Ripple Formation during Oblique Angle Etching

Abstract

Chemical removal of materials from the surface is a fundamental step in micro- and nano-fabrication processes. In conventional plasma etching, etchant molecules are non-directional and perform a uniform etching over the surface. However, using a highly directional obliquely incident beam of etching agent, it can be possible to engineer surfaces in the micro- or nano- scales. Surfaces can be patterned with periodic morphologies like ripples and mounds by controlling parameters including the incidence angle with the surface and sticking coefficient of etching particles. In this study, the dynamic evolution of a rippled morphology has been investigated during oblique angle etching (OAE) using Monte Carlo simulations. Fourier space and roughness analysis were performed on the resulting simulated surfaces. The ripple formation was observed to originate from re-emission and shadowing effects during OAE. Our results show that the ripple wavelength and root-mean-square roughness evolved at a more stable rate with accompanying quasi-periodic ripple formation at higher etching angles (θ > 60°) and at sticking coefficient values (Sc) 0.5 ≤ Sc ≤ 1. On the other hand, smaller etching angle (θ < 60°) and lower sticking coefficient values lead to a rapid formation of wider and deeper ripples. This result of this study can be helpful to develop new surface patterning techniques by etching.

A hybrid modeling framework for simulating plasma-surface interactions of rough polymeric substrates

“…The ionization process generates an additional electron and the target molecule is ionized. Taken from [31].…”

“…Etching particles with a non-unity sticking coefficient (s<1), which outline the probability of etching a surface atom, desorb/rebound-off from the first collision point, re-emitted, and ultimately etch another surface point after numerous re-emission steps. Taken from [31].…”

“…An O2 plasma can react with a wide range of polymers to produce a variety of O2containing functional groups 30 on the surface [10]. The formation of polar groups on the polymer surfaces, leads to growth of the polymer surface energy and significant increase of the polymers wettability 31 and adhesion to metals and different organic compounds [14]. The maximum density of functional groups at the outermost polymer surface is completed after a few seconds, most often after only few seconds [12].…”

“…[14] Fridman, Plasma Chemistry. 31 The wettability increase effect is correlated to plasma-stimulated creation of polar peroxide groups on the polymer surface. Specifically, the polar component of surface energy, which defines polar interactions between polymer surface and the liquid, expands during exposure in O2 plasma.…”