Laser nano-structuring deep inside silicon using bessel beams

Abstract

Current nano-fabrication methods for silicon (Si), while excellent, are limited to its surface. Novel laser-lithography methods are emerging to introduce subsurface (inchip) functionality to Si, however, the state-of-the-art is at the microfabrication level, with resolution limited to > 1 µm. Multiple challenges exist for breaking this fabrication barrier, such as the diffraction-limit and complex limiting nonlinear effects inside silicon. This thesis demonstrates the first nanofabrication capability deep inside silicon, achieved without altering the wafer above or below fabricated structures, with confinement in one- and two-dimensions at the nanoscale. We achieve this by exploiting nonlinear energy localization due to structured laser beams and also a new seeding-type effect. The approach is based on pre-formed laser-written inchip structures enabling the controlled formation of even smaller features. We also demonstrate laser polarization as a new parameter for in-chip fabrication control. Further, by exploiting a combination of parameters, including pulse energy, Bessel beam phase pattern, polarization and the laser focusing conditions, we demonstrate the first in-chip structures that are beyond the diffraction limit in terms of feature size, with resolution down to 120 nm ± 25 nm, thus, improving the state-of-the-art by about an order of magnitude. In order to demonstrate a proof-of-concept optical element, we fabricated the first in-chip nano-gratings, shown to be operating with an efficiency approaching 90%. This new nanofabrication capability, demonstrated for the important technological material silicon, may have significant implications for nano-photonics, micro/nano-fluidics, photonic-electronic integration, and micro/nano-electromechanical systems (MEMS/NEMS)-type systems.