Nanooptics and photonics

Proton beam writing setup for fabrication of 3D micro- and nano-structures
A.G. Ponomarev, S.V. Kolinko, V.A. Rebrov, S.V.Salivon
Institute of Applied Physics, National Academy of Sciences of Ukraine, 58, Petropavlivska St., 40000 Sumy, Ukraine. 
E-mail: ponom56@gmail.com

Proton beam writing is a direct writing techniques that uses a focused beam of MeV energy protons to fabricate in resistive materials of 3D micro- and nano-dimensions structures. Protons, being more massive than electrons therefore have deeper penetration in materials while maintaining a straight path. The structures have high aspect ratio with vertical, smooth sidewalls and low line-edge roughness. Calculations have also indicated that p-beam writing exhibits minimal proximity effects, since the secondary electrons induced in proton/electron collisions have low energy. High aspect ratio three-dimensional microstructures with nanometer details have a growing interest for optoelectronic devices, micro- and nano-electromechanical systems, for biochips using microfluidic channels and for other applications.
	In this presentation the new scanning proton microprobe on the base of compact electrostatic accelerator specialized for proton beam writing process is described. The microprobe setup has spatial resolution about 100 nm. The electrostatic two-coordinate scanner controls of focused proton beam moving over the resist surface. The main feature of this scanner is the high repeatability of beam positioning, the short dead time, and the possibility to attain a high scanning frequency up to 1 MHz. The multifunctional configurable input–output module NI 7852R is used in the scanning control system. This system ensures the positioning of the focused beam on the exposed sample in accordance with the preset scanning profile. The scanning profile is a 1D array (sequence of the (xi,yi) coordinates of the dot matrix points). The beam exposure time can be set the same for all points (pixels) or individual (ti) for each pixel. In addition, the exposure time for each pixel can be normalized in fluence (irradiation dose). First experiments on fabrication of micro diffraction grate patterns are presented. After electroplating these gratings are used to obtain a phase contrast image by means of interference from incoherent radiation from a conventional X-ray tube.