Droplet-Assisted Laser Direct Nanoscale Writing on Silicon

Abstract

Nano-structuring using laser direct writing technology has shown great potential for industrial applications. A novel application of water droplets to this technology is proposed in this paper. With a hydrophobic layer and a controlled substrate temperature, a layer of randomly distributed water droplets with a high contact angle is formed on the substrate. These liquid droplets can be used as lenses to enhance the laser intensity at the bottom of the droplets. As a result, nanoscale holes can be fabricated on the substrate by controlling the laser energy density. We successfully fabricated holes with a diameter of 600 nm at a substrate temperature of 12 ∘C and a power density of 1.2 × 108 W/cm2 in our experiments. We also found that the hole diameter was around a ninth of the water droplet diameter. Meanwhile, the machined holes are not affected much by the focal length of the lens, but a hole with less than 100 nm in diameter at the center was observed.

Keywords

• direct writing
• laser
• droplet
• nanoscale