IEC 62047-16:2015

IEC 62047-16 ®
Edition 1.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Semiconductor devices – Micro-electromechanical devices –
Part 16: Test methods for determining residual stresses of MEMS films – Wafer
curvature and cantilever beam deflection methods

Dispositifs à semiconducteurs – Dispositifs microélectromécaniques –
Partie 16: Méthodes d'essai pour déterminer les contraintes résiduelles des
films de MEMS – Méthodes de la courbure de la plaquette et de déviation de
poutre en porte-à-faux
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IEC 62047-16 ®
Edition 1.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Semiconductor devices – Micro-electromechanical devices –

Part 16: Test methods for determining residual stresses of MEMS films – Wafer

curvature and cantilever beam deflection methods

Dispositifs à semiconducteurs – Dispositifs microélectromécaniques –

Partie 16: Méthodes d'essai pour déterminer les contraintes résiduelles des

films de MEMS – Méthodes de la courbure de la plaquette et de déviation de

poutre en porte-à-faux
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.080.99 ISBN 978-2-8322-2294-2

– 2 – IEC 62047-16:2015 © IEC 2015
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Testing methods . 6
4.1 General . 6
4.2 Wafer curvature method . 6
4.2.1 General . 6
4.2.2 Test apparatus . 7
4.2.3 Measurement procedures . 7
4.2.4 Reports. 7
4.3 Cantilever beam deflection method . 8
4.3.1 General . 8
4.3.2 Test apparatus . 9
4.3.3 Measurement procedures . 9
4.3.4 Reports. 9
Bibliography . 11

Figure 1 – Schematic drawing of compressive residual stress induced curvature after
depositing thin film on substrate. 6
Figure 2 – Scheme for comprehensive residual stress induced curvature . 9

Table 1 – Mandatory details for the test of wafer curvature method . 8
Table 2 – Mandatory details for the report of beam deflection method . 10

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SEMICONDUCTOR DEVICES –
MICRO-ELECTROMECHANICAL DEVICES –

Part 16: Test methods for determining residual stresses of MEMS films –
Wafer curvature and cantilever beam deflection methods

FOREWORD
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International Standard IEC 62047-16 has been prepared by subcommittee 47F: Micro-
electromechanical systems, of IEC technical committee 47: Semiconductor devices.
The text of this standard is based on the following documents:
FDIS Report on voting
47F/209/FDIS 47F/214/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 4 – IEC 62047-16:2015 © IEC 2015
A list of all parts in the IEC 62047 series, published under the general title Semiconductor
devices – Micro-electromechanical devices, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
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SEMICONDUCTOR DEVICES –
MICRO-ELECTROMECHANICAL DEVICES –

Part 16: Test methods for determining residual stresses of MEMS films –
Wafer curvature and cantilever beam deflection methods

1 Scope
This part of IEC 62047 specifies the test methods to measure the residual stresses of films
with thickness in the range of 0,01 µm to 10 µm in MEMS structures fabricated by wafer
curvature or cantilever beam deflection methods. The films should be deposited onto a
substrate of known mechanical properties of Young’s modulus and Poisson’s ratio. These
methods are used to determine the residual stresses within thin films deposited on substrate
[1] .
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
IEC 62047-21, Semiconductor devices – Micro-electromechanical devices – Part 21: Test
method for Poisson's ratio of thin film MEMS materials
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
residual stress
σ
f
stress that remains after the original cause of the stresses (external forces, heat source) has
been removed
3.2
curvature
ĸ
amount by which a geometric object deviates from being flat
Note 1 to entry: In case of a circle, ĸ = 1/R where R is the radius.
3.3
body
object with mass, not only energy, that is three dimensional (extended in 3-dimensions of
space), has a trajectory of position and orientation in space, and is lasting for some duration
of time
___________
Numbers in square brackets refer to the Bibliography.

– 6 – IEC 62047-16:2015 © IEC 2015
4 Testing methods
4.1 General
The deposition of a film shall make the bi-layer structure to bend together due to residual
stresses in the film. The amount of deflection is directly related to the residual stresses of the
film.
There are two kinds of test methods such as wafer curvature method and cantilever beam
deflection method in order to measure the residual stress.
In the case of tensile residual stress, the substrate bonded to the film becomes concave,
whereas for a compressive residual stress, it becomes convex.
4.2 Wafer curvature method
4.2.1 General
Wafer curvature method should be used in a wafer level processing. A wafer should be biaxial
symmetric and stress free.
Stoney [2] used a bi-layer plate system composed of a stress bearing thin film, of uniform
thickness h , deposited on a relatively thick substrate, of uniform thickness h , and derived a
f s
simple Equation (1), so-called Stoney’s equation, relating the curvature, ĸ, of the system as
shown in Figure 1, to the stress, σ of the film as follows [3]:
f
E h κ
S s
σ = (1)
f
6(1-v )h
s f
where
f and s are film and substrate, respectively;
E is the Young’s modulus;
ν is Poisson’s ratio (see IEC 62047-21)
The formula has been extensively used in the literature to infer film stress changes from
experimental measurement of system curvature changes [4].
h
f
h
s
IEC
a) Substrate before depositing thin film b) After depositing thin film on substrate
Figure 1 – Schematic drawing of compressive residual stress
induced curvature after depositing thin film on substrate
The following assumptions should be satisfied in order to use Equation (1) [3]:
h
s
R, (κ = 1/R)
a) both the film thickness h and substrate thickness h should be uniform and small
f s
compared with the lateral dimensions;
b) the film shall cover the one side surface of a circular substrate;
c) the strains and rotations of the plate system should be very small;
d) the substrate material should be homogeneous, isotropic, and linearly elastic and the film
material should be isotropic;
e) the film stress states should be in-plane isotropic or equibiaxial (two equal stress
components in any two, mutually orthogonal in-plane directions) while the out-of-plane
direct stress and all shear stresses vanish;
f) the system’s curvature components are equibiaxial (two equal direct curvatures) while the
twist curvature vanishes in all directions;
g) all surviving stress and curvature components are spatially constant over the plate
system’s surface, a situation which is often violated in practice;
h) the edge effect near the periphery of the substrate should be inconsequential, and all
physical quantities should be invariant under a change in position.
i) in order to measure more accurate residual stress, curvatures of before and after thin film
deposition are measured and the stress of thin film is calculated by Equation (2) from the
modified Equation (1):
E h ∆κ
S s
σ = (2)
f
6(1-v )h
s f
where
∆ĸ is the difference of curvature before and after thin film deposition.
4.2.2 Test apparatus
More than one equipment or tool regarding contact methods (e.g. profilometry) or non-contact
(e.g. video, laser scanning) are used for measuring curvature radius (R). Measurement
accuracy is in the range of 0,1 nm to 0,1 µm which depends on measurement test apparatus.
4.2.3 Measurement procedures
The measurement procedures are as follows:
a) measure substrate thickness (h ) and thin film thickness (h );
s f
b) obtain the Young’s modulus (E ) of substrate and Poisson’s ratio (ν ) of substrate;
s s
c) measure radius of curvature (R) of system and calculate curvature (ĸ) or measure radii of
curvature (R) and calculate the difference of curvature (∆ĸ) before and after thin film
deposition of system;
d) calculate residual stress(σ ) according to Equation (1) or (2).
f
4.2.4 Reports
Calculate σ according to Equation (1) or (2) and write the value in Table 1.
f
– 8 – IEC 62047-16:2015 © IEC 2015
Table 1 – Mandatory details for the test of wafer curvature method
Parameters Values
Number of specimens
Substrate material and thickness (h )
s
Young’s modulus of substrate (E )
s
Poisson’s ratio of substrate (ν )
s
Film material and film thickness (h )

f
Substrate thickness (h )
s
Curvature radius (R) and curvature (ĸ) of system

regarding Equation (1)
Curvature radii (R) and calculate the difference of

curvature (∆ĸ) before and after thin film deposition
regarding Equation (2)
Stress of the film (σ )
f
4.3 Cantilever beam deflection method
4.3.1 General
Cantilever beam deflection method should be used in a piece or chip level processing. Given
a small deflection compared with the beam length, the radius of curvature in case of wafer
curvature method can be substituted by the length of the beam squared, L , divided by twice
the deflection, 2δ.
2 2 2
E h κ E h E h δ
δ
S S S
S S S
σ = = = (3)
f
2 2
( ) ( )
6 1−υ h 6 1−υ h
S f S f L 2 3(1−υ )h L
S f
Equation (3) involves the following assumption: there is no biaxial bending in thin film on
beam structure. This method shall be used to determine the residual stresses of thin film
materials by using a bi-layered beam structure. All the assumptions applied to the Stoney’s
equation of (Equation (1)) should be satisfied in this method.
In order to measure more accurate residual stress, cantilever deflections of before and after
thin film deposition of system should be measured and the stress of thin film is calculated by
Equation (4) from the modified Equation (3);
2 2 2
E h ∆κ E h E h
∆δ ∆δ
s s s s s s
σ = = = (4)
f
2 2
6(1-v )h 6(1-v )h 3(1-v )h
L L
s f s f s f
where
∆δ is the difference of deflection before and after thin film deposition.
Figure 2 shows scheme for comprehensive residual stress induced curvature, and Figures 2a)
and 2b) show residual state of thin film and beam bending after thin film deposition. Thickness
of the film h and the substrate h are provided in Figure 2a) and deflection δ induced by thin
f s
film deposition is provided in Figure 2b).

Film deposition
W
δ
L
IEC
IEC
a) Residual stress free state of thin film b) Beam bending after thin film deposition
Figure 2 – Scheme for comprehensive residual stress induced curvature
4.3.2 Test apparatus
A noncontact surface profiler (e.g. white light interferometric microscope, digital image
correlation method, confocal microscope, etc.) should be used to measure the surface profiles
and deflection (δ) of a film deposited on a substrate.
4.3.3 Measurement procedures
The measurement procedures are as fo
...