Geometric confinement of directly deposited features on hydrophilic rough surfaces using a sacrificial layer

Abstract

It is challenging to achieve high definition for inkjet-printed features on hydrophilic rough surfaces. In this study, a spreading diameter of ~5 mm was observed for a 10 pL inkjet droplet when it impacted onto a hydrophilic rough surface. A new geometric confinement method was employed to facilitate a much higher inkjet printing definition in the range of ~50 μm. A layer of water-soluble polyacrylic acid (PAA) was spin-coated onto a hydrophilic rough surface and then inkjet patterned. Subsequently, the PAA was made water-insoluble by subjecting the sample to a heat treatment with temperatures above 170 °C. The change in solubility of PAA during the heat treatment is found to be a crucial factor, which enables the physical confinement of the subsequently inkjet printed aqueous-based droplets. The thickness of the spin-coated sample also plays a critical role in the effectiveness of the physical confinement. The effectiveness of the proposed approach was demonstrated with an inkjet patterning process, in which a dielectric layer of 200 nm SiN x on a textured silicon wafer was selectively etched using 10 pL inkjet-printed droplets resulting in a line width of ~75 μm. When using a 1 pL printhead, the etched line width was as fine as ~30 μm.