Ultraviolet lithography on sloped surfaces utilizing diamond turned holograms

A lithography method by means of a diamond turned hologram (DTH) is presented, that allows patterning of sloped surfaces. The DTH is manufactured by a modified diamond turning process, using a piezoelectric actuator, the nano fast tool servo, which modulates the depth of cut within submicrometer range at a frequency up to 10 kHz. In order to machine a DTH to be applied as phase masks for ultraviolet lithography, workpiece materials have to feature a sufficient reflectivity and excellent machinability. Ultra-fine grained aluminium was identified as most suitable workpiece material, since its reflectivity measures around 80 % and a homogenous structure can be machined. The employed DTH is used in a lithography setup in conjunction with a helium cadmium laser emitting at a wavelength of λ = 325 nm. Patterns up to a linewidth of 30 μm were successfully and consistently transferred on a photoresist coated planar substrate with a tilt angle of 30° with respect to the optical axis.