Deep ion projection lithography in PMMA: Substrate heating and ion energy concerns

 Previous studies of deep ion projection lithography (DIPL) in various polymers using heavy ions from a medium energy accelerator have addressed the need for a less expensive technique. Here, a van de Graaff low energy accelerator has been used for DIPL with 8 MeV protons in 500 μm thick sheets of polymethylmethacrylate (PMMA). Standard type and strongly crosslinked PMMA were used. Although DIPL has not reached the same maturity as LIGA the advantages with DIPL are that it can be considerably cheaper, faster, and that it is possible to do 3-dimensional reproductions of the mask. The need for optimising a future DIPL irradiation system has led us to investigate the microscopic and macroscopic heating induced by the ion beam, as well as the heat transport. The DIPL technique, which enables high throughput production of LIGA-like structures in several insulating materials, has been used with success on thick PMMA.