Background Statement for SEMI Draft Document 4583B
REVISION OF SEMI M53-0706
PRACTICE FOR CALIBRATING SCANNING SURFACE INSPECTION
SYSTEMS USING CERTIFIED DEPOSITIONS OF MONODISPERSE
REFERENCE SPHERES ON UNPATTERNED SEMICONDUCTOR
WAFER SURFACES
Note: This background statement is not part of the balloted item. It is provided solely to assist the
recipient in reaching an informed decision based on the rationale of the activity that preceded the creation
of this document.
Note: Recipients of this document are invited to submit, with their comments, notification of any relevant
patented technology or copyrighted items of which they are aware and to provide supporting
documentation. In this context, “patented technology” is defined as technology for which a patent has
issued or has been applied for. In the latter case, only publicly available information on the contents of
the patent application is to be provided.
The primary purpose of this ballot is to revise M53 to allow reference particle materials other than
polystyrene latex (PSL) spheres. This change is desired as PSL spheres are damaged by repeated
exposure to short (uv) wavelength scanners. In particular, SiO2 spheres have been tried and appear to
work well with the M53 procedure. This is well documented in a presentation given at SEMICON Japan
2007 and another at the NA Spring Meeting 2008. The latter presentation may be reviewed at
http://teams.semi.org/stds_siawsistf titled “Silica Spheres Presentation 4/7/08”.
A previous version of this document was balloted and discussed at SEMICON Europa 2008. Two
negatives were received from Fritz Passek and Murray Bullis. The negative from Fritz Passek was
centered on how the document had implied the reference spheres diameters had to span the entire
dynamic range of the SSIS. Since there is substantial evidence that demonstrates that the model-based
calibration used can effectively extrapolate beyond the minimum and maximum diameters, the document
was revised, especially in ¶8.2 and ¶9.9, to reflect that extrapolation can occur. Since some SSISs
combine signals from multiple detectors to obtain a particle size, the document was revised by changing
all uses of “channel” with the more precise term “detector channel”. Other small changes were made to
address issues brought up later by Mr. Passek during the editorial process.
Murray Bullis’s negative centered on there being duplication with the terminology document M59, and
that a number of terms were being removed from M53 without being added to M59. Thus, this ballot will
also include the moving of several terms to M59, the removal of some redundant terminology and
abbreviations.
Ballot items:
1. This item is for changes only to M53 as marked in the document. Changes from the published standard
are indicated with underline for material to be added and strikeout for material to be deleted.
2. Move the terms “false count,” “missing count,” “nuisance count,” “threshold,” and “true count”,
currently in M53 to M59.
3. Remove the acronyms LLS, PSL, and SSIS from M53. They are already defined in M59. At the first
use of these acronyms in M53, write the term out, e.g., localized light scatterer (LLS).
4. Remove the terms “laser light scattering event,” “localized light scatterer,” and “scanning surface
inspection system,” from M53, since they are already defined in M59.
5. Move the definition of “Laser-light-scattering event,” currently defined in M53 as “a signal pulse that
exceeds a preset amplitude threshold, generated by the interaction of a laser beam with an LLS at a wafer
surface as sensed by a detector,” to M59, which currently defines it as “a signal pulse that exceeds a
preset threshold, generated by the interaction of a laser beam with a discrete scatterer at a wafer surface as
sensed by a detector; see also haze.”
6. Move the definition of “Localized light scatterer,” currently defined in M53 as “an isolated feature,
such as a particle or a pit, on or in a wafer surface, resulting in increased light scattering intensity relative
to that of the surrounding wafer surface; historically called light point defect because under high intensity
optical illumination features of sufficient size appear as isolated points of light,” to M59, which currently
defines it as “an isolated feature, such as a particle or a pit, on or in a wafer surface, resulting in increased
light-scattering intensity relative to that of the surrounding wafer surface; sometimes called light point
defect.”
7. Move the definition of “latex sphere equivalent” and the acronym LSE from M53 to M59. At the first
use of the acronym LSE in M53, write out the term, i.e., latex sphere equivalent (LSE).
8. Move the definition of “polystyrene latex” from M53 to M59.
This ballot will be reviewed by the Int’l Advanced Surface Inspection Task Force during its
meeting in the week of SEMICON JAPAN, December 3-5, 2008 in Makuhari Messe, Chiba, Japan,
and adjudicated by the Silicon Wafer Committee later that week.
Semiconductor Equipment and Materials International
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DRAFT
SEMI Draft Document 4583B
REVISION OF SEMI M53-0706
PRACTICE FOR CALIBRATING SCANNING SURFACE INSPECTION
SYSTEMS USING CERTIFIED DEPOSITIONS OF MONODISPERSE
REFERENCE SPHERES ON UNPATTERNED SEMICONDUCTOR
WAFER SURFACES
This standard was technically approved by the global Silicon Wafer Committee. This edition was approved
for publication by the global Audits and Reviews Subcommittee on May 16, 2006. It was available at
www.semi.org in June 2006 and on CD-ROM in July 2006. Originally published March 2003; previously
published March 2006.
1 Purpose
1.1 This practice describes calibration of SSIS dark field detector channels so that the SSIS will accurately size
PSL spheres deposited on unpatterned polished, epitaxial, or filmed semiconductor wafer surfaces.
1.2 This practice defines the use of latex sphere equivalent (LSE) signals as a means of reporting real surface
defects whose identity and true size are unknown.
1.3 This practice provides a basis for quantifying SSIS performance as used in related standards concerned with
parameters such as sensitivity, repeatability, and capture rate.
2 Scope
2.1 This practice covers
2.1.1 Requirements for the surface and other characteristics of the semiconductor substrates on which the reference
spheres are deposited to form reference wafers (see ¶ 8.1),
2.1.2 Selection of appropriate certified depositions of reference spheres for SSIS calibration, including size
distribution requirements to be met by the reference sphere depositions, but not the deposition method (see ¶ 8.2),
2.1.3 Generation of calibration curves using model-predicted scatter data that have response curve oscillations and
are thus not monotonic, and
2.1.4 Generation of monotonic calibration curves using model-predicted scatter data.
2.2 Although it was developed primarily for use in calibration of SSISs to be used for detection of localized light
scatterers (LLSs) on polished silicon wafers with geometrical characteristics as specified in SEMI M1, this practice
can be applied to SSISs to be used for detection of LLSs on other unpatterned semiconductor surfaces, provided that
suitable reference wafers are employed.
2.3 This practice does not in any way attempt to define the manner in which LSE values are used to define the true
size of LLSs other than PSL spheres (see ¶ 3.1).
2.4 This practice supports requirements listed in SEMI M52.
2.5 Appendix 1 covers a single-point calibration procedure that may be used in limited production applications but
which does not support requirements listed in SEMI M52.
2.6 Appendix 2 describes a method that may be used to determine the index of refraction of reference spheres that
are not PSL.
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.
3 Limitations
3.1 LLSs are normally assigned only LSE sizes, not physical diameters, because the response of an SSIS to an LLS
depends on the SSIS optical system characteristics as well as the size, shape, orientation and composition of the LLS.
The LSE size assigned to a particular LLS by an SSIS calibrated against PSL spheres may be different from that
assigned to the same LLS by another similarly calibrated SSIS of a different model, because different SSISs have
different optical system characteristics.
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development) activity. All other
reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Document Number: 4583B
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3.2 Reference spheres as sold in bulk may have specified characteristics (mean diameter uncertainty, diameter
distribution, spread between mean and modal diameter) that differ significantly from the characteristics of the
resulting deposition due to the transfer function of the deposition system. For this reason the practice is limited to
the use of reference sphere depositions that are appropriately characterized in accordance with SEMI M58 and
properly certified (see ¶ 8.4).
3.3 The largest reference sphere diameter that can be used in this practice depends on individual SSIS
characteristics, but is often limited to a diameter of about ten times the light source wavelength.
3.4 The smallest reference sphere diameter that can be used in this practice is determined by the sensitivity of the
SSIS under calibration.
NOTE 1: At the time of development of this edition of the practice, the smallest practical deposited reference spheres have
diameters approaching 30 nm, but as IC technology evolves to smaller and smaller critical dimensions, it is expected that
depositions of smaller diameter reference spheres will become available.
3.5 If the monotonic response curve is used and if the dynamic range of the detector channel under calibration
extends into a region where there are response curve oscillations in the non-monotonic response curve, then the PSL
sphere sizing accuracy will be reduced in that region.
3.6 Background Contamination
3.6.1 Both the deposition process and calibration procedures must be carried out in a Class 4 or better environment
as defined in ISO 14644-1.
NOTE 2: ISO class 4 is approximately the same as Class M2.5 (Class 10) as defined in Federal Standard 209E.
3.6.2 The presence of contamination with LSE sizes near that of the nominal reference sphere diameter on the
reference wafer may skew the results. This condition may result in a large error or poor sizing accuracy.
3.6.3 High levels of contamination on the reference wafer or wafers may overload the SSIS or obscure the peak of
the deposited reference sphere diameter distribution. This condition may also result in a large error or poor
equivalent sizing accuracy.
3.6.4 For these reasons, both the deposition process and calibration procedures must be carried out in a clean
environment, and the reference wafers must be handled in such a way as to avoid contamination between deposition
process and calibration.
3.7 If the surface roughness of the reference wafer or wafers is excessive, the peak of the reference sphere diameter
distribution may be obscured or distorted.
3.8 If the SSIS being calibrated is not operating in a stable condition, the calibration may not be appropriate for
subsequent use of the system. System stability can be evaluated by making repeated calibrations, in accordance with
this practice, over suitable time periods.
4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI M1 — Specifications for Polished Monocrystalline Silicon Wafers
SEMI M12 — Specification for Serial Alphanumeric Marking of the Front Surface of Wafers
SEMI M20 — Practice for Establishing a Wafer Coordinate System
SEMI M50 — Test Method for Determining Capture Rate and False Count Rate for Surface Scanning Inspection
Systems by the Overlay Method
SEMI M52 — Guide for Specifying Scanning Surface Inspection Systems for Silicon Wafers for the 130-nm,
90-nm, 65-nm, and 45-nm Technology Generations
SEMI M58 — Test Method for Evaluating DMA Based Particle Deposition Systems and Processes
SEMI M59 — Terminology for Silicon Technology
4.2 Federal Standard1
Fed Std 209E — Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones
1 Standardization Documents Order Desk, Bldg. 4 Section D, 700 Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS (This standard has
been superseded by ISO 14644-1 and may no longer be available.)
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development) activity. All other
reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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4.3 ISO Standard2
ISO 14644-1 Cleanrooms and associated controlled environments — Part 1: Classification of airborne particulates
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Abbreviations and Acronyms
5.1.1 CR — Capture rate
5.1.2 GNF — Gain-nonlinearity function
5.1.3 LLS — Localized light scatterer
5.1.4 LSE — Latex sphere equivalent
5.1.5 MPRC — Monotonic predicted response curve
5.1.6 MRC — Monotonic response curve
5.1.7 PRC — Predicted response curve
5.1.8 PSL — Polystyrene latex
5.1.9 RC — Response curve
5.1.10 SSIS — Scanning surface inspection system
5.2 Definitions of Terms
5.2.1 Definitions for general terms for silicon technology are found in SEMI M59.
5.2.2 Other Definitions
5.2.2.1 calibration diameter error — the deviation between a RC and the certified deposition diameter.
5.2.2.2 capture rate (CR) — the probability that a scanning surface inspection system (SSIS) detects a localized
light scatterer (LLS) of latex sphere equivalent (LSE) signal value at some specified SSIS operational setting.
5.2.2.3 certified deposition — a reference sphere deposition on an unpatterned wafer with the same surface films
and finish as the wafers to be examined by the calibrated SSIS with specific property values certified by a
technically valid procedure, accompanied by or traceable to a certificate that is issued by a certifying body.
5.2.2.3.1 Discussion — The deposition property value that must be certified is the peak sphere diameter., The
diameter distribution on the wafer and the reference sphere material must be specified. The diameter distribution is
determined by the deposition process, and the reference sphere material affects its index of refraction.
5.2.2.4 deposition — an approximately known number of reference spheres of known size distribution placed in a
known location on the surface of a reference wafer.
5.2.2.5 deposition process — the procedure used to place the reference spheres on the reference wafer.
5.2.2.6 dynamic range — of a scanning surface inspection system, the signal range covered by an instrument with
one set of measurement conditions.
5.2.2.6.1 Discussion — The useful dynamic range is limited on the small signal side by the background noise or
the inherent resolution of the instrument and on the large signal side by saturation of the detector and/or the related
electronics. The small signal limit is usually defined as the smallest LSE sphere diameter than can be measured with
a capture rate of at least 95%.
5.2.2.7 false count — a laser-light scattering event that arises from instrumental causes rather than from any feature
on or near (in) the wafer surface; also called false positive; compare nuisance count.
5.2.2.8 Discussion — False counts would not be expected to occur at the same point on the wafer surface during
multiple inspection scans, and hence they could be considered as random “noise” that could be identified by
examining the results of repeated scans.
2 International Organization for Standardization, ISO Central Secretariat, 1, rue de Varembé, Case postale 56, CH-1211 Geneva 20, Switzerland.
Telephone: 41.22.749.01.11; Fax: 41.22.733.34.30 Website: www.iso.ch; also available in the US from American National Standards Institute,
New York Office: 11 West 42nd Street, New York, NY 10036, USA. Telephone: 212.642.4900; Fax: 212.398.0023 Website: www.ansi.org, and
in other countries from ISO member organizations.
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development) activity. All other
reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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5.2.2.9 gain-nonlinearity function (GNF) — the relationship between the actual SSIS response and the modelpredicted SSIS response, given as a function with two or more independent and adjustable parameters.
5.2.2.9.1 Discussion —The GNF should be independent of the reference sphere material, because it is a relationship
between the SSIS detector response and the amount of light predicted to be incident upon the detector.
5.2.2.10 histogram — a representation of a partitioned (binned) data set as a bar graph in which the widths of the
bars are proportional to the sizes of the bins of the data set variable, and the height of each bar is proportional to the
frequency of occurrence of values of the variable within the bin.
5.2.2.10.1 Discussion — In presenting data for the size distribution of LLSs, the data set variable is usually the
derived LSE size; in presenting haze data, the data set variable is usually the haze in ppm. The data set is usually
partitioned into bins of equal size on either a linear or logarithmic scale, as appropriate. The bins at the low and
high ends of the data set variable range are customarily plotted with the same width as the remainder of the
histogram even though they may represent a larger or smaller range of the independent variable than the rest of the
bins.
5.2.2.11 laser-light scattering event — a signal pulse that exceeds a preset amplitude threshold, generated by the
interaction of a laser beam with an LLS at a wafer surface as sensed by a detector.
5.2.2.11.1 Discussion — The amplitude of the signal into a single detector, as measured for any combination of
incident beam direction and collection optics, does not by itself convey topographic information, for example,
whether the LLS is a pit or a particle. It does not allow the observer to deduce the size or origin of the scatterer
without other detailed knowledge, such as its index of refraction and shape. In a scanning surface inspection system,
laser-light scattering events and the background signal due to haze together comprise the signal due to light
scattering from a wafer surface.
5.2.2.12 latex sphere equivalent (LSE) — pertaining to a monodisperse polystyrene latex sphere that, under
identical test conditions, produces the same detected signal as the LLS under investigation.
5.2.2.12.1 Discussion — If the LLS is assumed to be due to a particle (or pit), the LSE size (diameter) of the
particle (or pit) is given in units of length followed by LSE; for example, 0.12 μm, LSE. This unit varies in different
ways for different materials from instrument to instrument because of differences in the optical systems and signal
processing procedures of different instruments. Therefore a particular LLS generally does not have the same LSE
size when measured on different model instruments or on different detector channels of the same instrument. If
elements of the optical system, such as incidence angle, collection solid angle, or polarization, of an SSIS can be
varied, the LSE size of a particular LLS is not necessarily the same for each configuration of the optical system.
5.2.2.13 localized light scatterer (LLS) — an isolated feature, such as a particle or a pit, on or in a wafer surface,
resulting in increased light scattering intensity relative to that of the surrounding wafer surface; historically called
light point defect because under high intensity optical illumination features of sufficient size appear as isolated
points of light.
5.2.2.13.1 Discussion — Localized light scatterers are observed by automated inspection techniques as laser-light
scattering events. Automated inspection techniques are quantitative in the sense that scatterers with different
scattering intensities can be segregated.
However, the amplitude of the scattered light intensity, or
“laser-light scattering event,” as measured by any combination of incident beam direction and collection optics, does
not by itself convey topographical information about the LLS; particles and pits cannot be distinguished solely on
the basis of single-detector-channel amplitude data. Also, the observer cannot deduce the size, shape, or
composition of the LLS from single-detector-channel amplitude alone. The presence of LLSs does not necessarily
decrease the utility of the wafer.
5.2.2.14 missing count — the case in which an LLS fails to produce a laser-light scattering event; also called false
negative.
5.2.2.15 monotonic predicted response curve (MPRC) — a predicted response curve derived from a PRC and
modified to be monotonic. A subscript appended to the MPRC, e.g., MPRCsilica or MPRCPSL, indicates the sphere
material for which the MPRC applies.
5.2.2.15.1 Discussion — The MPRC is identical to the PRCPSL in regions of small diameter and removes the
response curve oscillations in the PRCPSL at larger diameters. The MPRC may, for example, be a running average of
the PRCPSL, a fit to a function which has the appropriate limiting behavior (e.g., ~D6 at small diameter and ~D2 at
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development) activity. All other
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large diameter), or a modeled average response for an ensemble of real-world particles. The MPRC should be
developed by the SSIS manufacturer so that identical SSIS models will have the same MPRC.
5.2.2.16 monotonic response curve (MRC) — the monotonic relation between the actual SSIS signal and sphere
diameter, which differs from the RCPSL by being derived from the MPRC rather than the PRCPSL. . A subscript
appended to the MRC, e.g., MRCsilica or MRCPSL, indicates the sphere material for which the MRC applies.
5.2.2.17 nuisance count — a signal pulse that arises from discrete or area surface or near-surface features other than
the localized light scatterers being investigated; compare false count.
5.2.2.17.1 Discussion — The presence of nuisance counts is dependent on the threshold and gain settings and may
be a function of the optical configuration of the SSIS, the orientation of the wafer surface, or both.
5.2.2.18 polystyrene latex (PSL) — a colloidal aqueous solution of polystyrene microspheres from which certified
depositions can be made.
5.2.2.19 predicted response curve (PRC) — the model-predicted relation between scattered light intensity (or SSIS
signal response) and sphere diameter that is used to analyze scanner response near various sphere diameters. The
PRC depends upon sphere material and scanner design and is in general non-linear. It may contain regions with
response curve oscillations that make the response-diameter relationship multi-valued. A subscript appended to the
PRC, e.g., PRCsilica or PRCPSL, indicates the sphere material for which the PRC is calculated.
5.2.2.20 LSE sphere sizing uncertainty — an estimate of the relative uncertainty in the diameter reported by an
SSIS for a PSL sphere having any diameter in the calibration range, determined by combining contributions from
the calibration diameter errors and the certified deposition uncertainty.
5.2.2.21 reference wafer — for calibrating an SSIS in accordance with this practice, an unpatterned wafer with the
same surface films and finish as the wafers to be examined by the calibrated SSIS and upon which one or more
reference sphere depositions have a specified material and diameter distribution and have been certified to specified
uncertainties for peak diameter.
5.2.2.22 reference spheres — spherical particles having known diameter, diameter distribution, and index of
refraction.
5.2.2.22.1 Discussion — The index of refraction of the reference spheres may not be the same as that of the bulk
material. In the case of PSL spheres, it is safe to assume that the index of refraction is that of bulk polystyrene,
given by
n  A
B

C
(1)

4
where A = 1.5663, B = 0.00785 µm2, and C = 0.000334 µm4. A method suitable for determining the index of
refraction of non-PSL spheres is described in Appendix 2.
5.2.2.23 response curve (RC) — the relation between actual SSIS signal and sphere diameter. A subscript
appended to the RC, e.g., RCsilica or RCPSL, indicates the sphere material for which the RC applies.
5.2.2.23.1 Discussion — The RC depends on scanner design and is in general non-linear. It may contain regions
with response curve oscillations that make the response-diameter relationship multi-valued.
5.2.2.24 response curve oscillations — peaks and valleys in the response curve, which prevent the response curve
from being monotonic.
5.2.2.24.1 Discussion — The purpose of a calibration is to relate the amount of light captured by an SSIS to the
physical size of the light scatterer. The amount of light scattered from a localized light scatterer (LLS) that is
captured by the SSIS is a function of both the scattering characteristics of the LLS (including the directional
dependence of the scattering) and the geometry of the collection optics of the SSIS. For a given wavelength of
incident radiation and SSIS geometry, regular objects of certain sizes exhibit non-linearities, in the form of response
curve oscillations, so that the curve of scattering amplitude as a function of physical size of the scatterer may not be
monotonic. Thus, similar objects with modest variations in physical size can scatter the same amount of light into a
given detector. Different materials may exhibit response curve oscillations at different sizes. Response curve
oscillations occur for PSL sphere diameters greater than about half of the wavelength.
5.2.2.25 scanning surface inspection system (SSIS) — an instrument for rapid examination of the entire quality area
of a wafer to detect the presence of localized light scatterers or haze or both; also called particle counter and laser
surface scanner.
2
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development) activity. All other
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5.2.2.26 threshold — the level set on a scanning surface inspection system (SSIS) to discriminate between signal
pulses of different size.
5.2.2.26.1 Discussion — Thresholds may be set to discriminate between true counts and surface or electrical noise
(nuisance or false counts, respectively) or between different sizes of light scatterers. Because of spatial nonuniformity of the intensity of the scanning beam and the general use of overlapping scans in an SSIS, a localized
light scatterer with equivalent size near the threshold may generate a signal greater than or less than the threshold
depending on its location with respect to the path of the scanning beam. The former is identified as a true count and
the latter is identified as a missing count.
5.2.2.27 true count — a laser-light scattering event that arises from the localized light scatterers being investigated.
5.2.2.28 unimodal distribution — a distribution represented by a histogram with constant bin size that has a single
peak.
6 Summary of Practice
6.1 The SSIS being calibrated is set up with machine conditions identical with those to be used in examining
wafers.
6.2 Reference wafers with appropriate certified depositions are scanned by the SSIS.
6.3 The peak of the reference sphere diameter distribution deposited on each reference wafer is assigned to the
peak value of the SSIS signal units.
6.4 A predicted response curve is determined for each reference sphere material and for PSL using its index of
refraction and the appropriate parameters for the measurement conditions.
6.5 The actual SSIS signals and the predicted responses are used to determine the gain-nonlinearity function (GNF).
6.6 The PRCPSL and the GNF are used to determine the response curve for PSL (RCPSL), which may have response
curve oscillations.
6.6.1 Discussion — If PSL spheres were used as reference spheres, a graph of the RCPSL will lie very close to, but
may not exactly match, a graph of the recorded signal versus reference sphere diameter. If another sphere material
were used, a graph of the RCPSL will not match a graph of recorded signal versus reference sphere diameter. That is,
an SSIS calibrated to assign LSE diameters to LLSs will not correctly size non-PSL reference spheres.
6.7 The expanded PSL sphere sizing uncertainty is determined and compared to the requirements of SEMI M52.
6.8 A monotonic predicted response curve (MPRCPSL) may be generated from the PRCPSL to remove response curve
oscillations.
6.9 The MPRCPSL and the GNF may be used to determine the monotonic response curve (MRC PSL), which does not
have response curve oscillations.
6.10 A separate RCPSL and MRCPSL are developed for each detector channel.
6.11 Either the RCPSL or the MRCPSL is used to determine and report the LSE diameter.
7 Apparatus
7.1 Scanning Surface Inspection System — Designed to detect, size, and map localized light scatterers (LLSs) on
unpatterned semiconductor wafers, that has the following capabilities:
7.1.1 Scans the entire fixed quality area of the surface of a wafer with a laser beam,
7.1.2 Detects localized light scatterers as laser-light scattering events,
7.1.3 Has a user definable sensitivity threshold,
7.1.4 Can create a histogram of SSIS signals (i.e., number of laser light scattering events as a function of raw SSIS
signal) for any given region on the wafer,
7.1.5 Can either evaluate the histogram peak or output a data set file that can be imported to a spreadsheet or other
application program that can be used to generate the histogram peak,
7.1.6 Can either accept a user-provided calibration curve for each detector channel or can automatically perform the
steps given in § 9 below,
7.1.7 Is sufficiently repeatable for the intended application, and
7.1.8 Handles wafers in a Class 4 or better clean environment as defined in ISO 14644-1.
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
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8 Reference Wafers
8.1 Substrates — Use bare semiconductor wafers with a native oxide (or other filmed) surface of the type intended
to be tested with the SSIS to be calibrated as substrates for the certified depositions of the reference spheres. This is
particularly important because SSIS response is affected by the optical properties of the substrate. Bare silicon
wafer surfaces have different optical properties than wafers with film layers or wafers of different material. The
wafers must meet the dimensional requirements of SEMI M1 for the appropriate nominal wafer diameter. Wafers
nominally 200 mm in diameter and smaller shall be laser marked in accordance with SEMI M12, and wafers
nominally 300 mm in diameter shall be laser marked in accordance with ¶¶ 6.5.1.4–6.5.1.4.9 of SEMI M1, including
the optional alphanumeric mark described in ¶ 6.5.1.4.1 of SEMI M1.
8.2 Range and Number of Calibration Diameters — Choose the diameters of the reference spheres for the certified
depositions so that the measurement range for the intended application is significantly covered. Use spheres of size
ranging from less than the largest measurable size down to a size greater than that with an estimated capture rate of
95% and spaced approximately evenly on a logarithmic scale. The minimum and maximum sphere sizes do not
need to be at the extremes of the required calibration range, since this practice allows for extrapolation. Do not
exceed the dynamic range of the SSIS detector channel being calibrated. The number of certified depositions should
be at least 4 more than the number of adjustable parameters used for the GNF. A reference wafer may contain one
or more certified depositions.
NOTE 3: Best results are typically achieved when using the number, the sizes of reference spheres, and the extent of allowable
extrapolation recommended by the SSIS manufacturer.
8.3 Background Contamination
8.3.1 Handle and store reference wafers with great care to avoid contamination and damage.
8.3.2 Establish that the unimodal peaks in the SSIS LLS histogram generated from the reference sphere depositions
are well defined and well above the background level over all the response curve except near the threshold. Also
verify that each unimodal curve extends to less than 50% of its peak value on both sides of the peak within a
diameter range of ±2.5% of the reference sphere diameter at the peak of the distribution. Do not use depositions that
fail either of these criteria.
8.4 Data to Accompany Reference Wafers — The following information must accompany each reference wafer.
8.4.1 For each certified deposition on a reference wafer provide:
8.4.2 The deposition peak diameter and the uncertainty in accordance with the requirements of Row 4.3 of Table 3
of SEMI M52.
8.4.3 The maximum possible value of the deposition diameter distribution full width at half maximum (FWHM)
expressed as a percentage of peak diameter.
8.4.4 The approximate particle count of each certified deposition.
8.4.5 The approximate location of each certified deposition on the reference wafer by the x- and y-coordinates (as
specified in SEMI M20) of the center of the deposition area or by a map or drawing of the wafer.
8.4.6 Identification of the deposition system used for the deposition by model and serial number.
8.4.7 The date of production.
8.4.8 Wafer identification.
8.4.9 Name and address of the reference wafer manufacturer.
8.4.10 Identification of the deposited reference spheres by material, supplier, lot number and model.
9 Procedure
9.1 Obtain the required number of suitable reference wafers with certified depositions (see ¶ 8.2) to cover each
established range.
9.2 Set up the SSIS in accordance with the manufacturer’s instructions for the wafer diameter, sizes of reference
spheres, and other machine conditions to be used during the calibration procedure. Ensure that machine conditions
are identical with those to be used in examining wafers with the calibrated SSIS.
9.3 Ensure that the SSIS is operating properly for the selected machine conditions.
9.4 Load the first reference wafer into the SSIS.
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9.5 Scan the wafer.
9.6 Generate a data set file of the distribution of localized light scatterers as a function of reported SSIS signal.
9.7 Repeat ¶¶ 9.2–9.6 for each of the remaining certified depositions.
9.8 Determine the peak SSIS signal for each of the certified depositions used for the calibration.
9.9 For each reference sphere material and for PSL, create a PRC using the SSIS detector channel geometry, source
wavelength, source polarization and appropriate material constants over the range from less than the minimum
certified deposition diameter to greater than the maximum certified deposition diameter with a recommended
diameter spacing ofapproximately the illumination wavelength divided by 50 in order to accurately predict RC
oscillations. Calculate the PRC using the Bobbert-Vlieger model provided in the Modeled Integrated Scatter Tool
(MIST) program.3 Alternatively, use another program suggested by the instrument manufacturer, provided that it
can be shown to have as good or better results. Record the PRC values for each certified deposition by interpolating
the PRC for the reference sphere material at its certified diameter.
9.10 Obtain the GNF by adjusting the independent parameters for a best fit to the SSIS signals found in ¶ 9.8
versus the corresponding PRC values obtained in ¶ 9.9 . Typically the curve is a smooth straight line on a log-log
graph, so use the following form
GNF =  (predicted response) 

This function has two adjustable parameters ( and ). Alternatively, use another function form, provided that the
number of adjustable parameters is small, it is monotonic, and it describes a typical non-linearity for the type of
detector used.
9.11 Create an RC for each reference sphere material by applying the GNF determined in ¶ 9.10 to the PRC for that
material. Graph the RCs (as curves) and the peak SSIS signals determined in ¶ 9.8 (as points) against diameter on a
log-log scale.
9.12 Determine the calibration diameter error between the points and the curve for the corresponding reference
sphere material shown in the graph created in ¶ 9.11.
9.13 If a monotonic response is to be used for large particles, create the MPRCPSL from the PRCPSL using the
method specified by the SSIS manufacturer. If a non-monotonic response is to be used for large particles, go to ¶
9.16 .
9.14 Create an MRCPSL by applying the GNF determined in ¶ 9.14 to the MPRCPSL.
9.15 Determine the expanded PSL sphere sizing uncertainty by
U PSL  2  1   2 / N  M ,
2
2
(4)
where 1 is the relative standard uncertainty in the peak reference sphere diameters for the certified depositions, 2
is the standard deviation of the relative calibration diameter error (determined in ¶ 9.12 ), N is the number of
certified depositions, and M is the number of independent parameters in the GNF. SEMI M52 requires that 1 be
less than 1.5%; in the absence of specific values for 1, the maximum value accepted by SEMI M52 can be used.
9.16 Repeat the procedure of ¶¶ 9.2 –9.14 for all of the SSIS detector channels being calibrated.
9.17 Related Information 1 presents an example of this procedure based on one detector channel of a commercially
available SSIS.
10 Interpretation of Results
10.1 The expanded reference sphere sizing uncertainty found for each detector channel in ¶ 9.15 should be less than
2% in order to meet the requirements of SEMI M52.
10.2 If the decision has been made to allow the response to be non-monotonic for large particles, then use the RCPSL
to establish the LSE size of LLSs.
10.3 If the decision has been made to use the monotonic response for large particles, then use the MRC PSL to
establish the LSE size of LLSs.
3
This program can be downloaded without charge from the website of the National Institute of Standards and Technology:
http://physics.nist.gov/scatmech
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
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DRAFT
11 Report
11.1 Report the following information:
11.1.1 Operator identification;
11.1.2 Date and location of measurement;
11.1.3 Manufacturer, model, serial number, and software version of the SSIS;
11.1.4 Reference wafer characteristics as outlined in the certificates accompanying the reference wafers (see ¶ 8.4);
11.1.5 Histogram for each data set and the assigned peak value of the distribution of reported diameters together
with the certified peak diameter of the PSL sphere distributions used to generate the histogram; and
11.1.6 The GNF, the RCPSL, and the associated certified reference sphere diameters. If a monotonic response is to
be used for large particles, also report the MRCPSL.
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
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DRAFT
APPENDIX 1
SINGLE-POINT CALIBRATION
NOTICE: The material in this appendix is an official part of SEMI M53 and was approved by full letter ballot
procedures on November 29, 2005.
A1-1.1 Choose a single reference wafer with PSL sphere deposition CRM size near the LSE size of the smallest
LLS to be tested for in meeting a wafer specification.
NOTE 1: Because of possible non-linearities in the SSIS, single-point calibration is not recommended except in the immediate
vicinity of a single sphere size of interest, for example, the smallest size to be tested for in meeting a wafer specification.
A1-1.2 Set up the SSIS to be calibrated in accordance with ¶ 9.2 and ¶ 9.3.
A1-1.3 Load the appropriate reference wafer into the SSIS.
A1-1.4 Scan the wafer.
A1-1.5 Generate a data set file of the distribution of localized light scatterers as a function of reported size (LSE).
A1-1.6 Construct a histogram for the distribution in the data set file.
A1-1.7 Determine the standard deviation and peak diameter value from curve fits of the histogram.
A1-1.8 Associate the peak value of reported size (LSE) found to the certified value of PSL sphere diameter
deposited on the reference wafer.
A1-1.9 The procedure outlined in this appendix does not support the requirements of SEMI M52.
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
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DRAFT
APPENDIX 2
REFERENCE SPHERE INDEX DETERMINATION
A2-1.1 This appendix describes a method for determining the index of refraction of non-PSL reference spheres. It
requires an SSIS, but it does not require that the SSIS be of the same design as that for which the reference spheres
will be used to calibrate.
A2-1.2 Obtain two sets of reference wafers with certified depositions (see ¶ 8.2), one with PSL spheres and the other
with reference spheres of unknown index (the “unknown reference spheres”).
A2-1.3 Follow ¶¶ 9.1–9.10 using the PSL spheres. For the index of refraction of the PSL spheres, use
n  A
B

C
(A2-1)

4
where A = 1.5663, B = 0.00785 µm2, and C = 0.000334 µm4. Report the GNF.
A2-1.4 Repeat the measurement steps (¶¶ 9.2–9.6) for the unknown reference spheres, to obtain the signal Si for
each unknown reference sphere i.
A2-1.5 Estimate the anticipated minimum and maximum possible indices for the unknown reference spheres.
A2-1.6 For each index n ranging from the minimum to the maximum with a small step n, create a PRCn as per
¶ 9.9. Record the PRCn values for each unknown reference sphere i and for each index n, PRCni.
A2-1.7 For each index n and each unknown reference sphere i, calculate the GNF error from
(A2-2)
Eni  GNF(PRCni )  Si
2
A2-1.8 For each index n, calculate the sum of squares GNF error from
Fn   Eni
2
(A2-3)
i
A2-1.9 Plot Fn versus n. If there is no minimum, go back to ¶ 1.4, starting over with a new range of possible indices.
A2-1.10 Find the best value of n by fitting the data close to the minimum to a parabola and finding the minimum.
Use the best value of n for the index of the reference spheres at the operating wavelength of the SSIS.
A2-1.11 Follow steps ¶ 9.9–9.17 of the standard using the data from the reference spheres instead of the PSL
spheres and report the calibration diameter errors and the GNF.
A2-1.12 If the index of refraction, nbulk, for the bulk form of the material is known at the operating wavelength of the
SSIS, then an effective medium void fraction may be estimated from
(nbulk  n)(nbulk  n)(2nbulk  1)
2
x
(nbulk  1)(2nbulk  n 2 )
2
2
(A2-4)
A2-1.13 If both the effective medium void fraction and the wavelength dependence nbulk() of the index of refraction
of the bulk material are known, then the index of refraction of the reference spheres at other wavelengths  can be
estimated from
n( )  nbulk ( )
1  2[nbulk ( )]2 ( x  1)  2 x
1  x  [nbulk ( )]2 ( x  2)
(A2-5)
.
This is a draft document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted standard. Permission is granted to
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DRAFT
RELATED INFORMATION 1
EXAMPLE OF MULTI-POINT CALIBRATION WITH FIT TO MODELPREDICTED DATA
NOTICE: This related information is not an official part of SEMI M53 and was derived from the Automated Wafer
Surface Inspection Task Force. This related information was approved for publication by full letter ballot on
November 29, 2005.
R1-1 This related information provides an example of the procedure described in § 9. In all of this related
information, the reference spheres were PSL; subscripts on PRC, RC, MPRC, and MRC have been omitted and are
assumed to be PSL.
R1-2 Data were obtained on one detector channel of a commercially available SSIS. Column 1 of Table R1-1 lists
the certified diameters that were used in the calibration procedure. Column 2 of the table lists the measured peak
signals for each of the certified diameters. These signals have been multiplied by an unknown and arbitrary constant.
The peak signals range from Smin = 0.1254 to Smax = 373.2.
R1-3 The predicted response curve (PRC) was calculated using the Modeled Integrated Scatter Tool (MIST)
program.3 The parameters used for the model are given in Table R1-2. The PRC is shown in Figure R1-1. The
model-predicted response for each certified diameter is given in the third column of Table R1-1.
R1-4 Figure R1-2 shows a graph of the measured response values (second column of Table R1-1) versus the modelpredicted response values (third column of Table R1-1). On a log-log scale, it appears to be a straight line, so that
the GNF is chosen to be
GNF =  (predicted response)
(R1-1)
A best fit to the data yields the two adjustable parameters  = 1.18104 and  = 1.046. The best fit curve is also
shown in Figure R1-2.
R1-5 The RC was developed by applying the function of Equation R1-1 to the signal values of the PRC. The RC is
shown in Figure R1-3. The signals for the certified depositions are shown as points.
R1-6 The calibration diameter error is shown in the fourth column in Table R1-1. These deviations represent the
estimated errors in the measured diameters. The maximum value of this deviation is 1.5% and the standard
deviation is 0.6%. Since there are 14 calibration points and 2 degrees of freedom to the GNF, the expanded PSL
sphere sizing uncertainty is
U PSL  2 (1.5%) 2  (0.6%) 2 / 14  2  0.9% .
(R1-2)
Since this value is below 2%, the calibration meets the requirements of SEMI M52.
R1-7 An MPRC was generated from the PRC by the following procedure: (a) The PRC was re-evaluated with
diameters spaced by 2% over the range 30 nm to 1 µm. (b) For each diameter on the re-evaluated PRC, a straight
line was fit (on a log-log graph) to points having diameters within 25% of the given diameter. (c) The MPRC at each
diameter was then given by evaluating the straight line at that diameter. The MPRC is shown with the PRC in
Figure R1-1. In order to demonstrate the procedure, the method for creating an MPRC was adopted in lieu of one
provided by the manufacturer, and the range of particle sizes was extended.
R1-8 The MRC generated by applying the GNF to the MPRC is shown in Figure R1-3 with the RC. This MRC can
be used to size particles throughout the diameter range shown, since it is monotonic.
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DRAFT
Table R1-1 Example of Data for Calibration Procedure
Certified Diameter (nm)
Measured Response (arb. units) Predicted Response (arb. units)
Calibration Diameter Error
0.1254
1.746105
0.2%
75.1
0.4305
5.593105
0.4%
85.9
0.9855
1.225104
0.6%
86.4
0.9855
1.267104
0.0%
100.1
2.333
2.937104
0.3%
100.7
2.385
3.036104
0.5%
105.3
3.104
3.894104
0.5%
126.6
8.553
1.038103
0.8%
153.5
23.37
2.583103
0.2%
158.0
25.87
2.922103
0.4%
185.1
50.42
5.344103
0.6%
204.0
69.27
7.244103
0.6%
292.7
199.3
1.959102
0.8%
373.2
3.750102
1.1%
61.7
363.5
Table R1-2 Parameters Used in MIST
Parameter
Value
Model
Bobbert_Vlieger_BRDF_Model
Wavelength
488 nm
Refractive index of substrate
4.368+0.040i
Refractive index of substrate oxide
1.7387
Refractive index of PSL sphere
1.605
Thickness of substrate oxide:
1.6 nm
Incident angle
70°
Incident polarization
p (electric field in plane of incidence)
Collection geometry
All polar angles between 25° and 70°.
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0
10
Predicted Response (arb. units)
-1
10
-2
10
-3
10
-4
10
-5
10
Predicted Response Curve
Monotonic Predicted Response Curve
-6
10
600
700
800
900
1000
500
400
300
200
60
70
80
90
100
50
40
30
-7
10
PSL Sphere Diameter (nm)
Figure R1-1
Predicted Response Curve (PRC) Calculated from MIST and the Monotonic Predicted Response Curve
(MPRC)
Measured Response (arb. units)
1000
100
10
1
Measurement
Gain-Nonlinearity Function
0.1
-5
10
-4
10
-3
10
-2
10
-1
10
Predicted Response (arb. units)
Figure R1-2
Measured Response Values as a Function of Model-Predicted Response Values (points) and the GainNonlinearity Function (line)
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4
10
3
Response Curve (arb. units)
10
2
10
1
10
0
10
-1
10
Measurement
Response Curve
Monotonic Response Curve
-2
10
600
500
400
300
200
70
80
90
100
60
50
40
30
-3
10
Certified PSL Sphere Diameter (nm)
Figure R1-3
Response Curve (RC) and the Monotonic Response Curve (MRC)
NOTICE: SEMI makes no warranties or representations as to the suitability of the standard(s) set forth herein for
any particular application. The determination of the suitability of the standard(s) is solely the responsibility of the
user. Users are cautioned to refer to manufacturer’s instructions, product labels, product data sheets, and other
relevant literature respecting any materials or equipment mentioned herein. These standards are subject to change
without notice.
By publication of this standard, Semiconductor Equipment and Materials International (SEMI) takes no position
respecting the validity of any patent rights or copyrights asserted in connection with any item mentioned in this
standard. Users of this standard are expressly advised that determination of any such patent rights or copyrights, and
the risk of infringement of such rights are entirely their own responsibility.
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