ASTM F1049-00
(Practice)Standard Practice for Shallow Etch Pit Detection on Silicon Wafers
Standard Practice for Shallow Etch Pit Detection on Silicon Wafers
SCOPE
1.1 This practice is used to detect shallow etch pits, which may be related to the level of metallic impurities near the surface of silicon epitaxial or polished wafers.
1.2 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.
1.3 Silicon crystals doped either p- or n-type and with resistivities as low as 0.005 [omega][dot]cm may be evaluated. This practice is applicable for silicon wafers grown in either a (111) or (100) crystal orientation.
1.4 This practice utilizes a thermal oxidation process followed by a chemical preferential etchant to create and then delineate shallow etch pits.
1.5 The values stated in acceptable metric units are to be regarded as the standard. The values in parentheses are for information only.
1.6 This standard does not purport to address all of the safety concerns, 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 limitations prior to use. Specific hazard statements are given in Section 9.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 1049 – 00
Standard Practice for
Shallow Etch Pit Detection on Silicon Wafers
This standard is issued under the fixed designation F 1049; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 SEMI Standards:
SEMI C 1 Specifications for Reagents
1.1 This practice is used to detect shallow etch pits, which
M 17 Specification for a Universal Wafer Grid
may be related to the level of metallic impurities near the
surface of silicon epitaxial or polished wafers.
3. Terminology
1.2 This practice is not recommended for use in defect
3.1 Definitions:
density evaluations, but as a subjective means of estimating
3.1.1 haze—on a semiconductor wafer, non—localized
defect densities and distributions on the surface of a polished or
light scattering resulting from surface topography (micror-
epitaxial wafer.
oughness) or from dense concentrations of surface or near-
1.3 Silicon crystals doped either p-or n-type and with
surface imperfections. See also laser light scattering event.
resistivities as low as 0.005 V·cm may be evaluated. This
3.1.1.1 Discussion—Haze due to the existence of a collec-
practice is applicable for silicon wafers grown in either a (111)
tion of imperfections of the type that result in haze cannot be
or (100) crystal orientation.
readily distinguished by the eye or other optical detection
1.4 This practice utilizes a thermal oxidation process fol-
system without magnification. In a scanning surface inspection
lowed by a chemical preferential etchant to create and then
system, haze and laser-light scattering events comprise the
delineate shallow etch pits.
laser surface scanner signal due to light scattering from a wafer
1.5 The values stated in acceptable metric units are to be
surface.
regarded as the standard. The values in parentheses are for
3.1.2 shallow etch pits—etch pits that are small and shallow
information only.
in depth under high magnification, > 2003.
1.6 This standard does not purport to address all of the
3.1.2.1 Discussion—Shallow etch pits on silicon wafers are
safety concerns, if any, associated with its use. It is the
shown in Guide F 154 .
responsibility of the user of this standard to establish appro-
3.1.3 saucer pits—same as shallow etch pits, see 3.1.2.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. Specific hazard
4. Summary of Practice
statements are given in Section 9.
4.1 Silicon wafers, either epitaxial or polished, are ther-
mally oxidized and preferential etched. This will reveal small
2. Referenced Documents
etch pits, shallow in depth, when observed through an inter-
2.1 ASTM Standards:
2 ference contrast microscope. The distribution of the etch pits
D 5127 Guide for Electronic Grade Water
on the surface of the wafer are determined by illuminating the
F 154 Guide for Identification of Structures and Contami-
3 wafer with a high intensity lamp.
nants Seen on Specular Silicon Surfaces
F 1725 Guide for Analysis of Crystallographic Perfection of
5. Significance and Use
Silicon Ingots
5.1 High levels of etch pits are reported to indicate metallic
F 1727 Practice for Dection of Oxidation Induced Defects
contamination that is detrimental to wafer processing. This can
in Polished Silicon Wafers
be deduced from the density of etch pits on the surface of the
F 1809 Guide for Selection and Use of Etching Solutions to
wafer.
Delineate Structural Defects in Silicon
5.2 This practice is appropriate for process control, and
F 1810 Test Method for Counting Preferentially Etched or
research and development applications. Because its reproduc-
Decorated Surface Defects in Silicon Wafers
ibility has not been established by interlaboratory test, it is not
recommended for use in materials acceptance unless the parties
This practice is under the jurisdiction of ASTM Committee F-1 on Electronics
and is the direct responsibility of Subcommittee F01.06 on Silicon Materials and
Process Control. Available from Semiconductor Equipment and Materials International, 805 E.
Current edition approved June 10, 2000. Published August 2000. Originally Middlefield Rd., Mountain View, CA 94043.
published as F 1049 – 87. Last previous edition F 1049 – 95. Pearce, C. W., and McMahon, R. G., “Role of Metallic Contamination in the
Annual Book of ASTM Standards, Vol 11.01. Formation of 8Saucer’ Pit Defects in Epitaxial Silicon,” Journal of Vacuum Science
Annual Book of ASTM Standards, Vol 10.05. and Technology, Vol 14, No. 1, 1977, p. 40.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 1049
to the test have conducted correlation experiments to establish Analytical Reagents of the American Chemical Society. Other
the precision to be expected. grades may be used provided it is first ascertained that the
reagent is of sufficiently high purity to permit its use without
6. Interferences lessening the accuracy of the determination.
8.2 Purity of Water—Reference to water shall be understood
6.1 Etch artifacts are the primary cause of difficulty in
to mean either distilled water, or deionized water having a
identifying shallow etch pits. Etch artifacts are generated in
resistivity equal to or greater than Type II water as defined by
various ways such as gas bubble formation during etching,
Guide D 5127.
improperly cleaned surface prior to etching, or insufficient etch
8.3 Schimmel Etch for (100) and (111) Surfaces.
solution volume.
8.3.1 Chromic Acid Solution—Make a 0.75 M solution of
6.2 Excessive silicon staining (very dark color) during the
CrO to a 1-L glass volumetric flask and add sufficient water to
preferential etching may obscure or prevent the development of
make a solution volume of 1 L, or 1000 mL. The solution may
shallow etch pits on heavily doped p-type silicon material
be stored up to 6 months in either clean glass, TFE-
(<0.2V· cm).
fluorocarbon, polyethylene, or polypropylene bottles.
8.3.2 For Test Specimens with Resistivity Greater Than
NOTE 1—Light staining will not affect subsequent defect etch results.
However, heavy stains are undesirable. 0.2V·cmn-orp-Type—Immediately before using, add 2 parts
HF to 1 part chromic acid solution (see 8.3.1) by volume.
7. Apparatus
Prepare and mix in HF-proof beakers (see 7.2).
8.3.3 For Test Specimens with Resistivity Less Than 0.2
7.1 Narrow Beam Light Source—Tungsten filament with a
V·cm n- or p-Type—Immediately before using, add 2 parts HF
concentrated beam intensity greater than 16 klx (1500 fc) and
to 1 part chromic acid solution (see 8.3.1) and 1.5 parts water
a beam diameter of 20 to 40 mm (0.8 to 1.6 in.) at a position
by volume. Prepare and mix in HF-proof beakers (see 7.2).
100 mm (4 in.) from the light-source housing. The light beam
8.3.4 The specified chemicals shall have the following
shall not be collimated and shall be capable of forming an
nominal assay:
image of the bulb filament at the lamp focus length.
Chemical Assay, %
Chromium trioxide >98.0
NOTE 2—Some standard microscope illuminators meet these require-
Hydrofluoric acid, concen- 49 6 0.25
ments.
trated
7.2 Hydrofluoric Acid-Proof Chemical Laboratory
9. Safety Hazards
Apparatus—Fluorocarbon, polyethylene, or polypropylene
9.1 The chemicals used in this evaluation procedure are
beakers, graduates, tweezers, eye protection, apron, gloves, and
potentially harmful and must be handled in an acid exhaust
protective sleeves.
fume hood, with utmost care at all times.
7.3 Wafer Holders—HF acid-proof wafer carriers which
9.2 Warning: Hydrofluoric acid solutions are particularly
hold wafers. These are necessary if more than one wafer is to
hazardous. They should not be used by anyone who is not
be etched at a time.
familiar with the specific preventive measures and fir
...
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