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SEMI MF1725-1103 © SEMI 2003 1 SEMI MF1725-1103 PRACTICE FOR ANALYSIS OF CR YSTALLOGRAPHIC PERFECTION OF SILICON INGOTS This standard was technically approved by the Global Silicon Wafer Committ ee and is the d irect res…
SEMI MF1724-1104 © SEMI 2004 8
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SEMI MF1725-1103 © SEMI 2003 1
SEMI MF1725-1103
PRACTICE FOR ANALYSIS OF CRYSTALLOGRAPHIC PERFECTION
OF SILICON INGOTS
This standard 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 September 16, 2003. Initially available at
www.semi.org October 2003; to be published November 2003. Originally published by ASTM International
as ASTM F 1725-97. Last previous edition ASTM F 1725-02.
1 Purpose
1.1 The use of silicon wafers in many semiconductor
devices requires a consistent atomic lattice structure.
Crystal defects disturb local lattice energy conditions
that are the basis for semiconductor behavior. These
defects have distinct effects on essential semiconductor
device-manufacturing processes such as alloying and
diffusion.
1.2 This practice provides guidance regarding
procedures for analysis of crystal defects of silicon
ingots from which silicon wafers are cut.
1.3 This practice together with the referenced standards
may be used for process control, research and
development, and materials acceptance purposes.
2 Scope
2.1 This practice covers the analysis of the
crystallographic perfection in silicon ingots. The steps
described are sample preparation, etching solution
selection and use, defect identification, and defect
counting.
2.2 This practice is suitable for use in evaluating
silicon grown in either the [111] or the [100] direction
and doped either p or n type with resistivity greater than
0.005 Ω·cm.
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 Referenced Standards
3.1 SEMI Standards
SEMI C18 — Specification for Acetic Acid
SEMI C28 — Specifications and Guidelines for
Hydrofluoric Acid
SEMI C35 — Specifications and Guidelines for Nitric
Acid
SEMI MF26 — Test Method for Determining the
Orientation of a Semiconductor Single Crystal
SEM MF523 — Practice for Unaided Visual Inspection
of Polished Silicon Wafers
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
3.2 ASTM Standard
D 5127 — Guide for Ultra Pure Water Used in the
Electronics and Semiconductor Industry
1
NOTICE: Unless otherwise indicated, all documents
cited shall be the latest published versions.
4 Terminology
4.1 Defect-related terminology may be found in SEMI
MF1241.
5 Summary of Practice
5.1 The end portion of the silicon crystal, which
solidified last, may contain dislocations or other defects
such as slip. The portion containing the defects is
removed by sawing the crystal. A specimen wafer from
the end of the remaining ingot is obtained with a second
cut.
5.2 This wafer is mechanically lapped, chemically
polished, and then etched in a preferential defect
etching solution.
5.3 The etched surface is examined under bright light
illumination and examined microscopically to count
and classify the imperfections highlighted by the
preferential defect etching solution.
1 Annual Book of ASTM Standards, Vol 11.01. ASTM International,
100 Barr Harbor Drive, West Conshohocken, PA 10428, USA.
Telephone: 610-832-9585, Fax: 610-832-9555. Website:
www.astm.org
SEMI MF1725-1103 © SEMI 2003 2
6 Apparatus
6.1 Slicing Equipment — Suitable for removing wafers
of varied thickness from ingots.
6.2 Lapping or Grinding Equipment (optional) —
Suitable for removing saw damage.
6.3 Laboratory Equipment — Suitable for use with
hydrofluoric acid (fluorocarbon, polyethylene, or
polypropylene beakers, graduates, pipettes, and
nonmetallic wafer pickup tools).
6.4 Acid Sink — In a fume hood and facilities for
disposing of acids and their vapors.
6.5 Personnel Safety Equipment — For handling acids,
such as gloves, safety glasses, face shield, and gown.
7 Reagents and Materials
7.1 Purity of Reagents — All chemicals for which such
specifications exist shall conform to the assay and
impurity levels of Grade 1 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.
7.2 Purity of Water — Reference to water shall be
understood to mean Type E-3 or better water as
described in ASTM Guide D 5127.
7.3 Chemical Polishing Solution — A variety of
chemical polishing solutions exist. Those listed in
Table 1 have been found to produce satisfactory results.
Table 1 Volume Proportions
Formulation Nitric Acid,
(Assay:
> 99.7%)
Hydrofluoric
Acid,
(Assay:
49 ± 0.25%)
Acetic Acid,
(Assay: 70
to 71%)
A 6 1 1
B 5 3 3
C 5 10 14
D 5 1 2
7.4 An aqueous, nonionic surfactant detergent solution.
8 Safety Precautions
8.1 The chemicals used in polishing etches are
potentially harmful and must be handled in a chemical
exhaust fume hood, with the utmost care.
8.2 Hydrofluoric acid solutions are particularly
hazardous and the specific preventive measures must be
strictly observed.
8.3 Safety or protective gear should be worn while
handling these acid solutions or their components.
Safety requirements vary, but the essentials are: plastic
gloves, safety glasses, face shield, acid gown, and shoe
covers.
9 Procedure
9.1 Sample Selection — Take the sample for evaluation
from the crystal close to the discarded crystal portion
found at the last of the solidified crystal. Other samples
may be specified in producer-consumer relationships.
NOTE 1: Determination of the most logical point of sample
selection may be established by inspection of the bottom taper
of the crystal. If the crystal has a complete bottom taper, then
the sample should be obtained from the last point of a full
crystal diameter. If the crystal has lost zero dislocation
growth before the formation of a tapered bottom, obtain the
sample 1–crystal diameter above the point of lost zero
dislocation structure.
9.2 Orient the ingot to be sliced with either the x-ray or
optical method of SEMI MF26 so that the surface to be
exposed is within 5° of the desired plane. Slice a wafer,
0.5- to 2-mm thick, from the crystal. Identify ingot
growth lines on the sample by a mark or a ground flat
for future reference in counting defects.
NOTE 2: Defects observed by preferential etching may be
increasingly distorted as misalignment from the major
crystallographic plane increases.
9.3 Remove the residual saw damage by mechanical
lapping and chemical polishing or by chemical
polishing alone.
9.3.1 Wash the as-cut or lapped wafer in a nonionic
surfactant detergent solution and rinse thoroughly in
water. Drying may be hastened by use of a lint-free
paper towel. The surface must be uniformly matte in
appearance with no scratches, wax, dirt or water stains.
9.3.2 Chemical Polish
9.3.2.1 Place the sample in the bottom of a
hydrofluoric acid resistant beaker with the side to be
inspected facing upward. The beaker diameter need
only be larger than the wafer diameter.
9.3.2.2 Pour the room temperature chemical polish etch
(from Section 7.3) until the surface of the sample is
covered with about 1 cm of solution.
9.3.2.3 Agitate during etching to reduce bubble
formation and surface artifacts.
NOTE 3: The polish etch procedure in Section 9.3 describes
a facility for evaluation of a small number of samples. More
sophisticated facilities are used in commercial environments.
9.3.2.4 Rapidly dilute the etching solution with water
and flush the solution from the beaker after the sample
wafer develops mirror-polished surfaces.