Mask prototyping for ultradeep x-ray lithography: preliminary studies for mask blanks and high-aspect-ratio absorber patterns

The use of hard X-ray energies for ultra-deep X-ray lithography requires a thorough re-investigation of all issues associated with the LIGA technology materials issues and processes, in particular for the manufacture of high-energy-X- ray masks. Calculations were performed to compare various mask blanks in particular thick Kapton R and thinned silicon blanks. Absorber pattern formation schemes have been investigated using UV contact printing or X-ray lithography with SU8 photoresist. SU8 photoresist also offers an improved X-ray sensitivity over PMMA resist. Resist patterns over 500 micron deep with aspect ratio over 10 and vertical sidewalls were achieved in SU-8, allowing the use of medium energy range X-rays to obtain high quality patterns of much greater resist thickness.