PMMA- and copolymer e-beam resists are not light-sensitive in the visible UV range, they consequently don’t react to light exposure (no safe yellow light required) and are substantially less temperature-
If new and clean substrates (wafers) are used, a bake at approximately 200 °C for a few minutes is sufficient in order to dry the substrates, which however then have to be processed quickly.
Adhesion between substrate and coating is a sensitive feature of a resists, which is also true for e-beam resists. PMMA- and copolymer resists are however significantly less prone for adhesion problems than e-
By using very short-wavelength electrons for the exposure of the resists, an excellent resolution of up to 2 nm can be achieved (spot beam). Exposure is carried out by conventional e-beam equipment following the principle of direct writing or shaped beam procedure.
During development, a positive tone resist film is patterned by a removal of exposed areas, while unexposed areas are removed when negative resists are used. To achieve reproducible results,
For the removal of all e-beam resist coatings baked at lower temperatures (softbake), polar solvents may be used such as e.g. the recommended thinner AR 300-12 or AR 600-01, 600-07,
With respect to the achievable resolution, purely academic resolution values and industrially utilisable values represent two quite different aspects. Theoretically, resolutions of 2 nm are possible (single electron spot)
Electron beam resists of the AR 6000 and AR 7000 production line display quite different etch resistance features in dry etch processes such as e.g. argon sputter and CF 4 . Novolak-
Concentrated oxidising acids (sulphuric acid, nitric acid, aqua regia 1) , piranha 2) ) attack resist films already at room temperatures and are often used as remover for persistent resist structures.
With respect to the source materials used, e-beam resists fall into two different categories: PMMA resists (AR-P 6000) Novolak resists (AR-N/P 7000) » The general rule is that with increasing bake-