Daniel L. Callahan

Hardness, elastic modulus, and structure of very hard carbon films produced by cathodic‐arc deposition with substrate pulse biasing

The hardness, elastic modulus, and structure of several amorphous carbon films on silicon prepared by cathodic‐arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy (EELS), and cross‐sectional transmission electron microscopy. EELS analysis shows that the highest sp3 contents (85%) and densities (3.00 g/cm3) are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ∼20 nm surface layer which is structurally different and softer than the bulk.

The extent of phase transformation in silicon hardness indentations

The extent of phase transformation occurring in silicon during room-temperature indentation experiments has been examined by transmission electron microscopy of low-load microindents. The results show that the entire hardness impression arises from structural transformation and extrusion of a ductile high pressure phase. In particular, there is no dislocation activity or other mechanism of plastic deformation operating outside the clearly demarcated transformation zone. The observable impression consists of an amorphous transformation zone with an adjacent region of plastically extruded material and a layer of polycrystalline silicon at the near-surface transformation interface.

Sub‐100 nm lines produced by direct laser ablation in polyimide

Periodic line structures with a period of 167 nm and linewidths varying from 35 to 100 nm have been produced on polyimide by direct ablation with a KrF laser using an interferometric technique. Since ablation is a nonlinear process, the resolution can exceed that expected from the wavelength and numerical aperture of the system and the linewidth can be controlled by varying the laser fluence. This externally generated period of 167 nm prevents the spontaneous growth of periodic surface structures due to radiation remnants.

Deposition and analysis of lithium niobate and other lithium niobium oxides by rf magnetron sputtering

The deposition of thin films of lithium niobate (LiNbO3) on silicon with rf magnetron sputtering has been investigated. A matrix of experiments was designed to determine the effect of several parameters on the resulting film quality. Under optimized conditions, oriented polycrystalline films of LiNbO3 are produced that exhibit a columnar grain structure with the polar axis normal to the substrate surface. Deviations from sputtering parameters optimized for producing LiNbO3, have been shown to produce films of varying proportions of either LiNb3O8 or Li3NbO4 with LiNbO3. The stoichiometry, microstructure, and electrical properties of selected films have been investigated with Rutherford backscattering, diffractometry, transmission electron microscopy, and a variety of electrical measurement techniques.

Multilayers of amorphous carbon prepared by cathodic arc deposition

Filtered cathodic arc deposition is an effective technique for preparing amorphous hard carbon films of high quality. Pulsed biasing of the substrate leads to a variation of the ion energy. Therefore the film properties, which are influenced by the ion energy, can be changed over a wide range. Using an alternating high- and low-bias voltage, we have formed multilayers of hard and soft amorphous carbon films. The structure and mechanical properties of the multilayers were investigated by transmission electron microscopy and nanoindentation. They are discussed in relation to Monte Carlo computer simulations of the deposition process. It was found that the multilayer structure formation can be well predicted by the Monte Carlo computer code.

Origins of microplasticity in low-load scratching of silicon

Microstructural characterization of silicon wafers subjected to controlled low-load scratching with a sharp indenter reveals that considerable plastic deformation occurs prior to the onset of fracture. In particular, a completely ductile response to scratching is observed at or below a Vickers load of 1 g, corresponding to penetration depths of 200 nm or less. This anomalous plasticity arises primarily as a result of a pressure-induced semiconductor-to-metal phase transition (Mott transition). Various levels of subsurface dislocation activity and cracking also contribute to the deformation. The relationships among the phase transformation, dislocation activity, and the onset of fracture are discussed. These findings can be applied to other areas of contact damage demonstrating anomalous plasticity, such as hardness testing and ductile-regime turning.

Direct laser ablation of sub-100 nm line structures into polyimide

Periodic line structures with a period of 167 nm and linewidths varying from 30 to 100 nm have been produced in polyimide by direct ablation with a KrF laser using an interferometric technique. The characteristics of this interferometer as it applies to the ablation of these line structures, including linewidth and alignment sensitivity, are analyzed. The ability to control the linewidth by varying the average incident fluence is described theoretically and demonstrated experimentally. This externally generated period of 167 nm also prevents the spontaneous growth of laser induced periodic surface structures (LIPSS).

Thermal and mechanical coupling between successive pulses in KrF-excimer-laser ablation of polyimide

Multiple-shot effects in laser processing and ablation of polyimide are examined and are found to be the dominant phenomena for processes involving several hundreds or thousands of pulses. For fluences less than 260 mJ/cm2, it was found that it is impossible to cut through 75 μm polyimide foils for an arbitrarily large number of excimer pulses even though this fluence is more than ten times the single-shot ablation threshold. The halt in etching is due to the formation, over a number of shots, of a robust carbon matrix with a deep surface roughness which is also responsible for laser-induced electrical conductivity. The effect of thermal coupling between successive shots is shown to be a dominant factor in determining the electrical properties of the carbon layer. Differences in electrical conductivity of up to 12 orders of magnitude were found for only small differences in repetition rate. Transmission electron microscopy revealed the changes in microstructure responsible for the dramatic differences in electrical properties.

DEVELOPMENT OF FULLERENE-REINFORCED ALUMINUM

Powder metallurgy and casting have been used to produce aluminum with 1.3, 4, and 8 vol. % fullerene additions. Fullerene extract was mixed with Al and heat-treated to obtain various levels of dispersion of the fullerenes. Intergranular dispersion of stable fullerenes was accomplished by both powder metallurgy and casting; however, x-ray diffraction indicated the formation of some Al 4 C 3 . Homogeneous dispersion did not occur because of limited diffusion in the solid state or limited solubility of fullerene in Al in the liquid state. Enhancements in hardness over that for Al were observed yet were not comparable to precipitation hardened Al alloys since a less homogeneous dispersion was achieved. Interest in Al having fullerene additions is for development of fullerene strengthened materials where fullerenes act as nanosize dispersoids for dispersion strengthening of metals or as a lightweight reinforcement in metal-matrix composites.

ELECTROSTATIC ADHESION TESTING OF ELECTRONIC METALLIZATIONS

A novel technique is developed to measure quantitatively the adhesion strength of metallizations deposited on substrates such as silicon. Electrostatic adhesion testing employs electrostatic forces to generate delaminating stresses in thin metallic films. The interfacial adhesion strength is readily calculated from the electrode geometry and the applied electrostatic field at failure. Unlike other adhesion tests, this technique does not require any mechanical contact and is virtually independent of the plastic deformation of the film. Furthermore, this test provides direct strength measurements as opposed to work or energy of adhesion measurements obtained by the common peel test. The adhesion strengths of several metallizations (Cu, Al) are characterized using the electrostatic technique. The distribution of stress-at-failure data follows Weibull failure statistics. Field emission scanning electron microscopy reveals that the films are delaminated in a microblister-type mode. It is shown that electrostat...