Photomask Generation

Photomasks are generated in-house from CIF files using a David Mann 1600A pattern generator upgraded with an IBM PC control system, and a Jade 4M- 10AXYL step-and-repeat camera providing 10X reduction. The preferred mask generation program is Tanner Graphic's Ledit5, but any system capable of producing CIF files can be used. Both the pattern generator and the step-and- repeat camera use only high resolution silver halide emulsion photographic plates. Neither has a light source or optics capable of operating at the UV wavelengths necessary to expose photoresist, so chrome masks cannot be produced. The pattern generator can resolve 6 µ features with 6 µ spacing. The minimum feature size obtainable with the step-and-repeat camera is approximately 2.5 µ, limited primarily by the grain size of the photographic plates. Level-to-level pattern registration has an error in the same range, due to play in the mechanical system used for reticle alignment. The maximum die size routinely used with this mask generation system is approximately 3.5 mm square. The pattern generator can use plate sizes ranging from 50 mm to 100 mm square. The step-and-repeat camera can use only 50 mm square reticles, and produces only 75 mm square working plates. An Oriel 8410 photomask contact printer is available to produce copies of photomasks, including copies between plates of different sizes.

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