Transparent masks for aligned deep x-ray lithography/LIGA: low-cost well-performing alternative using glass membranes

Deep x-ray lithography/LIGA has proven to be a well established framework of x-ray based technologies for the fabrication of microstructures and pseudo three-dimensional objects. inherently, x-ray lithography/LIGA is not fully three-dimensional because of the principle of simple shadow printing onto resists of constant thickness. Thus, it would be impossible to obtain 3D spheres, but series of stacked monolithic 2D cylinders. Hence, until recently, LIGA was mainly concerned with simple uni-level (ID) monolithic structures, using optically opaque mask-membranes like Be, Si or Ti with grown-on Au absorbers. In the course for mastering pseudo three-dimensional microstructures like micro-coils or electromagnetic applications, an alignment in between the lithographic steps becomes necessary which requires optically transparent membrane materials, if optical alignment is chosen. Diamond or SiC membranes are the actual suitable materials for such purposes, but their pricing and/or process robustness inhibit their frequent use in simple projects. We would like to report on a new promissing material: a glued-on thin glass membrane. The advantages are incomparably lower costs compared to Diamond or SiC technologies, a considerable ease of fabrication, handling, quite favorable mechanical/optical properties, sufficient for lithographic purposes and multi-level deep x-ray lithography/LIGA activities.