In recent studies, we used the Interfacial Force Microscope in a nanoindenter mode to survey the nanomechanical properties of Au films grown on various substrates. Quantitative tabulations of the indentation modulus and the maximum shear stress at the plastic threshold showed consistent values over individual samples but a wide variation from substrate to substrate. These values were compared with film properties such as the surface roughness, average grain size and interfacial adhesion and no correlation was found. However, in a subsequent analysis of the the results, we found consistencies which support the integrity of the data and point to the fact that the results are sensitive to some property of the various film/substrate combinations. In the present paper, we discuss these consistencies and show recent measurements which strongly suggest that the property that is being probed is the residual stress in the films caused by their interaction with the substrate surfaces.

We have used grazing incidence x-ray diffraction to observe the structural evolution during growth of sputter-deposited epitaxial Fe films on Cu(001) and Pt(001). We find that on Cu(001), Fe is fcc up to a thickness of 10–12 monolayers, whereupon bcc Fe is observed in first the Pitsch and then the Bain orientations. The fcc Fe shows some relaxation of the misfit from the Cu, as do the Pitsch orientation bcc, which is in tension, and the Bain orientation bcc, which is in compression. All three Fe variants exist in a 40 monolayer thick film. On Pt(001) the Fe grows as bcc with the Bain orientation. However, a thin (20 å) bcc Fe film is transformed to fcc Fe with cube-on-cube orientation by subsequent deposition of Pt. This behavior is consistent with intermixing of Pt into the Fe layer, which lowers the mismatch and bulk chemical energies of the fcc phase relative to that of the bcc phase.

The mechanical properties are thought to play an important role in the performance of metallization materials for very large scale integration (VLSI) applications. From recent investigations on bulk materials it is known that Al-Si-Ge alloys can be very efficiently strengthened with only a small amount of the alloying elements. These alloys are potential candidates for future metallizations both because Si and Ge are compatible with the existing semiconductor technology, and because the resistivity is expected to be low.

We present the first results of detailed characterizations of Al-Si-Ge thin films as a function of sputter conditions and heat treatments. The microstructure was characterized using x-ray diffraction and transmission electron microscopy. The kinetics of precipitation were studied using resistance measurements. Room temperature hardness was investigated using nanoindentation, and the mechanical properties at temperatures up to 240°C were examined using a substrate curvature method. The correlation between precipitate structure and film properties is discussed.

With the development of microelectromechanical systems there is a need for stronger aluminum thin films that resist stress relaxation. A number of strengthening mechanisms are used extensively for bulk aluminum alloys, but very few have been used to improve the performance of thin films. Pure aluminum, standard microelectronicsmetallization (A1-.04Cu-.017Si), alloy T201 (Al-.046Cu-.006Ag-.004Mn-.003Mg-.003Ti), and alloy 2090 (Al-.026Cu-.021Li-.001Zr) were electron beam evaporated or sputter deposited onto (100) silicon substrates.. Stress versus temperature and stress relaxation were measured in the films. Pure aluminum and AlSiCu alloy films exhibited plastic deformation at low stresses and low temperatures. The T201 and 2090 films exhibited residual elastic stresses at room temperature of 350 MPa and 500 MPa, and did not plastically deform until 240°C at 100 MPa stress, or 270°C at 200 MPa stress, respectively. The T201 film also showed a low stress relaxation rate. We speculate that solid solution strengthening caused the increase in strength of the T201 film, and that age hardening caused the increase in strength of the 2090 film.

The mechanical behavior of the metal film on a polymer substrate becomes an important issue in microelectronics metallization. The metal/polymer structure is also useful to investigate the deformation behavior of very thin free-standing metal film since the flexible polymer serves as a deformable substrate. The tensile force-elongation curves have been measured using a microtensile tester for aluminum thin films, deposited on a PMDA-ODA polyimide film, in the thickness range from 60 rum to 480 nm. The stress-strain curves for aluminum films were constructed by subtracting these curves with polyimide curves measured separately. Tensile strength increases linearly with decreasing film thickness from 196 MPa to 408 MPa within the film thickness range studied. This is in good agreement with the published data for free-standing aluminum films in the same thickness range. The measured Young's modulus is lower than the bulk modulus and exhibits no systematic dependence on the film thickness. The microstructures of aluminum films have been examined using a transmission electron microscope (TEM). These films posses the (111)-textured columnar grain structures. Grain sizes exhibit log-normal distributions and the mean grain size increases monotonically with the film thickness. An attempt is made to evaluate the effect of film thickness and grain size on the strength of aluminum thin film and the result is discussed.

We have grown cathode-mounted amorphous hydrogenated boron carbide thin films by rf plasma decomposition of diborane and methane. The chemical composition, infrared absorption, optical absorption, microhardness and adhesion of these thin films were measured. As a function of increasing diborane concentration in the feedstock, we observe increasing boron and decreasing hydrogen concentrations, increasing infrared absorption at 1300 cm-1 due to boron icosahedra, increasing optical band gaps, dramatically increased microhardness, and increased adhesion to the underlying substrates of these thin films. These results provide evidence that the presence of boron icosahedra increases microhardness, adhesion, and optical band gaps.

The mechanical properties of resistive CuNi films sputtered on both silicon wafers and flexible Kapton foils are important for reliability and lifetime of resistors. Studies of stress-temperature dependence and stress relaxation, stress-strain measurements and scanning scratch tests were performed to investigate film stresses, elastic properties, plastic flow, stress for crack initiation and film adhesion. The growth and annealing stresses were found to be tensile and can be seen as the reason for resistance degradation by stress relaxation due to plastic flow. The strains for crack initiation of 0.2 % to 0.7 % depending on film thickness and annealing restrict the application in resistors on flexible substrates. The film adhesion can be improved by a NiCr base-layer.

There is increasing interest in the use of sol-gel derived films in tribological applications, and this necessitates an understanding of the mechanical properties of these films. Few investigations into the mechanical properties of sol-gel films have been undertaken, and in this study we have concentrated on measurement of the elastic modulus of sol-gel derived titania films as a preliminary stage in a full investigation of stress in sol-gel deposited thin films. Sol-gel films are often very thin and in order to understand the influence of the substrate on the measured elastic modulus, we have used a multiple coating technique to deposit titania films of increasing thickness on various substrates. A three point bending apparatus is used to measure the elastic modulus. The three-point bending apparatus has very low load and displacement measuring capabilities as is required for the very thin sol-gel films. Measurements of the compositional uniformity of the films have been performed using RBS, and this has been combined with film thickness measurements to determine the film porosity. This information ensures that the measured properties relate to intrinsic film properties. The results of all these measurements will be presented.

Plastic deformation in thin copper films has been studied at room temperature. Copper films having a thickness of 1 μm were made by sputtering onto nickel substrates with a Si3N4 underlayer and with or without a Si3N4 caplayer. Deformation experiments were conducted using a special micro-tensile tester built into a θ–θ diffractometer. The problems normally associated with tension tests of free-standing films were avoided by deforming the substrate and film together. In-situ x-ray measurements of the lattice spacings and lattice spacing distributions were used to determine both elastic and plastic strains. The effects of caplayer and annealing temperature on mechanical properties are reported.

Hard coatings of TiN and TiB2 have many interesting properties such as high thermal and electrical conductivity, high melting point, good thermodynamic stability and combination of these properties make them an interesting prospect for a wide range of tribological and electronic applications. It is understood that artificial multilayer structures have shown anamolously high hardness and modulii making them likely candidate for future protective coatings. Single layer of TiN, TiB2, and TiB2/TiN microlaminates coatings with varying thickness have been deposited on Si (100) and oxidized Si(111) substrates by in-situ pulsed laser deposition method. These films are deposited at 10 Hz repetition rate of excimer laser (λ = 248 nm). Our preliminary results show that elastic modulii and hardness values of multilayered coatings are superior than monolithic coatings of either of the two constituent materials. The coatings have been characterized by X-ray diffiractometer and AFM techniques. Detailed results have been presented to correlate the effect of microlaminate thickness on the mechanical properties.

Highly refractive amorphous TiO2 and Ta2O5 films with thicknesses between 270 and 514 nm were deposited on fused silica glass substrates by reactive evaporation and reactive ion plating. Density, hardness, and stiffness were investigated as a function of deposition process. The films were examined using Rutherford backscattering spectroscopy and were found to have densities between 72 and 100% of those of the corresponding bulk oxides. Nanoindentation studies indicated a strong correlation between density and both hardness and elastic stiffness of the oxide film materials. Hardness and modulus both varied by more than 40% over this density range.

Large residual stresses in diamond coatings may result in film failure through splitting, delamination and substrate failure. In addition, the CVD diamond growth environment may degrade the substrate mechanical properties. These issues are examined for diamond-coating of a tool steel alloy. Diamond growth was achieved on the steel substrate with the use of a titanium interlayer. Embrittlement of the Ti interlayer was not evident, however the substrate hardness was severely degraded.

Diamond films grown on molybdenum substrates are indented with conical diamond indenters to depths more than 5 times the thickness of the film. This causes delamination and spalling of the film. The effects of variations in indenter angle and film thickness are demonstrated. Using a radius of the delaminated area to the residual contact radius, sharper indenters are shown to cause a 10 to 20% change in that ratio. For films greater than 5 μm thick, there is no apparent film thickness effect. Possibilities for this observation are cracking due to bending stresses or the interfacial crack kinking out of the interface due to a reduction in compressive stresses, leading to mixed mode loading. The strain energy release rate of the interface for an 800 nm diamond film on molybdenum is between 2.4 and 7 J/m2.

We propose a mechanism by which cleavage-type crack growth along a metal/ceramic interface could proceed concomitantly with significant plastic dissipation in the metal. The large strain gradients in the immediate vicinity of the crack tip are postulated to lead to extensive local hardening. A simple, continuum-based model is used to identify a characteristic length scale ahead of the crack tip, within which the material can not plastically deform subject to the cracktip stress field. An analytical expression is derived for the crack-tip shielding afforded by the plastic zone. The coupling between the plastic dissipation and the ideal work of fracture is found to be synergistic, with slight variations in Griffith energy affecting order-of-magnitude changes in toughness. These results suggest a possible mechanism for a number of interfacial fracture phenomena observed in thick- and thin-film metal/ceramic systems, including segregation-induced interfacial embrittlement, the ductile-to-brittle transition, and stress corrosion cracking.

Nanoindentation, continuous nanoscratch testing, and transmission electron microscopy were used in this study to determine the structure-property relationships of thin tantalum nitride resistor films on aluminum nitride substrates. The films were sputter-deposited to a nominal thickness of 200 nm during one production run and then tested at room temperature. Most films were uniform in structure and thickness, consisting of fine equiaxed crystallites along the film-substrate interfaces and long columnar grains further away from the interface. However, one film varied greatly in thickness across the substrate. It had large crystallites along the film-substrate interface and clusters of columnar grains. Most importantly, it contained a far greater amount of porosity than the other films. The high porosity content led to significantly lower elastic moduli and hardness values than the low porosity films and a much greater susceptibility to fracture.

A new probing technique has been developed to test thin film mechanical properties. In the Microwedge Scratch Test (MWST), a wedge shaped diamond indenter tip is drawn along a fine line, while simultaneously being driven into the line. We compare microwedge scratching of Zone 1 and Zone T thin film specimens of sputtered W on SiO2. Symptomatic of its poor mechanical properties, the Zone 1 film displays three separate crack systems. Because of its superior grain boundary strength, the Zone T film displayed only one of these - an interfacial crack system. Using bimaterial linear elastic fracture mechanics, governing equations are developed for propagating interfacial cracks, including expressions for strain energy release rate, bending strain, and mode mixity. Grain boundary fracture strength information may be deduced from the Zone 1 films, while adhesion may be inferred from the Zone T films.

Adhesion failures of Ti2 and Ta2O5 thin films deposited by reactive evaporation (RE), reactive ion plating (IP) and plasma impulse chemical vapour deposition (PICVD) on fused silica, AF 45, TEMPAX and soda-lime glass substrates are investigated by means of a micro-scratch tester. The oxide films possess thickness between 60 and 500 nm and show different mass densities depending on the deposition conditions. Scratch testing exhibits well pronounced detachment for thicker films on hard substrates. The clearance of the scratch signal is reduced with decreasing layer thickness or for softer substrate materials. The test results are also influenced by the various substrates and different chemical and mechanical properties of the films due to the alternate deposition techniques.

The adhesion of thin films to substrates can be quantified using the blister test, which measures the crack extension force (G) required to propagate a crack along the film/substrate interface. We summarize the derivation of crack extension force for the blister test, and discuss how blister tests can be conducted by measuring only the pressure and volume of liquid injected into the test system. We describe a way to calculate the velocity of the interface crack front.

Data from blister tests of acrylate films (14 μm thick) on nitride substrates are analyzed. The critical crack extension forces (GC ) measured were 25 − 34 J/m2 for samples which had a commercial adhesion promoter at the interface, and 0.5 − 2.0 J/m2 without the adhesion promoter. GC was observed to increase with the velocity of the interface crack, and the dependence appears to obey a power-law.

Effects of mechanical properties of Cu/Cr metal films on the peel strength of Cr/PI interfaces have been studied. Cr and Cu thin films were successively sputter-deposited on in-situ RF plasma-treated polyimides, and 20 μm-thick Cu was electroplated. With increasing the yield strength of Cu/Cr films from 156 MPa to 325 MPa, peel strength of Cr/PMDA-ODA and Cr/BPDA-PDA were lowered from 75 g/mam to 57 g/mm and from 69 g/mm to 20 g/mm, respectively. With identical Cu/Cr metal films, lower peel strength was obtained on Cr/BPDA-PDA interfaces, compared to the values of Cr/PMDA-ODA. Peel strength was also decreased more pronouncedly on Cr/BPDA-PDA with increasing the yield strength of Cu/Cr metal films. With T/H (80°C/94% R.H.) exposure, however, peel strength was lowered much more pronouncedly on Cr/PMDA-ODA than on Cr/BPDA-PDA, especially for specimens with Cu/Cr metal films of lower yield strength.

The microstructure of Cu thin films in various deposition conditions and the influence of their microstructure on the adhesion strength between Cu/Cr films and polyimides were studied. Cr films (50 nm thick) and Cu films (500 or 1000 nm thick) were deposited on polyimide films by DC magnetron sputtering. The Ar pressure during Cu deposition was controlled to 5, 50, and 100 mtorr. The microstructure was characterized using SEM and TEM. The adhesion strength between Cu/Cr and polyimide was measured using a modified Tpeel test. Plastic deformation of the peeled metal was qualitatively measured using the XRD technique. The Cu film sputtered at 5 mtorr has a dense and uniform structure, while lowdensity regions or open boundaries between columns exist in the film deposited at higher pressure. As sputtering pressure increases, open boundaries are observed more frequently. The peel adhesion strength of Cr film to polyimide increases with Cu sputtering pressure. The adhesion change of Cu/Cr film can be interpreted as the difference in plastic deformation. Open boundaries in the Cu film seem to play an important role in increasing the amount of plastic deformation in the metal film during peeling.