Interfacial Adhesion Energy Research Articles

Effect of surface treatments on interfacial adhesion energy between UV-curable resist and glass wafer

The interfacial adhesion energy between the resist and the substrate is very important in nanoimprinting because of problems with the resist sticking or pulling off during separation of the mold from the substrate. Substrate surface treatments with a self-assembled monolayer or oxygen plasma provide good adhesion between a resist coating and a silica substrate. In this paper, we describe the adhesion properties of a resist and a glass wafer measured using the four-point bending test. The interfacial adhesion energy between the resist and the glass wafer was evaluated for various substrate surface treatments of adhesion promoters and anti-sticking layers. The interfacial fracture energy without treatment was 1.23 J/m 2, and was in the range 0.49–2.57 J/m 2 for the other treatments tested. The interfacial fracture surfaces were also investigated by field emission scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy to determine the fracture mode at the interfaces.

Aluminum Thermo Compression Bonding Characterization

AbstractWafer level bonding is an important technology for the manufacturing of numerous Microelectromechanical Systems. In this work the aluminum thermo-compression wafer bonding is characterized. The effects and significance of various bond process parameters and surface treatment methods are reported on the final bond interfaces integrity and strength. Experimental variables include the bonding temperature, bonding time, and bonding atmosphere (forming gas and inert gas). Bonded wafer samples were investigated with scanning acoustic microscopy, scanning electron microscopy, and four point bending test. Interfacial adhesion energy and bond quality were found to be positively correlated with bonding temperature. A bonding temperature of 500 °C or greater is necessary to obtain bond strengths of 8-10 J/m2.

Effect of Annealing Treatment Conditions on the Interfacial AdhesionEnergy of Electroless-plated Ni on Polyimide

The effect of annealing treatment conditions on the interfacial adhesion energy between electrolessplated Ni film and polyimide substrate was evaluated using a <TEX>$180^{\circ}$</TEX> peel test. Measured peel strength values are <TEX>$26.9{\pm}0.8,\;22.4{\pm}0.8,\;21.9{\pm}1.5,\;23.1{\pm}1.3,\;16.1{\pm}2.0\;and\;14.3{\pm}1.3g/mm$</TEX> for annealing treatment times during 0, 1, 3, 5, 10, and 20 hours, respectively, at <TEX>$200^{\circ}C$</TEX> in ambient environment. XPS and AES analysis results on peeled surfaces clearly reveal that the peeling occurs cohesively inside polyimide. This implies a degradation of polyimide structure due to oxygen diffusion through interface between Ni and polyimide, which is also closely related to the decrease in the interfacial adhesion energy due to thermal treatment in ambient conditions.

Interphase phenomena in nanoparticulate filled polyurethane/poly(vinyl acetate) polymer systems

AbstractPolyurethane (PU) and poly(vinyl acetate) (PVAc) are partially miscible polymers. The aim of this study was to investigate the influence of untreated and surface pretreated calcium carbonate (CaCO3) on the interphase properties of PU/PVAc polymer blends with possible compatibilization effects when the conditions of effective adhesion are achieved. With the aim to modify interface between filler and matrices, CaCO3 was pretreated by grafting PVAc on the filler surface using 60Co γ‐ray irradiation polymerization of vinyl acetate. A series of the PU/PVAc blends without and with the addition of CaCO3 were prepared using a Brabender plasticorder at 140°C. Surface characterization of the PU and PVAc polymers as well as the untreated and surface pretreated CaCO3 fillers was carried out by determination of the surface free energy. The adhesion between CaCO3 and phases in the polymer blends was predicted on the basis of the calculated adhesion parameters (interfacial free energy, spreading coefficient and work of adhesion) obtained from the surface free energy of components. Thermal and mechanical properties were investigated by tensile strength measurements and differential scanning calorimetry (DSC). The adhesion parameters were correlated with the mechanical and thermal properties as well as phase morphology observations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Effect of Ar+ Radiofrequency Plasma Treatment Conditions on the Interfacial Adhesion Energy Between Atomic-Layer-Deposited Al2O3 and Cu Thin Films in Embedded Capacitors

The effects of Ar+ radiofrequency (RF) plasma pretreatment conditions on the interfacial adhesion energy of a Cu/Cr/Al2O3 system were investigated for thin-film capacitors in embedded printed circuit board applications. The interfacial adhesion energy was evaluated from 90 deg peel tests by calculating the plastic deformation energy of peeled metal films from the energy balance relationship during the steady-state peeling process. The interfacial adhesion energy was fivefold higher after RF plasma pretreatment of the surface of 50-nm-thick Al2O3 prepared by atomic layer deposition. Atomic force microscopy, Auger electron spectroscopy, and x-ray photoemission spectroscopy results clearly reveal that this increase can be attributed to both mechanical interlocking and chemical bonding effects.

A novel evaluation method for interfacial adhesion strength in ductile dissimilar materials

The energy of interface adhesion between two elastic–plastic materials was directly evaluated as the mechanical work supplied exclusively to separate the interface. Interface crack extension was simulated by elastic plastic finite element models, where the nodes along the interface in the vicinity of crack tip were divided into two nodes and the nodal forces were gradually decreased to zero. While further plastic deformation takes place in the volume of materials during crack extension, the work done by these nodal forces against mutual displacement of crack surfaces should be consumed on the surfaces and thus equals to the interface adhesion energy. This technique was applied to a copper/polyimide system for flexible printed circuits in accordance with the new experimental results. In comparison to the results obtained by the conventional peel test, this technique yielded far smaller amount of interface energy successfully excluding the energy dissipated with bulk plastic deformation without any insertion of cohesive strip along the interface in the model.

Preparation and mechanical properties of aluminum-doped zinc oxide transparent conducting films

Aluminum-doped zinc oxide transparent conducting films were deposited in this study by magnetron sputtering under different sputtering powers and substrate temperatures. At low sputtering powers and substrate temperatures, the deposited films were constructed by spherical grains. With increasing power and temperature, the grains became facet with an obvious (002) preferred orientation. The crystallinity and grain size of the films increased as well, and consequently the electrical resistivity decreased. By nanoindentation tests, the hardness of the deposited films was measured and found to increase from 8 to 10 GPa with higher sputtering power and substrate temperature because of higher densification and crystallinity. During nanoindentation and nanoscratch tests, interface delamination occurred between the films and substrates, and the interface adhesion energy was accordingly obtained. From the measurement of nanoscratch tests, the adhesion energy was found to be improved from 0.49 to 0.86 or 0.79 J/m2, respectively, with higher sputtering power or substrate temperature because of the deeper penetration, higher densification and easier interface reaction of the deposited films.

Modeling the formation of spontaneous wafer direct bonding under low temperature

Low temperature wafer direct bonding is one of critical technologies in micro/nano fabrication. In this study, a description of interfacial requirements for spontaneous wafer direct bonding under low temperature is proposed. The model relates the occurrence of bonding to interfacial adhesion energy, interfacial nano-topography and elasticity of wafers. Its derivation is based on Johnson–Kendall–Roberts (JKR) theory and a competition between the bonding energy and the deformation of interfacial micro/nano-roughness. The analysis identifies three bonding possibilities, namely spontaneous bonding without voids, spontaneous bonding with voids, and bonding under external pressure with gap or un-bondable. To verify the model, experiments were carried out for silicon wafers with different surface nano-scale roughness.

Effect of plasma treatments on interface adhesion between SiOCH ultra-low- k film and SiCN etch stop layer

The effect of different plasma treatments on the interfacial bonding configurations and adhesion strengths between porous SiOCH ultra-low-dielectric-constant film and SiCN etch stop layer have been investigated in this study. From X-ray photoelectron spectroscopic analyses, interlayer regions of about 10 nm thick with complicated mixing bonds were found at SiOCH/SiCN interfaces. With plasma treatments, especially H 2/NH 3 two-step plasma, a carbon-depletion region of about 30 nm thick with more Si–O related bonds of high binding energy formed at the interface. Furthermore, the adhesion strengths of the SiOCH/SiCN interfaces were measured by nanoscratch and microscratch tests. For the untreated interface, the adhesion energy was obtained as about 0.22 and 0.44 J/m 2 by nanoscratch and microscratch tests, respectively. After plasma treatments, especially the H 2/NH 3 treatment, the interfacial adhesion energy was effectively improved to 0.41 and 0.89 J/m 2 because more Si–O bonds of high binding energy formed at the interfaces.

Effect of Post-Annealing Conditions on Interfacial Adhesion Energy of Cu-Cu Bonding for 3-D IC Integration

m-thick copper films deposited on silicon wafers were successfully bonded at 415 C/25 kN for 40 minutes in a thermo-compression bonding method that did not involve a pre-cleaning or pre-annealing process. The original copper bonding interface disappeared and showed a homogeneous microstructure with few voids at the original bonding interface. Quantitative interfacial adhesion energies were greater than 10.4 J/m as measured via a four-point bending test. Post-bonding annealing at a temperature that was less than 300 C had only a slight effect on the bonding energy, whereas an oxygen environment significantly deteriorated the bonding energy over 400 C. This was most likely due to the fast growth of brittle interfacial oxides. Therefore, the annealing environment and temperature conditions greatly affect the interfacial bonding energy and reliability in Cu-Cu bonded wafer stacks. Key word Adhesion, 3-D Integration, 4-point bending test, Cu-Cu bonding, post annealing

The Role of Polymer/Polymer Miscibility in Interfacial Healing Kinetics and Equilibrium Adhesion Energy: A Universal Approach

Interfacial strengthening of different polymers has a crucial role in blending them into new materials. Healing is one way to strengthen the interface via polymer interdiffusion across and forming new entanglements. In this research work, interfacial healing kinetics and equilibrium adhesion energy of polystyrene and poly(styrene-co-methyl methacrylate) containing different amounts of methyl methacrylate comonomer were studied using asymmetric wedge cleavage test. The results showed higher interfacial adhesion energy and enhanced healing kinetics by raising styrene monomer content of the copolymer. This may be attributed to the degree of segregation, χN, between the joint components. Interfacial healing rate depended on χN to the power –0.1. Interfacial adhesion energy, however, scaled as χN to the power –0.33, where χ is the Flory–Huggins interaction parameter and N is average degree of polymerization of the components. On the other hand, correlation of interfacial adhesion energy (G IC) with the characteristic number of interfacial entanglements (N ent) showed a fairly good agreement with the Cole et al.'s theory. Finally, joint interfacial adhesion energy enhanced with interfacial width divided by the product of mean entanglement length and degree of segregation, χN, irrespective of copolymer composition.

1203 異なる手法により評価された集積回路用銅薄膜配線材料の付着強度(S05-1 ナノ・マイクロ材料の強度・信頼性(1)銅薄膜の強度物性,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Different methods of quantitative evaluation for the interface adhesion between copper and cap layer in integrated circuits were compared. The same interface was subjected to the measurement The mode ratio of interface crack extension was different among those methods. However, by eliminating the influence of plastic deformation, the results showed almost the same value inspective of the methods applied. This suggests that there could be some cases where mode ratio does not have a significant influence on interface adhesion energy.

Interface Chemistry and Adhesion Strength Between Porous SiOCH Low-k Film and SiCN Layers

In this study, the interface chemistry and adhesion strength between a porous extra-low-dielectric-constant film and etch stop layers were investigated with different plasma treatments. An interlayer of thick between the porous film and layers was found to be composed of Si, N, C, and O. The interface was constructed by mixing bonds, including , , , , etc. Under and plasma treatments, a large amount of weak and bonds were broken, and more related bonds of high binding energy formed at the interfaces. Moreover, under the accumulation of sufficient shear stresses around the indented regions during nanoindentation tests, interface delamination between the porous film and layers occurred. The interface adhesion energy between untreated porous film and layers was accordingly measured as . After plasma treatments, especially plasma, the adhesion strength was effectively improved to .

Environmental influence on interface interactions and adhesion of Au/SiO 2

The mode I interfacial adhesion energy for as-deposited Au/SiO 2 was measured using a stressed overlayer test, and ranged from 0.39 ± 0.09 J/m 2 for spontaneous blisters to 0.37 ± 0.17 J/m 2 for indentation-induced blisters. After these films were heated to 100 °C and 300 °C for 1 h, the interfacial fracture energies increased, to 0.9 J/m 2 and 9.9 J/m 2, respectively. This was consistent with Au/SiO 2 films aged over an 8-year period, which had a mode I interfacial fracture energy between 1.2 J/m 2 and 1.9 J/m 2. The blister delamination was monitored over the course of over a year, and exhibited growth after an initial stabilization period. Subsequent testing of delaminations with controlled humidity reproduced this growth mechanism. Changes in interfacial adhesion energies are discussed in light of changes in interfacial chemistry and the exposure of an interfacial crack tip to humidity.

A pressurized blister test model for the interface adhesion of dissimilar elastic–plastic materials

A concept of the interface adhesion energy, Γ 0, has been proposed to characterize the quality of interface adhesion of the elastic–plastic materials system. A geometrically nonlinear finite element analysis of a blister test of an elastic–plastic film bonded to an elastic–plastic substrate has been conducted. The fracture process ahead of the crack tip at the interface between the thin film and the substrate is represented in terms of a built-in cohesive model, for which interface adhesion energy and the peak stress required for separation are basic parameters. Effects on the critical pressure of various influencing parameters are studied. The plastic work in the substrate contributes significantly to the critical pressure. Agreement between modeling prediction and measurement evidences the validity of the proposed concept and the method of extracting the interface adhesion energy.

Physico-chemical and thermodynamic aspects of fibroblastic attachment on RGDS-modified chitosan membranes

In the present study, the cell attachment/spreading behaviour of L929 mouse fibroblasts on chitosan membranes was evaluated by using physico-chemical properties. For this purpose chitosan membranes were prepared and then photochemically modified with the cell adhesive peptide RGDS (Arg-Gly-Asp-Ser). The physico-chemical properties of unmodified (CHI) and RGDS-modified chitosan (CHI-RGDS) membranes were evaluated by calculating surface free energy ( γ sv) and interfacial free energy ( γ sw) values using captive bubble contact angle measurements and harmonic mean equation. The cell attachment experiments were performed both in 10% FBS containing and serum-free media with CHI and CHI-RGDS membranes. Eventually, it was not possible to predict a direct relationship between the change in physico-chemical properties and L929 cell attachment behaviour. The experimental results obtained from cell attachment agree with the theoretical prediction for the free energy of adhesion except for the cell attachment on CHI membrane in serum-free medium. Although a negative interfacial free energy of adhesion was calculated for CHI membrane in serum-free medium (Δ F adh = −2.19 ergs/cm 2), the cell attachment was poor (∼70%) compared to CHI-RGDS (∼90%) and none of the cells were spread on CHI surface to gain a fibroblastic morphology. Negative energy of adhesion was calculated for CHI and CHI-RGDS in 10% FBS medium, in which ∼100% of cells were attached on the membranes correlating with the thermodynamic approach. It can be suggested that, adsorption of serum proteins strongly affected the cell attachment meanwhile the presence of biosignal RGDS molecules triggered the cell spreading in serum medium.

Adhesion energy of Cu/polyimide interface in flexible printed circuits

The adhesion strength of interfaces was evaluated for two Cu/polyimide laminates, which had the same interface but different polyimide film thickness. A new technique was applied to evaluate the bond energy of the interface, where micro scale polyimide film blocks were scratched off from the interface-side surface of the copper film. Energy consumed during plastic deformation was successfully calculated with the help of a numerical simulation for crack extension. Contrary to the results of conventional peel tests which yielded 340 J/m 2 and 580 J/m 2, respectively for the two samples, the interfacial adhesion energy was obtained as 30 J/m 2 and 25 J/m 2 by the new technique.

A constitutive theory of particulate-reinforced viscoelastic materials with partially debonded microvoids

In particulate-reinforced viscoelastic materials, the interfacial debonding between particles and matrix is usually a significant damage mechanism. In this paper, a new theoretical model of constitutive relation for particulate-reinforced viscoelastic materials is proposed. In the new constitutive model, both the reinforced effect of particles and weak effect due to microdamage evolution are taken into account. First, the deformation of a nucleated microvoid due to partially interfacial debonding between a particle and infinite viscoelastic matrix is analyzed in terms of Eshelby’s equivalent inclusion method. Secondly, the porosity of nucleated microvoids is calculated based on the computation of density function of nucleation rate, in which, the size distribution of particles is assumed to be a logarithmic normal function, and the debonding probability of interface between particles and matrix is assumed to obey Weibull’s distribution. Thirdly, a new definition of average stress and average strain for nucleated microvoids is proposed with considering the effect of nucleation time. Based on definition, a new constitutive model is suggested. This new model is consistent with experimental results. Finally, the effects of loading rate, interfacial adhesive energy, geometrical parameters of particles, and relaxation time on the constitutive relation are examined numerically. The simulation results indicate that the increase of loading rate, volume fraction of particles, and relaxation time of matrix not only reinforces the stiffness of composites, but also speeds up the evolution of microdamage. Such a competition mechanism should be taken into account when designing particulate-reinforced composites.

Analyses of interface adhesion between porous SiOCH low-k film and SiCN layers by nanoindentation and nanoscratch tests

In this study, an Si/PEOX/SiCN/SiOCH/SiCN multilayered film stack has been prepared by chemical vapor deposition. The bonding configurations between porous SiOCH film and SiCN etch stop layers have been analyzed by X-ray photoelectron spectroscopy, and the interface adhesion has been investigated by nanoindentation and nanoscratch tests. Elements of Si, C, N, and O constructed an interlayer region of about 10 nm with mixing bonds of Si to C, Si to N and Si to O at the interface between the porous SiOCH film and SiCN layers. During nanoindentation and nanoscratch tests, interface delamination occurred between SiOCH and SiCN layers due to the accumulation of sufficient shear stresses around the indented regions. The interface adhesion energy was accordingly measured as 1.68 J/m 2 by nanoindentation test with an applied load of 30 mN. With higher applied loads, the measured interface adhesion energy decreased. By the nanoscratch test, the interface adhesion energy was measured as about 0.91 J/m 2, lower than that obtained by nanoindentation test due to the mode mixity effect.

Adhesion properties of polymer/silicon interfaces for biological micro-/nanoelectromechanical systems applications

Polymers are used in biological micro-nanoelectromechanical systems (BioMEMS/NEMS) applications due to their desirable mechanical properties, biocompatibility, and reduced cost relative to silicon microfabrication processes. Understanding the interfacial properties of the films that are used in BioMEMS/NEMS serves as a useful tool in obtaining higher device yield and greater mechanical reliability. In this study, polystyrene (PS) and glycidyl-ether-bisphenol-A novolac polymer (SU8) on silicon substrates were investigated. SU8 is a commonly used material in MEMS/NEMS fabrication, while PS is evaluated for its potential use in BioMEMS/NEMS for interaction with biological cells. The aim is to examine the delamination of the interfaces. Nanoindentation was employed on the PS/Si and SU8/Si film systems coated with a thin metallic layer of Cr to facilitate delamination. The interfacial adhesion energy was determined from measuring the size of the resulting delamination and the contact radius. Scale effects were investigated by comparing the behavior of thin and thick PS and SU8 films, where a thickness dependence on the interfacial adhesion energy was observed. In addition to room temperature testing, film delamination experiments were conducted at 50 and 70°C by fitting the nanoindenter with a heating stage in order to study temperature effects. Nanoindentation-induced delamination is demonstrated for microstrips of PS and SU8 and the measured interfacial adhesion energy is compared to those obtained from films.