Habit and Morphology of Copper Precipitates in Silicon

Copper precipitates in silicon often agglomerate into elliptical disks lying in {110} planes of the host lattice, with their respective major axes pointing in the $\text{〈110〉}$ directions. As many as 12 such disks usually emanate from a nucleation center of some lattice defect, displaying a partially or fully developed rosette pattern silhouette under ir microscopy. Various patterns of precipitates in substrates of $\text{〈100〉}$ , $\text{〈111〉}$ , and $\text{〈120〉}$ crystallographic orientations are consistently explained by coordinate transformations of a hypothetical rosette pattern. In particular, the observations of precipitates in $\text{〈120〉}$ substrates have demonstrated the nonexistence of needle forms. The ratio of the two elliptical axes varies with copper concentration and quenching conditions. With the surface behaving as a sink, rapid quenching was usually necessary to achieve fully developed precipitates. There was no preference among the six equivalent {110} planes and the six $\text{〈110〉}$ directions in which elliptical disks precipitated about a point defect. There was, however, a preferred orientation tendency for the disks precipitated about a dislocation line. Some elliptical disks exhibited banded structure—probably a result of Ostwald ripening. The elliptical disks disappeared and reappeared during annealing cycles, exhibiting a memory effect.