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SEMI E141-0705 © SEMI 2005 3 5.1.11 measuring i nstrument — devi ce intended to be used to m ake measurements, alone or in conjunction with supplement ary device(s) 1 . 5.1.12 measuring syst em — complet e set of measuri…
SEMI E141-0705 © SEMI 2005 2
3.2 The standard is limited to the measurement of isotropic samples. It is limited to the application of Stokes
vectors, Jones-, or Muller - matrix formalisms for the mathematical treatment of the sequence of optical components
(see ¶7.6).
3.3 The ellipsometer equipment differs in the capability to measure all elements of the Stokes vector.
3.4 The ellipsometer equipment differs in the capability to measure the number of unknown optical properties of a
sample and in their capability to measure critical dimension parameters.
3.5 This standard does not address the calibration procedures of ellipsometer equipment.
4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI E30.5 — Specification for Metrology Specific Equipment Model (MSEM)
SEMI E89 — Guide for Measurement System Analysis (MSA)
SEMI E127 — Specification for Integrated Measurement Module Communications: Concepts, Behavior, and
Services (IMMC)
SEMI M20 — Practice for Establishing a Wafer Coordinate System
SEMI MF576 — Test Method for Measurement of Insulator Thickness and Refractive Index on Silicon Substrates
by Ellipsometry
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Definitions
5.1.1 calibration — set of operations that establish, under specified conditions, the relationship between values of
quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or
a reference material, and the corresponding values realized by standards
1
.
5.1.2 ellipsometry — a measurement method based on the principle of measuring the change of the polarization
state of light after reflection from the sample surface. Ellipsometry is commonly applied for the measurement of
layer thickness, refractive index and extinction coefficient, or critical dimensions.
5.1.3 in situ measurement — a measurement performed inside the processing chamber of an equipment. If a wafer
is used for this measurement, the wafer typically can be fed back into the process flow. The measurement data is
typically available within regular wafer-to-wafer processing time frame or within wafer processing time frame (e.g.
when performing layer thickness measurements during plasma etching).
5.1.4 in situ metrology — the science of measurement referring to in situ measurements.
5.1.5 in-line measurement — a measurement performed inside any portion of an equipment or work cell except the
processing chamber. If a wafer is used for this measurement, the wafer typically can be fed back into the process
flow. The measurement data is typically available within regular wafer-to-wafer processing time frame (e.g. layer
thickness measurements performed inside a cooling station of a cluster tool).
5.1.6 in-line metrology — the science of measurement referring to in-line measurements.
5.1.7 integrated metrology — the science of measurement using metrology equipment that is closely connected to
an equipment or work cell, characterized by the capability to perform in-line and in situ measurements.
5.1.8 layer thickness — the metric distance between two interfaces.
5.1.9 measurand — particular quantity subject to measurement
1
.
5.1.10 measurement — set of operations having the object of determining a value of a quantity
1
.
1 International vocabulary of basic and general terms in metrology, Second Edition, ISBN 92-67-01075-1, International Organization for
Standardization 1993.
SEMI E141-0705 © SEMI 2005 3
5.1.11 measuring instrument — device intended to be used to make measurements, alone or in conjunction with
supplementary device(s)
1
.
5.1.12 measuring system — complete set of measuring instruments and other equipment assembled to carry out
specified measurements
1
.
5.1.13 metrology — the science of measurement
1
. In semiconductor manufacturing, metrology denotes the science
of measurement to ascertain dimensions, quantity, or capacity; the techniques and procedures for using sensors and
measurement equipment to determine physical and electrical properties in wafer processing
2
.
5.1.14 metrology equipment — any equipment that collects and reports information on specific predetermined sites
or features on a substrate with consistent data structure, or reports general information about the entire substrate
3
.
6 Ellipsometer Equipment
6.1 Ellipsometer Equipment Specification
6.1.1 In the reflection ellipsometric measurement, a light beam with known state of polarization is directed towards
a specular reflecting sample surface. The change in both the amplitude and phase of the oscillating parallel and
perpendicular vector components of the electric field associated with the beam are measured after reflection from
the surface as the complex amplitude reflectance ratio (i.e. a change in the polarization of the light beam occurs).
There are several possible configurations for ellipsometer equipment, which can be described by the arrangement of
modules that comprise the optical components required to perform the ellipsometric measurement. In addition, the
optical components also induce changes in the polarization of the light beam.
6.1.2 For specification of the ellipsometer equipment, it is necessary to describe all modules and optical
components included both in the measuring and in the reflection process from the sample system and their position
within a coordinate system defined by the sample and the light beam. Additionally, information on the number of
wavelengths used for measurement and the method of data acquisition must be provided. The following definitions
are provided for ellipsometer equipment specification.
6.2 Ellipsometer module definition (see Figure 1)
6.2.1 ellipsometer modules — An ellipsometer consists of two modules, the polarizer module and the analyzer
module. The modules comprise the components used to establish and analyze the state of polarization of the incident
and reflected beam, respectively.
6.2.1.1 polarizer module — Arrangement of optical devices that generates a light beam of well-defined known state
of polarization for interacting with the sample system. The polarizer module includes the polarizer device and the
light source and may also include the compensator or modulator.
6.2.1.2 analyzer module — Arrangement of optical devices that allows measurement of the state of polarization of
the light beam after reflection from the sample system. The analyzer module may also include the compensator or
modulator,
and the detector.
6.2.1.3 incident beam — The light beam that passes from the light source through the polarizer module on the
sample surface.
6.2.1.4 reflected beam — The light beam that passes from the sample surface through the analyzer module.
6.2.1.5 plane of incidence — The plane spread by the incident and the reflected beam.
6.2.1.6 angle of incidence (
0
) — Angle between the incident beam and the normal vector of the sample surface.
6.3 Ellipsometer component definition (see Figure 1)
6.3.1 ellipsometer component — An optical device within the ellipsometer that intentionally changes the state of
polarization during the measurement.
6.3.1.1 polarizer (P) — Component that transmits light with a preferred polarization axis (typically linearly
polarized).
2 SEMATECH Official Dictionary, Rev 5.0, SEMATECH Inc., 2004 (Available through www.sematech.org).
3 SEMI International Standards: Compilation of terms. March 2004 (Available through www.semi.org).
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6.3.1.2 rotating polarizer (RP) — Component that transmits light with a preferred polarization axis (typically
linearly polarized) and that is rotating during measurement.
6.3.1.3 compensator (retarder) (C) — Component that can add a phase shift between the components of the electric
field (i.e. the field component parallel to the plane of incidence and perpendicular to the beam direction and the field
component perpendicular to the plane of incidence and to the beam direction, respectively) (see ¶6.4.2.3–¶6.4.2.6).
6.3.1.4 rotating compensator (retarder) (RC) — A rotating component that can add a phase shift between the
components of the electric field (i.e., the field component parallel to the plane of incidence and perpendicular to the
beam direction and the field component perpendicular to the plane of incidence and to the beam direction,
respectively) (see ¶6.4.2.3–¶6.4.2.6).
6.3.1.5 birefringence modulator (BM) — Component that can add a time-modulated phase shift between the
components of the electric field (i.e. the field component parallel to the plane of incidence and perpendicular to the
beam direction and the field component perpendicular to the plane of incidence and to the beam direction,
respectively) (see ¶6.4.2.3–¶6.4.2.6). The photoelastic modulator (PEM) is a component of this type.
NOTE 1: A PEM is an electro-optical modulator made of a suitable birefringent material. By applying an external electric field
to this material, its refractive index changes anisotropically, thus resulting in a phase shift of a transmitting light wave. By driving
the electric field resonantly, the phase of one polarization component of the transmitting light wave will be delayed periodically.
6.3.1.6 analyzer (A) — Component that transmits light with a preferred polarization axis (typically linearly
polarized).
6.3.1.7 rotating analyzer (RA) — Component that transmits light with a preferred polarization axis (typically
linearly polarized) and that is rotating during measurement.
6.3.1.8 sample (S) — Material or layer system to be analyzed. The sample is the reflecting component that changes
the state of polarization in a characteristic manner (typically, light is elliptically polarized after reflection) and that is
to be evaluated.
6.4 Ellipsometer Equipment Definition (see Figure 1)
6.4.1 sequence of ellipsometer components — The first item to be described for the definition of ellipsometer
equipment is the sequence of optical components beginning with the first component in the polarizer module after
the light source and including all the optical components to the analyzer module before the detector element. For this
definition, optical elements that do not intentionally affect the state of light polarization (e.g. the light source, the
detector, or the spectrometer) are not listed.
6.4.1.1 The most commonly applied ellipsometer equipment is listed below.
6.4.1.1.1 P C S A and P S C A — Null Ellipsometer.
6.4.1.1.2 P (C) S RA and P S (C) RA — Rotating Analyzer Ellipsometer (with) without Compensator.
6.4.1.1.3 RP (C) S A and RP S (C) A — Rotating Polarizer Ellipsometer (with) without Compensator.
6.4.1.1.4 P RC S A, P S RC A, and P RC S RC A — Rotating Compensator Ellipsometer.
6.4.1.1.5 P BM S A and P S BM A — Birefringence Modulation Ellipsometer (sample configuration: P PEM S A or
P S PEM A).
6.4.2 position of ellipsometer components — The second item to be described for the definition of ellipsometer
equipment is the position of the optical components within this coordinate system. The ellipsometer setup uses a
coordinate system defined by the sample surface and the light beam (see Figure 1).
6.4.2.1 definition of the optical system of coordinates — The optical system of coordinates is defined by the
electromagnetic field components, described as complex numbers, and the wave vector.
6.4.2.2 wave vector (k
) — The vector indicates the propagation direction of a light beam. The magnitude is given by
|k
| = 2
/
, with
being the wavelength of the light beam. The wave vector of the incident beam is k
i
and that of the
reflected beam is k
r
.
6.4.2.3 electric field vector (E
ip
) — Electric field strength of the incident beam parallel to the plane of incidence and
perpendicular to the wave vector of the incident beam.