IEC 62047-17:2015

IEC 62047-17 ®
Edition 1.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Semiconductor devices – Micro-electromechanical devices –
Part 17: Bulge test method for measuring mechanical properties of thin films

Dispositifs à semiconducteurs – Dispositifs microélectromécaniques –
Partie 17: Méthode d'essai de renflement pour la mesure des propriétés
mécaniques des couches minces
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IEC 62047-17 ®
Edition 1.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Semiconductor devices – Micro-electromechanical devices –

Part 17: Bulge test method for measuring mechanical properties of thin films

Dispositifs à semiconducteurs – Dispositifs microélectromécaniques –

Partie 17: Méthode d'essai de renflement pour la mesure des propriétés

mécaniques des couches minces
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.080.99 ISBN 978-2-8322-2295-9

– 2 – IEC 62047-17:2015 © IEC 2015
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and symbols. 6
3.1 Terms and definitions . 6
3.2 Symbols . 7
4 Principle of bulge test . 7
5 Test apparatus and environment . 8
5.1 General . 8
5.2 Apparatus . 9
5.2.1 Pressuring device . 9
5.2.2 Bulge (pressure) chamber. 9
5.2.3 Height measurement units . 9
5.3 Test environment . 10
6 Specimen . 10
6.1 General . 10
6.2 Shape and dimension of specimen . 10
6.3 Measurement of test piece dimension . 10
7 Test procedure and analysis . 11
7.1 Test procedure . 11
7.2 Data analysis . 12
8 Test report . 13
Annex A (informative) Determination of mechanical properties . 14
A.1 General . 14
A.2 Determination of mechanical properties using stress-strain curve . 14
A.3 Determination of mechanical properties using analysis of load-deflection . 16
Annex B (informative) Deformation measurement techniques . 19
B.1 General . 19
B.2 Laser interferometry technique . 19
B.3 Capacitance type measurement . 19
Annex C (informative) Example of test piece fabrication: MEMS process . 25
C.1 Test piece fabrication . 25
C.2 Measurement of shape of specimen . 26
Bibliography . 27

Figure 1 – Typical example of bulge specimen . 7
Figure 2 – Membrane window bulged by pressure . 8
Figure 3 – Typical example of bulge test apparatus . 8
Figure 4 – Bulge membrane window shapes . 10
Figure 5 – Example of typical pressure-height curve obtained from bulge test . 12
Figure A.1 – Determination of biaxial modulus in the stress-strain curve obtained from
bulge test . 18
Figure B.1 – Typical example of laser interferometer configuration . 21

Figure B.2 – Typical fringe patterns obtained from laser Michelson interferometry and
ESPI system . 22
Figure B.3 – Typical example of the measurement system using a photo detector . 23
Figure B.4 – Schematic of capacitance bulge tester . 23
Figure B.5 – Typical example of relationship between bulge height and capacitance
change . 24
Figure C.1 – Example of fabrication procedure for bulge test piece . 25

Table 1 – Symbols and designations of a specimen . 7
Table A.1 – Examples of various expressions of parameters, C and C (ν), for thin
1 2
square films . 17
Table A.2 – Examples of various expressions of parameters, C and C (ν), for thin
1 2
spherical films . 17

– 4 – IEC 62047-17:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SEMICONDUCTOR DEVICES –
MICRO-ELECTROMECHANICAL DEVICES –

Part 17: Bulge test method for measuring
mechanical properties of thin films

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62047-17 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/210/FDIS 47F/215/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.

A list of all parts in the IEC 62047 series, published under the general title Semiconductor
devices – Micro-electromechanical devices, can be found in 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
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 62047-17:2015 © IEC 2015
SEMICONDUCTOR DEVICES –
MICRO-ELECTROMECHANICAL DEVICES –

Part 17: Bulge test method for measuring
mechanical properties of thin films

1 Scope
This part of IEC 62047 specifies the method for performing bulge tests on the free-standing
film that is bulged within a window. The specimen is fabricated with micro/nano structural film
materials, including metal, ceramic and polymer films, for MEMS, micromachines and others.
The thickness of the film is in the range of 0,1 µm to 10 µm, and the width of the rectangular
and square membrane window and the diameter of the circular membrane range from 0,5 mm
to 4 mm.
The tests are carried out at ambient temperature, by applying a uniformly-distributed pressure
to the testing film specimen with bulging window.
Elastic modulus and residual stress for the film materials can be determined with this method.
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 62047-2:2006, Semiconductor devices – Micro-electromechanical devices – Part 2:
Tensile testing method of thin film materials
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
residual stress
σ
stress which exists in a specimen in the absence of an external load
3.1.2
biaxial modulus
M
elastic modulus in plane strain condition
3.1.3
membrane window
testing area, contacted directly with the pressure media and surrounded by a frame, in the
free standing film specimen
Note 1 to entry: See Figure 1.

1 2
IEC
Key
1 top view 2 side view
3 membrane window 4 thin film deposited

Figure 1 – Typical example of bulge specimen
3.2 Symbols
The symbols used in this document are presented in Table 1 below.
Table 1 – Symbols and designations of a specimen
Symbol Unit Designation
t µm thickness of a membrane or thin film
R radius of a bulged membrane window
µm
maximum vertical displacement at the centre of the bulged
h
µm
window
d mm diameter in a circular window
half-width and half-length of the rectangular window,
respectively.
a,b mm
In case of square window, a equals to b.
p MPa differential pressure applied to the membrane window
C , C coefficients in generalized linear-elastic bulge equation
1 2
4 Principle of bulge test
Nominally free-standing film specimen with a frame surrounding a bulging membrane window
as shown in Figure 1 is required and it should be mounted on a bulge testing system which
can apply differential pressure to the specimen. Here, the pressure should be uniformly
distributed over the film in the window and loaded to the film in a constant and relatively static
rate. The geometry of the membrane window can be circular, square and rectangular shape.
NOTE 1 With selection of window geometry, analysis for determining stress and strain of the bulged film is
performed with different models, i.e. a spherical or a cyclindrical pressure vessel model.
The film, subjected to the differential pressure, over the window deforms in the out-of-plane
bulged form. By measuring the height, h, and pressure, p, from the bulged window, as
presented in Figure 2, pressure-deflection response and/or stress-strain relationship is
obtained through analysis model which can be chosen. The mechanical properties of the film,
t
– 8 – IEC 62047-17:2015 © IEC 2015
such as elastic modulus and residual stress, can be determined with the pressure-deflection
curve or stress-strain curve.
NOTE 2 The details of the analytic models are described in Annex A.
R
p
IEC
Figure 2 – Membrane window bulged by pressure
5 Test apparatus and environment
5.1 General
With applying pressure to the specimen, deformation response, i.e. change in bulge height,
in the membrane window shall be measured. In general, bulge test apparatus can be
composed of pressuring device, specimen holder and bulging height measurement units as
shown in Figure 3.
9 8
IEC
Key
1 deflection measurement system 4 pressure chamber 7 pressure gauge
2 specimen 5 membrane window 8 inlet
3 O-ring 6 substrate 9 outlet
Figure 3 – Typical example of bulge test apparatus
h
5.2 Apparatus
5.2.1 Pressuring device
Pressuring device should be equipped to apply a specified continuous pressure with a
controlled rate or a certain level of pressure to the membrane window to be bulged. Pressure
media can be oil, gas and distilled water. In general, the device can be composed of a
pressure sensor and pressure controller. The controller should be with accuracy of 1 % in full
test scale.
NOTE At the pressures encountered in the tests, gas is over a million times more compressible than typical
liquids such as oil and distilled water.
5.2.2 Bulge (pressure) chamber
The pressure chamber should be as compact as possible, to reduce the compliance of the
test system. The volume, which has to be pressurized and which potentially contributes to the
compliance, would be minimized.
In the case liquid is used to pressurize the test system, the system contains as little air as
possible because even a small air bubble trapped inside the test system can dominate the
system’s compliance. It is recommended that the system including the chamber be designed
so that there are no places where air bubbles can hide and that the liquid can be refilled
easily. Special care shall be taken not to introduce air bubbles when samples is mounted and
removed.
The material of the chamber should be chosen considering the pressure media for the test
and testing pressure range.
In the case liquid is used to pressurize the test system, it is recommended that the testing
apparatus be made out of transparent acrylic sheet in order to see air bubbles and then to
minimize them trapped within the chamber.
The bulge chamber is connected to the pressurizing device and thus allows a specimen to be
deformed with fine control. The specimen is mounted on the bulge chamber by mechanical
clamping or epoxy gluing method, etc.
NOTE In the case of capacitance measurement type, the bulge chamber has an electrode and a mechanical
spacer. The electrode, which measures height change of a bulge specimen due to the deformation, is made of
copper-coated PCB. A mechanical spacer that is located between the specimen and the electrode controls a
sensitivity of capacitance change by adjusting thickness of the spacer.
The pressure inside the chamber shall be monitored and measured through suitable pressure
sensor which can be installed directly to the chamber or connected though tube transporting
the pressure without loss of the pressure to be measured.
It is recommended that exposition of the area of the pressure sensor to the pressure media
should be minimized and it has no indentation or internal cavities trapping air.
Nonlinearity and hysteresis of the pressure sensor is recommended to be less than 0,5 % and
be calibrated according to the pressure standard established in each country as a National
Standard.
5.2.3 Height measurement units
The height measurement unit should be installed in a position suitable to measure the
deformation of the membrane window and have a function of a continuous measurement
which is needed in order to determine the maximum deformation of the membrane window
bulged with applying pressure. The maximum deformation of the membrane window can be
determined from the measurement in full-field or top of the bulged area using the laser
interferometric system or capacitance type measurement system, which is described in detail
in Annex B.
– 10 – IEC 62047-17:2015 © IEC 2015
The resolution of the measurement device for the deflection measuring a bulged membrane
window by pressure should be in units of micrometer. The fine resolution of less than 0,1 % in
full scale is very important for an accurate measurement.
5.3 Test environment
It is recommended to perform a test under constant temperature and humidity. Temperature
change can induce thermal drift during deflection measurement. Temperature change during
the test should be less than 2 °C.
6 Specimen
6.1 General
The film materials used in the specimen shall be prepared by using the same fabrication
process as the actual device or materials fabrication.
There are many fabrication methods of the test piece depending on the applications. As an
example, the fabrication of the specimen with a frame is described in Annex B.
The film specimen without a frame can be prepared from the electroplating process.
6.2 Shape and dimension of specimen
The shapes of membrane windows can be rectangle, square and circle as shown in Figure 4.
Membrane window is surrounded with a thick substrate frame or frame jig which is not
deformed by pressure.
It is recommended that the half-width, a, of the rectangular and square membrane window and
the diameter, d, of the circular membrane be in the range from 0,5 mm to 4 mm.
In the case of rectangular window, the aspect ratio of length to width in a rectangular
membrane window is recommended to be equal to or greater than 4 due to plane strain
condition.
2a
2a
d
IEC
IEC
IEC
a) rectangular b) square c) circle
Figure 4 – Bulge membrane window shapes
6.3 Measurement of test piece dimension
To analyze the test results, the accurate measurement of the test piece dimension and
pressure is required since the dimensions are used to extract mechanical properties of test
materials. The thickness (t) and dimension of the window (width and length or diameter)
should be measured with very high accuracy with less than ±1 %. Special cares should be
taken to measure the window size by clearly dividing the window boundary.
The methods for measuring film thickness and accuracy given in Clause C.3 of
IEC 62047-2:2006 apply.
2b
Special care should be taken to avoid damage on the specimen during the measurement.
7 Test procedure and analysis
7.1 Test procedure
The test procedure is as follows:
a) The bulge specimen should be attached to the bulge chamber in an appropriate method,
such as mechanical clamping or epoxy gluing method etc., not to cause unwanted stress,
such as bending, shear or combined stress, or in-plane distortion on the membrane.
It is desired to test considering clamping effect on the change in the bulge height. Hard
clamping on the specimen often causes residual stress on a membrane window. However,
to avoid pressure leakage in the bulge chamber, proper sealing method is required for the
test.
The specimen can be mechanically clamped to the chamber with screws. In general,
specimen holder to which the specimen would be attached is screwed tightly on to the
chamber. To prevent any leakages, an O-ring between the specimen holder (or specimen)
and the chamber can be used. Special care is required to be taken in positioning the O-
ring on the chamber to avoid offset of bulge height.
NOTE 1 The specimen or specimen holder can be also attached to the chamber using epoxy with sufficient
adhesive strength.
b) To obtain quasi-static deformation of the film, pressure should be carefully controlled to
increase or decrease monotonically. The strain rate imposed on the test should be ranged
-7 -2
from 10 /s to 10 /s.
c) The test should be performed within the appropriate deformation of the bulge specimen; it
is recommended that the deformation should not be over 0,5 % and 2 % of strain for linear
elastic and elastic-plastic materials, respectively. The pressure-height curve obtained from
the test can be plotted as shown in Figure 5(a).
d) In case the elastic modulus would be determined from stress-strain curve, some de-
pressurizing steps during pressurizing can be applied. The de-pressurizing steps should
be provided at the well-timed instants and preferably at even intervals during pressurizing
process, as shown in Figure 5(b). It is recommended that the minimum pressure at each
de-pressuring step be greater than 50 % of the pressure level at the instant the de-
pressuring step starts.
The slope shall be determined from the linear stress-strain response obtained during de-
pressurizing step. Here, the slope means the biaxial elastic modulus of the film, M. See
Annex A.2.
Special care should be taken to avoid cyclic effect on the mechanical property of the film
with excessively repeating the de-pressurizing steps.
NOTE 2 Average values in modulus can be determined by reasonably repeating pressuring and
depressurizing steps.
e) During test, the pressure and deformation in the window should be precisely measured
simultaneously.
– 12 – IEC 62047-17:2015 © IEC 2015
4 3
30 p = 666 h + 8,81 × 10 h
Experimental Data
0,00 0,01 0,02 0,03 0,04 0,05 0,06
height: h, mm
IEC
a) for elastic film
0,35
0,30
0,25
p = 2 h + 350 h
0,20
0,15
0,10
0,05
Experimental Data
0,00
0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10
height: h, mm
IEC
b) for elastic-plastic material
Figure 5 – Example of typical pressure-height curve obtained from bulge test
7.2 Data analysis
The mechanical properties are determined according to two methods.
– Fitting method in pressure and height curve;
– Calculation in stress and strain curve.
Detailed analysis procedures are described in Annex A.
pressure: p ,kPa
pressure: p ,kPa
8 Test report
The test report should contain at least the following information:
a) references to this International Standard;
b) identification number of the specimen;
c) fabrication procedures of the specimen;
d) specimen material;
e) shape and dimension of the specimen and window;
f) measurement method;
g) description of testing apparatus;
h) pressure-deflection relationship;
i) measured properties and results: elastic modulus and residual stress, pressure-deflection
curve (if used).
– 14 – IEC 62047-17:2015 © IEC 2015
Annex A
(informative)
Determination of mechanical properties

A.1 General
Two quantities of pressure p and deflection height h obtained from experiment provide the
mechanical properties, such as elastic modulus and residual stress, of the film. These
properties can be determined with appropriate selection of analytic or experimental model, i.e.
the generalized linear-elastic bulge equation and stress-strain relationship.
A.2 Determination of mechanical properties using stress-strain curve
The shape of the film bulged during pressurizing can be modelled as a thin walled spherical or
cylindrical vessel with the window geometry employed in the experiment. That is, the
deflection height, h, and the corresponding pressure, p, for a circular and square window
geometry are related to the stress (σ) and strain (ε) relationship derived from the spherical
pressure vessel model while those for the rectangular window geometry are related to the
relationship from cylindrical pressure vessel model. For circular and square window geometry,
the stress and strain are determined as follows. [5, 8]
From the force equilibrium on the spherical pressure vessel model, the following relation can
be given:
pπR =σt2πR (A.1)
From the above equation, Equation (A.2) can be derived:
pR
σ = (A.2)
2t
From the geometry of the bulged window shown in Figure 2, the following equation can be
obtained:
2 2 2
(R − h) + a = R (A.3)
For the small deformation, h< a
R ≅ (A.4)
2h
The stress of the membrane can be obtained by substituting Equation (A.4) to Equation (A.2):
pa
σ = (A.5)
4ht
___________
Numbers in square brackets refer to the Bibliography.

The strain of the membrane can be derived from the geometrical relation of the membrane as
follows:
Rθ − a
(A.6)
ε =
a
where
θ is an angle of the membrane curvature;
ε is the strain of the membrane.
From geometrical considerations [5], the strain of the membrane can be given:
2 2
a 2h
ε = = (A.7)
2 2
6R 3a
In case of rectangular membrane with high aspect ratio (aspect ratio b/a > 4), stress and
strain are expressed by thin walled cylindrical pressure vessel. [7]
pR
σ =
t
(A.8)
a
R ≅ (A.9)
2h
pa
σ = (A.10)
2ht
Information about the specimen’s biaxial modulus (M) can be extracted from stress-strain
curve. Periodical pressurizing and de-pressurizing are required to obtain biaxial modulus. The
modulus is the slope of stress and strain curve during de-pressuring step as shown in
Figure A.1.
NOTE Biaxial modulus, M, is defined as E/(1-v) in case of circular and square membrane window and E/(1-v ) in
case of rectangular membrane window. Here, E and ν are elastic modulus and Poissons’ ratio, respectively.
The slope is recommended to be numerically determined with a best fit line (least squares
method) including a visual evaluation of the match between this line of a best fit and the
measured stress and strain readings. Using available and suitable computer software, the
linear slope shall be determined by a linear regression of stress over strain between the upper
stress point and the lower point. Here, the upper and lower stress point is recommended to be
90% of the stress at the instant the de-pressurizing starts and the minimum stress at the
instant the de-pressurizing ends, respectively.
The match between the straight line and the measured data shall be evaluated visually. It may
be useful to consider the coefficient of correlation r , which should be close to 1 (> 0,99), In
another way, the relative standard deviation is calculated. The relative standard deviation
takes into account the coefficient of correlation and the number of considered data points
among other statistical data. It should be less than 1 %.
The residual stress is defined at the strain of zero. It is recommended the stress be
determined at the nearest strain to zero within the strain data of less than 10 µε or at zero
strain linearly extrapolated with the slope of M and stress-strain data near zero strain.

– 16 – IEC 62047-17:2015 © IEC 2015
A.3 Determination of mechanical properties using analysis of load-deflection
From measurement of pressure p and deflection h of the bulged membrane, information about
the film’s mechanical properties is extracted. The residual stress, σ , and modulus, E, for a
square film of side, a, and thickness, t, can be estimated determined with a least-square fitting
between pressure and height curve with the generalized linear-elastic bulge equation, given
the following:
8Et
p = h (A.11)
spherical
3a (1 − v)
where
p is the differential pressure applied to the membrane window;
spherical
ν is Poissons’ ratio;
E is elastic modulus.
4Et
p = h (A.12)
cylindrical
4 2
3a (1− v )
where
p is the differential pressure applied to the membrane window.
cylindrical
The relationship between stress and strain is defined as follows:
σ = Mε +σ (A.13)
where
M is the elastic modulus in plane strain condition;
σ is the residual stress of the membrane window.
By rearranging the relationship between stress, strain and geometric parameters, the
pressure is derived as follows:
σ t 8Et
p = 4 h + h (A.14)
spherical
2 4
a 3a (1− v)
σ t 4Et
p = 2 h + h (A.15)
cylindrical
2 4 2
a 3a (1− v )
The generalized relationship between pressure and deflection is expressed by
σ t Et
(A.16)
p = C h + C (v) h
1 2
2 4
a a
where
C and C (v) are constants.
1 2
Here, h is the maximum height (deflection) at the center of the membrane, and ν is the
Poisson’s ratio of the material.

NOTE 1 From the above Formula (A.16), it can be found that the residual stress makes significant influence on
the thin film behavior at small deflection, while Young’s modulus controls the mechanical behavior at large
deflection. The lateral dimension of membrane is 100 times larger than the membrane thickness and the
displacement of the membrane is also much larger than the membrane thickness.
Numerical values of C and C (ν) are obtained by fitting with the experiments.
1 2
NOTE 2 To better fit with the experimental results, some various expressions for parameters of C and C (ν) were
1 2
proposed. Table A.1 and Table A.2 show typical examples of the expressions for thin square films and spherical
films respectively. More details can be found in the references listed in Tables A.1 and A.2.
Table A.1 – Examples of various expressions of parameters,
C and C (ν), for thin square films
1 2
Model C Ref.
C (ν)
Analytical 3,04 1,37 × (1,075 − 0,292ν) [1]
FEM 3,41 1,37 × (1,446 − 0,427ν) [1]
Analytical 3,45 1,994 × (1 − 0,271ν) [2]
Analytical 3,04 1,473 × (1 − 0,272ν) [3]
Analytical 3,39 (0,8 + 0,062ν) [4]

Table A.2 – Examples of various expressions of parameters,
C and C (ν), for thin spherical films
1 2
Model C C (ν) Ref.
1 2
Analytical 4,0 2,67 [1]
−
FEM 4,0 [1]
2,67 × (1,026 + 0,233ν)
Analytical 4,0 2,67 [5]
−
FEM 4,0 [5]
2,67 × (1,0 − 0,241ν)
– 18 – IEC 62047-17:2015 © IEC 2015
M
0,000 0 0,000 5 0,001 0 0,001 5 0,002 0 0,002 5 0,003 0 0,003 5 0,004 0
strain: ε, µm/µm
IEC
Figure A.1 – Determination of biaxial modulus in
the stress-strain curve obtained from bulge test
stress: σ , MPa
Annex B
(informative)
Deformation measurement techniques

B.1 General
For the bulge test, the free-standing membrane is deformed under pressurized loading and
the deformation is essential information for measuring the mechanical properties of the film
material. The deformation response is measured using various techniques; In-situ full field
displacement technique including laser interferometric method and electronic speckle pattern
interferometric (ESPI) method, laser scanning and capacitance method.
B.2 Laser interferometry technique
A laser interferometer, such as Michelson interferometry and electronic speckle pattern
interferometric (ESPI) system, can be used to determine the height of the bulge. From these
measurement systems, full field displacement over the bulged film window is measured.
In general, laser interferometry system is configured to detect the out-of-plane deformation.
Figure B.1 shows a typical example of the laser interferometry including Michelson
interferometry and ESPI system. As shown in Figure B.1, a source beam is split into two
identical beams via the optical arrangement of the interferometric system. One of these two
beams is reflected from the bulged surface of the film window and re-enters the interferometry.
It combines again with the other beam reflected off reference mirror. Path length difference
between two beams makes fringe pattern generated. The fringe pattern consists of a series of
dark fringes and bright fringes. Figure B.2 represents typical interferometric fringe patterns
obtained from the laser Michelson interferometry and ESPI system.
The deflection of the bulged window is determined by counting the number of fringes.
NOTE 1 Each white or black fringe corresponds to a displacement of λ/2, where λ is wavelength of the light
(laser).
NOTE 2 For laser Michelson interferometry, in general, a source of visible light with a fixed wavelength,
λ = 546 nm, is used, while, for ESPI system, He-Ne laser source with a wave length, λ = 632 nm, is imposed.
A photo detector and a spot infrared laser light source can be used to measure the maximum
deflection of the bulged film membrane. In general, the maximum height or deflection of the
membrane window is detected at the center of the window. To measure the deflection, the
detector such as the photo detector and the spot laser is positioned at the center of the
interference pattern or focused to the center of the membrane window. Figure B.3 shows a
typical example of the measurement system using a photo detector.
B.3 Capacitance type measurement
To obtain bulged height on a specimen, calculations are required depending on the test
conditions. Capacitance change is caused by height change during a test. To measure
capacitance change, the metal electrode and mechanical spacer is positioned over the center
of the membrane window [9]. The schematic of the capacitance measurement set up is shown
in Figure B.4.
NOTE 1 In order to measure the capacitance change with height change in membrane window during test, the
conducting film can be required.

– 20 – IEC 62047-17:2015 © IEC 2015
From pressure (p), film thickness (t) and capacitance measurement, the stress is calculated
by the following equation based on cylindrical bulge deformation.
NOTE 2 The relationship between bulge height, h and capacitance change, ∆C can be derived from the numerical
calculation; Figure B.5 shows a typical example of the derived relationship.
Rp
σ = , (B.1)
t
1 3
IEC
a) Laser interferometry
Key
1 CCD camera 5 interferometer
2 546 nm light source 6 chamber
3 computer 7 film surface
4 reference mirror
...