Competitiveness of negative tone resists for nanoimprint lithography

• A semi-analytical approach in a matrix form to handle the intensity distribution within photoresist layers.
• Thermal nanoimprint with well-defined residual layer (dR ⩽ 30 nm) and without physical self-assembly defects.
• Residual layer removal by development.

This paper presents a semi-analytical approach for the calculation of the mean relative intensity within photoresist layers of a given thickness on silicon – the mean intensity is the one obtained after a post exposure bake to remove standing wave effects. The approach is based on the handling of analytically determined intensity values in a matrix form. Transmission, reflection and absorption in an air/resist/substrate configuration are considered to calculate the intensity for a single wavelength or a multiple wavelength exposure. Swing curves of the mean relative intensity as a function of the total resist thickness indicate a novel application in the context of nanoimprint: a residual layer-free imprint can be obtained with residual layers of up to about 30 nm, as such thin layers always remain underexposed. Thus, when a negative tone photoresist is imprinted and is flood exposed after the imprint, any thin residual layer will be removable in a simple development step, thus avoiding any breakthrough etch. This is of particular interest for a further use of the imprinted structures with lift-off.

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