Deep UV laser induced periodic surface structures on silicon formed by self-organization of nanoparticles

TL;DR

This study explores the formation of laser-induced periodic surface structures on silicon using deep UV laser pulses, revealing a nanoparticle self-organization mechanism distinct from traditional theories, with implications for surface patterning and photoluminescence.

Contribution

It introduces a novel nanoparticle self-organization mechanism for ripple formation on silicon under deep UV laser irradiation, supported by a plasmonic model and experimental observations.

Findings

Ripple period increases with incidence angle.

Nanoparticles self-organize into ripples with shallow modulation.

Surface regions with lower fluence exhibit photoluminescence.

Abstract

We have investigated the formation of laser-induced periodic surface structures (LIPSS or ripples) on silicon upon excitation with p-polarized excimer laser pulses in the deep ultraviolet region (wavelength = 193 nm, pulse duration = 20 ns). Well-pronounced ripples with a period close to the laser wavelength were observed for pulse numbers N = 100 or higher, and the ripple period increased with the angle of incidence. While these results seem to be qualitatively consistent with the standard Sipe-theory, we observed a fundamentally different ripple formation mechanism and ripple morphology. At low pulse numbers, isolated nanoparticles with a size of a few tens of nanometers are observed at the silicon surface, which then start to agglomerate in 2D and self-organize to form ripples with a very shallow modulation depth as the pulse number increases. Employing a recently developed plasmonic model based on the propagation of a surface plasmon polariton on a rough surface, we demonstrate excellent quantitative agreement of the evolution of the ripple period with incidence angle. Finally, we show that surface regions exposed to lower laser fluence feature micro- and nanopores, which give rise to pronounced photoluminescence (PL) emission in the visible spectral region, as opposed to the nanoparticle-based ripples not showing PL.