Stress Analysis In Thin Films Research Articles

Residual stress and thermal properties of rubber‐modified epoxy systems for semiconductor package

AbstractThe thermal and mechanical breakage of epoxy coating due to easy cracking, poor toughness, and large residual stress, occurring during curing and thermal aging process, is the key factor responsible for damage of silicon device on semiconductor elements. In this study, modified epoxy resins containing an imide ring and polybutadiene rubber‐modified epoxy resin used as the toughening agents were prepared to investigate the residual stress generated during the curing and thermal aging process. The curing process and the thermal properties of the modified epoxy systems were assessed by differential scanning calorimetry and rotational rheometry, dynamic thermomechanical analysis, thermomechanical analysis, and thermogravimetric analysis. A thin film stress analyzer was used to analyze the changes in thermal stress of the modified epoxy systems during curing and cyclic stress and compared with the data from theoretical calculation. The results show that, with the increase in content of the toughening agent, the toughness of the modified epoxy systems was significantly improved, and the curing and thermal cycle stresses could be simultaneously reduced. Besides, we also envision the extension of the comprehensive evaluation method for residual stress described in this study to enable the modification of epoxy coatings prepared using a toughening agent, in the near future.

Mechanical modeling of metal thin films on elastomers for femtosecond laser patterned interconnects

In this work, we present the mechanical analysis of thin Au/Ti film deposited on elastomer substrate, e.g. Polydimethylsiloxane (PDMS) comparing to samples on Kapton®. After deposition, the metal was patterned by ultrashort (270 femtosecond) pulse laser ablation. Minimizing the thermal damage to the substrate, reducing Heat Affected Zone (HAZ) compared to previously demonstrated laser patterning with longer pulses. One of the major issues in the metallization of thick elastomers is the formation of wrinkles followed by brittle cracks in the metallic thin film during the process, deteriorating the metal lines performance and reliability. Such cracking has not been observed on polyimide. The crack formation was investigated using stress analysis of the metallic-elastomeric system, assuming that cracking appears when the stress in the metal film is exceeding a critical value. A general mechanical model and analysis of a multilayer and multi-material laminated system is presented and applied to the specific case of Au/Ti on PDMS. Using this model, the root cause for the stress development in the metallic film has been investigated.A series of samples had been prepared using various elastomer substrates made of Sylgard 184, Dow Corning PDMS. A series of samples was prepared using different monomer/cross-linker ratios in the range of 1:2 to 1:19 monomer to cross-linker weight percentage ratio. Using the thin film stress analysis, the inner stress between and inside the different layers was calculated. Based on the calculations, we could estimate the specific stress in the metallic film. Using this value, we could choose the right specific materials that would not surpass their critical failure stress. This hypothesis was tested and verified by the failure analysis conducted by optical microscope and scanning electrons microscopy (SEM) secondary electrons (SE) images. We report here on a good correlation between the mechanical analysis predictions and the various samples integrity. Therefore, using that model, we could define a “safe zone”, i.e. for what elastic modulus and Coefficient of Thermal Expansion (CTE) there are no “mud-crack” defects.

Nondestructive separation of residual stress and composition gradients in thin films by angle- and energy-dispersive X-ray diffraction. I. Theoretical concepts

Different X-ray measurement and data evaluation concepts are presented, which allow for residual stress analysis in thin films with pronounced gradients in chemical composition. These gradients lead to a variation in the strain-free lattice parameter a 0 with respect to the film thickness and superimpose the lattice strain induced by the film's inherent stresses. Non-consideration of a 0(z) gradients is shown to lead to considerable errors (`ghost stresses') in the residual stress depth profiles. With the simulated example of a TiC x N1−x film with a pronounced carbon gradient, the first part of this series introduces four approaches, which permit the separation of residual stress and composition depth distributions at different levels of approximation. They are based on lattice spacing depth profile measurements performed in either the sin2ψ mode or the scattering vector mode, or in combinations of these two scanning modes. Depending on the approach used for separating the residual stress and composition gradients, angle- or energy-dispersive diffraction has to be applied, employing monochromatic X-ray sources available in the laboratory or either white high-energy synchrotron radiation or the Bremsstrahlung of conventional X-ray tubes, respectively. The methods introduced here assume a biaxial residual stress state within the film. For a triaxial residual stress state with σ33 ≠ 0, a separation of stress and composition gradients is not straightforward, because an a 0(z) gradient cannot be distinguished from the hydrostatic part of the stress tensor.

Dimensionally stable and light-colored polyimide hybrid reinforced with layered silicate

Light-colored polyimide hybrids with a quaternary alkylammonium modified montmorillonite, Cloisite® 20A (C20A) were successfully synthesized via a solution intercalation method. The structural and morphological features of the PI/C20A hybrids were characterized by Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), field emission scanning electron microscopy (FE-SEM), and spherical aberration correction scanning transmission electron microscope (STEM). The dimensional stabilities were strongly dependent upon the chemical and morphological structures which were influenced by the Cloisite® 20A loading content. A critical Cloisite® 20A concentration was obtained for the evolution of both the structural and physical properties of the PI/C20A hybrids. The dynamic stress behaviors were investigated in situ by using the wafer bending method during thermal imidization of the softbaked PI/C20A hybrid precursor and thermally cured hybrid films using a thin film stress analyzer. The PI/C20A hybrid films exhibited stability at 510 °C, high glass transition and relatively low coefficient of thermal expansion, and an improved solvent resistance capacity. Open image in new window

Norbornene end-capped polyimide for low CTE and low residual stress with changes in the diamine linkages

The effects of norbornene (NE) crosslinking and diamine bridge linkages (ether, sulfone, and trifluoromethyl) on polyimide films were investigated. The purpose of this study was to study the behavior of the NE endcapped polyimide with different diamine bridge linkage structure at elevated temperatures on residual stress and modulus change. 5-Norbornene-2,3-dicarboxylic acid was introduced as the end-capping agent in order to increase the ratio of crosslinking in the structure through reverse Diels-Alder reaction. Wide angle X-ray diffraction (WAXD) was measured to study the relation of d-spacing and structure change of the bridge linkage of polymers through NE crosslinking. Coefficient of thermal expansion (CTE) and residual stress were measured to confirm the loaded stress between the substrate and polymer film through a thin film stress analyzer (TFSA). Storage (e′) and loss modulus (e″) were studied at elevated temperatures to study the relation of bridge linkage mobility of the polyimide at elevated temperature. Open image in new window

개환 복분해 중합을 통한 가교형 폴리이미드 박막의 잔류응력 거동 및 특성 분석

본 연구에서는 미세 전자 소자용 절연박막 및 차세대 플렉시블 디스플레이 기판으로서 사용이 기대되는 폴리이미드(PI)에 개환 복분해 중합(ring-opening metathesis polymerization)이 가능한 환형 말단 캡핑제(end-capping agent)인 cis-1,2,3,6-tetrahydrophthalic anhydride(CDBA)로 사슬 말단에 가교 반응이 된 가교형 폴리이미드를 합성하였다. 말단 캡핑제의 조성비에 따른 가교형 폴리이미드 박막의 잔류응력 거동은 thin film stress analyzer(TFSA)를 이용한 wafer bending mothod로 온도에 따라 연속적인 거동을 in-situ로 측정하였다. 열특성은 시차 주사 열량계(DSC), 열기계 분석기(TMA) 및 열 중량 분석기(TGA)를 이용하여 측정하였고, 광학 특성은 자외선/가시광선 분광광도계(UV-vis)와 색차계(spectrophotometer)를 이용하였으며, 네트워크 구조의 모폴로지(morphology) 변화를 통해 해석하였다. 말단 캡핑제의 조성비가 증가함에 따라 잔류응력은 27.9에서 -1.3 MPa로 초저응력 및 향상된 열 특성을 나타내었으나, 광학 특성은 감소됨을 보였다. 가교형 폴리이미드 박막의 우수한 특성 발현은 고집적도 다층 구조의 안정성 및 신뢰도가 요구되는 분야의 응용성이 확대될 것으로 기대된다. Crosslinked polyimides (PIs) were synthesized by reacting 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFDB) with various ratios of the cross-linkable, end-capping agent cis-1,2,3,6-tetrahydrophthalic anhydride (CDBA) via ring-opening metathesis polymerization. Residual stress behaviors were investigated in-situ during thermal imidization of the crosslinked PI precursors using a thin film stress analyzer (TFSA) by wafer bending method. The thermal properties were investigated via differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA). The optical properties were measured by ultraviolet-visible spectrophotometer (UV-vis) and spectrophotometry. All properties were interpreted with respect to their morphology of crosslinked networks. With increasing the amounts of the end-capping agent, the residual stress decreased from 27.9 to -1.3 MPa, exhibited ultra-low stress and high thermal properties. The minimized residual stress and enhanced thermal properties of the crosslinked PI makes them potential candidates for versatile high-density multi-layer structure applications.

Effects of Misalignment of Parallel Beam Optics on Thin Film Stress Analysis

Collecting reliable data is crucial in the research of residual stresses in thin films using X-ray diffraction. The parallel beam geometry has advantage of reliability compared to focusing beam geometry. Though care must be taken to the alignment. A small alignment error may cause a significant error in the stress value. We will show the sensitivity for the misalignment of the parallel beam optics, discuss requirements on hardware alignment and demonstrate a software correction for the presence of remaining hardware errors.

무색 투명 폴리이미드 박막의 잔류응력 거동 및 특성분석

이무수물인 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride(6FDA)에 bis(3-aminophenyl) sulfone(APS), bis[4-(3-aminophenoxy)-phenyl] sulfone(BAPS), 2,2-bis(4-aminophenyl)-hexafluoropropane(6FPD), 2,2-bis[4-(4-aminophenoxy)-phenyl]hexafluoropropane(6FBAPP), 2,2'-bis(trifluoromethyl)benzidine(TFDB) 및 1,4-phenylenediamine(PDA) 등 6종류의 디아민 단량체를 이용하여 폴리이미드(PI) 박막을 제조하였다. 이들 박막의 잔류응력 거동은 thin film stress analyzer(TFSA)를 이용하여 전구체의 열적 이미드화에 따라 in-situ로 측정하였으며, 모폴로지 변화를 통해 해석하였다. 박막의 분자 배향성 및 질서도에 따라 잔류응력은 23.1에서 12.5MPa의 값을 보였으며, 사슬이 강직할수록 감소하였다. 열 특성은 시차 주사 열량계(DSC), 열 중량 분석기(TGA) 및 열 기계 분석기(TMA)를 이용하여 측정하였고, 광학 특성은 자외선/가시광선 분광광도계(UV-vis)와 색차계를 이용하였다. 제조된 박막의 특성변화는 그 화학구조와 밀접한 관련이 있으며, 잔류응력과 광학 특성은 트레이드-오프(trade-off)됨을 확인할 수 있었다. A series of polyimide (PI) was prepared by reacting 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) as the anhydride and bis(3-aminophenyl) sulfone (APS), bis[4-(3-aminophenoxy)-phenyl] sulfone (BAPS), 2,2-bis(4-aminophenyl)-hexafluoropropane (6FPD), 2,2-bis[4-(4-aminophenoxy)-phenyl]hexafluoropropane (6FBAPP), 2,2'-bis(trifluoromethyl)benzidine (TFDB), or 1,4-phenylenediamine (PDA) as the diamine. Residual stress behaviors were detected in-situ during thermal imidization of the polyimide precursors using a thin film stress analyzer (TFSA), and interpreted with respect to their morphology. According to the molecular orientation and packing order, the residual stress varied from 23.1 to 12.5 MPa, decreased with increasing chain rigidity. The thermal properties of the PI films were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and thermomechanical analysis (TMA). Their optical properties were measured by ultraviolet-visible spectrophotometer (UV-vis), and spectrophotometry. The properties of PI films were found to be strongly dependent upon the morphological structure. However, trade-offs between residual stress and optical properties were identified.

Thermal stress analysis of thin films in the context of generalised thermoelasticity

This study deals with the three-dimensional generalised thermoelasticity based on Lord and Shulman's theory and Green and Lindsay's theory. The fundamental equations which include both theories, are used. The thermoelastic problems for a homogeneous and isotropic film whose surfaces are traction free and subjected to a partial heating are analysed by means of the Laplace and Fourier transforms. The state space approach is used in the transformed domains. The inversion are carried out numerically. The numerical calculations for temperature and stresses are carried out. The influence of the finite velocity of the thermal wave grows as the film thins.

Residual stress and mechanical properties of polyimide thin films

AbstractFour different structure polyimide thin films based on 1,4‐phenylene diamine (PDA) and 4,4′‐oxydianiline (ODA) were synthesized by using two different dianhydrides, pyromellitic dianhydride (PMDA) and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), and their residual stress behavior and mechanical properties were investigated by using a thin film stress analyzer and nanoindentation method. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. The morphological structure of polyimide thin films was characterized by X‐ray diffraction patterns and refractive indices. The residual stress was in the range of −5 to 38 MPa and increased in the following order: PMDA‐PDA < BPDA‐PDA < PMDA‐ODA < BPDA‐ODA. The hardness of the polyimide films increased in the following order: PMDA‐ODA < BPDA‐ODA < PMDA‐PDA < BPDA‐PDA. The PDA‐based polyimide films showed relatively lower residual stress and higher hardness than the corresponding ODA‐based polyimide films. The in‐plane orientation and molecularly ordered phase were enhanced with the increasing order as follows: PMDA‐ODA < BPDA‐ODA < BPDA‐PDA ∼ PMDA‐PDA. The PDA‐based polyimides, having a rigid structure, showed relatively better‐developed morphological structure than the corresponding ODA‐based polyimides. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Non-ambient X-ray diffraction residual stress analysis of thin films: tracing nanosize-related effects on thermoelastic constants and identifying sources of residual stresses

The stress evolutions at non-ambient temperatures in Ni and Pd layers (the thickness of each metal layer was 50 nm) were investigated employingin-situX-ray diffraction measurements in a temperature range between 173 and 523 K. Stress determinations were performed by analysing the X-ray diffraction data according to the sin2ψmethod on the basis of the crystallite group variant. The stress evolution in the Ni layer was correlated with the change of its coherently diffracting domain size and its microstrain with temperature. The advantage of measurements at temperatures below ambient to distinguish the thermal stresses from the effects of stress relaxation and emerging secondary stresses, arising from thermally activated processes (such as grain growth), is highlighted in this work for the first time. The possibility of using thein-situX-ray diffraction stress measurement to obtain coefficients of thermal expansion and thermoelastic slopes of thin films (with nanosized grains) is discussed in detail.

Correlation of residual stress and adhesion on copper by the effect of chemical structure of polyimides for copper‐clad laminates

AbstractBACKROUND: Polyimide films coated on copper are a potential new substrate for fabricating printed circuit boards; however, adhesion between the copper and polyimide films is often poor. The relations between residual stress and adhesion strength according to the development of molecular orientation of polyimide films with different chemical backbone structure coated on copper were studied.RESULTS: The effect of chemical structures on properties including the residual stress and the adhesion strength were widely investigated for four different polyimides. Diamine 4,4′‐oxydianiline (ODA) and dianhydrides 1,2,4,5‐benzenetetracarboxylic dianhydride (PMDA), 4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA) and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) were used to synthesize polyimide. In an attempt to quantify the interaction of thermal mismatch with the polyimide films depending on various structures, residual stress experiments between polyimide film and CuSi wafer were carried out over a range of 25–400 °C using in situ thin film stress analysis. A universal test machine was used to conduct 180° peel test (ASTM D903‐98) of polyimide film from cooper foil. The residual stress on CuSi (100) wafer decreased in the order 6FDA‐ODA > BTDA‐ODA > ODPA‐ODA > PMDA‐ODA, and the interfacial adhesion strength decreased in the order BTDA‐ODA (5 N mm−2) > ODPA‐ODA > PMDA‐ODA > 6FDA‐ODA. The results may suggest that the morphological structure, degree of crystallinity of chain orientation and packing significantly relate to the residual stress and adhesion strength in polyimide films. Wide‐angle X‐ray diffraction was used for characterizing the molecular order and orientation and X‐ray photoelectron spectroscopy was used for the analysis of components on copper after polyimide films were detached to confirm the existence of copper oxide chemical bonding and to measure the binding energy of elements on the copper surface.CONCLUSION: In this research, it is demonstrated that BTDA‐ODA polyimide has a low residual stress to copper, good adhesion property, good thermal property and low dielectric constant. Therefore, BTDA‐ODA would be expected to be a promising candidate for a two‐layer copper‐clad laminate. Copyright © 2007 Society of Chemical Industry

Measurement of Residual Stresses in Thin Films by Two-Dimensional XRD

This paper introduces the recent progress in two-dimensional X-ray diffraction as well as its applications in residual stress analysis in thin films. The stress measurement with twodimensional x-ray diffraction can be done with low incident angle and is not limited to the peaks with high two-theta angles like the conventional method. When residual stresses of thin films are measured, a low incident angle is preferred to maximize the diffraction signals from the thin films surfaces instead of from the substrates and matrix materials. Since one stress measurement at one fixed incident angle is possible, stress gradients in depth can be measured by series of incident angles. Some experimental examples are given to show the stress measurement at low and fixed incident angle.

Synthesis and characterization of new functional poly(urethane‐imide) crosslinked networks

AbstractTo synthesize new functional poly(urethane‐imide) crosslinked networks, soluble polyimide from 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride, 4,4′‐oxydianiline, and maleic anhydride and polyurethane prepolymer from polycaprolactone diol, tolylene 2,4‐diisocyanate and hydroxyl ethyl acrylate were prepared. Poly(urethane‐imide) thin films were finally prepared by the reaction between maleimide end‐capped soluble polyimide (PI) and acrylate end‐capped polyurethane (PU). The effect of polyurethane content on dielectric constant, residual stress, morphology, thermal property, and mechanical property was studied by FTIR, prism coupler, Thin Film Stress Analyzer (TFSA), XRD, TGA, DMTA, and Nano‐indentation. Dielectric constant of poly(urethane‐imide) thin films (2.39–2.45) was lower than that of pure polyimide (2.46). Especially, poly(urethane‐imide) thin films with 50% of PU showed lower dielectric constant than other poly(urethane‐imide) thin films did. Lower residual stress and slope in cooling curve were achieved in higher PU content. Compared to typical polyurethane, poly(urethane‐imide) thin films exhibited better thermal stability due to the presence of the imide groups. The glass transition temperature, modulus, and hardness decreased with increase in the flexible PU content even though elongation and thermal expansion coefficient increased. Finally, poly(urethane‐imide) thin films with low residual stress and dielectric constant, which are strongly affected by the morphological structure, chain mobility, and modulus, can be suggested to apply for electronic devices by variation of PU. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 113–123, 2006

X-ray residual stress analysis in thin films under grazing incidence – basic aspects and applications

Residual stress fields in polycrystalline materials induced by mechanical surface processing or coating often are highly inhomogeneous with respect to depth z below the sample surface. This even applies for thin films, the thickness of which is usually much smaller than the penetration depth t of the X-rays. Therefore, X-ray residual stress analysis in thin films is advantageously performed under grazing diffraction conditions. To avoid erroneous averaging over the film thickness, both the radiation used and the methods applied to analyse the residual stress distributions have to be adapted carefully to the particular situation. In this paper some fundamental aspects concerning the meaning of the X-ray penetration depth for very thin films and the important role of refraction in the generalised non-symmetric case of grazing incidence diffraction are discussed and illustrated by practical examples from different fields in thin film diffraction analysis.

Residual stress analysis of thin films and coatings through XRD 2 experiments

Residual stresses are one of the crucial parameters determining the performances of structural as well as functional materials. In the case of coatings and films, the substrate and the deposition process may determine very high residual stress fields which can affect both performances and surface integrity, since adhesion or cracking resistance can be strongly altered. The accurate and reliable assessment of residual stress is thus mandatory for the evaluation of these materials. In this paper we applied a new approach to evaluate the residual stress by means of the analysis of a single 2D-diffraction image collected by a laboratory X-ray microdiffractometer equipped with an image plate detector. The residual stress in thin films of LaCoO 3 was calculated and correlated to cubic-to-rhombohedral phase transformation.

Diffraction Stress Analysis in Thin Films and Coatings--Problems, Methods and Perspectives

X-ray stress analysis (XSA) at polycrystalline materials is usually a very time-consuming and demanding procedure. This especially applies to thin films and coatings with strong texture and/or steep residual stress gradients, the investigation of whi

220 LCD用大型硝子基板の薄膜応力解析(材料力学IV)

220 LCD用大型硝子基板の薄膜応力解析(材料力学IV)

Rietveld Texture and Stress Analysis of Thin Films by X-Ray Diffraction

Rietveld Texture and Stress Analysis of Thin Films by X-Ray Diffraction

Residual stress in fiber-textured thin films of cubic materials

The effect of fiber texture on the x-ray residual stress analysis in thin films of cubic materials is discussed according to different mechanical models. The x-ray elastic constants (XECs) were calculated from single-crystal elastic constants for Cu, cubic ZrO2, and TiN, in the case of a typical [111] fiber texture with different spread of orientations [expressed by the half-width at half-maximum of the (111) pole figure]. Calculations were performed according to Reuss, Voigt, and Hill models, considering different crystallographic directions in cubic structures, in order to underline the effect of the mechanical anisotropy and fiber texture. The results clearly indicated the dependence of the XECs on the sample tilting angle, with the notable exception of [111] and [200], which were texture oscillation-free directions. Profiting from this condition the residual stress gradient in a fiber-textured TiN thin film deposited on stainless steel was determined by the simultaneous analysis of texture and residual strain for the (111) and (200) reflections. Advantages and limits of the procedure are discussed together with the experimental results.