Contamination of silicon and oxidized silicon wafers during plasma etching

Neutron activation analysis has been used to study the type and level of contamination of silicon and oxidized silicon wafers exposed to various plasmas used in silicon device processing. Silicon wafers exposed to plasmas in a reactor previously used to remove SiN passivation layers from Au metallized wafers were found to be heavily contaminated with Au (up to ∼10¹⁴ atoms/cm²). Au contamination of oxidized silicon wafers similarly treated was two to three orders of magnitude smaller regardless of whether SiO₂ etched faster or slower than Si in the plasmas used. Wet chemical cleaning of contaminated Si subsequent to plasma exposure was relatively ineffective in removing residual Au. This is interpreted as indicating indiffusion of Au during plasma exposure of Si. Exposure to a polymer forming plasma reduced the level of Au contamination of Si by nearly two orders of magnitude due to effective “sealing” of reactor surfaces by polymer film. Further, the level of contamination of Si was observed to decrease by over two orders of magnitude with usage time of the reactor during a 300-day time period when no Au containing materials were introduced into the reactor.