Enhanced particle removal using viscoelastic fluids

The introduction and subsequent removal of highly elastic solutions from surfaces has recently allowed industry to effectively remove colloidal, particulate contaminants from high-grade silicon. The substrate is first coated with the polymeric cleaning solution, and then the solution is removed either by simply rinsing the surface using an impinging water jet or by siphoning the cleaning fluid from the surface. The advantage of this continuous process over conventional techniques is the noninvasive removal while generating limited nonhazardous aqueous waste. Our group investigated the use of polymeric liquids that effectively eliminate particles without damaging the delicate surfaces. To investigate this removal, we studied two different flow types (siphoning and rinsing) of various rheological fluids to understand the governing physics that allow for removal. In this publication, we show that the presence of local shear flows of a viscoelastic fluid having a large elongational viscosity can create polymer stresses that are much larger than the associated Newtonian shear stresses. The onset of this added polymer stress in the flow field correlates well to the increase in particle removal.