Vineet Kumar

Classical size effect in oxide-encapsulated Cu thin films: Impact of grain boundaries versus surfaces on resistivity

A methodology is developed to independently evaluate surface and grain boundary scattering in silicon dioxide-encapsulated, polycrystalline Cu thin films. The room-temperature film resistivity for samples with film thicknesses in the range of 27 to 1u200965 nm and different grain sizes (determined from approximately 400 to 1500 grains per sample) is compared to existing and empirical models of surface and grain boundary scattering. For the combined effects of surface and grain boundary scattering, the surface specularity parameter p is 0.6±0.2 and the grain boundary reflectivity coefficient R is 0.45±0.03. It is thereby shown that the resistivity contribution from grain boundary scattering is significantly greater than that of surface scattering for Cu thin films having Cu∕SiO2 surfaces and grain sizes similar to film thickness.

Microstructural analysis of lead-free solder alloys

Among the many issues related to the performance of lead-free solder alloys, the dependence of their mechanical properties on the microstructure and the stability of the microstructure stability are some of the most important issues. A comprehensive understanding of the process-microstructure-property relationships is essential. Toward that goal, a microtextural analysis is performed using orientation imaging microscopy (OIM) for alloy Sn-3.8Ag-0.7Cu (wt pct) processed at four different temperatures. Sn-3.8Ag-0.7Cu is one of the most promising lead-free solder alloys that has shown superior mechanical properties to other candidate lead-free solder alloys. However, a comprehensive understanding of their microstructure and the dependence of microstructure on processing conditions are still lacking. In the present work, a detailed microstructure characterization with respect to phase compositions, grain size and size distributions, texture, and orientation relationships between various phases are performed. The measured microstructural features are correlated with the soldering temperatures.

Orientation Imaging Microscopy With Optimized Convergence Angle Using CBED Patterns in TEMs

Grain size statistics, texture, and grain boundary distribution are microstructural characteristics that greatly influence materials properties. These characteristics can be derived from an orientation map obtained using orientation imaging microscopy (OIM) techniques. The OIM techniques are generally performed using a transmission electron microscopy (TEM) for nanomaterials. Although some of these techniques have limited applicability in certain situations, others have limited availability because of external hardware required. In this paper, an automated method to generate orientation maps using convergence beam electron diffraction patterns obtained in a conventional TEM setup is presented. This method is based upon dynamical diffraction theory that describes electron diffraction more accurately as compared with kinematical theory used by several existing OIM techniques. In addition, the method of this paper uses wide angle convergent beam electron diffraction for performing OIM. It is shown in this paper that the use of the wide angle convergent electron beam provides additional information that is not available otherwise. Together, the presented method exploits the additional information and combines it with the calculations from the dynamical theory to provide accurate orientation maps in a conventional TEM setup. The automated method of this paper is applied to a platinum thin film sample. The presented method correctly identified the texture preference in the sample.

Grain growth and void formation in dielectric-encapsulated Cu thin films

Grain growth in 40-nm-thick Cu films encapsulated by overand under-layers of SiO2, Al2O3, Si3N4, and MgO was investigated. The films were magnetron sputter deposited onto cooled SiO2/Si substrates in an ultrahigh vacuum purity environment. Ex situ annealing was performed at 400 and 800 °C in 1 atm reducing gas. Films deposited at −120 °C exhibited more extensive grain growth after annealing than films deposited at −40 °C. Films annealed at room temperature had grain sizes less than 35 nm. All films exhibited some void formation after annealing at 400 and 800 °C, but the films encapsulated in Al2O3 exhibited the lowest area fraction of voids. The mean grain sizes of the Al2O3-encapsulated films, as measured by the linear intercept method, were 86 and 134 nm after annealing at 400 and 800 °C, respectively.

Resistivity Size Effect in Encapsulated Cu Thin Films

The work addresses the resistivity increase in Cu interconnects with decreasing linewidth. The surface and grain boundary scattering parameters in Cu thin films encapsulated in SiO2 with and without Ta barrier layers are quantified, and grain boundary scattering is shown to be much greater than surface scattering. 21 samples and 17,882 Cu grains were measured to provide the grain size data. This work indicates that significant mitigation of the Cu resistivity increase with decreasing linewidth is possible, if the grain size can be maintained larger than the electron mean free path (39 nm at room temperature).

Geometric model of sintering of unequal-sized particles

Sintering is a materials processing method generally applied to high-melting point materials. Performance of a sintered product is influenced by its microstructure. The effects of processing parameters, such as sintering time and temperature, on the microstructure are usually understood with the help of geometric models. Most geometric models assume equal-sized particles in the powders. This assumption neglects coarsening by inter-particle mass transport and grain boundary migration. Moreover, this assumption is seldom true in practice; because, coarsening and grain boundary migration always occur during sintering, especially during sintering of nanosized and ultrafine particles. In this paper, we present a model to quantitatively describe the sintering process of powders with unequal-sized particles. The present model relies on calculations of diffusional flux for neck growth and coarsening during sintering. In addition, we derive an expression to describe the grain boundary migration. We apply the model to predict the sintering behaviour of two equal-sized particles, two unequal-sized particles and a row of unequal-sized particles. We validate the model by comparing with Kingery and Bergs model, phase field simulations, and sintering experiments. The comparison showed that the model can be used to predict the sintering process with a reasonable accuracy.