Investigation on the Drying Dynamics of Millimetric Water Droplets: Source of Watermarks on Silicon Wafers

摘要

Evaporation of unpinned sessile droplets with small contact angles (below 90°) is studied here extensively. We focused our work on the constant contact-angle mode in which the contact area of the droplet on the substrate decreases. A thorough understanding of droplet evaporation is of vital importance for examining the drying rate, the flow patterns observed inside drying drops, and the residual deposits. The concentration of each potential dissolved species (e.g. silica or silicic acid) can also be predicted and confronted to their solubility. We developed a theoretical model to predict the evaporation rate and the behavior of millimetric droplets taking into account the characteristics of the ambient and the substrate during the drying process. We discuss also the topology of watermarks on silicon wafers in the case of a predominant evaporation phenomenon.