Properties Of Thin Metal Films Research Articles

Multi-layer piezoelectric electrical energy transfer device

The continued development of microelectromechanical systems (MEMS) devices is dependent on continued innovation in materials development for application on the micrometer scale. The application of materials other than silicon is required to develop high-performance MEMS devices. Metals and alloys have a wide variety of mechanical properties (elastic modulus, strength, fracture toughness, and fatigue properties) and functional properties (electric and magnetic properties). This indicates that the use of metallic materials is promising to realize MEMS devices with higher performances. For designing MEMS devices, materials selection is important to enable durable MEMS devices, and it is required to know the mechanical properties of freestanding metallic thin films on the micrometer scale. In this chapter, mechanical properties of metallic thin films, which have been and will be used in MEMS devices, will be described.In the past decade, shape-memory alloy (SMA) thin films formed by sputter deposition have attracted considerable attention as a powerful microactuator. Current intensive research demonstrates that superior shape-memory characteristics are achieved in comparison to bulk materials due to unique fine microstructures. Simultaneously, much effort has been undertaken to develop and fabricate microdevices actuated by SMA thin films. This article reviews the research to date on shape-memory behavior and the mechanical properties of SMA thin films in connection with their peculiar microstructures. Promising applications such as microvalves are demonstrated, along with a focused discussion on process-related problems. All of the results indicate that thin-film shape-memory actuators are ready to contribute to the development of MEMS.

Local microwave characterization of metal films using a scanning microwave near-field microscope

In microwave integrated circuits, the performance of devices is often influenced by the homogeneity of microwave properties of metal thin films in the circuits. In this paper, a scanning microwave near-field microscope (SMNFM) has been designed using a coaxial resonator as the probe, to study the local microwave properties of the electronic devices. Several typical samples of metal films have been measured and the results have shown that we can image the local microwave properties by recording the changes of the resonant frequency and quality factor of the coaxial resonator probe. The spatial resolution of the SMNFM has been improved to be better than 5 μm by utilizing a probe with a structure similar to that used in a scanning tunnelling microscope. To demonstrate the ability of local microwave characterization, the surface resistances of Cr thin film and Ag/Cr multilayer have been imaged by the SMNFM.

Near-field and far-field optical properties of thin metallic films

Reflectivity measurements in an attenuated total internal reflection (ATIR) geometry and the variation of the transmitted intensity associated to the total electric field in a frustrated ATIR configuration using a photon scanning tunneling microscope (PSTM) of multilayered metallic films are presented as a function of the angle of incidence. Eigenmodes for total reflection and absorption associated with the optical properties of magnetic and nonmagnetic materials are theoretically and experimentally determined from the reflected and the transmitted spectra. Good agreement between theory and experiment demonstrates that PSTM is a powerful technique to characterize accurately and locally drastic variations of the intensity around optical modes of a multilayer system.

Constrained Diffusional Creep in Thin Copper Films

ABSTRACTThe mechanical properties of thin metal films have been investigated for many years. How- ever, the underlying mechanisms are still not fully understood. In this paper we give an overview of our work on thermomechanical properties and microstructure evolution in pure Cu and dilute Cu-Al alloy films. Very clean films were produced by sputtering and annealing under ultra-high vacuum (UHV) conditions. We described stress-temperature curves of pure Cu films with a constrained diffusional creep model from the literature. In Cu-1at.%Al alloy films, Al surface segregation and oxidation led to a “self-passivating” effect. These films showed an increased high- temperature strength because of the suppression of constrained diffusional creep; however, under certain annealing conditions, these films deteriorated due to void growth at grain boundaries.

“Reverse” Stress Relaxation in cu Thin Films

ABSTRACTIn this study we present investigation on the anelastic behavior of sputtered 1 [.proportional]m thin Cu films. Most of the literature that reports on the mechanical properties of thin metallic films is based on substrate curvature measurements. We have developed a new version of a bulge tester that combines the capacitive measurement of the bulge deflection of a membrane with a resonance frequency measurement of the residual stress in the membrane. A Cu membrane is plastically deformed to a pre-determined strain by controlled gas-pressure bulging of the membrane. After the bulging stress is removed, the residual tensile stress, which has been decreased by the plastic deformation, is then determined by measuring the resonant frequency as a function of time. Immediately after plastic straining, the residual (tensile) stress of membranes was observed to increase. At room temperature a maximum stress was typically reached in the order of an hour. At still longer times the stress decreased again as a result of creep. The transient increase in stress following plastic straining grew larger as the amount of plastic strain produced by bulging was increased. With higher temperatures the transient became both faster and larger. A model is presented that based on the mechanism of thermally activated glide separates the microstructure in a class of “soft” and “hard” grains solving the issue of an “apparent” increase in strain energy as a function of time after deformation.

Determination of constitutive properties of thin metallic films on substrates by spherical indentation using neural networks

The indentation test has been developed into a popular method for investigating mechanical properties of thin films. However, there exist only some empirical or semi-analytical methods for determining the hardness and Young’s modulus of a film from pyramidal indentation of the film on a substrate, where the deformation of film and substrate is subjected to be elastic–plastic. The aim of the present paper is to show how constitutive properties and material parameters may be determined by using a depth-load trajectory which is related to a fictitious bulk film material. This bulk film material is supposed to possess the same mechanical properties as the real film. It is assumed that the film and the substrate exhibit elastic–plastic material properties with nonlinear isotropic and kinematic hardening. The determination of the depth-load trajectory of the bulk film is a so-called inverse problem. This problem is solved in the present paper using both the depth-load trajectory of the pure substrate and the depth-load trajectory of the film deposited on this substrate. For this, use is made of the method of neural networks. Having established the bulk film depth-load trajectory, the set of material parameters entering in the constitutive laws may be determined by using e.g. the method proposed by Huber and Tsakmakis (Huber, N., Tsakmakis, Ch., 1999. Determination of constitutive properties from spherical indentation data using neural networks. Part II: plasticity with nonlinear isotropic and kinematic hardening. J. Mech. Phys. Solids 47, 1589–1607).

Magnetic properties of iron-and cobalt-implanted silicone polymers

Composite metal–polymer thin films were formed by implantation of 40 KeV Fe + and Co + ions into viscous and solid silicone substrates in the dose range of (0.3–1.5)×10 17 ions/cm 2. Morphology and magnetic properties of the synthesized films were investigated. TEM investigations showed that the microstructure of metal granular layers synthesized in silicone polymers strongly depends on an initial relaxation state of the target. Magnetic resonance studies revealed essential differences in the magnetic properties of thin metal films synthesized at different initial states of silicone substrate and with respect to the type of implanted ions (Fe or Co). A shift and broadening of FMR signal with the samples cooling are observed both for perpendicular and parallel orientation of the films with respect to the magnetic field. These effects are associated with the increase of the inter-particle interactions and superparamagnetism blocking in the particles. It was found that the viscous initial state of the polymer is a favourable factor for the high anisotropy of FMR response in Fe-implanted samples in contrast to the Co-based ones. The reasons for this have been discussed with respect to the morphology of Fe and Co synthesized films.

Optical properties of thin metal films

Optical constants of metallic thin films made from: Ag, Au, Hf, Ir, Mo, Nb, Os, Pd, Pt, Re, Rh, Ru, Ta, W, Zr n were determined on the basis of measured index of refraction in region of wave- length λ =†24n1216†A. Two types of relations were used for the calculation. Some of them were ob- tained, with taking into account that refractive index of absorbing medium can be presented in the form n = n - iae. Other were obtained from Maxwell boundary condition. Both approaches give rise to very close results for ae, however the dependences n =†f(λ) for λ > 200 A are essentially different. The reasons of such differences are discussed.

Evaluation of the mechanical properties of thin metal films

The nano-indentation method has been developed to evaluate the mechanical properties of metal films. In this study an indentation loading curve is employed to determine the yield strength and hardening index of an Al film on a Si substrate. The result is compared with that measured by a uniaxial tensile test with an Al film deposited on an Al foil. The yield strength of the Al film can be determined according to the testing results of this compound material and it agrees reasonably with that evaluated by the nano-indentation method. In addition, X-ray diffraction measurements of the four point bending specimen is used to measure the stress–strain curve of Cu films on steel substrate. The samples are prepared by ion beam enhanced deposition and magnetron-sputtering deposition. The results show that the strength of Cu film depends on the deposition technology and is much higher than that of the bulk material.

Crystallographic Characterization of Sputter Deposited Nb-Cu Thin Films Using Electron Backscatter Diffracted Patterns.

Crystallographic structure plays an important role in determining the fundamental physical properties of metallic thin films and superlattices, and structural characterization of such films is crucial for furthering the application of these materials [1]. Epitaxial films are usually characterized using a wide range of techniques including x-ray diffraction, REED, neutron diffraction, and highresolution electron microscopy. A complementary approach is electron backscatter patterns (EBSP), which is an SEM technique that can be used to measure crystallographic orientations of single or polycrystals [2].In this work, EBSPs have been used to characterize the crystallite size and orientation of sputterdeposited Cu films. The EBSPs were formed in a CamScan 44FE SEM and recorded using an ORTEX CCD camera system. The images were analyzed using the Channel+ software package, and orientation maps were plotted using Channel+Ice [3].

Numerical simulation for determining the mechanical properties of thin metal films using depth-sensing indentation technique

The finite element method (FEM) for elastoplastic large strain was employed to study the indentation experiment of Al film on Si substrate by a rigid spherical indenter. Two relationships between the mechanical properties of the film and the specific values of the load–displacement curve have been obtained. Using a hybrid method that involves the combination of these two relationships with nanoindentation test, the hardening index and yield strength of the metal film can be determined.

Epitaxial Growth and Magnetism

AbstractGrowth phenomena and magnetism of metallic films are not easy to describe at the same level of precision. A small variation of distances can drastically modify the magnetic properties of thin metallic films. In this contribution different aspects encountered in the growth of thin magnetic metallic films are addressed. Within an itinerant magnetism scheme, the main difficulty arises from the number of possible magnetic arrangements induced by the competition between nearest-neighbors Ferromagnetic and Antiferromagnetic couplings. However we show that the description of the electronic and magnetic structure at T = 0 K by well-established band structure frameworks provides useful and precise information on the growth of a transition metal on another. Due to the large amount of experimental data available, the Fe/Cr system is taken as an example. The influence of steps at the interface is discussed and the possibility of magnetic domains is shown. A simple model of growth taking into account variable interdiffusion rate and layer-by-layer quality is given. These simulations are used to explain experimental results where interdiffusion at the interface is very common.

Elastic and plastic properties of thin films on substrates: nanoindentation techniques

Recent progress in understanding the mechanical properties of thin films on substrates is briefly reviewed. We describe nanoindentation techniques that have been developed for measuring the elastic and plastic properties of thin films with thickness on the order of micrometers. We also report on efforts to understand the strength properties of thin metal films in terms of the motion and interaction of dislocations within them. The well-known size dependence of the hardness of soft, strain-hardenable metals is described in terms of the geometrically necessary dislocations created in small indentations. The very high strengths typically observed for thin films are interpreted in terms of the mechanics of dislocation motion and interaction in thin metal layers.

Effects of acoustic waves on activation of thin film Pd and Ni catalysts for ethanol and CO oxidation

The effects of acoustic wave excitation of surface acoustic waves (SAWs) and resonance oscillations (ROs) on catalytic and adsorptive properties of metal thin films have been studied. A 5–200 nm thick Pd thin film was deposited as a catalyst on the Rayleigh SAW propagation path of a 128°-rotated y-cut LiNbO3 single crystal. For ethanol oxidation, the introduction of a 10 MHz SAW increased acetaldehyde production. The activity enhancement varied, depending not only on the surface states (reduced and oxidized Pd surfaces), but also on the thickness of the Pd films: larger activity enhancement occurred for a thick Pd film with an oxidized surface. For CO oxidation, the oxidized Pd had slightly greater effect than reduced Pd, but catalyst activation with SAW-on was small over a whole range of film thickness for both the reduced and the oxidized Pd. The high-resolution IR reflection absorption spectra of CO adsorbed on a 40 nm Pd thin film deposited on the propagation path of a shear horizontal leaky SAW (36°-rotated y-cut LiTaO3) exhibited a large peak, assigned to bridging CO, at 1982 cm-1 and a small on-top CO peak at 2073 cm-1. With SAW-on, the intensity and position of both the peaks remained nearly unchanged, but a shoulder appeared on the bridging CO peak at ca. 1930 cm-1. A laser Doppler measurement showed that a vertical lattice displacement due to the Rayleigh SAW increased with increasing Pd film thickness, up to 50 nm, and was nearly constant over the range 50–200 nm, in which the magnitude of lattice displacement was larger for reduced than for oxidized Pd. SAW-induced catalyst activation is discussed on the basis of reaction mechanisms and the adsorbed states of the reactants. From the dependence of lattice displacement on the thickness and surface states of the Pd films, a model in which the SAW interacts with the charged carriers in the thin films and affects the adsorbed states of the reactants is proposed. Furthermore, it was demonstrated that RO generated on a Pd thin film deposited on z-cut LiNbO3 had a remarkable effect on its catalytic activity for ethanol oxidation.

Formation of Metallic Systems Far From Equilibrium By Pulsed Laser Deposition

ABSTRACTThe properties of metallic thin films prepared by pulsed laser deposition (PLD) strongly differ from samples grown by conventional thin film techniques like sputtering and evaporation. In many systems (Fe-Nb, Fe-Zr, Cu-Co, Fe-Ag and Ni-Ag), strongly supersaturated solid solutions are formed, a broader formation range occurring for amorphous samples, and nanocrystalline phases are produced. Additionally, metastable phases of larger thickness at the interfaces of multilayers occur. Reasons for these behaviors are discussed with respect to atomic mixing and implantation effects induced by the high instantaneous deposition rate during PLD and the high kinetic energy (>100 eV) of the deposited ions.

Nanoindentation Hardness of Soft Films on Hard Substrates: Effects of the Substrate

ABSTRACTThe ability to accurately measure the mechanical properties of thin metallic films is important in the semiconductor industry as it relates to device reliability issues. One popular technique for measuring thin film mechanical properties is nanoindentation. This technique has the advantage of being able to measure properties such as hardness and elastic modulus without removing a film from its substrate. However, according to a widely-held rule of thumb, intrinsic film properties can be measured in a manner which is not influenced by the substrate only if the indentation depth is kept to less than 10% of the film thickness, which is often not practical. In this work, a method for making substrate independent hardness measurements of soft metallic films on hard substrates is proposed. The primary issue to be addressed is the substrate-induced enhancement of indentation pile-up and the ways in which this pile-up influences the contact area determined from analyses of nanoindentation load-displacement data. Based on experimental observations of soft aluminum films on silicon, glass, and sapphire substrates, a simple empirical relationship is derived which relates the amount of pile-up to the contact depth. From this relationship, a simple method is developed which allows the intrinsic hardness of the film to be measured by nanoindentation methods even when the indenter penetrates through the film into the substrate.

Metal Microstructures in Advanced CMOS Devices

As advanced semiconductor device features shrink, grain boundaries and interfaces become increasingly more important to the properties of thin metal films. With film thicknesses decreasing to the range of 10 nm and the corresponding features also decreasing to sub-micrometer sizes, interface and grain boundary properties become dominant. In this regime the details of the surfaces and grain boundaries dictate the interactions between film layers and the subsequent electrical properties. Therefore it is necessary to accurately characterize these materials on the proper length scale in order to first understand and then to improve the device effectiveness. In this talk we will examine the importance of microstructural characterization of thin metal films used in semiconductor devices and show how microstructure can influence the electrical performance. Specifically, we will review Co and Ti silicides for silicon contact and gate conductor applications, Ti/TiN liner films used for adhesion and diffusion barriers in chemical vapor deposited (CVD) tungsten vertical wiring (vias) and Ti/AlCu/Ti-TiN films used as planar interconnect metal lines.

Thin metal films deposited at low temperature for optoelectronic device application

Thin metal layers play an important role in the development of electronic devices. Thin metal films deposited at low temperature (LT=77 K) have shown some unique properties which enhance device performance. The microstructure properties of thin metal films formed at room temperature (RT=300 K) and LT were investigated in this work. An insulating substrate was used for Au, Ag, and Al metal deposition. The surface morphology and microstructure of the metal films was studied by transmission electron spectroscopy (TEM) and atomic force microscopy (AFM). The resistance of the thin films was measured in situ as a function of film thickness and temperature. It was found that all LT thin films become electrically continuous at a much lower thickness than the RT films. Electrical measurements determined that the LT films demonstrated several orders of lower resistance compared to RT film at very thin (less than 100 Å) thickness, which could lead to the potential applications of these films on electronic and optoelectronic devices. It is observed by both TEM and AFM that the LT films showed much lower density of grain boundaries than the RT samples at the same thickness. This is consistent with the resistance measurement results.

The effect of self-ions bombardment on the structure and properties of thin metal films : O.V. KONONEMKO, Vacuum, 46(7), 685 (1995)

The effect of self-ions bombardment on the structure and properties of thin metal films : O.V. KONONEMKO, Vacuum, 46(7), 685 (1995)

The Improvement of Immunity to Electromigration by Means of Microstructural Design

AbstractIt is known from literature that the properties of thin films greatly depend on their structuare. Therefore, the microstructural design is attractive for control over the properties of thin metal films used for interconnect metallization.In this paper we discuss the potentialities of the self-ion assisted deposition technique for control over the grain and grain boundary structures of thin metal films and their properties such as resistivity and immunity to electromigration.It was found that resistivity of aluminum films deposited at the 6 kV bias was virtually equal to resistivity of bulk aluminum. Films deposited at the less bias or without it had higher resistivities. Abnormal grain growth was found in 6 kV-films. In films prepared without bias normal grain growth proceeds.