Poly electron beam lithography

Gold arrays are prepared by electron beam lithography (EBL) according to the following method. The bare substrate is a glass plate (10 mm X 10 mm) on which a thin indium tin oxide (ITO) substrate is evaporated. The ITO substrate is then spin coated (60 s, at 5000 rpm) with a 100 nm thick Poly methyl-methacrylate (PMMA) polymer,... 

Also worthy of mention is the introduction of conductive electron-beam resists that eliminate the charging effect that is so troublesome in electron-beam lithography. Todokaro et al. accomplished this by using a partially chloromethylated poly(diphenylsiloxane) as the top imaging resist in a bilayer system, and using the ionically conductive ammonium salt of poly(p-styrene sulfonate) (XXI) as the bottom layer. 

The problem in electron-beam lithography is that image distortion and pattern placement errors arise by resist charging during electron-beam exposure. 3-Alky-lated PTs, e.g. a copolymer made from 3-methyl- and 3-butylthiophene or water-soluble poly(3-thienyl-2-ethanesulfonate) as discharge interlayer and top layer eliminate the charging problem during the electron-beam exposure [144]. 

Typical resists include cyclized polyisoprene with a photosensitive crosslinking agent (ex bisazide) used in many negative photoresists, novolac resins with diazoquinone sensitizers and imidazole catalysts for positive photoresists, poly(oxystyrenes) with photosensitizers for UV resists, polysilanes for UV and X-ray resists, and polymethacrylates and methacrylate-styrenes for electron-beam resists (Clegg and Collyer, 1991). Also note the more recent use of novolac/diazonaphthoquinone photoresists for mid-UV resists for DRAM memory chips and chemically amplified photoacid-catalysed hydroxystyrene and acrylic resists for deep-UV lithography (Choudhury, 1997). 

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