Importance of electrokinetic phenomena in contamination control during semiconductor wet processing.

Abstract

The adsorption of metanil yellow [3-{{4-(phenylamino) phenyl}} benzene sulfonate] and colloidal silica on a commercially available, positively charge-modified nylon 66 membrane (N66 Posidyne) with an isoelectric point (IEP) of 7.6 was investigated. Challenge testing of N66 Posidyne with a 2.3 ppm colloidal silica dispersion has shown that the membrane adsorbed 0.015 μg of colloidal silica per cm². At a pH of 5.1, the adsorption of metanil yellow was found to increase with its solution concentration and reached a saturation value of 2.2 x 10¹⁴ ions/cm² at a solution concentration of 1.49 x 10⁻⁵M. A technique to incorporate positively charged groups onto the surface of microporous polypropylene and polyvinylidene fluoride membrane filters for the filtration of liquids used in the semiconductor industry has been developed using γ-irradiation. The electrical characteristics of prepared membranes were measured by streaming potential and dye challenge tests. The compatibility of these charge-modified membranes with ultrapure water was investigated. Results show that these charge-modified membranes are characterized by a positive zeta potential in the pH range from 4 to 9.3. From the dye challenge tests at a pH of 5.0, the density of positively charged sites on charge-modified membranes was calculated to be approximately five times larger than that of unmodified membranes. The modified membranes released less than 1 ppb of total organic carbon (TOC) into ultrapure water and thus appear to have potential for use in DI water system. The electrokinetic characteristics of silicon, silicon dioxide and silicon nitride wafers subjected to different cleaning procedures were measured using a streaming potential technique. A streaming potential cell for handling 5" wafers was designed and fabricated to make these measurements. The isoelectric point of silicon, silicon dioxide and silicon nitride was dependent on the cleaning method. Polystyrene latex (PSL) and aminopropyl/silica particle deposition from aqueous solutions onto silicon nitride was investigated and correlated with the electrokinetic potential data.