Studying patterns formed on rotating substrates can improve spin-rinsing techniques
Studying patterns formed on rotating substrates can improve spin-rinsing techniques lead image
Industrial spin-rinsing is an environmentally friendly alternative to traditional wafer cleaning processes in the fabrication of microelectronics on silicon wafers. This method relies on centrifugal forces to spread a liquid film over a substrate, but these forces also cause rivulets and ridges to appear on the spreading front. A new paper studies spreading front patterns during spin-rinsing to address this instability.
“The problem is that the rivulets can compromise the cleaning process,” said author Andrew Ylitalo.
The researchers studied the patterns formed by an impinging water jet on a rotating substrate at different conditions, adjusting jet flow rate and rotational frequency. For a qualitative analysis, the researchers visually classified the patterns formed into seven categories from circular to turbulent, and for a quantitative analysis, they studied the compactness ratio, a value that indicates the spreading front’s deviation from a perfect circle.
It is possible for different patterns to have the same compactness ratio, so a limitation of quantifying the morphology in this way is that it simplifies an entire shape into a single number without providing any information about the geometry of the rivulets. However, for cleaning applications, the main objective is to minimize the compactness ratio.
“We’re academically interested in the morphology, but the compactness ratio is sufficient for engineering purposes,” Ylitalo said.
The scientists tested bare, water-coated and aqueous surfactant-coated substrates. In all cases, the compactness ratio increased with rotational speed. The bare and aqueous surfactant-coated substrates generally had a larger compactness ratio due to interfacial tension along the spreading front of the jet.
The researchers hope their findings will help clean silicon wafers between microelectronic fabrication steps in an environmentally friendly way.
Source: “Evolution of rivulets during spreading of an impinging water jet on a rotating, precoated substrate,” by Andrew S. Ylitalo, Daniel J. Walls, David S. L. Mui, John M. Frostad, and Gerald G. Fuller, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5109806 .
