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Table 1 Acronyms for Wafer F latness Parameters Reference Plane Acronym Measurement Method Reference Surface Construction Area Measurement Parameter GBIR Global Back Ideal back surface Entire FQA Range (TIR) GF3R Global …

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5 Terminology
5.1 Acronyms related to wafer flatness parameters as
defined in SEMI M1, Appendix 1, Flatness Decision
Tree, are summarized in Table 1.
NOTE 1: The most commonly specified flatness measure-
ments for advanced IC production in 2004, the time of the last
revision of this standard, are SFQR with a site size of either
26 mm by 8 mm or 25 mm by 8 mm and GBIR (TTV).
5.2 Definitions related to wafer flatness can be found
in SEMI M1.
5.3 Definitions of other terms related to silicon
material technology can be found in SEMI MF1241.
6 Summary of Test Method
6.1 A calibration procedure is performed. This sets the
instrument's scale factor and other constants.
6.2 The wafer is supported by a small-area chuck and
is scanned along a prescribed pattern by both members
of an opposed pair of probes.
6.3 The paired displacement values are used to
construct a thickness data array (t[x,y]). This array
represents the front surface of the wafer when the back
surface of the wafer is ideally flat, as when pulled down
onto and ideally clean, flat chuck.
6.4 The data array is used to produce one or more of
the parameters required by the application.
6.4.1 If flatness measurements are required, a reference
plane and a focal plane suitable to the application are
constructed on the back or front surface.
6.5 Thickness or flatness, or both, values are calculated
and reported, as required.
7 Apparatus
7.1 Measuring Equipment — consisting of wafer-
holding device, multiple-axis transport mechanism,
probe assembly with indicator, and system controller/
computer, including data processor and suitable
software.
7.1.1 The measuring equipment shall have means to
input the choices listed in the Procedure (see Section 12
).
7.1.2 The measuring equipment shall be direct reading
with all necessary calculations performed internally and
automatically as outlined in Section 13 .
7.1.3 The system shall be equipped with an overrange
signal.
7.1.4 Instrument data reporting resolution shall be 10
nm or smaller.
7.1.5 The measuring equipment contains the following
subsystems:
7.1.5.1 Wafer-holding device, for example a chuck
whose face is perpendicular to the measurement axis,
and on which the wafer is placed for the measurement
scan. The nature and size of the wafer holding device
shall be agreed upon between the parties to the test.
7.1.5.2 Multiple-axis transport mechanism, which
provides a means for moving the wafer-holding device,
or the probe assembly, perpendicularly to the
measurement axis in a controlled fashion in several
directions. This motion must permit data gathering
over a prescribed scan pattern within the entire fixed
quality area. Data point spacing to be used shall be
agreed upon between the parties to the test.
7.1.5.3 Probe assembly with paired noncontacting
displacement-sensing probes, probe supports, and
indicator unit (see Figure 1).
t
a
b
D
Probe A
Probe B
Wafer
Fixture
t
a
b
D
Probe A
Probe B
Wafer
Fixture
Figure 1
Schematic View of Wafer, Probes, and Fixture
7.1.5.3.1 The probes shall be capable of independent
measurement of the distances a and b between the
probed site on each surface of the sample wafer and the
nearest probe surface.
7.1.5.3.2 The probes shall be mounted above and
below the wafer in a manner so that the probed site on
one surface of the wafer is opposite the probed site on
the other.
7.1.5.3.3 The common axis of these probes is the
measurement axis.
7.1.5.3.4 The probe separation D shall be kept constant
during calibration and measurement.
7.1.5.3.5 Displacement resolution shall be 10 nm or
better.
7.1.5.3.6 The probe sensor size shall be 4 × 4 mm, or
other value to be agreed upon between the parties to the
test.
SEMI MF1530-1104 © SEMI 2003, 2004 2
Table 1 Acronyms for Wafer Flatness Parameters
Reference Plane
Acronym
Measurement
Method
Reference Surface
Construction Area
Measurement
Parameter
GBIR Global Back Ideal back surface Entire FQA Range (TIR)
GF3R Global Front Three-point Range (TIR)
GF3D Global Front Three-point Deviation (FPD)
GFLR Global Front Least squares Entire FQA Range (TIR)
GFLD Global Front Least squares Entire FQA Deviation (FPD)
SBIR Site Back Ideal back surface Entire FQA Range (TIR)
SBID Site Back Ideal back surface Entire FQA Deviation (FPD)
SF3R Site Front Three-point Range (TIR)
SF3D Site Front Three-point Deviation (FPD)
SFLR Site Front Least squares Entire FQA Range (TIR)
SFLD Site Front Least squares Entire FQA Deviation (FPD)
SFQR Site Front Least squares Site Range (TIR)
SFQD Site Front Least squares Site Deviation (FPD)
SFSR Site Front Least squares Sub-site Range (TIR)
SFSD Site Front Least squares Sub-site Deviation (FPD)
8 Materials
8.1 Set-up Masters — suitable to accomplish
calibration and standardization as recommended by the
equipment manufacturer.
8.2 Reference Wafer — with total thickness variation
(TTV) value and flatness value similar to the product or
process to be monitored and with a data set that is used
to determine the level of agreement between the data
set obtained by the measuring equipment under test and
the reference wafer data set (see Section 9 ).
9 Suitability of Measuring Equipment
9.1 Determine the suitability of the measuring
equipment with the use of a reference wafer and its
associated data set in accordance with the procedures of
Sub-section 9.2 , or by performance of a statistically-
based instrument repeatability study to ascertain
whether the equipment is operating within the
manufacturer's stated specification for repeatability.
9.1.1 The reference wafer data set is a set of thickness
or flatness parameters based on corrected data in that all
possible interferences have been removed and the data
has been replanarized in accordance with this method.
9.1.2 Each reference wafer (artifact) is accompanied by
its own data set, the reference data set (RDS), in which
each parameter value is the average of a number of
values obtained for that parameter over a number of
“passes” (repeat measurements). The artifact is
measured on a measurement equipment under test and
its RDS is compared against the resultant-measured
sample data set. Delta-parameter and other values are
computed from the differences. The parameter used to
determine agreement between the artifact and the
measuring equipment under test and the acceptable
level of this agreement is to be agreed upon between the
parties to the test.
9.2 Procedure
9.2.1 Select a reference wafer of appropriate criteria
together with its associated reference data set (RDS).
9.2.2 Measure the reference wafer on the measurement
equipment under test to obtain a sample data set (SDS).
9.2.3 Subtract the two data sets on a parameter basis to
obtain a difference data set (DDS):
DDSSDSRDS
(1)
9.2.3.1 The DDS represents the differences between
the measurements made on the measuring equipment
under test and the reference data set. The DDS contains
many values.
9.2.4 The simplest metric that can be used to determine
acceptability is maximum difference, the largest
absolute value in the DDS. This represents the worst-
case disagreement between the results obtained from
the measurement equipment under test and the
reference data. Accept the measurement equipment as
suitable for measurement if the maximum difference is
less than a value that is agreed upon between the parties
to the test.
SEMI MF1530-1104 © SEMI 2003, 2004 3
9.2.5 More complex calculations may also be used to
determine acceptability. For example, a histogram of
the parameter values of the DDS along with statistical
measures (mean, sample standard deviation, etc.) may
be used. These measures may be compared to
application-specific limits or used to provide insight
into the nature and source of the difference, or both, as
arranged by agreement of the parties to the test.
10 Sampling
10.1 This test method is nondestructive and may be
used on either 100% of the wafers in a lot or on a
sampling basis.
10.1.1 If samples are to be taken, procedures for
selecting the sample from each lot of wafers to be tested
shall be agreed upon between the parties to the test, as
shall the definition of what constitutes a lot.
11 Calibration and Standardization
11.1 Calibrate the measuring equipment in accordance
with the manufacturer's instructions.
12 Procedure
12.1 Prepare the apparatus for measurement of wafers,
including selection of data display/output functions.
12.2 Select the fixed quality area (FQA) by specifying
the nominal edge exclusion EE.
12.3 Select the flatness parameter(s) to be determined
as follows:
12.3.1 Select the measurement method — global
flatness (G) or site flatness (S):
12.3.1.1 If S is chosen, then also specify site array
details:
12.3.1.1.1 site size,
12.3.1.1.2 location of sites relative to FQA center,
12.3.1.1.3 location of sites relative to each other,
rectilinear or tiled pattern, and
12.3.1.1.4 partial sites, included or excluded.
12.3.2 Select the reference surface — front (F) or back
(B).
12.3.3 Select the reference plane construction and area
as follows:
12.3.3.1 For global flatness measurements, select one
of the following global reference planes using all points
within the FQA to construct the reference plane:
12.3.3.1.1 Ideal back surface plane (I),
12.3.3.1.2 Three-point front surface plane (3), or
12.3.3.1.3 Least-squares front surface plane (L).
12.3.3.2 For site flatness measurements with a global
reference plane, select one of the following global
reference planes using all points within the FQA to
construct the reference plane:
12.3.3.2.1 Ideal back surface plane (I),
12.3.3.2.2
Three-point front surface plane (3), or
12.3.3.2.3 Least-squares front surface plane(L).
12.3.3.3 For site flatness measurements with a site
reference plane, select the following reference plane
using all points within the site that lie within the FQA
to construct the reference plane:
12.3.3.3.1 Site least-squares front surface plane (Q).
12.3.3.4 For scanner site flatness measurements with a
sub-site reference plane, select the following reference
plane using all points within the sub-site that lie within
the FQA to construct the reference plane:
12.3.3.4.1 Sub-site least squares front surface plane
(S).
12.3.4 Select the measurement parameter:
12.3.4.1 Global Flatness:
12.3.4.1.1 Range (Total indicator reading, TIR) (R), or
12.3.4.1.2 Deviation (Focal plane deviation, FPD) (D).
12.3.4.2 Site Flatness:
12.3.4.2.1 Range (TIR) — each site or maximum value
for all sites, or both, or
12.3.4.2.2 Deviation (FPD) — each site or maximum
value for all sites, or both, or
12.3.4.2.3 A map or histogram showing the
distribution of either or both of these values.
12.4 Introduce the test specimen into the measurement
mechanism and initiate the measurement sequence.
12.5 Use the resulting data set, whose elements are the
thicknesses [t(x,y)] as the basis to make thickness and
flatness calculations.
13 Calculations
13.1 The calculations of wafer thickness, total
thickness variation and the desired flatness parameter(s)
are performed automatically within the instrument. An
outline of the calculation structures is provided here to
indicate the nature of the procedure.
13.2 Thickness Determination
13.2.1 Determine the displacements (distances)
between each probe and the nearest surface of the wafer
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