Direct writing with an MeV proton beam: Development and Applications

Sammanfattning: This thesis presents work aimed at the development and application of a new lithography system for direct material patterning with the MeV proton beam at the Lund Nuclear Microprobe (NMP) facility. MeV proton beams are advantageous for use as a patterning tool due to their deep and well defined penetration through matter and their highly local energy deposition. This allows the fabrication of three dimensional microstructures with high aspect-ratio and density in various materials. This new and exciting application of nuclear microbeams is called Proton Beam Writing (PBW). In the work presented here, an MeV proton beam focused to micrometer size was used for high lateral resolution patterning. To achieve this, the existing beam and sample control and data-acquisition setups were complemented by use of nuclear electronics and a new beam blanker, resulting in a lithography system. The beam irradiation time and the position control were improved after the installation of a fast electrostatic beam blanker at the micro beamline. High-accuracy beam current measurement became possible when a new on-line pA-range measurement setup was added to the sub-micro beamline. Proton beam writing, using the new lithography system, was successfully performed and various complex microstructures in SU-8 negative resist and porous silicon were produced. The exposure process was optimised to achieve the minimum structure size and structures with the highest aspect and density ratios for a given beam size and resist thickness. The smallest microstructures 1.5 ?m in diameter, the highest density and aspect ratio of 4:1 and 20:1, respectively, in 4-95 ?m thick SU-8 resist were fabricated. An inversed anodisation at low fluence in porous silicon was demonstrated. It was shown that, with large exposure latitude PBW is a simple and easily controlled fabrication method. Two new applications of the PBW technique were realised. Structures with high aspect ratio and high density were used for the fabrication of thin opaque phosphor micro-grids in metal. The micro-grids represented an order of magnitude improvement for single ion detection resolution in Ion Photon Emission Microscopy (IPEM). The other application utilises MeV proton beam patterned porous p-type silicon that serves as an anchor plate for sample deposition intended for Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI MS). The new sample anchor plate confines an increased volume of analyte and enhances the sensitivity of the detection method.