'Thin films & coatings' Roadmap - Nano Mahidol

equired to understand the growth mechanism and consequently the control of
structural and morphological relaxation. According to the experts, in polymer thin
films, it’s especially important to understand the impact of the annealing process on
the thin film properties.
The temperature required and the long processing time (due to the slow cooling
required) hinders the cost-effectiveness of this process. Some experts highlighted
that research should perhaps focus on avoiding the need for annealing process.
Experts have also pointed out the incompatibility of the annealing process with
certain types of substrates as well as the difficulties to ensure process reproducibility.
2.3.2.2 Thermal oxidation
Thermal oxidation is a technique that uses very high temperatures (approximately.
700-1300 ºC) to increase the growth rate of oxide layers. This high temperature is
used to speed up the oxidation process (that for most of the materials used – e.g. Si -
would naturally occur at a lower pace). The process consists of exposing the raw
material substrate to an oxidizing environment (O 2 – dry oxidation – or H 2 O – wet
oxidation) and occurs at the surface of the substrate where the raw material is
progressively replaced by the correspondent oxide. The oxide growth rate is
positively affected by time, temperature, and pressure.
Main barriers to success and research paths
According to the experts, two main barriers still exist: the difficulties to ensure
process reproducibility and the need for in-situ observation of the process.
2.3.2.3 Ultra Violet (UV) curing
Ultraviolet (UV) curing could be used both to dry the coating (from liquid to solid) and
to cross-link thin film and substrate. A wide range of substrates is suitable for UV
curing, from metal sheets to thin polymeric films. There are two crucial parameters:
UV-light intensity and exposure duration. Some applications may require several
curing steps involving different intensities of light and duration of exposure.
When used for cross-linking, the UV-curing adhesive consists of 2 components:
adhesive resin and photo-initiator (already mixed up with the resin). The photoinitiator
only reacts with the resin after having absorbed suitable UV light (wavelength
and intensity).
Main barriers to success and research paths
According to the experts, when used for cross-linking purposes, a key issue is the
stress induced in the film during the cross-linking process. Suitable solutions would
require low/no-shrinkage cross-linking agents and the appropriate experimentation.
Other bottlenecks are the difficulties to cure complex 3D dimensional bodies by UV
curing; it’s very difficult to avoid (not irradiated) shadow zones. According to the
experts, this is a standardised process that works well within its resolution limits but
the equipment required becomes expensive for features under 100nm. In-situ
observation of the process has been pointed out as a possible means to overcome
these barriers
18 Roadmap report on
Thin films and coatings