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SEMI MF847-0705 © SEMI 2003, 2005 2 2.5 The values stat ed in SI units are to be regarded as the sta ndard. The inch- p ound val ues given in pa rentheses are for information only . NOTICE : This standard does not purpor…
SEMI MF847-0705 © SEMI 2003, 2005 1
SEMI MF847-0705
TEST METHODS FOR MEASURING CRYSTALLOGRAPHIC
ORIENTATION OF FLATS ON SINGLE CRYSTAL SILICON WAFERS
BY X-RAY TECHNIQUES
These test methods were technically approved by the global Silicon Wafer Committee. This edition was
approved for publication by the global Audits and Reviews Subcommittee on April 7, 2005. It was available
at www.semi.org in June 2005 and on CD-ROM in July 2005. Original edition published by ASTM
International as ASTM F 847-83. Last previous edition SEMI MF847-02.
1 Purpose
1.1 The orientation of flats on silicon wafers is an important materials acceptance requirement. The flats are used in
semiconductor device processing to provide consistent alignment of device geometries with respect to
crystallographic planes and directions.
1.2 The orientation of a wafer flat is the orientation of the surface of the flat (on the edge of the wafer). Flats are
usually specified with respect to a low-index plane, such as a (110) plane. In such cases the orientation of the flat
may be described in terms of its angular deviation from the low-index plane.
1.3 This standard covers two test methods for determining flat orientation.
1.4 Either one of these test methods is appropriate for process development and quality assurance applications.
Until the interlaboratory precision of these test methods has been determined, it is not recommended that they be
used between supplier and customer unless correlation studies are completed satisfactorily.
2 Scope
2.1 These test methods cover the determination of
, the angular deviation between the crystallographic orientation
of the direction perpendicular to the plane of a fiducial flat on a circular silicon wafer, and the specified orientation
of the flat in the plane of the wafer surface.
2.2 These test methods are applicable for wafers with flat length values in the range of those specified for silicon
wafers in SEMI M1. They are suitable for use only on wafers with angular deviations in the range from 5 to +5°.
2.3 The orientation accuracy achieved by these test methods depends directly on the accuracy with which the flat
surface can be aligned with a reference fence and the accuracy of the orientation of the reference fence with respect
to the X-ray beam.
2.4 Two test methods are covered as follows:
Test Method A — X-Ray Edge Diffraction Method §8 through §13
Test Method B — Laue Back Reflection X-Ray Method §14 through §18
2.4.1 Test Method A is nondestructive and is similar to Test Method A of SEMI MF26, except that it uses special
wafer holding fixtures to orient the wafer uniquely with respect to the X-ray goniometer. The technique is capable
of measuring the crystallographic direction of flats to a greater precision than the Laue back reflection method.
2.4.2 Test Method B is also nondestructive, and is similar to ASTM Test Method E 82, and to DIN 50 433, Part 3,
except that it uses “instant” film and special fixturing to orient the flat with respect to the X-ray beam. Although it
is simpler and more rapid, it does not have the precision of Test Method A because it uses less precise and less
expensive fixturing and equipment. It produces a permanent film record of the test.
NOTE 1: The Laue photograph may be interpreted to provide information regarding the crystallographic directions of wafer
misorientation; however, this is beyond the scope of the present test method. Users desiring to carry out such interpretation
should refer to ASTM Test Method E 82, to DIN 50 433, Part 3, or to a standard X-ray textbook.
1,2
With different wafer holding
fixturing, Test Method B is also applicable to determination of the orientation of a wafer surface.
1 Wood, E. A., Crystal Orientation Manual, (Columbia University Press, New York, NY, 1963).
2 Barret, C. S., and Massalski, T. B., The Structure of Metals, 3rd edition (McGraw-Hill, New York, NY, 1966).
SEMI MF847-0705 © SEMI 2003, 2005 2
2.5 The values stated in SI units are to be regarded as the standard. The inch-pound values given in parentheses are
for information only.
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 The alignment of the flat against the reference fence may be affected by the straightness of the flat. In the
unlikely event that the flat profile is convex, the flat orientation may not be unique. More often the flat surface will
touch the reference fence along two lines perpendicular to the wafer surface at two points. In this case, the
orientation determined is that of the plane through the two lines on the plane perpendicular to the wafer surface that
passes through the two points. In the latter cases, the orientation determined is that which is obtained in subsequent
processing of the wafer when the alignment is between the flat and a reference fence.
3.2 Misalignment of the various fixtures degrades both the interlaboratory reproducibility and the absolute accuracy
of both test methods. The single-instrument repeatability is not degraded provided the fixturing is rigid.
4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI M1 — Specifications for Polished Monocrystalline Silicon Wafers
SEMI M59 — Terminology for Silicon Technology
SEMI MF26 — Test Methods for Determining the Orientation of a Semiconductive Single Crystal
4.2 ASTM Standards
E 82 — Test Method for Determining the Orientation of a Metal Crystal
3
E 122 — Practice for Choice of Sample Size to Estimate a Measure of Quality for a Lot or Process
4
4.3 DIN Standard
50433, Part 3 — Determination of the Orientation of Single Crystals by Means of Laue Back Scattering
5
4.4 ANSI Standard
ANSI/ASQC Z1.4 — Sampling Procedures and Tables for Inspection by Attributes
6
4.5 Other Standard
Code of Federal Regulations, Title 10, Part 20, Standards for Protection Against Radiation
7
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Definitions
5.1.1 Terms relating to silicon technology are defined in SEMI M59.
3 Annual Book of ASTM Standards, Vol 03.01, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Telephone: 610-
832-9500, Fax: 610-832-9555, Website:
www.astm.org.
4 Annual Book of ASTM Standards, Vol 14.02.
5 Deutches Institut für Normung standards are available in both English and German editions from Beuth Verlag GmbH, Burggrafenstrasse 6,
10787 Berlin, Germany, Telephone: 49.30.2601-0, Fax: 49.30.2601.1263, Website:
www.beuth.de.
6 American National Standards Institute, American National Standards Institute, New York Office: 25 West 43rd Street, New York, NY 10036,
USA. Telephone: 212.642.4900, Fax: 212.398.0023, Website:
www.ansi.org
.
7 Published in Federal Register, Nov. 16, 1960. Available from Superintendent of Documents, U.S. Government Printing Office, Washington,
DC 20402.
SEMI MF847-0705 © SEMI 2003, 2005 3
6 Hazards
6.1 These test methods use X radiation; it is absolutely necessary to avoid personal exposure to X rays.
6.1.1 It is especially important to keep hands or fingers out of the path of the X rays and to protect the eyes from
scattered secondary radiation.
6.1.2 The use of commercial film badge or dosimeter service is recommended, together with periodic checks of the
radiation level at the hand and body positions with a Geiger-Muller counter calibrated with a standard nuclear
source.
NOTE 2: The present maximum permissible dose for total body exposure of an individual to external X-radiation of quantum
energy less than 3 MeV over an indefinite period is 1.25 R (3.22 × 10
4
C/kg) per calendar quarter (equivalent to 0.6 mR/h
(1.5 × 10
7
C/kg·h)) as established in the Code of Federal Regulations, Title 10, Part 20. The present maximum permissible dose
of hand and forearm exposure under the same conditions is 18.75 R (4.85 × 10
3
C/kg) per calendar quarter (equivalent to 9.3
mR/h (2.4 × 10
6
C/kg·h)). Besides the above stated regulations, various other government and regulatory organizations have
their own safety requirements.
6.1.3 It is the responsibility of the user to make sure that the equipment and the conditions under which it is used
meet applicable regulations.
7 Sampling
7.1 Unless otherwise specified, ASTM Practice E 122 shall be used.
7.2 When so specified, appropriate sample sizes shall be selected from each lot according to ANSI/ASQC Z1.4.
7.3 Inspection levels shall be agreed upon between the parties to the test.
TEST METHOD A — X-RAY EDGE DIFFRACTION METHOD
8 Summary of Test Method
8.1 In this test method a holding fixture that uniquely orients the wafer being tested with respect to its geometric
features is used to position the wafers with respect to the X-ray goniometer.
8.2 The goniometer is rotated to determine the Bragg angle with respect to the geometric features by X-ray
diffraction from the crystallographic planes of the wafer edge, first with the wafer front surface up and then with
front surface down.
8.3 The average angular deviation is calculated from the goniometer readings.
9 Apparatus
9.1 X-ray and Goniometer Apparatus — In accordance with ¶5.1 of SEMI MF26, except that the X-ray beam shall
be collimated using a vertical slit.
9.2 Wafer-Holding Fixture, to orient the sample wafer uniquely with respect to the X-ray goniometer (see Figure 1).
The fixture must include a vacuum hold-down with a flat horizontal surface and a reference fence perpendicular to
this surface. These components establish an x-y axis that is fixed with respect to the goniometer and the X-ray
beam. The exact dimensions of the fixture depend on the layout of the X-ray apparatus. The critical features are: