The focus of this paper is on the use of SUEX Thick Dry Film Sheet (TDFS) laminates which DJ DevCorp is developing
as a thick resist material in optical and X-ray lithography. Preliminary thick dry film sheets up to 1mm thickness were
successfully prepared and patterned at the CAMD X-ray beamlines and presented at HARMST 2007. Recently, new
results have been published using SUEX resist sheets in UV lithography showing great market potential including
plating molds for metal microparts, polymer MEMS, multilayer microfluidics structures, BioMEMS, medical devices,
wafer level packaging processes, and displays. The SUEX TDFS are available in a range of thicknesses from 100μm to
1mm or more and are pre-cut into a number of standard wafer sizes.
This new material is a modified epoxy formulation containing an antimony-free photo acid generator (PAG) prepared
under a highly controlled solvent-less process which provides uniform coatings between two throw-away layers of
protective polyester film. As part of our initial studies resist layers of 250, 500 and 1000μm were laminated onto regular
silicon wafers using a hot roll laminator at a speed of 1ft/min at 75°C. The entire substrate preparation takes about 1
hour and with practice users can prepare up to 10 substrates in this time which are typically ready to use within 2 hours.
In our efforts to develop a commercially viable product we have conducted experiments using standard equipment
available at CAMD (Quintel UV aligner and CAMD XRLM 1 and 4 beamline). Initial X-ray exposure tests were done
with a bottom dose ranging between 100 and 400 J/cm3 and a top/bottom dose ratio of less than 3 for sheets up to 2mm
in thickness. Exposure time for typical conditions of the CAMD storage ring (ring current ranging between 100 and
160mA, beam lifetime of about 10hrs at 100mA ring current) is about 10-15min for a 4' wafer. After exposure the
samples were immediately post exposure baked between 70°C and 110°C using a convection oven, taken out and cooled
to RT then relaxed up to 3 days before development to reduce stress. Development was done in PGMEA for up to 3
hours for the 1000μm thick samples followed by a short IPA rinse and drying in air.
Very high aspect ratios of 100 or more have been routinely patterned with nearly perfectly straight sidewalls (~1-1.5μm
deviation for a 1mm tall structure) and excellent image fidelity.