Photomask / Direct Write Lithography Documents

New nonpolymer materials, calixarene derivatives were tested as high-resolution negative resists for use in electron beam lithography. Arrays of 12-nm-diam dots with a 25 nm pitch were fabricated easily. The sensitivity of calixarene in terms of area dose ranged from 700 to 7000 µC/em², and the required dose for dot fabrication was about 10⁵ electrons/dot. The standard area dose for calixarene is almost 20 times higher than that for polymethyl methacrylate (PMMA), but the electron spot dose for dot fabrication by calixarene is almost the same as that for PMMA and other highly sensitive resists such as SAL (chemically amplified negative resist for electron beam made by Shipley). The electron spot dose for such extremely small dots does not seem to depend on standard area dose, but any resist tends to require the same dose under exposure in a 50 keV electron beam writing system. We propose a qualitative exposure model that suggests a tradeoff of dose and dot size. The calixarene seems to be promising material for nanofabrication.