ASTM F2358-04

Standard Guide for Measuring Characteristics of Sapphire Substrates

SIGNIFICANCE AND USE
The measurements described in this guide can significantly affect the function of the sapphire substrate.
Substrates with excessive form errors in the free state may cause processing errors in production.
The restrained state of the substrate is intended to simulate as closely as possible the form that the substrate will take in one of its intended uses. During processing, one surface of the substrate is sometimes forcibly restrained to a flat state through either vacuum or adhesion to a flat surface. The measurements in the clamped state are intended to model the form of the front surface of the substrate when the back surface is constrained to the reference plane. The form in the clamped state may have a direct impact on the performance of the substrate in use.
The user should determine whether the unrestrained or restrained measurements are most pertinent to the application and specify the appropriate parameters accordingly.
Knowledge of these characteristics can help the producer and consumer determine if the dimensional characteristics of a specimen substrate satisfy given geometrical requirements.
This guide is suitable for sapphire substrates in the as-sliced, lapped, polished, or other condition. Refer to SEMI M3 for substrate specifications.
Until the results of a planned interlaboratory evaluation of this guide are established, use of this guide for commercial transactions is not recommended unless the parties to the test establish the degree of correlation that can be obtained.
SCOPE
1.1 This guide covers a nondestructive procedure to determine the form of clean, dry sapphire substrates.
1.2 This guide is applicable to substrates 25 mm or larger in diameter, with a minimum thickness of 100 μm. This guide is independent of surface finish.
1.3 The measurements described in this guide may be applied to the entire global surface of the substrate, or to smaller localized areas.
1.4 The value of the measurements described in this guide will be affected by the amount of edge exclusion (that is, the area around the perimeter of the part which is ignored). The amount excluded should be agreed upon by the producer and consumer using this standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.
WITHDRAWN RATIONALE
This guide covers a nondestructive procedure to determine the form of clean, dry sapphire substrates.
Formerly under the jurisdiction of Committee F01 on Electronics and Subcommittee F01.15 on Compound Semiconductors, this guide was withdrawn in July 2011 without replacement due to its limited use by the industry.

General Information

• Status: Withdrawn
• Publication Date: 30-Apr-2004
• Withdrawal Date: 30-Jun-2011
• ICS: 25.100.70 - Abrasives
• Technical Committee: F01 - Electronics
• Drafting Committee: F01.15 - Compound Semiconductors

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: F2358 – 04
Standard Guide for
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Measuring Characteristics of Sapphire Substrates
This standard is issued under the fixed designation F2358; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.4 front surface—the preferred surface, as defined by the
user.
1.1 This guide covers a nondestructive procedure to deter-
3.1.5 quality area—the central area of a wafer surface,
mine the form of clean, dry sapphire substrates.
defined by a nominal edge exclusion, over which the specified
1.2 Thisguideisapplicabletosubstrates25mmorlargerin
values of a parameter apply. If the quality area is not circular,
diameter, with a minimum thickness of 100 µm. This guide is
the “circle defining the quality area” shall be defined as the
independent of surface finish.
minimum diameter circle which contains all of the data within
1.3 The measurements described in this guide may be
the quality area.
applied to the entire global surface of the substrate, or to
3.1.6 reference plane—the plane from which deviations are
smaller localized areas.
measured.
1.4 The value of the measurements described in this guide
3.1.7 restrained condition—this refers to the state of the
will be affected by the amount of edge exclusion (that is, the
substrate under test, when one side of the substrate is clamped
area around the perimeter of the part which is ignored). The
to an ideally flat surface; for example, when pulled down by a
amount excluded should be agreed upon by the producer and
vacuum onto an ideally clean flat chuck.
consumer using this standard.
3.1.8 sapphire substrate—generic term for any flat wafer,
1.5 This standard does not purport to address all of the
window, wafer carrier, or substrate made of sapphire material.
safety concerns, if any, associated with its use. It is the
These terms may be used interchangeably in this standard.
responsibility of the user of this standard to establish appro-
3.1.9 thickness—the distance through the substrate between
priate safety and health practices and determine the applica-
corresponding points on the front and back surfaces.
bility of regulatory requirements prior to use.
3.1.10 unrestrained condition—thisreferstothestateofthe
2. Referenced Documents
substrate under test, when the substrate is in a stress-free
2
condition with minimal deformation due to gravity.
2.1 SEMI Standard:
3.2 Definitions of Unrestrained Parameters:
M3 Specifications for Polished Monocrystalline Sapphire
3.2.1 sag—the distance from the apex of the best-fit sphere
Substrates
to a plane intersecting the sphere in a circle with a diameter
3. Terminology
equal to the diameter of the circle defining the quality area,
measured in an unclamped condition. This value will be
3.1 General Definitions:
positive(+)ifthemeasuredsurfaceisconvex,andnegative(−)
3.1.1 back surface—the surface opposite the front surface.
if the surface is concave. See Fig. 1.
If there is no difference between the front and back surfaces,
3.2.2 sori—the maximum distance above, plus the maxi-
then the surfaces may be determined arbitrarily, and are
mum distance below the front surface best-fit plane of a free,
therefore interchangeable.
unclamped substrate. See Fig. 2.
3.1.2 best-fit plane—the theoretical plane established by
3.3 Definitions of Restrained Parameters (see Note 1):
usingtheleastsquaresfitmethod,basedondataobtainedfrom
3.3.1 front-to-front deviation (FFD)—the maximum dis-
the quality area only.
tance above, plus the maximum distance below the front
3.1.3 best-fit sphere—the theoretical sphere established by
surface best-fit plane of a substrate, measured with the back
usingtheleastsquaresfitmethod,basedondataobtainedfrom
surface restrained. See Fig. 3.
the quality area only.
3.3.2 taper—the linear component of the variation in thick-
ness across a substrate, indicated by the angle between the
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This guide is under the jurisdiction of ASTM Committee F01 on Electronics
best-fit plane to the front surface and the ideally flat back
and is the direct responsibility of Subcommittee F01.15 on Compound Semicon-
surface of the substrate. See Fig. 4.
ductors.
Current edition approved May 1, 2004. Published June 2004. DOI: 10.1520/
3.3.3 total thickness variation (TTV)—the difference be-
F2358-04.
tween the maximum and minimum values of the thickness of
2
Available from Semiconductor Equipment and Materials International (SEMI),
the substrate. See Fig. 5.
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