High molecular weight polystyrene as very sensitive electron beam resist

Graphical abstractDisplay Omitted Highlights? We studied electron beam exposure properties of high molecular weight polystyrene. ? Its sensitivity increases linearly with molecular weight. ? For 900kg/mol, the sensitivity is 1.1µC/cm2 when exposed at 2keV. ? The sensitivity is one order higher than PMMA and ZEP-520A. ? Line array patterns of 100nm half pitch can be well defined in polystyrene. Previously we demonstrated ultra-dense patterning using 2kg/mol polystyrene negative electron beam resist that has low sensitivity 16]. To drastically improve its sensitivity, here we studied the exposure behavior of polystyrene with molecular weight of 90 and 900kg/mol. Very high sensitivity of 1µC/cm2 was obtained for 900kg/mol when exposed at 2keV. The sensitivity for 90kg/mol polystyrene is about one order lower. The resist has a contrast around 1.5 that is nearly independent of molecular weight for the current range of molecular weight. It can achieve fairly well-defined patterns of 150-200nm period line arrays. Polystyrene is a simple and low-cost resist with easy process control and practically unlimited shelf life. It is also considerably more resistant to drying etching than PMMA. Therefore, the current high molecular weight polystyrene could be employed for applications that need moderate resolution but high sensitivity for a reasonable exposure time.