Wafer drying processes are essential for final quality of un-patterned wafers as well as fabricated devices. The main application of wafer dryers are removing of remaining watermarks and rinsing off any residues from previous cleaning steps. A badly chosen drying step can result in surface contaminations and consequently degradation of process performance and yield. In other words, one has to be ensured that drying processes are not generating additional surface contaminations.
One of the common wafer drying processes in semiconductor manufacturing is the spin drying. In this technique, wafers are being rapidly mechanically rotated around an axis perpendicular to the wafer surface under nitrogen (N2) flow after rinsing with high purity deionized (DI) water. Spin drying is a fast and relatively simple drying technique.
However, in the industry, for the applications where a superior drying performance is required, techniques based on surface tension gradient are being employed. These are based on so called Marangoni effect. In this technique a liquid with a lower surface tension than water, typically isopropyl alcohol (IPA), is being added. IPA not only strips the water away from the surface of wafers, but also results in a significant increase of mass transfer at the wafer interface.