Nanoimprint lithography
Nanoimprint lithography (NIL) is a high throughput high resolution parallel patterning technique based on the deformation of a resist material using a patterned mold.
Two varieties of NIL are developed in LTM.
- The earliest one, thermal nanoimprint, uses thermoplastic material heated above its glass transition temperature, deformed under the suitable mold pressure before being cooled down and separated. This technique has now reached a good level of maturity allowing its use when photolithography is costly and/or does not provide a sufficient resolution at high throughput.
- The other technique, more recent, is UV based NIL where the resist is initially in a liquid phase and becomes solid by curing with appropriate dose of photons. Thanks to the liquid state of the resist, it becomes easier to displace at a larger distance the deformed resist which remained impossible in thermal NIL even with very high imprinting force. However, the UVNIL principle implies the use of transparent mold and low viscosity photosensitive resist. Those two requirements are much more constraining than their counterpart in thermal NIL (i.e. silicon mold, thermoplastic polymers).
 8'' Si wafers etched using thermal NIL mask |
 400 nm pillars imprinted on 8'' polycarbonate sheet |
Main objective of NIL studied performed in LTM is the development of such lithography on large surfaces such as 200 mm Si wafers.
Thermal NIL is developed using the EVG520HE equipment which allows the imprint of 200mm wafers in one step, whereas UV-NIL is performed using a step and repeat process on a EVG stepper. This technique is based on the use of a small mold (typically 2x2cm²) duplicated several times in order to imprint the surface of a 200 mm wafer.
Main issues studied in LTM to improve NIL processes are:
Study of the pattern formation
- Materials: comparison thermoplastics/monomers
- Control of the residual thickness and mold deformation
- Study of the influence of material viscosity
- Developement of anisotropic plasma etching processes
- Study of capillary phenomena
Development of UV curable materials
- Home made formulations of low viscosity materials
- Hybrid organic/inorganic silsesquioxane resists
- Study of the introduction of surfactants
Study of antisticking treatment
- Characterization of the degradation of fluorinated SAM coated on the mold surface, using XPS and Electron Spin Resonance. It is demonstrated that the degradation is due to free radicals realesed during photocuring
Development of controlled processes for applications
- Optics
- Magnetism
- Nanofluidics
