(Color online) Hybrid lithography process according to scheme A (see text), sketch (left), experimental details (right): after substrate treatment, the photoresist is spin-coated (h 0 = 200 nm), imprinted (T imp = 90 °C, t imp = 5 min, and p imp = 100 bar), exposed through a photomask (D = 500 mJ/cm2), and finally developed (t dev = 3 min). (a) 260 nm lines and spaces after imprint, the residual layer amounts to about hr = 30 nm. (b) Exposure through a photomask. Standing wave profiles within a plane resist film of 300 nm under broadband and i-line exposure including absorption. For broadband illumination, the Hg lines were summed-up (weighting: i: 40%, h: 28%, and g: 32%). Similar sensitivity for all three lines was assumed. Absorption was considered with an absorption coefficient of 1.2 μm−1. (c) Hybrid lithography result after development. Without PEB and without antireflective films below the photoresist, standing waves are present at the lithographic edges. Three distinct levels are observed in accordance with the relative intensity distribution [see (b)].
(Color online) Transition between exposed and unexposed region of preimprinted pattern (400 nm lines and spaces) subjected to hybrid lithography (500 mJ/cm2) with an additional PEB (100 °C and 1 min) to reduce standing wave effects. (a) Without the development step: strong reflow in unexposed region. (b) After 2 min development time: porous residues (can be removed by prolonged development time) and interconnected elevated patterns along the lithography edge (cavity loss, cannot be removed even with a prolonged development time).
(Color online) Demonstration of the viscosity increase due to exposure by means of an imprint experiment. The photoresist was locally exposed through a photomask (D = 350 mJ/cm2) before thermal imprint (T imp = 90 °C, t imp = 5 min, and p imp = 100 bar). The exposed region shows an increased viscosity, which is indicative of a molecular weight increase and/or partial cross-linking. Partially filled cavities make the viscosity difference visible. (a) Wide cavities, low filling level, regular filling: increased imprint depth in unexposed regions. (b) Small cavities, increased filling level: self-assembly defects in unexposed regions.
(Color online) Evaluation of the reflow response during PEB to exposure dose via UV-light and typical reflow examples (line width 260 nm, cavity width 260 nm, and residual layer 50 nm). (a) and (b) Typical sample cross sections with definition of evaluation parameters, (c) evaluation (see text). With increasing exposure dose the reflow is reduced, with doses higher than about 60 mJ/cm2 the imprinted patterns are stabilized.
Hybrid lithography results obtained with the negative tone resist ma-N 405 (T imp = 90 °C, D flood = 40 mJ/cm2, D = 180 mJ/cm2, T PEB = 100 °C, t PEB = 1 min, and t dev = 10 min). The standing waves are minimized and reflow is avoided. Flood exposure was applied after imprint before PEB. The residual layer is removed during development without any additional process step. (a) Line width 460 nm and cavity width 810 nm, (b) line width 260 nm and cavity width 360 nm.
Lift-off results obtained with ma-N 405 after a hybrid lithography process with a flood exposure before PEB. The lift-off (30 nm Au is sputtered and lifted in an ultrasonic bath at 50 °C) was performed without any additional step for residual layer removal. The 460 nm (a) and 260 nm (b) wide metal lines are well connected to the large, micron-sized metal film; there is no distinct narrowing of the metal line width, especially in the transition region at the line ends.
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