'Thin films & coatings' Roadmap - Nano Mahidol

process requires specific resists. The resist impedes reaching the maximum
resolution.
Main barriers to success and research paths
According to the experts, the resist is one of the main bottlenecks for EPL
development while for direct write the fact that the electron beam can’t pattern the
surface all at once (as the UV process does) makes the process very expensive for
large area surfaces.
Due to the high energy of the electrons, the region of the resist affected by their
impact is much bigger than the area where electrons impact (it’s the so-called
proximity effect) and has a negative impact on the quality of the patterns.
One possible approach for improving direct-write throughput is to create arrays of
electron beams. Carbon nanotubes can be good electron emitters and experimental
arrays have been created.
2.3.3.5 Ion beam lithography
Ion beam lithography is a maskless process using an ion beam for depositing (or
removing) many types of materials (incl. conductors and insulators).
Main barriers to success and research paths
As compared to e-beam lithography, the main limitation is the limited penetration
depth of ions into the resist layer but it addresses e-beam limitations such as the
proximity effect or resist’s sensitivity. According to the experts, price is the main
limitation for this process development.
2.3.3.6 Ion milling
This is a physical method where ion particles are accelerated by an ion beam and
directed to the surface of a substrate. The ions remove any material not protected by
a resist material by relieving the bonding energy between the individual atoms in the
structure and ejecting the host atoms. The substrate is normally mounted in a
rotating table inside a vacuum chamber. Several alternatives of this process combine
physical and chemical routes (Reactive Ion Etching) where ions also react at the
surface materials (e.g. forming another gaseous material).
Main barriers to success and research paths
It is a highly anisotropic and, according to the experts, a slow and non-selective
etching process. The last is especially important in multi-layer thin films.
2.3.3.7 Sputter etching
This is a physical method based on the same mechanism as sputter deposition.
Sputter deposition works as follows: ions are generated and directed at a target
material to sputter atoms from the target; then, the sputtered atoms get transported
to the substrate through a region of reduced pressure and condense on the
substrate, forming a thin film. The big difference in sputter etching is that substrate is
now subjected to the ion bombardment instead of the material target used in sputter
21 Roadmap report on
Thin films and coatings