Delamination Of Thin Films Research Articles

Effects of substrate compliance on circular buckle delamination of thin films

The present work analyzes circular delamination buckling in a film/substrate system based on the Von Karman nonlinear plate theory with the consideration of elastic deformation of the substrate. Due to the axisymmetry of circular buckling, the substrate deformation is modeled by coupled springs and the spring compliances are determined from the dimension analysis and finite element calculations. The numerical shooting method is used to solve the nonlinear post-buckling problem. The stress intensity factors, the energy release rate, and the phase angle are given here for a variety of the elastic mismatch between the film and the substrate. The results show that in some cases, the energy release rate can be several times larger than that derived from the widely used clamped edge condition.

Morphologies of expansion ridges of elastic thin films onto a substrate

A model of a thin film elastically attached to a rigid substrate is considered. In the case in which the film expands relative to the substrate and assuming certain nonlinear elastic behavior of the film, expansion ridges may appear, in which the material collapses, and the density is higher on average. By studying numerically this process, the possible morphologies of these collapsed regions are presented. They range from circular spots and straight stripes, to wiggle polygonal patterns and ring-shaped domains. The similarity of some of these results with patterns observed in delamination of thin films and biphase epitaxial growth is emphasized.

Thin film delamination: A discrete dislocation analysis

Interface delamination during indentation of micron-scale ceramic coatings on metal substrates is modeled using discrete dislocation (DD) plasticity to elucidate the relationships between delamination, substrate plasticity, interface adhesion, elastic mismatch, and film thickness. In the DD method, plasticity in the metal substrate occurs directly via the motion of dislocations, which are governed by a set of physically based constitutive rules for nucleation, motion and annihilation. A cohesive law with peak stress σ ^ characterizes the traction–separation response of the metal/ceramic interface. The indenter is a rigid flat punch and plane strain deformation is assumed. A continuum plasticity model of the same problem is studied for comparison. For low interface strengths (e.g. σ ^ < σ y ), DD and continuum plasticity results are quantitatively similar, with delamination being nearly independent of interface strength, and easier for thinner, lower-modulus films. For higher interface strengths ( σ ^ / σ y > 2 ), continuum plasticity predicts no delamination up to very high loads while the DD model shows a smooth increase in the critical indentation force for delamination with increasing interface strength. Tensile delamination in the DD model is driven by the accumulation of dislocations, and their associated high stresses, at the interface upon unloading. The DD model is thus capable of predicting the nucleation of cracks, and its dependence on material parameters, in realms of realistic constitutive behavior and/or small length scales where conventional continuum plasticity fails.

Viscosity Solution of the Hamilton-Jacobi Equation Arising from a Thin Film Blistering Model

The paper deals with a dynamical nonlinear model describing the self-driven delamination of compressed thin films. Some assumptions on the buckled shape allow us to describe the moving boundary of the film by a single Hamilton-Jacobi equation. We prove the existence and uniqueness of a viscosity solution to the associated evolution problem.

3013 繰り返しナノインデンテーションによるコーティング薄膜のはく離(S38 皮膜の磨耗および残留応力特性(2),S38 コーティング材料の皮膜特性とその評価)

The aim of this paper is to evaluate the cyclic interfacial strength by cyclic nanoindentation tests. The specimen used in this study is PET substrate/ITO coatings layered specimen. In this study mono cycle nanoindentation test and 10 cycle nanoindentation were conducted on each load, and these results were compared. From indentation load and displacement curves, we classified those results into 3 types (A-C). These three types relate the maximum loads. After the cyclic indentation, we observed the surface profile by the function of atomic force microscope. On Type A, the deviations were observed on the edge on indentations. On Type B, some elongates were observed in the indentations. In addition the number of elongates increased by repeating nanoindentation. These phenomena can be explained by simple models. In this study, two types of fracture modes are proposed. They are "subsidiary fracture mode" and "buckling mode". From the deviation of indentation load and displacement curve, we proposed the method to estimate the energy used for thin film delamination and the interfacial strength was evaluated. The results are good agreement with the interfacial strength evaluated by peel test.

Control of stress and delamination in single and multi-layer carbon thin films prepared by cathodic arc and RF plasma deposition and implantation

The build-up of intrinsic stress in carbon thin films deposited by vapour deposition is a major cause of delamination. The delamination issue is one of the main reasons preventing wider applications of carbon vapour deposited films. In this work, we studied single and multilayer thin films of carbon and found that under certain deposition conditions, we were able to produce thin films free from delamination. Furthermore, we were able to stop film delaminating by adding a control layer. Two methods were used to deposit the carbon films: (1) filtered cathodic arc deposition with both negative DC and pulsed bias applied to the substrate and (2) RF plasma CVD with negative pulse bias up to 30 kV, 60 Hz, 100 μs. Both single and multilayer structures of carbon with different sp 2 and sp 3 ratios were deposited and it was found that, under controlled conditions, the overall stress was maintained at acceptable levels. Moreover, it was found that an additional control layer stopped ongoing delamination of the film. The structures of these multilayers were studied using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).

Undulatory Delamination of Thin Polymer Films on Gold Surfaces

Using two-dimensional surface plasmon resonance measurements, we have observed the formation of traveling waves in the delamination of thin films of polydimethylsilane (PDMS) exposed to methanol. Films were spin-coated on a gold surface and the methanol was added to the top surface. The stress-induced instability caused by the swelling of the PDMS thin film when its edge is pinned to the gold surface leads to wrinkle formation and propagation at the interface. The periodic pattern is thought to be the result of an Asaro-Tiller-Grinfeld (ATG) instability.

Simulation of the delamination of thin films

We simulate thin film delamination using a lattice springs model. We use this model to construct a phase diagram of different delamination behaviours, produced by varying the compression of the film and also the radius to which local relaxation is allowed to take place about failing bonds. From this we see a progression from laminar and linear behaviours to radial and rounded features as compressive stress is increased. Sinusoidal telephone cord behaviour occurs only at a small range of fairly low stresses, and thin films.

A spectral scheme for the simulation of dynamic mode 3 delamination of thin films

Motivated by recent developments in laser-induced spallation testing of thin film structures, we develop a spectral scheme for the simulation of dynamic failure of thin films. In this first study, we focus on the anti-plane shear (mode 3) loading case. The scheme relies on an exact spectral representation of the elastodynamic solutions in the substrate and in the film, and their combination through interface conditions that involve general cohesive failure and/or frictional contact models. A detailed modal analysis of the response of a single spectral mode is performed to assess the stability and precision of the resulting numerical scheme. A set of dynamic fracture problems involving non-propagating and propagating cracks are simulated to show the ability of the numerical scheme to capture the effect of wave reflection on the near-tip stress and displacement fields, and on the dynamic motion of a crack along the film/substrate interface.

The coupling effect of interfacial adhesion and tensile residual stress on a thin membrane adhered to a flat punch

Adhesion and residual stress play a critical role in the performance and reliability of microdevices, in particular, the cross bridge of RF microswitches. To investigate their combinatorial influences on thin films, an elastic model is constructed for a clamped circular membrane in contact with the planar surface of a rigid cylindrical punch. External force applied to the punch leads to thin film delamination and ultimately ‘pull-off’ at a critical non-zero contact radius. Characteristic trends of the mechanical responses were obtained for fixed load and fixed grips in terms of pull-off force, punch displacement and contact radius. It is shown that when the residual stress falls below a critical threshold that is related to the elastic properties and dimensions of the film, its effect becomes negligible. Simple pull-off methods are suggested to measure the residual stress and adhesion energy. The obtained results have significant implications to various microelectromechanical systems that include contacting surfaces.

Employing Thin Film Failure Mechanisms to Form Templates for Nano-electronics

AbstractRecently, we showed that thin film stresses can be used to form well aligned and complex nanowire structures [1]. Within this approach we used stress to introduce cracks in a thin film. Subsequent vacuum deposition of metal leads to the formation of a metal layer on the thin film and of metal nanowires in the cracks of the film. Removal of the thin film together with the excess metal cover finishes the nanowire fabrication on the substrate. As stress can be intentionally introduced by choosing an appropriate thin film geometry that leads to a stress concentration, the cracks and consequently the nanowires can be well aligned. Meanwhile, we have demonstrated how to form thousands of parallel aligned nanowires, x-and y-junctions or nanowires with macroscopic contacts for sensor applications, simply by applying fracture mechanics in thin films. Christiansen and Gösele called this approach “constructive destruction” in a comment in Nature Materials [2]. This gives a hint how to overcome some problems of the approach, arising from the limits of thin film fracture. A generalization of the fracture approach by being “more destructive” can overcome this limitations. For example, it is difficult to form pairs of parallel wires with a nanometer distance of the pair, but a micrometer separation between the individual pairs. Structures like this are useful for many contact applications including sensor arrays or field effect transistors. As well as thin film fracture, thin film delamination can be well controlled by fracture mechanics. Our latest experiments show that the combination of both, fracture and delamination, forms an ideal shadow mask for vacuum deposition. Cracks with delaminated sides were used as templates for the deposition of pairs of parallel wires consisting out of different materials with only a few 10 nm separation. First, a metal was sputter deposited under an angle of approx. 45° through the delaminated crack, which was used as a shadow mask. Afterwards, a second deposition metal is deposited under the opposite 45° angle with respect to the sample normal, having the crack located in the middle between both deposition sources. The angle, the delamination height and the crack width determine the separation of the nanowire contacts. We present several examples which show how these mechanisms of mechanical failure of thin films can be turned into useful templates for various nanostructures. We will focus here on two thin film systems, that can be easily deposited in every lab. These are wet chemically deposited photo-resist and flash evaporated amorphous carbon. These examples are compared with finite element simulations of the thin film stress with the ANSYS program. Moreover, we show how the delamination cracks can be also used as masks for the removal of material. Channals with a width down to 20 nm produced by ion beam sputtering are shown.

Nanofluidic capillaries produced via femtosecond laser induced delamination of thin thermal oxide films from Si(100) substrates

AbstractHighly selective and repeatable delamination of thermal oxide films from Si(100) substrates has been performed using single and multiple femtosecond laser pulses forming bubbles or blisters. By overlapping the bubbles laterally, tubes or capillaries can be formed with a range of volumes suitable for nanofluidics. By scanning the sample through the laser using an automated translation stage, patterns of tubes with arbitrary complexity can be formed, while the scan velocity can easily control the volume of the tubes. The production time for capillaries in this fashion is considerably less than with other lithographic techniques, while the proximity of the tubes to the underlying silicon substrate yields the possibility for integrated devices. The mechanism responsible for the delamination will be discussed and the optimal laser and sample translation conditions will be presented which provide the most uniform tubes. Atomic force microscopy and optical microscopy of capillaries with a range of volumes will be presented.

Surface-Induced Selective Delamination of Amphiphilic ABA Block Copolymer Thin Films

We demonstrate the unforeseen property of selective adhesion/delamination of amphiphilic block copolymer films in coating hydrophobic and hydrophilic substrates. When spin-coated from THF solutions onto hydrophilic substrates (e.g., glass and O3-treated silicon wafer), amphiphilic poly(oligoethylene glycol methyl ether methacrylate) (POEGMA)-based ABA block copolymers 1 and 2 formed thin films with hydrophobic surfaces. Upon exposure to water, these films undergo a fast rearrangement to a hydrophilic surface before they delaminate from the substrate. In contrast, when deposited on a hydrophobic substrate (e.g., Au, Si, Ag), the same copolymer films do not undergo any surface rearrangement and remain as coherent thin films on the substrate. From contact angle measurements it becomes clear that the delamination is accompanied by a rapid surface rearrangement from a hydrophobic to hydrophilic nature. This rearrangement is not observed for the copolymer over hydrophobic surfaces despite the identical constitu...

Ion irradiation effects on the mechanical stability of compressed metallic thin films

Residual stresses in materials and components such as thin films in microelectromechanical systems are developed during the production process and may drastically limit their functionality and lifetime; their minimization is thus of utmost technical importance. Ion beam irradiation in polycrystalline Mo thin films sputter-deposited on (100) silicon wafer at room temperature has been used to reduce the residual stresses present in the layer and thus to improve the mechanical stability of the film/substrate set. Although a strong reduction of residual stresses in the whole film is evidenced, irradiation affects the film-substrate bond strength; defect creation at the film-substrate interface due to ion implantation induces thin-film delamination.

Sub-critical telephone cord delamination propagation and adhesion measurements

ABSTRACTThin film delamination can occur when the stored elastic energy per unit area in the film due to the residual stress exceeds the interfacial toughness. Telephone cord morphology is commonly observed in delaminating thin films under compressive stresses. Here, the biaxial film stress is partially relieved by film buckling in the direction perpendicular to the telephone cord propagation, and by “secondary” blister buckling in the direction of telephone cord propagation, which results in the sinusoidal fracture patterns.A superlayer indentation test, in which additional stress is supplied to the crack tip using a nanoindenter, can be used to measure the interfacial toughness. Estimates of the energy release rate for diamond-like carbon (DLC) films on magnetic media were obtained using the superlayer indentation test, as well as the delaminated buckling profiles. The results obtained by these two independent methods are in good agreement with each other. We find the average adhesion energy to be 6 J/m2 for DLC films on magnetic media.Normally telephone cord blisters “run out of steam” and stop once the interfacial toughness exceeds the strain energy release rate. It is possible to make blisters propagate further by either putting mechanical energy into the system, or by introducing liquids at the crack tip, thus reducing the film interfacial toughness. Environmental species can assist cracking and contribute to thin film delamination, which is readily observed in vintage mirrors. Crack propagation rates on the order of microns per minute were measured for DLC films in different fluid environments. We identify how telephone cord buckling delamination can be used as a test vehicle for studying crack propagation rates and environmentally assisted cracking in thin films.

In situ observations of the real-time stress-evolution and delamination of thin Ta films on Si(100)

Polycrystalline sputtered Ta coatings on Si(100) substrates were thermally tested for 1 h at 585 °C, while their stress evolution and eventual delamination were observed in situ and in real-time using a recently developed synchrotron X-ray white beam technique. Films deposited at ‘low’ (0.26–0.67 Pa), ‘intermediate’ (0.80–0.93 Pa), and ‘high’ (1.06–2.00 Pa) Ar pressures exhibited severe, moderate, and no blistering, respectively. These results were explained by the attendant stress data, which indicated the development of high, moderate, and low maximum compressive stress in the low, intermediate, and high-pressure coatings, respectively. Additionally, the structure of the films was probed before and after thermal testing using X-ray diffraction in both grazing incidence and θ−2 θ scanning geometries. It was determined that all coatings made a complete conversion to orthorhombic Ta 2O 5 after the 1 h thermal test, regardless of their deposition pressure.

A theoretical and numerical study of thin film delamination using the pull-off test

An accurate closed-form analytical solution for the strain energy release rate for a thin rectangular film loaded by a central line force using the pull-off test is derived in the presence of a tensile residual stress. The theoretical constitutive relation and the strain energy release rate agree very well with two-dimensional nonlinear finite element analysis for the entire deformation regime ranging from bending plate to stretching membrane. Fracture modes for this pull-off test are also investigated based upon the finite element analysis, offering additional insights to the interfacial delamination.

Adhesion of a flat punch adhered to a thin pre-stressed membrane

The mechanics of a circular membrane delaminating from a rigid punch is derived based on linear elasticity and an energy balance approach. Both the tensile prestress and the resulting concomitant stress upon external loading are considered. A "pull-off" phenomenon is predicted when the contact circle shrinks to a critical value between 0.1945 and 0.3679 of the film diameter, depending on the critical strain energy release rate and the prestress. These asymptotic limits match exactly with the prestress dominant model by Shanahan and prestress free model by Wan. Thin film delamination from a rectangular punch is also investigated. Unlike the circular punch, the rectangular contact is expected to reduce to a line contact with zero contact area at "pinch-off." The graphs and trends shown are useful in assessing thin film delamination assisted by a prestress.

Fracture patterns in thin films and multilayers

ABSTRACTWhile there are many stress relief mechanisms observed in thin films, excessive residual and externally applied stresses cause film fracture. In the case of tensile stress a network of through-thickness cracks forms in the film. In the case of compressive stress thin film buckling is observed in the form of blisters. Thin film delamination is an inseparable phenomenon of buckling. The buckling delamination blisters can be either circular, straight, or form periodic buckling patterns commonly known as telephone cord delamination morphology.While excessive biaxial residual stress is the key for causing thin film fracture, either in tension, or compression, it is the influence of the external stress that can control the final fracture pattern. In this paper we consider phone cord buckling delamination observed in compressed W/Si and TiWN/GaAs thin film systems, as well as spiral and sinusoidal though-thickness cracks observed in Mo/Si multilayers under 3-point high-temperature bending in tension.

Length scales for the fracture of nanostructures

Length scales are essential to the understanding of small volume deformation and fracture in emerging technologies. Recent analysis by two groups at the atomistic (Horstmeyer and Baskes, 1999) and mesoscopic (Gerberich et al., 2002) levels have shown the importance of the volume to surface ratio to the indentation size effect (ISE) at small depths of penetration. We have interpreted this in terms of the plastic work under the contact and the surface work associated with the creation of new surface or the excess surface stress. Treating this as a modified Griffith criterion the case is made that this same length scale should apply to the delamination of thin films. By making this simple equivalency in length scales, an R-curve analysis for crack growth resistance, GR ,i n thin film delamination emerges. This recovers the classic σ 2 ysh/E term as well as the fact that interfacial toughness should scale with the square root of incremental crack growth. Here σys is yield strength, h is thickness and E is modulus of the film. As applied to thin Cu and Au films bonded to silicon substrates, the model is in good agreement.