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SEMI E141-0705 © SEMI 2005 2 3.2 The standard is limited to the measurement of isotropic samples. It is li mited to the app lication of Stokes vectors, Jones-, o r Muller - m atrix formalisms for the m athematical treatm…
SEMI E141-0705 © SEMI 2005 1
SEMI E141-0705
GUIDE FOR SPECIFICATION OF ELLIPSOMETER EQUIPMENT FOR
USE IN INTEGRATED METROLOGY
This standard was technically approved by the global Metrics Committee. This edition was approved for
publication by the global Audits and Reviews Subcommittee on May 20, 2005. It was available at
www.semi.org in June 2005 and on CD-ROM in July 2005.
1 Purpose
1.1 The application of integrated metrology is anticipated to become a key factor for advanced process control in
future integrated circuit (IC) manufacturing. Important parameters, which are typically measured for the
characterization and qualification of device manufacturing steps, are the thickness and the optical properties of
fabricated layers and the critical dimensions (CD) of submicron structures. For the measurement principle of
ellipsometry, which is commonly applied in both applications, different equipment and, hence, procedures and
notations for data acquisition and modeling exist. If, therefore, ellipsometry is to be applied for integrated metrology
equipment, the physical and the software integration into the equipment should be standardized to avoid efforts for
specific installations depending on the equipment and fabrication environment.
1.2 The description of the mechanical integration of an ellipsometer into an equipment module (e.g. a front end
module or an equipment chamber) comprises the
specification of the ellipsometer equipment and the spatial arrangement of the ellipsometer modules and
components,
specification of the relative position of the ellipsometer equipment to the equipment module, and
specification of the mechanical interfaces to the equipment module.
1.3 A prerequisite for a standardized software integration of an ellipsometer is the standardized notation of the layer
counting method, the measurement parameters, the measurement data, and the measurement results. This document
describes the position of the metrology equipment with respect to the sample. The position of the measurement
position (i.e. the position of the measurement spot) refers to the description of the wafer surface coordinate system
as described in SEMI M20.
1.4 The purpose of this standard is to provide a guide for a unique specification of the most commonly applied
ellipsometer equipment, the comprised modules and components, and their spatial arrangement. In this standard, the
notation for parameters required in data acquisition and modeling is specified, and a unique notation for remote
access on measurement parameters, data, and results is provided. Derived from these definitions, the required
parameters to identify the calibration status of an ellipsometer are specified. Additionally, recommendations for
preferred physical units are given.
1.5 The standard is intended for use in integrated metrology, but may also be applicable for stand-alone metrology.
2 Scope
2.1 This standard covers reflection ellipsometric measurements in integrated metrology.
2.2 The standard covers the typical applications of ellipsometry, which are the determination of layer thickness and
optical properties.
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 The standard is limited to the measurement technique of ellipsometry although definitions may be applicable to
the measurement technique of polarimetry.
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).