semi合集-English.pdf - 第5353页
SEMI M53-1103 © SEMI 2003 4 signal due to haze togethe r comprise the signal due to light scattering from a wafer surface. 5.3.10 latex sphere e quivalent (LSE) — the diameter of a monodispe rse polyst yrene lat ex spher…
SEMI M53-1103 © SEMI 2003 3
4.3 ISO Standards
3
ISO 14644-1 Cleanrooms and associated controlled
environments — Part 1: Classification of airborne
particulates
ISO Guide 30: 1992 Terms and definitions used in
connection with reference materials
NOTICE: Unless otherwise indicated, all documents
cited shall be the latest published versions.
5 Terminology
5.1 Definitions for general terms for silicon technology
are found in SEMI MF1241.
5.2 Additional terminology is defined in SEMI M1.
5.3 Definitions
5.3.1 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.
5.3.2 certified reference material (CRM) — a material
accompanied by a certificate, one or more of whose
property values are certified by a procedure that
establishes its traceability to an accurate realization of
the unit in which the property values are expressed, and
for which each certified value is accompanied by an
uncertainty at a stated level of confidence [ISO Guide
30].
5.3.2.1 Discussion — In the context of this practice, a
CRM is a certified PSL sphere deposition on an
unpatterned wafer with the same surface films and
finish as the wafers to be examined by the calibrated
SSIS. The deposition property values that must be
certified are the peak sphere diameter and the diameter
distribution on the wafer and are determined by both
the PSL sphere source and the deposition process. The
wafer may contain more than one CRM. See Related
Information 1.
5.3.3 coefficient of variation (CV) — one standard
deviation, σ, expressed as a percentage of the mean of a
Gaussian distribution.
5.3.4 deposition — an approximately known number of
PSL spheres of known size distribution placed in a
known location on the surface of a reference wafer.
3 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.
5.3.5 deposition process — the procedure used to place
the PSL spheres on the reference wafer.
5.3.6 dynamic range — of a scanning surface
inspection system, the signal range covered by an
instrument with one set of measurement conditions.
5.3.6.1 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 PSL diameter than can be
measured with a capture rate of at least 95%.
5.3.7 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.
5.3.7.1 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.
5.3.8 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.
5.3.8.1 Discussion — In presenting data for the size
distribution of LLSs, the data set variable is usually the
derived LLS 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.
5.3.9 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.
5.3.9.1 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
SEMI M53-1103 © SEMI 2003 4
signal due to haze together comprise the signal due to
light scattering from a wafer surface.
5.3.10 latex sphere equivalent (LSE) — the diameter of
a monodisperse polystyrene latex sphere that, under
identical test conditions, produces the same detected
scattering intensity as the LLS under investigation.
5.3.10.1 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 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 will not necessarily be the same for each
configuration of the optical system.
5.3.11 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 an isolated point of light.
5.3.11.1 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-channel
amplitude data. Also, the observer cannot deduce the
size, shape, or composition of the LLS from single-
channel amplitude alone. The presence of LLSs does
not necessarily decrease the utility of the wafer.
5.3.12 missing count — the case in which an LLS fails
to produce a laser-light scattering event; also called
false negative.
5.3.13 multipoint calibration — a procedure for
calibrating the size response of an SSIS using a set of
accurately sized polystyrene latex spheres, deposited on
a wafer surface of the type to be inspected by the SSIS.
5.3.13.1 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, regular objects of certain sizes
exhibit non-linearities, usually in the form of a dip, 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. Different
materials may exhibit non-linearities at different sizes.
Because these effects tend to be less pronounced for
irregular particles such as may be found on polished
wafer surfaces, instrument calibration is usually carried
out by avoiding the sizes of spheres that correspond to a
dip. Sometimes, however, it is desired to fully
characterize the response of the SSIS to a particular
type of scatterer; in this case, the calibration can be
carried out with a set of particles with sizes that cover
the desired range with adequate density to ensure that
any non-linearities in the scattering amplitude-size
curve are detected.
5.3.14 nominal sphere size distribution — the stated
diameter distribution of a suspension of PSL spheres of
a certified diameter used in the calibration of SSISs.
5.3.14.1 Discussion — The nominal sphere size
distribution is usually expressed as the standard
deviation or the coefficient of variation of the
distribution about the certified diameter. Depending on
how the deposition is made, the size distribution of the
deposited spheres may be equal to the distribution in
the original suspension or it may be significantly
narrowed by the deposition process.
5.3.15 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.
5.3.15.1 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.
5.3.16 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 PSL sphere depositions have been certified
to specified uncertainties for peak diameter and
diameter distribution.
5.3.17 response curve (RC) — the modeled relation
between measured scattered light intensity (or SSIS
signal response) and PSL sphere peak diameters. The
SEMI M53-1103 © SEMI 2003 5
RC depends on the light source used, is in general non-
linear and may contain regions with dips that make the
response/diameter relationship multi-valued. (See
Section 3.3).
5.3.18 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.
5.3.19 threshold — the level set on a scanning surface
inspection system (SSIS) to discriminate between signal
pulses of different size.
5.3.19.1 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 non-uniformity 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.
5.3.20 true count — a laser-light scattering event that
arises from the localized light scatterers being
investigated.
5.3.21 unimodal distribution — a distribution
represented by a histogram with constant bin size that
has a single bell-shaped peak.
6 Summary of Practice
6.1 The range of LSE values to be used for calibration
is defined for each dark channel that is to be calibrated.
6.2 The number of calibration points required is
defined for each defined range.
6.3 Suitable reference wafers with certified PSL
distributions are obtained.
6.4 The reference wafers are scanned by the SSIS
being calibrated under machine conditions identical
with those to be used in examining wafers with the
calibrated SSIS.
6.5 The peak diameter of the PSL spheres deposited on
each reference wafer is assigned to the peak value of
the SSIS signal units.
6.6 An RC, the curve of SSIS channel response as a
function of SSIS calibration PSL sphere diameter, is
constructed through the data points obtained. A
separate calibration curve is developed for each
channel.
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 generate a data set file of the distribution of
the detected LLSs as a function of reported size (LSE),
7.1.5 Can generate a histogram from the data set file,
or can output the data set file in a form that can be
imported to a spreadsheet or other application program
that can generate the histogram,
7.1.6 Is sufficiently repeatable for the intended
application, and
7.1.7 Handles wafers in a Class 4 or better clean
environment as defined in ISO 14644-1.
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 PSL
spheres. This is particularly important because SSIS
response is affected by the optical properties of the
substrate. Semiconductor wafer surfaces, such as
unpatterned polished, epitaxial, or film layers, have
different optical properties. The wafers must meet the
dimensional requirements of SEMI M1 for the
appropriate nominal wafer diameter and must be laser
marked in a manner agreed upon between supplier and
user.
8.2 Range of Calibration Diameters — Choose the
diameters of the PSL spheres so that the measurement
range for the intended application is covered. Use
spheres of size ranging from the largest measurable size
down to a size with an estimated capture rate less than
50%. Do not exceed the dynamic range of the SSIS
channel being calibrated. Use sufficient sphere
diameters to achieve the required 5% PSL sphere sizing
accuracy of the response curve between calibration
points using a calibration curve that is produced by
fitting the calibration points. In the absence of other
criteria, choose spheres with diameter ratios of
approximately 1.7.
8.2.1 To accomplish the accuracy check (see Section
10.4.2), choose an additional set of PSL spheres of size