The mechanical properties of thin films on substrates are described and studied. It is shown that very large stresses may be present in the thin films that comprise integrated circuits and magnetic disks and that these stresses can cause deformation and fracture to occur. It is argued that the approaches that have proven useful in the study of bulk structural materials can be used to understand the mechanical behavior of thin film materials. Understanding the mechanical properties of thin films on substrates requires an understanding of the stresses in thin film structures as well as a knowledge of the mechanisms by which thin films deform. The fundamentals of these processes are reviewed. For a crystalline film on a nondeformable substrate, a key problem involves the movement of dislocations in the film. An analysis of this problem provides insight into both the formation of misfit dislocations in epitaxial thin films and the high strengths of thin metal films on substrates. It is demonstrated that the kinetics of dislocation motion at high temperatures are expecially important to the understanding of the formation of misfit dislocations in heteroepitaxial structures. The experimental study of mechanical properties of thin films requires the development and use of nontraditional mechanical testing techniques. Some of the techniques that have been developed recently are described. The measurement of substrate curvature by laser scanning is shown to be an effective way of measuring the biaxial stresses in thin films and studying the biaxial deformation properties at elevated temperatures. Submicron indentation testing techniques, which make use of the Nanoindenter, are also reviewed. The mechanical properties that can be studied using this instrument are described, including hardness, elastic modulus, and time-dependent deformation properties. Finally, a new testing technique involving the deflection of microbeam samples of thin film materials made by integrated circuit manufacturing methods is described. It is shown that both elastic and plastic properties of thin film materials can be measured using this technique.

Mechanical properties of thin films

Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth.

Microstructural evolution during film growth

▪ Abstract The synthesis of nanocrystalline diamond films from carbon-containing noble gas plasmas is described. The nanocrystallinity is the result of new growth and nucleation mechanisms, which involve the insertion of C2, carbon dimer, into carbon-carbon and carbon-hydrogen bonds, resulting in hetereogeneous nucleation rates on the order 1010 cm−2 s−1. Extensive characterization studies led to the conclusion that phase-pure diamond is produced with a microstructure consisting of randomly oriented 3–15-nm crystallites. By adjusting the noble gas/hydrogen ratio in the gas mixture, a continuous transition from micro- to nanocrystallinity is achieved. Up to 10% of the total carbon in the nanocrystalline films is located at 2 to 4 atom-wide grain boundaries. Because the grain boundary carbon is π-bonded, the mechanical, electrical, and optical properties of nanocrystalline diamond are profoundly altered. Nanocrystalline diamond films are unique new materials with applications in fields as diverse as tribolo...

Nanocrystalline diamond films1

Size dependence of nanostructures: Impact of bond order deficiency

Columnar microstructure in vapor-deposited thin films

Amorphisation and surface morphology development at low-energy ion milling

The formation of vacuum-deposited In thin films was studied by in situ electron microscopy. The dependence of melting point and crystallization temperature on particle size was measured. A preferred orientation was found to develop at a given crystallite size depending on the substrate temperature and on the ratio of impinging oxygen molecules to film atoms (K factor).

Formation Processes of Vacuum-Deposited Indium Films and Thermodynamical Properties of Submicroscopic Particles Observed by In Situ Electron Microscopy

TEM sample preparation by ion milling/amorphization

The authors studied the nucleation rate and the rate of crystal growth in a-Ge films, paying particular attention to the effects of residual gases. Activation energies for the relevant processes were obtained.

Crystallization processes in a-Ge thin films

The structure of evaporated amorphous silicon and amorphous silicon prepared by glow discharge technique is investigated using phase contrast electron microscopy and electron diffraction. While evaporated Si shows a supernetwork of density fluctuations commonly observed in evaporated amorphous tetrahedrally bonded semiconductors, glow discharge Si shows no such quasiperiodic heterogeneous density fluctuation. Electron diffraction patterns are obtained using a translation detector, which directly measures the electron intensity in the image plane of the electron microscope. From the resulting RDF it is concluded, that there is a higher degree of local order in glow discharge Si.



Mit Hilfe von Phasenkontrast-Elektronenmikroskopie und Elektronenbeugung wird die Struktur von aufgedampftem amorphem Silizium und von amorphem Silizium, das mit der “glow discharge” -Technik gewonnen wurde, untersucht. Wahrend aufgedampftes Si das Supernetzwerk von Dichtefluktuationen zeigt, wie es ublicherweise in aufgedampften tetraedrisch gebundenen amorphen Halbleitern gefunden wird, hat “glow discharge”-Si keine solche heterogene, quasiperiodische Dichtefluktuation. Mit Hilfe eines Translationsdetektors, der die Elektronenintensitat direkt in der Bildebene des Elektronenmikroskops mist, wird das Elektronenbeugungsspektrum aufgenommen. Aus der resultierenden RDF wird geschlossen, das der Grad der lokalen Ordnung in “glow discharge”-Si groser ist.

Arpad Barna

Papers

Amorphisation and surface morphology development at low-energy ion milling

Formation Processes of Vacuum-Deposited Indium Films and Thermodynamical Properties of Submicroscopic Particles Observed by In Situ Electron Microscopy

TEM sample preparation by ion milling/amorphization

Crystallization processes in a-Ge thin films

A comparative study of the structure of evaporated and glow discharge silicon