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Characterization and the reduction of residual stress and its gradient in thin films are important for improving the reliability of microelectromechanical systems (MEMS) devices. This study examined the room-temperature control of the residual stress gradient in sputtered titanium (Ti) films by helium (He) ion implantation. Ti micro-cantilever beam arrays were fabricated by surface micromachining and used to evaluate the residual stress gradient of the film by measuring the tip deflection of the cantilever beams. The as-fabricated Ti cantilever showed downward bending deformation as a result of the negative residual stress gradient in the film. To release the residual stress gradient, helium ions were implanted at various doses and energies into the Ti cantilever before releasing it from the substrate. The residual stress gradient could be controlled effectively by adjusting the implantation conditions. Almost straight Ti micro-cantilever beams with no residual stress gradient were achieved using the optimal implantation condition of He ions with a dose of 2.0 × 1015 at 80 KeV. The effects of He implantation on the surface properties, such as surface roughness and optical reflectance, were also investigated.

Aluminum (Al) thin films are used widely as an electronic material in a variety of applications because of their high conductivity, optical reflectance and low cost. In the present study, helium (He) and nitrogen (N2) ions were implanted in sputter-deposited Al thin films with different doses and energies, and the changes in the film properties, such as the surface roughness, optical reflectance, hardness and Young’s modulus, were investigated. The results showed that the implantation of both ions smooth the surface of Al thin films by decreasing the hillock density, resulting in low global surface roughness. In particular, in the case of He ion implantation, the moderated degradation of optical reflectance was observed compared to the film implanted with nitrogen ion. On the other hand, excessive ion implantation increased the local (short-range) surface roughness, which deteriorated the optical reflectance of the Al films. The continuous stiffness measurement technique in nano-indentation showed that ion implantation increased the hardness near the surface. He ion implantation hardened the surface of the Al thin film, and almost 2 times higher surface hardness was achieved with an ion dose of 1018 ions/cm2 at 40 KeV.

Oxidation-induced stress evolutions in Ta thin films were investigated using ex situ microstructure analyses and in situ wafer curvature measurements. It was revealed that Ta thin films are oxidized to a crystalline TaO2 layer, which is subsequently oxidized to an amorphous tantalum pentoxide (a-Ta2O5) layer. Initial layered oxidation from Ta to TaO2 phases abruptly induces high compressive stress up to about 3.5 GPa with fast diffusion of oxygen through the Ta layer. Subsequently, it is followed by stress relaxation with the oxidation time, which is related to the slow oxidation from TaO2 to Ta2O5 phases. The initial compressive stress originates from the molar volume expansion during the layered formation of TaO2 from the Ta layer, while the relaxation of the compressive stresses is ascribed to the amorphous character of the a-Ta2O5 layer. According to Kissinger's analysis of the stress evolution during an isochronic heating process, the oxygen diffusion process through the a-Ta2O5 layer is the rate-controlling stage in the layered oxidation process of forming a a-Ta2O5/TaO2/Ta multilayer and has an activation energy of about 190.8 kJ/mol.

Nanoindentation studies are carried out on epitaxial ZnO and GaN thin films on (0 0 0 1) sapphire and silicon substrates, respectively. A single discontinuity (‘pop-in’) in the load–indentation depth curve is observed for ZnO and GaN films at a specific depths of 13–16 and 23–26 nm, respectively. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the interaction behavior of the indenter tip with the pre-existing threading dislocations present in the films during mechanical deformation. It is observed that the ‘pop-in’ depth is dependent on lattice mismatch of the epitaxial thin film with the substrate, the higher the lattice mismatch the shallower the critical ‘pop-in’ depth.

Two types of porogens were tested to prepare porous low dielectric films. PCL porogens as well as Tetronic block copolymer porogens generate pores within the films thus lowering the dielectric constant. Tetronic porogens, however, yield porous films without significant matrix-porogen interactions and thus result in higher mechanical properties with lower dielectric constant, when compared with the PCL porogens.

The characteristics, such as deposition rate, microstructure, surface morphology and mechanical properties, of titanium aluminum nitride films synthesized by unbalanced magnetron sputtering (UBMS) and closed-field unbalanced magnetron sputtering (CFUBMS) were compared in this article. TiAlN films were deposited from an alloyed TiAl (50/50 at.%) target at various N 2 partial pressures by two types of magnetron sputtering: (i) the single UBMS and (ii) CFUBMS with four magnetron sources. The deposition rate of TiAlN films produced by CFUBMS with four magnetron sources was increased up to approximately 1.35 times in comparison with that obtained in the single UBMS. The results of AES and XRD analyses revealed that TiAlN films deposited by two types of magnetron sputtering have similar chemical composition and crystal structure as a function of the N 2 partial pressure. However, TEM analysis showed that TiAlN film synthesized by CFUBMS with four magnetron sources has a denser columnar structure and its column width and grain size were increased up to approximately two times compared with film by the single UBMS. In addition, the nanoindentation tests showed that the hardness and elastic modulus of films by CFUBMS have higher values than those of films by the single UBMS. This enhancement in the CFUBMS with four magnetron sources system on the mechanical properties could be attributed to the formation of dense and well-crystallized film by the high-level ion bombardment of growing film.

Dielectric cyclosiloxane bearing polysilsesquioxanes (CS-PSSQs) were prepared by acid catalyzed plymerization using 2,4, 6,8-tetramethyl-2,4,6,8-tetra(trimethoxysilylethyl)cyclotetrasoloxane. The molecular weight, and content of the functional end-groups of the CS-PSSQs were foud to be dependent on the process parameters, such as the molar ratio of water and catalyst to the -OCH 3 group ot the silane monomer, the amount of solvent, and the poly(e-caprolactone) (PCL) content, etc. Based on these CS-PSSQ prepolymers, nanoporous organic/inorganic hybrid thin films were fabricated by spin-coating mixtures of these prepolymers with star-shaped PLC on the silicon substrate, and subsquently heating them at 150 and 250°C for 1 minute each and the at 420°C for 1 hour. A dielectric constant as low as 2.28 was achieved for the nanoporous PCL/CS-PSSQ (3:7 v/v) film, along with low moisture absorption in ambient and water conditions, primarily due to the presence of hydrophobic moieties such as ethylene and methyl groups of the polymer and nano-sized hydrophobic pores inside the matrix, resulting in the film having stable dielectric properties. Moreover, the PCL/CL-PSSQ (3:7 v/v) nanohybrid film revealed a nanoporous structure containing ca. 1.52 nm of average-sized mesopores, as measured bye the N 2 adsorption method. The CS-PSSQ-only film showed high mechanical strenghts having an elastic modulus and hardness of 6.64 and 0.88 GPa, respectively, for the 7500 A thick film and 2.41 and 0.38 GPa, respectively, for the PCL/CS-PSSQ (3:7 v/v) film. In addition, the crack velocity of the CS-PSSQ-only film was foud to be ca. 10 -11 m.s -1 in ambient conditions and and aqueous enviroment, probably due to the enhanced hydrophobicity and mechanical toughness of the incorportated methyl group, siloxane unit and ethylene moieties in the polymer matrix.

This article reports on the mechanical properties enhanced by the variety of Cr content in the nanostructured TiN/CrN coating system. The coatings were synthesized using a closed field unbalanced magnetron sputtering method with separate Ti and Cr targets and characterized in terms of chemical composition, crystal orientation, layer structure and mechanical properties. The nanostructured TiN/CrN coatings synthesized in this work have a range of atomic concentration ratio of X =Cr/(Ti+Cr) from 0.15 to 0.59. The results from high-angle and low-angle XRD analysis show that the coating with X =0.15 is not a multi-layered film but a composite film of a mixed TiN and CrN with a grain size of approximately 16 nm. The hardness ( H ) of coatings was strongly dependent on the value of X and the maximum hardness and plastic deformation resistance ( H 3 / E 2 ) of approximately 41 and 0.36 GPa, respectively, were measured for the coating with X =0.15. These values are 1.6 and 3 times higher than those of the single TiN coating (27 and 0.12 GPa), respectively. Also, the wear resistance was largely increased than that of the single TiN coating. These enhancement of mechanical properties in the coating with X =0.15 could be attributed to the CrN doping effect, which has reduced the TiN grain size.

Several kinds of homogeneous organic-inor- ganic hybrid polymer thin films were designed with im- proved mechanical properties and low dielectric constants (3.0). Novel soluble siloxane-silsesquioxane hybrid poly- mers were synthesized with cyclic and/or cage silane mono- mers, which had triorganosiloxy (R3Si1/2), diorganosiloxane (R2SiO2/2), and organosilsesquioxane (RSiO3/2) moieties with ethylene bridges at the molecular level, by the hydro- lysis and condensation of 2,4,6,8-tetramethyl-2,4,6,8-tetra(t- rimethoxysilylethyl)cyclotetrasiloxane (a cyclic monomer). The electrical properties of these films, including the dielec- tric constant (2.51), leakage current (6.4 10 11 A/cm 2 at 0.5 MV/cm), and breakdown voltage (5.4 MV/cm) were fairly good. Moreover, the mechanical properties of the hy- brid films, including the hardness (7 GPa), modulus (1.2 GPa), and crack-free thickness (2 m), were excellent in comparison with those of previous spin-on-glass materials with low dielectric constants. The excellent mechanical properties were proposed to be due to the high contents of SiOOH groups (30%) and the existence of ethylene bridge and siloxane moieties in the hybrid polymer precursors. In addition, the mechanical properties of the hybrid films were affected by the contents of the cagelike structures. The more cagelike structures a hybrid film contained, the worse its mechanical properties were. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 626 - 634, 2003

By classification, two powder portions, one consisting of coarse particles and the other consisting of fine particles, were separated from a MgO-doped (1000 ppm) commercial-purity Al 2 O 3 powder. Examinations of microstructure evolution during hot pressing showed that extensive abnormal grain growth occurred for the coarse portion. For the fine portion, although there was an indication that grain-size distribution deviated from normal distribution on prolonged hot pressing, such extensive abnormal grain growth did not occur. Extensive abnormal grain growth also occurred when the coarse portion was mixed into a high-purity powder that exhibited no abnormal grain growth alone. Chemical analyses revealed that the coarse portion contained the higher concentration of impurities but lower concentration of magnesium than the fine portion. It was discussed that particle aggregates in the coarse portion might have been responsible for the higher concentration of impurities but lower concentration of magnesium and, thus, for the extensive abnormal grain growth.

We fabricated nanocomposite films comprising multi- walled carbon nanotubes (MWCNTs, diameter 10~40 nm, length > 1 mum) and nanocrystalline copper using a low cost electrochemical method. Owing to pulse deposition with several additives, MWCNTs were well-dispersed in the films through thickness and the nanocomposite films showed a dense structure without any voids. For the purpose of evaluation as a candidate for electronic interconnection, elastic modulus, hardness, electrical resistivity, and thermal conductivity of MWCNT/Cu nanocomposite films were measured using nanoindentation, four probe, and time-domain thermo-reflectance methods. It was found that the mechanical properties were more or less enhanced due to the addition of MWCNTs but electrical and thermal conductivities of nanocomposite films were drastically decreased. Further studies are needed for the application of electroplated MWCNT/Cu nanocomposite films as next generation interconnecting materials of electronic devices.

Micro-tensile properties of hard and soft thin films, TiN and Au, were evaluated by directly measuring tensile strain in film tension using the micro-ESPI(electronic Speckle Pattern Interferometry) technique. Micro-tensile stress-strain curves for these films were obtained and the properties were determined. TiN thin film 1 μm thick and Au films with two different thicknesses (t=0.5 μm and 1 μm) were deposited onto the silicon wafers, respectively, and micro-tensile specimens wide 50, 100 and 200 μm were fabricated using micromachining. In-situ measurement of the micro-tensile strain during tensile loading was carried out using the subsequent strain measurement algorithm and the ESPI system developed in this study. The micro-tensile curves showed that TiN thin film was a linear-elastic material showing no plastic deformation and Au thin film was an elastic-plastic material showing significant plastic flow. Effect of the specimen dimensions on mechanical properties was examined. It was revealed that tensile strengths for both films were slightly increased with increasing specimen width. Furthermore, variations of yielding strengths for the thin film Au with change of the dimension were investigated.