This paper reports the measurement of the mechanical properties of polycrystalline silicon carbide (poly-SiC) thin films using bulk-micromachined diaphragms as test structures. SiC is a high-temperature semiconductor with excellent wear resistanc Silicon bulk-micromachining was used to fabricate the poly-SiC diaphragms. First, 3 um-thick polysilicon films were deposited on 1000Å-thick silicon dioxide layers on 4-inch silicon wafers. Next, 2 um-thick poly-SiC films were grown on the polysilic An interferometrical technique was used to measure the deflection of each diaphragm for a range of applied pressures. Deflections were large, but kept below the elastic limit, which was verified by measuring the flatness of the diaphragms after repeate The extended paper will: (1) describe the test structure fabrication process; (2) detail the acquisition and analysis of the load-deflection data; and (3) evaluate poly-SiC as a structural material for MEMS.

¹ S. Roy, C. Zorman, C. Wu, A. Fleischman, and M. Mehregany, Mater, Res. Soc. Proc. 1997, 444, 81.

Any further development or utilisation of a multilayer in an interconnect system needs a precise identification of it's mechanical limits.

Results obtained by micromechanical tensile tests, performed in a SEM, on different sorts of multilayers, consisting of thin films of Ti, TiN, Al vapour deposited on ductile Ti substrates, will be presented.

The evolution of the damage (cracking and debonding) comes with or without the observation of the crack deviation at weak interfaces, which caused catastrophic debonding in some of the systems.

The results of the experiments, in terms of critical parameters (strains and stresses, cracking distances, material properties) are compared to the prediction of analytical models, which currently assume the elastic response of the layers and perfect bonding. Residual stresses, determined by a x-ray diffraction technique, are considered in the analysis of stress distributions during the cracking of the layers.

Taken together: the in-situ observations, residual stress determinations and the chemical analysis in the cracked zones, permit the identification of weak interfaces in the multilayers.

The mechanical stability of multilayered structures depends on their intrinsic as extrinsic properties. Among them, the thermoelastic properties of the materials consisting the layers, as the deposition conditions, which combined may induce internal stresses; also the microstructural imperfections, which offer sources of damage activation.

For example, contineous or sequential laser irradiations on multilayered mirrors, have shown that the observed damage (cracks, holes with or without debonded layers) starts from localized zones, which show growing imperfections.

With the aim to precise the mechanism which initiates the damage in the structure, we analysed the response to an external stress of multilayered samples, with and without "polluted" interfaces.

The "non polluted" samples correspond to mirror like polished substrates on which were deposited the layers. The "polluted" ones were obtained by the dispersion of fine diamond particles on the polished substrates, before the deposition.

The mechanically damage was induced by pulling the samples in tension in a SEM.

Critical parameters, characterizing the behaviour and describing the damage mechanisms are compared and discussed.

This paper focuses on the correlation of general properties (mechanical and microstructural) of single layers, bilayers and “gradient” layers of W and W© coatings, elaborated by DC reactive magnetron sputtering and their failure mecanisms during scratch test experiments. This study was motivated by the need to understand the elemental mechanical behaviour of single layers to optimise the promising W/W© multilayers.

Main characterisations were: (1) morphology and texture investigated by SEM and XRD (2) internal stresses and hardness and (3) adhesion measurements by means of scratch-test experiments.

Cristallites size of dense and fibrous W© film and columnar pure W layers are estimated. Compressive stresses of -3 GPa are found both in W and W© films deposited on steel substrate. Coatings hardness is found to be independent of the level of residual stress, but mainly correlated to the grain size and morphology of sputtered films. The behaviour of the coatings is investigated in details in terms of adhesion by extensive scratch test experiments. Main trends are the following: columnar W layer don’t exhibit flaking even at high loads, due to stress accomodation by the columnar structure. Significant chips are observed in the dense W© films resulting from the propagation and coalescence of cracks into the brittle material. The intermediate behaviour is observed in multilayer and gradient coatings. In this last case, the W ductile phase damps the propagation of cracks in the W-C film lowering the flaking of the composite. A correlation between film thickness and this behaviour is also discussed.