Diffusion Gettering of Au and Cu in Silicon

The gettering of Au and Cu by phosphorus diffused from and sources and by boron diffused from a source has been studied. Samples were intentionally contaminated with moderate to large amounts of Au and Cu to obtain impurity levels above the background level, then gettered and finally examined by ion backscattering. The solubilities of Au and Cu were experimentally measured for phosphorus diffusions at various temperatures. The gettering, using either phosphorus source, was found to take place in the silicon and not in the source glass and the Cu and Au atoms were on lattice sites. Differences in the shapes of the profiles of gettered Au for and diffused sources were found and these are discussed in terms of vacancy enhancement effects. In general, phosphorus diffusion gettering appears to operate by solubility enhancement and ion pairing of substitutional metal acceptors. Boron diffusion gettering is less effective than phosphorus, a result which is consistent with solubility calculations and physical arguments. When the solubility is exceeded new phases are formed. The formation of precipitates for boron diffusions has been studied by electron microscopy.