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21 March 2007 Gray-scale lithography of photosensitive polyimide and its graphitization
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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.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
S. Akbar, E. Imhoff, and F. Kub "Gray-scale lithography of photosensitive polyimide and its graphitization", Proc. SPIE 6519, Advances in Resist Materials and Processing Technology XXIV, 65191I (21 March 2007);

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