Polyimide nanostructures fabricated by nanoimprint lithography and its application as flexible imprint mould

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Proceedings of the International Conference on Micro- and Nano- Engineering 2005, 2005

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Polyimide nanostructures fabricated by nanoimprint lithography and its

application as flexible imprint mould

Cui, Bo; Cortot, Yann; Veres, Teodor

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Polyimide n a n o s t r n c t u r e s fabricated by n a n o i m p r i n t lithography a n d its application a s flexible i m p r i n t mould

Bo,

Industrial Materials Institute, National Research Council of Canada 75 de Mortagne Blvd, Boucherville, QC J4B6Y4, Canada phone: 1450-641-5231, fax: 1450-641 -5 105, email: bo.cui@nrc.ca

Polyimides have many desirables properties, such as low dielectric constant, high breakdown voltage, chemical resistance, wear resistance, stability at elevated temperatures, low thermal expansion, as well as excellent optical and mechanical properties. Polyimide microstructures are typically patterned either by photolithography for photosensitive type or by lithography plus etching for non-photosensitive type. In this work, we will investigate the high throughput nanopatterning of polyimide by nanoimprint lithography (NIL), and then explore its superior mechanical (such as very high tensile and compressive strength) and thermal properties by using it as a flexible NTL mould.

Two different approaches were used to pattern polyimide using NIL: moulding at its uncured state and complete curing afterwards, or moulding another polymer resist having lower Tg then transfer the pattern into the underneath cured polyimide.

For the first approach, the polyimide (HD Microsystems P12525, imidization temperature around 180°C) film was spin-coated and soft-baked at 105°C for 3 min then 120°C for 1 min on a hotplate to drive away the solvent. During NIL, the chamber was pumped to a low vacuum and heated to 120°C. At this point, pressure of 15 bar was applied and the temperature was ramped to 200°C at 20°C/min and held at 200°C for 2 min before removing the force. After NIL, hard-bake was carried out at 250°C for 10 min, which completed the imidization and further drove away the solvent. Due to volume shrinkage, the feature edge was found slightly rounded after hard bake.

For the second approach, the polyimide film was hard-baked at 350°C for 1 hour to completely drive away the solvent and imidize. PMMA was then spun on the film, patterned by NIL, and transferred into polyimide by RIE. Though more complicated than the first approach, this method is preferable for applications where nanostructured polyimide would experience temperature well above 200°C for prolonged time and evaporation of residual solvent is undesirable.

Fig.1 shows polyimide grating with 200 nm period and about 100 nm height fabricated by both methods. Using these polyimide moulds, PMMA grating patterned by NIL is shown in Fig. 2. We can see that the pattern has been well imprinted into PMMA.

Besides as a NIL mould, nanostructured polyimide can also serve as a substrate for SERS (surface enhanced Raman scattering) sensors due to its high temperature stability. We have found Ag or Au sputtering at elevated temperature was favourable for SERS-based sensors, and by nanostructuring the substrate, higher SERS signal was attained. Lastly, as polyimide has been proven to be a biocompatible material [l-21, efficient nanopatterning over large surface area with controlled architecture will open the way for interesting biomedical applications.

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