Effect of Plasma Treatment on the Spontaneous Formation and Morphology of Surface Nanobubbles on Silicon

TL;DR

This study investigates how oxygen plasma treatment and aging influence the spontaneous formation and morphology of nanobubbles on silicon surfaces, revealing conditions that promote nanobubble stability relevant for silicon fabrication.

Contribution

It demonstrates that aging plasma-treated silicon in atmospheric conditions leads to consistent nanobubble formation, challenging prior beliefs about nanobubble formation on silicon surfaces.

Findings

Nanobubbles with sub-10 nm height and sub-100 nm width form after aging in air.

Several days of aging are needed for stable nanobubble formation.

Surface nanobubbles are linked to atmospheric hydrocarbon adsorption.

Abstract

The formation of gaseous, spherical cap-shaped domains (so-called "surface nanobubbles") at the solid-liquid interface is a topic of fundamental interest due to the possible effects of nanobubbles on surface cleaning, wetting, and nanoscale patterning. This work investigates the spontaneous formation of surface nanobubbles on oxygen plasma-treated Si by PeakForce quantitative nanomechanics (PFQNM) imaging, X-ray photoelectron spectroscopy, and water contact angle measurements. Large quantities of surface nanobubbles with sub-10 nm height and sub-100 nm base width are observed on oxygen plasma-treated Si surfaces that have been "aged" in atmospheric conditions (stored in a plastic wafer container). Several days of aging time are required for surface nanobubbles to form on oxygen plasma-treated Si, at which point the bubbles are remarkably consistent in their properties across samples aged 5-12 days. The presence of surface nanobubbles on plasma-treated aged Si surfaces runs contrary to prior reports of infrequent nanobubble formation on Si/SiOx. Surface characterization supports a theory of post-plasma atmospheric hydrocarbon adsorption inducing changes in Si-wetting behavior to a sufficient extent that nanobubble formation can occur. The results are of importance in Si-based fabrication processes employing oxygen plasma treatment with subsequent DI water immersion.