Showing papers by "Carl V. Thompson published in 1989"

Grain size dependence of electromigration‐induced failures in narrow interconnects

Abstract: Measurements of the median time to failure (MTTF) and deviation in the time to electromigration‐induced failure (DTTF) of Al alloy thin‐film lines are reported. As the ratio of the linewidth to the grain size decreases, MTTF decreases to a minimum and then increases exponentially. DTTF continuously increases. We show that serial and parallel failure unit models can be used to explain the grain size and linewidth dependence of the MTTF and DTTF for interconnects. We further note that extrapolation to low cumulative failures based on serial failure models must be based on knowledge of the failure statistics of individual units.

Experimental evidence for nucleation during thin‐film reactions

Abstract: The reaction between solid layers to form a product phase has been studied using scanning calorimetry of multilayer Nb/Al and Ni/amorphous‐Si thin films. The most striking feature for both materials systems is the occurrence of two maxima in the reaction rate during the formation of a single product phase, suggesting a two step growth process. A model has been developed in which the first step is taken to be the nucleation and two‐dimensional growth to coalescence of the product phase, in the plane of the initial interface. The second step is taken to be the thickening of the product layer by growth perpendicular to the interface plane. The success of this simple model in describing the principal features of the experimental results on two different materials systems suggests that nucleation is an important aspect of phase formation and selection in these thin‐film reactions.

Focused ion beam induced deposition of low‐resistivity gold films

Abstract: Focused ion beam induced deposition of metals has up to now produced films with resistivities 30–5000 times higher than bulk values for metals because of high concentrations of impurities from the precursor gas incorporated into the films. We have demonstrated for the first time deposition of submicron Au films with resistivities approaching that of the bulk metal and carbon contents of <10 at. %. These results are particularly relevant to applications in integrated circuit restructuring and x‐ray lithography mask repair, where high film conductivity and purity improves interconnect quality and x‐ray opacity.

Effect of As4 overpressure on initial growth of gallium arsenide on silicon by molecular beam epitaxy

Abstract: We have demonstrated great improvement in the smoothness and defect density of GaAs films on Si by lowering the arsenic overpressure during growth of the initial layer (the first 500 A) of GaAs. We have studied the morphology and defect density of GaAs on Si films in which the initial layers were grown under either low As4 overpressure (7As4:1Ga, beam equivalent pressure) or high As4 overpressure (15As4:1Ga) conditions, with a constant gallium flux. In the early stages of growth there is a significant change in island morphology depending on the As4 overpressure. There is dramatic improvement of surface smoothness and crystal quality with reduced arsenic overpressure for 500‐A‐thick layers both immediately after growth at 350 °C and after heating to 580 °C. Diodes fabricated in 3.5‐μm‐thick films grown on initial layers that were grown under low arsenic overpressure have a very sharp reverse breakdown at voltages as high as 45 V, whereas diodes fabricated in films grown on initial layers that were grown u...

Relaxation phenomena in evaporated amorphous silicon films

Abstract: Power compensated differential scanning calorimetry, transmission electron microscopy, and density measurements were used to characterize relaxation phenomena associated with structural transitions in electron beam evaporated amorphous silicon thin films. Two transitions were observed in the amorphous films upon heating: a broad exothermic process below 600 K and an endothermic step beginning at 600 K. The broad exothermic process is due to the relief of bond distortions. The endothermic step is related to homogenization and densification of the structure of the amorphous silicon.

Numerical Modeling of Energy-Beam Induced Localized Melting of Thin SI Films

Abstract: We have developed a quantitative model, based on a two-dimensional finite difference enthalpy method, which accounts for the localized melting behavior of thin Si films on substrates. The model incorporates radiative and conductive heat flow components and takes account of the phase changes that occur during zone-melting recrystallization. Emphasis is placed on the effects resulting from the differences in reflectivity and emissivity between solid and liquid Si. The model provides quantitative information concerning the temperature profile of the Si film and the configuration of the solid-liquid interface. Results of the analysis indicate that there exist two distinct types of transition behavior: i) reflectivity-change dominated and ii) emissivity-change dominated. Partial melting and a nonplanar solid-liquid interface are characteristics of the reflectivity-change dominated behavior. The emissivity-change dominated behavior, on the other hand, can be characterized by explosive-like melting and a planar solid-liquid interface. The conditions and physical factors which give rise to these behaviors are discussed.

Kinetics and Thermodynamics of Amorphous Silicide Formation in Metal/Amorphous-Silicon Multilayer Thin Films

Abstract: Cross-sectional transmission and scanning transmission electron microscopy and thermodynamic and kinetic analysis have been used to characterize amorphous and crystalline nickel silicide formation in nickel/amorphous-silicon multilayer thin films. An amorphous-nickelsilicide layer was formed between the nickel and amorphous-silicon layers during deposition. Heating caused crystalline Ni2Si to form at the nickel/amorphous-nickel-silicide interface. The composition of the amorphous-siicide was determined to be approximately 1 Ni atom to 1 Si atom. Thermodynamic analysis indicates that amorphous-nickel-silicide could be in equilibrium with nickel and amorphous-silicon if there were kinetic barriers to the formation of the crystalline silicides. Kinetic analysis indicates that the “nucleation surface energies” of the crystalline silicides, other than Ni3Si, must be 1.6 to 3.0 times larger than that of amorphous-nickel-silicide.

The role of point defects in ion-bombardment-enhanced and dopant-enhanced grain growth in silicon thin films

Abstract: Both ion bombardment and the addition of electronically active dopants lead to enhancements in the rate of normal grain growth in polycrystalline silicon films. Models have been developed which explain these phenomena in terms of their effect on the vacancy concentrations at grain boundaries. Taken together, the models suggest a general relation between the enhanced grain growth rate and non-equilibrium point defect concentrations. To test this idea, grain growth experiments have been carried our with polycrystalline silicon films subject to both ion bombardment and doping. The experiments, which indicate that the contributions to the enhanced grain growth rate by doping and ion bombardment are approximately additive, are consistent with this general relationship.

The Effect of Annealing on the Structure of Epitaxial CaF2 Films on Si(100)

Abstract: We have studied the effect of different annealing conditions on the crystallinity and morphology of 1000A epitaxial CaF2 films on Si(100). The crystallinity of the films is improved by the anneals, with the highest anneal temperatures giving the greatest improvement. The results are consistent with the model previously proposed to explain the success of rapid thermal annealing in improving thicker epitaxial CaF2 films.

Structural Transitions in Titanium/Amorphous-Silicon Multilayers

Abstract: We report a quantitative investigation of silicidation in Ti/amorphous-Si thin-films using Differential Scanning Calorimetry (DSC), thin-film X-ray diffraction and Cross-sectional Transmission Electron Microscopy (XTEM). Multilayered thin films were used to facilitate calorimetric observation of the heat released or absorbed at many reacting interfaces. It is shown that calorimetric analysis, combined with structural analysis using X-ray diffraction and XTEM, is effective in providing both kinetic and thermodynamic information about interdiffusion reactions in thin films. The present paper describes experimental results for multilayers with an atomic concentration ratio of 1 Ti to 2 Si and modulation periods ranging from 10 to 60 nm. A thin amorphous titanium suicide layer was found to exist between the as-deposited Ti and a-Si layers. Heating the multilayer film caused the amorphous Ti-silicide to grow over a broad temperature range by an exothermic reaction. An endothermic relaxation occurs during the late stage of amorphous suicide growth. Heating to temperatures over 800K causes C49-TiSi2 to form at the a-si1icide/a-Si interface. Temperatures at which all the above structural transitions occur vary with modulation period. Analysis of the DSC data indicates an activation energy of 3.1 eV for the formation of C49-TiSio, which is attributed to both the nucleation and the early growth of the suicide. The heat of formation for C49-TiSi2 from a reaction of a-silicide and a-Si was found to be -30±5KJ/mol. Nucleation appears to be the controlling step in C49-TiSi2 formation.