High resolution electron beam lithography of PMGI using solvent developers

We report in this paper that typical solvent developers for PMMA can be used to develop PMGI (polydimethyl glutarimide) with a contrast much higher than that reported using base developers. Three developers were studied: methyl isobutyl ketone (MIBK), 2-ethoxyethanol (cellosolve), and methyl ethyl ketone (MEK). MIBK developer results in the highest contrast of 6.7 which is comparable to that of PMMA, followed by MEK (4.0) and then by cellosolve (2.6). The sensitivity is around 1000 μC/cm2, roughly four times that of PMMA and almost independent of the developers. Higher resist baking temperature leads to higher contrast for MEK and cellosolve, whereas for MIBK the optimum baking temperature is 200 °C. Both MIBK and MEK (but not cellosolve) developers can resolve 50 nm pitch grating with slight line distortion which is similar to that achievable by PMMA. Using a single step development, a double layer of PMMA and PMGI could be employed to facilitate the liftoff process or to fabricate a T-shaped gate structure, while a multilayer stack can be used to produce 3D metal structures by electroplating.