Thermal Nanoimprint Lithography (T-NIL)
The thermal imprint lithography (T-NIL) takes advantage of the characteristic properties of thermoplastic materials. When heated above its glas temperature (Tg), those materials can be molded and keep the shape when cooled to room temperature again.
A thin film of a thermoplastic polymer is prepared onto a substrate by applying e.g. spin-coating. As the film thickness of such a resist is typically defined by the concentration of the active components in an organic solvent, the thin film needs to be baked in order to remove the solvent. Afterwards, a stamp containing already predefined micro- or nanometer scaled patterns is brought into contact with the thin thermoplastic polymer film. Via heating the substrate-resist-stamp-stack markedly (approx. 60-80 K above Tg of the thermoplastic polymer) it becomes viscous and hence flowable. Simultaneously to the heating the now viscous thermoplastic polymer is then forced or pressed into the stamp cavities by applying a certain imprint pressure. After the cavities of the stamp have been completely filled with the thermoplastic polymer, it is solidified again by the means of cooling the system down below the polymers Tg. The stamp can be removed from the solidified NIL resist layer resulting in a negative topographical image of the stamp pattern in the resist. Finally, the imprinted structures will be transferred into the substrate by plasma etching steps in most of the use cases.
Since there usually occurs no curing during imprinting, the finally imprinted resist still shows its thermoplastic characteristic. Therefore, any thermal load after imprinting above the Tg of the resist will cause a reflow of the nanostructures and will destroy the originally imprinted pattern.
If thermally stable patterns are needed, alternative strategies should be considered (mr-I 9000M, mr-NIL 6000E, photo-NIL, UV-NIL). Our technical support can help you choose the perfect resist for your process and application.