Gray scale lithography GSL was implemented using an aqueous developing photosensitive polyimide, HD8820.
Silicon carbide high kilo-volt power diodes and transistors fabrication required a tapered barrier for dopant ion
implantation and annealing at elevated temperatures for formation of junction edge terminations. The GSL
photomask was made by electron beam lithography 32-bit gray scale intensity profile exposure of a silver doped
HEBS glass that is sensitive to electron beams but not to ultra-violet UV radiation. When the photosensitive
polyimide HD8820 was exposed through the gray scale photomask in a UV lithography system, the desired
polyimide tapered profile was obtained. The polyimide patterns were subsequently converted to amorphous graphite
at 650°C in a nitrogen furnace. Boron and aluminum high temperature ion implantations at several energies and
doses were performed and the resulting dopant profiles, characterized using secondary ion mass spectroscopy SIMS,
were found to correlate well with computer simulations. The GSL tapered photosensitive polyimide can therefore
serve as an effective ion implantation barrier to obtain precisely graded dopant profiles. Micro-optics components
such as gratings and Fresnel micro-lenses were also successfully fabricated using gray scale lithography of the
photosensitive polyimide.
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