SEMI M73 - Test Method for Extracting Relevant Characteristics from Measured Wafer Edge Profiles -

Abstract

1  Purpose
1.1  SEMI M1 specifies the contour of the shaped edge of silicon wafers by using templates that allow a wide variation in wafer edge profiles manufactured by silicon suppliers to still meet the specification.
1.2  In many advanced wafer applications, a much tighter specification of the edge profile is required to control variations in subsequent circuit processing. These specifications frequently include values for certain characteristics that describe the segments of the edge profile contour.
1.3  A prerequisite for specifying tighter tolerances on edge profiles is an agreement about the names of the relevant characteristics used for describing edge profiles and a method for extracting these characteristics from a measured edge profile. Therefore, in these test methods, terms used to describe the characteristics of the edge profile of silicon wafers are named and their meaning is illustrated by a schematic drawing.
1.4  This Standard covers two test methods for deriving these characteristics from a measured edge profile.
2  Scope
2.1  These test methods are both in use within the industry. They are based on fitting the measured edge profile over certain segments with straight lines, circular arcs, or tangent lines to obtain values for profile segment parameters such as:
• bevel angles,
• edge widths,
• apex lengths,
• apex angles,
• shoulder radii, and
• edge roundness
In addition, the locations of the reference points that separate the various segments of the edge profile are determined. These segment parameters are listed in order around the profile in Table 1 and are illustrated in Figure 1 and Figure 2.
2.2  Because the fitting locations and procedures differ considerably between the two methods, the results obtained for specific segment parameters are not likely to be identical.
2.3  Both test methods covered by this standard are applicable to all types of measured edge profiles on silicon wafers.
2.3.1  In Test Method 1, the specified edge width is used to determine the regions of the measured edge profile to be fitted and the coordinates of the reference point locations are derived from fitted regions of the measured edge profile. Test Method 1 describes how to:
• extract the edge profile parameters directly from the measured edge profile at defined distances from the periphery of the wafer and compare them with the specified values,
• reconstruct the edge profile using the extracted characteristics, and
• assess the agreement between the measured, target, and reconstructed profiles, enabling the user to see how representative the extracted parameters are regarding the measured profile.
2.3.2  In Test Method 2, the specified bevel angle is used to determine both the regions of the measured edge profile to be fitted and the coordinates of the reference points Ai and Bi. Test Method 2 describes how to:
• extract the edge profile characteristic parameters by fitting lines or arcs to portions of the measured edge profile at defined distances from the periphery of the wafer and compare them with the specified values,
• compare the fitted lines and arcs with the appropriate portions of the measured profile enabling the user to see how well fit the extracted parameters are in each segment.
NOTE 1: For both test methods, measured results for three different edge profile types are given as examples in Related Information 1 at the end of this Standard.
2.4  These test methods refer explicitly to silicon wafers, but they may also be applied to wafers of other materials.
2.5  These test methods do not cover requirements either for the equipment used to measure the edge profile or for the methodology of such measurement. They also do not describe how to assess the capability of either the equipment or the techniques for measuring edge profiles on wafers.
2.6  These test methods also do not cover evaluation of either surface finish or edge roll-off in the near-edge region.
2.7  The edge roundness parameters are evaluated independent of the test method.

Referenced SEMI Standards (purchase separately)
SEMI M1 — Specification for Polished Single Crystal Silicon Wafers
SEMI M20 — Practice for Establishing a Wafer Coordinate System
SEMI M59 — Terminology for Silicon Technology

Revision History
SEMI M73-0125 (technical revision)
SEMI M73-1013E (Reapproved 1019)
SEMI M73-1013E (editorial revision)
SEMI M73-1013 (technical revision)
SEMI M73-0309 (technical revision)
SEMI M73-1108 (first published)

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