In UV-based nanoimprint lithography (UV-NIL) a UV-transparent nanostructured stamp is brought into contact with a substrate, which is typically spin-coated with a UV-curable polymer, the nanoimprint resist. Subsequent UV-curing of the resist and separation of stamp and substrate result in the pattern transfer. For a succeeding reactive ion etching (RIE) step it is important to use thin resist layers and to make sure that in the areas where the polymer is pressed down as little polymer as possible remains. This means that homogeneous and ultra-thin residual layers have to be achieved. To achieve this, a conformal contact of stamp and substrate is of paramount importance, since it is the only way to ensure high fidelity pattern transfer. This is however difficult if not impossible to achieve, since the solid stamp and the substrate usually are not perfectly flat.
In a typical nanoimprint setup stamp and substrate are furthermore both mounted on solid parallel plates (the stamp and substrate holder), giving them little chance to adapt and compensate for the unevenness and causing additional distortions.
We investigated the effect of a thin flexible layer located below a silicon wafer as a substrate in combination with a rigid stamp made of quartz. Different geometries were considered and experimental results were compared with 2D finite element simulations.
We show that a correctly designed compliant layer can successfully compensate for effects like bending of the stamp or stamp holder during imprinting. Using a commercially available EVG®620 nanoimprinter in combination with a rigid stamp (the stamp size is 25 mm x 25 mm) we achieve homogeneous residual layers over the whole imprinting area with a thickness below 10 nm using this method. The requirements for subsequent reactive ion etching are therefore fulfilled.
Our finite element simulations accurately explain the experimental observations. A comparison of different experimental setups with corresponding simulations gives further insight into the details of the nanoimprint process.
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