Silicon wafers (diameter: 4 inch, thickness: 525 μm) were dehydrated at 180ºC for 30 min. in a forced ventilation oven. HMDS (hexamethyldisilazane, ABCR GmbH) adhesion promoter and
subsequently ma-P 1275 (Micro Resist Technology GmbH) positive photo resist were spin coated at 3000 rpm for 30 s.