Adhesion Inhibition of a Trace Metal onto Wafers Using Polystyrene Sulfonate

Abstract

In the production of semiconductors, ultrapure water is used for cleaning in each process. In recent years, the adverse effects of impurities in ultrapure water for cleaning have increased with the miniaturization and high integration of the circuit-line width of semiconductors. Therefore the demand for high-quality ultrapure water has increased. We examined the metal adhesion restraint on silicon wafers based on the adsorption of polystyrene sulfonate (PSA) and metal ions. PSA was microinjected into a sample of ultrapure water containing the metal, and a cleaning vessel was allowed to overflow with the sample. Subsequently, the wafers in the sample were immersed and the amount of the metal deposited on them was measured. In addition sulfur concentration was calculated. It was found that the adhesion of the metal ions adsorbed with PSA in ultrapure water on the wafers is suppressed. A metal adhesion restraint rate greater than 95% was obtained with the polyvalent metal ions. Furthermore, it was revealed that the adhesion of PSA to the wafer was negligible. We may apply this technique as a metal contamination restraint method for each cleaning process in the production of semiconductors.