Microcontamination of Silicon Wafer Surfaces by Copper and Silver

Microcontaminations of copper and silver on n-type silicon wafer surfaces were investigated by performing a series of electrochemical polarization measurements in 5% hydrofluoric acids and ethanol solutions in the absence and presence of various concentrations of copper and/or silver. The metallically contaminated wafer surfaces were characterized by scanning electron microscopy. It was revealed that the open-circuit potentials shifted to a more anodic direction and the corrosion current densities increased significantly when either copper or silver was present in solutions, and these became more pronounced when hoth copper and silver were introduced simultaneously into solutions. The polarization resistance showed a sensitive linear decrease with an increase of copper or silver concentrations, a strong indication of an accelerated electrochemical reaction. The contaminated wafer surfaces were covered by metallic nanocrystallites due to copper and silver deposition from solutions. When both copper and silver were present, the nanocrystallites coagulated with each other and various clusters were formed by combination with metallic atoms. As the concentration of copper and/or silver increased, the amounts of metallic nanocrystallites also increased, this, in turn. further promoted metallic microcontaminations and ultimately led to rougher water surfaces.