Iec 62047 6 2009

Semiconductor devices – Micro-electromechanical devices – Part 6: Axial fatigue testing methods of thin film materials Dispositifs à semiconducteurs – Dispositifs microélectromécaniques

Design of test piece

To reduce the impact of size, the test specimen must have dimensions comparable to those of the target device component The specimen's shape and dimensions should adhere to the guidelines outlined in Annex C of IEC 62047-2.

The specimen's plane shape dimensions must adhere to an accuracy of ±1% as outlined in IEC 62047-2 Additionally, the length of the parallel section of the test piece should exceed 2.5 times its width It is also crucial that the radius of curvature between the gripped ends and the parallel section is adequate to prevent fractures caused by stress concentration, as specified in sections C.1 and C.2 of IEC 62047-2.

The gauge marks specified in IEC 62047-2 are not necessary if the marks may concentrate stress or initiate fatigue fractures.

Preparation of test piece

The test piece must be produced using a method closely resembling that of the intended device for the thin film application It is essential to adhere to the fabrication procedures outlined in IEC 62047-2 Additionally, the substrate removal process should be selected with caution to avoid any damage to the test piece, as detailed in section C.3 of IEC 62047-2.

The number of test pieces should be determined adequately according to the thin films tested

Test piece thickness

The film thickness of each test piece must be measured directly, as it is typically not uniform across a wafer, with an accuracy requirement of within 5% To prevent mechanical damage from tools like stylus profilers, the film thickness at the step height of a window opening etched near the test piece can be utilized as a representative thickness Detailed methods for measuring film thickness and associated measurement errors are outlined in section C.4 of IEC 62047-2.

Storage prior to testing

The storage environment significantly influences the fatigue properties of thin films It is crucial to handle test pieces with care if there is a delay between their final preparation and testing Proper examination methods should be employed to verify that the surface of the specimens remains intact during storage If any deterioration is detected that was absent after preparation, testing must be avoided.

However, if the damage was introduced during the preparation processes, the test shall be performed

5 Testing method and test apparatus

General

The testing machine must feature a suitable gripping mechanism for the test piece and a system for applying cyclic loading This cyclic loading should primarily involve tensile-tensile mode loading.

For effective constant range force testing, it is essential to monitor both maximum and minimum forces, or alternatively, the mean force and force range Additionally, the testing machine must be equipped with a reliable constant force range control system In the case of constant displacement range testing, similar monitoring of maximum and minimum values is required.

Displacements, including mean displacement and displacement range, must be monitored, and the testing machine should feature a constant displacement range control system.

A test-piece failure detection system should be provided and the number of loading (or displacement) cycles to failure shall be recorded.

Method of gripping (mounting of test piece)

Each test piece shall be mounted so that the loading axis and test piece axis are aligned

When handling both ends of the test piece, it is crucial to prevent the application of excessive force or bending stress Refer to the gripping methods outlined in Annex A for proper techniques.

For optimal testing, it is recommended to use IEC 62047-2 standards for mounting test pieces Additionally, the testing apparatus should include a mechanism for aligning the test piece to ensure that its tensile axis is properly aligned with the loading direction of the apparatus.

Static loading test

Before conducting fatigue testing, it is advisable to perform static tensile testing on the test piece to establish the appropriate testing conditions This static tensile testing should adhere to the procedures outlined in IEC 62047-2.

Method of loading

In the event of a fracture occurring during the initial loading cycle, it is essential to document the fracture stress in the report During the constant force range test, both the maximum and minimum forces, or alternatively the mean force and force range, must remain unchanged Similarly, for the constant displacement range test, the maximum and minimum displacements, or the mean displacement and displacement range, should also be maintained consistently.

A load cell must be selected with a resolution that ensures 5% accuracy for the applied force, and its drift should not exceed 1% of the full-scale force during testing For detailed accuracy specifications, refer to Annex B in IEC 62047-2.

For constant displacement range testing, a displacement measurement system with a resolution adequate to guarantee 5 % accuracy of the applied displacement shall be used

Speed of testing

The frequency of the stress cycle is influenced by the testing environment, the type of testing machine, and the stiffness of the test piece It is essential to select a frequency that is optimal for the specific combination of these factors Proper frequency selection is crucial for the application of thin film materials, ensuring that the test piece does not heat up during cyclic loading due to rapid strain energy dissipation.

This practice does not apply to fatigue testing of viscoelastic films.

Environment control

The fatigue properties of thin films are significantly influenced by environmental conditions, necessitating careful monitoring of testing temperature and humidity It is essential to maintain the testing temperature within ±1 °C and relative humidity within ±5 % If controlling these parameters proves challenging, the specific values must be documented in the test report.

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Fatigue testing will proceed until either the test piece fractures or a specified number of cycles is reached The criteria for terminating the test, whether due to fracture or the completion of the predetermined cycles, will be detailed in the test report.

The test report shall include the following information

• Mandatory a) reference to this International Standard, i.e IEC 62047-6 b) test piece material

– in the case of a single crystal: crystallographic orientation c) method and details of test piece fabrication

– method of thin film deposition

– heat treatment (annealing) conditions d) shape and dimensions of test piece e) fatigue test conditions

– mean stress (in the case of displacement control, mean displacement)

– stress range (in the case of displacement control, displacement range)

– testing environment (temperature and relative humidity)

– wave form (sinusoidal, triangular, ramp)

The number of applied cycles to failure is crucial in testing If the test piece remains unfractured after a predetermined number of cycles, it is essential to record both the cycle count and the notation "no failure."

– in the case of polycrystalline thin film: texture and grain size b) internal stress c) surface roughness of test piece d) brief description of fracture characteristics

Technical background of this standard

A.1 Significance of axial loading fatigue testing for thin films

MEMS devices are fabricated from thin films on substrates, utilizing micromachining techniques akin to those in LSI processing The microstructure and surface roughness of these films are influenced by processing conditions, leading to potential micro/nano defects that can impact their mechanical properties Accurate measurement of these properties requires specimens prepared through the same processes as the actual devices, particularly for assessing the fatigue properties crucial for the durability and reliability of MEMS devices While fatigue tests on micro-sized components have been conducted using on-chip test structures and micro-sized specimens, the lack of standardized methods complicates data comparison across institutions Current standards for macro-sized materials, such as ISO 1099 and ASTM E 466-96, include established axial fatigue testing methods, which are essential for evaluating material fatigue properties Thus, a comprehensive discussion on the fatigue properties of MEMS devices necessitates a clear specification of the axial fatigue testing method applied to thin films.

A.2 Outline of round-robin tests performed in Japan [10]

This standard outlines the procedure for conducting axial tensile fatigue testing on thin film materials, derived from round-robin tests (RRT) carried out in Japan between 2003 and 2005.

The RRT was carried out with the participation of several universities and research institutes in Japan The materials used were single and polycrystalline Si thin films, and polycrystalline

Thin films were deposited on silicon wafers, and micro-sized specimens were prepared from these layers following IEC 62047-2 using photolithography Each test piece was designed to fit the testing machine at the specified institute, with standardized dimensions for the parallel parts as per IEC 62047-2 Axial fatigue tests were primarily conducted under force control, with careful measurements of load application, force, and displacement The impact of environmental factors, particularly humidity, on fatigue life was also analyzed Results were represented as S-N curves, allowing for a cross-comparison of fatigue life The validity of this standardized testing method was thoroughly investigated and summarized in the standard.

The design of the specimen's shape and dimensions must adhere to IEC 62047-2 standards The conditions for the axial fatigue test are influenced by the yield stress and fracture strength of the specimen Utilizing the same specimens for tensile testing simplifies the determination of fatigue test conditions Additionally, the specified geometry of the test piece's cross section plays a crucial role in this process.

IEC 62047-2 is proportionally reduced to that specified in ISO 6892 [11]

To accurately measure displacement on a test piece with gauge marks, it is essential to utilize interference light from laser-irradiated gauge marks, employing a double-field-of-view microscope to simultaneously observe two distant marks In cases where placing gauge marks is challenging or measuring the distance between them is impractical due to high loading cyclic frequencies, the displacement of the gripping device or actuator may be used as an alternative measurement method, with a detailed description of this approach included in the report.

The fatigue life of micro-sized materials is more significantly influenced by the testing environment compared to macro-sized materials, primarily due to their larger specific surface area.

Particularly, the fatigue life greatly depends upon the humidity during the test [4] Therefore, control of the humidity during fatigue testing is critical for micro-sized materials

Fatigue data, encompassing fatigue life and strength, is often widely dispersed, making statistical analysis crucial for accurately estimating these parameters For bulk materials, such analyses are governed by ISO 12107, which outlines how to determine the number of test specimens based on the desired reliability of the test results.

This standard is, however, limited to the analysis of fatigue data for materials exhibiting homogeneous behaviour due to a single mechanism of fatigue failure

In metallic thin film materials, fatigue is typically governed by a single mechanism, allowing for specimen determination based on ISO 12107 Conversely, silicon thin film materials exhibit multiple fatigue mechanisms, which remain unidentified This highlights the limitations of the analysis method outlined in ISO standards.

12107 cannot be directly applicable for determining the number of test pieces for Si thin film materials

[1] ASTM E 1823-05a, Standard terminology relating to fatigue and fracture testing

[2] Kahn, H., Ballarini, R., Mullen., R L., Heuer, A H., Electrostatically actuated failure of microfabricated polysilicon fracture mechanics specimens, Proceedings of the Royal

[3] Ando, T., Shikida, M and Sato, K., Tensile-mode fatigue testing of silicon films as structural materials for MEMS, Sensors and Actuators, A93 (2001) pp 70-75

[4] Muhlstein, C L., Brown, S B and Ritchie, R O., High-cycle fatigue and durability of polycrystalline silicon thin films in ambient air, Sensors and Actuators, A94 (2001), pp

[5] Sharpe Jr., W N and Bagdahn, J., Fatigue testing of polysilicon – a Review, Mechanics of Materials, 36 (2004) pp 3-11

[6] Namazu, T and Isono, Y., High-cycle fatigue damage evaluation for micro-nanoscale single crystal silicon under bending and tensile stressing, Proc 17th IEEE International

Conference on MEMS 2004, IEEE, Maastricht, Netherlands, (2004), pp 149-152

[7] Takashima, K and Higo, Y., Fatigue and fracture of a Ni-P amorphous alloy thin film on the micrometer scale, Fatigue & Fracture of Engineering Materials & Structures, 28

[8] ISO 1099, Metallic materials – Fatigue testing – Axial force-controlled method

[9] ASTM E 466-96, Standard practice for conducting force controlled constant amplitude axial fatigue tests of metallic materials

[10] Takashima, K, Round-Robin Test on Fatigue of Thin Films for MEMS Applications in

Japan, Proc 2nd Workshop on Characterization of Materials for MEMS/MST Devices,

[11] ISO 6892, Metallic materials – Tensile testing at ambient temperature

[12] ISO 12107, Metallic materials – Fatigue testing – Statistical planning and analysis of data

5 Méthode d’essai et appareillage d’essai 22

5.2 Méthode de fixation (montage de l’éprouvette d’essai) 22

Annexe A (informative) Contexte technique de la présente norme 25

Annexe C (informative) Mesure du déplacement 27

Annexe E (informative) Nombre d’éprouvettes d’essai 29

Partie 6: Méthodes d’essais de fatigue axiale des matériaux en couche mince

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Conception de l’éprouvette d’essai

To minimize the impact of size, it is essential that the test specimen has dimensions comparable to those of the target component of the device The shape and dimensions of the specimen should be based on Annex C of IEC 62047-2.

The dimensions of the test specimen's flat shape must fall within a precision range of ±1%, as specified in IEC 62047-2 The length of the parallel section of the test specimen should be more than 2.5 times its width Additionally, the curved section between the fixed ends and the parallel part must have a sufficiently large radius of curvature to prevent breakage due to stress concentration.

Les marques repères spécifiées dans la CEI 62047-2 ne sont pas nécessaires si les marques peuvent concentrer une contrainte ou initier des ruptures de fatigue.

Préparation de l’éprouvette d'essai

The test specimen should be manufactured using a process that closely resembles the method applied for the thin film layer It is essential to follow the procedures outlined in IEC 62047-2 for the fabrication of the test specimen Careful selection of the substrate removal process is crucial to prevent damage to the test specimen, as detailed in section C.3 of IEC 62047-2.

Il convient de déterminer correctement le nombre d'éprouvettes d’essai selon les couches minces soumises à l’essai Voir l’Annexe E.

Epaisseur de l’éprouvette d’essai

The thickness of each test specimen must be measured, as the layer thickness is typically not uniform across a wafer Measurement accuracy should be within 5% Each test specimen should be measured directly; however, the layer thickness at the height of a window opening etched near the test specimen can be used as the thickness to avoid mechanical damage caused by using a probe profiler Measurement methods for layer thickness and measurement errors are detailed in C.4 of IEC 62047-2.

Stockage avant essais

In the case of thin films, the storage environment can significantly impact fatigue properties If there is a time interval between final preparation and testing, it is crucial to ensure proper storage of the test specimens and to examine the samples using appropriate methods to confirm that the surface has not deteriorated during the storage period Any observed deterioration that was not present after the specimens were prepared should result in the cancellation of the tests.

Cependant, si le dommage s'est introduit au cours des processus de préparation, l'essai doit être réalisé

5 Méthode d’essai et appareillage d’essai

Généralités

It is essential to equip the testing machine with an appropriate fixture mechanism for the test specimen, as well as a mechanism for applying cyclic loads The cyclic load applied to the test specimen should fundamentally be a tensile-tensile load.

For strength testing within a constant range, it is essential to monitor both the maximum and minimum forces (or the average force and force range) Additionally, the testing machine should be equipped with a control system that maintains a constant force range In tests conducted within a constant displacement range, it is important to track the maximum and minimum displacements.

The average displacement and the range of displacement should be monitored, and it is advisable to equip the testing machine with a control system that maintains a constant displacement range.

Il convient de prévoir un système de détection de défaillance des éprouvettes d’essai, et le nombre de cycles de charge (ou de déplacement) doit être consigné.

Méthode de fixation (montage de l’éprouvette d’essai)

Each test specimen must be mounted to ensure that the load axis and the specimen axis are aligned When securing both ends of the test specimen, care must be taken to avoid applying excessive force and/or bending stress to the specimen The fastening methods are detailed in Appendix A.

CEI 62047-2 standards are recommended for the assembly of test specimens Additionally, it is essential to equip the testing apparatus with a specimen alignment mechanism to ensure that the tensile axis of the test specimen is aligned with the load direction of the testing equipment.

Essai de charge statique

The static tensile test of the test specimen is recommended prior to the fatigue test to establish the testing conditions This static tensile test must be conducted in accordance with the procedures outlined in IEC 62047-2.

Méthode de charge

If the specimen breaks during the first loading cycle, the rupture stress must be recorded and detailed in the report The maximum and minimum forces (or the average force and force range) should remain constant throughout the constant force range test Similarly, the maximum and minimum displacements (or the average displacement and displacement range) must be kept constant during the constant displacement range test.

A load cell with an appropriate resolution is essential to ensure an accuracy of 5% of the applied force Additionally, the drift of the load cell should be less than 1% of the full-scale force during testing Refer to Appendix B for further details.

CEI 62047-2 concernant la précision de la cellule de charge

For the constant displacement range test, a measurement system with suitable resolution must be employed to ensure an accuracy of 5% of the applied displacement Refer to Appendix C for further details.

Vitesse d’essai

Comme la fréquence du cycle de contrainte dépend de l’environnement d’essai, du type de machine d’essai employé, et de la rigidité de l’éprouvette d’essai, la fréquence doit être celle

When selecting the appropriate frequency for testing materials, it is crucial to consider the specific combination of environment, material, specimen, and testing machine Typically, the frequency should be chosen based on the application of thin-layer materials Additionally, it is important to ensure that the frequency does not cause the test specimen to heat up during the application of cyclic loading, as this can lead to rapid energy dissipation in the specimen.

Cette pratique ne s’applique pas à l’essai de fatigue des couches viscoélastiques.

Contrôle de l’environnement

The environment significantly influences the fatigue properties of thin films, making it essential to monitor the testing temperature and humidity during experiments It is recommended to maintain the testing temperature within ±1 °C and the relative humidity within ±5% If controlling these parameters proves challenging, the values should be documented in the test report.

The fatigue test should continue until the test specimen breaks or a predetermined number of cycles has been applied The criteria for termination, whether it be the rupture of the test specimen or the specified number of cycles, must be detailed in the test report.

Le rapport d'essai doit fournir les indications suivantes

• Obligatoires a) la référence à la présente Norme Internationale, c'est-à-dire la CEI 62047-6 b) le matériau de la pièce d’essai

– dans le cas d’un monocristal: l’orientation cristallographique c) la méthode et les détails de fabrication de l’éprouvette

– la méthode de dépôt de couches minces

– les conditions (de recuit) de traitement thermique d) la forme et les dimensions de l’éprouvette d’essai e) les conditions d’essai de fatigue

– la contrainte moyenne (dans le cas de commande de déplacement, de déplacement moyen)

– la gamme de contraintes (dans le cas de commande de déplacement, gamme de déplacements)

– l’environnement d’essai (température et humidité relative)

– la forme d’onde (sinusọdale, triangulaire, rampe)

– la fréquence f) le résultat d’essai de fatigue

The number of cycles applied before failure is crucial If the test specimen does not break within a predetermined number of cycles, it is important to record the cycle count along with the description "no failure."

– la définition (le type) de défaillance

In the case of polycrystalline thin films, key factors include the texture and grain size, internal stress, surface roughness of the test specimen, and a brief description of the fracture characteristics.

Contexte technique de la présente norme

A.1 Signification des essais de fatigue à charge axiale pour les couches minces

MEMS devices are typically fabricated from thin films deposited on a substrate, utilizing micro-machining techniques akin to those used in Large Scale Integration (LSI) processes The microstructure and surface roughness of these thin films are influenced by processing conditions and potential micro/nano defects that can arise during fabrication, which in turn affect their mechanical properties Therefore, it is crucial to measure the mechanical properties of thin films using samples prepared through the same process as the actual applied devices Notably, the fatigue properties of thin films are vital for designing durable and reliable MEMS devices To date, fatigue testing of miniaturized components, including thin films, has been conducted using on-chip test structures and miniaturized specimens However, the lack of standardized methods complicates the comparison of fatigue data across different institutions Currently, ISO 1099 and ASTM E 466-96 provide standardized testing methods for fatigue testing of macroscopic materials Among these, the axial fatigue test method was established first, with extended testing methods, including data processing techniques like S-N curves, specified The axial fatigue test serves as a fundamental method for evaluating material fatigue properties, similar to static load tensile testing Consequently, a general discussion of the fatigue properties of MEMS devices can be initiated by first specifying the method used for axial fatigue testing of thin films.

A.2 Aperỗu des essais inter-laboratoires ( round-robin ) pratiquộs au Japon [10]

La présente norme spécifie la méthode d’essai de fatigue pour force axiale de traction– traction des matériaux en couche mince fondée sur les résultats des essais inter-laboratoires

(RRT, round-robin test) sur l’essai de fatigue axiale des couches minces pratiqué de 2003 à

The RRT was conducted with the collaboration of several universities and research institutes in Japan The materials utilized included thin films of monocrystalline and polycrystalline silicon, as well as polycrystalline aluminum thin films, which were deposited on silicon wafers Microminiaturized specimens were prepared from the thin film on the same wafer in accordance with IEC 62047-2 using a photolithographic technique Each test specimen was designed to fit the specified testing machine, while the dimensions of the parallel parts of each specimen were standardized accordingly.

The CEI 62047-2 standard outlines axial fatigue testing primarily conducted under force control, where load application, force measurement, and displacement measurement were recorded The impact of environmental factors, particularly humidity, on fatigue life was also investigated Results were plotted on S-N curves, and a cross-comparison of fatigue life was performed The validity of the testing method as a standardized approach has been studied and summarized in this standard.

Il convient que la forme et les dimensions de l’éprouvette soient fondées sur la CEI 62047-2

The axial fatigue test condition is defined by the yield strength and the ultimate tensile strength of the specimen It is easier to determine fatigue test conditions when the same specimens are used for tensile testing Notably, the cross-sectional geometry of the test specimen specified in IEC 62047-2 is proportionally reduced compared to that specified in ISO 6892.

When reference marks are placed on the test specimen, the displacement should be measured using the interference of reflected light from the laser-irradiated reference mark, along with the simultaneous detection of both reference marks through a dual-field microscope that displays two distant reference marks If placing the reference marks on the test specimen is challenging or if the distance between them cannot be measured due to high cyclic loading frequency, the displacement of the fixture or actuator may be utilized, but such measurements must be documented in the report.

The testing environment significantly impacts the fatigue life of microminiaturized materials more than that of macroscopic materials due to their larger specific surface area Notably, the fatigue life is largely influenced by humidity during testing Therefore, controlling humidity during fatigue testing is crucial for microminiaturized materials.

In general, fatigue data, including fatigue life and resistance, are widely disseminated, making statistical analysis crucial for estimating fatigue life and resistance For bulk materials, these analyses are specified in ISO 12107 Based on this standard, the number of test specimens can be determined according to the required reliability of the test results However, this standard is limited to the analysis of fatigue data for materials exhibiting homogeneous behavior due to a single fatigue failure mechanism.

Pour des matériaux métalliques en couche mince, la fatigue est habituellement contrôlée par un mécanisme unique et le nombre d’éprouvettes peut être déterminé en se fondant sur l’ISO

However, for thin-film silicon materials, multiple fatigue mechanisms are involved, and the potential fatigue mechanisms have not yet been identified This suggests that the analysis method outlined in ISO 12107 cannot be directly applied to determine the number of test specimens for thin-film silicon materials.