Silane and disilane diluted in argon and hydrogen mixtures were pyrolyzed behind incident shock waves at temperatures ranging from 900 to 2000 K, pressures from 0.2 to 0.7 atm, and total concentration from 3 x 10 16 to 1 X 10 17 silicon atoms per em', Formation of silicon particles was monitored by the attenuation of laser beams of two different wavelengths, thereby determining particle size, number density, and fractional yield. The conversion of silane and disilane into silicon particles exhibited a pronounced maximum at about 1150 K, which was found to be affected by reaction pressure, initial reactant concentration, and addition of hydrogen. Selected silicon particle samples were examined by electron diffraction, transmission electron microscopy, and secondary ion mass spectrometry. The results indicated that the produced particles were spherical, ranging from 100 to 400 Ain diameter, loosely agglomerated, and contained about 15% hydrogen on an atomic basis. A detailed chemical kinetic model was developed that describes gas-phase pyrolysis of the parent molecule and homogeneous nucleation of silicon particles by 117 elementary reactions of 42 chemical species, and coagulation of the forming particles and their growth by gas-surface deposition reactions with a method of moments. The model predictions were found to be extremely sensitive to the values of optical constants assigned to the silicon particle material.

The ac electromigration of multilayered interconnect systems, consisting of TiW/AlSiCu and CVD-W/AlSiCu, is studied under stress of repetitive dual-pulse current waveforms at 2 MHz. By using a general ac waveform in which the peak current density of the first pulse jl is fixed and the second is varied from +jl to -j1, we obtain a continuous electromigration spectrum from dc through pulsed dc to pure ac conditions. Although an average current model fits the data well, there is a singularity in the median time-tofailure at pure-ac conditions. To avoid this singularity, a novel modification of the average current model, called the Average Current Recovery (ACR) model, is developed. It heuristically accounts for the degree of damage recovery during oppositepolarity pulses through a single recovery parameter.

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