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SEMI M20 Document Information:
Title
PRACTICE FOR ESTABLISHING A WAFER COORDINATE SYSTEM
Semiconductor Equipment and Materials International
Publication Date:
Nov 1, 2004
Scope:
This practice covers procedures for defining a wafer coordinate
system for locating uniquely any point on a wafer surface using the
wafer center as the origin and either Cartesian (x-y) or
polar (r) coordinates.
For unpatterned wafers, this wafer coordinate system can be used
directly or in conjunction with a rectangular or polar overlay
array.
This wafer coordinate system can also be used to locate the
origins or other reference points of other coordinate systems used
to define or report position data of site, die, or map arrays on
the front or back surface of a patterned or unpatterned wafer. In
this way, the array coordinate system may be referenced to the
physical geometry of the wafer. Selected modes of application of
the wafer coordinate system are given for information only in
Related Information 1.
This practice also covers procedures for defining a
three-dimensional x-y-z (or r-z) coordinate system for the
wafer.
NOTICE: This standard does not purport to
address safety issues, if any, associated with its use. It is the
responsibility of the users of this standard to establish
appropriate safety and health practices and determine the
applicability of regulatory or other limitations prior to use.
Purpose
Processing systems now employed in advanced device manufacturing
use aligning mechanisms to position the wafer rotationally and in
x-y prior to processing. Many of these scan the wafer
periphery and determine the geometric center of the wafer surface.
This is most often seen on stepping aligners, to minimize the
effects of wafer-to-wafer diameter variation in mixed aligner type
fabs. Similar centerreferencing subsystems are found on many
characterization systems. The wafer coordinate system provides a
method for referencing any other coordinate system, such as a site,
pattern, or mapping array, to the physical geometry of the wafer
surface.
If the points of the array lie on the front surface of the
wafer, only the x and y (or r and ) coordinates
are relevant. It has become increasingly important in semiconductor
material and device manufacturing to describe, in unambiguous
terms, the position of a point on a wafer that automatic
processing, test, or characterization equipment can recognize and
locate. For example, characterization equipment needs to report the
precise locations of defects and anomalies discovered in wafers
before or after processing in order to relate the presence or
absence of such defects and anomalies to device yield variations.
The wafer coordinate system can be used to establish the
coordinates of each point of interest, and, through transformation
to the yield analysis coordinate system, relate them to the die
yield map.
In response to these needs, this practice defines a wafer
coordinate system to facilitate the precise locating and reporting
of points on the wafer surface. If the point or points lie above or
below the surface, the z coordinate must also be used. Because the
zero point on the z-axis is application specific, this practice
treats the x-y-z (or r-z) system separately from the
surface coordinate system.
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