'Thin films & coatings' Roadmap - Nano Mahidol

2.3.3.2 Plasma etching
(Dry) chemical plasma etching replaces the wet processing method that uses
solvents for producing the pattern and uses power (in opposition to spontaneous) to
drive the reactions. Plasma etching process consists on the following steps: reactive
species generation, diffusion to the solid, adsorption at the surface, reaction at the
surface, reactive cluster desorption and diffusion away from the substrate.
Main features are its good selectivity, its fast etching rate and that results in highly
isotropic characteristics. Ion energy is lower than in the ion milling process.
Main barriers to success and research paths
According to the experts there are still some technical barriers blocking this process
further application: the adhesion mechanism of organic systems to given surfaces,
the need for improved selectivity, homogeneity and for getting perpendicular etched
walls.
Besides these technical barriers, this technology is considered to be very specific to
each application and there’s a lot of work to be done to communicate its potential to
industrial end-users.
2.3.3.3 Nanoimprint lithography (NIL)
NIL and a collection of similar techniques use a stamp to create a pattern, for
instance in a resist of thermoplastic film (e.g. PMMA). Once the substrate and resists
are prepared, the stamp is heated and pressed into the thin film / substrate to
transfer the desired pattern. Then the stamp is cooled down and removed. In
principle NIL could get resolutions below 10 nm. Alternatively, a stamp can be 'inked'
with the desired thin film material and then applied to a surface to transfer the thin
film pattern (this approach is sometimes referred to as soft lithography).
Main barriers to success and research paths
According to the experts, at the lab scale the equipment is easily made; however,
proper alignment and the need to avoid stamps distortions are issues to be
addressed to make this a robust approach ready for industrial up scaling. Other
process limitations are the difficulty to align multiple layers and the process
applicability limited to very specific substrates (though some approaches are more
limited than others).
2.3.3.4 Electron beam nanolithography
Electrons have higher energy (shorter wavelength) than UV light and this is used to
produce patterns with features with magnitudes below that of those achieved by UV
light (reaching 0.5 nm). Electrons are emitted from the electron gun of a scanning
electron microscope and directed to the sample using electron optics. The electron
beam is computer-driven and the process is run in a vacuum chamber. The approach
can be direct write (no mask is used), which is already used extensively in research
and for making masks for optical lithography, but this has very slow throughput. A
possibility for higher throughput being pursued by the semiconductor industry is
electron projection lithography (EPL), which uses a scanning beam and a mask. This
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Thin films and coatings