Jpm Johan Hoefnagels

Stretching-induced interconnect delamination in stretchable electronic circuits

Stretchable electronics offer increased design freedom of electronic products. Typically, small rigid semiconductor islands are interconnected with thin metal conductor lines on top of, or encapsulated in, a highly compliant substrate, such as a rubber material. A key requirement is large stretchability, i.e. the ability to withstand large deformations during usage without any loss of functionality. Stretching-induced delamination is one of the major failure modes that determines the amount of stretchability that can be achieved for a given interconnect design. During peel testing, performed to characterize the interface behaviour, the rubber is severely lifted at the delamination front while at the same time fibrillation of the rubber at the peel front is observed by ESEM analyses. The interface properties are established by combining the results of numerical simulations and peeling experiments at two distinct scales: the global force–displacement curves and local rubber lift geometries. The thus quantified parameters are used to predict the delamination behaviour of zigzag- and horseshoe-patterned interconnect structures. The accuracy of these finite element simulations is assessed by a comparison of the calculated evolution of the shape of the interconnect structures and the fibrillation areas during stretching with experimental results obtained by detailed in situ analyses.

Cavity ring down study of the densities and kinetics of Si and SiH in a remote Ar-H2-SiH4 plasma

Cavity ring down absorption spectroscopy is applied for the detection of Si and SiH radicals in a remote Ar-H2-SiH4 plasma used for high rate deposition of device quality hydrogenated amorphous silicon (a-Si:H). The formation and loss mechanisms of SiH in the plasma are investigated and the relevant plasma chemistry is discussed using a simple one-dimensional model. From the rotational temperature of SiH typical gas temperatures of ∼1500 K are deduced for the plasma, whereas total ground state densities in the range of 1015–1016 m−3 for Si and 1016–1017 m−3 for SiH are observed. It is demonstrated that both Si and SiH have only a minor contribution to a-Si:H film growth of ∼0.2% and ∼2%, respectively. From the reaction mechanisms in combination with optical emission spectroscopy data, it is concluded that Si and SiH radicals initiate the formation of hydrogen deficient polysilane radicals. In this respect, Si and SiH can still have an important effect on the a-Si:H film quality under certain circumstances.

Cavity ring down detection of SiH3 in a remote SiH4 plasma and comparison with model calculations and mass spectrometry

Spatially resolved SiH3 measurements are performed by cavity ring down spectroscopy on the SiH3 A2 A1←X2 A1 transition at 217 nm in a remote Ar–H2–SiH4 plasma used for high rate deposition of hydrogenated amorphous silicon. The obtained densities of SiH3 and its axial and radial distribution in the cylindrical deposition reactor are compared with simulations by a two-dimensional axisymmetric fluid dynamics model. The model, in which only three basic chemical reactions are taken into account, shows fairly good agreement with the experimental results and the plasma and surface processes as well as transport phenomena in the plasma are discussed. Furthermore, the SiH3 density determined by cavity ring down spectroscopy is in good agreement with the SiH3 density as obtained by threshold ionization mass spectrometry.

Time-resolved cavity ringdown study of the Si and SiH3 surface reaction probability during plasma deposition of a-Si:H at different substrate temperatures

Time-resolved cavity ringdown spectroscopy (τ-CRDS) has been applied to determine the surface reaction probability β of Si and SiH3 radicals during plasma deposition of hydrogenated amorphous silicon (a-Si:H). In an innovative approach, our remote Ar-H2-SiH4 plasma is modulated by applying pulsed rf power to the substrate and the resulting time-dependent radical densities are monitored to yield the radical loss rates. It is demonstrated that the loss rates obtained with this τ-CRDS technique equal the loss rates in the undisturbed plasma and the determination of the gas phase reaction rates of Si and SiH3 as well as their surface reaction probability β is discussed in detail. It is shown that Si is mainly lost in the gas phase to SiH4 [reaction rate kr=(3.0±0.6)×10−16m3s−1], while the probability for Si to react at an a-Si:H surface is 0.95<βSi<1 for a substrate temperature of 200°C. SiH3 is only lost in reactions with the surface and measurements of β of SiH3 for substrate temperatures in the range of 50...

Improvement of hydrogenated amorphous silicon properties with increasing contribution of SiH3 to film growth

From cavity ring down spectroscopy and threshold ionization mass spectrometry measurements in a remote Ar–H2–SiH4 plasma it is clearly demonstrated that the properties of hydrogenated amorphous silicon (a-Si:H) strongly improve with increasing contribution of SiH3 to film growth. The measurements corroborate the proposed dissociation reactions of SiH4 for different plasma settings and it is shown that film growth is by far dominated by SiH3 under conditions for which solar grade quality a-Si:H at deposition rates up to 10 nm/s has previously been reported.

Time-resolved cavity ring-down spectroscopic study of the gas phase and surface loss rates of Si and SiH3 plasma radicals

Abstract Time-resolved cavity ring-down spectroscopy (CRDS) has been applied to determine gas phase and surface loss rates of Si and SiH 3 radicals during plasma deposition of hydrogenated amorphous silicon. This has been done by monitoring the temporal decay of the radicals densities as initiated by a minor periodic modulation applied to a remote SiH 4 plasma. From pressure dependence, it is shown that Si is reactive with SiH 4 [(1.4±0.6)×10 −16 m −3 s −1 reaction rate constant], while SiH 3 is unreactive in the gas phase. A surface reaction probability β of 0.9 β ⩽1 and β =0.30±0.05 has been obtained for Si and SiH 3 , respectively.

Measuring time-dependent deformations in metallic MEMS

The reliability of metallic microelectromechanical systems (MEMS) depends on time-dependent deformation such as creep. Key to this process is the interaction between microstructural length scales and dimensional length scales, so-called size-effects. As a first critical step towards studying these size-effects in time-dependent deformation, a purely mechanical experimental methodology has been developed, which is presented here. The methodology entails the application of a constant deflection to a lm-sized free-standing aluminum-alloy cantilever beam for a prolonged period of time. After this load is removed, the deformation evolution is immediately recorded by acquiring surface topographies through confocal optical profilometry. Image correlation and an algorithm based on elastic beam theory are applied to the full-field beam profiles to correct drift and improve limited optical profilometry precision, yielding the tip deflection as function of time with a precision of 7% of the surface roughness. A proof-of-principle measurement reveals a remarkable time-dependent deflection recovery. Assumptions and errors of the methodology are analyzed. Finally, it is concluded that the methodology is most suitable for the investigation of creep due to the simplicity of specimen handling, preparation and setup design, while maximizing long term stability and deformation precision.

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

Time-dependent mechanical investigations of on-wafer specimens are of interest for improving the reliability of thin metal film microdevices. This paper presents a novel methodology, addressing key challenges in creep and anelasticity investigations through on-wafer tensile tests, achieving highly reproducible force and specimen deformation measurements and loading states. The methodology consists of a novel approach for precise loading using a pin-in-hole gripper and a high-precision specimen alignment system based on three-dimensional image tracking and optical profilometry resulting in angular alignment of?<0.1?mrad and near-perfect co-linearity. A compact test system enables in situ tensile tests of on-wafer specimens under light and electron microscopy. Precision force measurement over a range of 0.07??N to 250?mN is realized based on a simple drift-compensated elastically-hinged load cell with high-precision deflection measurement. The specimen deformation measurement, compensated for drift through image tracking, yields displacement reproducibility of?<6?nm. Proof of principle tensile experiments are performed on 5??m-thick aluminum-alloy thin film specimens, demonstrating reproducible Young?s modulus measurement of 72.6???3.7?GPa. Room temperature creep experiments show excellent stability of the force measurement and underline the methodology?s high reproducibility and suitability for time-dependent nano-force tensile testing of on-wafer specimens.

Characterization of time-dependent anelastic microbeam bending mechanics

This paper presents an accurate yet straightforward methodology for characterizing time-dependent anelastic mechanics of thin metal films employed in metalic microelectromechanical systems (MEMS). The deflection of microbeams is controlled with a mechanical micro-clamp, measured with digital holographic microscopy and processed with global digital image correlation (GDIC). The GDIC processing directly incorporates kinematics into the three-dimensional correlation problem, describing drift-induced rigid body motion and the beam deflection. This yields beam curvature measurements with a resolution of <1.5???10?6??m?1, or for films thinner than 5??m, a strain resolution of <4???. Using a simple experimental sequence, these curvature measurements are then combined with a linear multi-mode time-dependent anelastic model and a priori knowledge of the Youngs modulus. This allows the characterization of the material behaviour in the absence of an additional explicit force measurement, which simplifies the experimental setup. Using this methodology we characterize the anelasticity of 5??m-thick Al(1?wt%)-Cu microbeams of varying microstructures over relevant timescales of 1 to 1???105?s and adequately predict the time and amplitude response of experiments performed for various loading conditions. This demonstrates the validity of the methodology and the suitability for thin film mechanics research for MEMS development.

An in-situ experimental-numerical approach for interface delamination characterization

Interfacial delamination is a key reliability challenge in composites and micro-electronic systems due to (high density) integration of dissimilar materials. Predictive finite element models are used during the design and optimization stage to minimize delamination failures, however, they requires a relevant interface model to capture the (irreversible) crack initiation and propagation behavior observed in experiments. Therefore, a set of experimental-numerical tools is presented to enable accurate characterization of delamination mechanism(s) and prediction of the interface mechanics. First, a novel Miniature Mixed Mode Bending (MMMB) delamination setup is presented that enables in-situ SEM characterization of interface delamination mechanisms while sensitively measuring global load-displacement curves for the full range of mode mixities. Accurate determination of the critical energy release rate from the global load-displacement curve requires, however, identification and separation of bulk plastic contributions from the measured total energy dissipation; to this end, an analytical procedure is presented. Finally, a cohesive zone model suitable for mixed mode loading with realistic coupling is presented that can capture the range of interface failure mechanisms from damage to plasticity, as observed in-situ with SEM, as well as a parameter identification procedure. The set of experimental-numerical tools is validated on delamination measurements of a glue interface.