The objective of the work was to deposit semiconducting thin films with
controlled properties using unbalanced reactive magnetron sputtering. It
was decided to utilise this technique because it offers high deposition
rate and controllable in-situ ion bombardment of the growing film,
desirable attributes from both research and production perspectives.
Sputtering from a metal cathode in a reactive gas atmosphere introduces
process instabilities which can result in a low degree of control over the
stoichiometry, optical, electrical and structural properties of the films.
Whilst the focus of the study was to achieve repeatable control over
semiconducting film properties, additional areas of interest associated
with the reactive sputtering process were investigated as the project
developed.
Improvements in magnetron design have been made to remove iron
contamination from the extended poles, at the same time improving
cathode utilisation. A new technique of bonding polycrystalline silicon
cathodes to cooling shims has been developed using a sputtered threemetal
multilayer process.
DC sputtering of silicon in the presence of oxygen, nitrogen, nitrogen
and oxygen, and nitrogen and air has been used to produce films of
refractive index between 2.27 and 1.45 at rates between 0.5 and 2 nms-1
depending on composition. Refractive index and optical transmittance of
the films have been closely controlled by varying gas flow and
composition, and substitution of air for oxygen increased the sensitivity
so that indices of oxy-nitride films could be tailored to one decimal
place.
The deposition of Indium-tin-oxide (ITO) onto glass substrates has been
investigated, using a feedback control loop to control the otherwise
unstable process...cont'
