Lecture 10 - ME 601: Manufacturing in Micro- and...

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ME 601: Manufacturing in Micro- and Nanosystems Lecture 10: Electron Beam Lithography Resists and Processes
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Electron Beam Lithography Resists Analogous to photosensitive resist but chain scission or cross- linking results from e-beam exposure Can be positive or negative tone, conventional or chemically amplified Generally divided into two categories according to application: mask making (low resolution), direct write (high resolution) Sensitivity varies according to chemistry; low sensitivity = higher resolution
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PMMA Poly (methyl methacrylate), common positive resist with low sensitivity for high resolution applications Resist formulated from PMMA dissolved in solvent, typically chlorobenzene or anisole Sensitivity depends on molecular weight and developer concentration, can also be exposed by UV or X-ray Turns from positive to negative resist due to crosslinking reaction at very high exposure dose Disadvantage: poor etch resistance (selectivity), limits aspect ratios during DRIE Common trade- and nicknames: acrylic, Plexiglas, Acrylite, Lucite, Vitroflex
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Resist Application E-beam resist processed in same manner as that used for photolithography: spin coating, baking, chemical development Resist thickness varies with spin speed but can also be tuned by changing solids loading/molecular weight
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Recall positive resist remains where unexposed, negative resist remains where exposed Considering raster/vector scan nature of e-beam exposure, how does this affect process design considerations? Negative resist exhibits more beam
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Lecture 10 - ME 601: Manufacturing in Micro- and...

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