nano-processing

H. Schucka, Th. Veltena, T. Anhuta, D. Sauera, R. Le Harzicb, K. Königa
a Fraunhofer-Institute for Biomedical Engineering, D-66386 St. Ingbert, Germany
b JenLab GmbH, D-07745 Jena, Germany

Abstract

Sub-micrometer structuring has been performed on polymers, metal films and semiconductors using near 3
infrared, 90 MHz femtosecond laser pulses at <3 nJ pulse energy. A compact (65x62x48 cm ) multiport laser scanning microscope FemtoCut (JenLab GmbH) has been employed. A tuneable turn-key, one-box Chameleon (tunable from 720 - 930 nm) has been used as laser source.

Pulse energies in the sub-3 nJ range are sufficient to induce multiphoton ionisation when using a high NA 2
objective (e.g. NA = 1.3) in order to obtain transient TW/cm laser intensities. By exploiting this multiphoton effect, we were able to perform patterning of several types of material with sub-micron resolution. Depending on the pulse energy, cut widths of 350 nm and 900 nm have been achieved in 30 nm thin gold films. In polyimide Pyralin PI2611 (HD microsystems) we reached cut widths of 570 nm. Direct laser processing of silicon wafers resulted in cut widths of about 500 nm. Interestingly, besides the 500 nm cut we found two types of additional nanostructures. A first superficial layer contained non-homogenously distributed laser-induced nanocones which represent non-coherent structures. After removing this layer by etching with ammonium fluoride, a second highly coherent “ripple” structure became obvious. Most interestingly, these symmetric features possessed a wavelength (distance) of 50 – 70 nm. A clear dependence of the ripple structures on the polarization was proven.