ASTM F657-92(1999)

Standard Test Method for Measuring Warp and Total Thickness Variation on Silicon Wafers by Noncontact Scanning (Withdrawn 2003)

SCOPE
This standard was transferred to SEMI (www.semi.org) May 2003
1.1 This test method covers a noncontacting, nondestructive procedure to determine the warp and total thickness variation (TTV) of clean, dry silicon wafers in a free (unclamped) condition. The procedure uses a three-point back surface reference plane for determining warp.  
1.2 The test method is applicable to circular silicon wafers 50 mm or larger in diameter, and 100 [mu]m (0.004 in. approximately) and larger in thickness, independent of thickness variation and surface finish. The test method is applicable to wafers of semiconductors other than silicon with these same physical characteristics.  
1.3 This test method is not intended to measure surface flatness; warp, which is not to be confused with flatness, is a bulk property of the wafer.
1.4 This test method measures warp or TTV of a wafer with no mechanical force applied during the test. Therefore, the procedure described gives the unconstrained value of warp or TTV. Gravity-induced deflection alters the shape of the wafer and is included in the measurement.  
1.5 This standard does not purport to address the safety problems 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 limitations prior to use.  
1.6 For silicon wafers of diameter 3 in. or smaller, the values stated in inch-pound units are to be regarded as standard; the values stated in acceptable metric units in parentheses are for information only. For silicon wafers of diameter larger than 3 in., the values stated in acceptable metric units are to be regarded as standard whether or not they appear with parentheses; inch-pound units are for information only.

General Information

• Status: Withdrawn
• Publication Date: 31-Dec-1998
• Withdrawal Date: 09-May-2003
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 657 – 92 (Reapproved 1999)
Standard Test Method for
Measuring Warp and Total Thickness Variation on Silicon
Wafers by Noncontact Scanning
This standard is issued under the fixed designation F 657; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope M 1 Specifications for Polished Monocrystalline Silicon
Wafers
1.1 This test method covers a noncontacting, nondestructive
2.3 Federal Standard:
procedure to determine the warp and total thickness variation
GGG-P 463 C Surface Plate, Granite
(TTV) of clean, dry silicon wafers in a free (unclamped)
condition. The procedure uses a three-point back surface
3. Terminology
reference plane for determining warp.
3.1 Definitions of Terms Specific to This Standard:
1.2 The test method is applicable to circular silicon wafers
3.1.1 median surface— of a semiconductor wafer, the locus
50 mm or larger in diameter, and 100 μm (0.004 in. approxi-
of points in the wafer equidistant from the front and back
mately) and larger in thickness, independent of thickness
surfaces.
variation and surface finish. The test method is applicable to
3.1.2 thickness—of a semiconductor wafer, the distance
wafers of semiconductors other than silicon with these same
through the wafer between corresponding points on the front
physical characteristics.
and back surfaces.
1.3 This test method is not intended to measure surface
3.1.3 total thickness variation, TTV— of a semiconductor
flatness; warp, which is not to be confused with flatness, is a
wafer, the difference between the maximum and minimum
bulk property of the wafer.
values of the thickness of the wafer.
1.4 This test method measures warp or TTV of a wafer with
3.1.4 warp—of a semiconductor wafer, the difference be-
no mechanical force applied during the test. Therefore, the
tween the maximum and minimum distances of the median
procedure described gives the unconstrained value of warp or
surface of a free, unclamped wafer from a reference plane.
TTV. Gravity-induced deflection alters the shape of the wafer
3.1.4.1 Discussion—Although warp may be caused by un-
and is included in the measurement.
equal stresses on the two exposed surfaces of the wafer, it
1.5 For silicon wafers of diameter 3 in. or smaller, the
cannot be determined from measurements on a single exposed
values stated in inch-pound units are to be regarded as
surface. The median surface may contain regions with upward
standard; the values stated in acceptable metric units in
or downward curvature or both; under some conditions the
parentheses are for information only. For silicon wafers of
median surface may be flat (see 6.4 and Appendix X1).
diameter larger than 3 in., the values stated in acceptable metric
units are to be regarded as standard whether or not they appear
4. Summary of Test Method
with parentheses; inch-pound units are for information only.
4.1 The wafer is supported by three hemispherical points on
1.6 This standard does not purport to address the safety
a reference ring, and both surfaces are simultaneously scanned
concerns if any, associated with its use. It is the responsibility
along a prescribed pattern by both members of an opposed pair
of the user of this standard to establish appropriate safety and
of probes.
health practices and determine the applicability of regulatory
4.2 The displacements (distances) between each probe and
limitations prior to use.
the nearest surface of the wafer are determined (in pairs) at
2. Referenced Documents intervals along the scan pattern.
4.3 Half the difference between the largest and smallest of
2.1 ASME Standard:
2 the differences of the paired displacements is taken as a
B 46 Surface Texture
measure of the warp.
2.2 SEMI Standard:
4.4 The difference between the largest and smallest of the
sums of the paired displacements is taken as a measure of the
This test method is under the jurisdiction of ASTM Committee F-1 on total thickness variation.
Electronicsand is the direct responsibility of Subcommittee F01.06 on Electrical and
Optical Measurement.
Current edition approved Nov. 15, 1992. Published March 1993. Originally Available from the Semiconductor Equipment and Materials International, Inc.,
published as F 657 – 80. Last previous edition F 657 – 91. 805 E. Middlefield Rd., Mountain View, CA 94043.
2 4
Available from the American Society of Mechanical Engineers, 345 E. 47th St., Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
New York, NY 10017. Robbins Ave., Philadelphia, PA 19111-5094.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 657
5. Significance and Use 7.1.1.1 Three Hemispherical Support Pads, used to define
the plane of the reference ring and equally spaced within
5.1 Warp and thickness variation can significantly affect the
60.005 in. (60.13 mm) on the circumference of a circle whose
yield of semiconductor device processing.
diameter is 0.250 in. (6.35 mm) less than the nominal diameter
5.2 Knowledge of these characteristics can help the pro-
of the wafer as given in SEMI Specifications M 1. The support
ducer and consumer determine if the dimensional characteris-
pads shall be fabricated from tungsten carbide, or from a
tics of a specimen wafer satisfy given geometrical require-
material of the same or greater hardness, have a nominal
ments.
diameter of 0.125 in. (3.18 mm), and project 0.0625 6 0.0050
5.3 Changes in wafer warp during processing can adversely
in. (1.59 6 0.13 mm) above the upper surface of the reference
affect subsequent handling and processing steps.
ring. The upper bearing surface of each support pad shall be
5.4 This test method is suitable for measuring the warp and
polished, with a maximum surface roughness R of 10-μin.
A
TTV of silicon wafers used in semiconductor device process-
(0.25-μm) measured with 0.31-in. (0.8-mm) cutoff in accor-
ing in the as-sliced, lapped, or polished condition and for
dance with ASME B 46.
monitoring thermal and mechanical effects on the warp of
7.1.1.2 Three Cylindrical Guide Pins, used to assist the
silicon wafers during device processing.
operator to position the specimen wafer by eye, spaced
6. Interferences
approximately equally on the circumference of a circle whose
diameter is nominally equal to the sum of the diameter of the
6.1 Any change in the reference plane during scanning will
produce error in the indicated measurement equal to the axial pin and the maximum allowable wafer diameter as given in
SEMI Specifications M 1. The guide pins shall be at least 0.015
vector value of the deviation at the probe axes at the points of
largest and smallest differences. If such changes occur, there is in. (0.38 mm) higher than the support pads (see Fig. 1).
7.1.1.3 Probe Parking Position, cut-out area in the reference
the possibility that an incorrect location may be identified as an
extremum. ring outside the nominal wafer diameter to permit the ring to be
positioned so that the probe assembly is out of the way for
6.2 Non-parallelism of the reference plane to the granite
base surface will produce an error in the indicated measure- specimen or precision flat insertion and removal (see Fig. 1).
ment proportional to the non-parallelism.
NOTE 1—The plane defined by the reference ring is the plane tangent to
6.3 Foreign particles (dirt) between the measuring ring and
the three pads.
surface plate will introduce error.
NOTE 2—It is recommended that the guide pins be fabricated from a
6.4 This test method does not completely separate thickness
hard plastic material.
variation from warp. In some cases, the median surface may be
7.1.2 Probe Assembly with Indicator, paired, non-
flat but still show a non-zero value for warp.
contacting, displacement-sensing probes, probe supports, and
6.5 Vibration of the test specimen relative to the probe-
indicator unit. The probes shall be capable of independent
measuring axis will introduce error.
measurement of the distance between the probed site on each
6.6 Running probes off the test specimen during the scan
surface of the specimen slice and the plane of the reference
sequence will give false readings.
ring. The probes shall be mounted above and below the
6.7 Most equipment systems capable of this measurement
specimen position in a manner so that the probe site on one
have a definite range of wafer thickness combined with warp
surface of the specimen is opposite the probed site on the other.
which can be accommodated without readjustment. Any values
The common axis of mounting shall be perpendicular (62°) to
observed while in an over-range condition are invalid (see
the plane defined by the reference ring. The upper probe mount
7.1.2.3).
shall incorporate a positioning adjustment to accommodate the
6.8 In this test method, both TTV and warp are determined
wafer thickness range desired. The indicator unit shall be
using a specified partial scan pattern; thus, the entire surface is
capable of displaying the output from each probe individually
not sampled and use of another scan pattern may not yield the
and of being manually reset. The assembly shall satisfy the
same result.
following requirements:
7. Apparatus
7.1.2.1 Probe-sensing area (probed site) diameter shall be in
the range from 0.062 to 0.225 in. (1.57 to 5.72 mm), inclusive,
7.1 Warp—Measuring Equipment, consisting of movable
7.1.2.2 Displacement resolution of 10 μin. (0.25 μm) or
reference ring, fixed probe assembly with indicator, guide, and
better from a probed site,
surface plate as follows:
7.1.2.3 Displacement range (for each probe) of at least 6
7.1.1 Reference Ring, consisting of a closed base and three
0.010 in. (60.25 mm) about the nominal zero position,
hemispherical support pads; a different size ring is required for
7.1.2.4 Linearity within 0.5 % of the full-scale reading, and
use with each diameter of wafer to be measured (see Fig. 1).
7.1.2.5 For instruments operating in an automatic data-
Each reference ring shall be fabricated of a metal whose
−6
thermal coefficient of expansion shall not exceed 6 3 10 /°F sampling mode during scan, sampling capability of at least 100
data points per second.
at laboratory temperatures; be at least 0.75 in. (or 19 mm)
thick, with the bottom surface lapped flat to within 10 μin.
NOTE 3—The probe-sensing principle may be capacitive, optical, or
(0.25 μm); have an outside diameter approximately 2 in. (or 50
any other noncontacting means suitable for determinating the separation
mm) larger than the diameter of the specimen wafer with which
between probe and silicon surface; noncontacting is specified to prevent
it is intended to be used; and incorporate the following the probe from deflecting the specimen wafer.
features: NOTE 4—The indicator unit may conveniently incorporate ( 1) means
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 657
Dimensions, inches (mm)
Nominal Slice DiameterXY Z
2.000 (50.80) 1.750 (44.45) 2.515 (63.88) 4.00 (101.6)
3.000 (76.20) 2.750 (69.85) 3.525 (89.54) 5.00 (127.0)
3.150 (80.00) 2.900 (73.65) 3.669 (93.20) 5.15 (130.8)
3.543 (90.00) 3.293 (83.65) 4.063 (103.20) 5.54 (140.8)
3.937 (100.00) 3.687 (93.65) 4.457 (113.20) 5.94 (150.8)
4.921 (125.00) 4.671 (118.65) 5.441 (138.20) 6.92 (175.8)
5.906 (150.00) 5.656 (143.65) 6.425 (163.20) 8.00 (203.2)
7.874 (200.00) 7.624 (193.65) 8.394 (213.20) 10.25 (260.4)
FIG. 1 Reference Ring
for calculating and storing sums or differences of paired displacement
to within 40 μin. (1.0 μm).
measurements and for identifying the maximum and minimum values of
7.3 Set-up Thickness Masters, covering a range equal to the
these quantities, (2) means for zero-reading adjustment, and (3) switch-
nominal thickness of the wafer to be tested 60.005 in. (or 125
selectable display of stored calculated values, individual probe measure-
μm), in approximately 0.002-in. (or 50-μm) steps (a total of 6
ments, and the like. The display may be digital or analog (dial); digital
masters). Each master shall have surfaces flat to within 10 μin.
readout is recommended to eliminate interpolative errors on the part of the
(0.25 μm) and a thickness variation no greater than 50 μin.
operator.
(1.25 μm). The thickness of each master shall be known to
7.1.3 Guide—Means for restricting the motion of the refer-
within 50 μin. (1.25 μm). The diameter of each master shall be
ence ring so that the probe mounting axis does not approach
suitable for the ring with which it will be used.
closer to the edge of the specimen slice than 0.267 in. (6.78
mm) except at the parking position. NOTE 6—Silicon wafers satisfying the above requirements may be used
as set-up thickness masters.
NOTE 5—Depending on the design of the apparatus, a matching guide
may be required for each reference ring.
7.4 Precision Metal Flat, of the same nominal diameter as
the wafer to be tested and with one surface flat to 8 μin. (or 0.2μ
7.1.4 Surface Plate, granite, with a working surface at least
m) TIR, maximum. The thickness of the flat shall be such as to
large enough to accommodate the largest ring to be used,
permit the flat to be placed and measured in the specimen
meeting the requirements of Laboratory Grade AA as given in
position (see 9.2).
Federal Specification GGG-P 463C, and with provision for
accommodating the lower probe mount.
8. Sampling
7.2 System Mechanical Parallelism—With the reference
ring in position on the surface plate, the distance between the 8.1 This test method is nondestructive and may be used on
top of each pad and the upper surface of the plate shall be equal either a 100% or a sampling basis.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 657
8.1.1 If samples are to be taken, procedures for selecting the 9.2.2 Measure and record the distance between the bottom
sample from each lot of wafers to be tested shall be agreed probe and the bottom surface of the precision flat as the flat is
upon by the parties to the text, as shall the definition of what scanned in accordance with the pattern shown in Fig. 3.
constitutes a lot. Remove the flat.
9.2
...