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SEMI M20-1104 © SEMI 1991, 2004 3 x y ( x 1 , y 1 ) ( R 1 , 1 ) 1 x y ( x 1 , y 1 ) ( R 1 , 1 ) 1 x y ( x 1 , y 1 ) ( R 1 , 1 ) 1 NOTE: The primary fiducial may be a flat or a notch. Figure 1 Front Surface Co…
SEMI M20-1104 © SEMI 1991, 2004 2
coordinate system. Further, in SEMI E5, the coordinate
system axes do not rotate; the wafer rotates with respect
to these axes. In the wafer coordinate system, the
coordinate axes are referenced to the wafer itself,
independent of the physical position of the wafer in
space.
3.5 SEMI M12 and SEMI M13 specify the mark field
location for 100 mm, 125 mm, or 150 mm diameter
flatted wafers relative to the flat rather than the wafer
center. Thus, the mark field location may vary with
respect to the wafer center and the coordinates of the
corners of the mark field location (in the wafer
coordinate system) may vary from wafer to wafer.
However, the mark field location for notched wafers
150, 200, and 300 mm in diameter is referenced to the
wafer center.
3.6 There are some circumstances in which the front
surface of an unpatterned wafer is not readily
distinguished from the back surface.
4 Referenced Standards
4.1 SEMI Standards
SEMI E5 — SEMI Equipment Communications
Standard 2 Message Content (SECS-II)
SEMI M1 — Specifications for Polished
Monocrystalline Silicon Wafers
SEMI M12 — Specifications for Serial Alphanumeric
Marking of the Front Surface of Wafers
SEMI M13 — Specification for Alphanumeric Marking
of Silicon Wafers
SEMI M17 — Guide for a Universal Wafer Grid
NOTICE: Unless otherwise indicated, all documents
cited shall be the latest published versions.
5 Terminology
5.1 None.
6 Summary of Practice
6.1 Front Surface Coordinate System
6.1.1 The wafer is positioned with its front surface up.
6.1.2 The wafer center is located.
6.1.3 A right-handed Cartesian coordinate system is
erected.
6.1.4 The primary fiducial is located to be in the
negative y-direction.
6.1.5 Cartesian or polar coordinates (referenced to the
positive x-axis) are chosen according to the intended
application.
6.2 Back Surface Applications
6.2.1 The wafer is rotated about the bisector of the
primary fiducial (y-axis) until the back surface is up.
6.2.2 This reverses the direction of the x-axis, but
otherwise the back surface coordinate system is the
same as the front surface coordinate system.
6.3 Three-dimensional Coordinate System
6.3.1 Because the zero point on the z-axis is
application specific, only the direction of the z-
axis is
defined and the various possibilities for locating the
zero point are considered.
7 Procedure for Establishing Wafer
Coordinate Systems
7.1 Front Surface Coordinate System
7.1.1 Position the wafer front surface up.
7.1.2 Find the center of the wafer surface.
7.1.2.1 For purposes of this document, the periphery of
a wafer is assumed to be the smallest circle enclosing
the wafer, disregarding fiducials and all other edge
anomalies. Use the center of this circle as the center of
the wafer surface.
7.1.3 Erect a right-handed Cartesian coordinate system
with:
7.1.3.1 its origin at the center of the wafer surface,
7.1.3.2 the y-axis on the diameter in the plane of the
front surface which bisects the primary fiducial (flat or
notch), and
7.1.3.3 the x-axis on the diameter in the plane of the
front surface which is perpendicular to the bisector of
the primary fiducial (y-axis).
7.1.4 Orient the wafer so the primary fiducial is in the
negative y-direction (see Figure 1).
7.1.5 Take as the usual convention that the negative y-
direction is pointing downward (on a page) or toward
the operator (on a table or chuck or in a wafer carrier),
and that the positive x-axis points toward the right.
7.1.6 Reference the polar coordinates, r and θ to the
positive x-axis where
22
yxr (see Figure 1).
7.1.7 Choose Cartesian or polar coordinates according
to the application.
7.2 Back Surface Coordinates
7.2.1 Rotate the wafer around the bisector of the
primary fiducial (y-axis) until the back surface is up.
SEMI M20-1104 © SEMI 1991, 2004 3
x
y
(x
1
, y
1
)
(R
1
,
1
)
1
x
y
(x
1
, y
1
)
(R
1
,
1
)
1
x
y
(x
1
, y
1
)
(R
1
,
1
)
1
NOTE: The primary fiducial may be a flat or a notch.
Figure 1
Front Surface Coordinate System
7.2.2 With the primary fiducial in the negative y
direction (downward or toward the operator), the
positive x-axis points toward the left. In this way the x-
y-coordinates of a point on the back surface are the
same as the x-y coordinates of the point directly through
the wafer on the front surface.
7.3 Three-dimensional Coordinates
7.3.1 Place the wafer with the front surface up.
7.3.2 Erect the z-axis through the center of the wafer
surface and perpendicular to the plane of the surface
with the positive direction above the front surface (see
Figure 2).
7.3.3 Assign the zero point of the z-axis in accordance
with the application.
7.3.3.1 For example, for geometric measurements,
such as warp, the center of the z-axis may be at the
geometrical center of the wafer in three dimensions.
7.3.3.2 For front surface flatness measurements, the
zero point of the z-axis is usually taken at the reference
plane, which is chosen in accordance with the particular
flatness parameter being determined.
7.3.3.3 Other applications may require locating the
center of the z-axis at a different position.
7.3.3.4 For thickness or thickness variation
measurements, the zero point of the z-axis may be taken
at the center of the back surface of the wafer.
NOTE: The primary fiducial may be a flat or a notch.
Figure 2
Wafer Coordinate System with z-axis Direction
Indicated
SEMI M20-1104 © SEMI 1991, 2004 4
RELATED INFORMATION 1
APPLICATIONS OF THE WAFER COORDINATE SYSTEM
NOTICE: This related information is not an official part of SEMI M20. It was developed during the original
development of the document. This related information was approved for publication by full letter ballot
procedures.
R1-1 SEMI E5, in Stream 12 — Wafer Mapping, delineates how a coordinate system for reporting position data
may be communicated. The origin of this coordinate system, which is specified by the equipment when generating
the wafer map, may be the site at any of the four corners of the array or at the array center. In addition, the stream
provides for transmission of an arbitrary number of reference points to relate the map coordinate system to the
physical wafer. The wafer coordinate system may be used to establish the locations of these reference points and of
the origin of the map coordinate system.
R1-2 SEMI M17 defines a polar array of 1000 elements which can be used to identify the locations on a wafer of
extended defects such as slip. This array is consistent with the wafer coordinate system.
NOTICE: SEMI makes no warranties or representations as to the suitability of the standards set forth herein for any
particular application. The determination of the suitability of the standard is solely the responsibility of the user.
Users are cautioned to refer to manufacturer’s instructions, product labels, product data sheets, and other relevant
literature respecting any materials mentioned herein. These standards are subject to change without notice.
The user’s attention is called to the possibility that compliance with this standard may require use of copyrighted
material or of an invention covered by patent rights. By publication of this standard, SEMI takes no position
respecting the validity of any patent rights or copyrights asserted in connection with any item mentioned in this
standard. Users of this standard are expressly advised that determination of any such patent rights or copyrights, and
the risk of infringement of such rights, are entirely their own responsibility.
Copyright by SEMI® (Semiconductor Equipment and Materials
International), 3081 Zanker Road, San Jose, CA 95134. Reproduction
of the contents in whole or in part is forbidden without express written
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