In this study, poly(methyl methacrylate) (PMMA) was investigated as a negative resist by irradiation with
a high-fluence 2 MeV proton beam. The beam from a 1.7 MV Tandetron accelerator at the Plasma and
Beam Physics Research Facility (PBP) of Chiang Mai University is shaped by a pair of computer-controlled
L-shaped apertures which are used to expose rectangular pattern elements with 1–1000 lm side length.
Repeated exposure of rectangular pattern elements allows a complex pattern to be built up. After subsequent
development, the negative PMMA microstructure was used as a master mold for casting
poly(dimethylsiloxane) (PDMS) following a standard soft-lithography process. The PDMS chip fabricated
by this technique was demonstrated to be a microfluidic device.