We have investigated a phase transformation from PdSi to Pd2Si using x-ray diffraction and scanning electron microscopy combined with Auger-electron- spectroscopy analysis. PdSi initially formed by annealing an epitaxial Pd2Si layer on Si at 850?deC transformed to Pd2Si by a postannealing below 750?deC. After the phase transformation, small grains of Pd2Si and Si have been observed. Ninety percent of the surface area of the sample postannealed at 650?deC was covered with Pd2Si grains, while only 75% of the surface area was covered with Pd2Si grains for the sample postannealed at 750?deC. The period for the transformation was measured as a function of the postannealing temperature and had a concave temperature dependence with a minimum at 650?deC. The difference in the surface morphologies and the temperature dependence of the transformation period can be explained on the basis of nucleation and mass transport. The rate of the nucleation is a function of the supercooling which is faster at lower annealing temperatures. Mass transport for growth of Pd2Si nuclei is controlled by diffusion of atoms, the coefficient of which is higher at higher annealing temperatures.
ASJC Scopus subject areas
- Condensed Matter Physics