Gray scale lithography is becoming a popular technique for producing three-dimensional structures needed in fabricating photonics and MEMS devices. The structures are printed using a variable transmission mask to yield the required continuous tone intensity during image formation. In binary half tone imaging (i.e., BHT), the transmission through the mask is adjusted by varying the open area of sub-patterns. Design rules, fabrication tradeoffs and a layout methodology employing a novel primitive cell to aid in constructing the BHT masks are discussed Simulation is leveraged to tie the BHT design with expected imaging results. The overall process is exercised by fabricating a specific grayscale design for use in a photonic application. The BHT mask approach to gray scale lithography is a viable method to fabricate three-dimensional images offering MEMS and photonics communities a cost effective alternative to gray scale masks which rely on specialty materials and films.
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