Bilayer resist process for exposure with low-voltage electrons (STM-lithography)

With STM lithography employing a bilayer resist system, an electron sensitive top resist and a conductive bottom resist, it is possible to generate patterns with dimensions of 100 nm and less. Patterns with aspect ratios up to 8 at a width of 50 nm in flat silicon oxide surface have been achieved. We also demonstrate, that it is possible to operate on prepatterned substrates using a third planarizing resist layer. The exposure mechanism in our CARL top resist has been determined to work differently from the mechanism in the high electron energy regime. The low energy electrons directly cleave the t-butyl ester group. Chemical amplification was not observed. The maximum writing speed for complete exposure in the resist was 1-5 mu m/s at 20 pA writing current.