Delamination Of Thin Films Research Articles

Roughening and pinning of interface cracks in shear delamination of thin films

We investigate the roughening of shear cracks running along the interface betweena thin film and a rigid substrate. We demonstrate that short-range correlatedfluctuations of the interface strength lead to self-affine roughening of the crack frontas the driving force (the applied shear stress/stress intensity factor) increasestowards a critical value. We investigate the disorder-induced perturbations of thecrack displacement field and crack energy, and use the results to determine thecrack pinning force and to assess the shape of the critical crack. The analyticalarguments are validated by comparison with simulations of interface cracking.

A three-dimensional finite element analysis of interface delamination in a ductile film/hard substrate system induced by wedge indentation

Interface delamination and arching of a ductile thin film on a hard substrate subject to microwedge indentation were investigated systematically using a three-dimensional finite element method. A traction–separation law was introduced to simulate the cohesion and failure behavior of the interface between the film and the substrate. The effects of the interface strength and the length of the microwedge indenter on the onset and growth of interface delamination and film arching were analyzed. It was shown that a two-dimensional to three-dimensional transition of stress state occurs during indentation, depending on the indenter length and indentation depth. Conditions for using two-dimensional and three-dimensional models were suggested.

The macroscopic delamination of thin films from elastic substrates

The wrinkling and delamination of stiff thin films adhered to a polymer substrate have important applications in "flexible electronics." The resulting periodic structures, when used for circuitry, have remarkable mechanical properties because stretching or twisting of the substrate is mostly accommodated through bending of the film, which minimizes fatigue or fracture. To date, applications in this context have used substrate patterning to create an anisotropic substrate-film adhesion energy, thereby producing a controlled array of delamination "blisters." However, even in the absence of such patterning, blisters appear spontaneously, with a characteristic size. Here, we perform well-controlled experiments at macroscopic scales to study what sets the dimensions of these blisters in terms of the material properties and explain our results by using a combination of scaling and analytical methods. Besides pointing to a method for determining the interfacial toughness, our analysis suggests a number of design guidelines for the thin films used in flexible electronic applications. Crucially, we show that, to avoid the possibility that delamination may cause fatigue damage, the thin film thickness must be greater than a critical value, which we determine.

Cohesive zone modeling of interfacial delamination in PZT thin films

Previous experimental investigations [Shang, F., Kitamura, T., Hirakata, H., Kanno, I., Kotera, H., Terada, K., 2005. Experimental and theoretical investigations of delamination at free edge of interface between piezoelectric thin films on a substrate. International Journal of Solids and Structures 42 (5–6) 1729–1741] have demonstrated that multilayered Cr/PZT/PLT/Pt/Ti thin films deposited on single-crystal silicon substrates are delaminated along the interface between Cr and PZT layers in a brittle manner. This study starts with a model based on the cohesive zone concept and carries out numerical simulations to check the fracture behavior of this interfacial delamination. Three types of cohesive zone models (CZMs) are adopted, including the exponential, bilinear, and trapezoidal models. Characteristic CZM parameters are extracted through comparisons with experimental results. The simulation results show that (i) cohesive strength and work of separation are the dominating parameters in the CZMs; (ii) the bilinear CZM more suitably describes this brittle interfacial delamination; and (iii) in comparison with typical several mm-thick film/coating materials, the fracture energy of this weak Cr/PZT interface is quite low. Our study demonstrates the applicability of CZM in characterizing the interface fracture behavior of film materials with micrometer thicknesses.

822 SEAMによるDLC薄膜のはく離に関する非破壊観察(GS-3 計測・検査(2))

822 SEAMによるDLC薄膜のはく離に関する非破壊観察(GS-3 計測・検査(2))

Finite element crystal plasticity analysis of spherical indentation in bulk single crystals and coatings

The purpose of the present work is to investigate the anisotropy in the contact response of f.c.c and h.c.p single crystals. To this aim, spherical indentation experiments were simulated at a meso-scale, which is relevant to the interpretation of instrumented indentation experiments and micro-hardness tests in bulk single crystals and coatings. Within this framework, both the instrumented indentation load (P)-penetration depth (hs) curves and the pile up or sinking-in patterns developed around the indentation imprint were analyzed. The detailed assessment of plastic zone morphology and plastic strain localization features was also addressed to complete the micro-mechanical analysis of indentation experiments. An important outcome from the present work is the identification of very specific and orientation dependent locations within the film–substrate interface, where plastic strain localizes as indentation proceeds. These findings can be significant on the prediction of delamination and potential failure of coatings and thin films.

Reliability Study of High-Density EBGA Packages Using the Cu Metallized Silicon

The reliability of high-density enhanced ball grid array (EBGA) packages using the eight-layer Cu metallization silicon was discussed. The key failure mechanisms included the die cracking (in the vicinity of the edge) and thin film delamination. It was noticed that the failure was unique to the Cu metallization silicon. The large package body size (45 mm2) and the die size (approximately 15 mm2 ) provided additional manufacturing and reliability challenges. The die-edge defects induced during the wafer sawing process were exhibited to be the culprits of the die cracking and the thin film delamination failures. Additionally, the height of die attach fillets significantly influenced the stresses on the die edge, and the excessive fillet height was found to help extend initial cracks at the edge of the silicon. The results demonstrated the adoption of a dual-step wafer sawing scheme and resin blades would control the defects and reduce the failure rate dramatically. A mixture of low-stress encapsulation and die attach materials would help improve the overall reliability of the packages as well. The solder joint reliability of the package was very robust based on the board-level reliability testing results. The statistical analysis of the test results confirmed that most of the die cracking and thin film delamination failures were early-life failures and random. A good sample screening scheme and the process improvement procedure would help improve the reliability and insure the customer a low failure rate for the lifetime of the product. The predicted reliability of the package met the application life needs for the products with process improvement plans in place.

In situ infrared spectroscopic study of cubic boron nitride thin film delamination

This paper investigates the procedure of cubic boron nitride (cBN) thin film delamination by Fourier-transform infrared (IR) spectroscopy. It finds that the apparent IR absorption peak area near 1380 cm-1 and 1073 cm-1 attributed to the B—N stretching vibration of sp2-bonded BN and the transverse optical phonon of cBN, respectively, increased up to 195% and 175% of the original peak area after film delamination induced compressive stress relaxation. The increase of IR absorption of sp2-bonded BN is found to be non-linear and hysteretic to film delamination, which suggests that the relaxation of the turbostratic BN (tBN) layer from the compressed condition is also hysteretic to film delamination. Moreover, cross-sectional transmission electron microscopic observations revealed that cBN film delamination is possible from near the aBN(amorphous BN)/tBN interface at least for films prepared by plasma-enhanced chemical vapour deposition.

A theoretical study of a thin-film delamination using shaft-loaded blister test: Constitutive relation without delamination

This paper presents exact solutions for nonlinear large deflection of thin circular membrane loaded by a central point force using blister test with two types of boundary conditions and with or without residual stress cases. A comparison with existing solutions is presented, and a geometrically nonlinear finite element analysis (FEA) is conducted to verify our analytical solutions.

1064 nm激光脉冲致光学薄膜分层剥落损伤特性

1064 nm激光脉冲致光学薄膜分层剥落损伤特性

Peel process simulation of sealed polymeric film computational modelling of experimental results

PurposeThe purpose of this paper is to evaluate current simulation capabilities for thin film delamination on the basis of real test data as well as a contribution to its extension in order to partly substitute experimental investigations.Design/methodology/approachThe proposed model consists of a formulation that describes the behaviour of the bulk material and an approach that introduces the film's delamination capability. An implicit finite element framework with a cohesive zone implementation is used and described in detail. The numerical results on the basis of the a priori identified material parameters are related to the experimental work. In order to capture the obvious peel speed dependency of these delamination processes, a viscoelastic cohesive formulation is introduced and compared with a pure separation rate dependent cohesive material in the second part of this contribution.FindingsThe performed numerical simulations show a good approximation of the experimental peel process. The extension in order to take time‐dependent effects into account is required for the simulation of such problems. In contrast with the pure rate‐dependent model, the presented consistent formulation of the cohesive part is able to cover the whole range of observed material phenomena.Research limitations/implicationsOwing to the absence of suitable experimental single mode investigations of the sealed layer, the used cohesive material parameters are identified in relation to the pre‐existing experimental results. Furthermore, the resultant peel force has a constant value due to the assumed homogeneous cohesive material and therefore gives only a mean approximation of the experimental values at this stage of the investigation.Originality/valueThe numerical representation of such a thin film delamination process in relation to real experimental results shows the additional capabilities and the usability of the implicit finite element method with a cohesive zone implementation in a clear and illustrative way. The first proposed cohesive extension based on a rheological model shows the capability to cover the full range of time‐dependent interface layer behaviour.

Thin film delamination study duringin situcompressive testing by scanning micro X-ray diffraction

The delamination patterns result from relaxation phenomenon of high residual compressive stresses in the thin film mainly due to the deposition process and involve the propagation, from an initial buckle, of cracks at the film/substrate interface. They have been extensively investigated in various experimental and theoretical studies [1-4]. However, only a few experimental apparatus have been developed to measure the buckle growth dynamics. In fact, the additional compressive stress can be produced in the adherent thin film by using an experimental apparatus which allows the in-situ observation by AFM of the surface during deformation. Buckling patterns generated during the stress experiments are then described and discussed taking advantage of the high resolution offered by the atomic force microscopy (AFM). It has been observed that buckling structures may evolve from straight-sided wrinkles to either worm-like or varicose patterns when the applied stress is released. The formation of these two structures from the initial straight-sided wrinkles has been characterized. In particular, it has been found that one of the driving forces of delamination is the relaxation of the stresses along the longitudinal axis of the initial wrinkles. In the case of bubbles, the film does not recombine with the substrate; in situ picosecond acoustic experiments [2] would allow studying the adhesion between film and substrates in this region of interest. Finite element simulations have been done in order to investigate the delamination evolution [4]. Confrontations with in situ stress mapping measurements have to be achieved for validating and then improving these simulations.

Numerical simulation of laser-induced thin film delamination

Laser-induced thin film spallation has been developed to be one of the most powerful tools for quantitative measurement of thin film interfacial adhesion. High-energy laser pulse absorption generates stress pulse that can be used to delaminate a thin film–substrate interface. Interfacial strength is obtained from the measured surface motion of the thin film using elastic wave mechanics. Due to the short duration of the stress pulses, the dynamic interfacial debonding process usually happens within nanosecond duration, thus the interfacial strength measurement pertains to the intrinsic adhesion of the interface. In this paper, we performed detailed numerical simulations on various aspects of this experimental technique. Combining with experimental observations, the simulation results provide explanations of various phenomena and insights on the fundamental mechanisms of the laser-induced interface debonding process.

On adhesion energy estimates derived from the pressurized brittle delamination of a flexible thin film

This paper examines the problem of the development of a circular delamination due to pressurization at the interface of a flexible elastic film bonded to an elastic substrate. The analysis takes into consideration the elastic deformations of the thin film that can include pure flexure, flexure with shear deformations or large deflections and the elasticity of the substrate. The paper presents explicit results that could be used to estimate either the adhesion energy of the interface or the size of a blister created during the pressurization.

A Three-Dimensional Viscoelastic Analysis of Thin Film Delamination in a Peninsula Blister Specimen

The objective of this paper is to examine three-dimensional and viscoelastic effects in the peninsula blister test for thin film adhesion, which is considered an effective way to measure the interfacial fracture toughness of bonded thin film structures. As will be demonstrated in this paper, analytical solutions are sometimes inadequate for accurately simulating peninsula blister experiments because linear elastic behavior is assumed in the thin film as well as in the debonding process zone at the interface. For this purpose, a three-dimensional cohesive layer model and corresponding liquid loading simulation algorithm were developed and implemented into an in-house test-bed finite element analysis (FEA) code (NOVA-3D). Features such as three-dimensional mixed-mode debonding, large displacements and rotations, residual stresses in the thin film, and time-dependent (viscoelastic) effects in the thin film were considered. Numerical convergence and a stable debond growth were obtained over a fairly large debond length when suitably refined FEA mesh and liquid volume increment were employed. Detailed benchmark comparisons of the finite element predictions with analytical solutions and experimental results were performed, and good agreement was obtained.

Coarsening model of cavity nucleation and thin film delamination from single-crystalBaTiO3with proton implantation

The layer splitting mechanism of a proton implanted single crystal ferroelectric BaTiO3 thin film layer from its bulk BaTiO3 substrate has been investigated. The single crystal BaTiO3 thin film layer splits as the hydrogen gas diffuses and the internal cavity pressure increases. Ripening mechanism driven by the pressurized hydrogen in the implantation-induced damage zone makes coarsening of the cavities and causes the delamination of the thin layer during the annealing. A unique criterion relation of blister nucleation and evolution has been derived and a simplified debonding criterion is proposed in terms of dimensionless parameters based on the force equilibrium condition. A numerical simulation of two-bubble evolution and delamination of thin film is performed using a finite element method.

Thermal loading of laser induced plasma shockwaves on thin films in nanoparticle removal

Damage concerns, such as substrate/film material alterations, damage, and delamination of thin films, have become a central problem in sub-100 nm particle removal applications. In the laser induced plasma (LIP) removal technique both LIP shockwave and radiation heating are potential sources of thermomechanical damage. The specific objective of current study is to conduct a computational investigation of the LIP shockwave effect on the thermoelastic response of a thin chromium (Cr) film deposited on a quartz substrate and to identify the conditions leading to the onset of plastic film deformations. The experimentally characterized shockwave pressure and temperature (approximated from gas dynamic relations) were prescribed as boundary conditions in the computational analysis. From the shockwave arrival times for different travel distances, the shockwave radius as well as the velocity were obtained as a function of the shockwave propagation time. Radial (and circumferential) stresses, caused by thermal expansion of the Cr film, were most dominant and, hence, of damage concern. It is determined that the resultant temperature rise utilizing a 1064 nm Nd:yttrium-aluminum-garnet (YAG) laser (450 mJ) due to the film-shockwave interactions was not sufficiently high to initiate film and/or substrate damage. No material alteration/damage of the Cr film is predicted due to the temperature and pressure of LIP shockwaves at the firing distance of 2 mm, with a high strain rate gain factor of two (minimum), though damage was observed experimentally for 1064 nm Nd:YAG laser at the pulse energy of 370 mJ. Reported results indicate that the leading cause of observed thin film damage during nanoparticle removal is almost certainly radiation heating from the LIP core.

Modeling the buckling and delamination of thin films

I study numerically the problem of delamination of a thin film elastically attached to a rigid substrate. A nominally flat elastic thin film is modeled using a two-dimensional triangular mesh. Both compression and bending rigidities are included to simulate compression and bending of the film. The film can buckle (i.e., abandon its flat configuration) when enough compressive strain is applied. The buckled configurations of a piece of film with stripe geometry are investigated as a function of the compressive strain. It is found that the stable configuration depends strongly on the applied strain and the Poisson ratio of the film. Next, the film is considered to be attached to a rigid substrate by springs that can break when the detaching force exceeds a threshold value, producing partial delamination of the film. Delamination is induced by a mismatch of the relaxed configurations of film and substrate. The morphology of the delaminated film can be followed and compared with available experimental results as a function of model parameters. ``Telephone-cord,'' polygonal, and ``brainlike'' patterns qualitatively similar to experimentally observed configurations are obtained in different parameter regions. The main control parameters that select the different patterns are the strain mismatch between film and substrate and the degree of in-plane relaxation within the unbuckled regions.

Quantitative Adhesion Measures of Diamond Films Using A Blister Test

Adhesion properties of diamond thin films are essential to their performance in technical applications. To obtain the adhesive strength precisely and quantitatively has been the frontier issue to the related scientists and engineers. In this paper, a new experimental equipment for blister tests was designed purposely and fabricated considering related influencing facts. A free-standing window of diamond thin film with the support of silicon wafer was obtained by the aid of photolithography and anisotropic wet etching technology so as to improve the precision of quantitative adhesion measures of diamond films. The mechanics for calculating the quantitative driving force of blister-induced delamination of diamond thin film is presented, which is on base of intensive modeling and simulation. The laser interferometer measurement with fine solution was used to pick up dynamic signals of diamond thin film bulge deformation in micrometer scale and the relationship demonstration of stress to strain of the diamond thin film was available, as a consequence, the adhesive strength could be obtained precisely and quantitatively by the valid model. The paper confirms the accessibility to precise quantitative adhesion measures of diamond films and the results will be beneficial to wide application of diamond thin films in the related fields.

Guided self-assembly of integrated hollow Bragg waveguides

We describe the fabrication of integrated hollow waveguides through guided self-assembly of straight-sided, thin film delamination buckles within a multilayer system of chalcogenide glass and polymer. The process is based on silver photodoping, which was used to control both the stress and adhesion of the chalcogenide glass films. Straight, curved, crossing, and tapered microchannels were realized in parallel. The channels are cladded by omnidirectional dielectric reflectors designed for low-loss, air-core guiding of light in the 1550-1700 nm wavelength range. Loss as low as ~15 dB/cm was measured for channels of height ~2.5 mum, in good agreement with both an analytical ray optics model and finite difference numerical simulations. The loss is determined mainly by the reflectivity of the cladding mirrors, which is ~0.995 for the as-fabricated devices.