Considerations for the Deep X-ray Lithography with the SU-8 Resist

It is shown, that deep X-ray exposures of the SU-8 resist can achieve high resolution with substantially reduced exposure times. Irradiation at the synchrotron source of DCI at Lure (Paris) demonstrated a reduced exposure time for a 600μm thick SU-8, where the dose needed to obtain standing structures was 30J/cm3. Critical dimension measurements (CD) of the 600μm SU-8 resist structure have been obtained for the entire height of the structure and X-ray doses of 30J/cm3 achieved a CD gain per edge of +0.5μm, while doses of 40J/cm3 yielded a CD gain per edge of 0.9μm. However, the gain in the CD per edge is critically dependent on the solvent content in the resist. Doses of 40J/cm3 into a resist with a 2-4% residual solvent content yielded CD gains per edge of 0.3μm. Moreover, the variation in the CD per edge is less than 0.1μm along the entire height of the structure.