Development of Experimental Techniques/Facilities at JAEA R&D Centers

Takasaki Advanced Radiation Research Institute13-9 Microfabrication of Teflon with Ion Microbeams－ Development of New Microfabrication Techniques for Polymer Surfaces －3 MeV
H microbeam+Diameter of the beam
1 µm

3 MeV
H+ microbeam

250 keV
N+2 beam

Pre-irradiation

Fabrication ofmicro-protrusions

50 µm

Area not irradiatedwith H+ microbeam

130 µm130 µmArea pre-irradiated withscanned H+ microbeam

50 µm

Protrusions

50 µm

Area pre-irradiated withscanned H+ microbeam

Smooth10 µm

Fig.13-19 Microstructures on Teflon surfaces fabricatedwith scanned MeV H+ microbeams
When a 3 MeV H+ microbeam is scanned spirally from thecenter of a square or a circle, a pyramid or a cone is formed,
respectively.

Fig.13-20 Checkerboard pattern consisting of smooth andmicro-protrusion areas fabricated with a scanned H +microbeam before uniform N2+ beam irradiation
A 3 MeV H + microbeam is scanned horizontally to make acheckerboard pattern; subsequently, the entire surface isirradiated with a 250 keV N2+ beam. Only the H+-irradiated areas
become smooth.

At the TIARA ion accelerator facility at the Japan Atomic
Energy Agency/Takasaki, a microfabrication technique called
proton (H+) beam writing (PBW) has been established on thebasis of the techniques of focusing down an ion beam to a
1 µm spot size and scanning it arbitrarily over a target surface.
Concerning the resist materials, we have demonstrated PBW’s
specific ability to fabricate high-aspect-ratio microstructureswith chemical etching after irradiation. We have attempted toapply the technique to Teflon® (fluoropolymer), on which isdifficult to fabricate microstructures because of its chemicalinertness, and started research on microfabrication to berealized only with ion microbeams.
First, a revolutionary technique using a MeV H+ microbeam
was developed: fabrication of microstructures on a Teflon
surface through a process of local rising (Fig.13-19). A 3 MeV
H+ beam travels in a straight line to a depth of approximately
100 µm in Teflon. Along the trajectories, main-chain scission
is induced, and consequently degradation gases are formed.
The amount of the gases depends on the irradiation conditions

such as the beam current, irradiation time, and scanning
pattern. When the gases leave the inside of a Teflon target
as bubbles, they raise the irradiated area; as a result, themorphology is changed, as shown in Fig.13-19.
When a Teflon surface is irradiated with keV nitrogenmolecular ion (N+2 ) beams, an initial flat surface changes intoa lawn-like one covered with dense micro-protrusions. In
addition, we found the conditions under which H+ microbeam
irradiation does not induce any surface morphological changedue to the degradation gases but instead reduces the molecularweight. Subsequent N+2 beam irradiation makes the H+irradiated surface evaporate uniformly and very smoothly.
This morphological change was also applied to make a smoothsurface with micro-protrusion areas at the same ground level(Fig.13-20).
It is shown that only ion beam irradiation can enable themicrofabrication of chemically inert materials without any
chemical processes. We intend to expand this technique tovarious materials other than Teflon.

Reference
Kitamura (Ogawa), A. et al., Microfabrication on Teflon Surface by MeV-Proton-Microbeam and keV-Nitrogen-Ion-Beam Irradiation, Nuclear Instruments
and Methods in Physics Research B, vol.307, 2013, p.610-613.

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JAEA R&D Review 2013