Low-k dielectrics are currently starting to replace SiO2 in advanced on-chip interconnects. Being low surface energy materials, a major concern for the integration of such dielectrics in Cu damascene processes is given by adhesion failure at the interfaces of the low-k films with cap or liner layers during Chemical Mechanical Polishing (CMP). A cross-comparison between interface fracture energies as measured through four-point bending, CMP experiments and stress fields computed by Finite Element Modeling, shows that it is not possible to predict failures by setting a ‘universal’ threshold on adhesion strength.

In particular, we report on the critical role of CMP –induced shear stress on the onset of interface debonding, and the way the shear load is transmitted to the critical interfaces. The top-down load transmission depends on the position of the weak interfaces, and on the way the intermediate films in the stack can confine such load through their thickness and mechanical (elastic and plastic) properties.

A thin two-component epilayer grown on a solid surface may separate into distinct phases. Sometimes the phases select sizes about 10 nm, and order into an array of stripes or disks. However, the pattern types are limited and the location of the features is not controlled. This paper develops a dynamic model to simulate guided self-assembly. In particular, we look at the effect of surface chemistry on the pattern formation process. The simulations suggest that diverse patterns may be produced by tuning the surface chemistry of a substrate. In addition, the self-assembled features may be anchored at specific locations.

We used an electronic speckle pattern interferometer (ESPI) for nondestructive measurement in-situ displacement fields in microsystems. A four-step phase-shift technique and magnifier with long working distance were adopted to increase displacement resolution to ∼10−2 μm and spatial resolution to ∼2 μm. A thermal vacuum chamber was designed to induce thermal treatments, including annealing. From the identification of the residual-stress-free state, we quantitatively modeled thermal strains/stress fields, relaxation stresses during annealing, and residual stress fields. Thermoelasticity theory was applied to model the relationship between the relaxation stresses and the displacements measured by ESPI during the evolution of the residual-stress-free state. We assessed the surface residual stress fields of indented bulk Cu; a Fe-Ni lead frame of 100 μm width; and 0.5 μm Au film. In the indented Cu, the normal and shear residual stresses around the indented point range from –1.7 GPa to 700 MPa and –800 MPa to 600 MPa, respectively, and the residual stress in the bending area of the Fe-Ni lead frame was estimated at 148 MPa and verified using beam-bending theory. In the Au film, tensile residual stresses are uniformly distributed from 500 MPa to 800 MPa as verified by X-ray diffraction.

Gadolinium-doped ceria (GDC) thin films were grown by pulsed laser ablation on various oxide single crystal substrates including MgO, YSZ, LAO, NGO, and STO with different film-substrate lattice mismatch ratios. The film microstructures were characterized mainly by using electron microscopy. A clear influence of the filmsubstrate lattice mismatch on the film crystallinity has been observed. The GDC films usually exhibit columnar grain growth for a large range of film-substrate lattice mismatch ratios. A cube-on-cube growth of GDC film on MgO has been observed with a surprisingly high lattice mismatch ratio of 28%. The highest film crystallinity is obtained on the LAO substrates under a small compressive strain. This single-crystalline GDC film shows no columnar grain growth but presents a novel directionally-aligned precipitated Gd-rich nanoparticle system, which plays a specific role in relaxing various kinds of strain fields induced during the thin film growth to ensure the film crystallinity.

The deformation behavior of Al and Al-Mg thin films has been studied with the unique experimental approach of in-situ nanoindentation in a transmission electron microscope. This paper concentrates on the role of solute Mg additions in the transfer of plasticity across grain boundaries. The investigated Al alloys were deposited onto a Si substrate as thin films with a thickness of 200–300 nm and Mg concentrations of 0, 1.1, 1.8, 2.6 and 5.0 wt% Mg. The results show that in the Al-Mg alloys, the solutes effectively pin high-angle grain boundaries, while in pure Al considerable grain boundary motion is observed at room temperature. The mobility of low-angle grain boundaries is however not affected by the presence of Mg. In addition, Mg was observed to affect dislocation dynamics in the matrix.

Heteroepitaxial oxide thin films are usually grown on single crystal substrate which offer a similar lattice constant as the target material. In general, there are no substrates that are suitable for film fabrication and have a good lattice matching. In our previous report, we succeeded in fabricating a lattice constant tunable buffer by using a Ba1-xSrxTiO3 / BaTiO3 bilayer structure on SrTiO3. The in-plane lattice constant of the buffer layer can be tuned from 3.91 to 3.99 Å and the lattice constant is determined only by the Ba/Sr ratio in the Ba1-xSrxTiO3 layer. The buffer is suitable for growing both strain-free films and strained films. In this report we demonstrate the use of the lattice constant tunable buffer for strain control in SrRuO3 magnetic thin films. SrRuO3 has a magnetic anisotropy which changes under lattice strain. We show that the easy axis of magnetization is parallel to the film surface under tensile strain on a Ba0.5Sr0.5TiO3 buffer. The easy axis is perpendicular to the surface in compressively strained films. The tensile strain in a film also results in an increase of the ferromagnetic ordering temperature from a bulk value of 160 K to 164 K.

The dimensions of microelectronic devices are constantly being reduced due to the increasing operational demands imposed such as higher working frequencies, higher component density and lower power consumption. This affects the geometrical dimensions of the metallisation, i.e. its width and thickness. The mechanical properties of very thin films are considerably different from those of bulk materials and, also, the deposition method may influence the mechanical behaviour of the components. In order to obtain reliable metallisation it is therefore important to assess accurately the mechanical parameters of the interconnecting lines. As part of designing, developing and manufacturing of a stress micro-sensor there is a need to extract properties useful for performance prediction such as yield stress or creep relaxation behaviour. Part of the data may be obtained by nanoindentation but to have a more complete view, finite element analysis of the indentation cycle has to be employed. In this study nanoindentation testing was carried out at various depths on sputtered and evaporated aluminium layers with different thicknesses deposited on (100) silicon. The loading curves were then simulated by FEA and the results compared to identify the yield properties of the coating. Modelling data for thicker samples closely follows experimental data but for thinner coatings there is a considerable gradient in properties through the film thickness. By incorporating a peak load hold the creep behaviour of the metallization can also be assessed and modelling parameters developed.

A myriad of engineering applications involve contact between two surfaces, which induces localized plastic deformation near the surface asperities. As a generic problem in studying nanometer scale plastic deformation of solid surfaces, a unit process model of dislocation formation near a surface step under contact loading of a flat rigid surface is considered. The driving force on the dislocation is calculated using conservation integrals. The effect of surface adhesion, step size and lattice resistance on the dislocation driving force are analyzed in a continuum dislocation model, while the nucleation process is simulated atomistically. The driving force formula is used for a dislocation nucleation criterion and to get the equilibrium distance traveled by the dislocation away from the surface step. Results of the unit process model show that under a normal contact load dislocations nucleated in certain slip planes can only stay in a thin layer near the surface, while dislocations nucleated along other slip planes easily move away from the surface into the bulk material. The former dislocation is named anti-load dislocation and the latter dislocation is called pro-load dislocation. Embedded atom method (EAM) is utilized to perform the atomistic simulation of the unit-process model. As predicted by the continuum dislocation model, the atomistic simulations also indicate that surface adhesion plays significant role in dislocation nucleation process. Varying the surface adhesion leads to three different regimes of load-deflection instabilities, namely, just dislocation nucleation instability for no adhesive interaction, two distinct surface adhesion and dislocation nucleation instabilities for weak adhesive interaction and a simultaneous surface adhesion and dislocation nucleation instability for strong adhesive interaction. The atomistic simulations provide additional information on dislocation nucleation and growth near the surface steps. The results of dislocation segregation predict existence of a thin tensile-stress layer near the deformed surface and the results on the adhesion effect provides a cold-welding criterion.

In the present study the ion irradiation technique is used to investigate the origin of the stress-field in Mo layers grown by ion beam sputtering. Strain measurements were performed by X- ray Diffraction (XRD) using the sin2ψ method. The evolution of the sin2ψ plots with ion irradiation shows that the usual assumption of a biaxial stress state is not adequate to determine the true stress-free lattice parameter a0 of the film. A new stress model based on a triaxial state of stress, which includes a hydrostatic component linked to point defects induced volume distortions, is derived to interpret the XRD results. For pure Mo films, the obtained a0 parameter is close to the bulk value, while for Mo sublayers in Mo/Ni superlattices, the a0 value is lower due to intermixing between Ni and Mo. These results demonstrate that ion irradiation is a powerful tool for stress relaxation, which allows to obtain additional information on the respective contribution of chemical effects and growth defects to the a0 value.

The finite element method has been routinely used to calculate the image stresses of dislocation segments. When these segments intersect with surfaces, the image stresses at the surfaces diverge singularly. At the presence of these singularities, both convergence and accuracy of using the finite element method need to be examined critically. This article addresses these issues with the aim toward the application of dislocation dynamics simulations in thin films.

Deformation mechanisms of electroplated Cu thin films on TaN/SiO2/Si were investigated by performing isothermal annealing above 200 °C. Stress relaxation behavior during isothermal annealing was analyzed by curve fitting using exponential decay equations. During heating, fast relaxation and subsequent slow relaxation processes were observed. In contrast, during cooling, only slow relaxation process was observed. Among possible mechanisms for stress relaxation, diffusion creep was found to be the most plausible mechanism based on the obtained values of the activation energy. It was suggested that the slow relaxation process observed both in the heating and in the cooling processes was attributed to a grain-boundary diffusion creep. On the other hand, the fast relaxation process observed during heating was attributed to a surface-diffusion controlled mechanism. The surface diffusion mechanism was considered to be characteristic to Cu thin films that did not form stable surface oxide.

Controlling thin-film stress magnitudes and nonuniformities is a persistent and pervasive challenge for applications ranging from the semiconductor industry to nanotechnology. Consequently, the ability to accurately measure the intensity and spatial distribution of film stress is essential for fabrication process optimization. This paper describes novel extensions of the membrane resonance method to characterize in-plane film stress gradients. Arrays of freestanding membrane windows are fabricated by first depositing thin films over a silicon substrate. Back-etching then creates an array of membrane windows which are sequentially resonated with a compatible drive electrode. The technique was used to determine stress uniformity across electron projection lithography masks, which incorporate membrane window arrays. In addition, a procedure is presented for identifying the two principal stresses in individual membranes.

Metallic nanolayered composite materials can exhibit yield strengths one and a half to two times that of the constituents from which they are constructed. However, experimental data frequently show that there is a critical bi-layer period Λ below which the strength no longer increases with decreasing Λ To help understand the origins of this behavior and to guide future design of multilayers, maps of the internal stress and overall tensile macroyield stress are calculated as functions of the volume fractions of the two alternating constituents and bi-layer period, for a given lattice parameter ratio and elastic modulus ratio. Adopted here is a premise suggested by embedded atom simulations of Cu/Nb multilayers and recent experimental work on γ -Ni/γ-Ni3Al multilayers that the overall tensile strength is determined by the applied stress needed to eliminate the compressive bi-axial stress in the alternating layers. The results indicate that indeed, there is a critical bi-layer period below which the strength is independent of bi-layer period. In this regime, multilayer tensile strength is most effectively improved by increasing the stored compressive stress. This is achieved by decreasing the volume fraction of the compressively stressed phase. This manuscript extends previous work by providing closed-form expressions for the macroyield strength of free-standing multilayered thin films.

Pt-IrO2 films, approximately 200 nm thick, were fabricated by co-sputter deposition of Pt and Ir in an Ar-O2 mixture followed by annealing at 700°C in O2 for 4 hours. X-ray photoelectron spectroscopy and x-ray diffraction measurements indicate the presence of IrO2 throughout the thickness of the films. After a thermal cycle in vacuum to 700°C, the room temperature residual stress is significantly lower in the internally oxidized films than in pure Pt films of similar thickness subjected to identical cycling. Initial analysis of the behavior of the films during thermal cycling indicates that the primary cause for the difference in residual stress level is a decrease in the thermoelastic slope associated with the introduction of IrO2.

This study reported a novel method for tuning thin film mechanical properties by means of plasma surface modification. In order to demonstrate the feasibility of this approach, various plasma treatments, including O2, H2, NH3 atmospheres, were implemented to tune the Young's modulus and residual stress of SiO2 film. Without plasma treatment, the static tip deflection of 200μm long SiO2 cantilever was 9.01μm. After treatment with H2, O2, and NH3 plasma, the tip deformation of the treated cantilevers became 10.22μm, 8.28μm, and -6.84μm respectively. The Young's modulus of the SiO2 cantilever without plasma treatment was 76.3GPa. After treated with H2, O2, NH3 plasma, the Young's modului of those treated cantilevers became 70.8 GPa, 74.7 GPa, and 71.4 GPa, respectively. Hence, after H2 and NH3 plasma treatment, the equivalent elastic modulus of SiO2 cantilever could be reduced about 7%.

This paper presents a novel Membrane Deflection Fracture Experiment (MDFE) to investigate the fracture toughness of MEMS and other advanced materials in thin film form. It involves the stretching of freestanding thin-film membranes, in a fixed-fixed configuration, containing pre-existing cracks. The fracture behavior of ultrananocrystalline diamond (UNCD), a material developed at Argonne National Laboratory, is investigated to illustrate the methodology. When the fracture initiates from sharp cracks, produced by indentation, the fracture toughness was found to be 4.7 MPa m1/2. When the fracture initiates from blunt notches with radii about 100 nm, machined by focused ion beam (FIB), the mean value of the apparent fracture toughness was found to be 7.2 MPa m1/2. Comparison of these two values, using the model proposed by Drory et al. [9], provides a correction factor of 2/3, which corresponds to a mean value of ρ/2x=1/2.

ABSTRACT:Detailed finite-element computations and carefully designed indentation creep experiments were carried out in order to establish a robust and systematic method to accurately extract creep properties during indentation creep tests. Finite-element simulations confirmed that, for a power law creep material, the indentation creep strain field is indeed self-similar in a constant-load indentation creep test, except during short transient periods at the initial loading stage and when there is a deformation mechanism change. Self-similar indentation creep leads to a constitutive equation from which the power-law creep exponent, n, the activation energy for creep, Qc and so on can be evaluated robustly. Samples made from an Al-5.3mol%Mg solid solution alloy were tested at temperatures ranging from 573 K to 773 K. The results are in good agreement with those obtained from conventional uniaxial creep tests in the dislocation creep regime.

The transfer of strain between thin film features and the underlying substrate represents an important factor in the performance and reliability of semiconductor devices, particularly as the distances between these structures decrease. In order to characterize the interaction regions produced in the substrate due to strained thin film structures, we employed synchrotron-based x-ray diffraction techniques to map the enhanced diffracted intensity of the single-crystal Si substrate at sub-micron resolution. The dynamic-to-kinematic transition observed in the scattering of x-rays from deformed crystals makes this technique extremely sensitive to the amount of substrate deformation as a function of position. Measurements were conducted on 1 μm thick Ni dots evaporated onto Si (111) substrates and 0.24 μm thick, heteroepitaxially grown SiGe strips of various widths on Si (001). The interaction field resolved by the enhanced Si diffracted intensity in the substrate extended up to 100 times the thickness of these features. Although the boundary of the interaction field varied as a function of feature width, a characteristic curve was generated to describe the decay rate of enhanced Si diffracted intensity when the distance from the feature edge is normalized by a mean interaction distance (MID). The rate of decay of the strain fields predicted by traditional treatments of the mechanical interaction between the thin film and substrate did not correspond to the measured decay rates.

A discrete dislocation dynamics model is developed to establish the equations of motion for three-dimensional interacting dislocation loops in the semiconductor thin film – substrate system. The film is assumed to be an elastic layer and is perfectly bonded with another elastic substrate. Dislocation loops are discretized into segments, each of which is represented by a parametric space curve of specific shape functions and associated degree of freedom. The dislocation stress field is calculated as an essential ingredient in the dislocation dynamics method. Dislocation dynamics and interaction with film surface/interface are simulated.

Nanoindentation is an increasingly used tool to investigate the mechanical properties of very small volumes of material. It is usually a very consistent measure of the elastic response of material and plastic response to point contact loading. Nanoindentation experiments on gold single crystals display tremendous variation in the residual deformation. The depth of penetration, which is vital in hardness determination, can differ by as much as 100%. This large variability of the load-depth data is usually explained by surface differences such as crystal orientation, oxide thic kness, presence of multiple solid phases, or contamination layers. None of these reasons apply to the variation observed in the gold system. The onset of plastic deformation is observed at a stress level on the order of the theoretical yield strength. The difference in depth of penetration is independent of this elastic -plastic transition. This paper reports on attempts to correlate the depth of penetration to surface feature size and surface preparation procedures.