Electron Beam Resist Performance
Due to the scission efficiency generally being an order of magnitude higher than the crosslinking efficiency, most polymers used for positive tone electron beam lithography will crosslink (and therefore become negative tone) at doses an order of magnitude than doses used for positive tone exposure. Such large dose increases may be required to avoid shot noise effects.
A study performed at the Naval Research Laboratory indicated that low-energy (10–50 eV) electrons were able to damage ~30 nm thick PMMA films. The damage was manifest as a loss of material.
- For the popular electron-beam resist ZEP-520, a pitch resolution limit of 60 nm (30 nm lines and spaces), independent of thickness and beam energy, was found.
- A 20 nm resolution had also been demonstrated using a 3 nm 100 keV electron beam and PMMA resist. 20 nm unexposed gaps between exposed lines showed inadvertent exposure by secondary electrons.
- Hydrogen silsesquioxane (HSQ) is a negative resist that is capable of forming sub-30 nm lines in very thin layers, but is itself similar to porous, hydrogenated SiO2. It may be used to etch silicon but not silicon dioxide or other similar dielectrics.
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