In-chip laser nano-structuring inside silicon with spatially modulated beams

Recently, we demonstrated a laser-writing method that exploits nonlinear interactions to form subsurface (in-chip) modifications, created deep inside silicon [1]. This single-step, maskless method introduced a new capability, i.e., controlled 3D microfabrication capability at 1-µm resolution inside Si [1]. Here, we expand the technique for demonstrating, to the best of our knowledge, the first nanofabrication capability in Si, realized without damaging the wafer surface. In order to achieve this, we exploit the ‘non-diffracting’ nature of Bessel beams, which offer better spatial control in comparison to Gaussian beams. The laser pulses of ~5 ns, 1.55 µm and a few-microjoules energy are modulated with a spatial light modulator, before directed with a lens system, forming Bessel pattern inside the sample. The crystal structure is disrupted in the form of rod-like structures that have high aspect-ratios > 500, with structure-widths that are on the order of 250 nm, and of roughness ~30 nm. These in-chip nano-structures can potentially lead to novel infrared photonic elements for phase and polarization control at the nanoscale.

[1] Tokel et al, “In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon,” Nature Photonics, 11, 639, 2017.