Gettering efficiencies for Cu and Ni as a function of size and density of oxygen precipitates in p/p- silicon epitaxial wafers

Abstract

We have measured the gettering efficiencies for Cu and Ni in p/p-Si epitaxial wafers. The wafers were pretreated to obtain oxygen precipitates of different sizes and densities in the bulk. Gettering tests started with a reproducible spin-on spiking in the range of 1012 atoms/cm2, followed by thermal treatment to drive-in and redistribute the impurities in the wafer. Subsequently, the wafers were analyzed by a novel stratigraphical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. Gettering efficiencies for Ni did not depend on oxygen precipitate sizes and densities as long as ΔOi was larger than 0.2×1017 atoms/cm3 and the bulk micro defect densities were detectable by preferential etching (107 cm-3). In these cases, gettering efficiencies were 96–99% for Ni, while wafers not containing any measurable BMDs exhibited no detectable gettering. Cu exhibited a more complex behavior because the total Cu contamination was found to be divided into two species, one mobile and the other immobile species. A dependence on BMD size and BMD density of the Cu distributions in the wafers was also detected. Gettering effects were increased with increasing BMD densities and sizes. For BMD densities 1010 cm-3, gettering effects due to oxygen precipitates were one order of magnitude lower than in heavily boron-doped silicon.