New formulation for 2D photolithography with ultra-high resolution for photonic applications
Résumé
In this paper, we report on the development of a high resolution negative photoresist for 2D nanolithography. The formulation which is based on PMMA as polymer matrix contains a mixture of triacrylic monomer and a photoinitiator sensitive at both one and two photon activation. Thanks to PMMA, the liquid mixture thoroughly wet out the Silicon or glass substrate and make it possible the fabrication of ultrathin photopolymerizable films (50 – 1000 nm) with good surface roughness and high spatial resolution. During the writing process, continuous diffusion of oxygen at the interface of the ultrathin photopolymer film seems to play a determinant role in the control of polymerization growth. Surface relief gratings were generated using far and near field irradiation set-ups at different wavelengths (442 and 780 nm). The patterned polymer films were characterized by AFM and SEM. The influence of the mixture composition, the exposure time, the laser intensity and the spatial frequency was investigated. The material shows high resolution (up to 6000 t/mm) with polymer line-widths smaller than 60 nm corresponding to writing wavelength/13. The photopatterned polymer can be used as a mask for etching of Silicon or ZnO surfaces. Based on this study, 2D thick metamaterial structures that focalize light in the infrared domain (5-10 µm) are fabricated by Two Photon Polymerization and characterized at 5.64 µm using QCL (Quantum Cascade Laser) source and IR CCD Camera.