Klaus Zimmer

Excimer laser-induced material modification to create nanometer high smooth patterns in glass using mask projection

Laser swelling of borosilicate and soda-lime glass is shown for wavelengths of 193 and 248 nm. Very smooth patterns up to 45 nm high were generated by KrF laser (248 nm) irradiation of borosilicate glass at a fluence of 1.5 J/cm2. At 193 nm laser wavelength, lower heights (up to 13 nm) and lower swelling threshold fluences (0.1 J/cm2) were observed due to higher material absorption. For the less absorbing soda-lime glass higher fluences than for the borosilicate glass are needed to establish elevated structures. Gratings in borosilicate glass with sub-micron periodicity demonstrate the high resolution of the method. The results can be explained by a thermo-physical model based on the change of the glass transition temperature due to fast cooling after the pulsed laser irradiation.

Nano and micro structuring of fused silica using time-delay adjustable double flash ns-laser radiation

Large area, high speed, nanopatterning of surfaces by laser ablation is challenging due to the required high accuracy of the optical and mechanical systems fulfilling the precision of nanopatterning process. Utilization of self-organization approaches can provide an alternative decoupling spot precision and field of machining. The laser-induced front side etching (LIFE) and laser-induced back side dry etching (LIBDE) of fused silica were studied using single and double flash nanosecond laser pulses with a wavelength of 532 nm where the time delay ∆τ of the double flash laser pulses was adjusted from ∼50 ns to ∼10 μs. The fused silica can be etched at both processes assisted by a 10 nm chromium layer where the etching depth ∆z at single flash laser pulses is linear to the laser fluence and independent on the number of laser pulses, from 2 to 12 J/cm2, it is ∆z = δLIFE/LIBDE ⋅ Φ with δLIFE ∼ 16 nm/(J/cm2) and δLIBDE ∼ 5.2 nm/(J/cm2) ∼ 3 ⋅ δLIFE. At double flash laser pulses, the ∆z is dependent on the time delay ∆τ of the laser pulses and the ∆z slightly increased at decreasing ∆τ. Furthermore, the surface nanostructuring of fused silica using IPSM-LIFE (LIFE using in-situ pre-structured metal layer) method with a single double flash laser pulse was tested. The first pulse of the double flash results in a melting of the metal layer. The surface tension of the liquid metal layer tends in a droplet formation process and dewetting process, respectively. If the liquid phase life time ∆tLF is smaller than the droplet formation time the metal can be frozen in an intermediated state like metal bare structures. The second laser treatment results in a evaporation of the metal and in a partial evaporation and melting of the fused silica surface, where the resultant structures in the fused silica surface are dependent on the lateral geometry of the pre-structured metal layer. A successful IPSM-LIFE structuring could be achieved assisted by a 20 nm molybdenum layer at ∆τ ≥ 174 ns. That path the way for the high speed ultra-fast nanostructuring of dielectric surfaces by self-organizing processes. The different surface structures were analyzed by scanning electron microscopy (SEM) and white light interferometry (WLI).