Electronics

Control of heavy metals is critical in the process of silicon wafer cleaning and electroplating. Specifically designed Dequest® phosphonates grades do have the required purity and heavy metal chelation properties to be used in electronics applications.

Alkaline hydrogen peroxide based cleaning solutions are used for the cleaning of silicon wafers in semiconductor manufacturing. Although these cleaning mixtures have excellent particle removal capabilities they are very often not optimized for metallic contamination. It is known that metallic contamination when present in the bath will decrease the bath lifetime due to the metal catalyzed decomposition of peroxide. Moreover subsequent acid cleaning steps are required to remove residual metals from the wafer. Dequest® phosphonates are used to stabilize peroxide cleaning solutions and to reduce heavy metal contamination of silicon wafers.

Electroplating is the deposition of a thin metallic layer on a surface by passing an electric current through a solution in which the object has been immersed. The solution, or plating bath, contains dissolved salts of the metal or metals being deposited. A major portion of plating baths include cyanide as the sequestrant which holds the metal in solution. Cyanide works very well, but the highly toxic cyanide solutions must be carefully maintained at a basic pH to avoid evolution of hydrogen cyanide. Moreover disposal costs of the environmentally unacceptable cyanide are also rapidly escalating. Dequest® phosphonates can be used in eg Copper plating baths, in place of cyanide, to hold the desired metals in solution and to chelate trace metal impurities.