Alex A. Volinsky

Interfacial toughness measurements for thin films on substrates

Abstract There are more than 200 different methods for measuring adhesion, suggesting it to be material, geometry and even industry specific. This availability has exploded at least partly due to the arrival of dissimilar material interfaces and thin films and the ease with which microfabrication techniques apply to silicon technology. Having an eye toward those tests utilized for thin films, this paper reviews only a few of these techniques. The emphasis is on measuring thin film adhesion from the standpoint of fracture mechanics, when the film is mechanically or by other means removed from the substrate, and the amount of energy necessary for this process is calculated per unit area of the removed film. This tends to give values approaching the true work of adhesion at small thickness and greater values of the practical work of adhesion at larger thickness, all being in the 30–30,000 nm range. The resulting large range of toughnesses is shown to be dependent on the scale of plasticity achieved as controlled by film thickness, microstructure, chemistry and test temperature. While the tests reviewed largely address the measurement of elastic strain energy release rates, we also briefly address a few theoretical models which are specific to the resistance side of the delamination equation. The weight of the evidence suggests for ductile metallic films that the major extrinsic variables are film stress, extent of delamination, thickness and temperature while the major intrinsic ones are modulus, yield strength, the thermodynamic work of adhesion and one or more length scales. For some 25 film/substrate multilayers, with emphasis on Al, Au and Cu, the comparison of several theoretical models as to how the extrinsic and intrinsic variables intertwine is made.

Fracture toughness, adhesion and mechanical properties of low-K dielectric thin films measured by nanoindentation

The semiconductor industry is gradually moving from well-established AlySiO technology to the new Cuylow-k interconnects, 2 which brings a challenge in terms of poor thermal andyor mechanical properties of low-K dielectric films.Extensive nanoindentation studies have been undertaken on organo-silicate glass (OSG) low-K films to explore their mechanical and fracture properties.A cube corner indentation method was used to measure the fracture toughness of the OSG films, which ranges from 0.01 to 0.05 MPaOm .Film fracture was also observed during superlayer indentation adhesion testing.Interfacial cracks kinked into the film 1y2

Substrate effects on indentation plastic zone development in thin soft films

Plastic zone evolution in Al–2 wt% Si metal films on silicon and sapphire substrateswas studied using nanoindentation and atomic force microscopy (AFM). AFM wasused to measure the extent of plastic pileup, which is a measure of the plastic zoneradius in the film. It was found that the plastic zone size develops in a self-similarfashion with increasing indenter penetration when normalized by the contact radius,regardless of film hardness or underlying substrate properties. This behavior was usedto develop a hardness model that uses the extent of the plastic zone radius to calculatea core region within the indenter contact that is subject to an elevated contact pressure.AFM measurements also indicated that as film thickness decreases, constraint imposedby the indenter and substrate traps the film thereby reducing the pileup volume.I. INTRODUCTIONThe popularity of nanoindentation is due in large partto its ability to probe the mechanical properties of ma-terials in a nondestructive fashion without extensivesample preparation. However, it is often difficult tomeasure film properties independent of the substrateproperties. Several solutions to this problem have beenproposed with varying degrees of success, the simplestbeing the “10% rule,” by which it is proposed that thefilm properties can be measured for indentation depthsless than 10% of the total film thickness.However, this “rule of thumb” has several deficien-cies. The rule is too restrictive for soft coatings onhard substrates;

Nanostructured ion beam-modified Ge films for high capacity Li ion battery anodes

Nanostructured ion beam-modified Ge electrodes fabricated directly on Ni current collector substrates were found to exhibit excellent specific capacities during electrochemical cycling in half-cell configuration with Li metal for a wide range of cycling rates. Structural characterization revealed that the nanostructured electrodes lose porosity during cycling but maintain excellent electrical contact with the metallic current collector substrate. These results suggest that nanostructured Ge electrodes have great promise for use as high performance Li ion battery anodes.

Nanoindentation of Au and Pt/Cu thin films at elevated temperatures

This paper describes the nanoindentation technique for measuring sputter-deposited Au and Cu thin films’ mechanical properties at elevated temperatures up to 130 °C. A thin, 5-nm Pt layer was deposited onto the Cu film to prevent its oxidation during testing. Nanoindentation was then used to measure elastic modulus and hardness as a function of temperature. These tests showed that elastic modulus and hardness decreased as the test temperature increased from 20 to 130 °C. Cu films exhibited higher hardness values compared to Au, a finding that is explained by the nanocrystalline structure of the film. Hardness was converted to the yield stress using both the Tabor relationship and the inverse method (based on the Johnson cavity model). The thermal component of the yield-stress dependence followed a second-order polynomial in the temperature range tested for Au and Pt/Cu films. The decrease in yield stress at elevated temperatures accounts for the increased interfacial toughness of Cu thin films.

Mechanical properties and fracture toughness of organo-silicate glass (OSG) low-k dielectric thin films for microelectronic applications

The integration of chemical vapor deposited organo-silicate glass (OSG) interlayer dielectrics (ILD) has challenged the IC industry to formulate new methods of metrology and characterization. The impact of nanoindentation to understand and screen for integrated circuit failure mechanisms that are mainly predicated upon OSG nano-porosity is discussed. Failure modes include poor mechanical strength, low material stiffness, and brittle fracture due to low cohesive and adhesive fracture toughness, a particular danger during chemical-mechanical polishing (CMP). By developing a methodology to predict failure modes, we are able to screen multiple candidate low-k materials. Nanoindentation measurements of elastic modulus, hardness, and fracture toughness and what they reveal about OSG porosity are discussed.

Giant magnetoelectric effect in Ni–lead zirconium titanate cylindrical structure

The magnetoelectric (ME) coupling of a bilayered Ni–lead zirconate titanate composite structure synthesized by electrodeposition was studied in this paper. The ME voltage coefficient was measured in the range of 1–120kHz as the bias field is parallel to the axial. The results indicate that an electromechanical resonance appears at 59.9kHz. The bilayered cylindrical ME composite exhibits a special field dependence of ME coefficient. Either for the resonant state or the nonresonant state, above 1kOe, the ME voltage coefficient increased linearly with the strengthening of bias field, up to 30V∕cmOe at 8kOe.

Nanoindentaion techniques for assessing mechanical reliability at the nanoscale

Nanoindetation is a powerful technique for measuring mechanical properties of thin films. First applied over 20 years ago in the hard drive industry, it is now commonly used for other applications. This paper describes nanoindentation techniques for measuring thin films mechanical properties, including elastic modulus, hardness, adhesion and fracture toughness as applied for modern microelectronics reliability. Elastic, plastic and adhesion properties of Cu interconnects are discussed, including the influence of film microstructure, thickness and grain size. Elastic, fracture and adhesion properties of advanced low-K dielectrics also discussed along with the current challenges of nanoindentation data interpretation and analysis as applied for advanced electronic materials.

Microstructure and mechanical properties of chromium oxide coatings

Chromium oxide coatings were deposited on low-carbon steel by radiofrequency reactive magnetron sputtering at different oxygen flux values. X-ray diffraction, x-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy were used to investigate the microstructure of chromium oxide coatings. Varying oxygen flux changed the coating microstructure; as with increasing oxygen flux the chromium oxide coating undergoes amorphous-to-crystalline transformation. The coating developed strong (300) texture at higher oxygen flux. Hardness, elastic modulus, wear resistance, and adhesion were investigated by nanoindentation and pin-on-disk tests. With changes in the coating microstructure as a function of increased oxygen flux, hardness, elastic modulus, and wear resistance were improved, but its adhesion was weakened.

Rare earth elements recycling from waste phosphor by dual hydrochloric acid dissolution

This paper is a comparative study of recycling rare earth elements from waste phosphor, which focuses on the leaching rate and the technical principle. The traditional and dual dissolution by hydrochloric acid (DHA) methods were compared. The method of dual dissolution by hydrochloric acid has been developed. The Red rare earth phosphor (Y0.95Eu0.05)2O3 in waste phosphor is dissolved during the first step of acid leaching, while the Green phosphor (Ce0.67Tb0.33MgAl11O19) and the Blue phosphor (Ba0.9Eu0.1MgAl10O17) mixed with caustic soda are obtained by alkali sintering. The excess caustic soda and NaAlO2 are removed by washing. The insoluble matter is leached by the hydrochloric acid, followed by solvent extraction and precipitation (the DHA method). In comparison, the total leaching rate of the rare earth elements was 94.6% by DHA, which is much higher than 42.08% achieved by the traditional method. The leaching rate of Y, Eu, Ce and Tb reached 94.6%, 99.05%, 71.45%, and 76.22%, respectively. DHA can decrease the consumption of chemicals and energy. The suggested DHA method is feasible for industrial applications.