Thick silicon membranes as mask blank for SU-8 X-ray deep lithography

摘要

Home made masks having thick (35-50 μm) silicon membranes as blanks were used in deep X-ray lithography of SU8 - a negative tone photoresist. X-ray masks were fabricated by the following sequence of steps: (a) vacuum deposition of Ti and Au thin layers on a 220 μm thick (100) silicon wafer, (b) optical lithography of two different patterns in both negative (SU-8) or positive (AZ4620) photoresist (c) gold electroforming and (d) silicon substrate thinning with KOH etch to form the membrane. X-ray exposures was performed in the X-ray beam line of the LNLS synchrotron light source. The samples consisted of 125 !!m thick layers of SU-8 supported on silicon and assorted substrates. The optimum dose for silicon substrates have been used in the remaining substrates, namely, metallic thin films (Cr, Cu, Au, Pt), printed circuit board (PCB), quartz, alumina ceramic and glass. The influence of mask defects, substrate type and X-ray dose values on the lithography of SU-8 is discussed. Criteria for defining upper and lower dose values for SU-8 X-ray deep lithography was proposed on the basis of characteristic defects. Advantages in using SU-8 rather than PMMA in the LIGA technology are commented