  Aluminum oxide thin films were deposited on silicon substrates under
different deposition conditions using pulse pressure metal organic chemical
vapour deposition (PP-MOCVD). The current study investigates into the growth
mechanism of the deposited film and the control of the film morphology by
varying the processing parameters of PP-MOCVD - choice of solvent,
concentration, and presence of a shield. Aluminum sec-butoxide (ASB) was used
as the aluminum source while hexane and toluene were used as the solvents. The
films were deposited at 475oC at different precursor concentrations. It was
observed that the choice of solvent has no effect on the surface morphology,
but it influenced the deposition rate. The improved deposition rate, relatively
close enthalpy of vaporisation ({\Delta}H) values and uniformity of the film,
irrespective of the growth conditions, showed that hexane was a better solvent
for ASB than toluene. A hybrid mode of vapour deposition and vapour
condensation model for thin film growth is proposed where five different
mechanisms lead to a solid film formation. These include vapour phase
deposition under low arrival rate, vapour phase deposition under high arrival
rate, Leidenfrost aerosol formation, heterogeneous particle formation and
liquid droplet impingement. The important parameter that needs to be controlled
is the precursor flux arrival rate which can be controlled by varying the
precursor concentration, use of a solvent with a low {\Delta}H and the presence
of a shield over the substrate, which influences the surface morphology and the
growth rate of the films.
