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SEMI MF847 Document Information:
Title
TEST METHODS FOR MEASURING CRYSTALLOGRAPHIC ORIENTATION OF FLATS ON SINGLE CRYSTAL SILICON WAFERS BY X-RAY TECHNIQUES
Semiconductor Equipment and Materials International
Publication Date:
Jul 1, 2005
Scope:
These test methods cover the determination of a, 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.
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°.
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.
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
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.
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.
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.
Purpose
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.
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.
This standard covers two test methods for determining flat
orientation.
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.
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).
Keywords:
- crystallographic orientation
- flats
- Laue diffraction
- silicon
- single crystal
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