The mechanical properties of submicron scale columnar zinc structures, with average diameters between 130 and 1060 nm, were characterized by uniaxial microcompression tests. The zinc pillars were fabricated by electron beam lithography and electroplating and were found to be generally single crystalline, with a preferred out-of-plane orientation close to the [0001] directions. Post deformation microstructural analysis suggests that the zinc pillars maintain their single-crystalline structure, but without twin boundary formation. Interestingly, the engineering flow stress results indicate that small-scale zinc structures are insensitive to both strain rate and size.

A novel load–displacement sensing instrument has been designed and fabricated to characterize the fracture properties of brittle thin films at low temperature (approximately −30 °C) and pressure (1.6e-4 Pa) environments. In this study, the instrument was used to investigate the effects of harsh environments on the fracture behaviors of organosilicate glass (OSG) and silicon carbonitride (SiCN) thin films under four-point bend loading. Experimental results showed that the fracture strengths of film stacks are the highest when the environment contains a very low water molecule concentration. This condition can be achieved by purging the testing chamber with pure nitrogen or reducing the chamber pressure to less than 1 Pa. In contrast, cracks propagated readily along OSG/SiCN interfaces when experiments were performed in deionized water. The effects of low temperature (approximately −30 °C) and pressure on thin film fracture were also studied, and the results demonstrated that there is no observed degradation of the OSG fracture properties. X-ray photoelectron spectroscopy (XPS) technique was used to identify the chemical composition of the fracture surfaces.

The effects of ultraviolet (UV) radiation on ultra-low-k dielectric (ULK) thin film fracture toughness were studied. This work discusses both critical and subcritical crack growth behavior under different environments. The critical fracture toughness was measured as a function of applied phase angle by using the four-point bend flexure and mixed-mode double cantilever beam techniques. Results of critical fracture toughness obtained under different loading configurations and phase angles were found to increase with the UV treatment time. In contrast, mode I subcritical fracture toughness thresholds and the crack propagation velocity appeared to be insensitive to UV curing processes. This study revealed that subcritical fracture toughness values reduced with the moisture concentration in the environment.

Integrating porous low-permittivity dielectrics into Cu metallization is one of the strategies to reduce power consumption, signal propagation delays, and crosstalk between interconnects for the next generation of integrated circuits. The porosity and pore structure of these low-k dielectric materials, however, also affect other important material properties in addition to the dielectric constant. In this paper, we investigate the impact of porogen loading on the stiffness and cohesive fracture energy of a series of porous organosilicate glass (OSG) thin films using nanoindentation and the double-cantilever beam (DCB) technique. The OSG films were deposited by plasma-enhanced chemical vapor deposition (PECVD) and had a porosity in the range of 7−45%. We show that the degree of porogen loading during the deposition process changes both the network structure and the porosity of the dielectric, and we resolve the contributions of both effects to the stiffness and fracture energy of the films. The experimental results for stiffness are compared with micromechanical models and finite element calculations. It is demonstrated that the stiffness of the OSG films depends sensitively on their porosity and that considerable improvements in stiffness may be obtained through further optimization of the pore microstructure. The cohesive fracture energy of the films decreases linearly with increasing porosity, consistent with a simple planar through-pore fracture mechanism.

As silicon-based microelectronic devices continue to aggressively scale down in size, traditional BEOL dielectric materials have become obsolete due to their relatively high dielectric constant. Organosilicate glass (OSG) materials have emerged as the predominant choice for intermetal dielectrics in advancing technology nodes. A potential failure mechanism for this class of low-k dielectric films during the manufacturing process is catastrophic fracture due to channel cracking. To improve the mechanical strength and stability of these silicon-based materials, the use of post-deposition curing processes is under evaluation. In this work, the effects of UV curing on the properties of OSG films were characterized. After UV curing, film hardness and elastic modulus are improved, with no change in the residual film stress. The average film density increases linearly as a function of UV exposure time. Channel crack propagation velocities decrease with UV exposure. The improvements in the mechanical properties of OSG films are believed to correlate with the increasing Si-O-Si bond population. Comparisons between post-deposition UV and Electron Beam curing processes are provided.

One of the most common forms of cohesive failure observed in brittle thin film subjected to a tensile residual stress is channel cracking, a fracture mode in which through-film cracks propagate in the film. The crack growth rate depends on intrinsic film properties, residual stress, the presence of reactive species in the environments, and the precise film stack. In this paper, we investigate the effect of various buffer layers sandwiched between a brittle carbon-doped-silicate (CDS) film and a silicon substrate on channel cracking of the CDS film. The results show that channel cracking is enhanced if the buffer layer is more compliant than the silicon substrate. Crack velocity increases with increasing buffer layer thickness and decreasing buffer layer stiffness. This is caused by a reduction of the constraint imposed by the substrate on the film and a commensurate increase in energy release rate. The degree of constraint is characterized experimentally as a function of buffer layer thickness and stiffness, and compared to the results of a simple shear lag model that was proposed previously. The results show that the shear lag model does not accurately predict the effect of the buffer layer.

To improve capacitance delay performance of the advanced back-end-of-line (BEOL) structures, low dielectric constant organosilicate glass (OSG) has emerged as the predominant choice for intermetal insulator. The material has a characteristic tensile residual stress and low fracture toughness. A potential failure mechanism for this class of low-k dielectric films is catastrophic fracture due to channel cracking. During fabrication, channel cracks can also form in a time-dependent manner due to exposure to a particular environmental condition, commonly known as stress-corrosion cracking. Within this work, the environmental impacts of pressure, ambient, temperature, solution pH, and solvents upon the channel cracking of OSG thin films are characterized. Storage under high vacuum conditions and exposure to flowing dry nitrogen gas can significantly lower crack propagation rates. Cracking rates experience little fluctuation as a function of solution pH; however, exposure to aqueous solutions can increase the growth rate by three orders of magnitude.

For 90 nm node devices, the group of materials known as organosilicate glass (OSG) has emerged as the predominant choice for intermetal dielectrics. A potential failure mechanism for this class of low-k dielectric films during the manufacturing process is catastrophic fracture due to channel cracking. The use of an electron beam curing process is being investigated for improvement in the mechanical strength of these silicon-based materials. Within this work, the effects of curing dose (micro-C/cm2) upon the mechanical properties of OSG thin films were characterized. For a set process voltage and current, linear relationships exist between the dose and several mechanical film properties. Channel crack growth velocities were also measured for these cured materials. As the cure dose is increased, the crack growth rate decreases according to a power law relationship. The structural film changes induced by the electron beam cure process are addressed, focusing on their impact upon the mechanical strength of OSG thin films.

One of the most common forms of cohesive failure observed in brittle thin films subjected to a tensile residual stress is channel cracking, a fracture mode in which through-film cracks propagate in the film. The crack growth rate depends on intrinsic film properties, residual stress, the presence of reactive species in the environment, and the precise film stack. In this paper, we investigate the effect of various buffer layers sandwiched between a brittle carbon-doped-silicate (CDS) film and a silicon substrate on channel cracking of the CDS film. The results show that channel cracking is enhanced if the buffer layer is more compliant than the silicon substrate. Crack velocity increases with increasing buffer layer thickness and decreasing buffer layer stiffness. This is caused by a reduction of the constraint imposed by the substrate on the film and a commensurate increase in energy release rate. The degree of constraint is characterized experimentally as a function of buffer layer thickness and stiffness, and compared to the results of a simple shear lag model that was proposed previously.

A new method for making substrate-independent hardness measurements by nanoindentation techniques that applies to soft metallic films on very hard substrates is presented. The primary issue to be addressed is substrate-induced enhancement of indentation pileup and the ways it influences the indentation contact area. On the basis of experimental observations of soft aluminum films deposited on silicon, glass, and sapphire substrates, an empirical relationship was derived that relates the amount of pileup to the contact depth. From this relationship and the associated experimental observations, a method was developed that allows the intrinsic hardness of the film to be estimated, even when the indenter penetrates through the film into the substrate. The method should prove useful for very thin films (<100 nm) in which it is not possible to make measurements at penetration depths small enough to avoid subtrate effects.

The goal of this paper is to investigate the effects of film thickness and the presence of a passivation layer on the mechanical behavior of electroplated Cu thin films. In order to study the effect of passivating layers, freestanding Cu membranes were prepared using standard silicon micromachining techniques. Some of these Cu membranes were passivated by sputter depositing thin Ti films with thicknesses ranging from 20 nm to 50 nm on both sides of the membrane. The effect of film thickness was evaluated by preparing freestanding films with varying thickness but constant microstructure. To that effect, coatings of a given thickness were first vacuum annealed at elevated temperature to stabilize the microstructure. The annealed films were subsequently thinned to various thicknesses by means of chemical mechanical planarization (CMP) and freestanding membranes were prepared both with and without Ti passivation. The stress-strain curves of the freestanding Cu films were evaluated using the bulge test technique. The residual stress and elastic modulus of the film are not affected significantly by the passivation layer. The elastic modulus does not change with film thickness if the microstructure keeps constant. The yield stress increases if the film is passivated. For passivated films, yield stress is proportional to the inverse of the film thickness, which is consistent with the formation of a boundary layer of high dislocation density near the interfaces.

A new experimental technique is developed to measure the fracture toughness of a hard metal thin film deposited on a soft substrate. A pre-crack was fabricated in the thin film by using the advanced focused ion beam (FIB) milling techniques. The crack extension force was generated by means of the indentation sinking-in effect. The effect creates a bending moment and tensile stress on the hard thin film near the indentation, which promotes crack growth. The amount of crack tip blunting prior to the critical failure was measured from the FIB cross-sectioned micrographs. By using the crack tip opening displacement model (CTOD), the fracture toughness of the thin film was calculated. The results show the nickel phosphorus (NiP) thin film fracture toughness is at least 15.0MPa√m. The finite element method (FEM) was used to understand the modes of mixity near the crack tip. The results indicate the crack tip modes of mixity are dominated by the Mode I opening, provided the indentation is sufficiently far from the pre-crack or the indentation depths is small when compared with the film thickness.

Thin film delamination and sub-surface cracking represent important reliability issues for the semiconductor and thin film magnetic hard disk industries. Detecting such defects is often difficult and requires complicated specimen cross-sectioning and imaging. Because the sample preparation process itself may cause crack growth, such a method may be used only as a qualitative tool for defect characterization. In the present work, we introduce an in-situ non-destructive technique for detecting sub-surface cracks by continuously monitoring the contact stiffness while dragging a probe across a smooth surface at an ultra light load. As the probe encounters a sub-surface crack, the local contact stiffness decreases dramatically. The amount of reduction in contact stiffness depends on the crack size and geometry and the position of the crack relative to the surface. Results of the scanning stiffness microscopy experiments conducted on hard carbon and chromium thin films are described and discussed.

Cathodic arc deposition combined with macroparticle filtering of the plasma is an efficient and versatile method for the deposition of amorphous hard carbon films of high quality. The film properties can be tailored over a broad range by varying the energy of the carbon ions incident upon the substrate and upon the growing film by applying a pulsed bias technique. By varying the bias voltage during the deposition process specific properties of the interface, bulk film and top surface layer can be obtained. We report on nanoindentation and transmission electron microscopy studies as well as stress measurements of cathodic-arc amorphous hard carbon films deposited with varied bias voltage. The investigations were performed on multilayers consisting of alternating hard and soft amorphous carbon.