stacking fault a three dimension aspect.

This three dimensional aspect changes their light

scattering cross section when observed by an SSIS (see

Figures 3 through 7). Still more complicated are

overlapping stacking faults which scatter even more

than a single stacking fault of the same size (see figure

4). Other types of defects may be composites of

stacking faults and polysilicon growth which can also

appear larger than a single stacking fault of the same

lateral dimensions (see Figures 5 and 6). Related

characteristics include the following:

• Device characteristics that may be affected —

leakage and gate oxide integrity, from

crystallographic changes.

• Detection characteristics used for characterization

— side length and depth, orientation parallel to a

<110> direction.

• Discrimination characteristics used for

characterization — shape, length ~ epi layer

thickness: 1–10 µm. Stacking faults may cluster

(see Figure 7) and scatter more than a single

stacking fault.

• Specification characteristics used for wafer

qualification — Number per wafer. Since certain

types of epi stacking faults have no observed

impact on device performance while others are

killer defects no number can be assigned without a

clear identification of the type of epi stacking fault

that is involved.

Figure 1

A Mound. Magnification 1000 times using Nomarksi Interference Microscopy. Approximate SSIS scattering

event size 0.22 µm.

23 µm

Figure 2

This is a mound that does not have the sharp edges of an Epitaxial Stacking Fault, but is not as high as a

Bump. They are typically sized much smaller in a SSIS than their actual size, but some have facets that

scatter enough light to be more easily detected. Some people refer to this feature as a hillock which is a type

of mound. The shape can be either circular or square. Magnification 500 times using Nomarski Interference

Microscopy. Approximate SSIS event size: 0.15 µm