First results in patterning of ultra high aspect ratio microstructures by a 4T wave length shifter at BESSY

Both X-ray lithography beamlines at BESSY can be operated in three different modes: one coming from a dipole (1.3 T) is used for standard exposures for patterning PMMA and SU-8, while the other beamline, coming from a straight section of the storage ring, can be operated in soft wavelength mode (0.4 T) or alternatively in wave length shifter mode (4T). Using the soft wave length mode, copying processes for X-ray mask can be carried, while the very hard radiation generated in the wave length shifter (WLS) modes best for patterning ultra thick PMMA layers up to several mm in thickness. In WLS mode the higher magnetic field of 4T is shifting the critical photon energy to 7.7 keV compared to a standard dipole magnet with 2.5 keV. The lateral intensity homogeneity of this beamline is very high. Tests for using the WLS mode for ultra deep X-ray lithography (UDXRL) were performed and delivered very good results. PMMA layers of up to 4 mm in thickness were patterned successfully. Similar patterning methods to fabricate high aspect ratio micro parts were reported in literature.