On-chip stress relaxation testing method for freestanding thin film materials

Abstract

A stress relaxation method for freestanding thin films is developed based on an on-chip internal stress actuated microtensile testing set-up. The on-chip test structures are produced using microfabrication techniques involving cleaning, deposition, lithography, and release. After release from the substrate, the test specimens are subjected to uniaxial tension. The applied load decays with the deformation taking place during relaxation. This technique is adapted to strain rates lower than 10(-6)∕s and permits the determination of the strain rate sensitivity of very thin films. The main advantage of the technique is that the relaxation tests are simultaneously performed on thousands of specimens, pre-deformed up to different strain levels, for very long periods of time without monopolizing any external mechanical loading equipment. Proof of concept results are provided for 205-nm-thick sputtered AlSi(0.01) films and for 350-nm-thick evaporated Pd films showing unexpectedly high relaxation at room temperature.

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

“…These testing stages are amenable to in situ TEM characterization by performing the back etching of the wafer under the test specimen, see [354] and also [356,357] for applications to fatigue analysis. A MEMS based testing frame based on a concept of ''on chip'' actuation of elementary tensile testing structures through internal stress has recently been developed and applied to different deformation and fracture investigations of freestanding metallic thin films [358][359][360][361][362]. This method schematically depicted in Fig.…”

On-wafer time-dependent high reproducibility nano-force tensile testing

“…Reports on creep [19][20][21][22][23], time-dependent anelasticity [17,[24][25][26] and plastic deformation recovery [27] in thin metal films exist, though systematic studies into accompanying size-effects are rare [13,[28][29][30][31][32]. From an experimental point of view these studies are highly challenging: not only are high-precision small scale mechanical tests required on a relevant fraction of material, but these tests also require high reproducibility spanning long periods.…”

“…Simple displacement tracking of the gauge end has been done with high resolution displacement measurement techniques e.g. SEM [22], digital image tracking (DIT) of light microscopy images [85][86][87] and Fourier analysis of light microscopy images of displaced periodic structures [88]. Digital image tracking can be applied to both SEM and LM images to yield a precision of << 0.1 pixel [84].…”

On-Chip MEMS-Based Internal Stress Actuated Structures for the Mechanical Testing of Freestanding Thin Film Materials

“…The method is based on two key ideas: (1) the use of the high tensile internal stress present in a silicon nitride beam to deform another specimen beam attached to it owing to the etching of a sacrificial layer, (2) the use of a large number of simple elementary testing structures with different in-plane dimensions so as to extract the complete specimen stressstrain curve instead of building a simple complex stage. This concept has been successfully applied on brittle [11,12] and ductile films [10,11,13,14] with a thickness between 50 and 1000 nm for the characterization of the tensile mechanical response as well as the creep/relaxation behavior [14].…”

“…As a consequence, the stress and strain response does not correspond to the mechanical state directly after the release step but to the mechanical state at the time of the displacement measurement. Similarly, the creep/relaxation behavior can be investigated by monitoring the evolution of the displacement u with time [14].…”