Strain-induced transformation of amorphous spherical precipitates into platelets: Application to oxide particles in silicon

The spherical shape of an amorphous precipitate becomes unstable if the com bination (PR)-R-2 of precipitate radius R and pressure P exceeds some criti cal value. This critical value was found to be about 4.44 G sigma, where G is the matrix shear modulus and sigma is the specific energy of the precipi tate/matrix interface. Once this instability criterion is fulfilled, the in itially spherical particle will reduce the total free energy (the sum of st rain energy and the surface energy) by becoming a thin oblate spheroid (eff ectively, a platelet). The actual pressure P in the course of oxygen precip itation in silicon is controlled by a high self-interstitial supersaturatio n caused by emission of self-interstitials by growing precipitates. The dur ation of annealing necessary to reach the stage of collapse of spheres into platelets is calculated as a function of temperature and the precipitate d ensity. Calculated results are compatible with the experimentally observed annealing conditions for platelet formation. Another important example of s phere to platelet transformation is microdefect formation in vacancy-type s ilicon. In this case a large negative value of P is sufficient to induce co llapse. (C) 2001 American Institute of Physics.