Developing high technologies but in economic manners is necessary and also feasible for developing countries. At Chiang Mai University, Thailand, we have developed MeV-ion microbeam technology based on a 1.7-MV Tandetron tandem accelerator with our limited resources in a cost-effective manner. Instead of using expensive and technically complex electrostatic or magnetic quadrupole focusing lens systems, we have developed cheap MeV-ion microbeams using programmed L-shaped blade aperture and capillary techniques for MeV ion beam lithography or writing and mapping. The programmed L-shaped blade micro-aperture system consists of a pair of L-shaped movable aperture pieces which are controlled by computer to cut off the ion beam for controlling the beam size down to the micrometer order. The capillary technique utilizes our home-fabricated tapered glass capillaries to realize microbeams. Either system can be installed inside the endstation of the MeV ion beam line of the accelerator. Both systems have been applied to MeV-ion beam lithography or writing of micro-patterns for microfluidics applications to fabricate lab-on-chip devices. The capillary technique is being developed for MeV-ion beam mapping of biological samples. The paper reports details of the techniques and introduces some applications.

For soft lithography, the conventional negative tone resists, such as SU-8, that are used to create the mold have a number of drawbacks. PMMA, which is normally used as a positive tone resist, can be used as a negative resist by using high-fluence irradiation conditions. In this report, we outline optimization of the irradiation conditions for PMMA thin films using 2MeV H+ ions to exploit their ability to work as a negative tone resist at ion fluences above 1.0×1015ionscm−2. The main aim was to induce cross-linking while maintaining the exposed regions free of blisters and maintaining short irradiation times. We found that by using a two-step process with a low-flux irradiation, followed by a high-flux irradiation, the exposure time could be shortened by ∼50%. We also found that ion fluences greater than 5.0×1015ionscm−2 minimized the distortion in stitched regions.

Several recent reports have indicated that a tapered glass capillary tube with a tip size on the order of micrometers has a focusing effect on transmitted ion beams. In relation to our particular area of interest, this could be a simple and cheap way to generate a focused ion beam for ion beam lithography and beam-in-air analysis and irradiation applications. Here, details of the method and the equipment used to produce a tapered glass microcapillary tube will be described. The equipment, which is simply called a “glass microcapillary puller”, is made using an induction heater. This method ensures that the glass tube, which is inserted inside and along the central axis of the solenoid, is heated uniformly in all directions. The heating temperature is adjusted by a power control, with a maximum temperature of approximately 2,000C. The pulling tension is varied over a wide range by using different weights. Application of the tapered glass microcapillary for 2 MeV H+ ion beam lithography is also demonstrated.

In soft lithography, a pattern is produced in poly(dimethylsiloxane) (PDMS) elastomer by casting from a master mould. The mould can be made of poly(methylmethacrylate) (PMMA) resist by utilising either its positive or negative tone induced by an ion beam. Here we have investigated the irradiation conditions for achieving complete cross-linking and absence of blister formation in PMMA so that its negative characteristic can be used in making master moulds. PMMA thin films approximately 9 µm thick on Si were deposited by spin coating. The 2-MeV H+ ion beam was generated using a 1.7-MV tandem Tandetron accelerator. The beam was collimated to a 500×500 µm2 cross section using programmable proximity aperture lithography system with a real-time ion beam monitoring system and a high precision current integrator. The irradiated areas were investigated by a standard scanning electron microscope and a profilometer. It was found that both the ion beam flux and the stopping power of the ions in the polymer have a critical influence on the blister formation.

In this study, poly(methyl methacrylate) (PMMA) was investigated as a negative resist by irradiation with a high-fluence 2MeV proton beam. The beam from a 1.7MV 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 1–1000μm 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.