Copper gettering by aluminum precipitates in aluminum-implanted silicon

Abstract

Copper in Si is shown to be strongly gettered by Al-rich precipitates formed by implanting Al to supersaturation and then annealing. At temperatures ranging from 600 to 800 °C a layer containing Al precipitates is found to getter Cu from Cu silicide located on the opposite side of a 0.25 mm Si wafer, indicating a substantially lower chemical potential for the Cu in the molten-Al phase. Cu gettering proceeds rapidly until an atomic ratio of approximately 2 Cu atoms to 1 Al atom is reached in the precipitated Al region, after which the gettering process slows down. Redistribution of Cu from one Al-rich layer to another at low Cu concentrations demonstrates that a segregation-type gettering mechanism is operating. Cu gettering occurs primarily in the region containing the precipitated Al rather than in the region where the Al is entirely substitutional.