Silicon nanoparticle deposition on silicon dioxide and silicon nitride : techniques, mechanisms and models
Leach, William Thomas
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This dissertation presents three studies discussing silicon nanoparticle deposition on two dielectric surfaces: silicon dioxode and silicon nitride. Attention is focused on growth of nanoparticles with a high areal density (1012 cm -2) and uniform size (~5 nm) for use as discrete charge storage elements in flash memory. Where possible, mechanisms that underlie nanoparticle formation and growth are revealed, and a model depicting the evolution of nanoparticle populations is presented. In the first study, the role of surface bound silicon adatoms is explored through quantitative surface seeding experiments. Disilane is cracked on a hot tungsten filament, liberating hydrogen gas and atomic silicon at a predictable and controllable rate. This technique is used to seed dielectric surfaces with known amounts of silicon prior to chemical vapor deposition (CVD), resulting in enhanced nanoparticle nucleation and higher densities. In the second study, temperature programmed desorption experiments are used to reveal SiO desorption kinetics for silicon rich SiO2 surfaces. This result combined with the knowledge of an adatom dependant nucleation mechanism provides insight into CVD of nanoparticles on SiO2 at various temperatures, and this system is contrasted to nanoparticle growth on Si3N4 surfaces where adatom desorption is negligible. In the third study, a quantitative model of nanoparticle growth is developed that allows kinetic mechanisms to be tested against experimental data. This model is based on a nanoparticle population balance and describes the evolution of nanoparticle density and size distribution over time. Two equations describing nucleation kinetics are put forth and their predictions are tested against CVD data. Overall, knowledge of chemical pathways involved in adatom deposition and depletion enable one to understand nucleation behavior and explain numerous trends related to nanoparticle formation. Additional understanding of nanoparticle growth and coalescence provides a basis for describing the entire evolution of a surface, from the early stages of nucleation to film growth.