SU-8 as resist material for deep X-ray lithography

A new negative tone resist for deep X-ray lithography is presented. This resist is a nine parts to one mixture of the EPON SU-8 resin with 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)propane (Tetrachlorobisphenol A, TCBA), the latter acting as the photoinitiator. The resist was irradiated at the synchrotron source of DCI at LURE. It was dried for 7 to 20 days beforehand over silica gel while under a light vacuum (20 mbar). Best results for a 150 mum high resist were obtained with a X-ray bottom dose of 3 kJ cm(-3) and a post exposure bake at 33 degreesC. Differential Scanning Calorimetry measurements (DSC) determined the glass transition temperature of the resist. The glass transition for the undried, loose resist was 34.7 degreesC, and it was 28.7 degreesC when the resist was pressed on a silicon substrate. For a sample of the dried resist, the glass transition was 33.4 degreesC for the loose resist and 29.8 degreesC when it was pressed on a Silicon substrate. CD measurements were made on top surface of a set of 100 mum long columns structures, which were produced in 150 mum of this resist. These structures have a constant 100 mum pitch, and the structures themselves varied in width from 20 to 17 mum. For these structures, the CD was calculated to be 0.15 +/- 0.03 mum.