The crystal structure of η-Cu₃Si precipitates in silicon

Abstract

The crystal structure of Cu-Si precipitates in silicon has been studied by means of transmission electron diffraction and microscopy. The precipitates are shown to be of the equilibrium Cu3Si phase, probably of the low-temperature η” form. Consistent with earlier X-ray diffraction data for this phase, the crystal structure of the precipitates is determined to be based on a trigonally distorted b.c.c. arrangement. The lattice is orthorhombic (C), and is a two-dimensional long-period superlattice, which it is suggested is based on the intermediate-temperature η' phase; lattice parameters aη” = 76.76, bη” = 7.00, cη” = 21.94 Å. On the basis of the diffraction data for the precipitates, it is suggested that the ηand η' phases are both trigonal, space groups R{\bar 3}m and R{\bar 3} respectively, with lattice parameters aη = 2.47 Å, αη = 109.74° and aη' = 4.72 Å, αη' = 95.72°.