Silicon nanoparticle deposition on silicon dioxide and silicon nitride : techniques, mechanisms and models
Abstract
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.